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39Ar geochronology of the Rushan gold deposit: Implications for processes of ore-fluid infiltration in the eastern Jiaodong gold province, China
Journal Pre-proofs Textures of auriferous quartz-sulfide veins and 40Ar/39Ar geochronology of the Rushan gold deposit: Implications for process of ore- fluid infiltration in the eastern Jiaodong gold province, China Sheng-Xun Sai, Jun Deng, Kun-Feng Qiu, Daniel P. Miggins, Liang Zhang PII: DOI: Reference:
S0169-1368(19)30602-X https://doi.org/10.1016/j.oregeorev.2019.103254 OREGEO 103254
To appear in:
Ore Geology Reviews
Received Date: Revised Date: Accepted Date:
2 July 2019 18 November 2019 25 November 2019
Please cite this article as: S-X. Sai, J. Deng, K-F. Qiu, D.P. Miggins, L. Zhang, Textures of auriferous quartz-sulfide veins and 40Ar/39Ar geochronology of the Rushan gold deposit: Implications for process of ore- fluid infiltration in the eastern Jiaodong gold province, China, Ore Geology Reviews (2019), doi: https://doi.org/10.1016/j.oregeorev. 2019.103254
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Textures
of
auriferous
quartz-sulfide
veins
and
40Ar/39Ar
geochronology of the Rushan gold deposit: Implications for process of ore- fluid infiltration in the eastern Jiaodong gold province, China Sheng-Xun Saia, b, Jun Denga, *, Kun-Feng Qiua, Daniel P. Migginsc, Liang Zhanga
a
State Key Laboratory of Geological Processes and Mineral Resources, China
University of Geosciences, Beijing 100083, China b Department
of Geological Sciences, Jackson School of Geosciences, University
of Texas at Austin, Austin, TX 78712, USA c
College of Earth, Ocean and Atmospheric Sciences, Oregon State University,
Corvallis, OR 97331, USA
Manuscript submitted to Ore Geology Reviews *Corresponding author: Jun Deng State Key Laboratory of Geological Processes and Mineral Resources China University of Geosciences 29# Xue-Yuan Road, Haidian District Beijing 100083, China Phone: (+86-10) 8232 2301 (O) Fax: (+86-10) 8232 1006 Email: [email protected]
Abstract The Rushan gold deposit, located in the eastern part of the world-class Jiaodong gold province, contains the largest gold resource within a single faultcontrolled quartz vein in China. Processes involved in auriferous quartz vein deposition are not clear, and the precise gold mineralization age remains controversial for this deposit. New
40Ar/39Ar
dating data on sericite from ores and
altered rocks suggest that the Rushan gold deposit formed between ca. 122 Ma and 117 Ma, which overlap or are slightly younger than those of gold deposits in northwestern Jiaodong province. The age differences between samples from different locations indicate that the quartz veins on the margin of the orebody may be younger than those in the center, suggesting a single and protracted gold mineralization event lasting for about 5 My. Differences between gold mineralization
ages
and
emplacement/cooling
ages
of
the
ore-hosting
Kunyushan granite imply that they are not genetically related and that the Kunyushan granite is unable to provide any thermal input to the mineralization system. This also applies to the Sanfoshan monzonite as it marginally postdated gold mineralization and lacks any spatial association with it. Internal textures of high-angle shear veins and low-angle extension veins indicate that episodic fluctuations from supralithostatic to hydrostatic fluid pressure triggered the multiple ore-controlling fault ruptures induced by breach of supralithostatic fluids under a seismogenic regime. In this model, the controlling fault starts to slip with both reverse and sinistral kinematics, and dilatational zones are created. The ore-forming fluids then migrate upwards along the fault,
due to the large pressure difference between the dilatational zones and the deep parts of the fault, causing hydraulic fracture in the host rocks and earlier quartz veins. Large volumes of quartz, pyrite, and other ore components are precipitated due to fluid immiscibility caused by pressure fluctuations, and new quartz veins form along both sides of the earlier quartz veins. The fault is now sealed by these new quartz veins and the fluid pressure starts to build until the next breach cycles. Orebodies with complex internal textures were thus deposited incrementally in these cycles, closely fitting the classic fault-valve model, in this case under a weak regional NW-SE transpressional stress.
Keywords: Auriferous quartz-sulfide veins; Vein textures; Sericite dating; Rushan deposit; Jiaodong gold province
40Ar/39Ar
1. Introduction Jiaodong has a proven gold resource of more than 4,000 tonnes from over 150 gold deposits (Yang et al., 2014a), making it the most important gold producer in China (Li et al., 2015; Deng and Wang, 2016; Deng et al., 2018). Gold deposits are structurally controlled by NE to NNE-trending faults (Deng et al., 2003; Li et al., 2003). Five gold belts, namely the Sanshandao gold belt, the Jiaojia gold belt and the Zhaoyuan-Pingdu gold belt in northwestern Jiaodong, the Penglai-Qixia gold belt in the center, and the Muping-Rushan gold belt in eastern Jiaodong, are defined according to the faults which bound them and their related gold deposits. Previous researchers have generally moved towards consensus on the spatial architecture of orebodies, hydrothermal alteration types and distribution, compositions and isotopic features of ore-forming fluids, as well as geochemical nature of the gold ores (e.g. Fan et al., 2007; Tang et al., 2008; Wang et al., 2010; Goldfarb and Santosh, 2014; Guo et al., 2014, 2017; Yang et al., 2014a, 2016a, 2016b; Deng et al., 2015a, 2019; L. Yang et al., 2015, 2018). However, the precise
gold
mineralization
age
remains
controversial
and
previous
geochronological studies were mainly focused on northwestern Jiaodong. In recent years, numerous geochronological studies have revealed that the gold deposits in northwestern Jiaodong formed at ca. 125 to 115 Ma as a single metallogenic event (e.g. Li et al., 2003; Zhang et al., 2003; Ma et al., 2017; Yang et al., 2017; Zhang et al., 2019a), although there may have been an earlier ~130 Ma gold event in the Zhaoyuan-Pingdu belt (Yang et al., 2014b, 2016c). By
contrast, limited geochronological data in the Muping-Rushan gold belt have yielded highly dispersed ages (Table 1). Considering the variation in ages from 156.7 Ma to 104.8 Ma, arguments on whether gold formation represents one continuous evolving event or multiple distinct short episodes within a goldforming period, as well as the precise timing of each episode, continues (Table 1 and references therein). Complex internal textures are recorded in quartz veins in the MupingRushan gold belt, as the deposition of quartz veins is clearly controlled by fault movements. Such movements cause ore- fluid migration and enhancement of permeability along the fault as a consequence of fluid pressure and shear stress fluctuation (Sibson, 1988; Cox, 1995; Robert et al., 1995). Although progress has been
made
on
the
nature
of
ore-forming
fluids,
through
study
of
microthermometric features of fluid inclusions and the types of gold complexes in transporting fluids (Hu et al., 2005, 2007; Zeng et al., 2006; Xue et al., 2018), detailed studies of quartz vein depositional processes are scarce. The Rushan gold deposit, located in the center of the Muping-Rushan gold belt, contains the largest gold resource within a single fault-controlled quartz vein in China (Hu et al., 2004, 2006). The age of mineralization for this deposit, however, is particularly controversial (Table 1). Based on detailed observation of the internal textures and microstructural features of the quartz veins, together with sericite
40Ar/39Ar
ages obtained from different locations in the main orebody
and its adjacent alteration zone, this paper constrains the precise time and duration of gold mineralization event(s) in the Rushan gold deposit. Furthermore,
the formation of the gold deposit was further understood by examining the processes such as fluid pressure fluctuation and coupling between fluid flux and fault movement which control its formation.
2. Regional geology The Jiaodong gold province lies in the eastern part of the North China block, is bounded by the crustal-scale Tan-Lu Fault Zone to the west, and is adjacent to the subduction belt of the Pacific Plate to the east (Fig. 1a; Deng et al., 2003; Tang et al., 2008; Zhang et al., 2019b). Jiaodong is composed of the Jiaobei and Sulu Terranes, and the former is divided into the Jiaobei Uplift in the north and Jiaolai Basin in the south (Fig. 1b). The nearly parallel Taocun, Guocheng-Jimo, Zhuwu and Qingdao-Haiyang Faults comprise the Muping-Jimo Fault Zone (Fig. 1), which is the northern part of the regional Wulian-Qingdao-Yantai Fault Zone. This Fault Zone is regarded as the boundary between the Jiaobei Terrane and the Sulu Terrane (Zhang et al., 2007). Gold deposits in Jiaodong are strictly controlled by NE to NNE-trending faults. The mineralization styles are mainly classified as disseminated and stockwork veinlet style (Jiaojia style) hosted in extensively altered and cataclastic wallrock zones in the footwall of regional faults, and auriferous quartz-vein-style (Linglong style) deposited in high angle brittle faults, but there are also breccia style deposits controlled by low- angle detachment faults on the northern boundary of the Jiaolai Basin (Deng et al., 2003, 2015b; Yang et al., 2014a; Li et al., 2015).
Among the five major gold belts, the Muping-Rushan belt (also referred to as the Muru belt) is the only one that is located in the Sulu Terrane. The Sulu Terrane is characterized by widely exposed ultrahigh-pressure metamorphic rocks (UHP) composed of granitic gneiss, coesite-bearing eclogite, marble and other siliceous rocks (Webb et al., 2006). The Sulu UHP, constituting the east part of the world class Dabie-Sulu UHP belt, formed during Triassic continentcontinent collision between the Yangtze and North China blocks (Yang et al., 2003). The metamorphic basement of the Sulu Terrane comprises mainly Paleoproterozoic schist, paragneiss, calc-silicate rocks, marble and graphitebearing schist of the ca. 2.5-1.9 Ga Jingshan Group (Dong et al., 2010; Liu et al., 2013), which mainly occurs as discrete blocks in the southwest part of the Muping-Rushan gold belt (Fig. 2). Both the Jingshan Group and Sulu UHP are intruded by multiple pulses of Mesozoic granitic magmas, and the dominant Mesozoic granitoid in the Muping-Rushan gold belt, the Kunyushan granite, is subdivided into three phases: Duogushan weak gneissic granodiorite, Washan weak gneissic monzonite and Wuzhuashan weak gneissic porphyraceous monzonite (Zhang et al., 1995). The Kunyushan granite was emplaced at 161138 Ma (Hu et al., 2004; Guo et al., 2005; Zhang, 2011) and hosts the vast majority of gold resources in the Muping-Rushan belt. It shows affinity to S-type granites, and was derived from partial melting of the thickened crust (Guo et al., 2005). The late Cretaceous Sanfoshan monzonite intruded the Kunyushan granite in the southeast part of the Muping-Rushan belt at 118-113 Ma (Guo et
al., 2005; Goss et al., 2010; Zhang, 2011), most likely due to an intensive mantlecrust interaction event (Guo et al., 2005; Goss et al., 2010). The gold deposits are controlled by the Muping-Rushan Fault Zone that consists of a series of nearly parallel NNE-striking faults that largely dip steeply SE (Fig. 2). They are referred to as the Qinghushan-Tangjiagou Fault, the Shigou-Wushan Fault (also called the Jinniushan Fault), the Chahe-Sanjia Fault, the Jiangjunshi-Quhezhuang Fault, the Gekou Fault and the Laohuwo-Hezi Fault, from west to east. They constitute a graben structure regionally (Li and Yang, 1993), and secondary faults are developed on both sides of these faults.
3. Deposit geology The Rushan gold deposit (also referred to as the Jinqingding deposit) is located in the center of the Muping-Rushan gold belt. The orebodies are primarily hosted in the Washan monzonite pluton in the center of the Kunyushan granite, in which the Jingshan Group metamorphic rocks occur as discrete ellipsoidal enclaves with their long axes oriented NW-SE (Fig. 3). Numerous maficintermediate dykes including lamprophyres intruded along the NNE-NE striking faults (Deng et al., 2017), and some lamprophyres may post-date the orebodies as shown by cross-cutting relationships (e.g. Fig. 4a). The Rushan deposit is controlled by the NNE striking JiangjunshiQuhezhuang Fault. This fault generally strikes NNE 20°, with a variation of 5-30° in ore-hosting sections. Small branching and secondary faults are commonly developed in places where the strike and dip change. Although the main fault
plane is poorly exposed due to quartz veins within it, fault gouge, cleavages, striations and steps are visible in some places. Figure 4b shows a set of striations that indicate that sinistral movement of the Jiangjunshi-Quhezhuang Fault is overprinted by another set of normal slip striations, suggesting that normal faulting post-dates sinistral faulting. Sinistral and reverse slip on the fault induced by transpressional stress is substantiated by cleavage relationships and the well-oriented breccias in the fault zone, as well as by drag structures beside the main fault plane (cf. figure I-6 in Li, 2011). Such fault movement during gold mineralization has also been confirmed based on detailed interpretation of striations and steps on the fault plane from different sections where there are quartz-sulfide veins (Hu, 1995). Rushan is characterized as an auriferous quartz-vein-style deposit with the No. II lode as the dominant orebody that accounts for more than 90% of the proven resource. It shows roughly S-shaped, stratiform-like lenses, from 0.2 to 7.0 m (average 1.7 m) thick, that strike 5-30° and dip 65-90° SE (NW locally), extending along both strike and dip directions without interference from other quartz veins. The orebody expands where the strike of the JiangjunshiQuhezhuang Fault strikes from NE to NNE and the dip is gentler. The gold grade varies from 1.5 to 30.0 g/t with an average of 10.4 g/t gold. Narrow alteration zones are symmetrically distributed along both sides of the quartz veins. With increasing distance from the main fault, proximal narrow sericite-quartz alteration zones (Figs. 3c, 5a) transition gradually to a quartz alteration zone, which further grades into a distal potassic alteration zone (Fig.
3c). The sericite-quartz and quartz alteration zones are absent in some places where the quartz veins are wrapped directly by potassic altered rocks (Fig. 5b, de).
4. Internal textures of quartz veins and paragenetic sequence of hydrothermal minerals Based on the strike and dip of the quartz veins, internal textures and crosscutting relationships, both high-angle shear veins and low-angle extension veins are identified in the Rushan gold deposit. 4.1 High-angle shear veins The shear veins are hosted in the high-angle reverse faults/ fractures that had sinistral kinematics during mineralization. A variety of textures are recorded in shear veins, including not only the infill by massive uniform milky-white quartz, but also distinct textures such as layered quartz veins and host rock fragments, making the total shear veins laminated with abundant host rock enclaves. Host rock fragments are common in high-angle veins, and can be divided into breccias and laminae according to their size, shape and strike. Host rock breccias normally occur at dilatational sites in the shear veins, where they are in angular lenses, blocks or pudding-shape enclaves with diameters varying from less than 1 cm to 1-2 m. The large breccias are normally located in the center and tips of the dilatation zones without significant displacement or rotation, whereas the smaller breccias are randomly oriented within the entire shear vein with noticeable displacement and rotation (Fig. 5b). The breccias are cemented
and cut by crustiform and comb-like milky-white and smoky-gray quartz veinlets (Fig. 5b). Notably, the breccias near the margin of the shear veins display less alteration than those in the center (Fig. 5b). Laminae of host rock, with a thickness of no more than 30 cm (Fig. 5c), are also well developed in the veins, forming both discontinuous tabular and platy laminae parallel to the host rock contact, as also recorded by Chen (2017). An intact shear vein commonly consists of multiple quartz layers (Fig. 5d-e), with the milky-white quartz layers along the sides of the smoky-gray quartz layers. Some of the host rock breccias in the smoky-gray quartz layer are cut by the milky-white quartz layer, and there are breccias of smoky-gray quartz in the milky-white quartz layer (Fig. 5e). The quartz grains near the boundary of each layer are normally euhedral, comb-like with clear growth zoning (Fig. 6a), with the aspect ratio of the quartz decreasing towards the center of the layer where growth zoning is absent (Fig. 6b). Coarse-grained euhedral to subhedral pyrite grains occur as clusters on the boundaries of coarse-grained quartz (Fig. 6c), whereas anhedral pyrite grains occur as either a fine fill in thin quartz-sulfide veinlets (Fig. 6i) or as a disseminated component among quartz grains (Fig. 6d). Although some of the coarse-grained quartz and pyrite grains are intensively fragmented, the original shapes of the minerals are still recognizable due to low displacements among fragments (Fig. 6e-f), suggesting the involvement of hydraulic fracturing. Where filled by sulfides, the micro-fractures in pyrite are dominantly filled by galena (Fig. 6g-h), with lesser sphalerite. Notably, gold
minerals occur mainly in the micro-fractures of pyrite and normally have a close spatial relationship with base-metal sulfides, typically galena (Fig. 6g-h). Crack-seal texture is a significant piece of evidence to support the episodic ore-fluid migration. The meso-scale crack-seal veins separate different layers of quartz in the shear vein (Fig. 5d), and earlier quartz and pyrite are cut by microscale crack-seal veinlets. For instance, Figure 6i shows a single crack-seal veinlet cutting earlier coarse-grained quartz. Fragments of the host quartz vein are randomly distributed in the crack-seal veinlet, and fine pyrite grains normally occur close to the veinlet boundary. This may indicate a small discrete pulse in the fluid flux that precipitated the earlier coarse-grained quartz. By contrast, crack-seal veinlets filled with euhedral coarse-grained pyrite may suggest infiltration of a later fluid (Fig. 6j). The dark-gray elongate slab with multiple crack-seal structures between the shear vein and host rock (Fig. 5d) comprises fine quartz-pyrite-sericite-calcite fragments from the vein wall and matrix-like fine mineral grains from the rock contact (Fig. 6k). This argues strongly for multiple fluid events, as the fluids cracked and sealed the vein-rock contact multiple times and minerals on both sides were thus both fractured and pulverized. Open-space filling textures such as vugs in quartz (Fig. 5a, e) are developed in high-angle shear veins. Figure 6l shows open space filled by later calcite, and the smaller discrete euhedral quartz grains inside the open space are also cemented by calcite. There are vugs in some samples with euhedral quartz growth into open space (Fig 9e). Mills et al. (2015) describe similar textures, some with pyrite infilling vugs.
4.2 Low-angle extension veins High-angle veins normally have a close spatial association with the lowangle veins (Fig. 7a), which normally occur as single veins or vein arrays (Fig. 7). Host rock laminae (Fig. 7c) and breccias (Fig. 7d) in the low-angle veins are cemented by milky-white quartz and distributed parallel to the host rock wall. Open space textures such as vugs develop laterally along the low-angle veins, where groups of vugs parallel the host rock wall (Fig. 7c). The open space texture and the absence of displacement along the veins suggest that formation of low-angle veins involved extensional fracturing and subsequent sealing (Cox, 1995; Robert et al., 1995). Coarse-grained pyrite lies along the contact between quartz veins and host rocks (Fig. 7d), and along the contact between host rock laminae and massive quartz (Fig. 7c). Moreover, disseminated galena grains and aggregates also occur in these low-angle extension veins (Fig. 7c). 4.3 Paragenetic sequence of hydrothermal minerals The ore minerals in the Rushan deposit are primarily pyrite, followed by galena and sphalerite, with minor chalcopyrite, pyrrhotite, electrum, native gold and petzite. Liu et al. (2010) recorded calaverite, hessite and tellurobismuthite from the deeper part of the No. II Orebody, and proposed a Au-Ag telluride precipitation order of hessite-petzite-calaverite-native gold, which characterizes gradual enrichment of gold during evolution of the ore-forming process. The gangue minerals mainly consist of quartz, sericite, calcite and K-feldspar, with trace amount of monazite first reported by Sun et al. (2002). Gold minerals mainly precipitated in micro-fractures in pyrite, associated
with sulfides such as galena, sphalerite and chalcopyrite. Lesser visible gold occurs as inclusions in pyrite and quartz or on the margins of sulfides and quartz, with minor invisible gold in coarse-grained pyrite (Mills et al., 2015; Chen, 2017). Four stages in the paragenetic sequence of hydrothermal minerals are thus identified based on cross-cutting relationships between veins, internal textures of veins, mineral assemblages and precipitation order (Fig. 8). Stage 1 is defined by milky-white veins in alteration zones, with coarse-grained quartz (Fig. 6a-b), sericite (Fig. 6b), and minor coarse-grained euhedral to subhedral aggregated pyrite (Fig. 6c). Stage 2 is characterized by 1) smoky-gray veins with hydraulically-fractured earlier-formed coarse-grained minerals (Fig. 6e-f), 2) crack-seal veinlets filled by fine-grained anhedral quartz, pyrite and sericite (Fig. 6i), and 3) earlier formed coarse quartz grains self-sealed by finer-grained quartz (Fig. 6b). Additionally, anhedral disseminated pyrite occur on the boundaries of quartz (Fig. 6d), and disseminated monazite is associated with pyrite in this stage (Sun et al., 2002). Stage 3 is typified by fractured pyrite grains, and base-metal sulfides, such as galena, sphalerite and chalcopyrite, in these micro-fractures in pyrite (Fig. 6g-h). Gold minerals are typically within micro-fractures in pyrite or are intergrown with base metal sulfides (Fig. 6g-h), in the order hessite-petzitecalaverite-native gold (electrum). Sericite, quartz and pyrite are in variable proportions in these first three stages (Fig 8). Stage 4 marks the termination of one major fluid episode, as calcite occurs as a small cubic block surrounded by a thin layer of fine-grained quartz in a coarser-grained quartz vein (Fig. 5e), as veins or veinlets that cut the earlier-formed quartz-sulfide veins (Fig. 6f), and
infills in the vugs of euhedral/suhedral quartz aggregates (Fig. 6l). Minor pyrite was also deposited during this stage. It is apparent that the entire mineralization event may not consist of a single fluid evolution from Stage 1 to Stage 4, but may involve episodic fluid events in which hydrothermal minerals were deposited to produce a Stage 1 to Stage 4 paragenetic sequence. This is indicated by the presence of smoky-gray quartz breccias in milky-white quartz layers (Fig. 5e), crack-seal textures at the contact of quartz veins and host rocks (Figs 5d, 6k) and crack-seal veinlets filled by later euhedral pyrite in earlier coarse-grained quartz veins (Fig. 6j).
5. Geochronology of gold mineralization 5.1. Sample collection and description Sample JQD15D004B6 from an intensive sericite-quartz altered zone adjacent to the No. II Orebody, Sample JQD15D004B2 from the margin of the No. II Orebody, and Sample JQD15D015B2 from the central part of the No. II Orebody were selected for
40Ar/39Ar
geochronology. Detailed sample information
and locations are shown in Table 2. Feldspar in Sample JQD15D004B6 has been completely altered to sericite and quartz (Fig. 9a). Sericite penetrates the earlier recrystallized quartz (Fig. 9b), and it encapsulates quartz and pyrite or shows a close spatial association with them (Fig. 9c). Massive sericite is developed in this sample (Fig. 9d). The vuggy milky-white ore Sample JQD15D004B2 has euhedral quartz that has grown into open spaces (Fig. 9e). Sericite is distributed among euhedral
quartz crystals (Fig. 9f) or around clusters of subhedral pyrite grains (Fig. 9g) suggesting simultaneous formation. Native gold and hessite fill the microfractures in euhedral-subhedral pyrite grains (Fig. 9h). Another sample of ore (Sample JQD15D015B2) is composed of smokygray quartz with disseminated pyrite (Fig. 9i). Sericite grains locally accompany quartz and disseminated pyrite (Fig. 9j, l), or occur as infillings intergrown with fine-grained pyrite in quartz veinlets (Fig. 9k) and stockworks (Fig. 9l). 5.2 Analytical procedures In order to obtain the best possible
40Ar/39Ar
ages, samples were first
examined using a petrographic microscope. This was to ensure purity of samples and that there were no post-mineralization structural events that might affect the argon results from the sericite. Initial mineral separations for sericite aggregates was conducted at the Langfang Geoscience Company, Hebei, China, following traditional crushing, sieving, electromagnetic separation and heavy-liquid mineral separation techniques. All the mineral separates were then further purified at the Argon Geochronology mineral separation laboratory at Oregon State University. The mineral separates were rinsed multiple times with acetone, ethanol, and deionized water and dried in a drying oven at 55 °C. Once the samples were dried they were sieved to >250 μm. The separates were then separated into two different parts as magnetic and non-magnetic splits using a Frantz Isodynamic Separator. Several of the magnetic portions of the samples were reduced to smaller size fractions using a mortar and pestle to obtain purer splits of sericite.
The sericite was then filtered and the lighter separates left on the filter paper were dried and sieved to either >250 μm or >150 μm depending on their grain sizes. The sericite concentrates were further purified by using a binocular microscope and handpicked to a purity of >99%. Larger sericite flakes were obtained by scraping the thin quartz-sericitepyrite veins or quartz-sericite aggregates from the host rock using dental picks and fine-tipped tweezers. This mixture of sericite and other material was further refined by rinsing, sieving and electromagnetic separation in order to make an initial concentration of sericite. The sericite flakes were then further purified to >99% purity following the same procedures as those for sericite aggregates. Sericite separates were weighted and encapsulated in aluminum foil, along with the neutron flux monitor Fish Canyon Tuff (FCT-2-NM) sanidine grains (28.201±0.023 Ma; Kuiper et al., 2008) which were encapsulated in copper foil. The capsules were loaded into a quartz vial and vacuum sealed. The quartz vial was then irradiated for 6 hours at a cadmium-lined irradiation position CLICIT at the Oregon State University TRIGA reactor. Once the required cool down period was achieved, samples were unpacked and transferred into copper trays and put under vacuum in the CO2 laser lines. Sericite aliquots were analyzed using a ThermoFisher Scientific ARGUS VI multi-collector mass spectrometer, which is linked to an Ultra-High Vacuum (UHV) stainless steel gas extraction/purification line and Synrad 25 Watt CO2 laser system. Samples were incrementally heated from low power to high power settings. Each experiment consists of baseline, blank and sample measurements
which were conducted in a certain sequence. Laser and extraction line blanks were collected during the course of the entire heating experiment. Samples were continuously heated until the
39Ar
was fully extracted. This methodology
produces analytical data from the cutting-edge ARGUS VI multi-collector mass spectrometer that allows for a ~10 times improvement in precision compared to traditional spectrometers (Phillips and Matchan, 2013). With the extremely high precision ages it is possible to pick up minute signals from inclusions in the sample that can affect what would normally have been a flat plateau age on older instrumentation. Argon isotopic results are corrected for system blanks, radioactive decay, mass discrimination, reactor-induced interference reactions and atmospheric argon contamination. Decay constants reported by Min et al. (2000) are utilized for age calculation. Isotope interference corrections as determined using the ARGUS
VI
are:
(36Ar/37Ar)Ca
0.0006425±0.0000059;
=
(40Ar/39Ar)K
0.0002703±0.0000005; =
0.000607±0.000059;
(39Ar/37Ar)Ca
=
(38Ar/39Ar)K
=
0.012077±0.000011. Ages were calculated assuming an atmospheric
40Ar/36Ar
ratio of 295.5±0.5 (Nier, 1950). Data reduction and age calculation were processed using Ar-Ar Calc 2.7.0 (Koppers, 2002). Plateau ages are defined as including >50% of the total where the
40Ar/39Ar
39Ar
released with at least three consecutive steps,
ratio for each step is in agreement with the mean at the 95%
confidence level. In some cases only weighted mean ages are given. 5.3 40Ar/39Ar dating results and interpretation For samples where both flake and aggregate aliquots were obtained, both
were analyzed to clarify whether there is an age difference in different phases from the same sample and determine the reliability of individual phases. Ages are shown in Table 3 to Table 7 and age spectra are shown in Figure 10. Only flakes were separated for Sample JQD15D004B6 in the sericitequartz alteration zone adjacent to the orebody, the flakes underwent 33 heating steps (Table 3). The first step provides a young apparent age of 97.06 Ma, and the first 8 steps display a stepladder pattern, suggesting slight argon loss for the first few steps. The age spectrum becomes stable in the following steps, and it starts to fall in the remaining steps and the apparent age uncertainties increase because of the small amount of 39Ar been analyzed. The sericite reveals a humpbacked age spectrum overall, and the flat steps with highest apparent ages give a weighted mean age of 119.18±0.20 Ma, indicating the minimum age for the sample (McDougall and Harrison, 1999). The inverse isochron age of 119.12±1.00 Ma is consistent with the weighted mean age (Fig. 10b). The initial 40Ar/36Ar
of this analysis is 307.28±142.21 and is within error of the accepted
40Ar/36Ar
atmosphere ratio of 295.5±0.5, as defined in this paper.
