Tungsten Mineralization Research Articles

Insights into the anatectic origin of granites parental to tungsten mineralization: A case study from the trans‐Aravalli terrane, NW India

AbstractPotential progenitors for W (±Sn) deposits include peraluminous granites of S‐type affinity. The anatectic origin of such granites parental to W mineralization has received little attention. This study focuses on Balda Granite (BG), a peraluminous intrusion parental to W‐rich ore bodies in the Sirohi region (NW India). We reflect upon the potential source for BG and investigate its anatectic origin through open‐system phase equilibria modeling. On the prograde path, muscovite‐ and biotite‐dehydration reactions at 675–745°C and 755–870°C yield ~10 and 13 wt.% melt, respectively. Si, K, Al, and Fe contents of the cumulative melt increased with progressive anatexis. Modeling results suggest high‐T (>800°C) stability of the peritectic garnet, which is abundantly observed in the leucosome‐dominated migmatitic patches. Cumulative melt extracted till 868°C was chosen to model the crystal fractionation along three polybaric gradients of 30, 45, and 60°C/kbar. As the modeled anatectic melt cooled, its peraluminosity and maficity decreased progressively. With the intermediate cooling gradient of 45°C/kbar, the melt achieved complete crystallization at ~7 km, the depth at which the BG had been emplaced and evolved into a W‐rich residual (fractionated) model melt. In terms of peraluminosity, and major and trace element (Lu, Sc, Dy, Y, Yb) chemistry, the fractionated (residual) model melt compares well with BG. This study also models the W concentration in the anatectic melt during its generation and fractional crystallization. We argue for the origin of BG through high‐T anatexis of Sirohi Group metapelites and cooling (and fractional crystallization) of the parent anatectic melt at the maximum gradient of 45°C/kbar. Thus, a high‐T anatectic origin of granites parental to W deposits may be more prevalent than so far inferred.

Prospects of Processing Tungsten Ores from the Akchatau Deposit

An overview of the composition of wolframite ores of the Akchatau deposit and the technologies for processing concentrates using NaOH and Na2CO3 by hydro- and pyrometallurgical methods is given, and the disadvantages associated with both the technology and the equipment are noted. To develop a technology for processing Akchatau wolframite concentrates, samples of ore materials were taken, the chemical and mineralogical composition of the samples was studied, and enrichment was carried out to obtain rich concentrates. The kinetics of the sintering of the wolframite concentrate with soda was investigated, the dependences of the degree of transformation of the tungsten minerals into sodium tungstate were obtained, and the rate constants, the order of the reaction, and the values of the apparent activation energy were calculated. The results of sintering an enlarged sample of wolframite concentrate with soda in a muffle furnace are presented. After the subsequent leaching, studies were carried out to purify the obtained solutions of sodium tungstate from the impurities while eliminating the operations of the neutralizing solutions through the use of electrodialysis with an MK-40 cation-exchange membrane. The scheme of processing the wolframite ores of Akchatau is proposed.

Genesis of tungsten mineralization in the Yangla copper-polymetallic deposit, northwest Yunnan, China: Evidence from in situ U-Pb dating, trace elements, Sr isotopes, fluid inclusions, and H-O isotopes of scheelite

Scheelite is one of the main ore minerals in tungsten deposits, and its geochemical features can be used to examine and constrain tungsten mineralization. The Yangla deposit is one of the most important Cu-polymetallic skarn-porphyry deposits in the “Sanjiang” polymetallic metallogenic domain, Southwest China, hosting 150 Mt of Cu ores with economic concentrations of Pb, Zn, and Sb. The newly discovered tungsten mineralization in the Yangla deposit remains poorly understood. Hence, in order to ascertain the timing of tungsten mineralization, investigate its genetic relationship with magmatism and ore genesis, and elucidate the source, nature, and evolution of the ore-forming fluids, we performed a combined study of geochronology, in-situ trace elements, fluid inclusions, H-O isotopes, and in-situ Sr isotopic compositions of scheelite. In-situ U-Pb dating of scheelite showed that the timing of tungsten mineralization was 30 Ma. This mineralization age is significantly later than the published Cu mineralization age (∼230 Ma), skarn (∼231 Ma), and granitoid emplacement age (∼230 Ma) in the Yangla ore district. In-situ trace element analyses revealed that scheelite is depleted in Mo, Mn, and Ta and slight enriched in Sr, Y, REEs, and Au. It is also characterized by HREE-depleted chondrite-normalized patterns with strongly positive Eu anomalies. Our data reveal that 3Ca2+ = (2REE)3++□Ca (site vacancy) is the main substitution mechanism that controls REEs in scheelite. The low concentrations of Mo, negative Ce anomalies, and positive Eu anomalies of scheelite indicate a reduced condition. Preliminary REEs features indicate that the genesis of scheelite may be related to vein-type W (Au) deposits. The homogenization temperatures for fluid inclusions present a strongly decreasing trend (328 to 173 ℃), indicate that cooling is the predominant mechanism for the formation of scheelite. The δD and δ18Ofluid values from fluid inclusions of scheelite vary broadly from −161.70 ‰ to −133.30 ‰ and from 6.32 ‰ to 9.80 ‰, respectively, indicating a mixture of magmatic and meteoric water, with possible involvement of magma degassing and fluid–rock interaction. The initial 87Sr/86Sr ratios of scheelites (0.71931– 0.72117) are significantly higher than those of the granodiorite (0.71149 – 0.71990) and basalt (0.70562 – 0.70995) in the Yangla ore district, indicating that the Oligocene magmatism and Devonian marble with radiogenic Sr isotopic compositions contributed to tungsten mineralization. The fluid-rock interaction between the ore-forming fluids derived from the concealed granitoids and the Devonian wall rocks may play an important role in tungsten mineralization and provide significant Ca for scheelite precipitation. Thus, the tungsten mineralization should be associated with Oligocene magmatism, ruling out the genetic relationship with Late Triassic magmatism and being significantly different from the skarn-porphyry Cu-Pb-Zn mineralization at Yangla.

