Evolution of the carbonatite Mo-HREE deposits in the Lesser Qinling Orogen: Insights from in situ geochemical investigation of calcite and sulfate

Ore Geology Reviews 113 (2019) 103069

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Evolution of the carbonatite Mo-HREE deposits in the Lesser Qinling Orogen: Insights from in situ geochemical investigation of calcite and sulfate

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Tian Baia, Wei Chena, , Shao-Yong Jianga,b a State Key Laboratory of Geological Processes and Mineral Resources, Collaborative Innovation Center for Exploration of Strategic Mineral Resources, China University of Geosciences, Wuhan 430074, China b Faculty of Earth Resources, China University of Geosciences, Wuhan 430074, China

A R T I C LE I N FO

A B S T R A C T

Keywords: Carbonatite Mo-HREE deposits Calcite Sulfate Lesser Qinling Orogen

The Early Mesozoic Huanglongpu and Huangshui’an carbonatites in the Lesser Qinling Orogen are unique as they are associated with economic molybdenite mineralization and relatively enriched in heavy rare earth elements (HREE) compared to typical carbonatites. The carbonatites are composed of dominant calcite, quartz, sulfate (barite-celestite series), K-feldspar, and minor sulfides (molybdenite, galena, pyrite, sphalerite), rare earth minerals (monazite-(Ce), bastnasite-(Ce), parisite-(Ce), parisite-(Y), aeschynite-(Ce) and allanite-(Ce)), Nb oxides and silicates. The Lesser Qinling carbonatites formed in three mineralization stages, i.e., an early quartzK-feldspar stage (I), a middle sulfide-rare earth mineral stage (II), and a late sulfate-biotite stage (III). The δ13C (−4.78 to −6.93‰) and δ18O (7.10 to 9.48‰) for calcite from the Lesser Qinling carbonatites generally plot within the primary carbonatite field. Bulk rock trace element compositions display strong enrichments of U, Pb, Mo and HREE compared to typical carbonatites. In situ Sr isotopic compositions of calcite overlap that of sulfate for both Huanglongpu and Huangshui’an carbonatites. Huangshui’an calcite and sulfate are characterized by 87 Sr/86Sr ratios of 0.70579–0.70640, which are slightly enriched compared to those (0.70498–0.70582) for Hunglongpu calcite and sulfate. Calcite from the Lesser Qinling carbonatites display variable chondrite normalized REE patterns, with the (La/Yb)CN ratios (0.30–12.9) and REE abundances (323–3840 ppm) decreasing from early to late stages. In addition, calcite with HREE enrichments of 69.2–386 ppm is the dominant mineral that controls the HREE budget of these carbonatites. Sulfate shows an extremely light REE (LREE) enriched pattern [(La/Yb)CN > 5677] with REE contents ranging from 706 to 4027 ppm. Combined with other trace element abundances (e.g., Pb) within calcite, the variable REE contents can be explained by distinct mineralization at different evolution stages. The late stage HREE enrichment within calcite can be explained by intense sulfate mineralization.

1. Introduction The Qinling Orogen is located in the central part of China, which separates the Yangtze Craton and the North China Craton (Chen et al., 2017; Li and Pirajno, 2017). It is well endowed with mineral resources and hosts one of the world’s most important Mo provinces with a total reserve of ~6 Mt Mo metal (Mao et al., 2008; Deng et al., 2016; Li and Pirajno, 2017). Most of the molybdenum deposits are associated with Late Mesozoic (Late Jurassic-Early Cretaceous) porphyry and porphyryskarn systems (Yang and Wang, 2017), and the majority of late Mesozoic deposits are located in the northeastern part of the Qinling Orogen (Li and Pirajno, 2017). The Jurassic-Cretaceous Mo mineralization is believed to be related to tectonic reactivation and lithospheric thinning of eastern China, which was induced by underthrusting of the Paleo⁎

Pacific plate beneath eastern China (Mao et al., 2008). Recently, increasing amounts of Triassic Mo mineralization have been identified in the Qinling Orogen, including the porphyry molybdenum deposits concentrated in the western and middle part of the Qinling Orogen (e.g., Wenquan; Qiu et al., 2017), orogenic-type Mo quartz veins in the northeastern part of the Qinling Orogen (e.g., Zhifang and Dahu; Ni et al., 2012; Deng et al., 2016; Jian et al., 2015), and carbonatite related Mo deposits in the Lesser Qinling Orogen (e.g., Huanglongpu, Huayangchuan and Huangshui’an; Fig. 1; Xu et al., 2007, 2010, 2011; Huang et al., 2009; Song et al., 2015, 2016; Smith et al., 2018). In addition, the Triassic also marks the important Au mineralization period in the Qinling-Dabie Orogen (e.g., Liziyuan Au deposit; Yang et al., 2013; Jian et al., 2015). The Triassic Au-Mo mineralization in the Qinling Orogen is related to the final collision between the Yangtze

Corresponding author. E-mail addresses: [email protected] (W. Chen), [email protected] (S.-Y. Jiang).

https://doi.org/10.1016/j.oregeorev.2019.103069 Received 4 January 2019; Received in revised form 4 July 2019; Accepted 6 August 2019 Available online 08 August 2019 0169-1368/ © 2019 Elsevier B.V. All rights reserved.

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Fig. 1. (a) Geological map of the carbonatite Mo-HREE deposits in the Qinling orogenic belt (modified from Song et al., 2016); (b–d) field observations of the Lesser Qinling carbonatite veins with observed mineral phases identified in the field in (d). Abbreviations: MF = Machaoying Fault, SS = Shangdan Suture, MS = Mianlue Suture.

(Dasgupta et al., 2004; Yaxley and Brey, 2004; Shatskiy et al., 2017), immiscible liquids from silicate magma with enriched CO2 (Halama et al., 2005), or products of extensive fractionation from a CO2-rich silicate magma (Harmer and Gittins, 1998). The fractionated carbonatite melt can be highly enriched in most incompatible elements, and carbonatites serve as the most important resources for the supply of

Craton and the North China Craton and the subsequent post-collisional extension (Jian et al., 2015; Li and Pirajno, 2017). Carbonatite and associated silicate rocks are important for mineral resources such as REE and Nb (e.g., the Bayan Obo REE-Nb-Fe deposit and Mountain Pass REE deposit; Smith et al., 2016). Carbonatites are formed as low degree partial melts of carbonated peridotite or eclogite 2