Both sericite flakes and aggregates were dated for Sample JQD15D004B2 (Tables 4-5) from a milky-white quartz vein on the margin of the orebody. Sixteen and 32 heating steps were applied on flakes and aggregates, respectively. Both aliquots yield younger apparent ages for the first few steps, implying slight argon loss, but are followed by concordant flat spectrum that yield plateau ages of 117.95±0.24 Ma and 116.97±0.17 Ma comprising 74.69% and 70.66% of the 39Ar released, respectively (Fig. 10c, e). The age of the flakes is slightly older than
that of the aggregates, while the plateau of the aggregates is slightly flatter than that of the flakes (Fig. 10c, e). Excess argon possibly from potential inclusions in the flakes may account for the slightly older apparent age in the second heating step for the flake aliquot, which is also supported by increasing
36Ar
extracted in
the second step (Table 4). Both inverse isochrons suggest an age of ~117 Ma (Fig. 10d, f), which is very close to the age for the aggregates. The aggregates that contain more radiogenic argon cluster close to the X-axis, thus making the inverse age less robust (Fig. 10f). The initial
40Ar/36Ar
for both the flakes
(350.79±76.10) and aggregates (285.22±43.57) are within error of the accepted 40Ar/36Ar
atmosphere ratio. However, the spectrum of flakes is more discordant
and the majority of the gas was released at low temperature (Fig. 10c). Taking into account a higher MSWD of 4.07 for the flakes, it is possible that the age of the flakes is close to that of the aggregates at 116.97 Ma, but the slight excess argon coming from inclusions has elevated the age. Therefore, the age for the sericite is likely to be 117 Ma based on the fact that both inverse isochrons indicate that the amounts of trapped gas for the steps chosen in the plateaus are identical (Fig. 10d, f). For Sample JQD15D015B2 from a smoky-gray quartz-pyrite vein in the center of the orebody, both sericite flakes and aggregates underwent 34 heating steps (Tables 6-7). The low temperature ages may imply slight argon loss, whereas the intermediate steps did not suffer from argon loss, and the remaining few steps yield decreasing apparent ages with large error bars, constituting arc age spectra (Fig. 10g, i). Since these spectra are discordant, they can only give
weighted mean ages of 121.64±0.18 Ma and 119.28±0.16 Ma that respectively account for 25.00% and 38.01% of the total
39Ar
released (Fig. 10g, i): these
ages are interpreted as minimum ages (McDougall and Harrison, 1999). The inverse isochron ages for the flakes and aggregates are 121.22±0.70 Ma and 119.35±0.29 Ma (Fig. 10h, j), which are in agreement with their corresponding weighted mean ages. The initial 40Ar/36Ar ratios for both the flakes (349.94±85.00) and aggregates (275.64±59.14) are within error of the accepted
40Ar/36Ar
atmosphere ratio. Nearly all argon in the aggregates is radiogenic and they cluster close to the X-axis (Fig. 10j), making it difficult to generate a reliable inverse isochron.
6. Discussion 6.1 Timing and duration of gold mineralization in the Rushan deposit The close paragenetic relations among pyrite, quartz and sericite (Fig. 9) suggest that the temperature of the hydrothermal ore fluid was in the range of 225-400 °C (McCuaig and Kerrich, 1998). This has been confirmed by fluid inclusion studies that give homogenization temperatures of 170-377 °C for fluids in alteration zones and quartz veins (Hu et al., 2005). Therefore, the ore-forming temperature is consistent with the sericite argon closure temperature (350±50 °C, McDougall and Harrison, 1999) and the ages obtained represent the crystallization ages of sericite. Considering the close syn-genetic relationship between sericite and quartz plus pyrite (Figs. 8-9), and that sericite was deposited episodically from fluids that precipitated major vein minerals during
vein deposition (see Section 4.3 for more details), sericite crystallization is interpreted to have been contemporaneous with gold mineralization. Therefore, the argon crystallization ages of sericite represent the timing of gold mineralization. Interestingly, the ages of sericite aggregates are 0.98-2.36 My younger than those of their corresponding sericite flakes (Fig. 10), which provides new insights into selection of analyzed samples. The aggregates obtained following traditional separation processes are composed of tiny 10-20 μm sericite chips (Kent and McDougall, 1995), and the closure temperature of these chips may be lower than that of the corresponding medium-fine flakes because of a grain size effect, which would make their measured ages slightly younger. However, the ages of sericite aggregates and flakes are remarkably consistent in general. The sericite in Sample JQD15D015B2 from the smoky-gray quartz-pyrite vein in the center of the orebody yields a minimum age of 121.64-119.28 Ma (Fig. 10g, i), which is slightly older than equivalent ages of sericite from Sample JQD15D004B2 (117.95-116.97 Ma; Fig. 10c, e), a milky-white pyrite-quartz vein on the margin of the orebody. This suggests that the quartz veins in the center of the orebody formed slightly earlier than those on the margin. The host rock Sample JQD15D004B6 adjacent to the orebody is interpreted to have undergone incremental water-rock interactions because of episodic fluid injections, and its intermediate sericite
40Ar/39Ar
age of 119.18 Ma (Fig. 10a) probably represents
an integrated feedback of multiple fluid events throughout the entire mineralization event.
Previous studies obtained mineralization ages varying from 156.7 Ma to 104.8 Ma for the Rushan deposit (Table 1 and references therein). However some of the geochronological data are unreliable due to inappropriate samples or techniques: 1). a mixing age is often obtained with Rb-Sr dating on sericitequartz altered whole-rocks due to mixtures of minerals from variable sources; 2). the K-feldspar from alteration zones chosen for
40Ar/39Ar
analysis very likely
contains residual magmatic K-feldspar and is commonly retrogressively altered to sericite, thus resulting in a cooling or meaningless age; 3).
40Ar/39Ar
dating on
fluid inclusions is misleading due to the inevitable influence of abundant secondary fluid inclusions (Luo et al., 2000). Sericite is commonly co-precipitated with gold and ore minerals, and the relatively high closure temperature of sericite argon system means high resistance to disturbance from post-mineralization thermal events, making it a widely used mineral to constrain the timing of mineralization. However, it could be misleading if sericite is not properly selected. For example, the old
40Ar/39Ar
sericite age of 156.7±0.6-155.8±0.05 Ma (Li, 2004) is probably due to a mixture of hydrothermal sericite and magmatic muscovite from the wall rock considering no co-existence relations between sericite and gold and associated sulfide minerals were provided, and the age of wall rock granite is 161-138 Ma (Fig. 11; Hu et al., 2004; Guo et al., 2005; Zhang, 2011). Hu et al. (2006) reported a sericite
40Ar/39Ar
age of 128.8±0.1 Ma for a sample from intensively sericite-
quartz altered host rock adjacent to the auriferous quartz vein, and this age was further interpreted to represent an earlier hydrothermal mineralization event.
However, the variation in apparent ages in each heating step makes it unconvincing to build a robust plateau age, given the criteria required by the MM5400 Mass Spectrometer used in their study. On the other hand, the sericite chosen has a coarse grain size and may be mixed with magmatic muscovite, since similar ages are acquired based on
40Ar/39Ar
analyses on biotite from the
fresh Kunyushan granite near the Rushan gold deposit (129.0-126.9 Ma, Li et al., 2006), biotite from the fresh Kunyushan granite near the Denggezhuang gold deposit (129.0±0.6 Ma, Zhang et al., 1995), white mica from a synkinematic pegmatite vein in the Sulu Terrane (128.2±0.7 Ma, Webb et al., 2006). Hence a mixed age or cooling age was probably obtained in their study. Li et al. (2006) conducted sericite
40Ar/39Ar
dating on sericite from ore samples in the Rushan
gold deposit, and an ore-forming age of 109.3-107.7 Ma was proposed based on the dating results of six aliquots from two samples. Careful microscopic observation and EPMA analysis proved the purity of the sericite selected. However, the integrated ages in their study are systematically 2-8 My lower than the corresponding plateau ages, and the lower temperature steps for our samples have yielded apparent ages between 110-102 Ma (Fig. 10c, g). Therefore, the young ages in their study may have resulted from argon loss induced by post-mineralization structural or hydrothermal events (McDougall and Harrison, 1999). Notably, Hu et al. (2004) identified hydrothermal zircons based on zircon morphology, common Pb contents, Th/U ratio, and compositions of fluid inclusions in zircons. A SHRIMP U-Pb age of 117±3 Ma was obtained for the
hydrothermal zircons, and, although the error is high, this age is in agreement within error with our dating results. In addition, sericite
40Ar/39Ar
ages for the
Yinggezhuang deposit (120.02±0.38 Ma), Xipo deposit (121.65±0.48 Ma) and Sanjia deposit (116.51±0.47 Ma) were obtained by Chen (2017), and these ages from different gold deposits in the Muping-Rushan belt are also in accordance with the results presented here. Therefore, the gold mineralization in the Rushan gold deposit is interpreted to have occurred from ca. 122 to 117 Ma, with this range overlapping or being slightly younger than published ages of the gold deposits in northwestern Jiaodong (e.g. Li et al., 2003; Yang et al., 2014b, 2017; Bi and Zhao, 2017; Ma et al., 2017; Zhang et al., 2019a). No crosscutting relationships between the major vein forming Orebody II and other mineralized veins nor superimposition of alteration zones around Orebody II are recorded in this and previous studies (e.g. Li et al., 1996). A single metallogenic event involving episodic fluid events may best characterize the Rushan gold deposit, with duration of gold mineralization probably lasting for about 5 My, from ca. 122 Ma to 117 Ma. The Kunyushan granite intruded Jingshan Group metamorphic rocks and Sulu UHP at 160-138 Ma (Fig. 11; Hu et al., 2004; Guo et al., 2005; Zhang, 2011), and it cooled down through 300±50 °C (closure temperature of biotite 40Ar/39Ar
system, McDougall and Harrison, 1999) at 129-127 Ma (Zhang et al.,
1995; Li et al., 2006). Subsequently, ore-forming fluids migrated upwards along faults and auriferous quartz veins were precipitated at 122-117 Ma. The magmatic-hydrothermal system induced by a single intrusive event generally is
sustained for no more than 1 My, and the total duration lasts less than 10 My given slow cooling caused by deep intrusion of magma (Cathles et al., 1997; Henry et al., 1997). Therefore, such a significant temporal gap between granite emplacement and cooling and gold mineralization indicates that the Kunyushan granite and gold metallogeny are not genetically related. Moreover, the closure temperature for the biotite 40Ar/39Ar system (300±50 °C, McDougall and Harrison, 1999) is lower than the temperature of the ore-forming fluid (Hu et al., 2006), meaning that the ore-fluid temperature was higher than that of the host rock during ore-formation and not the reverse as in a magmatic-hydrothermal system. The timing of gold mineralization just overlaps intrusion of the Sanfoshan monzonite, which intruded the Kunyushan granite in the southeastern part of the gold belt at 118-113 Ma (Guo et al., 2005; Goss et al., 2010; Zhang, 2011). However, the earliest formation ages of 118-117 Ma proposed by Goss et al (2010) is tenuous given that no more than ten zircon grains in each sample produced discordant isochrones. Instead, the Sanfoshan monzonite probably intruded at ca.116-113 Ma (e.g. Guo et al., 2005; Zhang, 2011), a timing outside the range of ages of gold mineralization. In addition, the Sanfoshan monzonite is not spatially associated with the Rushan gold deposit, and the No. II orebody extends down-dip for more than 1 km without notable change in alteration, mineralogy, and ore fluid chemistry (e.g. Hu et al., 2005). These constraints effectively rule out a magmatic hydrothermal origin for the Rushan deposit.
6.2 Fault dynamics, fluid pressure fluctuation and fault valve behaviour
Statistical data on orientations of the syn-mineralization conjugate joints which are filled by quartz-sulfide veins in different sections of the JiangjunshiQuhezhuang Fault suggest that the maximum compressional stress, σ1, during gold deposition was NW-SE with a subhorizontal plunge (Hu, 1995; Gao et al., 2011). Such a stress is consistent with the σ1 constrained for the neighboring Shigou-Wushan Fault during gold mineralization (He and Zhang, 2006). The Jiangjunshi-Quhezhuang Fault is interpreted to have had sinistral and reverse motion during gold mineralization, with low total fault slip along the synstructural vein (cf. Cox, 2016). The low displacements are consistent with the low differential stress value of 83-103 MPa estimated from lattice dislocation of quartz from the high-angle quartz veins in the Rushan deposit (Gao et al., 2011). This suggests that regional σ1 was low, accounting for sparse evidence of regional compression or transpression in the district. Although rare, there is confirmatory evidence from the Jiaolai Basin, where the widespread conjugate shear joints in the upper Laiyang formation suggest a NWW-SEE compressional stress that may account for the disconformity between the Laiyang formation and overlying Qingshan formation (Ren et al., 2007). The occurrence of H2O-CO2 primary fluid inclusions with highly varied CO2 volumetric proportions in the Rushan deposit (Hu et al., 2005) suggest that fluids were trapped under sub-solvus conditions. These inclusions homogenize within the same temperature range, supporting a model in which trapped inclusions formed by fluid immiscibility of a parental homogeneous fluid (Ramboz et al., 1982). Pressures of fluid inclusions that trapped immiscible fluids are estimated
through the isochore intersection method (Fig. 12). Isochores are calculated based on the equations of Bakker (1999) for CO2-H2O fluid inclusions using the microthermometric data from Hu et al. (2005), and the trapping temperatures are estimated using Loucks' (2000) statistical method. The lithostatic and hydrostatic pressure range are estimated in order to compare with the pressures of the ore-forming fluids. Yao et al. (2006) estimated that Cretaceous geothermal gradients in the neighboring basins adjacent to the Jiaodong Peninsula were ca. 45 °C/km. Considering that the geothermal gradient in a stable terrane is normally lower than that of nearby basins, a maximum geothermal gradient of 40 °C/km and a minimum value of 30 °C/km are assumed. In addition, an average rock density of 2.7 g/cm3 and fluid density of 1.0 g/cm3 are also utilized to build the pressure gradients. The pressures of CO2-H2O fluid inclusions corresponding to their trapping temperatures are in the range of 247 to 108 MPa, showing remarkable pressure fluctuations from supralithostatic to nearly hydrostatic (Fig. 12): this range is broadly in agreement with that calculated by Hu et al. (2005). Abrupt drops from lithostatic to hydrostatic pressures would cause a dramatic decrease in silica solubility and thus massive quartz deposition (Rimstidt, 1997), as recorded at Rushan. High-angle shear veins and low-angle extension veins are common in lode gold deposits controlled by movement on high-angle reverse strike-slip faultfracture systems (Sibson, 1990; Groves, et al., 1998; Nauyen et al., 1998; Zhang et al., 2019c). The internal textures of both types of veins provide effective
insights into fluid evolution during quartz veining. The existence of the dark-gray elongate slab with multiple crack-seal structures at the contact of the quartz vein and its host rock (Figs. 5d, 6k) argues strongly for existence of episodic fluid events. Episodic fluctuation of fluid pressure from supralithostatic to hydrostatic, the fault valve model (Sibson et al., 1988), is considered to have played a vital role in the deposition of high- angle and low-angle veins (e.g. Sibson et al., 1988; Cox, 1995, 2016; Goldfarb et al., 2005). In this model, the formation of faultrelated quartz veins in overpressured, high fluid-flux regimes is related to multiple earthquake ruptures released along regional major faults (Sibson et al., 1988), where earthquakes may relate to swarm seismicity, rather than main-shock to after-shock sequences (Cox, 2016). Some of the larger ruptures within swarms are spatially associated with “mini-after-shock” bursts whose activity decays with time (Cox, 2016). The Jiangjunshi-Quhezhuang Fault had sinistral and reverse movement during gold mineralization, with this type of high-angle oblique fault regarded as the most effective “valve” to trigger the uprise of fluids and fluctuation of fluid pressure (Sibson et al., 1981). 6.3 Process of progressive vein formation On the basis of sericite ages of samples from different locations, and characteristics of internal textures and microstructures of the high-angle shear veins, the detailed processes for deposition of such veins are proposed with reference to the fault valve model. It is interpreted that the ore-controlling fault remains sealed before gold mineralization. Fluid pressure below the seismogenic zone keeps building up
because of continuous supply, and when it is higher than lithostatic values, the low-angle fractures open up and failure is triggered on the fault section near the base of the seismogenic zone, nucleating an earthquake rupture that reactivates the fault (Fig. 13a). Dilatational space is formed due to the sinistral-reverse slip on the fault and it is more developed especially in fault segments with low dip (Fig. 13b), and thin wallrock laminae will be detached from the host rock contact. The large stress difference between the dilatational space and the rupture zone draws the geo-pressured fluid reservoir at depth upwards along the fault. Once the fluids are injected into the dilatational zone, they fracture the host rock and fluid immiscibility takes place due to the abrupt drop of fluid pressure (Cox, 1995). The intense supersaturation of silica results in massive deposition of quartz (Fig. 6b), and coarse-grained pyrite is precipitated as aggregates (Fig. 6c) to form the milky-white quartz layer, with the host rock breccias cemented by quartz and pyrite (Fig. 5b). Meanwhile, the detached host rock laminae are cemented and dragged into the same strike as that of the fault as a consequence of the oblique slip (Fig. 13c). As the rate of fluid pressure and temperature decrease declines, silica precipitates relatively slowly as euhedral comb-like to drusy quartz crystals with growth zoning (Fig. 6a), and with long axes at a high angle to the host rock wall. The coarse-medium grained pyrite, meanwhile, precipitates at the contact between wall rock and quartz veins, as well as boundaries of the host rock laminae in the quartz veins, to form thin sulfide laminae (Fig. 5c).
Subsequently, the supercharged fluids induced by “mini-aftershock” bursts fractures some of the pre-existing pyrite and quartz (Fig. 6e-f), thin sericitequartz-sulfide veinlets cut earlier-deposited coarse-grained minerals (Fig. 6i), and anhedral disseminated pyrite forms at the boundaries of quartz (Fig. 6d). As hydraulic fracturing continues, the concentration of metallic elements such as Ag, Au, Cu, Pb, Te and Zn in the fluid increases with the deposition of quartz and pyrite (Zhao et al., 1996; Liu et al., 2010), and they precipitate in the microfractures of early pyrite (Figs. 6g-h, 9h) or at interstitial boundaries. Carbonate occurs dominantly as calcite, and as the last mineral to form in each major fluid episode, it either fills the vugs (Fig. 6l) and the micro-fractures that truncate the earlier minerals (Fig. 6f), or occurs as discrete blocks in quartz veins (Fig. 5e). The milky-white quartz layer that formed earlier is thus partly rendered into the smoky-gray layer due to the multiple hydraulic fracturing and consequent deposition of fine grained minerals (Fig. 13d). The local existence of vugs implies that the rate of fracture propagation is higher than that of fluid supply in such places, such that the quartz is deposited slowly in equilibrium with a weakly supersaturated fluid. However, if the rate of fracture propagation is lower than that of fluid supply in terms of the whole dilatational zone, the fault is sealed because of the constant decrease in permeability induced by fluid discharge (Fig. 13d). At this stage, the fluid pressure starts to rise again until the next major rupture occurs. Once the next fault rupture is triggered, the stress releases preferentially along structural weaknesses such as contacts between the early quartz vein and
the host rock, and thus new dilatational spaces are created on both margins of the early quartz vein (Fig. 13e). The slightly older age for Sample JQD15D015B2 (Fig. 10g, i) from the smoky-gray quartz layer and the slightly younger age for Sample JQD15D004B2 (Fig. 10c, e) from the milky-white layer are consistent with this model. Early sulfide laminae formed along the host rock-vein contact are therefore detached from the wallrock and attached to the margin of the quartz vein (Fig. 13e). The upwelling ore-forming fluids enter the new dilatational space and the precipitation processes described above are renewed, resulting in the repetitive banding of the resultant quartz-pyrite vein (Fig 13f). The early-formed host rock breccias are progressively further altered due to interaction with the renewed fluid activity, and therefore the host rock breccias near the margin of the orebody are generally less altered than those in the center. In addition, the earlyformed quartz layers are frequently fractured by later fluids, as indicated by the quartz veinlet enclosing euhedral pyrite grains (Fig. 6j), host rock breccias truncated by the milky-white quartz layer in the outermost margin of the orebody (Fig. 5e), the smoky-gray quartz breccias in the milky-white quartz layer (Fig. 5e), and the dark-gray elongate slabs with multiple crack-seal structures at the contact of quartz vein and host rock (Figs. 5d, 6k). The gold-rich quartz lodes, featuring complex internal textures, are thus formed incrementally by episodic fault-valve processes.
7. Conclusion Gold mineralization at the Rushan gold deposit occurred between ca. 122 and 117 Ma, and thus overlap or are slightly younger than gold deposits in the northwestern Jiaodong Peninsula. The age difference between sericite samples from different spatial locations in the orebody suggests that the quartz veins on the margin of the orebody may be younger than those in the vein center. The temporal gap between mineralization age and emplacement plus cooling age of the ore-hosting Kunyushan granite negates a genetic relationship between them. The Sanfoshan monzonite is not spatially associated with gold mineralization and is slightly younger, thus negating a genetic relationship between them. High-angle shear veins and low-angle extension veins are reported for the first time from the Rushan gold deposit. Quartz vein deposition and gold mineralization were controlled by fault valve behavior under a weak NW-SE regional
transpressional
stress,
in
which
episodic
fluctuations
from
supralithostatic to hydrostatic fluid pressure triggered multiple fault ruptures induced by breaches of supralithostatic fluids under a seismogenic regime. The sequence of events is interpreted to be as follows: 1) the fault starts to slip with both reverse and sinistral motion, and dilatational zones are created; 2) the orefluids migrate upwards along the fault due to the large pressure difference between the dilatational zones and the deeper segments of the fault; 3) host rocks and earlier-deposited quartz veins are hydraulically fractured by renewed fluid flux; 4) abundant quartz, pyrite, gold, and other ore-related minerals are precipitated during fluid immiscibility caused by pressure fluctuations, and new
quartz veins formed along both margins of earlier quartz veins; 5) the fault is sealed by deposition of new quartz veins and the fluid pressure increases until the next breach cycle; and 6) resultant quartz veins with complex internal crackseal textures were deposited incrementally during these cycles. The combined result was the generation of a single strike-extensive quartz vein with incredibly complex internal structures and textures.
Acknowledgements Thanks are due to Professor Anthony Koppers for the help he gave during 40Ar/39Ar
analysis. Discussions with Professor Richard Ketcham provided useful
insights into our understanding of the argon data. We thank Drs. Zhongliang Wang, Binghan Chen, Yue Liu and Sirui Wang for their help in the field survey. Thorough reviews by two anonymous reviewers and the editorial assistance of Professor Franco Pirajno are gratefully acknowledged. The paper was dramatically improved by careful editing by Professor David Groves. This work was financially supported by the National Natural Science Foundation of China (41230311, 41572069), the National Key Research Program of China (2016YFC0600107-4), the Fundamental Research Funds for the Central Universities, China (2-9-2017-257), the Most Special Fund from the State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences (MSFGPMR201804) and the 111 Project of the Ministry of Science and Technology (BP0719021). S.X. Sai is indebted to grants from Scholarship
Program of the China Scholarship Council (201706400006) and the Society of Economic Geologists 2016 Graduate Students Fellowship.
Conflict of interest No conflict of interest exits in the submission of this manuscript, and the manuscript is approved by all authors for publication. I would like to declare on behalf of my co-authors that the work described is original research that has not been published previously, and is not under consideration for publication elsewhere, in whole or in part.
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Headings for tables Table 1 Previously published mineralization ages from the Muping-Rushan gold belt.
Table 2 Samples for sericite 40Ar/39Ar dating in the Rushan deposit.
Table 3
40Ar/39Ar
step heating data for sericite flakes from sericite-quartz
alteration Sample JQD15D004B6 in the Rushan gold deposit.
Table 4
40Ar/39Ar
step heating data for sericite flakes from gold ore Sample
JQD15D004B2 in the Rushan gold deposit.
Table 5
40Ar/39Ar
step heating data for sericite aggregates from gold ore Sample
JQD15D004B2 in the Rushan gold deposit.
Table 6
40Ar/39Ar
step heating data for sericite flakes from gold ore Sample
JQD15D015B2 in the Rushan gold deposit.
Table 7
40Ar/39Ar
step heating data for sericite aggregates from gold ore Sample
JQD15D015B2 in the Rushan gold deposit.
Figure captions Fig. 1 Geological sketch map of the North China Block and Jiaodong Peninsula (modified from Deng et al., 2019). GJF, Guocheng-Jimo Fault; HSF, HaiyangShidao Fault; JJF, Jiaojia Fault; MRF, Muping-Rushan Fault Zone; QHF, Qingdao-Haiyang Fault; QXF, Qixia Fault; RCF, Rongcheng Fault; SSDF,
Sanshandao Fault; TCF, Taocun Fault; WHF, Weihai Fault; WQYF, WulianQingdao-Yantai Fault Zone; ZPF, Zhaoyuan-Pingdu Fault; ZWF, Zhuwu Fault.
Fig. 2 Geological map of the Muping-Rushan gold belt (modified from Li et al., 1996 and Hu et al., 2007). CSF, Chahe-Sanjia Fault; GKF, Gekou Fault; JNSF, Jinniushan Fault; JQF, Jiangjunshi-Quhezhuang Fault; LHF, Laohuwo-Hezi Fault; QTF, Qinghushan-Tangjiagou Fault.
Fig. 3 Geological map of the Rushan gold deposit and cross-section showing the alteration zones (a-b, modified from Chen, 2017); profile at -865m level displaying the alteration zones, structures and the No. II Orebody (c).
Fig. 4 Field photographs showing the characteristics of the ore-controlling fault. (a) High-angle fault filled by the No. II Orebody, and lamprophyre which intrudes the Orebody; (b) Striations and steps indicating sinistral movement, overprinted by striations and steps indicating normal faulting. All in profile views.
Fig. 5 Field photographs showing the internal textures of high-angle shear veins. (a) Contact of sericite-quartz alteration zone and the No. II Orebody; (b) Host rock breccias in the No. II orebody, and potassic alteration zone wraps the Orebody directly; (c) Host rock and sulfide laminae in the No. II Orebody; (d) Quartz vein layers separated by dark crack-seal veins; (e) Host rock breccia in smoky-gray quartz layer truncated by milky-white quartz layer, smoky-gray quartz breccia in milky-white quartz layer, and cubic calcite block in smoky-gray quartz
layer. (a), (b) and (e) are upward views; (c) and (d) are profile views. Stars in (a) and (b) mark the precise locations of the samples for 40Ar/39Ar geochronology.
Fig. 6 Microstructures of high-angle shear veins. (a) Euhedral coarse quartz grains with clear growth zones on the margin of vein; (b) Euhedral-subhedral coarse-grained quartz without growth zones in the center of the quartz vein, and self-sealed quartz veinlets inside the coarse-grained quartz; (c) Cluster of slightly fractured pyrite aggregates, and later galena on the boundaries of pyrite; (d) Disseminated anhedral pyrite; (e) Fractured coarse-grained quartz; (f) Fractured coarse-grained pyrite cut by calcite veinlet; (g-h) Gold minerals and galena fill micro-fractures in pyrite; (i) Crack-seal veinlet with fragments of host quartz vein; (j) Quartz veinlet with euhedral pyrite grains; (k). Fine fragments of minerals in quartz vein and matrix-like minerals in host rock; (l) Open space in quartz filled by calcite. Au, gold; Cal, calcite; El, electrum; Ga, galena; Q, quartz; Ptz, petzite; Py, pyrite; Ser, sericite.
Fig. 7 Field photographs showing the internal textures of low-angle extension veins. (a) Low-angle extension veins adjacent to high-angle shear vein; (b) Lowangle extension veins in Jingshan Group metamorphic rocks; (c) Host rock laminae and series of vugs parallel to host rock wall; (d) Discontinuous pyrite laminae parallel to host rock wall, and angular host rock breccias in low-angle vein. All in profile view.
Fig. 8 Paragenetic sequence of hydrothermal minerals in the Rushan gold deposit. Thickness of the solid lines represents the relative abundance of minerals.