Tracing metal source of copper-rich tungsten mineralization: Evidence from individual fluid inclusion analysis of the Huangsha Cu-rich W deposit in South China

The Huangsha Cu-rich W deposit, located in the northeast part of the Nanling region, is a typical large-size wolframite-quartz vein-type W deposit with considerable reserves of copper. Wolframite and chalcopyrite usually distribute in the same quartz veins, while field and petrographic observation show that wolframite commonly precipitates earlier than coexisting quartz and sulfides. Veined quartz can be divided into three successive generations (Q1, Q2, and Q3) based on SEM-CL imaging, and only Q2 is strictly coeval with chalcopyrite and other sulfides. Primary two-phase aqueous (type Lw) fluid inclusions are identified from wolframite with homogenization temperatures of 292 to 327 ℃ and salinities of 6.9 to 9.9 wt% NaCl equiv. Pseudosecondary two-phase aqueous (type Lq) and vapor-rich (type Vq) fluid inclusions are recognized from Q2, supporting the occurrence of fluid immiscibility. Homogenization temperatures of type Lq inclusions in Q2 range from 200 to 258 ℃ with salinities of 4.3 to 7.7 wt% NaCl equiv. LA-ICP-MS analysis shows that all inclusions contain Na and K as the major cations. For all the detected elements, type Lw inclusions in wolframite have higher concentration ratios X/Na than type Lq inclusions to varying degrees. The ore-forming fluid in both W and Cu mineralization stages share the same characteristics of high B concentrations, consistent Rb/Cs ratios and evolving nature of ore metals, indicating that W and Cu were sourced from the same magmatic fluid but precipitated in different mineralization stages. The variation of fluid Sr concentration likely indicates fluid-rock interaction during precipitation of wolframite, whereas the deposition of chalcopyrite is possibly influenced by fluid cooling and immiscibility. Compared with typical porphyry Cu systems and W/Sn mineralized systems worldwide, the ore-forming fluid in the W mineralization stage at Huangsha shows considerably higher mineralization potential of Cu, which is consistent with the geological fact. The Cu contents in initial W ore-forming fluids may serve as an indicator in identifying Cu-rich W deposits.

Contribution discrepancy of two distinct wall rocks to wolframite mineralization from Dongshanwan quartz-vein tungsten deposit, Southern Great Xing’an Range, China

The Southern Great Xing’an Range is a significant polymetallic metallogenic belt in Northeast China. The ages of granite related to tungsten mineralization have been well quantified, however, the timing and mechanism of quartz vein-type wolframite deposition remain unclear. Therefore, our study focused on the Dongshanwan tungsten deposit, representing a typical wolframite-bearing quartz vein-type deposit in the Southern Great Xing’an Range. Quartz vein-type tungsten mineralization was mainly contained in the Early Cretaceous granite porphyry, with few exceptions in the Permian tuff. Representative wolframite samples were collected from intragranitic (Wol-I) and intra-tuff (Wol-II) quartz veins for wolframite U–Pb dating, electron probe microanalysis (EPMA), and trace elemental analysis. Wolframite U–Pb dating recognized an Early Cretaceous mineralization event at 139–141 Ma, consistent with the previous Dongshanwan granite’s ages (∼142 Ma) but much younger than tuff (∼260 Ma). All the wolframite samples belonged to the ferberite series (FeO/MnO = 4.0–6.9), which indicates a link to the highly fractionated granite. Wol-I showed high contents of Nb, Ta, Sc, and HREEs and a strongly negative Eu anomaly (0.02–0.29), while these elements in Wol-II were approximately one order of magnitude lower than in Wol-I and the Eu anomaly was highly variable (0.17–1.02). The redox characteristics reflected by the Eu anomaly of wolframite may correspond to the variations in oxygen fugacity. Based on petrology, geochemistry, and element mass migration, this study suggests that the granite porphyry and tuff in the Dongshanwan deposit contributed differently to the wolframite precipitation even if the ore-forming fluids were of a common magmatic-hydrothermal origin. The exsolved fluid reserved in the closed system interacts with granite to achieve continuous enrichment in Nb, Ta, Sn, and REEs and accepts external Fe supply from granite alteration to precipitate Wol-I. In contrast, the fluids in relatively open and non-granitic systems have lower Nb, Ta, Sn, and REEs than the former, and Fe supply depends on the alteration of tuff. The abundance of fluorite and the non-CHARAC (CHArge-and-RAdius-Controlled) behavior of Y/Ho and Zr/Hf in the wolframite suggested that fluorine plays an important role in the migration and enrichment of tungsten and other elements during tungsten mineralization.

