Trace element geochemistry of magnetite: Implications for ore genesis of the Talate skarn Pb-Zn (-Fe) deposit, Altay, NW China

Accepted Manuscript Trace element geochemistry of magnetite: Implications for ore genesis of the Talate skarn Pb-Zn (-Fe) deposit, Altay, NW China Deng-Feng Li, Hua-Yong Chen, Pete Hollings, Li Zhang, Xiao-Ming Sun, Yi Zheng, Xiao-Ping Xia, Bin Xiao, Cheng-Ming Wang, Jing Fang PII: DOI: Reference:

S0169-1368(16)30692-8 http://dx.doi.org/10.1016/j.oregeorev.2017.03.015 OREGEO 2153

To appear in:

Ore Geology Reviews

Received Date: Revised Date: Accepted Date:

14 November 2016 3 March 2017 13 March 2017

Please cite this article as: D-F. Li, H-Y. Chen, P. Hollings, L. Zhang, X-M. Sun, Y. Zheng, X-P. Xia, B. Xiao, CM. Wang, J. Fang, Trace element geochemistry of magnetite: Implications for ore genesis of the Talate skarn PbZn (-Fe) deposit, Altay, NW China, Ore Geology Reviews (2017), doi: http://dx.doi.org/10.1016/j.oregeorev. 2017.03.015

This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Trace element geochemistry of magnetite: Implications for ore genesis of the Talate skarn Pb-Zn (-Fe) deposit, Altay, NW China Deng-Feng Li a, b, c, Hua-Yong Chenb,d*, Pete Hollingse, Li Zhangb, Xiao-Ming Suna , Yi Zhengf, Xiao-Ping Xiab, Bin Xiaob ,

Cheng-Ming Wangb , Jing Fangb

a. School of Marine Sciences, Sun Yat-sen University, Guangzhou 510006, China

b. Key Laboratory of Mineralogy and Metallogeny, Chinese Academy of Sciences, Guangzhou 510640, China

c. Guangdong Provincial Key Laboratory of Marine Resources and Coastal Engineering, Guangzhou 510006, China

d. State Key Laboratory of Geologic Processes and Mineral Resources, China University of Geosciences, Wuhan, Hubei,

430074, China

e. Department of Geology, Lakehead University, 955 Oliver Road, Thunder Bay, Ontario P7B 5E1, Canada

f. Department of Earth Sciences, Sun Yat-sen University, Guangzhou 510472, China

*Corresponding author: Huayong Chen. Address: Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, 511 Kehua Street, Tianhe District, Guangzhou 510640, Guangdong, China E-mail: [email protected] (H.Y. Chen)

1

Abstract The Talate skarn Pb-Zn (-Fe) deposit is hosted in the Kangbutiebao Formation of the Abagong polymetallic belt, Altay (NW China). The Talate magnetite comprises the magmatic-hydrothermal / hydrothermal disseminated and massive magnetite types and formed during the early skarn and quartz-magnetite stage. The magmatic-hydrothermal disseminated magnetite is Nb-Ta-Ti-depleted, whereas the hydrothermal disseminated magnetite associated with skarn alteration is geochemically similar to the Ca-skarn (with slight Ta-Mg-Ni depletions). The massive magnetite ores have similar Ni concentrations with the Ca-skarn, but contain minor depletions in Sn, Sc, Ta, Nb, Mg and Co, probably attributed to magma-host rock interactions. The Talate hydrothermal disseminated magnetite contains lower Sn than magnetite from typical skarn deposits, and likely resulted from cassiterite crystallization as it is found co-precipitated with disseminated magnetite. Both magmatic-hydrothermal and hydrothermal disseminated magnetite are characterized by narrow Ti concentration range and variable Co/Ni ratios, which likely reflect rapid cooling rate and significant fluid-rock interaction during multiple successive stages of skarn alteration, as the Co has a higher solubility over the Ni in the ore-forming fluid. Whereas the Talate massive magnetite contains wider Ti concentration range and in some cases with 120° triple junctions, the Co/Ni ratios (mostly < 0.1) of these massive magnetite grains fall within the bracket of Kangbutiebao Formation (Co/Ni = ~ 1) and the magmatic deriving fluid (Co/Ni = ~ 0.01), which was probably generated by equilibration fluid-rock interaction. The high (Al + Mn) and low (Ti +V) and Ni/(Cr + Mn) values for all the Talate hydrothermal magnetite support a typical skarn origin, and the textural and trace element features of the Talate magnetite are analogous to those of typical Ca-skarn Fe deposits worldwide. 2

Keywords: Talate Pb-Zn (-Fe) deposit; Magnetite; Trace elements; Chinese Altay; Skarn.

1

Introduction The Abagong polymetallic belt is located in the Chinese Altay (NW China), which is part of

the Central Asian Orogenic Belt (CAOB) (Fig. 1; Chen et al., 2012; Pirajno, 2013; Xiao and Kusky, 2009). Numerous Au and base metal deposits are located along the Abagong Fault (Fig. 2), including (from northwest to southeast) the Dadonggou Pb-Zn (Xu et al., 2011b; Zheng et al., 2015), Wulasigou Pb-Zn-Cu (Zheng et al., 2012), Qiaxia Pb-Zn (Zhang et al., 2014), Sarekuobu Au (Xu et al., 2008; Zhang et al., 2014), Tiemurt Pb-Zn-Cu (Zhang et al., 2012), Hongdun Pb-Zn, Abagong Pb-Zn-Fe (Yang et al., 2013) and Talate Pb-Zn (-Fe) (Li et al., 2014) deposits. Some aspects of the Talate Pb-Zn (-Fe) deposit including isotopic and fluid inclusion compositions (Zhang et al., 2015) as well as the geochronology have been well constrained (Li et al., 2013, 2014). Li et al. (2013, 2014) have proposed that Talate is a skarn deposit, with alteration and mineralization stages subdivided into four stages based on the mineral assemblage and vein crosscutting relationships, i.e., the early skarn (I), late skarn (II), quartz-sulfide (III) and carbonate (IV) stage. In contrast, Zhang et al. (2015) suggested there were two distinct mineralization periods associated with submarine volcanic sedimentary exhalative processes and metamorphic hydrothermal overprinting. Similarly previous studies of the ore forming fluids have been interpreted to be the result of either metamorphism (Li et al., 2013, 2014) or overprinting of a VMS system (Zhang et al., 2015), which will affect not only the ore model construction, but also the prospectivity of Kalan Basin.

3

Magnetite is a common accessory mineral in many rocks and ores. It forms over a wide range of geologic conditions and can incorporate various trace elements in its cubic spinel structure (Dare et al., 2014b; Nadoll et al., 2012). Recent in-situ LA-ICP-MS (laser ablation inductively coupled plasma mass spectrometry) studies demonstrated that magnetite trace element geochemistry can serve as petrogenetic indicator in determining ore fluid compositions, physicochemical conditions and discriminating ore deposit types (Acosta-Gongora et al., 2014; Chen et al., 2015; Chung et al., 2015; Dare et al., 2014a, 2012; Hu et al., 2015; Nadoll, 2011; Nadoll et al., 2014b; Smithies and Champion, 2000). Magnetite (Fe3O4) has been identified in the Talate late skarn and quartz-magnetite stages (Li et al., 2014), and with its possible genetic link with the ore-hosting Devonian Kangbutiebao Formation volcanic-sedimentary rocks (Xu et al., 2011b; Xu et al., 2008; Yang et al., 2013; Zhang et al., 2014) and association with magmatism and/or metamorphism (Li et al., 2014; Wan et al., 2012; Xu et al., 2010; Yang et al., 2008; Zhang et al., 2011) are still debatable. In this paper, we present new petrographic description and LA-ICP-MS trace elemental data of the Talate magnetite, with the purpose of trying to understand the magnetite genesis and nature of the late skarn and quartz-magnetite stages ore forming fluids and constrain the physicochemical conditions before the deposition of the Pb-Zn mineralization.