Fig. 9 Characteristics of samples chosen for
40Ar/39Ar
dating. (a) Gray-green
sericite-quartz altered rock; (b) Sericite cuts recrystallized quartz; (c) Sericite and muscovite in close spatial relationship with pyrite; (d) Massive sericite grains and later calcite veinlet; (e) Specimen showing contact of sericite-quartz alteration zone and vuggy milky-white quartz vein; (f) Sericite and coarse-grained quartz with growth zoning; (g) Sericite closely associated with pyrite cluster; (h) Gold minerals and hessite in micro-fractures in pyrite; (i) Smoky-gray quartz vein with disseminated pyrite; (j) Sericite associated with disseminated pyrite; (k) Sericite and pyrite in fine veinlet that cuts coarse quartz grains; (l) Stockwork filled by sericite, quartz and pyrite. Hes, hessite; Mus, muscovite; the other mineral abbreviations are the same as those in Figure 6.
Fig. 10
40Ar/39Ar
plateau and inverse isochron ages (2σ) for sericite from the
Rushan gold deposit.
Fig. 11 Diagram indicating the ages with 2σ analytical uncertainties determined for minerals and whole rocks from the Rushan deposit and the nearby area. Data source: magmatic zircon U–Pb from Hu et al. (2004), Guo et al. (2005) and
Zhang (2011); hydrothermal zircon U–Pb from Hu et al. (2004); biotite
40Ar/39Ar
from Zhang et al. (1995) and Li et al. (2006); sericite 40Ar/39Ar from this study.
Fig. 12 P-T diagram with isochores for fluid inclusions trapped under sub-solvus conditions. Gray vertical box is the homogenization temperatures for CO2-H2O fluid inclusions. Blue arrow corresponds to pressure fluctuation at trapping temperatures estimated from the method proposed by Loucks (2000). Fluid inclusion micro-thermometric data are from Hu et al. (2005).
Fig. 13 Cartoon showing the incremental emplacement of the high-angle shear veins. Note 160-138 Ma is the formation age for the ore-hosting Kunyushan granite: age data from Hu et al. (2004), Guo et al. (2005) and Zhang (2011).
Table 1. Previously published mineralization ages from the Muping-Rushan gold belt Deposit
Sample
Method
Age (Ma)
References
sericite-quartz altered rock
Rb-Sr
113.3±4.4
Zhang et al. (1994)
altered K-feldspar
Rb-Sr
121.3±0.6
Zhang et al. (1994)
sericite-quartz altered rock
Rb-Sr
104.8±1.5
Zhai et al. (1996)
108.2±0.3sericite
40
39
Ar/ Ar
Rushan
107.4±0.2 156.7±0.6-
Li (2004)
155.8±0.1 hydrothermal
Shrimp U-
zircon in quartz vein
Pb
sericite
40
sericite
40
altered K-feldspar
40
sericite-quartz altered rock fluid inclusions in quartz Denggezhuang
39
Ar/ Ar
117.0±3.0 109.3±0.3107.7±0.5
Hu et al. (2004) Li et al.(2006)
Ar/ Ar
39
128.8±0.1
Hu et al. (2006)
Ar/ Ar
39
118.7±1.2
Cao (2013)
Rb-Sr
118.0±9.0
Zhang et al. (1995)
117.5
Zhao et al. (1996)
40
39
Ar/ Ar
altered K-feldspar
40Ar/39Ar
123.4±0.5
Xue et al. (2019)
sericite
40Ar/39Ar
104.8±1.1
Xue et al. (2019)
altered K-feldspar
40Ar/39Ar
111.2±0.7
Cui (2012)
sericite
40Ar/39Ar
120.0±0.4
Chen (2017)
Xipo
sericite
40Ar/39Ar
121.7±0.5
Chen (2017)
Hubazhuang
sericite
Rb-Sr
126.5±5.6
Cai et al. (2011)
Sanjia
sericite
40Ar/39Ar
116.5±0.5
Chen (2017)
Yinggezhuang
Table 2 Sample descriptions for sericite 40Ar/39Ar dating in the Rushan deposit Sample
Location Intensive
Rock type
Minera l
Phase
sericite-quartz Sericite-
JQD15D004B alteration zone adjacent to the quartz
Sericit
6
e
No. II Orebody near the N7 altered
Aggregate
Measuring Point in Level -865m granite JQD15D004B
Margin of the No. II Orebody
Milky-white
Sericit
Flake and
quartz ore
e
aggregate
JQD15D015B near the E4 Transverse Drift in Smoky-gray
Sericit
Flake and
2
e
aggregate
2
near the N7 Measuring Point in Level -865m Center of the No. II Orebody Level -865m
quartz ore
1
Table 3 40Ar/39Ar step heating data for sericite flakes from sericite-quartz alteration Sample
2
JQD15D004B6 in the Rushan gold deposit Me asure ment s
R elati ve Abu nda nce
18E2 7207
0.2 %
18E2 7208
0.3 %
18E2 7210
0.4 %
18E2 7211
0.5 %
18E2 7212
0.6 %
18E2 7214
0.7 %
18E2 7215
0.8 %
18E2 7216
0.9 %
18E2 7218*
1.0 %
18E2 7219*
1.1 %
18E2 7220*
1.2 %
18E2 7222*
1.3 %
18E2 7223*
1.4 %
18E2 7224*
1.5 %
18E2 7226*
1.7 %
36
A r [f A ] 6 . 8 8 1 . 1 2 0 . 4 7 0 . 2 8 0 . 1 4 0 . 1 4 0 . 0 6 0 . 0 6 0 . 0 3 0 . 0 3 0 . 0 5 0 . 0 2 0 . 0 2 0 . 0 2 0 . 0 2
37
Ar [f A]
0. 2 5
11 .5 5
1. 01
0. 2 9
27 8. 60
0. 38
0. 3 8
16 8. 07
0. 38
0. 4 3
86 .5 9
0. 40
0. 6 1
59 .7 8
0. 43
0. 6 7
58 .4 2
0. 42
1. 2 3
27 .3 3
0. 55
1. 2 1
28 .2 9
0. 53
1. 8 1
15 .7 6
0. 79
2. 1 8
12 .7 8
0. 89
1. 4 2
11 .9 5
0. 94
3. 3 6
3. 03
3. 50
2. 8 9
4. 38
2. 45
3. 4 5
3. 54
2. 95
3. 7 4
2. 68
4. 01
38
39
A r [f A ] 1 . 5 1 0 . 8 6 0 . 6 7 0 . 6 7 0 . 3 3 0 . 5 2 0 . 2 0 0 . 2 2 0 . 1 4 0 . 1 4 0 . 2 8 0 . 1 2 0 . 1 7 0 . 0 8 0 . 1 0
A r [f A ] 1 4. 2 6 5 3. 6 8 5 0. 2 6 5 1. 4 7 2 5. 6 2 4 1. 4 4 1 6. 4 7 1 7. 3 3 1 2. 1 0 1 1. 4 5 2 3. 0 0
0. 68 1. 15 1. 35 1. 36 2. 77 1. 82 4. 47 4. 40 6. 78 6. 94 3. 33
Age
A r [fA ]
40(r )/39 (k)
0. 1 1
25 33. 09
0. 0 1
35. 09
±0 .7 3
97 .0 6
0. 0 7
25 52. 60
0. 0 1
41. 94
±0 .0 7
0. 0 7
22 75. 49
0. 0 1
42. 89
0. 0 7
22 90. 40
0. 0 1
0. 0 8
11 42. 82
0. 0 7
40
(Ma)
Ar (r)
40
Ar (k)
39
K/C a
(%)
(%)
± 1. 96
19.7 4
3.46
0.5 31
± 0.0 11
11 5. 43
± 0. 18
87.9 0
12.9 8
0.0 83
± 0.0 01
±0 .0 6
11 7. 95
± 0. 16
94.5 3
12.1 7
0.1 28
± 0.0 01
43. 08
±0 .0 6
11 8. 47
± 0. 16
96.7 2
12.4 8
0.2 55
± 0.0 02
0. 0 1
43. 19
±0 .0 7
11 8. 76
± 0. 19
96.6 9
6.21
0.1 84
± 0.0 02
18 31. 23
0. 0 1
43. 35
±0 .0 6
11 9. 17
± 0. 16
98.0 1
10.0 5
0.3 05
± 0.0 03
0. 1 0
72 8.4 0
0. 0 1
43. 37
±0 .0 9
11 9. 22
± 0. 23
97.9 7
3.99
0.2 59
± 0.0 03
0. 0 9
76 8.3 3
0. 0 1
43. 52
±0 .0 8
11 9. 62
± 0. 22
98.0 8
4.20
0.2 63
± 0.0 03
0. 1 2
53 3.8 6
0. 0 2
43. 44
±0 .1 1
11 9. 40
± 0. 28
98.3 3
2.93
0.3 30
± 0.0 05
0. 1 2
50 3.9 4
0. 0 2
43. 35
±0 .1 1
11 9. 19
± 0. 29
98.4 5
2.78
0.3 85
± 0.0 07
0. 0 8
10 12. 75
0. 0 1
43. 42
±0 .0 7
11 9. 36
± 0. 20
98.6 0
5.58
0.8 28
± 0.0 16
8. 35
9. 5 3
0. 1 4
41 7.5 1
0. 0 2
43. 27
±0 .1 3
11 8. 97
± 0. 33
98.8 0
2.31
1.3 54
± 0.0 95
5. 55
1 3. 2 4
0. 1 1
58 0.6 7
0. 0 1
43. 40
±0 .1 0
11 9. 32
± 0. 27
98.9 5
3.21
1.2 99
± 0.0 64
11 .0 0
7. 3 4
0. 1 7
32 2.8 0
0. 0 2
43. 31
±0 .1 5
11 9. 07
± 0. 41
98.5 0
1.78
0.8 93
± 0.0 53
9. 42
8. 0 5
0. 1 5
35 2.9 4
0. 0 2
43. 27
±0 .1 4
11 8. 97
± 0. 37
98.7 2
1.95
1.2 90
± 0.1 03
56
18E2 7227*
1.9 %
18E2 7228*
2.2 %
18E2 7230*
2.5 %
18E2 7231
2.8 %
18E2 7232
3.1 %
18E2 7234
3.4 %
18E2 7235
3.8 %
18E2 7236
4.2 %
18E2 7238
4.6 %
18E2 7239
5.0 %
0 . 0 3 0 . 0 1 0 . 0 1 0 . 0 2 0 . 0 2 0 . 0 2 0 . 0 2 0 . 0 2 0 . 0 2 0 . 0 1
2. 4 1
3. 50
3. 10
5. 2 7
1. 47
7. 40
4. 6 6
1. 85
5. 86
3. 1 5
1. 26
8. 64
3. 6 4
0. 55
19 .9 2
2. 8 0
0. 79
13 .0 8
3. 7 2
0. 46
22 .2 3
3. 8 2
0. 47
22 .5 8
3. 4 5
1. 05
10 .4 6
4. 2 1
0. 10
10 3. 47
0 . 1 5 0 . 0 7 0 . 0 7 0 . 0 9 0 . 0 6 0 . 0 9 0 . 0 6 0 . 0 4 0 . 0 4 0 . 0 2
6. 57
1 1. 6 6
0. 1 2
51 1.7 6
0. 0 2
43. 27
±0 .1 1
11 8. 96
± 0. 28
98.5 5
2.83
1.4 33
± 0.0 89
13 .9 7
4. 5 4
0. 2 3
19 9.3 4
0. 0 4
43. 17
±0 .2 2
11 8. 68
± 0. 57
98.3 9
1.10
1.3 27
± 0.1 97
14 .1 6
4. 5 3
0. 2 6
19 9.5 7
0. 0 4
43. 24
±0 .2 4
11 8. 88
± 0. 65
98.2 0
1.10
1.0 55
± 0.1 24
9. 83
6. 2 7
0. 1 9
27 4.2 1
0. 0 3
42. 84
±0 .1 8
11 7. 82
± 0. 47
97.9 3
1.52
2.1 31
± 0.3 68
15 .5 9
4. 7 0
0. 2 3
20 5.7 3
0. 0 4
42. 69
±0 .2 2
11 7. 42
± 0. 58
97.5 2
1.14
3.6 56
± 1.4 57
10 .4 3
6. 4 1
0. 1 8
27 8.4 3
0. 0 3
42. 43
±0 .1 7
11 6. 73
± 0. 45
97.6 5
1.55
3.4 86
± 0.9 12
18 .4 5
3. 6 3
0. 3 3
15 7.7 0
0. 0 5
42. 01
±0 .3 0
11 5. 60
± 0. 79
96.8 1
0.88
3.3 65
± 1.4 96
23 .6 6
3. 5 2
0. 3 1
15 4.5 1
0. 0 5
42. 55
±0 .2 9
11 7. 05
± 0. 76
96.9 8
0.85
3.1 99
± 1.4 45
22 .2 3
2. 9 5
0. 3 7
12 9.0 2
0. 0 6
41. 96
±0 .3 4
11 5. 47
± 0. 90
95.9 6
0.72
1.2 12
± 0.2 54
57 .9 5
1. 2 8
0. 8 6
56. 89
0. 1 3
41. 43
±0 .7 7
11 4. 07
± 2. 04
92.9 6
0.31
5.3 35
± 11. 04 0
Table 3 40Ar/39Ar step heating data for sericite flakes from sericite-quartz alteration Sample JQD15D004B6 in the Rushan gold deposit (continued) 18E2 7240
5.4 %
18E2 7242
5.7 %
18E2 7243
6.1 %
18E2 7244
6.5 %
18E2 7246
7.0 %
18E2 7247
7.5 %
18E2 7248
8.0 %
0 . 0 2 0 . 0 1 0 . 0 1 0 . 0 3 0 . 0 2 0 . 0 1 0 .
3. 6 2
0. 10
10 9. 70
4. 5 1
0. 09
11 6. 54
4. 3 5
0. 20
56 .2 9
2. 0 0
0. 10
10 6. 63
2. 8 6
0. 25
41 .7 5
4. 0 8
0. 01
98 4. 06
3. 8
0. 08
13 8.
0 . 0 1 0 . 0 1 0 . 0 1 0 . 0 3 0 . 0 1 0 . 0 1 0 .
89 .4 7
1. 3 2
0. 8 4
58. 37
0. 1 3
40. 62
±0 .7 4
11 1. 90
± 1. 97
62 .7 6
0. 8 0
1. 3 8
36. 51
0. 2 1
41. 18
±1 .2 3
11 3. 38
± 3. 28
65 .3 6
0. 8 9
1. 2 8
40. 76
0. 1 9
41. 19
±1 .1 4
11 3. 41
± 3. 04
31 .8 1
1. 5 3
0. 7 3
71. 73
0. 1 1
40. 74
±0 .6 5
11 2. 23
± 1. 74
13 8. 14
1. 0 2
1. 0 6
48. 19
0. 1 6
40. 79
±0 .9 5
11 2. 36
± 2. 54
72 .9 5
0. 6 4
1. 7 3
30. 18
0. 2 5
40. 77
±1 .5 3
11 2. 30
± 4. 10
97 .5
0. 6
1. 7
30. 22
0. 2
40. 97
±1 .5
11 2.
± 4.
57
9 1. 8 1 8 9. 7 3 9 0. 0 5 8 6. 8 9 8 6. 7 4 8 5. 8 4 8 4.
0.3 2
5.82 8
± 12.78 7
0.1 9
3.69 6
± 8.615
0.2 2
1.96 4
± 2.212
0.3 7
6.65 3
± 14.18 9
0.2 5
1.79 2
± 1.496
0.1 5
25.6 74
± 505.2 99
0.1 5
3.44 8
± 9.562
18E2 7250
3 4
8.5 %
0 2 0 . 0 2
3 2. 6 5
66 0. 04
22 3. 83
0 1 0 . 0 2
4
3
9
46 .7 6
1. 0 0
1. 1 1
5 47. 68
0. 1 6
40. 83
9
83
25
±0 .9 9
11 2. 46
± 2. 65
9 2 8 5. 5 1
0.2 4
J value= 0.00157149 ± 0.00000099; Total fusion age=117.38 ± 0.17 Ma (2σ); * represents the steps chosen for weighted mean age calculation
5
58
9.74 0
± 43.60 3
6
Table 4 40Ar/39Ar step heating data for sericite flakes from gold ore Sample JQD15D004B2 in
7
the Rushan gold deposit Mea surem ents
Re lativ e Abu ndan ce
18E27 180
0.2 %
18E27 181*
0.3 %
18E27 183*
0.4 %
18E27 184*
0.5 %
18E27 185*
0.6 %
0. 0 4
1. 5 6
0. 1 1
10 1.1 9
0. 0 8
18E27 187
0.7 %
0. 0 4
1. 4 3
0. 1 1
93. 95
0. 0 6
18E27 188
0.8 %
0. 0 3
1. 7 8
0. 0 8
12 7.8 5
0. 0 5
18E27 189
0.9 %
0. 0 3
1. 8 6
0. 0 1
19 28. 12
0. 0 5
18E27 191
1.0 %
0. 0 2
2. 2 1
0. 0 3
35 9.5 8
0. 0 4
18E27 192
1.1 %
0. 0 2
2. 1 2
0. 0 5
21 0.8 3
0. 0 4
18E27 193
1.2 %
0. 0 2
2. 3 3
0. 0 4
27 6.6 2
0. 0 3
18E27 195
1.3 %
0. 0 2
2. 4 4
0. 0 6
17 9.4 1
0. 0 2
18E27 196
1.4 %
0. 0 2
2. 1 0
0. 1 5
69. 69
0. 0 3
18E27 197
1.5 %
0. 0 3
1. 7 5
0. 0 5
19 4.6 5
0. 0 3
18E27 199
1.7 %
0. 0 3
1. 7 7
0. 0 6
17 5.4 8
0. 0 1
18E27 200
1.9 %
0. 0 3
1. 8 4
0. 2 0
51. 02
0. 0 2
36
37
38
A r [f A ] 3. 3 4 0. 9 1 0. 1 9 0. 0 8
0. 2 6 0. 3 0 0. 5 0 0. 7 7
A r [f A ] 0. 6 1 1. 2 9 0. 3 6 0. 2 7
A r [f A ] 1. 1 4 1. 9 0 0. 5 4 0. 2 0
18. 16 8.3 0 28. 09 38. 15
0. 8 8 0. 5 1 1. 7 9 4. 9 5 1 2. 8 1 1 5. 2 3 1 8. 0 5 2 0. 4 4 2 7. 0 2 2 7. 2 8 3 2. 7 4 4 1. 8 6 3 4. 0 5 3 4. 6 4 7 7. 4 5 5 1. 8 0
39
Ar [f A]
A r [fA ]
40
38 .4 3 14 0. 89 41 .5 3 15 .3 1
0. 0 7 0. 0 6 0. 0 7 0. 1 0
25 13. 58 63 06. 14 18 32. 92 67 7.6 0
0. 0 1 0. 0 0 0. 0 0 0. 0 1
5. 75
0. 2 1
25 5.9 1
0. 0 1
5. 10
0. 2 1
22 6.9 5
3. 59
0. 3 0
3. 32
40(r )/39( k)
Age (Ma)
40
39
Ar (r)
Ar (k)
(% )
(% ) 14 .1 1 51 .7 1 15 .2 5
K/ C a
±0 .1 9 ±0 .0 5 ±0 .0 6 ±0 .0 9
10 9. 82 11 8. 13 11 7. 88 11 7. 70
± 0. 51 ± 0. 15 ± 0. 16 ± 0. 24
60 .7 7 95 .7 5 96 .9 0 96 .4 8
42.6 9
±0 .1 9
11 7. 67
± 0. 50
95 .9 3
2. 11
2 3. 2
± 47.0
0. 0 1
42.3 3
±0 .1 9
11 6. 73
± 0. 51
95 .1 8
1. 87
2 0. 1
± 37.8
16 0.9 1
0. 0 2
42.4 2
±0 .2 7
11 6. 95
± 0. 73
94 .5 9
1. 32
1 8. 2
± 46.6
0. 3 6
14 8.9 7
0. 0 2
42.3 7
±0 .3 2
11 6. 82
± 0. 84
94 .3 7
1. 22
2 6 5. 1
± 102 23.2
2. 46
0. 4 3
11 0.9 3
0. 0 2
42.4 4
±0 .3 8
11 7. 02
± 1. 02
94 .1 1
0. 90
3 6. 5
± 262. 5
2. 29
0. 4 7
10 3.6 1
0. 0 3
42.3 6
±0 .4 2
11 6. 80
± 1. 12
93 .6 0
0. 84
1 9. 9
± 83.9
2. 25
0. 5 0
10 1.5 6
0. 0 2
42.2 3
±0 .4 4
11 6. 45
± 1. 19
93 .4 9
0. 83
2 4. 7
± 136. 5
1. 59
0. 6 6
74. 03
0. 0 3
42.8 4
±0 .5 9
11 8. 08
± 1. 58
91 .9 9
0. 58
1 1. 4
± 41.1
2. 38
0. 4 8
10 7.7 6
0. 0 2
42.2 1
±0 .4 2
11 6. 41
± 1. 13
93 .3 4
0. 87
6. 7
± 9.3
2. 31
0. 4 6
10 6.2 1
0. 0 3
42.1 4
±0 .4 1
11 6. 21
± 1. 10
91 .6 7
0. 85
1 8. 4
± 71.8
2. 28
0. 5 2
10 4.7 9
0. 0 3
42.5 8
±0 .4 6
11 7. 39
± 1. 21
92 .7 3
0. 84
1 5. 7
± 55.3
2. 95
0. 3 6
13 4.8 1
0. 0 2
42.9 4
±0 .3 3
11 8. 36
± 0. 88
93 .9 7
1. 08
6. 4
± 6.5
59
39.7 5 42.8 6 42.7 6 42.7 0
5. 62
2 7. 3 4 7. 1 4 9. 4 2 4. 7
± 9.9 ± 7.8 ± 27.8 ± 18.8
8 9
J value= 0.00157517 ± 0.00000099; Total fusion age=116.76 ± 0.18 Ma (2σ); * represents the steps chosen for plateau age calculation
10
60
11
Table 5 40Ar/39Ar step heating data for sericite aggregates from gold ore Sample
12
JQD15D004B2 in the Rushan gold deposit Mea surem ents
Re lativ e Abu nda nce
18E27 120
0.3 %
18E27 122*
0.4 %
18E27 123*
0.5 %
18E27 124*
0.6 %
18E27 126*
0.7 %
18E27 127*
0.8 %
18E27 128*
0.9 %
18E27 130*
1.0 %
18E27 131*
1.1 %
18E27 132*
1.2 %
18E27 134*
1.3 %
18E27 135*
1.4 %
18E27 136*
1.5 %
18E27 138*
1.7 %
18E27 139*
1.9 %
18E27 140*
2.2 %
18E27 142*
2.5 %
18E27 143*
2.8 %
18E27 144*
3.1 %
18E27 146*
3.4 %
36
37
38
A r [f A ] 1. 7 0 0. 2 4 0. 1 4 0. 1 0 0. 0 8 0. 0 6 0. 0 6 0. 0 4 0. 0 4 0. 0 3 0. 0 3 0. 0 3 0. 0 3 0. 0 3 0. 0 3
0. 7 1 0. 8 3 0. 9 4 1. 1 1 1. 1 7 1. 3 7 1. 4 5 1. 8 2 1. 9 2 2. 1 6 1. 9 9 2. 4 0 2. 6 6 2. 2 0 2. 3 1
A r [f A ] 4. 9 6 8. 0 8 1. 1 9 1. 1 0 1. 4 7 3. 8 5 2. 1 7 1. 0 6 1. 0 0 0. 6 3 1. 0 7 0. 9 1 1. 3 6 1. 0 9 0. 4 0
27 .5 4
A r [f A ] 6. 9 3 4. 0 4 2. 0 4 1. 2 2 0. 8 9 0. 6 4 0. 5 9 0. 4 7 0. 4 1 0. 3 9 0. 3 6 0. 3 3 0. 3 3 0. 4 0 0. 3 9
0. 3 7 0. 4 1 0. 6 1 0. 8 3 1. 1 2 1. 4 5 1. 6 7 1. 9 5 2. 4 3 2. 3 9 2. 6 6 2. 8 6 2. 8 2 2. 3 9 2. 5 2
0. 0 3
2. 5 7
0. 0 6
19 1. 50
0. 3 1
0. 0 4 0. 0 3 0. 0 4 0. 0
1. 9 2 2. 5 7 1. 7 3 2. 0
0. 3 8 0. 2 9 0. 4 3 0. 0
27 .8 4 34 .9 3 25 .1 9 27 1.
0. 4 0 0. 2 9 0. 4 0 0. 3
2. 51 1. 49 8. 74 9. 02 7. 16 2. 98 5. 11 10 .0 5 10 .6 0 16 .2 6 10 .0 5 11 .9 3 8. 16 9. 60
39
A r [fA]
52 7. 05 32 6. 68 16 4. 88 97 .8 0 72 .5 4 51 .3 4 48 .6 8 38 .2 0 32 .9 9 31 .5 1 29 .7 8 26 .8 6 25 .5 7 32 .9 3 31 .4 8
0. 1 6 0. 1 6 0. 1 6 0. 1 6 0. 1 7 0. 1 7 0. 1 7 0. 1 7 0. 1 7 0. 1 7 0. 1 7 0. 1 7 0. 1 7 0. 1 7 0. 1 7
222 91. 96 139 50. 02 702 2.2 1 415 7.0 5 309 2.9 1 219 3.4 8 207 9.4 5 163 2.2 7 141 2.2 9 134 8.5 0 127 5.8 8 114 9.8 0 109 3.7 5 141 1.2 2 134 7.7 6
0. 0 0 0. 0 0 0. 0 1 0. 0 0 0. 0 0 0. 0 1 0. 0 1 0. 0 1 0. 0 1 0. 0 1 0. 0 1 0. 0 1 0. 0 1 0. 0 1 0. 0 1
3. 3 9
24 .6 1
0. 1 7
105 2.7 0
0. 0 1
2. 5 0 3. 0 6 2. 3 4 2. 9
31 .9 8 23 .1 2 33 .0 9 25 .2
0. 1 7 0. 1 7 0. 1 7 0. 1
136 9.3 3
0. 0 1 0. 0 1 0. 0 1 0. 0
Ar [f A]
40
992 .05 141 8.1 9 108 2.8
61
40(r )/39( k)
40
Age (Ma)
41.3 5
0. 14
42.4 9
0. 14
42.3 3
0. 14
42.2 0
0. 14
42.3 3
0. 14
42.3 9
0. 14
42.3 7
0. 14
42.4 1
0. 14
42.4 8
0. 14
42.4 8
0. 14
42.5 1
0. 15
42.5 0
0. 15
42.4 7
0. 15
42.5 7
0. 14
42.5 2
0. 15
42.4 6
0. 15
42.4 7
0. 14
42.5 6
0. 15
42.4 8
0. 14
42.5 5
0. 15
Ar (r) (% )
11 4. 02 11 7. 08 11 6. 66 11 6. 31 11 6. 65 11 6. 82 11 6. 77 11 6. 86 11 7. 06 11 7. 06 11 7. 12 11 7. 10 11 7. 03 11 7. 29 11 7. 16
± 0. 36 ± 0. 37 ± 0. 37 ± 0. 37 ± 0. 37 ± 0. 38 ± 0. 38 ± 0. 38 ± 0. 38 ± 0. 38 ± 0. 39 ± 0. 39 ± 0. 39 ± 0. 38 ± 0. 39
97 .7 5 99 .5 0 99 .3 9 99 .2 9 99 .2 7 99 .2 2 99 .1 9 99 .2 4 99 .2 3 99 .2 8 99 .2 0 99 .2 7 99 .3 0 99 .3 2 99 .3 0
11 6. 99
± 0. 39
99 .2 5
11 7. 04 11 7. 27 11 7. 04 11 7.
± 0. 39 ± 0. 40 ± 0. 39 ± 0.