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LREE (defined as atomic mass smaller than Eu; Chakhmouradian and Wall, 2012; Smith et al., 2016). The Lesser Qinling carbonatites (Huanglongpu, Huangshui’an, Huayangchuan and Jialu) are quite unique since they contain significant amount of economical molybdenite mineralization and serve as one of the important molybdenum deposits in the east Qinling-Dabie orogenic belt (Mao et al., 2011; Li and Pirajno, 2017). In addition, both bulk carbonatite and dominant calcite display relatively flat chondrite normalized REE patterns with strong HREE (defined as atomic mass greater than Gd) enrichments, which is distinct compared to most carbonatites worldwide, which are typically LREE enriched (Xu et al., 2007; Song et al., 2015, 2016; Smith et al., 2018). These carbonatite veins contain calcite (> 50 vol%) and quartz (30–50 vol%) as the dominant minerals. The enrichment of both Mo and HREE in the early Mesozoic carbonatite vein remains unresolved. Huang et al. (2009) proposed that Lesser Qinling carbonatites originated from the fractional crystallization of the alkaline silicate-carbonate melt forming from partial melting of the enriched lithospheric mantle in a post-collisional extensional setting during the late Triassic, and the enrichment of Mo and Pb was inherited from the mantle domain EM1. Alternatively, the Huanglongpu carbonatites were considered to form by the melting of a subducted carbonate-bearing slab, and the magma metasomatized the thickened eclogitic lower crust that resulted in high levels of HREE and Mo (Song et al., 2016). Moreover, molybdenum and silica enrichment in the Huanglongpu carbonatite veins was believed to be amplified by the intense fractionation of the cumulate calcite, non-silicate minerals, and a fluid strongly enriched in LREE, Mo, Pb and S (Xu et al., 2007, 2010; Song et al., 2015). Alteration with different ligands present (e.g., Cl−, CO32−, SO42−) was suggested to account for the LREE-HREE fractionation in the Huanglongpu carbonatite veins (Smith et al., 2018). Here we focus on a detailed mineralogical investigation of the Lesser Qinling carbonatites (both Huanglongpu and Huangshui’an) combined with in situ geochemical and isotopic analyses of the dominant minerals. We aim to conduct a detailed trace element and Sr isotopic investigation of the dominant calcite and sulfate within these unique carbonatite veins and provide constrains for the evolution of the carbonatite and give hints for Mo and HREE enrichments.

intermediate to felsic meta-volcanic rocks (Gao et al., 1998). The Xiong'er Group is overlain by the Meso- to Neoproterozoic Guandaokou and Luanchuan Groups which are composed of metasedimentary rocks, carbonate and clastic rocks, sandstone, conglomerate, shall, quartzite, phyllite, trachyandesite and trachyte (Xu et al., 2011; Jian et al., 2015). The Huanglongpu carbonatite consists of the Dashigou, Yuantou, Qinlongtou, and Taoyuan Mo deposits, which are all situated in the Luonan county of the Shaanxi province. Carbonatite veins intruded into the Mesoproterozoic volcanic, carbonate and clastic rocks except for those in Yuantou that intruded into the Neoarchean Taihua gneiss (Song et al., 2015). The Dashigou carbonatite occurs in veins that discontinuously extend for 6 km, controlled by the main fault in the NE direction, and single veins reach the length of several to hundreds of meters (Fig. 1b–d). The Dashigou deposit has a molybdenite Re-Os age of 221.5 ± 0.3 Ma (Stein et al., 1997), and molybdenite from the Yuantou deposit yielded a consistent Re-Os age of 225.0 ± 7.6 Ma (Song et al., 2015). Monazite from Huanglongpu (Dashigou) was dated with weighted mean U-Pb and Th-Pb ages of 208.9 ± 4.6 Ma and 213.6 ± 4.0 Ma, respectively (Song et al., 2016). Dashigou is a large Mo deposit with reserves of 8.9 × 104 t and a grade of 0.075–0.114 % (Song et al., 2015), and it has been open-pit mined in the recent past years. Taoyuan deposit has a Mo reserve of 3.8 × 104 t with a grade of 0.041–0.096 %, whereas the reserves for the rest Mo deposits are not reported (Song et al., 2015). The Huangshui’an carbonatite, located in the Songxian county of Henan province, occurs in veins that are controlled by a main fault in the NW direction and intruded into the Neoarchean Taihua gneiss (Huang et al., 2009). The molybdenite-bearing carbonatites from Huangshui’an were determined with a Re-Os age of 208.4 ± 3.6 Ma (Cao et al., 2014). Huangshui’an holds a Mo reserve of 19.86 × 104 t with an average grade of 0.082% (Cao et al., 2014). The carbonatite veins usually reach the length of 100–379 m with an average thickness of 20–30 m (Huang et al., 2009). Silicification, feldspathization and carbonation are common in the contact between carbonatite and wall rocks (Huang et al., 2009; Cao et al., 2014).

2. Geological background

Major element analyses of bulk rock for the Lesser Qinling carbonatites were determined by PANalytcial Axions Max, X-Ray Flourescence (XRF) Spectrometer at the Aoshi Analytical Company. Fresh Lesser Qinling carbonatite samples were grounded to 200 mesh. Sample powder was fluxed with Na2NO3 and LiBO2 to make homogeneous glass disks for X-ray fluorescence analysis at 1150–1200 °C. Major elements were determined with the standards of SARM-4, NCSDC-73510, NCSDC-73303, GBW-7238, and SARM-32 with analytical uncertainties better than 5%. Whole rock trace element analyses for Lesser Qinling carbonatites were carried out at the State Key Laboratory of Geological Processes and Mineral Resources (GPMR), China University of Geosciences (Wuhan). About 50 mg of powered sample was dissolved in high-pressure Teflon bombs using a HF + HNO3 mixture. Detailed sample-digesting procedure for trace element analyses by ICP-MS was given in Liu et al. (2008a). The trace elements were measured by an Agilent 7500a ICP-MS with the rock standards of AGV-2, BCR-2, BHVO-2 and RCG-2. Duplicate analyses of samples and rock standards suggest the analytical precision is generally better than 5% and the accuracy is better than 10%. In situ trace element compositions for calcite, barytocelestite and barite in 100 μm thick thin sections were determined with a RESOlution 193 nm Excimer ArF laser ablation system coupled to a Thermo iCap-Q inductively coupled plasma mass spectrometer (ICP-MS) at GPMR. Samples and standards were ablated with a repetition rate of 10 Hz, laser spot size of 33 μm and energy density of 3–5 J/cm2. Approximately every ten sample analyses were bracketed by a set of NIST612, BIR-1G, BCR-2G and BHVO-2G standards. The detailed

3. Analytical methods

The Qinling orogenic belt, located in the central part of China, is the suture zone between the North China Craton and the Yangtze Craton and stretches in west to east orientation. It constitutes a significant part of the central orogenic belt in China. The Qinling orogen is separated into four tectonic unit parts, the Lesser Qinling orogenic belt, the North Qinling orogenic belt, the South Qinling orogenic belt and the Songpan fold belt at the northern margin of the Yangtze Craton (Fig. 1a). These are separated by main sutures including the Machaoying fault, the Shangdan suture and the Mianlue suture from north to south, respectively (Fig. 1a). The Qinling orogenic belt formed by multi-stage collision between the North China Craton and the Yangtze Craton, and the final Triassic collisional orogeny occurred along the Mianlue suture between 242 and 227 Ma (Wu et al., 2006; Dong and Santosh, 2016). During the late Triassic, the orogen evolved into a post-collisional extensional domain with emplacement of many post-collisional intrusions including lamprophyre dikes, rapakivi-textured dikes and granitic rocks (Qin et al., 2010; Jian et al., 2015). The lesser Qinling orogenic belt lies within the Huaxiong Block that is located at the southern margin of the North China Block (Fig. 1a). The Huaxiong Block is composed of Archaean amphibolite to granulite faces of the Taihua Group (2806–2841 Ma; Kröner et al., 1988) and granite–greenstone of the Dengfeng terrain (2512 Ma; Kröner et al., 1988). The majority of the early Mesozoic Mo deposits in the Qinling orogenic belt are hosted within the Archean Taihua terrain (Fig. 1a). In addition, The Huaxiong Block is unconformably overlain by the Mesoproterozoic (1780–1770 Ma) Xiong'er Group which composes of 3