A Novel Process of Tungsten Flotation for Sustainable Exploitation of Tungsten Resources

Tungsten as key metal in various fields is indispensable metal resource for global economy. Sustainable exploitation of tungsten resources is still challenging. This work makes attempt to solve the difficulty in flotation separation of tungsten minerals from Yaogangxian tungsten ore. Systematical analysis of mineralogical properties of tungsten ore was performed. A process for tungsten flotation from tungsten ore was developed for exploitation of tungsten resources. The major valuable element in the ore is tungsten, and the grade of tungsten is 0.22%. The distribution of scheelite is nonuniform, and it is majorly distributed in 0.02~0.32 mm. The intergrowth and inclusion of scheelite occur with other minerals such as calcite, diopside, grossularite, and fluorite. The liberation of scheelite reaches 92.40% for -0.074 mm accounting for 75.48%. Process factors including Na2CO3, flotation collector, modified sodium silicate solution, and lead nitrate are studied, and the optimized conditions are Na2CO3 1600 g/t, GY-107 (640 g/t for roughing and 240 g/t for scavenging), modified sodium silicate solution 4200 g/t, and lead nitrate 400 g/t. The open-circuit and closed-circuit flotation processes for tungsten separation are designed, and it is verified for effective separation of tungsten minerals. For the closed-circuit flotation, the grade of tungsten concentrate is 7.30%, while the recovery reaches 85.89%. This work provides technical insights into tungsten separation from tungsten ore.

Tungsten minerals flotation with 4-alkoxy benzohydroxamic acid: The structure-performance relationship of its C3 derivatives

To improve the flotation recovery of tungsten minerals, 4-alkoxy benzohydroxamic acids containing C3 alkyl (C3OBs), namely 4-propoxy benzohydroxamic acid (POB), 4-iso-propoxy benzohydroxamic acid (IPOB) and 4-allyloxy hydroxamic acid (AOB), were designed as scheelite and wolframite collectors. The micro-flotation results uncovered that C3OBs exhibited stronger collecting ability towards Pb(Ⅱ)-activated scheelite and wolframite than benzohydroxamic acid (BHA) and the collecting ability of C3OBs was in sequence of POB > IPOB > AOB. The density functional theory (DFT) calculation indicated that the alkoxy oxygen atom of C3OBs contributed to their highest occupied molecular orbital (HOMO), and the HOMO energy followed the order as IPOB > POB > AOB > BHA. The higher HOMO energy, the stronger electron-donating activity. Nevertheless, IPOB didn’t return the highest flotation recovery of tungsten minerals. On the other hand, the hydrophobicity of these four hydroxamate collectors was in sequence of POB > IPOB > AOB > BHA, corresponding to the results of contact angle, micro-flotation and adsorption capacity. Therefore, the hydrophobization of the four hydroxamate collectors played a key role in their flotation performance to the Pb(II)-activated scheelite and wolframite. Moreover, this work offered a new approach for developing superior collectors.

Age and Isotope-Geochemical Characteristics of Ta, Nb, W, Sn Mineralization Associated with Rare-Metal Granites (Khangilay Ore District, Eastern Transbaikalia)

The age relations between the formation of the parent massif and the crystallization time of the associated ore mineralization were established based on isotope-geochronological study of the massif-deposits of the Khangilay ore cluster with various metallogenic specialization in Eastern Transbaikalia. In the Orlovka Li–F granite massif, the crystallization time of columbite–tantalite (145 ± 1 Ma) and cassiterite (144.2 ± 0.3 Ma) (U-Pb, ID-TIMS) is almost identical to the crystallization time of zircon (140.6 ± 2.9 Ма (U-Pb, SHRIMP) and 145 ± 1 Ma (U-Pb, CA-ID-TIMS)), which is an age marker of the formation of massifs. This fact testifies to the magmatogenic nature of rare-metal mineralization. In the Spokojnoye massif – the “standard type” of rare-metal peraluminous granites—a 0.6–3.8 Ma time gap was revealed between the time of massif formation (141.3 ± 1.8 Ма, U-Pb, SHRIMP, 146.9 ± 0.7 Ма, Rb-Sr isotopic system) and crystallization of wolframite (141.8 ± 0.6, Rb-Sr isotopic system and 140.1 ± 1.4 Ма, Sm-Nd isotopic system). This interval likely corresponds to the life time of the hydrothermal system, which produced tungsten mineralization.