2

Geological framework The Central Asian Orogenic Belt (CAOB) extends from the Urals in the west to the Pacific

margin in the east. It is one of the world's largest accretionary orogens and has an evolution

4

history that spans across ca. 800 m.y. (ca. 1000 – 250 Ma; Jahn et al., 2000a, b, c; Jahn, 2004b; Windley et al., 2007; Safonova et al., 2011; Chen et al., 2012) (Fig. 1a). The Chinese Altay in the northern margin of Xinjiang Province (NW China) is an important part of the CAOB (Fig. 1b). It contains four tectonic units, including (from northwest to southeast) (Chen et al., 2012): (1) the Late Devonian–Early Carboniferous Nurt volcanic basin developed on a pre-Devonian crystalline basement; (2) the Keketuohai Paleozoic magmatic arc (or the Central Altay terrane) that contains Precambrian high-grade metamorphic rocks, Neoproterozoic to Early Triassic granites, and the giant Keketuohai pegmatite field; (3) the Kelan Devonian-Carboniferous basin developed on the southern margin of the pre-Devonian metamorphic rocks; and (4) the Armantay–Erqis accretionary complex consisting of high-grade metamorphic rocks (gneiss and schist), Devonian–Carboniferous fossiliferous sedimentary rocks, and post-orogenic dioritic dikes (276.7 ± 2.9 and 273.2 ± 4.3 Ma; Cai et al., 2016). The NW-trending faults in the Kelan Basin commonly separate different stratigraphic units: for example, the Keyingong Fault separates the Kulumuti Group and the Kangbutiebao Formation, whereas the Abagong Fault separates the Kangbutiebao and Altay formations (Fig. 2A). The Devonian-Carboniferous Kelan basin is bounded by the Abagong Fault in the north and Erqis Fault in the south, and is composed mainly of volcano-sedimentary rocks of the Lower Devonian Kangbutiebao Formation, the Middle-Upper Devonian Altay Formation, with subordinate Carboniferous volcano-sedimentary units. Middle-Upper Silurian schist and gneiss, and Devonian marine volcanic rocks are distributed in the Ashele, Chonghu’er, Kelan and Maizi volcano-sedimentary basins (Fig. 3).

5

The Middle Ordovician Kulumuti Group comprises mainly migmatite and schist (Fig. 3). The metamorphic rocks are only locally exposed in the northwestern vicinity of the Talate mine and unconformably overlie the Habahe Group low- or high-grade metamorphosed clastic rocks (Windley et al., 2002). Detrital zircon dating has yielded youngest ages of 465–576 Ma with a few older grains formed between 766–972 Ma and 1321–2572 Ma (Wang et al., 2014). The Lower Devonian Kangbutiebao Formation (zircon U-Pb ages: ca. 412 − 388 Ma; Chai et al., 2009; Zheng et al., 2013) hosts many Pb-Zn (-Cu-Fe) deposits in the Ashele, Chonghu’er, Kelan and Maizi basins (Fig. 3; Geng et al., 2012; Li et al., 2012; Shan et al., 2012). Rocks of the Kangbutiebao Formation were deformed and metamorphosed to greenschist facies during the Hercynian Orogeny (Late Paleozoic) with a typical metamorphic mineral assemblage of biotite + chlorite + epidote + actinolite. The overlying Middle Devonian Altay Formation (zircon U-Pb ages: ca. 380 – 354 Ma) comprises metamorphosed sandstone, siltstone and limestone (Geng et al., 2010). The sediments were interpreted to have been deposited in a fore-arc basin environment (Fig. 3; Wang et al., 2006). Granitoids in the region include those at Qiemuqieke (462 Ma; Wang et al., 2006) and Abagongbei-Tiemurte (ca. 462 – 458 Ma; Chai et al., 2010).

3

The Talate Pb-Zn (-Fe) deposit The Talate Pb-Zn (-Fe) deposit is important in the Abagong Pb-Zn-Fe district, and is

characterized by higher Zn grade than other Pb-Zn-Fe occurrences in the area (Fig. 2B; Li et al., 2014). Talate currently contains a reserve of 2.52 million tonnes (Mt) of ore at 7.93% combined Pb and Zn with associated Fe (~ 27 %) (0.35% cut-off; Yuan et al., 2011). The Lower Devonian Kangbutiebao Formation, which comprises granulite, marble, metamorphosed rhyolite and tuff, 6

is the main host rock of the Talate and other Pb-Zn-Fe deposits in this area (Fig. 2B). The ore bodies are located in the contact zone of the meta-conglomerate and the felsic volcanic lavas (Figs. 2C and 3). Alteration minerals at Talate include skarn-related garnet, epidote, tremolite and actinolite, as well as pyrite, calcite and quartz. The Pb-Zn mineralization is spatially related to skarn, and the sulfides are mainly disseminated but locally occurring as bands and veinlets. Li et al. (2014) subdivided the Talate alteration and mineralization into four stages based on the mineral assemblage and vein crosscutting relationships, i.e., the early skarn (I), late skarn (II), quartz-sulfide (III) and carbonate (IV) stage. Stage II is the main magnetite mineralization stage. Stage I is primarily made up of anhydrous minerals (e.g., garnet and diopside) with some pyrite. The sulfur isotope composition (δ34S) of the Stage I pyrite is 2.6‰ (Li et al., 2014), close to the average magmatic sulfur (i.e., −3‰ to + 3‰; Hoefs, 1997). There is some disseminated magnetite which may have been originally magmatic or magmatic hydrothermal (as they coprecipitated with cassiterite and tourmaline)(Duchoslav et al., 2016), similar magnetite grains were found inside the garnet and diopside, which indicates that these magnetite grains predate the garnet of stage I (Fig. 5A). Stage II alteration contains hydrous minerals of epidote, tremolite, actinolite and hornblende with abundant magnetite and pyrite. The ore fluid temperatures were estimated (based on fluid inclusion studies) to be 271 to 426 °C, and the δ34S values range from 5.0 to 5.2‰, indicative of fluid-rock interactions with metasedimentary host rocks that contain heavier sulfur isotopes (Hoefs, 1997). Ar-Ar dating of Stage II biotite yielded 227.6 ± 2.2 Ma (Li et al., 2014). Stage III alteration is characterized by sphalerite, galena, pyrite, chalcopyrite and pyrrhotite and trace arsenopyrite. The ore fluid temperatures were estimated to be 204 – 269 °C, 7

with negative δ34S values reported (−1.7 and −6.2‰) (Li et al., 2014). Stage III biotite yielded an Ar-Ar age of 214.1 ± 2.1 Ma (Li et al., 2014). Stage IV alteration is dominated by calcite and some pyrite, the fluid temperatures were estimated to be 175 to 211 °C, with a δ34S value reported to be −2.2‰ (Li et al., 2014). The Talate alteration / mineralization paragenetic sequence is shown in Figure 4, and a detailed description can be found in Li et al. (2014). The Talate magnetite can be divided into fine-grained disseminated (locally as thin veins; Fig. 5A) and massive magnetite (Figs. 5B). The disseminated magnetite (~40% of the total magnetite) could be further subdivided into primary (magmatic-hydrothermal) magnetite (Fig. 5C) and secondary (hydrothermal) magnetite (Fig. 5D). The magmatic-hydrothermal disseminated magnetite either coexists with cassiterite and tourmaline or is hosted in the garnet, suggesting coeval crystallization with cassiterite and predating the garnet of stage I (Fig. 5C), while the hydrothermal disseminated magnetite commonly replaced garnet and was, in turn, crosscut by Stage III pyrite veins (Fig. 5D). Some of the euhedral massive magnetite grains are characterized by 120° triple junctions, whereas the subhedral to anhedral grains occur with anhedral quartz and pyrite (Fig. 5E). The coarse-grained anhedral magnetite grains are locally cut by Stage III galena veins, indicating that the magnetite was pre-Stage III (Fig. 5F).

4

Methodology All samples were collected from Stage II. Polished thin sections were prepared and examined

with optical microscopy to characterize the mineralogical and textural relationships, esp. those related to magnetite. Double polished thin sections (60 − 100 µm thick) were prepared for LA-ICP-MS analysis at the Key Laboratory of Mineralogy and Metallogeny, Guangzhou 8

Institute of Geochemistry, Chinese Academy of Sciences (GIGCAS). The analysis was undertaken with a Coherent GeoLasPro 193-nm laser ablation system coupled with an Agilent 7700x ICP-MS. 160 successive laser pulses (4 Hz) with a spot size of 44 µm ablated the sample surfaces for about 40 s after monitoring the gas blank for 20 s. The generated aerosols were carried out by a helium carrier gas, and then mixed with an argon carrier gas via a T-connector before entering the ICP-MS for acquisition of ion-signal intensities. Details of the operating conditions for the instrument were as outlined by Liu et al. (2008). External reference materials KL2 and ML3B were used to calibrate element contents, and 57Fe was used as the normalizing element for multi-standard calibration (Liu et al., 2008). Thirty-seven isotopes (29Si,

238

Na,

39

K,

31

P,

45

Sc,

51

V,

52

Cr,

59

Co,

60

Ni,

65

Cu,

66

Zn,

71

Ga,

74

Ge,

85

Sr, 89Y, 90Zr, 93Nb, 95Mo, 107 Ag, 111Cd, 115In, 118Sn, 137Ba, 179Hf, 181Ta, 182W, 208 Pb, 209Bi, 232Th,

Ca,

23

Al,

88

Mg,

42

27

Fe,

Mn,

25

Ti,

57

and

55

49

Rb,

U) were analyzed based on the methods of Liu et al. (2008) and Dare et al. (2014). Ten

magnetite grains per section were analyzed, and ML3B was analyzed twice for every five analyses to correct the time-dependent drift of sensitivity and mass discrimination. The time resolved software was used to acquire all analyses. All raw data obtained by ICP-MS were processed off-line using ICPMSDataCal (Liu et al., 2008). Signals were used for selecting the best interval to avoid inclusions or zoning, and then reduced by subtracting gas background from each element analyzed.