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analytical methods are similar to that described in Liu et al. (2008b) and Chen et al. (2011). All off-line integration of background and analytical signals and drift correction and quantitative calibration for trace element analyses were reducted using ICPMS DataCal (Liu et al., 2008b). Time-resolved analytical signals for each mineral analysis were carefully checked. Acquisitions were discarded with anomalous signal changes in the time resolved signal spectral that indicate ablation of a different phase (i.e., inclusion). The analytical uncertainties for most trace elements in calcite and sulfate are within 10%, and better than 5% for REEs (Liu et al., 2008b; Chen et al., 2011). The carbon and oxygen isotopic compositions for calcite separates were determined at GPMR, using a Thermo MAT-253 stable isotope ratio mass spectrometer (IR-MS). The detailed procedure of conventional orthophosphoric acid digestion was reported in McCrea (1950). Approximately 80 to 100 μg of calcite powder and 0.15 ml of concentrated H3PO4 (“150%”) were placed in sealed tubes. Carbon and oxygen isotope data were reported in per mil notation (‰) using standard δ notation as δ18O and δ13C values relative to the Vienna standard mean ocean water (V-SMOW) and Vienna PeeDee belemnite (V-PDB), respectively. The precision of δ18O and δ13C values of repeated analyses of both GBW04416 and GBW04417 carbonate standards and samples are better than ± 0.2‰ and ± 0.1‰ (2 s), respectively. In situ Sr isotopic compositions for calcite, barytocelestite and barite were analyzed using the RESOlution 193 nm laser ablation system coupled to a Nu Plasma II Multi Collector (MC) ICP-MS at GPMR. The measurements involved corrections of critical spectral interferences that included Kr, Rb, and doubly charged REEs (e.g., Ramos et al., 2004; Paton et al., 2007). Detailed methods follow those described in Chen and Simonetti (2014) and Chen et al. (2018). Analyses of calcite and sulfate were carried out using spot sizes of 75 μm and 15 μm, respectively, with a repetition rate of 10 Hz and an energy density of ~5–8 J/cm2. Every 5 to 7 sample analyses were bracketed by an analysis of an in-house coral standard as the external standard to check the analytical reliability and stability. The obtained Sr isotopic composition for the coral standard is 0.70915 ± 0.00005 (2σ, n = 30), which is similar to the isotopic value of 0.70923 ± 0.00002 determined by a Finnigan Triton TIMS at the State Key Laboratory for Mineral Deposits Research in Nanjing University (Chen et al., 2018).

Table 1 Summary of the major mineral paragenesis of Lesser Qinling Carbonatites.

celestite series) precipitate in the late stage as the increase of oxygen fugacity. The most dominant calcite crystallizes over all the mineralization stages from early to late. Early quartz-K-feldspar stage (I): This stage is dominated by the crystallization of white-colored coarse-grained anhedral quartz (> 1cm; Fig. 2a, b) and coarse-grained euhedral calcite (Cal-I; > 1cm; Fig. 2a, b), associating with minor K-feldspar and a small quantity of magnetite and sulfides including pyrite and galena (Fig. 2a). As shown in both hand specimens (Fig. 2b) and petrographic images (Fig. 2c–f), finer grained middle stage calcite (Cal-II) crystallizes along the fractures or grain boundaries of the coarse-grained calcite (Cal-I) and quartz in the early stage. Some early anhedral quartz generally displays a jagged rim (Fig. 2e). K-feldspar occurs disseminated within the veins, and most abundantly along the vein margins. Molybdenite rarely occurs in the early mineralization stage, whereas pyrite and galena start to precipitate in this stage. Middle sulfide-rare earth mineral stage (II): This stage is the dominant molybdenite deposition stage. Abundant fine-grained calcite (Cal-II) with the grain size of 0.5–2 mm crystallizes, together with sulfides (molybdenite, pyrite, galena), rare earth minerals (monazite-(Ce), parisite-(Ce), allanite-(Ce)), pyrochlore super-group minerals (oxyuranobetafite and uranpyrochlore) and minor quartz (Fig. 3a–o). It is worth noting that calcite (Cal-II) in this stage is characterized by a finer grained size compared to the early stage (Fig. 2b–d, Fig. 3). Both sulfides and rare earth minerals are dominantly identified in the middle stage (Fig. 3b–i). The rare earth mineral association includes both light rare earth minerals such as monazite-(Ce), allanite-(Ce), bastnaesite(Ce) and parisite-(Ce) and heavy rare earth minerals such as xenotime(Y) and parisite-(Y) (Fig. 3b, d). Monazite-(Ce), as the earliest light rare earth mineral, either disseminates along the calcite grain boundaries (Fig. 3b) or occurs associated with xenotime-(Y) (Fig. 3d). The rim of

4. Mineralogy and paragenesis The mineralized carbonatite veins at both Huanglongpu and Huangshui’an mainly consist of fine- or medium- grained pink euhedral calcite and anhedral quartz, which are the dominant gangue minerals and make up > 50 vol% and 35 vol%, respectively (Table 1). The sulfate minerals, in barite-celestite series, are among the most important minor mineral phases (approximately 8 vol% on average) within the carbonatite veins. Pyrite, molybdenite and galena are the most common sulfide phases. Other accessory minerals include K-feldspar, biotite, augite, aegirine, magnetite and rare earth minerals (e.g., monazite-(Ce), bastnaesite-(Ce) and parisite-(Ce)). Nb and U oxides (e.g., oxyuranobetafite and uranpyrochlore) can be found in these carbonatites as well, which were also reported in Smith et al. (2018). Molybdenite is commonly disseminated within the dominant calcite and quartz phases or occurs as thin, platy aggregates/films in the boundary layer between carbonatite veins and wall rocks. Of interest, it also shares a common association with pyrochlore super-group minerals, uraninite, rare earth minerals (including monazite-(Ce), allanite-(Ce), bastnaesite-(Ce), xenotime-(Y), parisite-(Ce) and parisite-(Y)), and/or inequigranular sulfate. Three mineralization stages are identified for the Lesser Qinling carbonatite veins (both Huanglongpu and Huangshui’an) as shown in Table 1. In general, quartz and other silicates (e.g., K-feldspar) crystallized in the early mineralization stage. Sulfide and REE-minerals mostly precipitate in the middle stage, whereas sulfate minerals (barite4

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Fig. 2. Petrographic images of the early mineralization stage. (a) coarse-grained euhedral calcite in the early stage associated with coarse-grained anhedral quartz; (b) fine-grained calcite in the middle stage crystallizes in the fracture of the coarse-grained calcite in the early stage; (c–d) quartz and calcite in the middle stage occurs in the fracture and grain boundary of calcite in the early stage; (e–f) early stage quartz with jagged rim and calcite in the middle stage crystallize along the fracture or grain boundary of the early quartz. Abbreviations: Cal-I = calcite in the early stage, Cal-II = calcite in the middle stage, Pcl = pyrochlore, Qtz = quartz.