99 .1 9 99 .1 8 99 .1 1 99 .0
Ar (k)
39
(%) 29.1 0 18.0 4 9.10 5.40 4.01
K/ C a 4 5. 7 1 7. 4 5 9. 7 3 8. 1 2 1. 2
± 2.3 ± 0.5 ± 10. 4 ± 6.9 ± 3.0
2.84
5. 7
± 0.3
2.69
9. 6
± 1.0
2.11 1.82 1.74 1.64 1.48 1.41 1.82 1.74
1.36
1.77 1.28 1.83 1.39
1 5. 4 1 4. 1 2 1. 4 1 2. 0 1 2. 7 8. 1 1 3. 0 3 3. 9 1 8 4. 7 3 5. 8 3 4. 1 3 3. 4 2 9
± 3.1 ± 3.0 ± 6.9 ± 2.4 ± 3.0 ± 1.3 ± 2.5 ± 18. 7 ± 707 .4 ± 19. 9 ± 23. 8 ± 16. 8 ± 158
18E27 147*
3.8 %
18E27 148*
4.2 %
18E27 150*
4.6 %
18E27 151*
5.0 %
18E27 152*
5.4 %
3
4
4
74
1
2
2
7
0. 0 3 0. 0 3 0. 0 3 0. 0 5
2. 2 7 2. 2 5 2. 1 2 1. 6 3
0. 2 2 0. 1 6 0. 2 0 3. 9 9
50 .5 3 74 .3 3 54 .4 7
0. 2 5 0. 2 4 0. 2 4 0. 2 8
3. 7 9 3. 9 4 4. 3 0 3. 2 5
20 .0 4 19 .7 4 19 .9 1 22 .7 5
0. 1 8 0. 1 8 0. 1 8 0. 1 7
0. 0 3
2. 1 1
0. 0 2
57 2. 34
0. 2 0
4. 8 5
15 .9 8
0. 1 8
2. 75
3 859 .91 847 .33 854 .93 979 .51 688 .61
1 0. 0 1 0. 0 1 0. 0 1 0. 0 1 0. 0 2
42.4 6
0. 15
42.4 6
0. 15
42.4 6
0. 15
42.4 7
0. 15
42.5 1
0. 16
25
39
9
11 6. 99 11 6. 99 11 7. 01 11 7. 04
± 0. 40 ± 0. 40 ± 0. 40 ± 0. 40
98 .9 7 98 .9 2 98 .8 7 98 .6 3
11 7. 12
± 0. 42
98 .6 1
1. 1 3 9. 0 5 3. 9 4 2. 1
2.0
1.26
2. 5
± 0.1
0.88
3 7 5. 2
± 429 4.5
1.11 1.09 1.10
± 39. 4 ± 80. 2 ± 45. 9
Table 5 40Ar/39Ar step heating data for sericite aggregates from gold ore Sample JQD15D004B2 in the Rushan gold deposit (continued)
13 14
0. 0 3 0. 0 3 0. 0 3
2. 1 6 2. 1 6 2. 1 8
0. 0 3 0. 0 3 0. 0 1
38 0. 48 38 0. 48 90 7. 61
0. 1 5 0. 1 5 0. 1 3
6.5 %
0. 0 2
3. 0 5
0. 0 6
16 8. 50
0. 0 6
18E27 158*
7.0 %
0. 0 2
3. 4 8
0. 1 0
10 2. 30
0. 0 4
18E27 159
7.5 %
0. 0 1
4. 7 8
0. 1 5
74 .0 0
0. 0 3
18E27 160
8.0 %
0. 0 1
4. 3 7
0. 0 2
52 9. 35
0. 0 2
18E27 162
8.5 %
0. 0 2
3. 4 4
0. 1 3
78 .6 9
0. 0 3
18E27 154*
5.7 %
18E27 154*
5.7 %
18E27 155*
6.1 %
18E27 156*
5. 9 9 5. 9 9 7. 3 3 1 6. 3 5 2 2. 9 6 3 7. 8 1 5 6. 3 4 2 7. 4 2
12 .9 9 12 .9 9 10 .9 4
0. 1 9 0. 1 9 0. 2 0
11 6. 95 11 6. 95 11 6. 86
± 0. 44 ± 0. 44 ± 0. 46
98 .3 3 98 .3 3 98 .0 4
0. 7 2 0. 7 2 0. 6 0
4. 56
0. 3 1
199 .24
0. 28
11 6. 63
± 0. 74
96 .8 3
0. 2 5
30.6
± 103 .2
3. 45
0. 3 6
42.3 8
0. 33
11 6. 80
± 0. 88
96 .3 2
0. 1 9
14.5
± 29. 6
1. 43
0. 1 6
42.8 4
0. 75
11 8. 03
± 2. 01
94 .1 7
0. 0 8
4.2
± 6.2
52. 06
0. 2 0
42.5 2
0. 93
11 7. 17
± 2. 49
91 .6 3
0. 0 6
23.2
± 246 .1
78. 12
0. 1 3
41.6 5
0. 60
11 4. 84
± 1. 60
93 .3 1
0. 1 0
5.7
± 8.9
560 .55
0. 0 2 0. 0 2 0. 0 2
42.4 4
0. 16
42.4 4
0. 16
42.4 1
0. 17
0. 0 5
42.3 2
152 .02
0. 0 7
0. 8 1
64. 96
1. 12
1. 0 0
1. 75
0. 6 6
560 .55 473 .38
J value=0.00157418 ± 0.00000099; Total fusion age=116.07 ± 0.20 Ma (2σ); * represents the steps chosen for plateau age calculation
15
62
204. 6 204. 6 396. 7
± 155 6.7 ± 155 6.7 ± 720 1.4
16
Table 6 40Ar/39Ar step heating data for sericite flakes from gold ore Sample JQD15D015B2 in
17
the Rushan gold deposit Mea surem ents
Re lativ e Abu nda nce
18E27 061
0.2 %
18E27 062
0.3 %
18E27 064
0.4 %
18E27 065
0.5 %
18E27 066
0.6 %
18E27 068
0.7 %
0. 0 6
1. 5 1
0. 0 1
10 47. 97
0. 3 4
2. 7 1
26 .8 0
0. 0 8
11 89. 33
0. 0 3
18E27 069
0.8 %
0. 0 7
1. 3 7
0. 0 0
25 78. 03
0. 2 9
3. 3 8
23 .1 4
0. 0 8
10 33. 29
0. 0 3
18E27 070
0.9 %
18E27 072*
1.0 %
18E27 073*
1.1 %
0. 0 5 0. 0 4 0. 0 4
2. 0 0 2. 2 3 2. 1 9
0. 0 2 0. 1 0 0. 0 4
66 0.3 6 10 2.0 8 27 3.5 2
0. 2 5 0. 2 1 0. 2 0
3. 8 1 4. 6 4 4. 7 1
19 .5 0 16 .3 0 16 .0 1
0. 0 8 0. 1 0 0. 1 0
86 7.6 9 72 7.0 1 71 4.4 8
0. 0 4 0. 0 4 0. 0 4
18E27 074*
1.2 %
0. 0 4
2. 1 3
0. 0 0
39 65. 75
0. 2 0
4. 8 9
16 .2 8
0. 1 0
72 6.4 1
0. 0 4
18E27 076*
1.3 %
18E27 077*
1.4 %
18E27 078*
1.5 %
18E27 080*
1.7 %
18E27 081*
1.9 %
18E27 082
2.2 %
18E27 084
2.5 %
18E27 085
2.8 %
0. 0 5 0. 0 5 0. 0 5 0. 0 6 0. 0 8 0. 0 6 0. 0 4 0. 0
1. 8 0 1. 8 7 1. 7 6 1. 5 3 1. 2 6 1. 6 0 2. 5 0 3. 1
0. 0 3 0. 0 8 0. 1 0 0. 0 3 0. 0 5 0. 0 6 0. 0 3 0. 1
34 1.8 1 12 5.0 1 10 1.4 8 33 8.3 6 19 1.4 0 15 5.8 4 34 6.6 3 86. 85
0. 2 6 0. 2 2 0. 2 1 0. 2 3 0. 2 7 0. 2 4 0. 1 4 0. 1
3. 8 1 4. 1 8 4. 4 4 4. 3 0 3. 4 9 3. 9 8 6. 9 5 8. 8
20 .6 6 17 .7 3 16 .7 2 18 .7 0 21 .8 0 18 .6 2 10 .9 8 7. 46
0. 0 8 0. 0 9 0. 0 9 0. 0 9 0. 0 8 0. 0 9 0. 1 2 0. 1
92 3.4 3 79 3.6 8 75 0.8 6 83 9.7 7 98 0.8 9 83 2.4 5 49 1.1 4 33 4.2
0. 0 3 0. 0 4 0. 0 4 0. 0 4 0. 0 3 0. 0 4 0. 0 7 0. 1
36
37
38
A r [f A ] 5. 0 8 1. 5 4
0. 2 5 0. 2 8
A r [f A ] 0. 2 0 0. 1 4
A r [f A ] 1. 3 1 1. 8 2
0. 7 3 0. 5 4
26 .4 5 12 7. 05
0. 1 5
0. 7 3
0. 0 1
13 23. 75
0. 6 4
1. 4 4
0. 0 8 0. 0 7
1. 2 6 1. 3 5
0. 0 3 0. 0 2
31 8.4 9 60 9.3 3
0. 4 2 0. 3 8
47. 94 73. 10
40
A r [fA ]
0. 0 8 0. 0 6
25 52. 89 58 48. 87
0. 0 1 0. 0 1
50 .9 7
0. 0 7
22 58. 80
0. 0 1
2. 2 0 2. 4 8
33 .7 2 29 .8 4
0. 0 7 0. 0 7
14 94. 65 13 21. 92
0. 0 2 0. 0 2
39
Ar [f A]
40
63
40(r )/39( k)
Age (Ma)
Ar (r) (% )
Ar (k)
39
(%)
± 0. 30 ± 0. 06
11 0. 35 11 7. 69
± 0. 80 ± 0. 15
41 .1 6 92 .2 3
± 0. 06
12 0. 34
± 0. 16
98 .0 4
± 0. 07 ± 0. 07
12 0. 83 12 0. 75
± 0. 18 ± 0. 19
98 .4 4 98 .4 2
43.7 0
± 0. 07
12 1. 04
± 0. 20
98 .4 9
4.65
43.7 4
± 0. 08
12 1. 13
± 0. 21
97 .9 3
4.01
± 0. 09 ± 0. 10 ± 0. 10
12 1. 26 12 1. 49 12 1. 49
± 0. 23 ± 0. 27 ± 0. 27
98 .4 0 98 .3 6 98 .2 9
± 0. 10
12 1. 44
± 0. 28
98 .2 8
± 0. 08 ± 0. 09 ± 0. 10 ± 0. 09 ± 0. 08 ± 0. 09 ± 0. 13 ± 0.
12 1. 74 12 1. 71 12 1. 81 12 1. 63 12 1. 72 12 1. 22 12 1. 15 12 1.
± 0. 23 ± 0. 25 ± 0. 26 ± 0. 24 ± 0. 22 ± 0. 24 ± 0. 35 ± 0.
98 .3 7 98 .1 8 97 .9 6 97 .8 0 97 .7 1 97 .9 2 97 .8 3 97 .4
39.7 3 42.4 6 43.4 4 43.6 3 43.6 0
43.7 9 43.8 7 43.8 7 43.8 5 43.9 7 43.9 6 43.9 9 43.9 2 43.9 6 43.7 7 43.7 5 43.6 9
4.59 22.0 3 8.84
5.85 5.17
3.38 2.83 2.77
2.82
3.58
K / C a
5 6
± 54
3 9 9 2 9 2 8 4 6 4 7 6 7 1 1 3 3 2 7 1 3 5 5 4 7 2 1 8 2 2 7 3 3 3 0 2
± 583 ± 775 17 ± 295 6 ± 935 2 ± 237 37 ± 139 902 ± 731 3 ± 146 ± 996 ± 216 761 ± 206 6
3.07
9 2
± 229
2.90
7 3
± 148
2 6 1 1 8 6 1 3 1 1 6 5 2 8
± 176 3
3.24 3.78 3.23 1.90 1.29
± 712 ± 407 ± 114 5 ± 48
3
2
2
0
18E27 086
3.1 %
0. 0 3
3. 4 1
0. 0 1
19 46. 46
0. 0 7
18E27 088
3.4 %
0. 0 3
3. 1 7
0. 0 0
71 34. 37
0. 0 7
18E27 089
3.8 %
0. 0 3
3. 4 7
0. 0 5
19 4.7 0
0. 0 6
18E27 090
4.2 %
0. 0 4
2. 4 4
0. 0 5
20 9.2 8
0. 0 8
18E27 092
4.6 %
0. 0 4
2. 1 2
0. 1 7
60. 31
0. 0 8
1 1 3. 7 1 1 4. 3 1 1 4. 6 1 1 2. 7 4 1 1. 5 0
6
2
0
18
01
47
9
5. 50
0. 2 1
24 6.6 6
0. 1 3
43.4 7
± 0. 23
12 0. 42
± 0. 63
96 .9 7
5. 72
0. 2 0
25 7.9 1
0. 1 2
43.6 3
± 0. 23
12 0. 83
± 0. 61
4. 68
0. 2 5
21 1.5 5
0. 1 5
43.6 0
± 0. 28
12 0. 76
6. 08
0. 2 0
27 6.2 4
0. 1 2
43.6 6
± 0. 22
5. 83
0. 2 1
26 4.9 4
0. 1 2
43.3 7
± 0. 23
0.95
4 4 6
± 173 69
96 .7 9
0.99
1 7 9 8
± 256 595
± 0. 76
96 .4 3
0.81
3 9
± 152
12 0. 93
± 0. 59
96 .0 8
1.05
5 2
± 219
12 0. 14
± 0. 61
95 .4 0
1.01
1 4
± 17
Table 6 40Ar/39Ar step heating data for sericite flakes from gold ore Sample JQD15D015B2 in the Rushan gold deposit (continued)
18 19
18E27 093
5.0 %
0. 0 4
2. 1 7
0. 1 3
75. 26
0. 0 5
18E27 094
5.4 %
0. 0 3
2. 6 4
0. 0 4
26 4.8 7
0. 0 5
18E27 096
5.7 %
0. 0 3
2. 5 7
0. 0 6
18 6.6 4
0. 0 5
18E27 097
6.1 %
0. 0 4
2. 0 9
0. 0 2
47 1.9 2
0. 0 7
18E27 098
6.5 %
0. 0 5
1. 8 1
0. 0 5
19 8.1 7
0. 0 4
18E27 100
7.0 %
0. 0 6
1. 5 2
0. 0 1
72 7.1 7
0. 0 5
18E27 101
7.5 %
0. 0 4
2. 2 6
0. 0 2
47 1.5 2
0. 0 2
18E27 102
8.0 %
0. 0 5
1. 8 1
0. 0 4
24 0.8 4
0. 0 6
18E27 104
8.5 %
0. 0 4
2. 1 6
0. 0 3
41 9.3 2
0. 0 4
1 7. 8 4 1 7. 7 5 1 8. 3 3 1 3. 2 8 2 1. 1 6 2 0. 8 5 4 0. 2 1 1 5. 9 3 2 3. 2 0
4. 21
0. 2 7
19 4.1 0
0. 1 7
43.0 8
± 0. 31
11 9. 36
± 0. 82
93 .5 1
0.73
3. 72
0. 3 0
17 0.5 3
0. 1 9
43.1 6
± 0. 34
11 9. 58
± 0. 92
94 .1 4
3. 61
0. 3 2
16 6.1 7
0. 1 9
43.1 5
± 0. 36
11 9. 55
± 0. 95
5. 07
0. 2 2
23 2.0 8
0. 1 4
43.2 5
± 0. 25
11 9. 82
3. 35
0. 3 3
15 7.9 6
0. 2 0
42.7 6
± 0. 38
3. 74
0. 2 9
17 4.5 0
0. 1 8
42.1 3
1. 79
0. 6 4
88. 70
0. 3 6
2. 80
0. 3 8
13 4.3 8
2. 02
0. 5 8
99. 52
1 4
± 21
0. 6 4
40
± 214
93 .8 6
0. 6 3
28
± 103
± 0. 68
94 .5 4
0. 8 8
100
± 948
11 8. 50
± 1. 02
90 .5 7
0. 5 8
30
± 117
± 0. 33
11 6. 81
± 0. 89
90 .2 1
0. 6 5
115
± 167 9
43.2 6
± 0. 72
11 9. 84
± 1. 93
87 .0 8
0. 3 1
36
± 342
0. 2 4
42.6 0
± 0. 44
11 8. 08
± 1. 19
88 .6 9
0. 4 9
30
± 143
0. 3 2
43.3 4
± 0. 65
12 0. 06
± 1. 74
87 .8 5
0. 3 5
34
± 286
J value=0.00157418 ± 0.00000099; Total fusion age=119.77 ±0.16 Ma (2σ); * represents the steps chosen for weighted mean age calculation
20
64
21
Table 7 40Ar/39Ar step heating data for sericite aggregates from gold ore Sample
22
JQD15D015B2 in the Rushan gold deposit Mea surem ents
Re lativ e Abu nda nce
18E27 000
0.2 %
18E27 001
0.3 %
18E27 003
0.4 %
18E27 004
0.5 %
18E27 005
0.6 %
18E27 007
0.7 %
18E27 008
0.8 %
18E27 009
0.9 %
18E27 011
1.0 %
18E27 012
1.1 %
18E27 013
1.2 %
18E27 015*
1.3 %
18E27 016*
1.4 %
18E27 017*
1.5 %
18E27 019*
1.7 %
18E27 020*
1.9 %
18E27 021*
2.2 %
18E27 023*
2.5 %
18E27 024*
2.8 %
18E27 025*
3.1 %
36
37
38
A r [f A ] 1. 0 8 0. 5 6 0. 2 1 0. 1 3 0. 0 9 0. 0 4 0. 0 7 0. 0 5 0. 0 5 0. 0 3
0. 3 0 0. 3 7 0. 5 9 0. 9 1 1. 1 9 2. 2 8 1. 5 6 2. 1 6 1. 9 7 3. 3 3
A r [f A ] 0. 4 8 0. 7 6 0. 4 9 0. 2 4 0. 1 5 0. 2 4 0. 1 7 0. 1 3 0. 1 3 0. 0 7
14 8.2 7
A r [f A ] 0. 7 8 3. 0 3 2. 1 6 1. 4 2 1. 0 7 0. 4 9 0. 8 1 0. 5 5 0. 5 9 0. 3 5
1. 3 0 0. 3 3 0. 4 5 0. 6 9 0. 8 8 1. 9 3 1. 1 9 1. 6 8 1. 5 6 2. 7 6
44 .1 4 23 5. 46 17 5. 64 11 5. 06 85 .5 0 38 .3 3 65 .2 6 43 .4 1 46 .5 1 27 .5 5
0. 0 5
2. 1 5
0. 0 0
54 12. 21
0. 4 9
1. 9 9
0. 0 3 0. 0 4 0. 0 3 0. 0 5 0. 0 4 0. 0 6 0. 0 4 0. 0 6 0. 0
3. 5 4 2. 4 4 3. 6 4 2. 0 5 2. 4 7 1. 7 8 2. 7 0 1. 7 8 1. 3
0. 0 2 0. 0 2 0. 0 6 0. 0 5 0. 0 3 0. 0 6 0. 0 8 0. 0 5 0. 0
50 3.5 0 45 9.2 4 18 7.5 6 20 0.5 6 31 2.1 5 19 1.3 4 12 9.4 6 21 4.7 4 14 1.4
0. 3 0 0. 4 7 0. 2 9 0. 5 3 0. 3 9 0. 5 7 0. 3 6 0. 5 3 0. 7
3. 0 2 2. 0 0 3. 1 0 1. 7 4 2. 5 3 1. 7 3 2. 5 9 1. 7 7 1. 3
21. 56 13. 70 20. 85 44. 03 72. 69 42. 24 62. 20 77. 49 86. 75
40
A r [fA ]
0. 0 7 0. 0 6 0. 0 6 0. 0 6 0. 0 6 0. 0 7 0. 0 6 0. 0 7 0. 0 7 0. 0 8
18 84. 21 97 47. 50 74 20. 88 48 96. 56 36 51. 35 16 46. 40 28 05. 95 18 69. 72 20 08. 14 11 91. 85
0. 0 1 0. 0 0 0. 0 0 0. 0 1 0. 0 1 0. 0 2 0. 0 1 0. 0 1 0. 0 1 0. 0 2
40 .3 3
0. 0 7
17 44. 95
0. 0 1
24 .1 9 38 .1 4 23 .0 6 42 .9 6 32 .2 8 45 .0 2 29 .4 7 43 .2 4 57 .3
0. 0 8 0. 0 7 0. 0 8 0. 0 7 0. 0 7 0. 0 7 0. 0 7 0. 0 7 0. 0
10 49. 44 16 52. 45 10 01. 53 18 64. 12 14 01. 99 19 56. 21 12 81. 35 18 78. 93 24 95.
0. 0 2 0. 0 1 0. 0 2 0. 0 1 0. 0 2 0. 0 1 0. 0 2 0. 0 1 0. 0
39
Ar [f A]
40
65
40(r )/39( k) 35.4 8 40.7 0 41.8 9 42.2 3 42.3 9 42.6 2 42.6 9 42.7 6 42.8 6 42.9 5 42.9 3 43.0 5 43.0 1 43.0 9 43.0 5 43.0 6 43.0 7 43.1 2 43.0 6 43.0 8
Age (Ma)
Ar (r) (% )
± 0. 07 ± 0. 05 ± 0. 05 ± 0. 05 ± 0. 05 ± 0. 06 ± 0. 06 ± 0. 06 ± 0. 06 ± 0. 07
98 .8 2 11 2. 91 11 6. 11 11 7. 01 11 7. 45 11 8. 07 11 8. 25 11 8. 43 11 8. 70 11 8. 94
± 0. 18 ± 0. 13 ± 0. 14 ± 0. 14 ± 0. 15 ± 0. 17 ± 0. 15 ± 0. 16 ± 0. 16 ± 0. 19
83 .1 2 98 .3 1 99 .1 5 99 .2 3 99 .2 6 99 .2 3 99 .2 8 99 .2 7 99 .2 6 99 .2 8
± 0. 06
11 8. 90
± 0. 17
99 .2 2
± 0. 08 ± 0. 06 ± 0. 08 ± 0. 06 ± 0. 07 ± 0. 06 ± 0. 07 ± 0. 06 ± 0.
11 9. 21 11 9. 11 11 9. 32 11 9. 23 11 9. 25 11 9. 28 11 9. 39 11 9. 25 11 9.
± 0. 20 ± 0. 17 ± 0. 20 ± 0. 16 ± 0. 18 ± 0. 16 ± 0. 18 ± 0. 16 ± 0.
99 .2 4 99 .2 7 99 .2 1 99 .2 2 99 .1 5 99 .1 2 99 .1 6 99 .0 9 99 .0
Ar (k)
39
(%) 2.81 14.9 8 11.1 8 7.32 5.44 2.44 4.15 2.76 2.96 1.75
2.57
1.54 2.43 1.47 2.73 2.05 2.86 1.88 2.75 3.65
K / C a
3 9
± 17
1 3 3 1 5 5 2 0 4 2 5 2 6 8 1 6 5 1 4 2 1 5 6 1 6 7 8 8 4 8 4 8 9 7 3 0 1 7 2 3 5 4 4 1 4 3 4 7 1 6 4 3 7 1 3 3
± 37 ± 65 ± 180 ± 366 ± 57 ± 206 ± 220 ± 271 ± 495 ± 957 794 ± 492 6 ± 670 7 ± 644 ± 141 9 ± 258 7 ± 132 9 ± 425 ± 159 4 ± 955
18E27 027*
3.4 %
18E27 028*
3.8 %
18E27 029*
4.2 %
18E27 031*
4.6 %
18E27 032*
5.0 %
8
7
7
0. 0 5 0. 0 8 0. 0 6 0. 0 8 0. 0 6
1. 9 6 1. 2 9 1. 6 3 1. 2 8 1. 7 7
0. 1 3 0. 0 3 0. 1 6 0. 0 3 0. 1 2
9 77. 54 40 6.5 4 64. 75 35 6.3 5 88. 44
0
8
9
6
14
1
0. 4 8 0. 7 2 0. 4 5 0. 5 7 0. 3 9
2. 0 7 1. 2 9 2. 0 4 1. 6 5 2. 4 8
38 .5 0 58 .7 2 36 .7 6 46 .5 0 31 .1 4
0. 0 7 0. 0 6 0. 0 7 0. 0 7 0. 0 7
16 75. 90 25 58. 62 16 01. 86 20 26. 33 13 58. 21
0. 0 1 0. 0 1 0. 0 2 0. 0 1 0. 0 2
43.1 3 43.1 5 43.0 8 43.0 6 43.0 6
06
29
15
9
± 0. 06 ± 0. 06 ± 0. 06 ± 0. 06 ± 0. 07
11 9. 44 11 9. 47 11 9. 30 11 9. 24 11 9. 25
± 0. 17 ± 0. 15 ± 0. 17 ± 0. 16 ± 0. 18
99 .0 9 99 .0 2 98 .8 7 98 .8 1 98 .7 3
7 2.45 3.74 2.34 2.96 1.98
1 2 3 9 6 6
± 191 ± 785 2
9 8
± 128
6 7 6 1 1 4
± 481 9 ± 201
Table 7 40Ar/39Ar step heating data for sericite aggregates from gold ore Sample JQD15D015B2 in the Rushan gold deposit (continued)
23 24
0. 0 6 0. 0 4 0. 0 6 0. 0 5 0. 0 4
1. 6 4 2. 4 2 1. 6 1 2. 1 0 2. 4 0
0. 0 6 0. 0 5 0. 0 3 0. 1 1 0. 0 1
18 3.3 6 20 8.7 4 39 8.6 2
10 88. 39
0. 3 9 0. 2 2 0. 2 5 0. 1 4 0. 1 2
7.5 %
0. 0 4
2. 7 0
0. 0 4
24 1.6 7
0. 0 8
18E27 041
8.0 %
0. 0 4
2. 6 5
0. 0 2
53 5.2 8
0. 0 8
18E27 043
8.5 %
0. 0 3
3. 4 7
0. 0 3
36 8.9 5
0. 0 4
18E27 033*
5.4 %
18E27 035*
5.7 %
18E27 036
6.1 %
18E27 037
6.5 %
18E27 039
7.0 %
18E27 040
92. 55
2. 5 4 4. 4 4 4. 0 1 6. 9 6 7. 9 7 1 1. 1 8 1 1. 9 7 2 3. 1 0
32 .2 7 17 .6 3 21 .0 4 11 .7 5
0. 0 7 0. 0 9 0. 0 8 0. 1 2 0. 1 5
14 06. 58 77 0.8 7 91 8.2 4 51 6.2 6 39 5.2 1
0. 0 2 0. 0 3 0. 0 3 0. 0 5 0. 0 6
6. 41
0. 1 9
28 4.4 9
0. 0 8
5. 26
0. 2 2
23 3.4 0
3. 48
0. 3 2
15 6.6 9
8. 99
± 0. 07 ± 0. 09 ± 0. 08 ± 0. 12 ± 0. 15
11 9. 12 11 9. 17 11 8. 49 11 8. 41 11 8. 03
± 0. 18 ± 0. 24 ± 0. 22 ± 0. 33 ± 0. 40
98 .6 7 98 .4 4 98 .0 0 97 .2 7 96 .9 6
2. 0 5 1. 1 2 1. 3 4 0. 7 5 0. 5 7
42.7 2
± 0. 20
11 8. 32
± 0. 53
96 .2 9
0. 1 0
42.3 0
± 0. 24
11 7. 20
± 0. 63
0. 1 5
42.6 4
± 0. 35
11 8. 13
± 0. 94
43.0 1 43.0 3 42.7 8 42.7 5 42.6 1
236
± 864
157
± 657
353
± 281 1
46
± 85
429
± 933 4
0. 4 1
65
± 315
95 .4 0
0. 3 4
120
± 128 7
94 .7 2
0. 2 2
52
± 385
J value= 0.00158303 ± 0.00000101; Total fusion age=116.97±0.15 Ma (2σ); * represents the steps chosen for plateau age calculation
25
66
26
Highlights
27 28
Gold mineralization initiated at 121.64 Ma and terminated at 116.97 Ma.
29 30
The middle part of the quartz vein orebody formed slightly earlier than the marginal part.
31 32
Episodic fluids pressure fluctuations from supralithostatic to hydrostatic trigger
33
incremental deposition of quartz veins.
34 35
Ore-hosting Kunyushan granite is not genetically related and provides no heat to gold
36
mineralization system.