5

Results The full dataset of the 90 analyses are listed in Appendix I and a summary of trace element

composition is given in Table 2. 9

Compared to hydrothermal disseminated and massive magnetite, the trace element composition of the magmatic-hydrothermal magnetite is characterized by lower Cu = 0.11–1.39 ppm with the average at 0.47 ppm, and Zn = 2.43–1725 ppm with the average at 72 ppm, and Ge = 0.15–3.47 ppm with the average at 1.31 ppm. The hydrothermal disseminated magnetite is characterized by highest Zn (up to 1871 ppm), Cu (up to 7312 ppm) and Ge (up to 10.5 ppm) concentrations. While the massive magnetite has moderate Cu, Zn and Ge concentrations (Cu = 0.17–56.8 ppm, Zn 16.9–1249 ppm and Ge = 0.34–4.4 ppm). The Ti contents of magmatic-hydrothermal, hydrothermal disseminated and massive magnetite are 16 to 1885 averaging 561 ppm, 1 to 735 averaging 316 ppm and 32 to 697 ppm with an average of 218 ppm, respectively. The corresponding Sn concentrations are 0.55 to 2.47 with an average of 1.31 ppm, 0.14 to 0.59 with an average of 0.30 ppm, and 0.12 to 0.99 with an average of 0.28 ppm, respectively. All magmatic-hydrothermal / hydrothermal disseminated and massive magnetite have similar Mn, Co and Ga contents. The average concentrations of magmatic-hydrothermal, hydrothermal and massive magnetite are Mn = 1934, 1165 and 2426 ppm, Co = 2.93, 1.77 and 1.60 ppm and Ga = 12.4, 13.1 and 8.8 ppm, respectively, but the Ni contents in massive magnetite (up to 538 ppm) are greater than hydrothermal disseminated magnetite (up to 18.2 ppm) and of magmatic-hydrothermal disseminated magnetite (up to 4.8 ppm) (Figs. 6A–C). All magnetite types show positive Ga vs. Ti correlation (Fig. 6D). Both magmatic-hydrothermal and hydrothermal disseminated magnetite are characterized by a wider Ge range (<0.1 to <100 ppm) but narrower Ga range (~ 1 to 20 ppm) than those of massive magnetite, with the latter displaying positive Ga vs. Ge correlations (Fig. 6E). In the Ni vs. Sn, Ge vs. Sn and Mn vs. Sn 10

diagrams, data points of the three magnetite types fall into three distinct populations, among which the magmatic-hydrothermal disseminated magnetite datapoints have the highest Sn concentrations (up to 2.46 ppm) (Figs. 6F–H). The Co/Ni ratio of these magmatic-hydrothermal magnetite and hydrothermal are broadly similar with range from 0.01 to 6.18 (average at 0.72) and 0.01 to 3.84 (average at 0.42), respectively. While the Co/Ni ratio of the massive magnetite ranges from 0.31 to 343, averaging 31.4.

6

Discussion 6.1

Petrography and genesis of the Talate magnetite

At Talate, fine-grained magmatic-hydrothermal disseminated magnetite could be discriminated from hydrothermal grains for the following reasons: 1) these magmatic-hydrothermal disseminated

magnetite grains were hosted within garnet grains and coexisted with cassiterite (Fig. 5C) indicating that they were precipitated earlier or simultaneously with the garnet; 2) a previous study (Li et al., 2014) indicated that the ore fluids that precipitated these magmatic-hydrothermal disseminated magnetite are closer to magmatic derived fluid, as the sulfur isotope composition (δ34S) of the Stage I pyrite is 2.6‰, which is close to the average magmatic fluids (i.e., −3‰ to + 3‰; Hoefs, 1997), while the δ34 S values in the stage II (the hydrothermal fluid) range from 5.0 to 5.2‰, indicative of fluid-rock interactions with metasedimentary host rocks that contain heavier sulfur isotopes (Hoefs, 1997); 3) trace element of these magmatic-hydrothermal magnetite grains are characterized by higher Sn than these of hydrothermal disseminated magnetite, which suggest that the fluid temperature of stage I (magmatic-hydrothermal) is higher than the stage II 11

(hydrothermal) due to the Sn concentration being positively correlated with the temperature, which agrees with the previous fluid inclusion study of Talate (Li et al., 2014). These magmatic-hydrothermal disseminated magnetite coexists with cassiterite (Fig. 5C), and is characterized by higher Ti and Sn concentrations than the hydrothermal disseminated and massive magnetite (Figs. 6D, F-H), and may have been generated by exsolution of primary magmatic fluid with higher Ti and Sn concentrations (Wang et al., 2012). The crystallization of cassiterite implies that the hydrothermal magnetite that formed later should be Sn depleted, which is consistent with our Talate hydrothermal disseminated and massive magnetite data. Hydrothermal magnetite was likely formed after garnet as it commonly appears in garnet fractures (Fig. 5D). All three Talate magnetite types were locally cut by later sulfide (galena / pyrite / pyrrhotite) veins (Fig. 5F), indicating that the magnetite mineralization likely predated sulfides. The presence of replacement textures and crosscutting relationships between magnetite and other major sulfide minerals (chalcopyrite, sphalerite and galena) indicate that the Pb-Zn bearing ore fluids may have modified the magnetite compositions, consistent with the elevated Zn concentrations (up to 1871 ppm) in both the hydrothermal disseminated and massive magnetite.

The coarse subhedral to euhedral massive magnetite grains are distinct from the disseminated magnetite (Fig. 5E): The former is locally characterized by triple junction grain boundaries (~120o), Two models have been proposed to explain the triple junction texture: 1) high-temperature annealing in a closed system (i.e., magmatic magnetite; Ciobanu and Cook, 2004), and 2) fluid-assisted recrystallization / replacement in an open system (i.e., quartz; Hu et al., 2015; Nakamura and Watson, 2001). The fluid temperature should not belong to the high-temperature annealing system as fluid inclusion study in Talate indicated that the magnetite 12

precipitation temperature is less than 400 oC (Li et al., 2014). On the contrary, thin quartz veins within crack-seal textures represent for open space filling are common in the massive magnetite, suggesting a local extensional tectonic regime (Sibson et al., 1988), which indicate the triple junction texture in massive magnetite were probably derived from fluid-assisted recrystallization / replacement in an open system.

6.2

Controlling factors for magnetite precipitation

A number of factors can influence trace element partition in magnetite, including temperature, sulfur and oxygen fugacities (ƒS2-ƒO2), cooling rate and fluid-rock interactions (Dare et al., 2014). If the temperature is the major control of Fe-substitution in magnetite, then skarn and porphyry deposits which would form at similar temperatures and fluid compositions should yield magnetite with similiar trace element compositions, however, Nadoll et al. (2014) proposed that the magnetite in skarn systems tend to be more enriched in Mg, Al, Co, Ni compared to porphyry magnetite (Nadoll et al., 2014a), which suggests that the temperature is not the critical factor controlling composition. The redox conditions (ƒS2-ƒO2) may also be less important because: 1) with the absence of hematite and pyrrhotite, the ore fluids of stage II were mainly within the magnetite stable area (blue field in Figure 7A) indicating there should have no significant change in oxygen fugacity; 2) increasing ƒO2 would convert V3+ to V4+, which decreases the V content in magnetite (Takeno, 2005). The V contents of the three Talate magnetite types are similar, indicating that ƒ O2 of the magnetite mineralization fluids was relatively constant. The reduced sulfur added to the system suggested by the sulfur isotope did by Li et al. (2014) leading to increase of ƒs2, which trigger the precipitation of sulfides of stage III.