some monazite-(Ce) grains is altered to apatite and parisite-(Y) possibly due to the reactions of

Sparse celestite and barite start to crystallize in the middle stage (Fig. 3l–n). Moreover, subhedral quartz in the middle stage is overgrown by a layer of aegirine (Fig. 3m, n) due to the reaction of

3REE(PO4 ) + 5Ca2 + + F− = Ca5 (PO4 )3 F + 3REE3 + Monazite

Apatite

8SiO2 + 2Ca2 + + CO32 − + 2Na+ + 2Fe2 + + 2Mg2 + + 10OH− Quartz ⏟ fluid Hydrothermal

and

REE(PO4 ) + Ca2 + + 3CO32 − + 2F− = Ca(REE,Y)2 (CO3 )3 F2 + 2PO34− Monazite

= 4(Na, Ca)(Fe, Mg)Si2 O6 + 2CO2 + 5H2 O

parisite - (Y)

Aegirine

Autometasomatism could be a common process for the rare earth mineralization within the Lesser Qinling carbonatites (Smith et al., 2018). For instance, parisite-(Ce) identified within both allanite-(Ce) and synchysite-(Ce) crystals is possibly the result of autometasomatism as shown in Fig. 3e, f. The majority of molybdenite precipitates in the middle stage, which is densely disseminated along the fine-grained calcite (Cal-II) boundary or is commonly associated with oxyuranobetafite, parisite-(Ce), allanite-(Ce) and pyrite (Fig. 3c, g, h, l). Pyrite and galena precipitate slightly earlier than rare earth minerals, whereas monazite is commonly cross cut by fractures containing molybdenite in these rocks (Fig. 3h). Exsolution of betafite and uraninite can be identified in the fracture and/or grain boundary of oxyuranobetafite (Fig. 3j), which is possibly due to the reaction of

Minor augite crystallizes in association with quartz, altered monazite and parisite-(Ce) (Fig. 3o). Late sulfate-biotite stage (III): This stage is dominated by the mineralization of sulfate (barite-celestite series), fine-grained euhedral or anhedral calcite (Cal-III) and biotite, associated with decreasing abundances of molybdenite and quartz (Fig. 4a-l). The dark grey vein as shown in Fig. 4b composes of fine-grained anhedral calcite (Cal-III) and quartz, which forms in a fracture of the early and middle stage calcite (Cal-I and Cal-II). The late stage calcite (Cal-III) is the finest in these Lesser Qinling carbonatites, whose grain size is smaller than 1 mm (mostly between 0.05 and 0.5 mm; Fig. 4c, d). Sulfate occurs as both coarse-grained disseminates and fine-grained aggregates, and the latter commonly form as veinlets along the grain boundaries of coarsegrained sulfate and/or carbonate (Fig. 4e, f). Quartz together with altered biotite is identified along the grain boundary of calcite (Cal-III) (Fig. 4g). A small quantity of molybdenite occurs in the shape of radial aggregates filling sparsely in the fractures of calcite (Cal-III; Fig. 4h, i) or earlier pyrite and galena (Fig. 4j) and sulfate (Fig. 4j, k, l). In addition, overgrowth of hematite on the earlier pyrite and the mineralization of wulfenite associated with molybdenite both suggest the increase of oxygen fugacity (Fig. 4k, l). In the late stage, less quartz and silicate minerals crystallize compared to the early stage. Hypergene anhydrite can be found in the late stage, which marks the end of the endogenic mineralization.

(Ux , Ca1 − x−y , REE y )2 (Ti, Nb)2 O6 (O, OH) + 2xO2 + 2(x+ y)Ca2 + Oxyuranobetafite

= Ca2 (Ti, Nb) 2 O6 (OH, O) + 2xUO2 + 2yREE3 + Betafite

Uraninite

In addition, chevkinite-(Ce) is altered to pyrochlore, titanite and Nbbearing rutile as shown in Fig. 3k possibly due to the reaction of

2(REE, Ca)4 (Ti,Fe, Nb)5 (Si2 O7 )2 O8 + O2 = 2(Ca, REE)2 (Nb, Ti)2 O7 Chevkinite − (Ce)

Pyrochlore

+ 4(Ca, REE)(Ti,Fe,Nb)SiO5 Titanite

+ 2(Ti,Nb,Fe)O2 + 4SiO2 Rutile

Quartz

5

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Fig. 3. Petrographic images of the middle mineralization stage. (a) hand specimen with dominant pink calcite and pyrite; (b) REE mineralization of monazite disseminated within dominant calcite; (c) molybdenite mineralization in the middle stage; (d–o) back scattered electron (BSE) images of middle mineralization stage; (d–f) various REE mineralization and some display autometasomatism; (g–l) molybdenite mineralization associated with pyrochlore super-group and rare earth minerals; (j) oxyuranobetafite is altered to betafite and uraninite; (k) Ce-bearing cervandonite is metasomatized into titanite and rutile; (m–n) aegirine overgrows the euhedral hexagon quartz; (o), anhedral quartz associated with augite and autometasomatism of monazite-(Ce) into Ce-bearing parisite. Abbreviations are consistent with Fig. 2, and additions are listed in the following: Aeg = aegirine, All-(Ce) = Ce-bearing allanite, Ap = apatite, Aug = augite, Bet = betafite, Bet-(U) = oxyuranobetafite, Brt = barite, Cls = celestite, Hem = hematite, Py = pyrite, Mnz-(Ce) = Ce monazite, Mol = molybdenite, Par-(Y) = Y-bearing parisite, Par-(Ce) = Cebearing parisite, Rtrutile, Rt-(Nb) = Nb-bearing rutile, Syn-(Ce) = Ce-bearing synchysite, Ttn = titanite, Ura = uraninite, Xen = xenotime. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

5. Results

deposits (Fig. 6b). Thus, these chondrite normalized REE patterns for the Lesser Qinling carbonatites display flatter trends with lower (La/ Yb)CN ratios (4.33–37.34) compared to that of typical carbonatites (Fig. 6b; Chakhmouradian et al., 2016).