37 38 39 40
67
41 42
68
43 44
69
45 46
70
47 48
71
49 50
72
51 52
73
53 54
74
55 56
75
57 58
76
59 60
77
61 62
78
63 64
79
65 66
80
67 68
81
69 70
82
71
83
S0169-1368(19)30602-X https://doi.org/10.1016/j.oregeorev.2019.103254 OREGEO 103254
To appear in:
Ore Geology Reviews
Received Date: Revised Date: Accepted Date:
2 July 2019 18 November 2019 25 November 2019
Please cite this article as: S-X. Sai, J. Deng, K-F. Qiu, D.P. Miggins, L. Zhang, Textures of auriferous quartz-sulfide veins and 40Ar/39Ar geochronology of the Rushan gold deposit: Implications for process of ore- fluid infiltration in the eastern Jiaodong gold province, China, Ore Geology Reviews (2019), doi: https://doi.org/10.1016/j.oregeorev. 2019.103254
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© 2019 Published by Elsevier B.V.
Textures
of
auriferous
quartz-sulfide
veins
and
40Ar/39Ar
geochronology of the Rushan gold deposit: Implications for process of ore- fluid infiltration in the eastern Jiaodong gold province, China Sheng-Xun Saia, b, Jun Denga, *, Kun-Feng Qiua, Daniel P. Migginsc, Liang Zhanga
a
State Key Laboratory of Geological Processes and Mineral Resources, China
University of Geosciences, Beijing 100083, China b Department
of Geological Sciences, Jackson School of Geosciences, University
of Texas at Austin, Austin, TX 78712, USA c
College of Earth, Ocean and Atmospheric Sciences, Oregon State University,
Corvallis, OR 97331, USA
Manuscript submitted to Ore Geology Reviews *Corresponding author: Jun Deng State Key Laboratory of Geological Processes and Mineral Resources China University of Geosciences 29# Xue-Yuan Road, Haidian District Beijing 100083, China Phone: (+86-10) 8232 2301 (O) Fax: (+86-10) 8232 1006 Email: [email protected]
Abstract The Rushan gold deposit, located in the eastern part of the world-class Jiaodong gold province, contains the largest gold resource within a single faultcontrolled quartz vein in China. Processes involved in auriferous quartz vein deposition are not clear, and the precise gold mineralization age remains controversial for this deposit. New
40Ar/39Ar
dating data on sericite from ores and
altered rocks suggest that the Rushan gold deposit formed between ca. 122 Ma and 117 Ma, which overlap or are slightly younger than those of gold deposits in northwestern Jiaodong province. The age differences between samples from different locations indicate that the quartz veins on the margin of the orebody may be younger than those in the center, suggesting a single and protracted gold mineralization event lasting for about 5 My. Differences between gold mineralization
ages
and
emplacement/cooling
ages
of
the
ore-hosting
Kunyushan granite imply that they are not genetically related and that the Kunyushan granite is unable to provide any thermal input to the mineralization system. This also applies to the Sanfoshan monzonite as it marginally postdated gold mineralization and lacks any spatial association with it. Internal textures of high-angle shear veins and low-angle extension veins indicate that episodic fluctuations from supralithostatic to hydrostatic fluid pressure triggered the multiple ore-controlling fault ruptures induced by breach of supralithostatic fluids under a seismogenic regime. In this model, the controlling fault starts to slip with both reverse and sinistral kinematics, and dilatational zones are created. The ore-forming fluids then migrate upwards along the fault,
due to the large pressure difference between the dilatational zones and the deep parts of the fault, causing hydraulic fracture in the host rocks and earlier quartz veins. Large volumes of quartz, pyrite, and other ore components are precipitated due to fluid immiscibility caused by pressure fluctuations, and new quartz veins form along both sides of the earlier quartz veins. The fault is now sealed by these new quartz veins and the fluid pressure starts to build until the next breach cycles. Orebodies with complex internal textures were thus deposited incrementally in these cycles, closely fitting the classic fault-valve model, in this case under a weak regional NW-SE transpressional stress.
Keywords: Auriferous quartz-sulfide veins; Vein textures; Sericite dating; Rushan deposit; Jiaodong gold province
40Ar/39Ar
1. Introduction Jiaodong has a proven gold resource of more than 4,000 tonnes from over 150 gold deposits (Yang et al., 2014a), making it the most important gold producer in China (Li et al., 2015; Deng and Wang, 2016; Deng et al., 2018). Gold deposits are structurally controlled by NE to NNE-trending faults (Deng et al., 2003; Li et al., 2003). Five gold belts, namely the Sanshandao gold belt, the Jiaojia gold belt and the Zhaoyuan-Pingdu gold belt in northwestern Jiaodong, the Penglai-Qixia gold belt in the center, and the Muping-Rushan gold belt in eastern Jiaodong, are defined according to the faults which bound them and their related gold deposits. Previous researchers have generally moved towards consensus on the spatial architecture of orebodies, hydrothermal alteration types and distribution, compositions and isotopic features of ore-forming fluids, as well as geochemical nature of the gold ores (e.g. Fan et al., 2007; Tang et al., 2008; Wang et al., 2010; Goldfarb and Santosh, 2014; Guo et al., 2014, 2017; Yang et al., 2014a, 2016a, 2016b; Deng et al., 2015a, 2019; L. Yang et al., 2015, 2018). However, the precise
gold
mineralization
age
remains
controversial
and
previous
geochronological studies were mainly focused on northwestern Jiaodong. In recent years, numerous geochronological studies have revealed that the gold deposits in northwestern Jiaodong formed at ca. 125 to 115 Ma as a single metallogenic event (e.g. Li et al., 2003; Zhang et al., 2003; Ma et al., 2017; Yang et al., 2017; Zhang et al., 2019a), although there may have been an earlier ~130 Ma gold event in the Zhaoyuan-Pingdu belt (Yang et al., 2014b, 2016c). By
contrast, limited geochronological data in the Muping-Rushan gold belt have yielded highly dispersed ages (Table 1). Considering the variation in ages from 156.7 Ma to 104.8 Ma, arguments on whether gold formation represents one continuous evolving event or multiple distinct short episodes within a goldforming period, as well as the precise timing of each episode, continues (Table 1 and references therein). Complex internal textures are recorded in quartz veins in the MupingRushan gold belt, as the deposition of quartz veins is clearly controlled by fault movements. Such movements cause ore- fluid migration and enhancement of permeability along the fault as a consequence of fluid pressure and shear stress fluctuation (Sibson, 1988; Cox, 1995; Robert et al., 1995). Although progress has been
made
on
the
nature
of
ore-forming
fluids,
through
study
of
microthermometric features of fluid inclusions and the types of gold complexes in transporting fluids (Hu et al., 2005, 2007; Zeng et al., 2006; Xue et al., 2018), detailed studies of quartz vein depositional processes are scarce. The Rushan gold deposit, located in the center of the Muping-Rushan gold belt, contains the largest gold resource within a single fault-controlled quartz vein in China (Hu et al., 2004, 2006). The age of mineralization for this deposit, however, is particularly controversial (Table 1). Based on detailed observation of the internal textures and microstructural features of the quartz veins, together with sericite
40Ar/39Ar
ages obtained from different locations in the main orebody
and its adjacent alteration zone, this paper constrains the precise time and duration of gold mineralization event(s) in the Rushan gold deposit. Furthermore,
the formation of the gold deposit was further understood by examining the processes such as fluid pressure fluctuation and coupling between fluid flux and fault movement which control its formation.
2. Regional geology The Jiaodong gold province lies in the eastern part of the North China block, is bounded by the crustal-scale Tan-Lu Fault Zone to the west, and is adjacent to the subduction belt of the Pacific Plate to the east (Fig. 1a; Deng et al., 2003; Tang et al., 2008; Zhang et al., 2019b). Jiaodong is composed of the Jiaobei and Sulu Terranes, and the former is divided into the Jiaobei Uplift in the north and Jiaolai Basin in the south (Fig. 1b). The nearly parallel Taocun, Guocheng-Jimo, Zhuwu and Qingdao-Haiyang Faults comprise the Muping-Jimo Fault Zone (Fig. 1), which is the northern part of the regional Wulian-Qingdao-Yantai Fault Zone. This Fault Zone is regarded as the boundary between the Jiaobei Terrane and the Sulu Terrane (Zhang et al., 2007). Gold deposits in Jiaodong are strictly controlled by NE to NNE-trending faults. The mineralization styles are mainly classified as disseminated and stockwork veinlet style (Jiaojia style) hosted in extensively altered and cataclastic wallrock zones in the footwall of regional faults, and auriferous quartz-vein-style (Linglong style) deposited in high angle brittle faults, but there are also breccia style deposits controlled by low- angle detachment faults on the northern boundary of the Jiaolai Basin (Deng et al., 2003, 2015b; Yang et al., 2014a; Li et al., 2015).
Among the five major gold belts, the Muping-Rushan belt (also referred to as the Muru belt) is the only one that is located in the Sulu Terrane. The Sulu Terrane is characterized by widely exposed ultrahigh-pressure metamorphic rocks (UHP) composed of granitic gneiss, coesite-bearing eclogite, marble and other siliceous rocks (Webb et al., 2006). The Sulu UHP, constituting the east part of the world class Dabie-Sulu UHP belt, formed during Triassic continentcontinent collision between the Yangtze and North China blocks (Yang et al., 2003). The metamorphic basement of the Sulu Terrane comprises mainly Paleoproterozoic schist, paragneiss, calc-silicate rocks, marble and graphitebearing schist of the ca. 2.5-1.9 Ga Jingshan Group (Dong et al., 2010; Liu et al., 2013), which mainly occurs as discrete blocks in the southwest part of the Muping-Rushan gold belt (Fig. 2). Both the Jingshan Group and Sulu UHP are intruded by multiple pulses of Mesozoic granitic magmas, and the dominant Mesozoic granitoid in the Muping-Rushan gold belt, the Kunyushan granite, is subdivided into three phases: Duogushan weak gneissic granodiorite, Washan weak gneissic monzonite and Wuzhuashan weak gneissic porphyraceous monzonite (Zhang et al., 1995). The Kunyushan granite was emplaced at 161138 Ma (Hu et al., 2004; Guo et al., 2005; Zhang, 2011) and hosts the vast majority of gold resources in the Muping-Rushan belt. It shows affinity to S-type granites, and was derived from partial melting of the thickened crust (Guo et al., 2005). The late Cretaceous Sanfoshan monzonite intruded the Kunyushan granite in the southeast part of the Muping-Rushan belt at 118-113 Ma (Guo et
al., 2005; Goss et al., 2010; Zhang, 2011), most likely due to an intensive mantlecrust interaction event (Guo et al., 2005; Goss et al., 2010). The gold deposits are controlled by the Muping-Rushan Fault Zone that consists of a series of nearly parallel NNE-striking faults that largely dip steeply SE (Fig. 2). They are referred to as the Qinghushan-Tangjiagou Fault, the Shigou-Wushan Fault (also called the Jinniushan Fault), the Chahe-Sanjia Fault, the Jiangjunshi-Quhezhuang Fault, the Gekou Fault and the Laohuwo-Hezi Fault, from west to east. They constitute a graben structure regionally (Li and Yang, 1993), and secondary faults are developed on both sides of these faults.
3. Deposit geology The Rushan gold deposit (also referred to as the Jinqingding deposit) is located in the center of the Muping-Rushan gold belt. The orebodies are primarily hosted in the Washan monzonite pluton in the center of the Kunyushan granite, in which the Jingshan Group metamorphic rocks occur as discrete ellipsoidal enclaves with their long axes oriented NW-SE (Fig. 3). Numerous maficintermediate dykes including lamprophyres intruded along the NNE-NE striking faults (Deng et al., 2017), and some lamprophyres may post-date the orebodies as shown by cross-cutting relationships (e.g. Fig. 4a). The Rushan deposit is controlled by the NNE striking JiangjunshiQuhezhuang Fault. This fault generally strikes NNE 20°, with a variation of 5-30° in ore-hosting sections. Small branching and secondary faults are commonly developed in places where the strike and dip change. Although the main fault
plane is poorly exposed due to quartz veins within it, fault gouge, cleavages, striations and steps are visible in some places. Figure 4b shows a set of striations that indicate that sinistral movement of the Jiangjunshi-Quhezhuang Fault is overprinted by another set of normal slip striations, suggesting that normal faulting post-dates sinistral faulting. Sinistral and reverse slip on the fault induced by transpressional stress is substantiated by cleavage relationships and the well-oriented breccias in the fault zone, as well as by drag structures beside the main fault plane (cf. figure I-6 in Li, 2011). Such fault movement during gold mineralization has also been confirmed based on detailed interpretation of striations and steps on the fault plane from different sections where there are quartz-sulfide veins (Hu, 1995). Rushan is characterized as an auriferous quartz-vein-style deposit with the No. II lode as the dominant orebody that accounts for more than 90% of the proven resource. It shows roughly S-shaped, stratiform-like lenses, from 0.2 to 7.0 m (average 1.7 m) thick, that strike 5-30° and dip 65-90° SE (NW locally), extending along both strike and dip directions without interference from other quartz veins. The orebody expands where the strike of the JiangjunshiQuhezhuang Fault strikes from NE to NNE and the dip is gentler. The gold grade varies from 1.5 to 30.0 g/t with an average of 10.4 g/t gold. Narrow alteration zones are symmetrically distributed along both sides of the quartz veins. With increasing distance from the main fault, proximal narrow sericite-quartz alteration zones (Figs. 3c, 5a) transition gradually to a quartz alteration zone, which further grades into a distal potassic alteration zone (Fig.
3c). The sericite-quartz and quartz alteration zones are absent in some places where the quartz veins are wrapped directly by potassic altered rocks (Fig. 5b, de).
4. Internal textures of quartz veins and paragenetic sequence of hydrothermal minerals Based on the strike and dip of the quartz veins, internal textures and crosscutting relationships, both high-angle shear veins and low-angle extension veins are identified in the Rushan gold deposit. 4.1 High-angle shear veins The shear veins are hosted in the high-angle reverse faults/ fractures that had sinistral kinematics during mineralization. A variety of textures are recorded in shear veins, including not only the infill by massive uniform milky-white quartz, but also distinct textures such as layered quartz veins and host rock fragments, making the total shear veins laminated with abundant host rock enclaves. Host rock fragments are common in high-angle veins, and can be divided into breccias and laminae according to their size, shape and strike. Host rock breccias normally occur at dilatational sites in the shear veins, where they are in angular lenses, blocks or pudding-shape enclaves with diameters varying from less than 1 cm to 1-2 m. The large breccias are normally located in the center and tips of the dilatation zones without significant displacement or rotation, whereas the smaller breccias are randomly oriented within the entire shear vein with noticeable displacement and rotation (Fig. 5b). The breccias are cemented
and cut by crustiform and comb-like milky-white and smoky-gray quartz veinlets (Fig. 5b). Notably, the breccias near the margin of the shear veins display less alteration than those in the center (Fig. 5b). Laminae of host rock, with a thickness of no more than 30 cm (Fig. 5c), are also well developed in the veins, forming both discontinuous tabular and platy laminae parallel to the host rock contact, as also recorded by Chen (2017). An intact shear vein commonly consists of multiple quartz layers (Fig. 5d-e), with the milky-white quartz layers along the sides of the smoky-gray quartz layers. Some of the host rock breccias in the smoky-gray quartz layer are cut by the milky-white quartz layer, and there are breccias of smoky-gray quartz in the milky-white quartz layer (Fig. 5e). The quartz grains near the boundary of each layer are normally euhedral, comb-like with clear growth zoning (Fig. 6a), with the aspect ratio of the quartz decreasing towards the center of the layer where growth zoning is absent (Fig. 6b). Coarse-grained euhedral to subhedral pyrite grains occur as clusters on the boundaries of coarse-grained quartz (Fig. 6c), whereas anhedral pyrite grains occur as either a fine fill in thin quartz-sulfide veinlets (Fig. 6i) or as a disseminated component among quartz grains (Fig. 6d). Although some of the coarse-grained quartz and pyrite grains are intensively fragmented, the original shapes of the minerals are still recognizable due to low displacements among fragments (Fig. 6e-f), suggesting the involvement of hydraulic fracturing. Where filled by sulfides, the micro-fractures in pyrite are dominantly filled by galena (Fig. 6g-h), with lesser sphalerite. Notably, gold
minerals occur mainly in the micro-fractures of pyrite and normally have a close spatial relationship with base-metal sulfides, typically galena (Fig. 6g-h). Crack-seal texture is a significant piece of evidence to support the episodic ore-fluid migration. The meso-scale crack-seal veins separate different layers of quartz in the shear vein (Fig. 5d), and earlier quartz and pyrite are cut by microscale crack-seal veinlets. For instance, Figure 6i shows a single crack-seal veinlet cutting earlier coarse-grained quartz. Fragments of the host quartz vein are randomly distributed in the crack-seal veinlet, and fine pyrite grains normally occur close to the veinlet boundary. This may indicate a small discrete pulse in the fluid flux that precipitated the earlier coarse-grained quartz. By contrast, crack-seal veinlets filled with euhedral coarse-grained pyrite may suggest infiltration of a later fluid (Fig. 6j). The dark-gray elongate slab with multiple crack-seal structures between the shear vein and host rock (Fig. 5d) comprises fine quartz-pyrite-sericite-calcite fragments from the vein wall and matrix-like fine mineral grains from the rock contact (Fig. 6k). This argues strongly for multiple fluid events, as the fluids cracked and sealed the vein-rock contact multiple times and minerals on both sides were thus both fractured and pulverized. Open-space filling textures such as vugs in quartz (Fig. 5a, e) are developed in high-angle shear veins. Figure 6l shows open space filled by later calcite, and the smaller discrete euhedral quartz grains inside the open space are also cemented by calcite. There are vugs in some samples with euhedral quartz growth into open space (Fig 9e). Mills et al. (2015) describe similar textures, some with pyrite infilling vugs.
4.2 Low-angle extension veins High-angle veins normally have a close spatial association with the lowangle veins (Fig. 7a), which normally occur as single veins or vein arrays (Fig. 7). Host rock laminae (Fig. 7c) and breccias (Fig. 7d) in the low-angle veins are cemented by milky-white quartz and distributed parallel to the host rock wall. Open space textures such as vugs develop laterally along the low-angle veins, where groups of vugs parallel the host rock wall (Fig. 7c). The open space texture and the absence of displacement along the veins suggest that formation of low-angle veins involved extensional fracturing and subsequent sealing (Cox, 1995; Robert et al., 1995). Coarse-grained pyrite lies along the contact between quartz veins and host rocks (Fig. 7d), and along the contact between host rock laminae and massive quartz (Fig. 7c). Moreover, disseminated galena grains and aggregates also occur in these low-angle extension veins (Fig. 7c). 4.3 Paragenetic sequence of hydrothermal minerals The ore minerals in the Rushan deposit are primarily pyrite, followed by galena and sphalerite, with minor chalcopyrite, pyrrhotite, electrum, native gold and petzite. Liu et al. (2010) recorded calaverite, hessite and tellurobismuthite from the deeper part of the No. II Orebody, and proposed a Au-Ag telluride precipitation order of hessite-petzite-calaverite-native gold, which characterizes gradual enrichment of gold during evolution of the ore-forming process. The gangue minerals mainly consist of quartz, sericite, calcite and K-feldspar, with trace amount of monazite first reported by Sun et al. (2002). Gold minerals mainly precipitated in micro-fractures in pyrite, associated
with sulfides such as galena, sphalerite and chalcopyrite. Lesser visible gold occurs as inclusions in pyrite and quartz or on the margins of sulfides and quartz, with minor invisible gold in coarse-grained pyrite (Mills et al., 2015; Chen, 2017). Four stages in the paragenetic sequence of hydrothermal minerals are thus identified based on cross-cutting relationships between veins, internal textures of veins, mineral assemblages and precipitation order (Fig. 8). Stage 1 is defined by milky-white veins in alteration zones, with coarse-grained quartz (Fig. 6a-b), sericite (Fig. 6b), and minor coarse-grained euhedral to subhedral aggregated pyrite (Fig. 6c). Stage 2 is characterized by 1) smoky-gray veins with hydraulically-fractured earlier-formed coarse-grained minerals (Fig. 6e-f), 2) crack-seal veinlets filled by fine-grained anhedral quartz, pyrite and sericite (Fig. 6i), and 3) earlier formed coarse quartz grains self-sealed by finer-grained quartz (Fig. 6b). Additionally, anhedral disseminated pyrite occur on the boundaries of quartz (Fig. 6d), and disseminated monazite is associated with pyrite in this stage (Sun et al., 2002). Stage 3 is typified by fractured pyrite grains, and base-metal sulfides, such as galena, sphalerite and chalcopyrite, in these micro-fractures in pyrite (Fig. 6g-h). Gold minerals are typically within micro-fractures in pyrite or are intergrown with base metal sulfides (Fig. 6g-h), in the order hessite-petzitecalaverite-native gold (electrum). Sericite, quartz and pyrite are in variable proportions in these first three stages (Fig 8). Stage 4 marks the termination of one major fluid episode, as calcite occurs as a small cubic block surrounded by a thin layer of fine-grained quartz in a coarser-grained quartz vein (Fig. 5e), as veins or veinlets that cut the earlier-formed quartz-sulfide veins (Fig. 6f), and
infills in the vugs of euhedral/suhedral quartz aggregates (Fig. 6l). Minor pyrite was also deposited during this stage. It is apparent that the entire mineralization event may not consist of a single fluid evolution from Stage 1 to Stage 4, but may involve episodic fluid events in which hydrothermal minerals were deposited to produce a Stage 1 to Stage 4 paragenetic sequence. This is indicated by the presence of smoky-gray quartz breccias in milky-white quartz layers (Fig. 5e), crack-seal textures at the contact of quartz veins and host rocks (Figs 5d, 6k) and crack-seal veinlets filled by later euhedral pyrite in earlier coarse-grained quartz veins (Fig. 6j).
5. Geochronology of gold mineralization 5.1. Sample collection and description Sample JQD15D004B6 from an intensive sericite-quartz altered zone adjacent to the No. II Orebody, Sample JQD15D004B2 from the margin of the No. II Orebody, and Sample JQD15D015B2 from the central part of the No. II Orebody were selected for
40Ar/39Ar
geochronology. Detailed sample information
and locations are shown in Table 2. Feldspar in Sample JQD15D004B6 has been completely altered to sericite and quartz (Fig. 9a). Sericite penetrates the earlier recrystallized quartz (Fig. 9b), and it encapsulates quartz and pyrite or shows a close spatial association with them (Fig. 9c). Massive sericite is developed in this sample (Fig. 9d). The vuggy milky-white ore Sample JQD15D004B2 has euhedral quartz that has grown into open spaces (Fig. 9e). Sericite is distributed among euhedral
quartz crystals (Fig. 9f) or around clusters of subhedral pyrite grains (Fig. 9g) suggesting simultaneous formation. Native gold and hessite fill the microfractures in euhedral-subhedral pyrite grains (Fig. 9h). Another sample of ore (Sample JQD15D015B2) is composed of smokygray quartz with disseminated pyrite (Fig. 9i). Sericite grains locally accompany quartz and disseminated pyrite (Fig. 9j, l), or occur as infillings intergrown with fine-grained pyrite in quartz veinlets (Fig. 9k) and stockworks (Fig. 9l). 5.2 Analytical procedures In order to obtain the best possible
40Ar/39Ar
ages, samples were first
examined using a petrographic microscope. This was to ensure purity of samples and that there were no post-mineralization structural events that might affect the argon results from the sericite. Initial mineral separations for sericite aggregates was conducted at the Langfang Geoscience Company, Hebei, China, following traditional crushing, sieving, electromagnetic separation and heavy-liquid mineral separation techniques. All the mineral separates were then further purified at the Argon Geochronology mineral separation laboratory at Oregon State University. The mineral separates were rinsed multiple times with acetone, ethanol, and deionized water and dried in a drying oven at 55 °C. Once the samples were dried they were sieved to >250 μm. The separates were then separated into two different parts as magnetic and non-magnetic splits using a Frantz Isodynamic Separator. Several of the magnetic portions of the samples were reduced to smaller size fractions using a mortar and pestle to obtain purer splits of sericite.
The sericite was then filtered and the lighter separates left on the filter paper were dried and sieved to either >250 μm or >150 μm depending on their grain sizes. The sericite concentrates were further purified by using a binocular microscope and handpicked to a purity of >99%. Larger sericite flakes were obtained by scraping the thin quartz-sericitepyrite veins or quartz-sericite aggregates from the host rock using dental picks and fine-tipped tweezers. This mixture of sericite and other material was further refined by rinsing, sieving and electromagnetic separation in order to make an initial concentration of sericite. The sericite flakes were then further purified to >99% purity following the same procedures as those for sericite aggregates. Sericite separates were weighted and encapsulated in aluminum foil, along with the neutron flux monitor Fish Canyon Tuff (FCT-2-NM) sanidine grains (28.201±0.023 Ma; Kuiper et al., 2008) which were encapsulated in copper foil. The capsules were loaded into a quartz vial and vacuum sealed. The quartz vial was then irradiated for 6 hours at a cadmium-lined irradiation position CLICIT at the Oregon State University TRIGA reactor. Once the required cool down period was achieved, samples were unpacked and transferred into copper trays and put under vacuum in the CO2 laser lines. Sericite aliquots were analyzed using a ThermoFisher Scientific ARGUS VI multi-collector mass spectrometer, which is linked to an Ultra-High Vacuum (UHV) stainless steel gas extraction/purification line and Synrad 25 Watt CO2 laser system. Samples were incrementally heated from low power to high power settings. Each experiment consists of baseline, blank and sample measurements
which were conducted in a certain sequence. Laser and extraction line blanks were collected during the course of the entire heating experiment. Samples were continuously heated until the
39Ar
was fully extracted. This methodology
produces analytical data from the cutting-edge ARGUS VI multi-collector mass spectrometer that allows for a ~10 times improvement in precision compared to traditional spectrometers (Phillips and Matchan, 2013). With the extremely high precision ages it is possible to pick up minute signals from inclusions in the sample that can affect what would normally have been a flat plateau age on older instrumentation. Argon isotopic results are corrected for system blanks, radioactive decay, mass discrimination, reactor-induced interference reactions and atmospheric argon contamination. Decay constants reported by Min et al. (2000) are utilized for age calculation. Isotope interference corrections as determined using the ARGUS
VI
are:
(36Ar/37Ar)Ca
0.0006425±0.0000059;
=
(40Ar/39Ar)K
0.0002703±0.0000005; =
0.000607±0.000059;
(39Ar/37Ar)Ca
=
(38Ar/39Ar)K
=
0.012077±0.000011. Ages were calculated assuming an atmospheric
40Ar/36Ar
ratio of 295.5±0.5 (Nier, 1950). Data reduction and age calculation were processed using Ar-Ar Calc 2.7.0 (Koppers, 2002). Plateau ages are defined as including >50% of the total where the
40Ar/39Ar
39Ar
released with at least three consecutive steps,
ratio for each step is in agreement with the mean at the 95%
confidence level. In some cases only weighted mean ages are given. 5.3 40Ar/39Ar dating results and interpretation For samples where both flake and aggregate aliquots were obtained, both
were analyzed to clarify whether there is an age difference in different phases from the same sample and determine the reliability of individual phases. Ages are shown in Table 3 to Table 7 and age spectra are shown in Figure 10. Only flakes were separated for Sample JQD15D004B6 in the sericitequartz alteration zone adjacent to the orebody, the flakes underwent 33 heating steps (Table 3). The first step provides a young apparent age of 97.06 Ma, and the first 8 steps display a stepladder pattern, suggesting slight argon loss for the first few steps. The age spectrum becomes stable in the following steps, and it starts to fall in the remaining steps and the apparent age uncertainties increase because of the small amount of 39Ar been analyzed. The sericite reveals a humpbacked age spectrum overall, and the flat steps with highest apparent ages give a weighted mean age of 119.18±0.20 Ma, indicating the minimum age for the sample (McDougall and Harrison, 1999). The inverse isochron age of 119.12±1.00 Ma is consistent with the weighted mean age (Fig. 10b). The initial 40Ar/36Ar
of this analysis is 307.28±142.21 and is within error of the accepted
40Ar/36Ar
atmosphere ratio of 295.5±0.5, as defined in this paper.