Age and Isotope-Geochemical Characteristics of Ta, Nb, W, Sn Mineralization Associated with Rare-Metal Granites (Khangilay Ore District, Eastern Transbaikalia)

The age relations between the formation of the parent massif and the time of crystallization of the associated ore mineralization were established on the basis of isotope-geochronological study of the massifs-deposits of the Khangily ore district with various metallogenic specialization in Eastern Transbaikalia. In the Orlovka massif of Li-F granites, the crystallization time of columbite-tantalite (145 ± 1 Ma) and cassiterite (144.2 ± 0.3 Ma) (U-Pb, ID-TIMS) is almost identical to the crystallization time of zircon (140.6 ± 2.9 Ма (U-Pb, SHRIMP) and 145 ± 1 Ma (U-Pb, CA-ID-TIMS)) – an age marker of the formation of massifs. This fact testifies to the magmatogenic nature of rare-metal mineralization. In the Spokojnoye massif – the “standard type” of rare-metal peraluminous granites – a time gap with an interval of 0.6–3.8 Ma was revealed between the time of formation of the massif (141.3 ± 1.8 Ма, U-Pb, SHRIMP, 146.9 ± 0.7 Ма, Rb-Sr isotopic system) and crystallization of wolframite (141.8 ± 0.6, Rb-Sr isotopic system and 140.1 ± 1.4 Ма, Sm-Nd isotopic system). Perhaps this interval corresponds to the time of formation of the hydrothermal system, with which tungsten mineralization is genetically related.

The genetic association between vein and skarn type tungsten mineralization in the Yaogangxian tungsten deposit, South China: Constraints from LA-ICP-MS analysis of individual fluid inclusion

The large-scale Yaogangxian W deposit, located in central of the Nanling metallogenic belt, South China, comprises independent quartz vein-type and skarn-type W mineralization. Wolframite-bearing quartz veins occur invariably in metasandstone and slate to the northwest of the Yaogangxian granitic intrusion, whereas scheelite-skarn are mainly hosted by the limestone to the east. The vertical extension of single wolframite-bearing quartz vein can reach up to 1000 m and we focused on the vein samples collected from the deepest level (26 level) which likely recorded early magmatic fluids. For skarn mineralization, two scheelite precipitation stages were recognized, namely scheelite-1 in retrograde stage and scheelite-2 from sulfide-stage. To reveal the fluid sources and characteristics of two mineralizing systems, detailed petrography and microthermometry analyses were carried out on fluid inclusion assemblages (FIA) in scheelite, wolframite and their coexisting quartz. Fluid compositions were obtained from individual fluid inclusion (FI) in ore and gangue minerals via laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) analysis. These data aid elucidation on the source and nature of fluids in the two distinct W mineralization styles. The chemical compositions of FIs hosted in wolframite and scheelite points to a common magmatic source. The fluid in the scheelite ore section exhibits lower As and B than the wolframite ore section, indicating that boiling may have occurred at early skarn stage. Fluid evolution in the two mineralizing systems suggest that formation of diverse W mineralization styles is mainly controlled by different host lithology and fluid processes. In the wolframite ore section, ore-forming fluid recorded in the deepest level of vein show elevated As, B, K and Rb contents than previously reported ore-forming fluid obtained from the tip of the vein. This likely indicate absence of intensive fluid immiscibility in the deep during wolframite formation, which may rather be accompanied by fluid-rock interaction. In the scheelite ore section, constant injection of meteoric water is revealed. FI hosted in scheelite-1 and 2 exhibit similar compositions, and the lower K content in scheelite-2 fluid is thought to be caused by sericitization in the retrograde stage skarn. The Mo content of scheelite decreased from the retrograde stage to sulfide-stage, indicating a decrease in oxygen fugacity. Based on these conclusion and previous geological and geochronological studies, we propose a metallogenic model of the coupled wolframite-quartz vein and scheelite-skarn mineralization.

From granite to highly evolved pegmatite: A case study of the Shangkelan rare-metal granite–pegmatite system (Altai, NW China)

The Shangkelan granite–pegmatite is known for its internal zonation and tungsten mineralization in the Chinese Altai. However, the genetic relationship between the granite and pegmatite and the W mineralization mechanism in Shangkelan remains unclear. Here we present monazite U–Pb ages and Nd isotopic composition, and whole-rock and muscovite chemical compositions of each zone of the stock, to address these issues. From bottom to top, the stock mainly consists of alkali-feldspar granite (AFG) and granitic pegmatite (GP). Monazite LA-ICP-MS U–Pb dating and Nd isotopic analyses reveal that the AFG and GP have identical ages and similar εNd(t) values, 189 ± 2 Ma and −0.79–+0.38 and 190 ± 1 Ma and −0.70–+0.01, respectively. Whole-rock geochemical results show that the stock is highly fractionated and has a differential trend characterized by increasing Rb, Cs, and Tl contents, decreasing W, Ba, and Sr contents, and Zr/Hf ratios from the AFG to GP. Both primary (magmatic) and secondary (hydrothermal) muscovites have been recognized in Shangkelan. From the AFG to GP, element concentrations and ratios of primary muscovite form well-defined differentiation trends marked by gradual increases in Rb, Cs, and Nb, and decreases in W, K/Rb, and Nb/Ta. Based on the gradational contacts in field, identical monazite ages, and similar Nd isotopic compositions, together with the differentiation trends of incompatible elements (such as Rb and Cs) in bulk-rock and primary muscovite and alkali metal Rayleigh fractionation modeling results, we consider that the AFG is parental to GP and they were produced by continuous fractional crystallization of a common magma source. Additionally, for the monazites Nd isotopes, their two-stage Nd model ages of 1034–939 Ma and slightly negative to positive εNd(t) values (−0.79–+0.38) indicate that the magma sources were mainly derived from the reworking of the Stenian–Tonian basement. Secondary muscovite precipitated from the fluids that exsolved from the parental AFG melt has high contents of F and W. Tungsten may be dissolved as H3WO4F2− in the fluids. The greisenization caused the destabilization of H3WO4F2− and eventually led to the precipitation of wolframite in Shangkelan.