5.1. Bulk rock chemical compositions for Huanglongpu and Huangshui’an carbonatites The bulk rock major element data for the Lesser Qinling carbonatite veins are presented in the Supplementary Table 1 and Fig. 5. Based on the carbonatite classification diagram of Gittins and Harmer (1997), most of the Lesser Qinling carbonatite samples plot in the calciocarbonatite field and on the trend defining the mineralization of calcite and apatite (Fig. 5). Compared to typical anorogenic carbonatites, Lesser Qinling carbonatites are abundant in BaO and SrO with the contents as high as 10.53 wt% and 14.58 wt% (Supplementary Table 1), respectively, which is dominated by the late stage sulfate mineralization. In addition, some of the early carbonatite veins contain abundant quartz with high SiO2 content (e.g., up to 50.6 wt%), which is almost outside of the definition of carbonatite that contains over 50 modal percent of carbonate (Le Maitre 2002). These are similar to the widedistributed quartz veins in the Qinling Orogen (e.g., Dahu, Zhifang; Ni et al., 2012; Deng et al., 2016). The bulk rock trace element compositions for the carbonatite samples from Lesser Qinling are listed in the Supplementary Table 2 and shown in Fig. 6a, b. They show relatively consistent primitive mantle normalized trace element patterns in the spider diagram (Fig. 6a). In general, these patterns display strong positive anomalies of Ba, U, Mo and Pb and negative anomalies of the high-field-strength-elements (HFSEs) such as Nb, Ta, Zr and Hf, which are distinct compared to both typical carbonatites and the Mo-porphyry veins in the Qinling orogen (Fig. 6a). Compared to the bulk rock compositions for worldwide carbonatites, the carbonatite veins display strong enrichments of U, Pb, Mo and HREEs (including Y) (Fig. 6a). Compared to the Mo porphyry veins in the Lesser Qinling Orogen, these are characterized by the depletion of HFSEs (e.g., Th, Nb, Ta, Zr, Hf) and show enrichments in most of the incompatible elements (Fig. 6a; Chen et al., 2017). The abundances of Nb, Th and U show large variation ranging from 0.17 to 166 ppm, 0.11 to 67 ppm and 0.33 to 145 ppm, respectively. The abundances and distribution of these elements are dominantly controlled by the pyrochlore super-group minerals as shown in Table 1 and Fig. 3. Huanglongpu carbonatite in general shows slightly higher contents of the incompatible elements compared to Huangshui’an carbonatite (Fig. 6a). Molybdenum contents within the bulk Huanglongpu and Huangshui’an carbonatites also display large variation that range from 0.49 to 2309 ppm, which suggests the heterogeneous distribution of molybdenite among samples forming in different stages (Figs. 2–4). The chondrite normalized REE patterns do show variations between the Lesser Qinling carbonatite samples (Fig. 6b), for instance, (La/ Nd)CN vary from 4.33 to 37.34 (Supplementary Table 2). The enrichments of LREE in the Lesser Qinling carbonatite are up to several thousands of ppm (Supplementary Table 2), which is similar to that for typical carbonatites (Fig. 6b). The LREE variation is possibly induced by the variable distribution of rare earth minerals and/or pyrochlore super-group minerals, calcite and sulfate in different mineralization stages (Table 1). Of interest, the bulk trace element compositions display significant HREE (from Ho to Lu) enrichments of several hundreds of ppm (Supplementary Table 2), which is distinct from the relatively depleted HREE signatures in both typical carbonatites and Mo-porphyry

5.2. In situ trace element compositions for dominate calcite and sulfate The trace element compositions of the dominant carbonate and sulfate minerals within the Lesser Qinling carbonatite veins were determined using LA-ICP-MS. Calcite is abundant in Sr and LREE but depleted in HFSEs (Ti, Nb, Zr, Hf, Ta, Th and U) which is similar to the average calcite in typical carbonatites (Supplementary Table 3; Fig. 6c). Of note, calcite within Lesser Qinling carbonatite shows enriched contents of Pb (tens of ppm) and HREE (up to 386 ppm; Supplementary Table 3), which is distinctively more enriched compared to that for the average calcite in typical carbonatites (Fig. 6c). All calcite in Lesser Qinling carbonatites show consistent flat to slightly LREE enriched chondrite normalized REE patterns (Fig. 6d), and the (La/Yb)N ratios vary from 0.30 to 12.94 with the majority smaller than 5 (Supplementary Table 3). In general, Huanglongpu calcite is characterized by a more REE enriched signature (1160 ppm on average) compared to Huangshui’an calcite (681 ppm on average). Moreover, Huangshui’an calcite shows a negative Eu anomaly which is not so significant in the Huangshui’an calcite (Fig. 6d). Of interest, chondrite normalized REE patterns of calcite vary from early to late stage based on the distinct mineral paragenesis (Fig. 6e). The early coarse-grained calcite (Cal-I) is characterized by the highest REE enrichments (1033–1945 ppm) with the largest (La/Yb)CN ratios varying from 3.40 to 5.06 (Fig. 6e). The middle-stage calcite (Cal-II) displays the intermediate LREE enrichments with HREE contents comparable to that for the early stage (Fig. 6e). The average (La/Yb)CN ratio for the middle-stage calcite is 1.95 and average REE content is 680 ppm. The late stage calcite (Cal-III) shows the highest HREE enrichments (202–386 ppm) and associated smallest (La/Yb)CN ratios that vary from 0.30 to 0.78 (Fig. 6e). Calcite forming within different stages in the Lesser Qinling carbonatites displays distinct REE compositions and patterns, and in general LREE contents decrease whereas HREE contents increase from early to late (Fig. 6e). Trace element compositions of sulfate minerals (celestite-barite series) from the Lesser Qinling carbonatites were determined by LAICP-MS as shown in Supplementary Table 3 and Fig. 6f. Sulfate from Lesser Qinling carbonatites display relatively consistent trace element compositions except for several altered sulfate minerals (Supplementary Table 3; Fig. 6f). Similar to calcite, Huanglongpu sulfate is slightly more enriched in REE compared to Huangshui’an sulfate. The chondrite normalized REE patterns reveal that sulfate in the Lesser Qinling carbonatites are enriched in LREE but depleted in HREE and show obvious positive Eu anomalies (Fig. 6f). It is noteworthy that positive correlations were observed between REE and both P and Pb abundances for the sulfate (Fig. 6g, h). The positive correlation between P and REE can be explained by the substitution scheme of REE3+ + P5+ = Ba2+(Sr2+) + S6+. 5.3. C-O-Sr isotope compositions of dominant minerals Carbon and oxygen isotopic data of calcite in Lesser Qinling 7

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Fig. 4. Petrographic images of the late mineralization stage. (a) calcite in the late stage with a sulfate vein; (b-d) calcite in different stages within one sample; (e-f) sulfate occurs as coarse-grained disseminates or fine-grained aggregation in the grain boundary of calcite; (g) altered biotite occurs in the grain boundary of calcite; (h-l) back scattered electron images of the late mineralization stage; (h-i) molybdenite and pyrite associated with sulfate minerals such as barite and celestite; (j) molybdenite mineralized in the fracture or grain boundary of earlier pyrite and galena; (k-l) wulfenite and hematite are identified in the fracture of sulfate. Abbreviations are consistent with Fig. 2&3, and additions are listed in the following: Bi = biotite, Cal-III = calcite in late stage, Gal = galena, Sul = sulfate, Wul = wulfenite.

the field for primary carbonatite as defined by Keller and Hoefs (1995). In situ strontium isotope ratios of calcite and sulfate from the Lesser Qinling carbonatites were reported in Supplementary Table 5. Huanglongpu calcite displays limited 87Sr/86Sr variations from 0.70508 to 0.70549, which are consistent with that of the sulfate (0.70500–0.70582; Fig. 8). Huangshui’an calcite display slightly higher 87 Sr/86Sr ratios that range from 0.70579 to 0.70658, with similar Sr isotopic range recorded in the Huangshui’an sulfate (0.70604–0.70623;

carbonatites are presented in Supplementary Table 4. The carbon isotopic compositions of calcite in the Huanglongpu carbonatite lie in a narrow range between −6.75 and −6.93‰, and the oxygen isotope ratio varies slightly between 8.69 and 9.48‰ (Fig. 7; Xu et al., 2009; 2010). Calcite in the Huangshui’an carbonatite shows slightly higher δ13C and lower δ18O compositions that vary from −4.78 to −5.71‰ and 7.10 to 8.68‰, respectively (Fig. 7). As shown in Fig. 7, both C and O isotopic compositions of the Lesser Qinling carbonatites plot within 8