Both sericite flakes and aggregates were dated for Sample JQD15D004B2 (Tables 4-5) from a milky-white quartz vein on the margin of the orebody. Sixteen and 32 heating steps were applied on flakes and aggregates, respectively. Both aliquots yield younger apparent ages for the first few steps, implying slight argon loss, but are followed by concordant flat spectrum that yield plateau ages of 117.95±0.24 Ma and 116.97±0.17 Ma comprising 74.69% and 70.66% of the 39Ar released, respectively (Fig. 10c, e). The age of the flakes is slightly older than
that of the aggregates, while the plateau of the aggregates is slightly flatter than that of the flakes (Fig. 10c, e). Excess argon possibly from potential inclusions in the flakes may account for the slightly older apparent age in the second heating step for the flake aliquot, which is also supported by increasing
36Ar
extracted in
the second step (Table 4). Both inverse isochrons suggest an age of ~117 Ma (Fig. 10d, f), which is very close to the age for the aggregates. The aggregates that contain more radiogenic argon cluster close to the X-axis, thus making the inverse age less robust (Fig. 10f). The initial
40Ar/36Ar
for both the flakes
(350.79±76.10) and aggregates (285.22±43.57) are within error of the accepted 40Ar/36Ar
atmosphere ratio. However, the spectrum of flakes is more discordant
and the majority of the gas was released at low temperature (Fig. 10c). Taking into account a higher MSWD of 4.07 for the flakes, it is possible that the age of the flakes is close to that of the aggregates at 116.97 Ma, but the slight excess argon coming from inclusions has elevated the age. Therefore, the age for the sericite is likely to be 117 Ma based on the fact that both inverse isochrons indicate that the amounts of trapped gas for the steps chosen in the plateaus are identical (Fig. 10d, f). For Sample JQD15D015B2 from a smoky-gray quartz-pyrite vein in the center of the orebody, both sericite flakes and aggregates underwent 34 heating steps (Tables 6-7). The low temperature ages may imply slight argon loss, whereas the intermediate steps did not suffer from argon loss, and the remaining few steps yield decreasing apparent ages with large error bars, constituting arc age spectra (Fig. 10g, i). Since these spectra are discordant, they can only give
weighted mean ages of 121.64±0.18 Ma and 119.28±0.16 Ma that respectively account for 25.00% and 38.01% of the total
39Ar
released (Fig. 10g, i): these
ages are interpreted as minimum ages (McDougall and Harrison, 1999). The inverse isochron ages for the flakes and aggregates are 121.22±0.70 Ma and 119.35±0.29 Ma (Fig. 10h, j), which are in agreement with their corresponding weighted mean ages. The initial 40Ar/36Ar ratios for both the flakes (349.94±85.00) and aggregates (275.64±59.14) are within error of the accepted
40Ar/36Ar
atmosphere ratio. Nearly all argon in the aggregates is radiogenic and they cluster close to the X-axis (Fig. 10j), making it difficult to generate a reliable inverse isochron.
6. Discussion 6.1 Timing and duration of gold mineralization in the Rushan deposit The close paragenetic relations among pyrite, quartz and sericite (Fig. 9) suggest that the temperature of the hydrothermal ore fluid was in the range of 225-400 °C (McCuaig and Kerrich, 1998). This has been confirmed by fluid inclusion studies that give homogenization temperatures of 170-377 °C for fluids in alteration zones and quartz veins (Hu et al., 2005). Therefore, the ore-forming temperature is consistent with the sericite argon closure temperature (350±50 °C, McDougall and Harrison, 1999) and the ages obtained represent the crystallization ages of sericite. Considering the close syn-genetic relationship between sericite and quartz plus pyrite (Figs. 8-9), and that sericite was deposited episodically from fluids that precipitated major vein minerals during
vein deposition (see Section 4.3 for more details), sericite crystallization is interpreted to have been contemporaneous with gold mineralization. Therefore, the argon crystallization ages of sericite represent the timing of gold mineralization. Interestingly, the ages of sericite aggregates are 0.98-2.36 My younger than those of their corresponding sericite flakes (Fig. 10), which provides new insights into selection of analyzed samples. The aggregates obtained following traditional separation processes are composed of tiny 10-20 μm sericite chips (Kent and McDougall, 1995), and the closure temperature of these chips may be lower than that of the corresponding medium-fine flakes because of a grain size effect, which would make their measured ages slightly younger. However, the ages of sericite aggregates and flakes are remarkably consistent in general. The sericite in Sample JQD15D015B2 from the smoky-gray quartz-pyrite vein in the center of the orebody yields a minimum age of 121.64-119.28 Ma (Fig. 10g, i), which is slightly older than equivalent ages of sericite from Sample JQD15D004B2 (117.95-116.97 Ma; Fig. 10c, e), a milky-white pyrite-quartz vein on the margin of the orebody. This suggests that the quartz veins in the center of the orebody formed slightly earlier than those on the margin. The host rock Sample JQD15D004B6 adjacent to the orebody is interpreted to have undergone incremental water-rock interactions because of episodic fluid injections, and its intermediate sericite
40Ar/39Ar
age of 119.18 Ma (Fig. 10a) probably represents
an integrated feedback of multiple fluid events throughout the entire mineralization event.
Previous studies obtained mineralization ages varying from 156.7 Ma to 104.8 Ma for the Rushan deposit (Table 1 and references therein). However some of the geochronological data are unreliable due to inappropriate samples or techniques: 1). a mixing age is often obtained with Rb-Sr dating on sericitequartz altered whole-rocks due to mixtures of minerals from variable sources; 2). the K-feldspar from alteration zones chosen for
40Ar/39Ar
analysis very likely
contains residual magmatic K-feldspar and is commonly retrogressively altered to sericite, thus resulting in a cooling or meaningless age; 3).
40Ar/39Ar
dating on
fluid inclusions is misleading due to the inevitable influence of abundant secondary fluid inclusions (Luo et al., 2000). Sericite is commonly co-precipitated with gold and ore minerals, and the relatively high closure temperature of sericite argon system means high resistance to disturbance from post-mineralization thermal events, making it a widely used mineral to constrain the timing of mineralization. However, it could be misleading if sericite is not properly selected. For example, the old
40Ar/39Ar
sericite age of 156.7±0.6-155.8±0.05 Ma (Li, 2004) is probably due to a mixture of hydrothermal sericite and magmatic muscovite from the wall rock considering no co-existence relations between sericite and gold and associated sulfide minerals were provided, and the age of wall rock granite is 161-138 Ma (Fig. 11; Hu et al., 2004; Guo et al., 2005; Zhang, 2011). Hu et al. (2006) reported a sericite
40Ar/39Ar
age of 128.8±0.1 Ma for a sample from intensively sericite-
quartz altered host rock adjacent to the auriferous quartz vein, and this age was further interpreted to represent an earlier hydrothermal mineralization event.
However, the variation in apparent ages in each heating step makes it unconvincing to build a robust plateau age, given the criteria required by the MM5400 Mass Spectrometer used in their study. On the other hand, the sericite chosen has a coarse grain size and may be mixed with magmatic muscovite, since similar ages are acquired based on
40Ar/39Ar
analyses on biotite from the
fresh Kunyushan granite near the Rushan gold deposit (129.0-126.9 Ma, Li et al., 2006), biotite from the fresh Kunyushan granite near the Denggezhuang gold deposit (129.0±0.6 Ma, Zhang et al., 1995), white mica from a synkinematic pegmatite vein in the Sulu Terrane (128.2±0.7 Ma, Webb et al., 2006). Hence a mixed age or cooling age was probably obtained in their study. Li et al. (2006) conducted sericite
40Ar/39Ar
dating on sericite from ore samples in the Rushan
gold deposit, and an ore-forming age of 109.3-107.7 Ma was proposed based on the dating results of six aliquots from two samples. Careful microscopic observation and EPMA analysis proved the purity of the sericite selected. However, the integrated ages in their study are systematically 2-8 My lower than the corresponding plateau ages, and the lower temperature steps for our samples have yielded apparent ages between 110-102 Ma (Fig. 10c, g). Therefore, the young ages in their study may have resulted from argon loss induced by post-mineralization structural or hydrothermal events (McDougall and Harrison, 1999). Notably, Hu et al. (2004) identified hydrothermal zircons based on zircon morphology, common Pb contents, Th/U ratio, and compositions of fluid inclusions in zircons. A SHRIMP U-Pb age of 117±3 Ma was obtained for the
hydrothermal zircons, and, although the error is high, this age is in agreement within error with our dating results. In addition, sericite
40Ar/39Ar
ages for the
Yinggezhuang deposit (120.02±0.38 Ma), Xipo deposit (121.65±0.48 Ma) and Sanjia deposit (116.51±0.47 Ma) were obtained by Chen (2017), and these ages from different gold deposits in the Muping-Rushan belt are also in accordance with the results presented here. Therefore, the gold mineralization in the Rushan gold deposit is interpreted to have occurred from ca. 122 to 117 Ma, with this range overlapping or being slightly younger than published ages of the gold deposits in northwestern Jiaodong (e.g. Li et al., 2003; Yang et al., 2014b, 2017; Bi and Zhao, 2017; Ma et al., 2017; Zhang et al., 2019a). No crosscutting relationships between the major vein forming Orebody II and other mineralized veins nor superimposition of alteration zones around Orebody II are recorded in this and previous studies (e.g. Li et al., 1996). A single metallogenic event involving episodic fluid events may best characterize the Rushan gold deposit, with duration of gold mineralization probably lasting for about 5 My, from ca. 122 Ma to 117 Ma. The Kunyushan granite intruded Jingshan Group metamorphic rocks and Sulu UHP at 160-138 Ma (Fig. 11; Hu et al., 2004; Guo et al., 2005; Zhang, 2011), and it cooled down through 300±50 °C (closure temperature of biotite 40Ar/39Ar
system, McDougall and Harrison, 1999) at 129-127 Ma (Zhang et al.,
1995; Li et al., 2006). Subsequently, ore-forming fluids migrated upwards along faults and auriferous quartz veins were precipitated at 122-117 Ma. The magmatic-hydrothermal system induced by a single intrusive event generally is
sustained for no more than 1 My, and the total duration lasts less than 10 My given slow cooling caused by deep intrusion of magma (Cathles et al., 1997; Henry et al., 1997). Therefore, such a significant temporal gap between granite emplacement and cooling and gold mineralization indicates that the Kunyushan granite and gold metallogeny are not genetically related. Moreover, the closure temperature for the biotite 40Ar/39Ar system (300±50 °C, McDougall and Harrison, 1999) is lower than the temperature of the ore-forming fluid (Hu et al., 2006), meaning that the ore-fluid temperature was higher than that of the host rock during ore-formation and not the reverse as in a magmatic-hydrothermal system. The timing of gold mineralization just overlaps intrusion of the Sanfoshan monzonite, which intruded the Kunyushan granite in the southeastern part of the gold belt at 118-113 Ma (Guo et al., 2005; Goss et al., 2010; Zhang, 2011). However, the earliest formation ages of 118-117 Ma proposed by Goss et al (2010) is tenuous given that no more than ten zircon grains in each sample produced discordant isochrones. Instead, the Sanfoshan monzonite probably intruded at ca.116-113 Ma (e.g. Guo et al., 2005; Zhang, 2011), a timing outside the range of ages of gold mineralization. In addition, the Sanfoshan monzonite is not spatially associated with the Rushan gold deposit, and the No. II orebody extends down-dip for more than 1 km without notable change in alteration, mineralogy, and ore fluid chemistry (e.g. Hu et al., 2005). These constraints effectively rule out a magmatic hydrothermal origin for the Rushan deposit.
6.2 Fault dynamics, fluid pressure fluctuation and fault valve behaviour
Statistical data on orientations of the syn-mineralization conjugate joints which are filled by quartz-sulfide veins in different sections of the JiangjunshiQuhezhuang Fault suggest that the maximum compressional stress, σ1, during gold deposition was NW-SE with a subhorizontal plunge (Hu, 1995; Gao et al., 2011). Such a stress is consistent with the σ1 constrained for the neighboring Shigou-Wushan Fault during gold mineralization (He and Zhang, 2006). The Jiangjunshi-Quhezhuang Fault is interpreted to have had sinistral and reverse motion during gold mineralization, with low total fault slip along the synstructural vein (cf. Cox, 2016). The low displacements are consistent with the low differential stress value of 83-103 MPa estimated from lattice dislocation of quartz from the high-angle quartz veins in the Rushan deposit (Gao et al., 2011). This suggests that regional σ1 was low, accounting for sparse evidence of regional compression or transpression in the district. Although rare, there is confirmatory evidence from the Jiaolai Basin, where the widespread conjugate shear joints in the upper Laiyang formation suggest a NWW-SEE compressional stress that may account for the disconformity between the Laiyang formation and overlying Qingshan formation (Ren et al., 2007). The occurrence of H2O-CO2 primary fluid inclusions with highly varied CO2 volumetric proportions in the Rushan deposit (Hu et al., 2005) suggest that fluids were trapped under sub-solvus conditions. These inclusions homogenize within the same temperature range, supporting a model in which trapped inclusions formed by fluid immiscibility of a parental homogeneous fluid (Ramboz et al., 1982). Pressures of fluid inclusions that trapped immiscible fluids are estimated
through the isochore intersection method (Fig. 12). Isochores are calculated based on the equations of Bakker (1999) for CO2-H2O fluid inclusions using the microthermometric data from Hu et al. (2005), and the trapping temperatures are estimated using Loucks' (2000) statistical method. The lithostatic and hydrostatic pressure range are estimated in order to compare with the pressures of the ore-forming fluids. Yao et al. (2006) estimated that Cretaceous geothermal gradients in the neighboring basins adjacent to the Jiaodong Peninsula were ca. 45 °C/km. Considering that the geothermal gradient in a stable terrane is normally lower than that of nearby basins, a maximum geothermal gradient of 40 °C/km and a minimum value of 30 °C/km are assumed. In addition, an average rock density of 2.7 g/cm3 and fluid density of 1.0 g/cm3 are also utilized to build the pressure gradients. The pressures of CO2-H2O fluid inclusions corresponding to their trapping temperatures are in the range of 247 to 108 MPa, showing remarkable pressure fluctuations from supralithostatic to nearly hydrostatic (Fig. 12): this range is broadly in agreement with that calculated by Hu et al. (2005). Abrupt drops from lithostatic to hydrostatic pressures would cause a dramatic decrease in silica solubility and thus massive quartz deposition (Rimstidt, 1997), as recorded at Rushan. High-angle shear veins and low-angle extension veins are common in lode gold deposits controlled by movement on high-angle reverse strike-slip faultfracture systems (Sibson, 1990; Groves, et al., 1998; Nauyen et al., 1998; Zhang et al., 2019c). The internal textures of both types of veins provide effective
insights into fluid evolution during quartz veining. The existence of the dark-gray elongate slab with multiple crack-seal structures at the contact of the quartz vein and its host rock (Figs. 5d, 6k) argues strongly for existence of episodic fluid events. Episodic fluctuation of fluid pressure from supralithostatic to hydrostatic, the fault valve model (Sibson et al., 1988), is considered to have played a vital role in the deposition of high- angle and low-angle veins (e.g. Sibson et al., 1988; Cox, 1995, 2016; Goldfarb et al., 2005). In this model, the formation of faultrelated quartz veins in overpressured, high fluid-flux regimes is related to multiple earthquake ruptures released along regional major faults (Sibson et al., 1988), where earthquakes may relate to swarm seismicity, rather than main-shock to after-shock sequences (Cox, 2016). Some of the larger ruptures within swarms are spatially associated with “mini-after-shock” bursts whose activity decays with time (Cox, 2016). The Jiangjunshi-Quhezhuang Fault had sinistral and reverse movement during gold mineralization, with this type of high-angle oblique fault regarded as the most effective “valve” to trigger the uprise of fluids and fluctuation of fluid pressure (Sibson et al., 1981). 6.3 Process of progressive vein formation On the basis of sericite ages of samples from different locations, and characteristics of internal textures and microstructures of the high-angle shear veins, the detailed processes for deposition of such veins are proposed with reference to the fault valve model. It is interpreted that the ore-controlling fault remains sealed before gold mineralization. Fluid pressure below the seismogenic zone keeps building up
because of continuous supply, and when it is higher than lithostatic values, the low-angle fractures open up and failure is triggered on the fault section near the base of the seismogenic zone, nucleating an earthquake rupture that reactivates the fault (Fig. 13a). Dilatational space is formed due to the sinistral-reverse slip on the fault and it is more developed especially in fault segments with low dip (Fig. 13b), and thin wallrock laminae will be detached from the host rock contact. The large stress difference between the dilatational space and the rupture zone draws the geo-pressured fluid reservoir at depth upwards along the fault. Once the fluids are injected into the dilatational zone, they fracture the host rock and fluid immiscibility takes place due to the abrupt drop of fluid pressure (Cox, 1995). The intense supersaturation of silica results in massive deposition of quartz (Fig. 6b), and coarse-grained pyrite is precipitated as aggregates (Fig. 6c) to form the milky-white quartz layer, with the host rock breccias cemented by quartz and pyrite (Fig. 5b). Meanwhile, the detached host rock laminae are cemented and dragged into the same strike as that of the fault as a consequence of the oblique slip (Fig. 13c). As the rate of fluid pressure and temperature decrease declines, silica precipitates relatively slowly as euhedral comb-like to drusy quartz crystals with growth zoning (Fig. 6a), and with long axes at a high angle to the host rock wall. The coarse-medium grained pyrite, meanwhile, precipitates at the contact between wall rock and quartz veins, as well as boundaries of the host rock laminae in the quartz veins, to form thin sulfide laminae (Fig. 5c).
Subsequently, the supercharged fluids induced by “mini-aftershock” bursts fractures some of the pre-existing pyrite and quartz (Fig. 6e-f), thin sericitequartz-sulfide veinlets cut earlier-deposited coarse-grained minerals (Fig. 6i), and anhedral disseminated pyrite forms at the boundaries of quartz (Fig. 6d). As hydraulic fracturing continues, the concentration of metallic elements such as Ag, Au, Cu, Pb, Te and Zn in the fluid increases with the deposition of quartz and pyrite (Zhao et al., 1996; Liu et al., 2010), and they precipitate in the microfractures of early pyrite (Figs. 6g-h, 9h) or at interstitial boundaries. Carbonate occurs dominantly as calcite, and as the last mineral to form in each major fluid episode, it either fills the vugs (Fig. 6l) and the micro-fractures that truncate the earlier minerals (Fig. 6f), or occurs as discrete blocks in quartz veins (Fig. 5e). The milky-white quartz layer that formed earlier is thus partly rendered into the smoky-gray layer due to the multiple hydraulic fracturing and consequent deposition of fine grained minerals (Fig. 13d). The local existence of vugs implies that the rate of fracture propagation is higher than that of fluid supply in such places, such that the quartz is deposited slowly in equilibrium with a weakly supersaturated fluid. However, if the rate of fracture propagation is lower than that of fluid supply in terms of the whole dilatational zone, the fault is sealed because of the constant decrease in permeability induced by fluid discharge (Fig. 13d). At this stage, the fluid pressure starts to rise again until the next major rupture occurs. Once the next fault rupture is triggered, the stress releases preferentially along structural weaknesses such as contacts between the early quartz vein and
the host rock, and thus new dilatational spaces are created on both margins of the early quartz vein (Fig. 13e). The slightly older age for Sample JQD15D015B2 (Fig. 10g, i) from the smoky-gray quartz layer and the slightly younger age for Sample JQD15D004B2 (Fig. 10c, e) from the milky-white layer are consistent with this model. Early sulfide laminae formed along the host rock-vein contact are therefore detached from the wallrock and attached to the margin of the quartz vein (Fig. 13e). The upwelling ore-forming fluids enter the new dilatational space and the precipitation processes described above are renewed, resulting in the repetitive banding of the resultant quartz-pyrite vein (Fig 13f). The early-formed host rock breccias are progressively further altered due to interaction with the renewed fluid activity, and therefore the host rock breccias near the margin of the orebody are generally less altered than those in the center. In addition, the earlyformed quartz layers are frequently fractured by later fluids, as indicated by the quartz veinlet enclosing euhedral pyrite grains (Fig. 6j), host rock breccias truncated by the milky-white quartz layer in the outermost margin of the orebody (Fig. 5e), the smoky-gray quartz breccias in the milky-white quartz layer (Fig. 5e), and the dark-gray elongate slabs with multiple crack-seal structures at the contact of quartz vein and host rock (Figs. 5d, 6k). The gold-rich quartz lodes, featuring complex internal textures, are thus formed incrementally by episodic fault-valve processes.
7. Conclusion Gold mineralization at the Rushan gold deposit occurred between ca. 122 and 117 Ma, and thus overlap or are slightly younger than gold deposits in the northwestern Jiaodong Peninsula. The age difference between sericite samples from different spatial locations in the orebody suggests that the quartz veins on the margin of the orebody may be younger than those in the vein center. The temporal gap between mineralization age and emplacement plus cooling age of the ore-hosting Kunyushan granite negates a genetic relationship between them. The Sanfoshan monzonite is not spatially associated with gold mineralization and is slightly younger, thus negating a genetic relationship between them. High-angle shear veins and low-angle extension veins are reported for the first time from the Rushan gold deposit. Quartz vein deposition and gold mineralization were controlled by fault valve behavior under a weak NW-SE regional
transpressional
stress,
in
which
episodic
fluctuations
from
supralithostatic to hydrostatic fluid pressure triggered multiple fault ruptures induced by breaches of supralithostatic fluids under a seismogenic regime. The sequence of events is interpreted to be as follows: 1) the fault starts to slip with both reverse and sinistral motion, and dilatational zones are created; 2) the orefluids migrate upwards along the fault due to the large pressure difference between the dilatational zones and the deeper segments of the fault; 3) host rocks and earlier-deposited quartz veins are hydraulically fractured by renewed fluid flux; 4) abundant quartz, pyrite, gold, and other ore-related minerals are precipitated during fluid immiscibility caused by pressure fluctuations, and new
quartz veins formed along both margins of earlier quartz veins; 5) the fault is sealed by deposition of new quartz veins and the fluid pressure increases until the next breach cycle; and 6) resultant quartz veins with complex internal crackseal textures were deposited incrementally during these cycles. The combined result was the generation of a single strike-extensive quartz vein with incredibly complex internal structures and textures.
Acknowledgements Thanks are due to Professor Anthony Koppers for the help he gave during 40Ar/39Ar
analysis. Discussions with Professor Richard Ketcham provided useful
insights into our understanding of the argon data. We thank Drs. Zhongliang Wang, Binghan Chen, Yue Liu and Sirui Wang for their help in the field survey. Thorough reviews by two anonymous reviewers and the editorial assistance of Professor Franco Pirajno are gratefully acknowledged. The paper was dramatically improved by careful editing by Professor David Groves. This work was financially supported by the National Natural Science Foundation of China (41230311, 41572069), the National Key Research Program of China (2016YFC0600107-4), the Fundamental Research Funds for the Central Universities, China (2-9-2017-257), the Most Special Fund from the State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences (MSFGPMR201804) and the 111 Project of the Ministry of Science and Technology (BP0719021). S.X. Sai is indebted to grants from Scholarship
Program of the China Scholarship Council (201706400006) and the Society of Economic Geologists 2016 Graduate Students Fellowship.
Conflict of interest No conflict of interest exits in the submission of this manuscript, and the manuscript is approved by all authors for publication. I would like to declare on behalf of my co-authors that the work described is original research that has not been published previously, and is not under consideration for publication elsewhere, in whole or in part.
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Headings for tables Table 1 Previously published mineralization ages from the Muping-Rushan gold belt.
Table 2 Samples for sericite 40Ar/39Ar dating in the Rushan deposit.
Table 3
40Ar/39Ar
step heating data for sericite flakes from sericite-quartz
alteration Sample JQD15D004B6 in the Rushan gold deposit.
Table 4
40Ar/39Ar
step heating data for sericite flakes from gold ore Sample
JQD15D004B2 in the Rushan gold deposit.
Table 5
40Ar/39Ar
step heating data for sericite aggregates from gold ore Sample
JQD15D004B2 in the Rushan gold deposit.
Table 6
40Ar/39Ar
step heating data for sericite flakes from gold ore Sample
JQD15D015B2 in the Rushan gold deposit.
Table 7
40Ar/39Ar
step heating data for sericite aggregates from gold ore Sample
JQD15D015B2 in the Rushan gold deposit.
Figure captions Fig. 1 Geological sketch map of the North China Block and Jiaodong Peninsula (modified from Deng et al., 2019). GJF, Guocheng-Jimo Fault; HSF, HaiyangShidao Fault; JJF, Jiaojia Fault; MRF, Muping-Rushan Fault Zone; QHF, Qingdao-Haiyang Fault; QXF, Qixia Fault; RCF, Rongcheng Fault; SSDF,
Sanshandao Fault; TCF, Taocun Fault; WHF, Weihai Fault; WQYF, WulianQingdao-Yantai Fault Zone; ZPF, Zhaoyuan-Pingdu Fault; ZWF, Zhuwu Fault.
Fig. 2 Geological map of the Muping-Rushan gold belt (modified from Li et al., 1996 and Hu et al., 2007). CSF, Chahe-Sanjia Fault; GKF, Gekou Fault; JNSF, Jinniushan Fault; JQF, Jiangjunshi-Quhezhuang Fault; LHF, Laohuwo-Hezi Fault; QTF, Qinghushan-Tangjiagou Fault.
Fig. 3 Geological map of the Rushan gold deposit and cross-section showing the alteration zones (a-b, modified from Chen, 2017); profile at -865m level displaying the alteration zones, structures and the No. II Orebody (c).
Fig. 4 Field photographs showing the characteristics of the ore-controlling fault. (a) High-angle fault filled by the No. II Orebody, and lamprophyre which intrudes the Orebody; (b) Striations and steps indicating sinistral movement, overprinted by striations and steps indicating normal faulting. All in profile views.
Fig. 5 Field photographs showing the internal textures of high-angle shear veins. (a) Contact of sericite-quartz alteration zone and the No. II Orebody; (b) Host rock breccias in the No. II orebody, and potassic alteration zone wraps the Orebody directly; (c) Host rock and sulfide laminae in the No. II Orebody; (d) Quartz vein layers separated by dark crack-seal veins; (e) Host rock breccia in smoky-gray quartz layer truncated by milky-white quartz layer, smoky-gray quartz breccia in milky-white quartz layer, and cubic calcite block in smoky-gray quartz
layer. (a), (b) and (e) are upward views; (c) and (d) are profile views. Stars in (a) and (b) mark the precise locations of the samples for 40Ar/39Ar geochronology.
Fig. 6 Microstructures of high-angle shear veins. (a) Euhedral coarse quartz grains with clear growth zones on the margin of vein; (b) Euhedral-subhedral coarse-grained quartz without growth zones in the center of the quartz vein, and self-sealed quartz veinlets inside the coarse-grained quartz; (c) Cluster of slightly fractured pyrite aggregates, and later galena on the boundaries of pyrite; (d) Disseminated anhedral pyrite; (e) Fractured coarse-grained quartz; (f) Fractured coarse-grained pyrite cut by calcite veinlet; (g-h) Gold minerals and galena fill micro-fractures in pyrite; (i) Crack-seal veinlet with fragments of host quartz vein; (j) Quartz veinlet with euhedral pyrite grains; (k). Fine fragments of minerals in quartz vein and matrix-like minerals in host rock; (l) Open space in quartz filled by calcite. Au, gold; Cal, calcite; El, electrum; Ga, galena; Q, quartz; Ptz, petzite; Py, pyrite; Ser, sericite.
Fig. 7 Field photographs showing the internal textures of low-angle extension veins. (a) Low-angle extension veins adjacent to high-angle shear vein; (b) Lowangle extension veins in Jingshan Group metamorphic rocks; (c) Host rock laminae and series of vugs parallel to host rock wall; (d) Discontinuous pyrite laminae parallel to host rock wall, and angular host rock breccias in low-angle vein. All in profile view.
Fig. 8 Paragenetic sequence of hydrothermal minerals in the Rushan gold deposit. Thickness of the solid lines represents the relative abundance of minerals.