Prospectivity Mapping of Tungsten Mineralization in Southern Jiangxi Province Using Few-Shot Learning

The development of mineral prospectivity mapping (MPM), which aims to outline and prioritize mineral exploration targets, has been spurred by advances in data-driven machine learning algorithms. Supervised data-driven MPM is a typical few-shot task, suffering from a scarcity of labeled data, the over-fitting of models and an uncertainty of predictions. The main objective of this contribution is to propose a robust framework of few-shot learning (FSL), combining data augmentation and transfer learning to enable the generation of prospectivity models with excellent predictive efficiency and low uncertainty. The mineral systems approach was used to transfer a conceptual mineral system into mappable exploration criteria. Synthetic minority over-sampling technique (SMOTE) was employed to augment and balance the labeled dataset, allowing for model pre-training with the large synthetic training dataset of a source domain. The knowledge derived from pre-trained models was then transferred to the target domain by fine-tuning, and the prospectivity model was generated in light of over-fitting and uncertainty assessments. The proposed FSL framework was applied to tungsten prospectivity mapping in southern Jiangxi Province. The results indicated that the SMOTE-ed balanced dataset boosted the classification accuracy in the training process. The FSL models yielded an arch-shaped prediction point pattern which was favorable for focusing potential targets with high probability and low uncertainty. The FSL models achieved a high predictive performance (test AUC = 0.9172) and the lowest quantitative over-fitting value compared to the models derived from the benchmark algorithms of random forest and support vector machine. Four levels of potential targeting zones, considering both predictive efficiency and uncertainty, were extracted from the resulting FSL prospectivity map. The final high-potential and low-risk exploration targets only cover 4.27% of the area, but capture 41.53% of known tungsten deposits, thus achieving a superior predictive performance. This study highlights the capability of FSL framework to control over-fitting and generate high-confidence exploration targets with low levels of uncertainty.

Tungsten mineralization formed by single-pulsed magmatic fluid: Evidence from wolframite-hosted fluid inclusion from the giant Dajishan “five floor” style W-polymetallic deposit

The giant Dajishan W-polymetallic deposit, located in the Nanling metallogenic belt, is a typical steeply dipping wolframite-quartz vein-type deposit. From top to bottom, the W ore grade is highest in the middle and decreases towards both ends. In No. 23 wolframite-quartz vein of the north group, the thickness of the veins increases from 0.1 ∼ 0.2 m thick in the 517 m level to a maximum of 0.6 ∼ 2.0 m in the 267 m level. According to the “Five Floor” prospecting model, the No. 23 vein corresponds to veinlet (517 m), moderate vein (467 ∼ 417 m), and thick vein zones (367 m ∼ 267 m). Primary wolframite-hosted fluid inclusions show homogenization temperatures display a slight but explicit decrease by about 20 °C in average from bottom to top, recording the essential fluid cooling process. The phase ratios (20 to 30 vol% vapor proportions) and salinities (6.3 to 10.0 wt% NaCl equiv.) are constant at all levels, indicating that neither meteoric water mixing nor fluid boiling/immiscibility is obvious during wolframite formation. The fluids contain NaCl and KCl as major salts, B as the subordinate component, with trace elements including Li, Rb, Cs, Zn, Pb, etc. The significant narrow ranges of K/Na (0.296 to 0.664), Rb/Na (0.008 to 0.018), and Cs/Na ratios (0.032 to 0.076) illustrate that wolframite ore-forming fluids come from the initial fluids derived from a highly-evolved granitic magma. In major host metasandstone, muscovitization and tourmalinization lead to the release of Na, B, and Al from the fluid into the wall rock, and liberation of Fe from the wall rock into the fluid. Wall rock composition data show that muscovitization is the main mechanism of changes in Fe contents. Preliminary calculations indicate that fluid-rock interaction may contributes minor iron to the ore-forming fluids. Combining these results, we support that “Five Floor” style W mineralization in Dajishan is formed by a single-pulsed magmatic fluid. The vertical zonation of vein thickness and ore grade in the “Five Floor” model is predominately controlled by temperature, pressure, and local tectonic regime, but it is less dependent on the fluid chemical composition.