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precipitation in different mineralization stages. The early mineralization stage (I) is dominated by quartz and calcite (Cal-I) mineralization, whereas calcite (Cal-I) contains the most abundant LREE enrichments (> 1000 ppm; Fig. 6e) and also Pb abundances (> 70 ppm). The coupled decreasing trend of both LREE and Pb within calcite is induced by calcite mineralization. When sulfides (i.e., galena and pyrite) start to precipitate in the early to middle stages, Pb concentration within calcite (Cal-II) decreases significantly from approximately 80 to 40 ppm with insignificant changes in LREE abundances, which is shown as the horizontal trend in Fig. 9a. In the middle stage as shown in Table 1 and Fig. 4, a minor quantity of rare earth minerals such as monazite-(Ce) and parisite-(Ce) start to precipitate, and precipitation of the rare earth minerals cause significant decrease of LREE abundances in calcite (CalII) from approximately 1500 to 500 ppm shown as the vertical trend in Fig. 9a. The LREE mineralization in this stage was also reported previously by Smith et al. (2018). In the late stage, the mineralization is dominantly controlled by sulfate and calcite (Cal-III), and precipitation of both minerals decreases the LREE and Pb abundances within calcite (Cal-III; Fig. 9a). In spite of various rare earth minerals identified in this study and previous investigations (Song et al., 2016; Smith et al., 2018), they contribute little to the bulk REE budgets as stated above. Rare earth minerals within the Lesser Qinling carbonatites mainly occur in the middle stage, which dominantly affect the LREE abundances in the middle stage calcite (Cal-II) (Fig. 9a). As reported in Fig. 6e, the late stage calcite (Cal-III) displays enriched HREE signatures. This is also shown in Fig. 9b, with the significant enrichment of HREE in the range of approximately 100 to 200 ppm. This is possibly induced by the intense sulfate mineralization in the late stage (Fig. 4), which is characterized by significantly high (La/Yb)CN ratios > 10,000 and depleted HREE (Supplementary Table 3; Fig. 6f). The role of sulfate and/or sulfur in the formation of REE deposits might be underestimated in previous studies.

Fig. 5. Lesser Qinling carbonatites plotted on the carbonatite nomenclature defined by Gittins and Harmer (1997). Arrows demonstrate the principal mineralogical controls on the whole-rock composition following Broom-Fendley et al. (2017b).

Fig. 8). The reported Sr isotopic compositions are similar to the reported bulk isotopic compositions of calcite and barytocelestite from the Huanglongpu and Huangshui’an carbonatite veins, respectively (Huang et al., 2009).

6. Discussion 6.1. The evolution of REE enrichment controlled by mineral fractionation Calcite, as the most common and dominant mineral within carbonatites with abundant trace element compositions, has been used to trace REE enrichment and evolution at different mineralization stages (e.g., Moore et al., 2015; Chakhmouradian et al., 2016). Calcite is the dominant carbonate mineral within the Lesser Qinling carbonatites, and it contains higher HREE contents compared to that from typical carbonatites (Fig. 6). A trivial quantity of heavy rare earth minerals was identified dominantly in the middle mineralization stage both in this study and previous investigations (Figs. 2–4; Song et al., 2016; Smith et al., 2018). They contribute little to the bulk HREE budget and partially (approximately 30%) to the bulk LREE budget due to their minor modal distributions. In addition, rare earth minerals within the Lesser Qinling carbonatites mainly occur early in the middle stage, which dominantly affects the LREE abundances in the middle stage calcite (Cal-II). For the rest of the carbonatite, rare earth minerals (e.g., monazite) contribute little to the REE budget. As shown in Supplementary Table 1, the P2O5 content of these rocks is ~0.01 wt%. The trace P abundance in the bulk rock (approximately 50 ppm) suggests that the modal content of monazite can be neglected in these samples. Thus calcite with HREE abundances up to hundreds of ppm serves as the dominant mineral that controls the HREE budget of these carbonatites. Moreover, calcite with LREE abundances of 254–3561 ppm also serves as one of the dominant minerals that controls the LREE budget of these carbonatites, especially in the early and late mineralization stages. As shown in Fig. 6e, calcite displays distinct REE enrichment in different mineralization stages. Of note, late stage calcite (Cal-III) characterized by the highest HREE enrichment is observed in this study and previous investigations (Fig. 6e; Smith et al., 2018). Thus, REE abundances together with other trace element compositions within calcite have the potential to serve as the petrogenetic indicator to trace the evolution of REE enrichment in carbonatites. As shown in the diagram of LREE vs. Pb (Fig. 9a), the chemical signature of calcite varies according to distinct mineral fractionation/

6.2. The role of sulfur in the formation of HREE deposits Giant and large carbonatite related REE deposits are enriched in F and/or P either in the melt or in the final deposition of rare earth minerals as bastnaesite or monazite (Smith et al., 2016), such as Bayan Obo, Mountain Pass, Mushgai Khudag, Amba Dongar and Bear Lodge (Poletti et al., 2016; Smith et al., 2016; Song et al., 2016). Sulfates (barite and celestite) occur as common mineral phases at the known carbonatite-related large REE deposits such as Mountain Pass (Poletti et al., 2016), Mushgai Khudag (Samoilov and Kovalenko, 1983; Smith et al., 2016), Bayan Obo (Song et al., 2018) and also the currently mining Maoniuping REE deposit (Xie et al., 2009, 2015). For instance, based on the detailed melt-fluid inclusion studies, the ore forming fluid for the Maoniuping deposit is considered to be a supercritical CO2-H2O system enriched in Na+, K+ and SO42−, which transported REE and formed the dominant mineral assemblage of calcite, barite, aegirine, arfvedsonite and bastnaesite (Xie et al., 2009, 2015). Sulfate serves as a common ligand in transferring REE in diverse geological settings such as seafloor vent fluids and geothermal hot springs (e.g., Lewis et al., 1998). REE(SO4)2− is the predominate stable species in the hydrothermal fluids that is rich in sulfate, and SO42− as the transferring or complexing ligand displays minimal difference between LREE and HREE complex ion stability (Wood, 1990; Haas et al., 1995; Migdisov and Williams-Jones, 2008). Sulfate in the late mineralization stage from the Lesser Qinling carbonatites is characterized by extremely high (La/Yb)CN ratios and depleted HREE, and sulfate mineralization induces HREE enrichment and LREE depletion in calcite (Fig. 9). Thus, sulfate may serve as an important ligand in transporting REE with minimal fractionation between LREE and HREE, whereas the deposition of sulfate favors LREE significantly compared to HREE in the Lesser Qinling carbonatites. Sulfate induced HREE enrichment has been observed elsewhere in carbonatite complexes. For instance, the barite mineralization associated with apatite (Ap-3) crystallization in the 9

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Fig. 6. Trace element compositions of the bulk carbonatite and dominant minerals. (a) primitive mantle-normalized trace element distribution patterns of the Lesser Qinling carbonatites. Trace element compositions of the calciocarbonatite and porphyry are taken from Woolley and Kempe (1989) and Chen et al. (2017), respectively. Normalization values are from Sun and McDonough (1989); (b) chondrite normalized REE diagram of the bulk carbonatite, normalization values are from McDonough and Sun (1995); (c) trace element geochemistry of calcite normalized by average calcite compositions in carbonatite. Average calcite compositions in carbonatite are calculated by data collected from Chen and Simonetti (2013), Chakhmouradian et al. (2016), Dawson and Hinton (2003), Halama et al. (2005), Ionov and Harmer (2002) and Wu et al. (2011); (d–f) chondrite normalized REE diagrams of the Lesser Qinling calcite (d), calcite in different mineralization stages (e) and sulfate (f), respectively, and normalization values are from McDonough and Sun (1995); (g) and (h) demonstrate positive correlations between REE and both P (g) and Pb (h) within sulfate, respectively.