13

Experimental studies indicated that grain sizes of silicates and titanomagnetites (magnetite subtype) decrease with increasing cooling rate (Zhou et al., 2000), and a similar phenomenon could be found in hydrothermal systems, as the TEM images showing the size and shape evolution of iron oxide nanoparticles as a function of time, which means if the iron oxide nanoparticles is cooled slowly, dendrites have a longer time to grow before they begin to get into neighboring dendrites. Thus, a large grain size is formed (Ahmad and Phul, 2015). Consequently, the Talate magmatic-hydrothermal and hydrothermal disseminated magnetite may reflect relatively high cooling rate, which leads to the observed narrow Ti concentration range, and the vice versa is true for the Talate massive magnetite (Mollo et al., 2013) (Fig. 7C). Slow cooling rate for the coarse-grained magnetite can also generate the characteristic 120° triple junction texture, which is widely regarded to reflect textural equilibration and slow recrystallization (Hu et al., 2015). The primary and hydrothermal disseminated magnetite have a wide range of Co/Ni ratios from < 0.01 to 8, with most concentrated around 1, and the hydrothermal disseminated magnetite is characterized by higher Ni content than those of primary ones; whereas the massive magnetite has lower Co/Ni ratios typically less than 0.5 (Fig. 7D) but characterized by highest Ni concentration. These distinct Co/Ni ratios of massive magnetite could reflect the interaction process of magnetite-forming fluids (low Co/Ni = ~ 0.01; Bajwah et al., 1987; Brill, 1979) with host rock units (the Kangbutiebao Formation, Co/Ni = ~ 1; Shan et al., 2011) along the flow path. The Co/Ni ratios of massive magnetite (mostly < 0.1) are ideally fall within the bracket of magmatic-hydrothermal fluid and marine sediment, which was probably generated by equilibration fluid-rock interaction. 14

However, the Co/Ni ratios of disseminated magnetite (primary and hydrothermal) tend to be more scattered, and some of the higher ratios overflows the bracket of magmatic-hydrothermal fluid and the Kangbutiebao marine sediment, which can be more likely explained by the significant fluid-rock interaction at the beginning of the skarn alteration and mineralization (Meinert, 1992; Nadoll, 2011). Experimental data show that the chlorinated Co tetrahedral complexes has reached its full stability at a lower temperature (~ 250 oC) than these of Ni (Liu et al., 2011; Tian et al., 2012), which means that Co concentration in the minerals will be higher than Ni and leads to high Co/Ni ratios. Similarly, Liu et al. (2012) has proved by experiment that the solubility of the Co pentlandite is at least 100 × greater than these of pentlandite in aqueous solution, resulting in far more higher Co concentration than these of Ni concentration in the ore-forming fluid, which may also explain the high Co/Ni ratios and also why Co-rich deposit is more apparent than Ni-rich deposit (Liu et al., 2012). The behavior of Co and Ni in the hydrothermal fluid could explain these high Co/Ni ratios in the disseminated magnetite grains occurred at Talate. This case exemplifies the complex controls on the geochemistry of magnetite which might be further complicated by multiple successive stages of alteration (Nadoll, 2011; Nadoll et al., 2010). Even so, the hydrothermal disseminated magnetite show much analogy to those of hydrothermal magnetite during the early skarn alteration and mineralization in the skarn deposits (Frietsch, 1970).

6.3

Implications on ore deposit type

The Ni/Cr ratios of the massive magnetite are similar to those of typical hydrothermal magnetite from, e.g., skarn or IOCG deposits, However, the magmatic-hydrothermal 15

disseminated magnetite show similarities with the magnetite derived from the magmatic fluids (Fig. 8A; Dare et al., 2014). Some of the hydrothermal disseminated magnetite grains have inherited Ni/Cr and Ti contents from magmatic-hydrothermal disseminated magnetite, as they partially replaced the magmatic-hydrothermal magnetite.(Dupuis and Beaudoin, 2011; Nadoll et al., 2014a) (Figs. 8B and C). The high (Al + Mn) contents in the Talate hydrothermal disseminated and massive magnetite are indicative of a hydrothermal skarn genesis (Fig. 8B), as also supported by the low Ni/(Cr + Mn) values (Fig. 8C). The Talate magmatic-hydrothermal magnetite has Nb-Ta-Ti depletions, whereas the hydrothermal disseminated magnetite is geochemically similar to the Ca-skarn with slightly Ta-Mg-Ni depletions (Fig. 9). The massive magnetite ores have similar Ni composition with the Ca-skarn, but with minor depletions in Sn, Sc, Ta, Nb, Mg and Co (Fig. 9), which should be attributed to the interactions of the magma with compositionally different host rocks (Fig. 3; Kangbutiebao Formation: tuff, rhyolite, marble and granulite) (Nadoll, 2011; Zhao and Zhou, 2015). High (Al + Mn), low (Ti +V) and Ni/(Cr + Mn) values all suggest a hydrothermal skarn origin for the Talate magnetite (Figs. 8B and C), which is consistent with ore geology and fluid geochemistry of Talate (Li et al., 2014). The biotite

40

Ar/39Ar isotope plateau ages of 227.6

(stage II) and 214.1 Ma (sulfide stage III) are significantly younger than the ore-hosting Kangbutiebao Formation (ca. 410 Ma; (Chai et al., 2009; Zheng et al., 2015), precluding a syngenetic genesis such as VMS. Fluids associated with the quartz-magnetite stage are characterized by high temperatures, high salinities and CO2-rich and distinct from typical syngenetic deposits as well as the orogenic deposits (Li et al., 2014). Therefore, the Talate Pb-Zn 16

(-Fe) deposit is most likely interpreted to be a skarn-type system formed in a continental collision orogeny (Li et al., 2014). We propose that the primary disseminated magnetite is derived from magmatic-hydrothermal fluids with higher temperatures than these of hydrothermal disseminated magnetite based on the fluid inclusion study, and the hydrothermal disseminated magnetite may have been generated during the extensive late skarn alteration with lower formation temperatures. The narrow Ti concentration range and variable Co/Ni ratios may have resulted from rapid cooling (and thus precipitation) (Fig. 7D) during the interactions of magmatic-hydrothermal fluids with the Kangbutiebao Formation volcano-sedimentary rocks. Some massive magnetite ores may have formed when the cooling rate decreased and were precipitated in a local extensional tectonic regime that provided sufficient time and space for the massive magnetite growth, whereas some other massive magnetite ores may have formed by fluid-assisted re-crystallization in an open system, leading to wider Ti concentration range and 120° triple junction texture (Figs. 10A and C).

7

Conclusions Trace element compositions of massive and disseminated magnetite from the Talate Pb-Zn

(-Fe) deposit in the Abagong polymetallic belt (NW China) varies. The Talate magnetite can be subdivided into three types an early the magmatic-hydrothermal and intermediate hydrothermal disseminated magnetite and the late massive magnetite. Tin is depleted in all the magnetite types compared with other skarn deposits, likely because cassiterite precipitated during the early magmatic-hydrothermal magnetite crystallization. Cooling rates and fluid rock interactions may 17

have played an important role in generating the textural and trace element characteristics of the Talate magnetite. The fine-grained disseminated magnetite (magmatic-hydrothermal or hydrothermal) with a narrow range of Ti concentrations likely resulted from a rapid cooling rate, whereas the massive magnetite formed as a result

of slow cooling. Both the

magmatic-hydrothermal and hydrothermal disseminated magnetite are characterized by variable Co/Ni ratios reflecting interactions between the magma with the compositionally distinct Kangbutiebao Formation host rocks during successive alteration stages, as the Co is easier to mobilise than the Ni. In contrast, the massive ones ideally fall within the bracket of marine sediment and magmatic-deriving fluid, which was probably generated by equilibration fluid-rock interaction. The high (Al + Mn) and low (Ti +V) and Ni/(Cr + Mn) values support a skarn origin for the hydrothermal Talate magnetite consistent with studies of the ore geology.

Acknowledgements This study was financial supported by the NSFC (41572059, 41072062 and 40730421), Chinese National Basic Research 973-Program (2014CB440802), Creative and Interdisciplinary Program, CAS (Y433131A07) and CAS/SAFEA International Partnership Program for Creative Research Teams (20140491534). Dr. Congying Li is thanked for her contribution in magnetite trace element analysis. The staffs of the Geological Team 706 of Xinjiang Bureau of Nonferrous Metals are thanked for the field support. The Editor Franco Pirajno, Drs. Bo Wan, Tong Hou and an anonymous reviewer are thanked for their constructive reviews that greatly improved the quality of this paper.