Tungsten and tin deposits in South China: Temporal and spatial distribution, metallogenic models and prospecting directions

South China is one of the most important tungsten-tin metallogenic areas in the world. Based on the up-to-date geological and chronological data of more than 130 deposits of economic significance, this paper preliminarily summarized the main types and temporal-spatial distribution characteristics of the large-scale tungsten and tin mineralization related to granite in South China. The statistical results show that skarn and quartz-vein types are the most important tungsten metallogenic styles, while skarn and cassiterite-sulfide types are the most important tin metallogenic styles in South China. Tungsten and tin mineralization related to granite in South China are multi-aged, but the largest scale of mineralization is developed within the Yanshanian period. Tungsten mineralization, the majority of which represented by the Nanling and Ganbei metallogenic belts, mainly formed from the Late Jurassic to Early Cretaceous (160 ∼ 120 Ma), while the most important tin mineralization formed in the Late Cretaceous (110 ∼ 80 Ma, peaking at 90 ∼ 80 Ma) and Late Jurassic (160 ∼ 150 Ma) as represented by the Youjiang Basin and Nanling metallogenic belt, respectively. The combined occurrence of different mineralization styles or metal assemblages in individual deposit and sometimes within the same orefield is the most striking feature of granite-related tungsten-tin deposits in South China, and a comprehensive understanding of their patterns are of great significance to guide ore prospecting. To address this issue, this paper proposed several combined metallogenic models and prospecting directions for tungsten-tin mineralization in South China based on recent researches and exploration progresses from typical examples including the Yaogangxian, Chuankou, Maoping, Shizhuyuan, Dachang and Gejiu deposits or orefields. In addition, conventional petrological and mineralogical characteristics that differentiates tungsten and tin granites are summarized, and on this basis the chemical composition of both melt inclusion and early stage fluid inclusion from granitic magmatic-hydrothermal systems were tested as new index to evaluate the tungsten and tin mineralization potential of granitic system.

Insights into the Crustal Evolution and Tungsten Mineralization of the West Cathaysia Block: Constraints from the Inherited Zircons from the Mesozoic Dengfuxian and Paleozoic Tanghu Plutons, South China

The formation and evolution of the ancient continental crust are crucial issues in solid-earth geology which are commonly associated with global tectonic events and the formation of economically valuable magmatic-hydrothermal ore deposits. The Cathaysia Block, one of the ancient continents in Southeast Asia, can be subdivided into two parts: the West Cathaysia Block and the East Cathaysia Block. Unlike the East Cathaysia Block, no Precambrian rocks are exposed in the West Cathaysia Block, constraining further understanding of the formation and evolution of this block. In this study, a total of four hundred and thirty-three zircon U-Pb dating analyses and two hundred and eighteen Lu-Hf isotopic analyses on zircon grains from the Jurassic Dengfuxian granites and Ordovician Tanghu granites, Nanling Range, were carried out. LA-ICP-MS zircon U-Pb dating yields mean average 206Pb/238U ages of 152.6 ± 2.2 Ma (MSWD = 1.6) and 442.4 ± 1.7 Ma (MSWD = 3.8), which are regarded as the rock-forming age for the Jurassic Dengfuxian granites and Ordovician Tanghu granites, respectively. The 207Pb/206Pb ages of the inherited zircons from the Jurassic Dengfuxian granites and Ordovician Tanghu granites range from 522 Ma to 3395 Ma, hosting two major peaks at the 0.9–1.0 Ga and 2.4–2.5 Ga. In contrast to the East Cathaysia Block, the West Cathaysia Block lacks the age peak of 1.8–1.9 Ga, indicating that the West Cathaysia Block was not influenced by the assembly of the Columbia supercontinent in the Paleo-Proterozoic. In combination with the Lu-Hf isotopes, we proposed that the crust evolution of the West Cathaysia Block in Archean is dominated by juvenile crustal growth events, and dominated by the crustal reworking since the Proterozoic. The long duration of crustal reworking in the West Cathaysia Block resulted in the enrichment of lithophile elements (e.g., W, Sn, Nb, and Ta) in the crust of that region. Therefore, the Jurassic granites in the Nanling Range, which are mainly derived from the partial melting of Proterozoic basement rocks, became associated with large-scale tungsten polymetallic mineralization.