Fig. 9 Characteristics of samples chosen for
40Ar/39Ar
dating. (a) Gray-green
sericite-quartz altered rock; (b) Sericite cuts recrystallized quartz; (c) Sericite and muscovite in close spatial relationship with pyrite; (d) Massive sericite grains and later calcite veinlet; (e) Specimen showing contact of sericite-quartz alteration zone and vuggy milky-white quartz vein; (f) Sericite and coarse-grained quartz with growth zoning; (g) Sericite closely associated with pyrite cluster; (h) Gold minerals and hessite in micro-fractures in pyrite; (i) Smoky-gray quartz vein with disseminated pyrite; (j) Sericite associated with disseminated pyrite; (k) Sericite and pyrite in fine veinlet that cuts coarse quartz grains; (l) Stockwork filled by sericite, quartz and pyrite. Hes, hessite; Mus, muscovite; the other mineral abbreviations are the same as those in Figure 6.
Fig. 10
40Ar/39Ar
plateau and inverse isochron ages (2σ) for sericite from the
Rushan gold deposit.
Fig. 11 Diagram indicating the ages with 2σ analytical uncertainties determined for minerals and whole rocks from the Rushan deposit and the nearby area. Data source: magmatic zircon U–Pb from Hu et al. (2004), Guo et al. (2005) and
Zhang (2011); hydrothermal zircon U–Pb from Hu et al. (2004); biotite
40Ar/39Ar
from Zhang et al. (1995) and Li et al. (2006); sericite 40Ar/39Ar from this study.
Fig. 12 P-T diagram with isochores for fluid inclusions trapped under sub-solvus conditions. Gray vertical box is the homogenization temperatures for CO2-H2O fluid inclusions. Blue arrow corresponds to pressure fluctuation at trapping temperatures estimated from the method proposed by Loucks (2000). Fluid inclusion micro-thermometric data are from Hu et al. (2005).
Fig. 13 Cartoon showing the incremental emplacement of the high-angle shear veins. Note 160-138 Ma is the formation age for the ore-hosting Kunyushan granite: age data from Hu et al. (2004), Guo et al. (2005) and Zhang (2011).
Table 1. Previously published mineralization ages from the Muping-Rushan gold belt Deposit
Sample
Method
Age (Ma)
References
sericite-quartz altered rock
Rb-Sr
113.3±4.4
Zhang et al. (1994)
altered K-feldspar
Rb-Sr
121.3±0.6
Zhang et al. (1994)
sericite-quartz altered rock
Rb-Sr
104.8±1.5
Zhai et al. (1996)
108.2±0.3sericite
40
39
Ar/ Ar
Rushan
107.4±0.2 156.7±0.6-
Li (2004)
155.8±0.1 hydrothermal
Shrimp U-
zircon in quartz vein
Pb
sericite
40
sericite
40
altered K-feldspar
40
sericite-quartz altered rock fluid inclusions in quartz Denggezhuang
39
Ar/ Ar
117.0±3.0 109.3±0.3107.7±0.5
Hu et al. (2004) Li et al.(2006)
Ar/ Ar
39
128.8±0.1
Hu et al. (2006)
Ar/ Ar
39
118.7±1.2
Cao (2013)
Rb-Sr
118.0±9.0
Zhang et al. (1995)
117.5
Zhao et al. (1996)
40
39
Ar/ Ar
altered K-feldspar
40Ar/39Ar
123.4±0.5
Xue et al. (2019)
sericite
40Ar/39Ar
104.8±1.1
Xue et al. (2019)
altered K-feldspar
40Ar/39Ar
111.2±0.7
Cui (2012)
sericite
40Ar/39Ar
120.0±0.4
Chen (2017)
Xipo
sericite
40Ar/39Ar
121.7±0.5
Chen (2017)
Hubazhuang
sericite
Rb-Sr
126.5±5.6
Cai et al. (2011)
Sanjia
sericite
40Ar/39Ar
116.5±0.5
Chen (2017)
Yinggezhuang
Table 2 Sample descriptions for sericite 40Ar/39Ar dating in the Rushan deposit Sample
Location Intensive
Rock type
Minera l
Phase
sericite-quartz Sericite-
JQD15D004B alteration zone adjacent to the quartz
Sericit
6
e
No. II Orebody near the N7 altered
Aggregate
Measuring Point in Level -865m granite JQD15D004B
Margin of the No. II Orebody
Milky-white
Sericit
Flake and
quartz ore
e
aggregate
JQD15D015B near the E4 Transverse Drift in Smoky-gray
Sericit
Flake and
2
e
aggregate
2
near the N7 Measuring Point in Level -865m Center of the No. II Orebody Level -865m
quartz ore
1
Table 3 40Ar/39Ar step heating data for sericite flakes from sericite-quartz alteration Sample
2
JQD15D004B6 in the Rushan gold deposit Me asure ment s
R elati ve Abu nda nce
18E2 7207
0.2 %
18E2 7208
0.3 %
18E2 7210
0.4 %
18E2 7211
0.5 %
18E2 7212
0.6 %
18E2 7214
0.7 %
18E2 7215
0.8 %
18E2 7216
0.9 %
18E2 7218*
1.0 %
18E2 7219*
1.1 %
18E2 7220*
1.2 %
18E2 7222*
1.3 %
18E2 7223*
1.4 %
18E2 7224*
1.5 %
18E2 7226*
1.7 %
36
A r [f A ] 6 . 8 8 1 . 1 2 0 . 4 7 0 . 2 8 0 . 1 4 0 . 1 4 0 . 0 6 0 . 0 6 0 . 0 3 0 . 0 3 0 . 0 5 0 . 0 2 0 . 0 2 0 . 0 2 0 . 0 2
37
Ar [f A]
0. 2 5
11 .5 5
1. 01
0. 2 9
27 8. 60
0. 38
0. 3 8
16 8. 07
0. 38
0. 4 3
86 .5 9
0. 40
0. 6 1
59 .7 8
0. 43
0. 6 7
58 .4 2
0. 42
1. 2 3
27 .3 3
0. 55
1. 2 1
28 .2 9
0. 53
1. 8 1
15 .7 6
0. 79
2. 1 8
12 .7 8
0. 89
1. 4 2
11 .9 5
0. 94
3. 3 6
3. 03
3. 50
2. 8 9
4. 38
2. 45
3. 4 5
3. 54
2. 95
3. 7 4
2. 68
4. 01
38
39
A r [f A ] 1 . 5 1 0 . 8 6 0 . 6 7 0 . 6 7 0 . 3 3 0 . 5 2 0 . 2 0 0 . 2 2 0 . 1 4 0 . 1 4 0 . 2 8 0 . 1 2 0 . 1 7 0 . 0 8 0 . 1 0
A r [f A ] 1 4. 2 6 5 3. 6 8 5 0. 2 6 5 1. 4 7 2 5. 6 2 4 1. 4 4 1 6. 4 7 1 7. 3 3 1 2. 1 0 1 1. 4 5 2 3. 0 0
0. 68 1. 15 1. 35 1. 36 2. 77 1. 82 4. 47 4. 40 6. 78 6. 94 3. 33
Age
A r [fA ]
40(r )/39 (k)
0. 1 1
25 33. 09
0. 0 1
35. 09
±0 .7 3
97 .0 6
0. 0 7
25 52. 60
0. 0 1
41. 94
±0 .0 7
0. 0 7
22 75. 49
0. 0 1
42. 89
0. 0 7
22 90. 40
0. 0 1
0. 0 8
11 42. 82
0. 0 7
40
(Ma)
Ar (r)
40
Ar (k)
39
K/C a
(%)
(%)
± 1. 96
19.7 4
3.46
0.5 31
± 0.0 11
11 5. 43
± 0. 18
87.9 0
12.9 8
0.0 83
± 0.0 01
±0 .0 6
11 7. 95
± 0. 16
94.5 3
12.1 7
0.1 28
± 0.0 01
43. 08
±0 .0 6
11 8. 47
± 0. 16
96.7 2
12.4 8
0.2 55
± 0.0 02
0. 0 1
43. 19
±0 .0 7
11 8. 76
± 0. 19
96.6 9
6.21
0.1 84
± 0.0 02
18 31. 23
0. 0 1
43. 35
±0 .0 6
11 9. 17
± 0. 16
98.0 1
10.0 5
0.3 05
± 0.0 03
0. 1 0
72 8.4 0
0. 0 1
43. 37
±0 .0 9
11 9. 22
± 0. 23
97.9 7
3.99
0.2 59
± 0.0 03
0. 0 9
76 8.3 3
0. 0 1
43. 52
±0 .0 8
11 9. 62
± 0. 22
98.0 8
4.20
0.2 63
± 0.0 03
0. 1 2
53 3.8 6
0. 0 2
43. 44
±0 .1 1
11 9. 40
± 0. 28
98.3 3
2.93
0.3 30
± 0.0 05
0. 1 2
50 3.9 4
0. 0 2
43. 35
±0 .1 1
11 9. 19
± 0. 29
98.4 5
2.78
0.3 85
± 0.0 07
0. 0 8
10 12. 75
0. 0 1
43. 42
±0 .0 7
11 9. 36
± 0. 20
98.6 0
5.58
0.8 28
± 0.0 16
8. 35
9. 5 3
0. 1 4
41 7.5 1
0. 0 2
43. 27
±0 .1 3
11 8. 97
± 0. 33
98.8 0
2.31
1.3 54
± 0.0 95
5. 55
1 3. 2 4
0. 1 1
58 0.6 7
0. 0 1
43. 40
±0 .1 0
11 9. 32
± 0. 27
98.9 5
3.21
1.2 99
± 0.0 64
11 .0 0
7. 3 4
0. 1 7
32 2.8 0
0. 0 2
43. 31
±0 .1 5
11 9. 07
± 0. 41
98.5 0
1.78
0.8 93
± 0.0 53
9. 42
8. 0 5
0. 1 5
35 2.9 4
0. 0 2
43. 27
±0 .1 4
11 8. 97
± 0. 37
98.7 2
1.95
1.2 90
± 0.1 03
56
18E2 7227*
1.9 %
18E2 7228*
2.2 %
18E2 7230*
2.5 %
18E2 7231
2.8 %
18E2 7232
3.1 %
18E2 7234
3.4 %
18E2 7235
3.8 %
18E2 7236
4.2 %
18E2 7238
4.6 %
18E2 7239
5.0 %
0 . 0 3 0 . 0 1 0 . 0 1 0 . 0 2 0 . 0 2 0 . 0 2 0 . 0 2 0 . 0 2 0 . 0 2 0 . 0 1
2. 4 1
3. 50
3. 10
5. 2 7
1. 47
7. 40
4. 6 6
1. 85
5. 86
3. 1 5
1. 26
8. 64
3. 6 4
0. 55
19 .9 2
2. 8 0
0. 79
13 .0 8
3. 7 2
0. 46
22 .2 3
3. 8 2
0. 47
22 .5 8
3. 4 5
1. 05
10 .4 6
4. 2 1
0. 10
10 3. 47
0 . 1 5 0 . 0 7 0 . 0 7 0 . 0 9 0 . 0 6 0 . 0 9 0 . 0 6 0 . 0 4 0 . 0 4 0 . 0 2
6. 57
1 1. 6 6
0. 1 2
51 1.7 6
0. 0 2
43. 27
±0 .1 1
11 8. 96
± 0. 28
98.5 5
2.83
1.4 33
± 0.0 89
13 .9 7
4. 5 4
0. 2 3
19 9.3 4
0. 0 4
43. 17
±0 .2 2
11 8. 68
± 0. 57
98.3 9
1.10
1.3 27
± 0.1 97
14 .1 6
4. 5 3
0. 2 6
19 9.5 7
0. 0 4
43. 24
±0 .2 4
11 8. 88
± 0. 65
98.2 0
1.10
1.0 55
± 0.1 24
9. 83
6. 2 7
0. 1 9
27 4.2 1
0. 0 3
42. 84
±0 .1 8
11 7. 82
± 0. 47
97.9 3
1.52
2.1 31
± 0.3 68
15 .5 9
4. 7 0
0. 2 3
20 5.7 3
0. 0 4
42. 69
±0 .2 2
11 7. 42
± 0. 58
97.5 2
1.14
3.6 56
± 1.4 57
10 .4 3
6. 4 1
0. 1 8
27 8.4 3
0. 0 3
42. 43
±0 .1 7
11 6. 73
± 0. 45
97.6 5
1.55
3.4 86
± 0.9 12
18 .4 5
3. 6 3
0. 3 3
15 7.7 0
0. 0 5
42. 01
±0 .3 0
11 5. 60
± 0. 79
96.8 1
0.88
3.3 65
± 1.4 96
23 .6 6
3. 5 2
0. 3 1
15 4.5 1
0. 0 5
42. 55
±0 .2 9
11 7. 05
± 0. 76
96.9 8
0.85
3.1 99
± 1.4 45
22 .2 3
2. 9 5
0. 3 7
12 9.0 2
0. 0 6
41. 96
±0 .3 4
11 5. 47
± 0. 90
95.9 6
0.72
1.2 12
± 0.2 54
57 .9 5
1. 2 8
0. 8 6
56. 89
0. 1 3
41. 43
±0 .7 7
11 4. 07
± 2. 04
92.9 6
0.31
5.3 35
± 11. 04 0
Table 3 40Ar/39Ar step heating data for sericite flakes from sericite-quartz alteration Sample JQD15D004B6 in the Rushan gold deposit (continued) 18E2 7240
5.4 %
18E2 7242
5.7 %
18E2 7243
6.1 %
18E2 7244
6.5 %
18E2 7246
7.0 %
18E2 7247
7.5 %
18E2 7248
8.0 %
0 . 0 2 0 . 0 1 0 . 0 1 0 . 0 3 0 . 0 2 0 . 0 1 0 .
3. 6 2
0. 10
10 9. 70
4. 5 1
0. 09
11 6. 54
4. 3 5
0. 20
56 .2 9
2. 0 0
0. 10
10 6. 63
2. 8 6
0. 25
41 .7 5
4. 0 8
0. 01
98 4. 06
3. 8
0. 08
13 8.
0 . 0 1 0 . 0 1 0 . 0 1 0 . 0 3 0 . 0 1 0 . 0 1 0 .
89 .4 7
1. 3 2
0. 8 4
58. 37
0. 1 3
40. 62
±0 .7 4
11 1. 90
± 1. 97
62 .7 6
0. 8 0
1. 3 8
36. 51
0. 2 1
41. 18
±1 .2 3
11 3. 38
± 3. 28
65 .3 6
0. 8 9
1. 2 8
40. 76
0. 1 9
41. 19
±1 .1 4
11 3. 41
± 3. 04
31 .8 1
1. 5 3
0. 7 3
71. 73
0. 1 1
40. 74
±0 .6 5
11 2. 23
± 1. 74
13 8. 14
1. 0 2
1. 0 6
48. 19
0. 1 6
40. 79
±0 .9 5
11 2. 36
± 2. 54
72 .9 5
0. 6 4
1. 7 3
30. 18
0. 2 5
40. 77
±1 .5 3
11 2. 30
± 4. 10
97 .5
0. 6
1. 7
30. 22
0. 2
40. 97
±1 .5
11 2.
± 4.
57
9 1. 8 1 8 9. 7 3 9 0. 0 5 8 6. 8 9 8 6. 7 4 8 5. 8 4 8 4.
0.3 2
5.82 8
± 12.78 7
0.1 9
3.69 6
± 8.615
0.2 2
1.96 4
± 2.212
0.3 7
6.65 3
± 14.18 9
0.2 5
1.79 2
± 1.496
0.1 5
25.6 74
± 505.2 99
0.1 5
3.44 8
± 9.562
18E2 7250
3 4
8.5 %
0 2 0 . 0 2
3 2. 6 5
66 0. 04
22 3. 83
0 1 0 . 0 2
4
3
9
46 .7 6
1. 0 0
1. 1 1
5 47. 68
0. 1 6
40. 83
9
83
25
±0 .9 9
11 2. 46
± 2. 65
9 2 8 5. 5 1
0.2 4
J value= 0.00157149 ± 0.00000099; Total fusion age=117.38 ± 0.17 Ma (2σ); * represents the steps chosen for weighted mean age calculation
5
58
9.74 0
± 43.60 3
6
Table 4 40Ar/39Ar step heating data for sericite flakes from gold ore Sample JQD15D004B2 in
7
the Rushan gold deposit Mea surem ents
Re lativ e Abu ndan ce
18E27 180
0.2 %
18E27 181*
0.3 %
18E27 183*
0.4 %
18E27 184*
0.5 %
18E27 185*
0.6 %
0. 0 4
1. 5 6
0. 1 1
10 1.1 9
0. 0 8
18E27 187
0.7 %
0. 0 4
1. 4 3
0. 1 1
93. 95
0. 0 6
18E27 188
0.8 %
0. 0 3
1. 7 8
0. 0 8
12 7.8 5
0. 0 5
18E27 189
0.9 %
0. 0 3
1. 8 6
0. 0 1
19 28. 12
0. 0 5
18E27 191
1.0 %
0. 0 2
2. 2 1
0. 0 3
35 9.5 8
0. 0 4
18E27 192
1.1 %
0. 0 2
2. 1 2
0. 0 5
21 0.8 3
0. 0 4
18E27 193
1.2 %
0. 0 2
2. 3 3
0. 0 4
27 6.6 2
0. 0 3
18E27 195
1.3 %
0. 0 2
2. 4 4
0. 0 6
17 9.4 1
0. 0 2
18E27 196
1.4 %
0. 0 2
2. 1 0
0. 1 5
69. 69
0. 0 3
18E27 197
1.5 %
0. 0 3
1. 7 5
0. 0 5
19 4.6 5
0. 0 3
18E27 199
1.7 %
0. 0 3
1. 7 7
0. 0 6
17 5.4 8
0. 0 1
18E27 200
1.9 %
0. 0 3
1. 8 4
0. 2 0
51. 02
0. 0 2
36
37
38
A r [f A ] 3. 3 4 0. 9 1 0. 1 9 0. 0 8
0. 2 6 0. 3 0 0. 5 0 0. 7 7
A r [f A ] 0. 6 1 1. 2 9 0. 3 6 0. 2 7
A r [f A ] 1. 1 4 1. 9 0 0. 5 4 0. 2 0
18. 16 8.3 0 28. 09 38. 15
0. 8 8 0. 5 1 1. 7 9 4. 9 5 1 2. 8 1 1 5. 2 3 1 8. 0 5 2 0. 4 4 2 7. 0 2 2 7. 2 8 3 2. 7 4 4 1. 8 6 3 4. 0 5 3 4. 6 4 7 7. 4 5 5 1. 8 0
39
Ar [f A]
A r [fA ]
40
38 .4 3 14 0. 89 41 .5 3 15 .3 1
0. 0 7 0. 0 6 0. 0 7 0. 1 0
25 13. 58 63 06. 14 18 32. 92 67 7.6 0
0. 0 1 0. 0 0 0. 0 0 0. 0 1
5. 75
0. 2 1
25 5.9 1
0. 0 1
5. 10
0. 2 1
22 6.9 5
3. 59
0. 3 0
3. 32
40(r )/39( k)
Age (Ma)
40
39
Ar (r)
Ar (k)
(% )
(% ) 14 .1 1 51 .7 1 15 .2 5
K/ C a
±0 .1 9 ±0 .0 5 ±0 .0 6 ±0 .0 9
10 9. 82 11 8. 13 11 7. 88 11 7. 70
± 0. 51 ± 0. 15 ± 0. 16 ± 0. 24
60 .7 7 95 .7 5 96 .9 0 96 .4 8
42.6 9
±0 .1 9
11 7. 67
± 0. 50
95 .9 3
2. 11
2 3. 2
± 47.0
0. 0 1
42.3 3
±0 .1 9
11 6. 73
± 0. 51
95 .1 8
1. 87
2 0. 1
± 37.8
16 0.9 1
0. 0 2
42.4 2
±0 .2 7
11 6. 95
± 0. 73
94 .5 9
1. 32
1 8. 2
± 46.6
0. 3 6
14 8.9 7
0. 0 2
42.3 7
±0 .3 2
11 6. 82
± 0. 84
94 .3 7
1. 22
2 6 5. 1
± 102 23.2
2. 46
0. 4 3
11 0.9 3
0. 0 2
42.4 4
±0 .3 8
11 7. 02
± 1. 02
94 .1 1
0. 90
3 6. 5
± 262. 5
2. 29
0. 4 7
10 3.6 1
0. 0 3
42.3 6
±0 .4 2
11 6. 80
± 1. 12
93 .6 0
0. 84
1 9. 9
± 83.9
2. 25
0. 5 0
10 1.5 6
0. 0 2
42.2 3
±0 .4 4
11 6. 45
± 1. 19
93 .4 9
0. 83
2 4. 7
± 136. 5
1. 59
0. 6 6
74. 03
0. 0 3
42.8 4
±0 .5 9
11 8. 08
± 1. 58
91 .9 9
0. 58
1 1. 4
± 41.1
2. 38
0. 4 8
10 7.7 6
0. 0 2
42.2 1
±0 .4 2
11 6. 41
± 1. 13
93 .3 4
0. 87
6. 7
± 9.3
2. 31
0. 4 6
10 6.2 1
0. 0 3
42.1 4
±0 .4 1
11 6. 21
± 1. 10
91 .6 7
0. 85
1 8. 4
± 71.8
2. 28
0. 5 2
10 4.7 9
0. 0 3
42.5 8
±0 .4 6
11 7. 39
± 1. 21
92 .7 3
0. 84
1 5. 7
± 55.3
2. 95
0. 3 6
13 4.8 1
0. 0 2
42.9 4
±0 .3 3
11 8. 36
± 0. 88
93 .9 7
1. 08
6. 4
± 6.5
59
39.7 5 42.8 6 42.7 6 42.7 0
5. 62
2 7. 3 4 7. 1 4 9. 4 2 4. 7
± 9.9 ± 7.8 ± 27.8 ± 18.8
8 9
J value= 0.00157517 ± 0.00000099; Total fusion age=116.76 ± 0.18 Ma (2σ); * represents the steps chosen for plateau age calculation
10
60
11
Table 5 40Ar/39Ar step heating data for sericite aggregates from gold ore Sample
12
JQD15D004B2 in the Rushan gold deposit Mea surem ents
Re lativ e Abu nda nce
18E27 120
0.3 %
18E27 122*
0.4 %
18E27 123*
0.5 %
18E27 124*
0.6 %
18E27 126*
0.7 %
18E27 127*
0.8 %
18E27 128*
0.9 %
18E27 130*
1.0 %
18E27 131*
1.1 %
18E27 132*
1.2 %
18E27 134*
1.3 %
18E27 135*
1.4 %
18E27 136*
1.5 %
18E27 138*
1.7 %
18E27 139*
1.9 %
18E27 140*
2.2 %
18E27 142*
2.5 %
18E27 143*
2.8 %
18E27 144*
3.1 %
18E27 146*
3.4 %
36
37
38
A r [f A ] 1. 7 0 0. 2 4 0. 1 4 0. 1 0 0. 0 8 0. 0 6 0. 0 6 0. 0 4 0. 0 4 0. 0 3 0. 0 3 0. 0 3 0. 0 3 0. 0 3 0. 0 3
0. 7 1 0. 8 3 0. 9 4 1. 1 1 1. 1 7 1. 3 7 1. 4 5 1. 8 2 1. 9 2 2. 1 6 1. 9 9 2. 4 0 2. 6 6 2. 2 0 2. 3 1
A r [f A ] 4. 9 6 8. 0 8 1. 1 9 1. 1 0 1. 4 7 3. 8 5 2. 1 7 1. 0 6 1. 0 0 0. 6 3 1. 0 7 0. 9 1 1. 3 6 1. 0 9 0. 4 0
27 .5 4
A r [f A ] 6. 9 3 4. 0 4 2. 0 4 1. 2 2 0. 8 9 0. 6 4 0. 5 9 0. 4 7 0. 4 1 0. 3 9 0. 3 6 0. 3 3 0. 3 3 0. 4 0 0. 3 9
0. 3 7 0. 4 1 0. 6 1 0. 8 3 1. 1 2 1. 4 5 1. 6 7 1. 9 5 2. 4 3 2. 3 9 2. 6 6 2. 8 6 2. 8 2 2. 3 9 2. 5 2
0. 0 3
2. 5 7
0. 0 6
19 1. 50
0. 3 1
0. 0 4 0. 0 3 0. 0 4 0. 0
1. 9 2 2. 5 7 1. 7 3 2. 0
0. 3 8 0. 2 9 0. 4 3 0. 0
27 .8 4 34 .9 3 25 .1 9 27 1.
0. 4 0 0. 2 9 0. 4 0 0. 3
2. 51 1. 49 8. 74 9. 02 7. 16 2. 98 5. 11 10 .0 5 10 .6 0 16 .2 6 10 .0 5 11 .9 3 8. 16 9. 60
39
A r [fA]
52 7. 05 32 6. 68 16 4. 88 97 .8 0 72 .5 4 51 .3 4 48 .6 8 38 .2 0 32 .9 9 31 .5 1 29 .7 8 26 .8 6 25 .5 7 32 .9 3 31 .4 8
0. 1 6 0. 1 6 0. 1 6 0. 1 6 0. 1 7 0. 1 7 0. 1 7 0. 1 7 0. 1 7 0. 1 7 0. 1 7 0. 1 7 0. 1 7 0. 1 7 0. 1 7
222 91. 96 139 50. 02 702 2.2 1 415 7.0 5 309 2.9 1 219 3.4 8 207 9.4 5 163 2.2 7 141 2.2 9 134 8.5 0 127 5.8 8 114 9.8 0 109 3.7 5 141 1.2 2 134 7.7 6
0. 0 0 0. 0 0 0. 0 1 0. 0 0 0. 0 0 0. 0 1 0. 0 1 0. 0 1 0. 0 1 0. 0 1 0. 0 1 0. 0 1 0. 0 1 0. 0 1 0. 0 1
3. 3 9
24 .6 1
0. 1 7
105 2.7 0
0. 0 1
2. 5 0 3. 0 6 2. 3 4 2. 9
31 .9 8 23 .1 2 33 .0 9 25 .2
0. 1 7 0. 1 7 0. 1 7 0. 1
136 9.3 3
0. 0 1 0. 0 1 0. 0 1 0. 0
Ar [f A]
40
992 .05 141 8.1 9 108 2.8
61
40(r )/39( k)
40
Age (Ma)
41.3 5
0. 14
42.4 9
0. 14
42.3 3
0. 14
42.2 0
0. 14
42.3 3
0. 14
42.3 9
0. 14
42.3 7
0. 14
42.4 1
0. 14
42.4 8
0. 14
42.4 8
0. 14
42.5 1
0. 15
42.5 0
0. 15
42.4 7
0. 15
42.5 7
0. 14
42.5 2
0. 15
42.4 6
0. 15
42.4 7
0. 14
42.5 6
0. 15
42.4 8
0. 14
42.5 5
0. 15
Ar (r) (% )
11 4. 02 11 7. 08 11 6. 66 11 6. 31 11 6. 65 11 6. 82 11 6. 77 11 6. 86 11 7. 06 11 7. 06 11 7. 12 11 7. 10 11 7. 03 11 7. 29 11 7. 16
± 0. 36 ± 0. 37 ± 0. 37 ± 0. 37 ± 0. 37 ± 0. 38 ± 0. 38 ± 0. 38 ± 0. 38 ± 0. 38 ± 0. 39 ± 0. 39 ± 0. 39 ± 0. 38 ± 0. 39
97 .7 5 99 .5 0 99 .3 9 99 .2 9 99 .2 7 99 .2 2 99 .1 9 99 .2 4 99 .2 3 99 .2 8 99 .2 0 99 .2 7 99 .3 0 99 .3 2 99 .3 0
11 6. 99
± 0. 39
99 .2 5
11 7. 04 11 7. 27 11 7. 04 11 7.
± 0. 39 ± 0. 40 ± 0. 39 ± 0.