18

References Acosta-Gongora, P., Gleeson, S.A., Samson, I.M., Ootes, L., Corriveau, L., 2014. Trace Element Geochemistry of Magnetite and Its Relationship to Cu-Bi-Co-Au-Ag-U-W Mineralization in the Great Bear Magmatic Zone, NWT, Canada. Econ. Geol. 109, 1901–1928. Ahmad, T., Phul, R., 2015. Magnetic Iron Oxide Nanoparticles as Contrast Agents: Hydrothermal Synthesis, Characterization and Properties. Solid State Phenom. 232, 111–145. Bajwah, Z.U., Seccombe, P.K., Offler, R., 1987. Trace element distribution, Co: Ni ratios and genesis of the Big Cadia iron-copper deposit, New South Wales, Australia. Miner. Depos. 22, 292–300. Brill, B., 1979. Trace-element contents and partitioning of elements in ore minerals from CSA Cu-Pb-ZN deposit, Australia. Can. Mineral. 27, 263–273. Cai, K., Sun, M., Jahn, B., Xiao, W., Long, X., Chen, H., Xia, X., Chen, M., Wang, X., 2016. Petrogenesis of the Permian Intermediate-Mafic Dikes in the Chinese Altai, Northwest China: Implication for a Postaccretion Extensional Scenario. J. Geol. 124, 481–500. Chai, F., Dong, L., Yang, F., Liu, F., Geng, X., Huang, C., 2010. Age, geochemistry and petrogenesis of Tiemierte granites in the Kelang basin at the southern margin of Altay, Xinjiang. Acta Petrol. Sin. 26, 377–386. Chai, F.M., Mao, J.W., Dong, L.H., Yang, F.Q., Liu, F., Geng, X.X., Zhang, Z.X., 2009. Geochronology of metarhyolites from the Kangbutiebao Formation in the Kelang basin, Altay Mountains, Xinjiang: Implications for the tectonic evolution and metallogeny. Gondwana Res. 16, 189–200. Chen, W.T., Zhou, M.-F., Gao, J.-F., Hu, R., 2015. Geochemistry of magnetite from Proterozoic Fe-Cu deposits in the Kangdian metallogenic province, SW China. Miner. Depos. 1–15. 19

Chen, Y.J., Pirajno, F., Wu, G., Qi, J.P., Xiong, X.L., 2012. Epithermal deposits in North Xinjiang, NW China. Int. J. Earth Sci. 101, 889–917. Chung, D., Zhou, M.-F., Gao, J.-F., Chen, W.T., 2015. In-situ LA–ICP-MS trace elemental analyses of magnetite: The late Palaeoproterozoic Sokoman Iron Formation in the Labrador Trough, Canada. Ore Geol. Rev. 65, 917–928. Ciobanu, C.L., Cook, N.J., 2004. Skarn textures and a case study: The Ocna de Fier-Dognecea orefield, Banat, Romania. Ore Geol. Rev. 24, 315–370. Dare, S.A.S., Ames, D.E., Lightfoot, P.C., Barnes, S.J., Beaudoin, G., 2014a. Mineral chemistry and supporting databases for TGI4 project on “Trace elements in Fe-oxides from fertile and barren igneous complexes: Investigating their use as a vectoring tool in the intrusions that host Ni-Cu-PGE deposits” 12. doi:10.4095/293640 Dare, S.A.S., Barnes, S., Beaudoin, G., 2012. Variation in trace element content of magnetite crystallized from a fractionating sulfide liquid , Sudbury , Canada : Implications for provenance discrimination. Geochim. Cosmochim. Acta 88, 27–50. Dare, S.A.S., Barnes, S.J., Beaudoin, G., Méric, J., Boutroy, E., Potvin-Doucet, C., 2014b. Trace elements in magnetite as petrogenetic indicators. Miner. Depos. 49, 785–796. Duchoslav, M., Marks, M.A.W., Drost, K., McCammon, C., Marschall, H.R., Wenzel, T., Markl, G., 2016. Changes in tourmaline composition during magmatic and hydrothermal processes leading to

tin-ore

deposition:

The

Cornubian

Batholith,

SW

England.

Ore Geol.

Rev.

doi:10.1016/j.oregeorev.2016.11.012 Dupuis, C., Beaudoin, G., 2011. Discriminant diagrams for iron oxide trace element fingerprinting of mineral deposit types. Miner. Depos. 46, 319–335. 20

Frietsch, R., 1970. Trace elements in magnetite and hematite mainly from northern Sweden. Swedish Geological Survey. Ser. C No. 646. Svenska reproduktions AB (distr.). Geng, X., Yang, F., Chai, F., Liu, M., Guo, X., Guo, Z., Liu, F., Zhang, Z., 2012. LA-ICP-MS U-Pb dating of volcanic rocks from Dadonggou ore district on southern margin of Altay in Xinjiang and its geological implications. Miner. Depos. 5, 15. Geng, X., Yang, F., Yang, J., Huang, C., Liu, F., Chai, F., Zhang, Z., 2010. Characteristics of fluid inclusions in the Tiemurte Pb-Zn deposit, Altay, Xinjiang and its geological significance. Acta Petrol. Sin. 26, 695–706. Hoefs, J., 1997. Stable isotope geochemistry. Springer, Germany. Hu, H., Lentz, D., Li, J.-W., McCarron, T., Zhao, X.-F., Hall, D., 2015. REEQUILIBRATION PROCESSES IN MAGNETITE FROM IRON SKARN DEPOSITS. Econ. Geol. 110, 1–8. Li, D., Zhang, L., Chen, H., Zheng, Y., Hollings, P., Wang, C., Fang, J., 2014. Ore genesis of the unusual Talate Pb–Zn (–Fe) skarn‐type deposit, Altay, NW China: constraints from geology, geochemistry and geochronology. Geol. J. 49, 599–616. Li, D., Zhang, L., Zheng, Y., 2013. Fluid inclusion study and ore genesis of the Talate Fe-Pb-Zn deposit in Allay, Xinjiang. Acta Petrol. Sin. 29, 178–190. Li, Y., Zhou, G., Chai, F.M., 2012. LA–ICP–MS U–Pb ages and geological implications of the Habahe Pluton at the Southern Margin of the Altay, Xinjiang. Xinjiang Geol. 30, 146–151. Liu, J., Mao, J.W., Ye, H.S., Zhang, W., 2008. Geochemical characteristics and zircon La-ICP-MS U-Pb dating of granite from Hukeng intrusion, Jiangxi Province, South China. Geochim. Cosmochim. Acta 72, A558–A558. Liu, W., Borg, S.J., Testemale, D., Etschmann, B., Hazemann, J.-L., Brugger, J., 2011. Speciation and 21

thermodynamic properties for cobalt chloride complexes in hydrothermal fluids at 35–440 C and 600bar: an in-situ XAS study. Geochim. Cosmochim. Acta 75, 1227–1248. Liu, W., Migdisov, A., Williams-Jones, A., 2012. The stability of aqueous nickel(II) chloride complexes in hydrothermal solutions: Results of UV-Visible spectroscopic experiments. Geochim. Cosmochim. Acta 94, 276–290. Meinert, L.D., 1992. Skarns and skarn deposits. Geosci. Canada 19. Mollo, S., Putirka, K., Iezzi, G., Scarlato, P., 2013. The control of cooling rate on titanomagnetite composition: Implications for a geospeedometry model applicable to alkaline rocks from Mt. Etna volcano. Contrib. to Mineral. Petrol. 165, 457–475. Nadoll, P., 2011. Geochemistry of magnetite from hydrothermal ore deposits and host rocks. Thesis 1275–1292. Nadoll, P., Angerer, T., Mauk, J.L., French, D., Walshe, J., 2014a. The chemistry of hydrothermal magnetite: A review. Ore Geol. Rev. 61, 1–32. doi:Doi 10.1016/J.Oregeorev.2013.12.013 Nadoll, P., Mauk, J.L., Hayes, T.S., Koenig, A.E., Box, S.E., 2012. Geochemistry of magnetite from hydrothermal ore deposits and host rocks of the Mesoproterozoic Belt Supergroup, United States. Econ. Geol. 107, 1275–1292. Nadoll, P., Mauk, J.L., Leveille, R.A., Koenig, A.E., 2014b. Geochemistry of magnetite from porphyry Cu and skarn deposits in the southwestern United States. Miner. Depos. 1–23. Nadoll, P., Mauk, J.L., LeVeille, R., Koenig, A.E., 2010. Geochemistry of magnetite from Cu–Mo porphyry+ skarn, and Climax Mo deposits in the western United States, in: Ima. p. 507. Nakamura, M., Watson, E.B., 2001. Experimental study of aqueous fluid infiltration into quartzite: implications for the kinetics of fluid redistribution and grain growth driven by interfacial energy 22

reduction. Geofluids 1, 73–89. Pirajno, F., 2013. The Geology and Tectonic Settings of China’s Mineral Deposits. Springer, Germany. Rudnick, R.L., Gao, S., 2003. 3.01 - Composition of the Continental Crust. Treatise on Geochemistry 3, 1–64. Shan, Q., Zeng, Q., Li, N., Yang, W., Luo, Y., Jiang, Y., Yu, X., 2012. Zircon U-Pb ages and geochemistry of the potassic and sodic rhyolites of the Kangbutiebao Formation in the southern margin of Altay, Xinjiang. Acta Petrol. Sin. 28, 2132–2144. Shan, Q., Zeng, Q., Luo, Y., Yang, W., Zhang, H., Qiu, Y., Yu, X., 2011. SHRIMP U-Pb ages and petrology studies on the potassic and podic rhyolites in Altai, North Xinjiang. Acta Petrol. Sin. 27, 3653–3665. Sibson, R.H., Robert, F., Poulsen, K.H., 1988. High-angle reverse faults, fluid-pressure cycling, and mesothermal gold-quartz deposits. Geology 16, 551–555. Smithies, R.H., Champion, D.C., 2000. The Archaean high-Mg diorite suite: links to tonalite–trondhjemite–granodiorite magmatism and implications for early Archaean crustal growth. J. Petrol. 41, 1653–1671. Takeno, N., 2005. Atlas of Eh-pH diagrams. Geol. Surv. Japan open file Rep. 419, 102. Tian, Y., Etschmann, B., Liu, W., Borg, S., Mei, Y., Testemale, D., O’Neill, B., Rae, N., Sherman, D.M., Ngothai, Y., Johannessen, B., Glover, C., Brugger, J., 2012. Speciation of nickel (II) chloride complexes in hydrothermal fluids: In situ XAS study. Chem. Geol. 334, 345–363. Wan, B., Xiao, W.J., Zhang, L.C., Han, C.M., 2012. Iron mineralization associated with a major strike–slip shear zone: Radiometric and oxygen isotope evidence from the Mengku deposit, NW 23