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Fig. 7. Carbon and oxygen isotopic compositions of calcite within the Lesser Qinling carbonatites. Isotope data of the Huanglongpu carbonatite previously reported is also plotted as a comparison (Xu et al., 2010).

Fig. 9. Trace element compositions of calcite in different mineralization stages. (a) LREE vs Pb; (b) HREE vs LREE.

anomaly relative to those from the granite porphyry along the Lesser Qinling Orogen (Song et al., 2015). Quartz and K-feldspar were believed to represent primary products in the carbonatitic liquid (Song et al., 2015). Thus, carbonate, quartz, K-feldspar and sulfate minerals within the Lesser Qinling carbonatites are considered to form from a common mantle source. The combined Sr-Nd-Pb isotopic composition for the Lesser Qinling carbonatites together with similar aged quartz-vein molybdenum deposits (i.e., Dahu and Zhifang) along the Qinling orogen were plotted in Fig. 10 (Xu et al., 2007, Ni et al., 2012; Song et al., 2015; Deng et al., 2016). The Lesser Qinling carbonatites consist of Sr isotopic composition similar to EM1 (Fig. 10a), whereas the Nd isotopic composition is slightly more radiogenic compared to EM1 (Fig. 10a). As shown in Fig. 10a, Dahu and Zhifang quartz veins contain more radiogenic Sr and Nd isotopic signatures compared to those for the Lesser Qinling carbonatites. Interestingly, these quartz veins display a mixing isotopic signature between the carbonatite inherited upper mantle source that is similar to EM1 and the basement rocks (Taihua and Xiong’er group; Fig. 10). The Lesser Qinling carbonatites display similar 206Pb/204Pb and 208Pb/204Pb ratios compared to the Dahu and Zhifang quartz veins (Fig. 10b, c). The Pb isotopic compositions for the Lesser Qinling carbonatites and Mo-quartz veins can be explained by the mixing of the EM1 mantle endmember and the basement rocks of Taihua and Xiong’er group (Fig. 10d). Hence, the combined C-O-S-Sr-Nd-Pb isotopic compositions for the Lesser Qinling carbonatites suggest the origin from an EM1 like mantle with minor assimilation of the basement rocks (Taihua and Xiong’er group).

Fig. 8. In situ 87Sr/86Sr ratios of calcite and sulfate in the Huanglongpu and Huangshui’an carbonatites.

Songwe Hill carbonatite resulted in the associated HREE enrichment in the late-stage apatite (Broom-Fendley et al., 2017a). Thus fractionation or deposition of sulfate might be a common process in the generation of HREE enrichment within carbonatite complexes. 6.3. Sources for the Lesser Qinling carbonatite The C and O isotopic compositions for these Lesser Qingling carbonatites plot within the field for primary carbonatite (Fig. 7; Keller and Hoefs, 1995), which suggest their pristine origin from the mantle. Quartz in Huanglongpu carbonatites shows consistent O isotopic compositions of 8.1–10.2‰ which are similar to the associated calcite reported in this study (Song et al., 2015). Sulfur isotopic compositions (δ34S) of the carbonatitic liquids calculated using the galena and barite mineral pair are estimated to be around 1‰, which is similar to the mantle-derived value (Schneider, 1970; Huang et al., 1984; Song et al., 2016). As shown by in situ Sr isotope analysis for calcite forming in different stages within Lesser Qinling carbonatites including Huanglongpu and Huangshui’an, it displays Sr isotopic composition in a narrow range (Fig. 8). In addition, the late-stage sulfate also has a similar Sr isotopic composition compared to the calcite (Fig. 8). Previous chemical investigations of K-feldspar and quartz within Huanglongpu indicated lower Zr, Hf and higher HREE abundances and negligible Eu

6.4. Formation model Triassic Au-Mo mineralization along the Qinling orogen is related to the final collision between the North China Craton and the Yangtze Craton, and the subsequent post-collisional extensional process (Jian et al., 2015). During the early Triassic period, Mianlue oceanic crust was subducted beneath the South Qinling Orogen. With the 11

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Fig. 10. Sr, Nd and Pb isotopic features of the Lesser Qinling carbonatites. DMM, HIMU, EM1 and EM2 are the mantle end-member components, as defined by Zindler and Hart (1986). Sr, Nd and Pb isotopic compositions of Dahu and Zhifang deposits in the Lesser Qinling orogenic belt and the host rocks of Taihua and Xiong’er group are plotted as a comparison. Isotope ratios for Dahu and Zhifang are from Ni et al. (2012) and Deng et al. (2016), respectively; isotopic compositions for the Taihua and Xiong’er basement can be found in Huang et al. (1984), Ni et al. (2012) and Zhu et al. (2014).

enrichment of HREE in the late-stage calcite.

continuative collision between the North China Block and the Yangtze Block, lower crust of the South Qinling Orogen was under thrusted beneath the southern margin of the North China Block, leading to the crustal thickening of the Lesser Qinling (Xu et al., 2009; Wu and Zheng, 2013). There is increasing evidence that many of the Mo and Cu-Mo porphyry deposits that supply much of the World’s molybdenum formed in magmatic hydrothermal systems are dominated by vapor and low- to intermediate- density supercritical aqueous fluids, and these fluids were responsible for the transport of a large proportion of the molybdenum to the site of deposition (Zajacz et al., 2008; Lerchbaumer and Audetat, 2012; Seo et al., 2012; Hurtig and Williams-Jones, 2014). Supercritical fluids act as a powerful transporting agent because of increased solubility of trace elements (Zheng et al., 2011; Sheng et al., 2013). Carbonate fluids in orogenic settings such as the Qinling orogenic belt are probably in the supercritical state because of the unusual P-T condition due to the thickened lower crust (Fig. 11). Similarly, the dominant ore-forming fluids for the orogenic Mianning-Dechang carbonatites are considered as a supercritical CO2-H2O system enriched in K, Na and SO42− based on fluid inclusion investigations (Xie et al., 2009). Fluids in supercritical condition display distinct physical and chemical properties. The supercritical fluid could efficiently dissolve and transport not only LILE and LREE but also HREE as well as HFSE (Eckert et al., 1996; Weingartner and Franck, 2005; Sheng et al., 2013). Moreover, silica solubility may increase and complete miscibility may be achieved between hydrous melt and aqueous solutions in supercritical fluids, which may serve as efficient mass-transport agents in the subduction zones (Hermann et al., 2006; Zheng et al., 2011). Thus, these Lesser Qinling carbonatite veins may form as C–H–O supercritical fluids derived from the EM1 like mantle beneath the Lesser Qinling Orogen, which are characterized by the enriched Mo, HREE and Si signature compared to typical anorogenic carbonatites (Fig. 11). Moreover, fractional crystallization/precipitation of certain paragenetic minerals at different mineralization stages further contribute to the