99 .1 9 99 .1 8 99 .1 1 99 .0
Ar (k)
39
(%) 29.1 0 18.0 4 9.10 5.40 4.01
K/ C a 4 5. 7 1 7. 4 5 9. 7 3 8. 1 2 1. 2
± 2.3 ± 0.5 ± 10. 4 ± 6.9 ± 3.0
2.84
5. 7
± 0.3
2.69
9. 6
± 1.0
2.11 1.82 1.74 1.64 1.48 1.41 1.82 1.74
1.36
1.77 1.28 1.83 1.39
1 5. 4 1 4. 1 2 1. 4 1 2. 0 1 2. 7 8. 1 1 3. 0 3 3. 9 1 8 4. 7 3 5. 8 3 4. 1 3 3. 4 2 9
± 3.1 ± 3.0 ± 6.9 ± 2.4 ± 3.0 ± 1.3 ± 2.5 ± 18. 7 ± 707 .4 ± 19. 9 ± 23. 8 ± 16. 8 ± 158
18E27 147*
3.8 %
18E27 148*
4.2 %
18E27 150*
4.6 %
18E27 151*
5.0 %
18E27 152*
5.4 %
3
4
4
74
1
2
2
7
0. 0 3 0. 0 3 0. 0 3 0. 0 5
2. 2 7 2. 2 5 2. 1 2 1. 6 3
0. 2 2 0. 1 6 0. 2 0 3. 9 9
50 .5 3 74 .3 3 54 .4 7
0. 2 5 0. 2 4 0. 2 4 0. 2 8
3. 7 9 3. 9 4 4. 3 0 3. 2 5
20 .0 4 19 .7 4 19 .9 1 22 .7 5
0. 1 8 0. 1 8 0. 1 8 0. 1 7
0. 0 3
2. 1 1
0. 0 2
57 2. 34
0. 2 0
4. 8 5
15 .9 8
0. 1 8
2. 75
3 859 .91 847 .33 854 .93 979 .51 688 .61
1 0. 0 1 0. 0 1 0. 0 1 0. 0 1 0. 0 2
42.4 6
0. 15
42.4 6
0. 15
42.4 6
0. 15
42.4 7
0. 15
42.5 1
0. 16
25
39
9
11 6. 99 11 6. 99 11 7. 01 11 7. 04
± 0. 40 ± 0. 40 ± 0. 40 ± 0. 40
98 .9 7 98 .9 2 98 .8 7 98 .6 3
11 7. 12
± 0. 42
98 .6 1
1. 1 3 9. 0 5 3. 9 4 2. 1
2.0
1.26
2. 5
± 0.1
0.88
3 7 5. 2
± 429 4.5
1.11 1.09 1.10
± 39. 4 ± 80. 2 ± 45. 9
Table 5 40Ar/39Ar step heating data for sericite aggregates from gold ore Sample JQD15D004B2 in the Rushan gold deposit (continued)
13 14
0. 0 3 0. 0 3 0. 0 3
2. 1 6 2. 1 6 2. 1 8
0. 0 3 0. 0 3 0. 0 1
38 0. 48 38 0. 48 90 7. 61
0. 1 5 0. 1 5 0. 1 3
6.5 %
0. 0 2
3. 0 5
0. 0 6
16 8. 50
0. 0 6
18E27 158*
7.0 %
0. 0 2
3. 4 8
0. 1 0
10 2. 30
0. 0 4
18E27 159
7.5 %
0. 0 1
4. 7 8
0. 1 5
74 .0 0
0. 0 3
18E27 160
8.0 %
0. 0 1
4. 3 7
0. 0 2
52 9. 35
0. 0 2
18E27 162
8.5 %
0. 0 2
3. 4 4
0. 1 3
78 .6 9
0. 0 3
18E27 154*
5.7 %
18E27 154*
5.7 %
18E27 155*
6.1 %
18E27 156*
5. 9 9 5. 9 9 7. 3 3 1 6. 3 5 2 2. 9 6 3 7. 8 1 5 6. 3 4 2 7. 4 2
12 .9 9 12 .9 9 10 .9 4
0. 1 9 0. 1 9 0. 2 0
11 6. 95 11 6. 95 11 6. 86
± 0. 44 ± 0. 44 ± 0. 46
98 .3 3 98 .3 3 98 .0 4
0. 7 2 0. 7 2 0. 6 0
4. 56
0. 3 1
199 .24
0. 28
11 6. 63
± 0. 74
96 .8 3
0. 2 5
30.6
± 103 .2
3. 45
0. 3 6
42.3 8
0. 33
11 6. 80
± 0. 88
96 .3 2
0. 1 9
14.5
± 29. 6
1. 43
0. 1 6
42.8 4
0. 75
11 8. 03
± 2. 01
94 .1 7
0. 0 8
4.2
± 6.2
52. 06
0. 2 0
42.5 2
0. 93
11 7. 17
± 2. 49
91 .6 3
0. 0 6
23.2
± 246 .1
78. 12
0. 1 3
41.6 5
0. 60
11 4. 84
± 1. 60
93 .3 1
0. 1 0
5.7
± 8.9
560 .55
0. 0 2 0. 0 2 0. 0 2
42.4 4
0. 16
42.4 4
0. 16
42.4 1
0. 17
0. 0 5
42.3 2
152 .02
0. 0 7
0. 8 1
64. 96
1. 12
1. 0 0
1. 75
0. 6 6
560 .55 473 .38
J value=0.00157418 ± 0.00000099; Total fusion age=116.07 ± 0.20 Ma (2σ); * represents the steps chosen for plateau age calculation
15
62
204. 6 204. 6 396. 7
± 155 6.7 ± 155 6.7 ± 720 1.4
16
Table 6 40Ar/39Ar step heating data for sericite flakes from gold ore Sample JQD15D015B2 in
17
the Rushan gold deposit Mea surem ents
Re lativ e Abu nda nce
18E27 061
0.2 %
18E27 062
0.3 %
18E27 064
0.4 %
18E27 065
0.5 %
18E27 066
0.6 %
18E27 068
0.7 %
0. 0 6
1. 5 1
0. 0 1
10 47. 97
0. 3 4
2. 7 1
26 .8 0
0. 0 8
11 89. 33
0. 0 3
18E27 069
0.8 %
0. 0 7
1. 3 7
0. 0 0
25 78. 03
0. 2 9
3. 3 8
23 .1 4
0. 0 8
10 33. 29
0. 0 3
18E27 070
0.9 %
18E27 072*
1.0 %
18E27 073*
1.1 %
0. 0 5 0. 0 4 0. 0 4
2. 0 0 2. 2 3 2. 1 9
0. 0 2 0. 1 0 0. 0 4
66 0.3 6 10 2.0 8 27 3.5 2
0. 2 5 0. 2 1 0. 2 0
3. 8 1 4. 6 4 4. 7 1
19 .5 0 16 .3 0 16 .0 1
0. 0 8 0. 1 0 0. 1 0
86 7.6 9 72 7.0 1 71 4.4 8
0. 0 4 0. 0 4 0. 0 4
18E27 074*
1.2 %
0. 0 4
2. 1 3
0. 0 0
39 65. 75
0. 2 0
4. 8 9
16 .2 8
0. 1 0
72 6.4 1
0. 0 4
18E27 076*
1.3 %
18E27 077*
1.4 %
18E27 078*
1.5 %
18E27 080*
1.7 %
18E27 081*
1.9 %
18E27 082
2.2 %
18E27 084
2.5 %
18E27 085
2.8 %
0. 0 5 0. 0 5 0. 0 5 0. 0 6 0. 0 8 0. 0 6 0. 0 4 0. 0
1. 8 0 1. 8 7 1. 7 6 1. 5 3 1. 2 6 1. 6 0 2. 5 0 3. 1
0. 0 3 0. 0 8 0. 1 0 0. 0 3 0. 0 5 0. 0 6 0. 0 3 0. 1
34 1.8 1 12 5.0 1 10 1.4 8 33 8.3 6 19 1.4 0 15 5.8 4 34 6.6 3 86. 85
0. 2 6 0. 2 2 0. 2 1 0. 2 3 0. 2 7 0. 2 4 0. 1 4 0. 1
3. 8 1 4. 1 8 4. 4 4 4. 3 0 3. 4 9 3. 9 8 6. 9 5 8. 8
20 .6 6 17 .7 3 16 .7 2 18 .7 0 21 .8 0 18 .6 2 10 .9 8 7. 46
0. 0 8 0. 0 9 0. 0 9 0. 0 9 0. 0 8 0. 0 9 0. 1 2 0. 1
92 3.4 3 79 3.6 8 75 0.8 6 83 9.7 7 98 0.8 9 83 2.4 5 49 1.1 4 33 4.2
0. 0 3 0. 0 4 0. 0 4 0. 0 4 0. 0 3 0. 0 4 0. 0 7 0. 1
36
37
38
A r [f A ] 5. 0 8 1. 5 4
0. 2 5 0. 2 8
A r [f A ] 0. 2 0 0. 1 4
A r [f A ] 1. 3 1 1. 8 2
0. 7 3 0. 5 4
26 .4 5 12 7. 05
0. 1 5
0. 7 3
0. 0 1
13 23. 75
0. 6 4
1. 4 4
0. 0 8 0. 0 7
1. 2 6 1. 3 5
0. 0 3 0. 0 2
31 8.4 9 60 9.3 3
0. 4 2 0. 3 8
47. 94 73. 10
40
A r [fA ]
0. 0 8 0. 0 6
25 52. 89 58 48. 87
0. 0 1 0. 0 1
50 .9 7
0. 0 7
22 58. 80
0. 0 1
2. 2 0 2. 4 8
33 .7 2 29 .8 4
0. 0 7 0. 0 7
14 94. 65 13 21. 92
0. 0 2 0. 0 2
39
Ar [f A]
40
63
40(r )/39( k)
Age (Ma)
Ar (r) (% )
Ar (k)
39
(%)
± 0. 30 ± 0. 06
11 0. 35 11 7. 69
± 0. 80 ± 0. 15
41 .1 6 92 .2 3
± 0. 06
12 0. 34
± 0. 16
98 .0 4
± 0. 07 ± 0. 07
12 0. 83 12 0. 75
± 0. 18 ± 0. 19
98 .4 4 98 .4 2
43.7 0
± 0. 07
12 1. 04
± 0. 20
98 .4 9
4.65
43.7 4
± 0. 08
12 1. 13
± 0. 21
97 .9 3
4.01
± 0. 09 ± 0. 10 ± 0. 10
12 1. 26 12 1. 49 12 1. 49
± 0. 23 ± 0. 27 ± 0. 27
98 .4 0 98 .3 6 98 .2 9
± 0. 10
12 1. 44
± 0. 28
98 .2 8
± 0. 08 ± 0. 09 ± 0. 10 ± 0. 09 ± 0. 08 ± 0. 09 ± 0. 13 ± 0.
12 1. 74 12 1. 71 12 1. 81 12 1. 63 12 1. 72 12 1. 22 12 1. 15 12 1.
± 0. 23 ± 0. 25 ± 0. 26 ± 0. 24 ± 0. 22 ± 0. 24 ± 0. 35 ± 0.
98 .3 7 98 .1 8 97 .9 6 97 .8 0 97 .7 1 97 .9 2 97 .8 3 97 .4
39.7 3 42.4 6 43.4 4 43.6 3 43.6 0
43.7 9 43.8 7 43.8 7 43.8 5 43.9 7 43.9 6 43.9 9 43.9 2 43.9 6 43.7 7 43.7 5 43.6 9
4.59 22.0 3 8.84
5.85 5.17
3.38 2.83 2.77
2.82
3.58
K / C a
5 6
± 54
3 9 9 2 9 2 8 4 6 4 7 6 7 1 1 3 3 2 7 1 3 5 5 4 7 2 1 8 2 2 7 3 3 3 0 2
± 583 ± 775 17 ± 295 6 ± 935 2 ± 237 37 ± 139 902 ± 731 3 ± 146 ± 996 ± 216 761 ± 206 6
3.07
9 2
± 229
2.90
7 3
± 148
2 6 1 1 8 6 1 3 1 1 6 5 2 8
± 176 3
3.24 3.78 3.23 1.90 1.29
± 712 ± 407 ± 114 5 ± 48
3
2
2
0
18E27 086
3.1 %
0. 0 3
3. 4 1
0. 0 1
19 46. 46
0. 0 7
18E27 088
3.4 %
0. 0 3
3. 1 7
0. 0 0
71 34. 37
0. 0 7
18E27 089
3.8 %
0. 0 3
3. 4 7
0. 0 5
19 4.7 0
0. 0 6
18E27 090
4.2 %
0. 0 4
2. 4 4
0. 0 5
20 9.2 8
0. 0 8
18E27 092
4.6 %
0. 0 4
2. 1 2
0. 1 7
60. 31
0. 0 8
1 1 3. 7 1 1 4. 3 1 1 4. 6 1 1 2. 7 4 1 1. 5 0
6
2
0
18
01
47
9
5. 50
0. 2 1
24 6.6 6
0. 1 3
43.4 7
± 0. 23
12 0. 42
± 0. 63
96 .9 7
5. 72
0. 2 0
25 7.9 1
0. 1 2
43.6 3
± 0. 23
12 0. 83
± 0. 61
4. 68
0. 2 5
21 1.5 5
0. 1 5
43.6 0
± 0. 28
12 0. 76
6. 08
0. 2 0
27 6.2 4
0. 1 2
43.6 6
± 0. 22
5. 83
0. 2 1
26 4.9 4
0. 1 2
43.3 7
± 0. 23
0.95
4 4 6
± 173 69
96 .7 9
0.99
1 7 9 8
± 256 595
± 0. 76
96 .4 3
0.81
3 9
± 152
12 0. 93
± 0. 59
96 .0 8
1.05
5 2
± 219
12 0. 14
± 0. 61
95 .4 0
1.01
1 4
± 17
Table 6 40Ar/39Ar step heating data for sericite flakes from gold ore Sample JQD15D015B2 in the Rushan gold deposit (continued)
18 19
18E27 093
5.0 %
0. 0 4
2. 1 7
0. 1 3
75. 26
0. 0 5
18E27 094
5.4 %
0. 0 3
2. 6 4
0. 0 4
26 4.8 7
0. 0 5
18E27 096
5.7 %
0. 0 3
2. 5 7
0. 0 6
18 6.6 4
0. 0 5
18E27 097
6.1 %
0. 0 4
2. 0 9
0. 0 2
47 1.9 2
0. 0 7
18E27 098
6.5 %
0. 0 5
1. 8 1
0. 0 5
19 8.1 7
0. 0 4
18E27 100
7.0 %
0. 0 6
1. 5 2
0. 0 1
72 7.1 7
0. 0 5
18E27 101
7.5 %
0. 0 4
2. 2 6
0. 0 2
47 1.5 2
0. 0 2
18E27 102
8.0 %
0. 0 5
1. 8 1
0. 0 4
24 0.8 4
0. 0 6
18E27 104
8.5 %
0. 0 4
2. 1 6
0. 0 3
41 9.3 2
0. 0 4
1 7. 8 4 1 7. 7 5 1 8. 3 3 1 3. 2 8 2 1. 1 6 2 0. 8 5 4 0. 2 1 1 5. 9 3 2 3. 2 0
4. 21
0. 2 7
19 4.1 0
0. 1 7
43.0 8
± 0. 31
11 9. 36
± 0. 82
93 .5 1
0.73
3. 72
0. 3 0
17 0.5 3
0. 1 9
43.1 6
± 0. 34
11 9. 58
± 0. 92
94 .1 4
3. 61
0. 3 2
16 6.1 7
0. 1 9
43.1 5
± 0. 36
11 9. 55
± 0. 95
5. 07
0. 2 2
23 2.0 8
0. 1 4
43.2 5
± 0. 25
11 9. 82
3. 35
0. 3 3
15 7.9 6
0. 2 0
42.7 6
± 0. 38
3. 74
0. 2 9
17 4.5 0
0. 1 8
42.1 3
1. 79
0. 6 4
88. 70
0. 3 6
2. 80
0. 3 8
13 4.3 8
2. 02
0. 5 8
99. 52
1 4
± 21
0. 6 4
40
± 214
93 .8 6
0. 6 3
28
± 103
± 0. 68
94 .5 4
0. 8 8
100
± 948
11 8. 50
± 1. 02
90 .5 7
0. 5 8
30
± 117
± 0. 33
11 6. 81
± 0. 89
90 .2 1
0. 6 5
115
± 167 9
43.2 6
± 0. 72
11 9. 84
± 1. 93
87 .0 8
0. 3 1
36
± 342
0. 2 4
42.6 0
± 0. 44
11 8. 08
± 1. 19
88 .6 9
0. 4 9
30
± 143
0. 3 2
43.3 4
± 0. 65
12 0. 06
± 1. 74
87 .8 5
0. 3 5
34
± 286
J value=0.00157418 ± 0.00000099; Total fusion age=119.77 ±0.16 Ma (2σ); * represents the steps chosen for weighted mean age calculation
20
64
21
Table 7 40Ar/39Ar step heating data for sericite aggregates from gold ore Sample
22
JQD15D015B2 in the Rushan gold deposit Mea surem ents
Re lativ e Abu nda nce
18E27 000
0.2 %
18E27 001
0.3 %
18E27 003
0.4 %
18E27 004
0.5 %
18E27 005
0.6 %
18E27 007
0.7 %
18E27 008
0.8 %
18E27 009
0.9 %
18E27 011
1.0 %
18E27 012
1.1 %
18E27 013
1.2 %
18E27 015*
1.3 %
18E27 016*
1.4 %
18E27 017*
1.5 %
18E27 019*
1.7 %
18E27 020*
1.9 %
18E27 021*
2.2 %
18E27 023*
2.5 %
18E27 024*
2.8 %
18E27 025*
3.1 %
36
37
38
A r [f A ] 1. 0 8 0. 5 6 0. 2 1 0. 1 3 0. 0 9 0. 0 4 0. 0 7 0. 0 5 0. 0 5 0. 0 3
0. 3 0 0. 3 7 0. 5 9 0. 9 1 1. 1 9 2. 2 8 1. 5 6 2. 1 6 1. 9 7 3. 3 3
A r [f A ] 0. 4 8 0. 7 6 0. 4 9 0. 2 4 0. 1 5 0. 2 4 0. 1 7 0. 1 3 0. 1 3 0. 0 7
14 8.2 7
A r [f A ] 0. 7 8 3. 0 3 2. 1 6 1. 4 2 1. 0 7 0. 4 9 0. 8 1 0. 5 5 0. 5 9 0. 3 5
1. 3 0 0. 3 3 0. 4 5 0. 6 9 0. 8 8 1. 9 3 1. 1 9 1. 6 8 1. 5 6 2. 7 6
44 .1 4 23 5. 46 17 5. 64 11 5. 06 85 .5 0 38 .3 3 65 .2 6 43 .4 1 46 .5 1 27 .5 5
0. 0 5
2. 1 5
0. 0 0
54 12. 21
0. 4 9
1. 9 9
0. 0 3 0. 0 4 0. 0 3 0. 0 5 0. 0 4 0. 0 6 0. 0 4 0. 0 6 0. 0
3. 5 4 2. 4 4 3. 6 4 2. 0 5 2. 4 7 1. 7 8 2. 7 0 1. 7 8 1. 3
0. 0 2 0. 0 2 0. 0 6 0. 0 5 0. 0 3 0. 0 6 0. 0 8 0. 0 5 0. 0
50 3.5 0 45 9.2 4 18 7.5 6 20 0.5 6 31 2.1 5 19 1.3 4 12 9.4 6 21 4.7 4 14 1.4
0. 3 0 0. 4 7 0. 2 9 0. 5 3 0. 3 9 0. 5 7 0. 3 6 0. 5 3 0. 7
3. 0 2 2. 0 0 3. 1 0 1. 7 4 2. 5 3 1. 7 3 2. 5 9 1. 7 7 1. 3
21. 56 13. 70 20. 85 44. 03 72. 69 42. 24 62. 20 77. 49 86. 75
40
A r [fA ]
0. 0 7 0. 0 6 0. 0 6 0. 0 6 0. 0 6 0. 0 7 0. 0 6 0. 0 7 0. 0 7 0. 0 8
18 84. 21 97 47. 50 74 20. 88 48 96. 56 36 51. 35 16 46. 40 28 05. 95 18 69. 72 20 08. 14 11 91. 85
0. 0 1 0. 0 0 0. 0 0 0. 0 1 0. 0 1 0. 0 2 0. 0 1 0. 0 1 0. 0 1 0. 0 2
40 .3 3
0. 0 7
17 44. 95
0. 0 1
24 .1 9 38 .1 4 23 .0 6 42 .9 6 32 .2 8 45 .0 2 29 .4 7 43 .2 4 57 .3
0. 0 8 0. 0 7 0. 0 8 0. 0 7 0. 0 7 0. 0 7 0. 0 7 0. 0 7 0. 0
10 49. 44 16 52. 45 10 01. 53 18 64. 12 14 01. 99 19 56. 21 12 81. 35 18 78. 93 24 95.
0. 0 2 0. 0 1 0. 0 2 0. 0 1 0. 0 2 0. 0 1 0. 0 2 0. 0 1 0. 0
39
Ar [f A]
40
65
40(r )/39( k) 35.4 8 40.7 0 41.8 9 42.2 3 42.3 9 42.6 2 42.6 9 42.7 6 42.8 6 42.9 5 42.9 3 43.0 5 43.0 1 43.0 9 43.0 5 43.0 6 43.0 7 43.1 2 43.0 6 43.0 8
Age (Ma)
Ar (r) (% )
± 0. 07 ± 0. 05 ± 0. 05 ± 0. 05 ± 0. 05 ± 0. 06 ± 0. 06 ± 0. 06 ± 0. 06 ± 0. 07
98 .8 2 11 2. 91 11 6. 11 11 7. 01 11 7. 45 11 8. 07 11 8. 25 11 8. 43 11 8. 70 11 8. 94
± 0. 18 ± 0. 13 ± 0. 14 ± 0. 14 ± 0. 15 ± 0. 17 ± 0. 15 ± 0. 16 ± 0. 16 ± 0. 19
83 .1 2 98 .3 1 99 .1 5 99 .2 3 99 .2 6 99 .2 3 99 .2 8 99 .2 7 99 .2 6 99 .2 8
± 0. 06
11 8. 90
± 0. 17
99 .2 2
± 0. 08 ± 0. 06 ± 0. 08 ± 0. 06 ± 0. 07 ± 0. 06 ± 0. 07 ± 0. 06 ± 0.
11 9. 21 11 9. 11 11 9. 32 11 9. 23 11 9. 25 11 9. 28 11 9. 39 11 9. 25 11 9.
± 0. 20 ± 0. 17 ± 0. 20 ± 0. 16 ± 0. 18 ± 0. 16 ± 0. 18 ± 0. 16 ± 0.
99 .2 4 99 .2 7 99 .2 1 99 .2 2 99 .1 5 99 .1 2 99 .1 6 99 .0 9 99 .0
Ar (k)
39
(%) 2.81 14.9 8 11.1 8 7.32 5.44 2.44 4.15 2.76 2.96 1.75
2.57
1.54 2.43 1.47 2.73 2.05 2.86 1.88 2.75 3.65
K / C a
3 9
± 17
1 3 3 1 5 5 2 0 4 2 5 2 6 8 1 6 5 1 4 2 1 5 6 1 6 7 8 8 4 8 4 8 9 7 3 0 1 7 2 3 5 4 4 1 4 3 4 7 1 6 4 3 7 1 3 3
± 37 ± 65 ± 180 ± 366 ± 57 ± 206 ± 220 ± 271 ± 495 ± 957 794 ± 492 6 ± 670 7 ± 644 ± 141 9 ± 258 7 ± 132 9 ± 425 ± 159 4 ± 955
18E27 027*
3.4 %
18E27 028*
3.8 %
18E27 029*
4.2 %
18E27 031*
4.6 %
18E27 032*
5.0 %
8
7
7
0. 0 5 0. 0 8 0. 0 6 0. 0 8 0. 0 6
1. 9 6 1. 2 9 1. 6 3 1. 2 8 1. 7 7
0. 1 3 0. 0 3 0. 1 6 0. 0 3 0. 1 2
9 77. 54 40 6.5 4 64. 75 35 6.3 5 88. 44
0
8
9
6
14
1
0. 4 8 0. 7 2 0. 4 5 0. 5 7 0. 3 9
2. 0 7 1. 2 9 2. 0 4 1. 6 5 2. 4 8
38 .5 0 58 .7 2 36 .7 6 46 .5 0 31 .1 4
0. 0 7 0. 0 6 0. 0 7 0. 0 7 0. 0 7
16 75. 90 25 58. 62 16 01. 86 20 26. 33 13 58. 21
0. 0 1 0. 0 1 0. 0 2 0. 0 1 0. 0 2
43.1 3 43.1 5 43.0 8 43.0 6 43.0 6
06
29
15
9
± 0. 06 ± 0. 06 ± 0. 06 ± 0. 06 ± 0. 07
11 9. 44 11 9. 47 11 9. 30 11 9. 24 11 9. 25
± 0. 17 ± 0. 15 ± 0. 17 ± 0. 16 ± 0. 18
99 .0 9 99 .0 2 98 .8 7 98 .8 1 98 .7 3
7 2.45 3.74 2.34 2.96 1.98
1 2 3 9 6 6
± 191 ± 785 2
9 8
± 128
6 7 6 1 1 4
± 481 9 ± 201
Table 7 40Ar/39Ar step heating data for sericite aggregates from gold ore Sample JQD15D015B2 in the Rushan gold deposit (continued)
23 24
0. 0 6 0. 0 4 0. 0 6 0. 0 5 0. 0 4
1. 6 4 2. 4 2 1. 6 1 2. 1 0 2. 4 0
0. 0 6 0. 0 5 0. 0 3 0. 1 1 0. 0 1
18 3.3 6 20 8.7 4 39 8.6 2
10 88. 39
0. 3 9 0. 2 2 0. 2 5 0. 1 4 0. 1 2
7.5 %
0. 0 4
2. 7 0
0. 0 4
24 1.6 7
0. 0 8
18E27 041
8.0 %
0. 0 4
2. 6 5
0. 0 2
53 5.2 8
0. 0 8
18E27 043
8.5 %
0. 0 3
3. 4 7
0. 0 3
36 8.9 5
0. 0 4
18E27 033*
5.4 %
18E27 035*
5.7 %
18E27 036
6.1 %
18E27 037
6.5 %
18E27 039
7.0 %
18E27 040
92. 55
2. 5 4 4. 4 4 4. 0 1 6. 9 6 7. 9 7 1 1. 1 8 1 1. 9 7 2 3. 1 0
32 .2 7 17 .6 3 21 .0 4 11 .7 5
0. 0 7 0. 0 9 0. 0 8 0. 1 2 0. 1 5
14 06. 58 77 0.8 7 91 8.2 4 51 6.2 6 39 5.2 1
0. 0 2 0. 0 3 0. 0 3 0. 0 5 0. 0 6
6. 41
0. 1 9
28 4.4 9
0. 0 8
5. 26
0. 2 2
23 3.4 0
3. 48
0. 3 2
15 6.6 9
8. 99
± 0. 07 ± 0. 09 ± 0. 08 ± 0. 12 ± 0. 15
11 9. 12 11 9. 17 11 8. 49 11 8. 41 11 8. 03
± 0. 18 ± 0. 24 ± 0. 22 ± 0. 33 ± 0. 40
98 .6 7 98 .4 4 98 .0 0 97 .2 7 96 .9 6
2. 0 5 1. 1 2 1. 3 4 0. 7 5 0. 5 7
42.7 2
± 0. 20
11 8. 32
± 0. 53
96 .2 9
0. 1 0
42.3 0
± 0. 24
11 7. 20
± 0. 63
0. 1 5
42.6 4
± 0. 35
11 8. 13
± 0. 94
43.0 1 43.0 3 42.7 8 42.7 5 42.6 1
236
± 864
157
± 657
353
± 281 1
46
± 85
429
± 933 4
0. 4 1
65
± 315
95 .4 0
0. 3 4
120
± 128 7
94 .7 2
0. 2 2
52
± 385
J value= 0.00158303 ± 0.00000101; Total fusion age=116.97±0.15 Ma (2σ); * represents the steps chosen for plateau age calculation
25
66
26
Highlights
27 28
Gold mineralization initiated at 121.64 Ma and terminated at 116.97 Ma.
29 30
The middle part of the quartz vein orebody formed slightly earlier than the marginal part.
31 32
Episodic fluids pressure fluctuations from supralithostatic to hydrostatic trigger
33
incremental deposition of quartz veins.
34 35
Ore-hosting Kunyushan granite is not genetically related and provides no heat to gold
36
mineralization system.
37 38 39 40
67
41 42
68
43 44
69
45 46
70
47 48
71
49 50
72
51 52
73
53 54
74
55 56
75
57 58
76
59 60
77
61 62
78
63 64
79
65 66
80
67 68
81
69 70
82
71
83