China. Ore Geol. Rev. 44, 136–147. Wang, R.C., Yu, A.P., Chen, J., Xie, L., Lu, J.J., Zhu, J.C., 2012. Cassiterite exsolution with ilmenite lamellae in magnetite from the Huashan metaluminous tin granite in southern China. Mineral. Petrol. 105, 71–84. Wang, T., Hong, D.-W., Jahn, B.-M., Tong, Y., Wang, Y.-B., Han, B.-F., Wang, X.-X., 2006. Timing, Petrogenesis, and Setting of Paleozoic Synorogenic Intrusions from the Altai Mountains, Northwest China: Implications for the Tectonic Evolution of an Accretionary Orogen. J. Geol. 114, 735–751. Wang, Y., Long, X., Wilde, S.A., Xu, H., Sun, M., Xiao, W., Yuan, C., Cai, K., 2014. Provenance of Early Paleozoic metasediments in the central Chinese Altai: Implications for tectonic affinity of the Altai-Mongolia terrane in the Central Asian Orogenic Belt. Lithos 210, 57–68. Windley, B.F., Kröner, A., Guo, J., Qu, G., Li, Y., Zhang, C., 2002. Neoproterozoic to Paleozoic geology of the Altai orogen, NW China: new zircon age data and tectonic evolution. J. Geol. 110, 719–737. Xiao, W., Kusky, T., 2009. Geodynamic processes and metallogenesis of the Central Asian and related orogenic belts: Introduction. Gondwana Res. 16, 167–169. Xu, J., Ding, R., Xie, Y., Zhong, C., Shan, L., 2008. The source of hydrothermal fluids for the Sarekoubu gold deposit in the southern Altai, Xinjiang, China: Evidence from fluid inclusions and geochemistry. J. Asian Earth Sci. 32, 247–258. Xu, J., Xiao, X., Chi, H.G., Wang, L.L., Lin, L.H., Chu, H.X., Gong, Y.H., Xu JH Chi HG, Wang LL, Lin LH, Chu HX and Gong YH, X.X., 2011. Fluid inclusion study on gold-copper mineralization in Lower Devoni an strata of the Kelan basin , Altay , China. Acta Petrol. Sin. 27, 24

1299–1310. Xu, L., Mao, J., Yang, F., Daniel, H., Zheng, J., 2010. Geology, geochemistry and age constraints on the Mengku skarn iron deposit in Xinjiang Altai, NW China. J. Asian Earth Sci. 39, 423–440. Yang, F., Mao, J., Chai, F.M., Liu, F., Zhou, G., Geng, X., Liu, G., Xu, L., 2008. Ore-forming fluids and metallogenesis of Mengku iron deposit in Altay, Xinjiang. Miner. Depos. 27, 659–680. Yang, F., Mao, J., Liu, F., Chai, F., Geng, X., Zhang, Z., Guo, X., Liu, G., 2013. A review of the geological characteristics and mineralization history of iron deposits in the Altay orogenic belt of the Xinjiang, Northwest China. Ore Geol. Rev. 54, 1–16. Yuan, J.J., Wang, H.N., Zhang, H.J., Yang, X.F., Kang, J.C., 2011. Geological Characteristics and Prospecting Range of Talate iron-Pb-Zn Deposit in Altay,Xinjiang. Sci. &Tech. Inf. 23, 61–65 Zhang, H., Xu, J., Guo, X., Xiao, X., Lin, L., R, Y., Cheng, X., 2015. Metamorphic overprints on the Talate Pb-Zn deposit in Altay: Evidences from geology and fluid inclusions. Acta Petrol. Sin. 31, 1063–1078. Zhang, L., Chen, H., Chen, Y., Qin, Y., Liu, C., Zheng, Y., Jansen, N.H., 2012. Geology and fluid evolution of the Wangfeng orogenic-type gold deposit, Western Tian Shan, China. Ore Geol. Rev. 49, 85–95. Zhang, L., Chen, H., Zheng, Y., Qin, Y., Li, D., 2014. Geology, fluid inclusion and age constraints on the genesis of the Sarekuobu gold deposit in Altay, NW China. Geol. J. 49, 635–648. Zhang, Z.X., Yang, F.Q., Chai, F.M., Liu, F., Geng, X.X., Lü, S.J., Jiang, L.P., Zhong, T.Z., Ouyang, L.J., 2011. The study of REE geochemistry of Wutubulake iron deposit in Altay, Xinjiang. Miner. Depos 30, 87–102. Zhao, W.W., Zhou, M.-F., 2015. In-situ LA–ICP-MS trace elemental analyses of magnetite: The 25

Mesozoic Tengtie skarn Fe deposit in the Nanling Range, South China. Ore Geol. Rev. 65, 872–883. Zheng, Y., Zhang, L., Chen, Y.-J., Qin, Y.-J., Liu, C.-F., 2012. Geology, fluid inclusion geochemistry, and 40Ar/39Ar geochronology of the Wulasigou Cu deposit, and their implications for ore genesis, Altay, Xinjiang, China. Ore Geol. Rev. 49, 128–140. Zheng, Y., Zhang, L., Li, D.-F., Kapsiotis, A., Chen, Y.-J., 2015. Genesis of the Dadonggou Pb–Zn deposit in Kelan basin, Altay, NW China: Constraints from zircon U–Pb and biotite 40Ar/39Ar geochronological data. Ore Geol. Rev. 64, 128–139. Zhou, W., Van Der Voo, R., Peacor, D.R., Zhang, Y., 2000. Variable Ti-content and grain size of titanomagnetite as a function of cooling rate in very young MORB. Earth Planet. Sci. Lett. 179, 9–20.

Figure captions Fig. 1. Sketch map showing the tectonic framework of North Xinjiang (modified after Chen et al., 2012).

Fig. 2. (A) Geologic map of the Abagong polymetallic ore belt (modified after Geological Team 706, 2000); (B) Geologic map of the Talate Pb-Zn (-Fe) skarn-type deposit (modified after Li et al., 2014); (C) Sketch geologic profile for the Talate Exploration Line 144.

Fig. 3. Generalized stratigraphic columns of the Kelan Basin (modified after Chai et al., 2009).

26

Fig. 4. Paragenetic sequence of the Talate Pb-Zn (-Fe) deposit. Abbreviations: M-H-Mgt = magmatic-hydrothermal disseminated magnetite; H-Mgt = hrdrothermal disseminated magnetite; M-Mgt = massive magnetite

Fig. 5. (A) Disseminated magnetite in garnet cut by galena vein; (B) Massive magnetite cut by pyrite vein; (C) Magmatic-hydrothermal disseminated magnetite with cassiterite and tourmaline (reflected light); (D) Hydrothermal disseminated magnetite in garnet cut by pyrite vein; (E) Massive magnetite with quartz-filled crack-seal and 120° triple junction textures; (F) Massive magnetite cut by galena veins. Abbreviations: Py = pyrite, Grt = garnet, Mgt = magnetite, Qtz = quartz, Gn = galena, Cst cassiterite, Tur = tourmaline.

Fig. 6. Binary plots of: (A) Ni vs. Mo; (B) Ni vs. Co; (C) Ni vs. Ga; (D) Ti vs. Ga; (E) Ge vs. Ga; (F) Sn vs. Ni; (G) Sn vs. Ge; (H) Mn vs. Sn.

Fig. 7. (A) Phase diagram of the system Fe–S–O. Abbreviations: Po = pyrrhotite; Hem= hematite. Other abbreviations are as in Figure 5. Solid lines show stability fields of Fe-S-O minerals. The fluid temperature and pressure (350 °C and 2000 Bar) for magnetite precipitation are from Li et al. (2014); (B) V vs. Ni correlation diagram; (C) Ti concentrations of the disseminated and massive magnetite; (D) Ni vs. Co/Ni plot.

27

Fig. 8. Magnetite discrimination diagrams (A) Ti vs. Ni/Cr (after Dare et al., 2014); (B) (Al + Mn) vs. (Ti + V) (after Dupuis and Beaudoin, 2011 and Nadoll, 2011); (C) (Ti + V) vs. (Al + Mn) (Dupuis and Beaudoin, 2011).