Palaeostress analysis using fault-slip data from the Xiangdong tungsten deposit in the central south China continent: Evolution of intraplate stress in the Middle Mesozoic

In the central South China continent, the Xiangdong tungsten deposit associated with Late-Jurassic granitic intrusion offers an opportunity to examine the evolution of intraplate stress between the Late Jurassic and Early Cretaceous, which was a time of transition from regional shortening to regional extension. NE–ENE-striking, steeply-dipping, opening-mode tungsten-bearing quartz veins constitute the deposit. Favorable conditions for vein formation where densely spaced arrays have non-curving tips occur under remote stress with a large stress difference and hence in this case probably aligned with the horizontal maximum principal stress axis. Palaeostress analysis using fault-slip data measured on the side walls of underground mine levels yielded the optimal solution of two stresses characterized by an NNW–SSE-shortening strike-slip regime and an NNW–SSE extensional regime. Based on field observations, the first tectonic phase existed during meso- and epi-thermal mineralization, probably owing to the collision between the Siberia and Mongolia–Sino-Korean continents far to the north at the time, and the second tectonic phase appeared after hydrothermal mineralization, as a result of Cretaceous regional rifting. Therefore, multiple strike-slip deformations would have involved the study area during hypo- and epi-thermal mineralization in the Late Jurassic. This evidence does not support the mainstream extension model for Mesozoic tungsten mineralization in central South China.

Characteristics of REEs and Trace Elements in Scheelite and Muscovite Ar–Ar Isotopic Dating of the Daping Tungsten Deposit

The recently discovered Daping tungsten deposit is located about 25 km north of Tongcheng County, Hubei Province, in the northern margin of the Sijiapu granite deposit of the Mufushan composite batholith. The ore body is produced in the northeast-oriented greisenization granite and quartz vein, and belongs to the greisen-vein-type scheelite deposit. The resources of the Daping W deposit have a value of 7935 t W and the average grade is 0.201% WO3. Based on mineralogical and petrographic studies, scheelite is classified into two types. A study of the geochemical characteristics of rare earth elements (REEs) and trace elements indicated that some scheelite specimens showed LREE depletion. Meanwhile, the total amount of scheelite rare earth elements (REEs) is low and the ratio of LREE/HREE ranges from 0.40~2.72 in the Daping W deposit. The contents of REEs and trace elements in the two types of scheelite differ significantly. Type I scheelite has an average ∑REE content of 195.65 ppm, an LREE/HREE value of 0.5, an Eu anomaly (δEu) of 0.78, Mo of 366.20 ppm, Sn of 22.62 ppm, and Sr of 264.80 ppm. However, type II scheelite features an average ∑REE of 111.28 ppm, an LREE/HREE ratio of 1.43, a δEu of 1.56, Mo of 188.48 ppm, Sn of 0.15 ppm, and Sr of 829.93 ppm. The content level of Mo in the two types of scheelite is not high, indicating that this whole metallogenic environment is a reduction environment. However, this is a complex process. The presence of type I scheelite with negative Eu anomalies and relatively high Mo content indicates that the ore-forming environment in the early period of the greisen stage was relatively oxidizing. In contrast, type II scheelite contains large amounts of Sr and large positive Eu anomalies, which are likely to be released from plagioclase in the granite during greisenization. The extremely low composition of Mo in type II scheelite is closely related to the reducing environment in the later period of the greisen stage. Because Mo probably exists in its Mo4+ state, it may be difficult for it to replace W6+ in the scheelite lattice. Additionally, comparing the contents of Sn and Sr in different types of scheelite shows that the metallogenic environment changes from relative oxidation to the reduction of scheelite. The variation in trace elements and REEs in scheelite over time reflects a complex magmatic–hydrothermal mineralization environment. Additionally, the Ar–Ar system dating results for muscovite that is closely associated with scheelite in the greisenization granite vein indicate that a muscovite 40Ar/39Ar plateau age of about 133 Ma represents the time of tungsten mineralization. This muscovite 40Ar/39Ar dating result is close to the previous zircon U-Pb age data of the biotite monzogranite (ca. 140–145 Ma), which is the largest intrusion in the orefield. Meanwhile, the new age data reported here confirm that the Daping tungsten deposit represents a Mesozoic magmatic–hydrothermal mineralization event with a setting of lithospheric extension in the Mufushan composite batholith.

Mechanisms of ore formation in Silurian (Caledonian) scheelite deposits of the Nanling Range, South China: A case study from the Pingtan W deposit

The Pingtan scheelite deposit is a newly-discovered Caledonian W deposit situated in the northwestern portion of the Miao’ershan granitic batholith in the Nanling Range. The W mineralization can be divided into three stages, the altered granite-scheelite stage (I), the quartz-scheelite stage (II) and the quartz-sulfide stage (III). This contribution characterizes the mechanisms of ore formation of the deposit using fluid inclusion microthermometry, H-O isotopes, and in situ S isotopes. Fluid inclusion microthermometry demonstrates that the scheelite mainly formed at moderate to high temperatures (∼260–380 °C for stage I and ∼ 240–300 °C for stage II). The inclusions were trapped at maximum pressures of ∼ 140 MPa, which corresponds to a maximum depth of ∼ 5.3 km. Homogenization temperatures of the inclusions decrease slightly from stage I to stage II mineralization, and more drastically from stage II to stage III, whereas their salinity decreases gradually during the entire mineralization process. Raman spectroscopy indicates that fluid inclusions in stages I and II contain CO2, CH4, and N2, whereas those in stage III mainly contain H2O. The presence of native bismuth, pyrrhotite, and marcasite, and the presence of CH4-bearing fluid inclusions suggest reduced ore-forming conditions during Stages I and II. The δ34SCDT value (+0.8 to + 5.3 ‰, average 3.2 ‰) of sulfides and the δ18Ovsmow value of ore-bearing quartz, which decreases from Stage I (δ18Ovsmow = +5.1 to + 6.3 ‰) to Stage III (δ18Ovsmow = − 1.5 ‰ to + 0.6 ‰), as well as the presence of abundant fluid inclusions with daughter minerals in the first two stages, supports a magmatic origin for the ore-forming material, with exogenic fluid input after the tungsten mineralization stage. Based on the results of this contribution, boiling may be the dominant mechanism for the formation of W deposits in the Nanling Range.