7. Conclusions 1. Three main mineralization stages are identified for the Lesser Qinling carbonatites, including an early quartz-K-feldspar stage (I), a middle sulfide-rare earth mineral stage (II), and a late sulfatebiotite stage (III). 2. Bulk chemical compositions for the Lesser Qinling carbonatites display distinct depletions of HFSEs and enrichments in HREE and Mo. This is distinct from both typical carbonatites and Mo bearing porphyry veins in the Qinling orogenic belt. 3. The chondrite normalized REE patterns for calcite vary from LREE enriched to depleted, whereas sulfates show extremely LREE enriched trends. Calcite from distinct mineralization stages is characterized by different trace element signatures, and late stage HREE enrichment within calcite is caused by intense sulfate mineralization. 4. Based on the mineralogical, chemical and isotopic investigations, the Lesser Qinling carbonatites are believed to originate from the EM1 mantle with minor contamination of Xiong’er and Taihua basement as C–H–O supercritical fluids which are enriched in Mo, HREE and Si, and sulfate precipitation in the late stage further contributes to the HREE enrichment in calcite. Acknowledgements Prof. Cheng Xu from Peking University and Dr. Song Wenlei from Mendel University in Brno are thanked for their help in the field. We appreciate constructive reviews from two anonymous reviewers and also editorial work of editor Huayong Chen. This study is financially supported by the National Key R&D Program of China (No. 2017YFC0602405), the National Natural Science Foundation of China (No. 41530211, 41673035), the Fundamental Research Funds for the 12

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Fig. 11. Formation model of the Lesser Qinling carbonatite related Mo-HREE deposit. (a) shows the geodynamic background in the Qinling Orogenic belt (after Li and Pirajno (2017)) and carbonatite intrusions in the Lesser Qinling; (b) demonstrates the origin of the Lesser Qinling carbonatites possibly as supercritical fluids that are enriched in Mo, HREE and Si, which forms from the EM1 mantle beneath Lesser Qinling.

Central Universities (No. CUGCJ1709) and the special fund from the State Key Laboratory of Geological Processes and Mineral Resources (No. MSFGPMR03-2).

insights into a complex crystallization history. Chem. Geol. 353, 151–172. Chen, W., Simonetti, A., 2014. Evidence for the multi-stage petrogenetic history of the Oka carbonatite complex (Québec, Canada) as recorded by perovskite and apatite. Minerals 4, 437–476. Chen, W., Lu, J., Jiang, S.Y., Ying, Y.C., Liu, Y.S., 2018. Radiogenic Pb reservoir contributes to the rare earth element (REE) enrichment in South Qinling carbonatite. Chem. Geol. 494, 80–95. Chen, Y.J., Wang, P., Li, N., Yang, Y.F., Pirajno, F., 2017. The collision-type porphyry Mo deposit in Dabie Shan. China. Ore Geol. Rev. 81, 405–430. Dawson, J.B., Hinton, R.W., 2003. Trace-element content and partitioning in calcite, dolomite and apatite in carbonatite, Phalaborwa, South Africa. Miner. Mag. 67, 921–930. Dasgupta, R., Hirschmann, M.M., Withers, A.C., 2004. Deep global cycling of carbon constrained by the solidus of anhydrous, carbonated eclogite under upper mantle conditions. Earth Planet. Sci. Lett. 227, 73–85. Deng, X.H., Chen, Y.J., Santosh, M., Yao, J.M., Sun, Y.L., 2016. Re–Os and Sr–Nd–Pb isotope constraints on source of fluids in the Zhifang Mo deposit, Qinling Orogen. China. Gondwana Res. 30, 132–143. Dong, Y.P., Santosh, M., 2016. Tectonic architecture and multiple orogeny of the Qinling Orogenic belt, Central China. Gondwana Res. 29, 1–40. Eckert, C.A., Knutson, B.L., Debenedetti, P.G., 1996. Supercritical fluids as solvents for chemical and materials processing. Nature 383, 313–318. Gao, S., Zhang, B.R., Jin, Z.M., Kernb, H., Luo, T.C., Zhao, Z.D., 1998. How mafic is the lower continental crust? Earth Planet. Sci. Lett. 161, 101–117. Gittins, J., Harmer, R.E., 1997. What is ferrocarbonatite? A revised classification. J. Afr. Earth Sc. 25, 159–168. Haas, J.R., Shock, E.L., Sassani, D.C., 1995. Rare earth elements in hydrothermal systems: estimates of standard partial molal thermodynamic properties of aqueous complexes of the rare earth elements at high pressures and temperatures. Geochim. Cosmochim. Acta 59, 4329–4350. Halama, R., Vennemann, T., Siebel, W., Markl, G., 2005. The Grønnedal-Ika carbonatite–syenite complex, South Greenland: carbonatite formation by liquid immiscibility. J. Petrol. 46, 191–217. Harmer, R.E., Gittins, J., 1998. The case for primary, mantle-derived carbonatite magma. J. Petrol. 39, 1895–1903.

Appendix A. Supplementary data Supplementary data to this article can be found online at https:// doi.org/10.1016/j.oregeorev.2019.103069. References Broom-Fendley, S., Brady, A.E., Wall, F., Gunn, G., Dawes, W., 2017a. REE minerals at the Songwe Hill carbonatite, Malawi: HREE-enrichment in late-stage apatite. Ore Geol. Rev. 81, 23–41. Broom-Fendley, S., Wall, F., Spiro, B., Ullmann, C.V., 2017b. Deducing the source and composition of rare earth mineralising fluids in carbonatites: insights from isotopic (C, O, Sr-87/Sr-86) data from Kangankunde. Malawi. Contrib. Mineral. Petrol. 172, 11–12. Cao, J., Ye, H.S., Li, H.Y., Li, Z.Y., Zhang, X.K., He, W., Li, C., 2014. Geological characteristics and molybdenite Re-Os isotopic dating of Huangshui’an carbonatite veintype Mo (Pb) deposit in Songxian County, Henan Province. Miner. Deposits 33, 53–69 (in Chinese with English abstract). Chakhmouradian, A., Wall, F., 2012. Rare earth elements: minerals, mines, magnets (and more). Elements 8, 333–340. Chakhmouradian, A.R., Reguir, E.P., Coueslan, C., Yang, P., 2016. Calcite and dolomite in intrusive carbonatites II. Trace-element variations. Miner. Petrol. 110, 361–377. Chen, L., Liu, Y.S., Hu, Z.C., Gao, S., Zong, K.Q., Chen, H.H., 2011. Accurate determinations of fifty-four major and trace elements in carbonate by LA-ICP-MS using normalization strategy of bulk components as 100%. Chem. Geol. 284, 283–295. Chen, W., Simonetti, A., 2013. In-situ determination of major and trace elements in calcite and apatite, and U-Pb ages of apatite from the Oka carbonatite complex:

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