Fig. 9. The Upper Continental Crust-normalized multi-element diagrams for (A and B) magmatic-hydrothermal / hydrothermal disseminated magnetite and (C) massive magnetite. Normalization values are from Rudnick and Gao (2003).

Fig. 10. Schematic diagram of the evolution of disseminated and massive magneite. (A) Disseminated magnetite (Fig. B in garnet) coexists with massive magnetite (Fig. C); (B) Anhedral disseminated magnetite in garnet; (C) The massive magnetite with 120° triple junction texture.

28

87°

91°

A

B

Nurt Basin

Altay

46°

W Junggar lt Fau ute b t la Da

800km

N

Fig.2

Armantay–Erqis Accretionary Terrane

N

0

Altay

Ke

Er

lan

qis

Fa

Ba

sin

ult

100

200km

Eastern European Craton Fig. B

Ka

Central Altay Terrane

Erqis Suture

Karamay

Siberian Craton

Arcbic Craton

CAOB

hi th C Nor ton a r C Tethys tectonic Zone

North Xinjiang lak um u Tarim

Indian Craton

na

E Junggar

Junggar Basin Kalameili Fault Urumqi Kan

gurt

42°

Siberia Plate

ag F

Hami

Tur pan Basin ault

Kazakhstan Plate

Mesozoic-Cenozoic Basin

Tarim Plate

Sutures (red) and Faults (black)

A

Ke

yin

go

ng

Fa

ult

N

4 km ta

Al yF

Tie

au

m

lt

Ab

ur

ag

Altay

tF

on

au

lt

gF

au

lt

n

yn

du

yS

ng

ta

Al

Ho

Fig. B

cli

t

ul

ne

Fa Hongdun

C

B

ZK144-1 ZK144-2 ZK144-4

Line144 45

o

N

400 m 180.13m

Ab ag

ong

Fa

Ke

Ore body

ult

yin

go

ng

Line 144 45 o

Breccia-bearing tuff

293.62m

Fa

ult Felsic volcanic lava 467.23M

Metaconglomerate 100m

Siltstone Limestone Felsite

Altay/Abagong Fault

Altay Fm.

Middle

Sandstone

Upper

Breccia

Granulite Pb-Zn (-Fe) mineralization Marble Metamorphised Tuff and rhyolite Quartz and/or Mica schist

Migmatite

Keyinggong Fault

Kulumuti Group

Silurian

Metamorphised Tuff and rhyolite

Granulite interlayered with marble

Lower

Kangbutiebao Fm.

Lower

Devonian

Lamazhao granuite (276 Ma; Wang et al., 2005)

Mine

Stag ral

e

Cassiterite M-H-Mgt Tourmaline Garnet Diopside H-Mgt M-Mgt Epidote Tremolite Actinolite Hornblende Sphalerite Galena Chalcopyrite Arsenopyrite Pyrrhotite Calcite Biotite Pyrite Quartz

E-skarn

QM stage

QS stage

QC stage

B

A

Mgt Grt

Grt

Py vein

Gn Mgt

Mgt Grt

Mgt

Bi

Py vein 10 mm

10 mm

C

D

Cst

Mgt

Mgt Mgt Py vein

Qtz Tur

Grt

Cst

Mgt Cst

F

E

Mgt o

~120

Mgt

Qtz vein Mgt

Mgt

Mgt Gn vein Qtz Gn vein Gn

Gn

100

10000

B

A

1

Co (ppm)

Mn (ppm)

10

1000

0.1 0.01

100 0.1

1

10

100

0.001 0.1

1000

1

10

100

1000

100

D

Ga (ppm)

C

Ga (ppm)

100

Ni (ppm)

Ni (ppm)

10

1 0.1

1

10

100

10

1 10

1000

100

Ni (ppm)

1000

10000

1

10

Ti (ppm)

100

1000

E

F

Ni (ppm)

Ga (ppm)

100

10

10

1

1 0.01

0.1

1

10

100

0.1 0.01

0.1

Ge (ppm)

Sn (ppm) 10000

100

H

G

Mn (ppm)

Ge (ppm)

10

1

1000

0.1

0.01 0.01

0.1

1

Sn (ppm)

10

100 0.01

Magmatic-hydrothermal Hydrothermal Massive 0.1

1

Sn (ppm)

10

1000

-10

A

B

m

350 oC 2000 bar

gt

-20

Po Mgt

Decreasing ƒO2

10

Magmatic -hydrothermal hydrothermal

1

Hem

Po -

-25

100

Ni (ppm)

-M Py

Mg t

logƒS2

P

Py

-15

e y-H

-40

-30

Massive

0.1 10

-20

100

logƒO2

1000

V (ppm) 1000

10000

D

C 100

Ni (ppm)

Ti (ppm)

1000

max

100

up quatile (95%) median mean lower quatile (5%) min

1 Co/Ni=1

Sample

9 -2

6 -4

9 -1

7 -2

0 -2

0 -3

2 -2

71 -1

26

10 11 TL -

10

0.1 0.0001

0.001

0.01

Co/Ni

0.1

10

1×106

A Magmatic Mgt

100000

10000

Ti (ppm)

Hydrothermal Mgt

IOCG

Porphyry 1000

100

Ag-Pb-Zn veins 10

Skarn

1 0.01

0.1

Serpentinization 1

10

100

1000

10000

Ni/Cr (in ppm)

hy ry

10

Sk

arn

Po rp

B Skarn

1

Al+Mn (wt. %)

Fe-Ti, V Porphyry

0.1

IOCG 0.01

Kiruna

BIF

0.001 0.01

0.1

1

10

Ti+V (wt. %) 10

C Opemiska 1

Kinuna (BIF)

Ni/(Cr+Mn)

IOCG

Porphyry

Fe-Ti, V

0.1

0.01

Magmatic -hydrothermal

Skarn

hydrothermal Massive 0.001 0.01

0.1

1

Ti+V (wt. %)

10

10000

A

/Bulk Continental Crust

1000

Magmatic-hydrothermal Ca-skarn (Dare et al., 2014)

100 10 1 0.1 0.01 0.001 0.0001

Al

Ge

W

Sn

Sc

Ta

Nb

Mo

Ga

Mn

Mg

Ti

Zn

Co

V

Ni

Cr

Increasing compatibility into magnetite 10000

B

Hydrothermal Ca-skarn (Dare et al., 2014)

/Bulk Continental Crust

1000 100 10 1 0.1 0.01 0.001 0.0001

Al

Ge

W

Sn

Sc

Ta

Nb

Mo

Ga

Mn

Mg

Ti

Zn

Co

V

Ni

Cr

Ni

Cr

Increasing compatibility into magnetite 10000

C

/Bulk Continental Crust

1000

Massive Mgt Ca-skarn (Dare et al., 2014)

100 10 1 0.1 0.01 0.001 0.0001

Al

Ge

W

Sn

Sc

Ta

Nb

Mo

Ga

Mn

Mg

Ti

Increasing compatibility into magnetite

Zn

Co

V

A

Qtz vein

Magmatic

Magnetic Grt Fig.B

High Ti and low Co/Ni Magmatic fluid

Mgt

Fig.C

Rapid cooling rate

st B -ho d i lu ion f y c ntl rat sta inte n Co rock Magmatic hydrothermal disseminated Mgt Mgt Hydrothermal disseminated Mgt

Hydrothermal

Disseminated Mgt in skarn mineral like Grt

Mgt Magnetic Grt Mgt

1. Wide range of Ti and Co/Ni 2. Disseminated Mgt recrystallization

Remainling fluid slowly precipitated in an open-space system

C

Qtz vein

Tr

Mgt

Mgt

120o ~ 120o

Massive Mgt 500 um

Table. 1 Geochronological data of magmatism and metamorphism in the southern Altay area. Sample

Location

Lithology

Mineral

Method

Age (Ma)

Source

Plagiogranite

Zircon

SHRIMP

416 ± 5

Zhang et al., 2003

Magmatism Kuerti Chonghuer

48°20′N, 87°30′E;

Plagiogranite; tonalite

Zircon

SHRIMP

413 ± 3.8

Zeng et al., 2007

Kelan

47°44′05.8 N, 88°26′54.1″E

Meta-rhyolites

Zircon

SHRIMP

407–412

Chai et al., 2009

Habahe

48°09′44″N, 86°41′44″E;

Monzonitic granite

Zircon

LA-ICP-MS

406.3 ± 2.1

Li et al., 2012

Mengku

47°31′08″N, 89°00′04″E

Gneissic plagiogranite

Zircon

SHRIMP

404 ± 8

Yang et al., 2010

Mengku Iron Mine

Rhyolite

Zircon

LA-ICP-MS

404 ± 5

Wan et al., 2012

Tielieke

Biotite granite

Zircon

LA-ICP-MS

403 ± 5

Tong et al., 2005

Keketale

47°51′12″N, 88°14′40″E

Rhyolite

Zircon

SHRIMP

402.2 ± 6.0

Shan et al., 2011

Tiemurt

47°51′54″N, 88°14′50″E

Rhyolite

Zircon

SHRIMP

400.8 ± 8.4

Shan et al., 2011

Aweitan

47°40′N, 88°01′E

Granodiorite

Zircon

SHRIMP

400 ± 6

Wang et al., 2006

Qiongkuer

47°38′26″N, 88°53′59″E

Biotite granite

Zircon

LA-ICP-MS

399 ± 4

Tong et al., 2006

Kanasi

48°47′11″N, 87°02′30″E

Biotite adamellite

Zircon

LA-ICP-MS

398 ± 5

Tong et al., 2007

Keketale

47°21′07″N, 89°11′37″E

Rhyolite

Zircon

LA-ICP-MS

396.7 ± 1.4

Shan et al., 2012

Dadonggou

47°56′39″N, 88°06′38″E

Rhyolite

Zircon

LA-ICP-MS

394.0 ± 6.0

Shan et al., 2012

Dadonggou

47°56′20.6″N, 88°07′24.1″E;

Rhyolite

Zircon

LA-ICP-MS

389–401

Geng et al., 2012

Qinghe

46°35′06.2″N, 90°14′41.9″E

Gneiss

Zircon

SHRIMP

281 ± 3

Hu et al., 2006

Altay

47°50′N, 87°55′E

Sillimanite gneiss

Monazite

Th–U–Pb CHIME

262 ± 10

Zheng et al., 2007

Fuyun

46°57′N, 89°38′E

Granulites

Zircon

SHRIMP

255 ± 2

Chen et al., 2006

Skarn

Zircon

LA-ICP-MS

250 ± 2

Wan et al., 2012

Metamorphism

Mengku Iron Mine

Table. 2 Average trace element concentrations in the Talate deposit Sample

Mgt type

FeO(wt. %)

MgO

Al2O3

SiO2

11TL-26

Magmatic

N=10

Min

90.0

18

985

37

117

21

1.72

788

0.08

1.30

0.00

15

hydrothermal

Max

90.8

18

985

222

1885

65

132

2316

0.90

18

0.40

Disseminated

Average

90.4

18

985

130

887

53

32

1442

0.33

4.78

Median

90.4

18

985

130

876

57

12

1434

0.26

2

1

2

2

10

10

10

10

n

Ti

V

Cr

Mn

Co

Ni

Pb

Zn

Bi

Nb

Y

Co/Ni

Ni/Cr

0.02

0.00

0.00

0.01

0.02

526

21.98

0.05

0.11

0.32

3.84

0.04

71

2.47

0.01

0.02

0.13

0.72

2.56

0.00

20

0.17

0.00

0.00

0.13

0.20

10

10

10

10

10

10

10

10

10

11TL-171

Magmatic

Min

92.7

36

159

122

411

125

3.78

1165

0.41

0.41

0.00

34

0.09

0.00

0.00

0.56

0.01

N=10

hydrothermal

Max

92.9

72

224

154

768

180

319

2678

3.16

3.72

207.40

1871

2173

2.69

1.45

5.98

0.18

Disseminated

Average

92.8

54

191

138

586

153

112

1562

1.91

1.43

21.50

581

732

0.73

0.42

1.81

0.06

Median

92.8

54

191

138

552

154

87

1352

2.11

0.96

0.65

360

512

0.51

0.18

1.25

0.02

2

2

2

2

10

10

10

10

10

10

10

10

10

10

10

10

10

n 11TL-22

Magmatic

Min

86.1

66

299

32

581

120

0.94

1086

0.74

0.69

0.00

46

0.04

0.00

0.00

0.56

0.04

N=10

hydrothermal

Max

88.6

66

429

1551

992

254

34

1517

4.51

1.70

3.48

148

1884

0.71

0.78

5.14

1.80

Disseminated

Average

87.3

66

364

791

792

145

9.41

1394

2.80

1.46

0.50

78

256

0.16

0.09

2.09

0.45

Median

87.3

66

364

791

766

128

5.08

1439

2.41

1.54

0.01

65

24

0.02

0.01

1.60

0.28

2

1

2

2

10

10

10

10

10

10

10

10

10

10

10

10

10

n 11TL-19

Hydrothermal

Min

91.2

48

9.33

101

151

115

7.93

2157

0.00

4.74

0.00

25

0.06

0.00

0.00

0.00

0.09

N=10

Disseminated

Max

92.9

48

173

191

266

134

70

3138

0.07

7.19

1.88

1725

7275

0.01

0.06

0.01

0.91

Average

92.0

48

91

146

197

123

21

2492

0.02

6.44

0.22

229

836

0.00

0.01

0.00

0.46

Median

92.0

48

91

146

192

124

13

2412

0.02

6.52

0.00

32

0.25

0.00

0.00

0.00

0.48

n

2

1

2

3

10

10

10

10

10

10

10

10

10

10

10

10

10

11TL-20

Hydrothermal

Min

91.8

18

61

185

296

104

7.94

1677

1.12

3.11

0.00

12

0.00

0.00

0.00

0.23

0.03

N=10

Disseminated

Max

92.6

162

126

212

970

134

164

4454

9.93

5.35

0.02

70

0.82

0.06

27

2.53

0.48

Average

92.2

90

93

199

486

119

52

3018

3.85

4.50

0.00

40

0.33

0.02

2.74

0.94

0.25

Median

92.2

90

93

199

454

120

35

3072

2.64

4.61

0.00

41

0.29

0.01

0.02

0.57

0.24

2

2

2

2

10

10

10

10

10

10

10

10

10

10

10

10

10

n 11TL-27

Hydrothermal

Min

91.3

30

243

122

100

131

32

2020

0.12

2.83

0.00

9

0.00

0.00

0.00

0.02

0.01

N=10

Disseminated

Max

93.1

282

476

244

520

134

244

3268

1.61

5.17

0.01

31

0.06

0.02

0.04

0.57

0.14

Average

92.2

156

359

183

296

132

97

2410

0.45

3.86

0.00

18

0.03

0.00

0.01

0.13

0.06

Median

92.2

156

359

183

290

132

76

2271

0.30

3.80

0.00

18

0.03

0.00

0.01

0.08

0.05

2

2

2

2

10

10

10

10

10

10

10

10

10

10

10

10

10

n 11TL-30

Hydrothermal

Min

91.6

60

28

26

300

87

6.23

2011

1.63

2.34

0.00

12

0.01

0.00

0.00

0.31

0.08

N=10

Disseminated

Max

92.1

156

79

159

735

209

47

3940

13.48

6.22

0.00

65

0.64

0.09

0.07

4.04

1.00

Average

91.9

108

54

93

574

131

21

2619

6.08

4.07

0.00

29

0.17

0.02

0.02

1.65

0.29

Median

91.9

108

54

93

587

129

17

2400

6.60

3.87

0.00

24

0.13

0.01

0.01

1.40

0.21

2

2

2

2

10

10

10

10

10

10

10

10

10

10

10

10

10

Min

91.3

78

93

42

216

184

7.09

928

0.00

56

0.00

38

0.06

0.00

0.00

0.00

0.82

Max

91.4

144

219

42

697

386

115

3164

0.23

188

0.01

107

1003

0.22

0.15

0.00

13.49

Average

91.3

111

156

42

423

285

34

2473

0.03

97

0.00

50

126

0.03

0.05

0.00

4.81

Median

91.3

111

156

42

420

289

23

2719

0.01

94

0.00

45

10.25

0.01

0.02

0.00

4.43

2

2

2

1

10

10

10

10

10

10

10

10

10

10

10

10

10

n 11TL-46 N=10

Massive

n

11TL-29 N=10

Massive

Min

92.0

66

145

90

32

67

0.00

2358

1.29

52

0.00

43

0.03

0.00

0.00

0.00

0.00

Max

92.1

66

145

249

289

95

52

4288

7.82

539

0.93

1249

405

0.01

0.35

0.09

343.24

Average

92.0

66

145

169

141

81

12

3165

2.29

167

0.13

224

57

0.00

0.08

0.02

61.72

Median

92.0

66

145

169

121

80

2.81

3153

1.53

94

0.02

87

1.49

0.00

0.01

0.02

29.61

2

1

1

2

10

10

10

10

10

10

10

10

10

10

10

10

10

n

The concentration of Fe, Mg, Al and Si are from EPMA

Highlights The Talate Talate Pb-Zn (-Fe) is located in Abagong polymetallic belt of the Chinese Altay (NW China). The Talate magnetite comprises the igneous / hydrothermal disseminated and massive types. Fluid-rock interaction has played an important role in trace element variations during the multiple stages of alteration and mineralization. The textural and trace element features of the Talate magnetite are analogous to those of typical Ca-skarn Fe deposits worldwide.

29