Apatite and fluorite control the transport of tungsten in calcium-bearing hydrothermal fluids

Minerals associated with ores (gangue minerals) record the physicochemical conditions of ore-forming fluids. Whether and/or how they affect the solubility of ore minerals, however, is rarely evaluated. Here, we present results of an experimental study of the solubility of scheelite (responsible for >70% of the global supply of tungsten). They show that phosphate and fluoride sequester calcium from scheelite to form apatite and/or fluorite. These gangue minerals, which are common in tungsten deposits, vary in abundance depending on pH and the phosphorus/fluorine content of the fluid. Because of their precipitation, scheelite dissolution releases hundreds of ppm of tungsten to the fluid, especially at near neutral pH. This suggests that the presence of phosphorus/fluorine in a tungsten-bearing hydrothermal fluid may prevent the deposition of scheelite due to the formation of apatite/fluorite, or lead to the dissolution of scheelite and, in turn, enrich the fluid in tungsten. Models based on our data show that magmatic-hydrothermal phosphorus- and fluorine-rich fluids are enriched in tungsten by a factor of up to 220 during high-temperature alteration, and form high-grade deposits of ferberite on cooling, or of scheelite because of their interaction with calcium-enriched rocks. Thus, the concentration of fluorine and phosphorus, as well as pH, are key factors affecting the transport and deposition of tungsten in calcium-bearing hydrothermal systems that, if they act synergistically, can efficiently remobilize early low-grade tungsten mineralization and enrich the ore-forming fluids in tungsten, leading to the formation of giant deposits. Such competition between ore and gangue minerals for components of the mineralizing fluid is also probably a feature of hydrothermal systems involving other metals and should be considered in future studies of the genesis of the corresponding ores.

Textural and LA-ICP-MS trace element analyses reveal co-enriched Au-Sb-W metallogeny in the Woxi deposit, west Jiangnan Orogen, South China

It is well-known that tungsten and antimony are commonly enriched in the gold deposit and occur as Au-Sb or Au-W deposits. However, the Woxi deposit, located in the West Jiangnan Orogen of South China, is remarkably co-enriched in the Au-Sb-W elemental association. This deposit is characterized by multistage Au mineralization and reactivation of structures developed in the Neoproterozoic metamorphic rocks, but the detailed mechanism of its co-enriched Au-Sb-W metallogeny is still unclear. Here, we perform detailed petrographic observations and ore mineral textural and pyrite compositional analyses by using SEM and LA-ICP-MS to constrain ore-forming physiochemical conditions and to decipher the Au-Sb-W metallogenic mechanism in the Woxi deposit. The Woxi deposit consists of nine auriferous quartz lodes in the shape of stratiform, tabular, and lenticular, which are surrounded by alteration halos in the Neoproterozoic slate. These orebodies are distributed along the bedding-parallel fracture zones of the EW-striking and N-dipping in the purplish red slate of the Madiyi Formation, below the regional EW-striking Woxi fault. Four stages of hydrothermal mineralization and alteration processes could be recognized in the Woxi. Stage 1 occurs in bleached slate, and consists of euhedral, porous, and coarse auriferous pyrite (Py1), with slight arsenopyrite, siderite, and rutile. Stage 2 mainly consists of subhedral to euhedral and compositional zoning auriferous pyrite (Py2) and scheelite (Sch1), with slight wolframite and apatite hosted in quartz veinlets and native gold enclaved in Sch1. Stage 3 is characterized by scheelite (Sch2) and stibnite, with slight native gold and dendritic-shaped anhedral auriferous pyrite (Py3) hosted in quartz veins. Stage 4 features a quartz-calcite-barite-chlorite mineral assemblage that occurred as veinlets, or in the pressure shadows of Py1. Gold is mainly incorporated in the three stages (S1 to S3) of arsenian pyrite (Py1to Py3) as invisible gold and, to a lesser extent, formed visible native gold at late S2 and S3, tungsten mineralization occurs mainly as scheelite (Sch1) and wolframite at S2, with a minor amount of scheelite (Sch2) at S3, and antimony mineralization is mainly occurred as stibnite at S3. Furthermore, invisible gold most likely occurs as nanoscale particles of Au-Bi-Pb-bearing tellurides in Py1, and may be hosted in the structurally bounded lattice of Py2 and Py3.The SEM study presents highly developed dissolution-reprecipitation microstructures in hydrothermal minerals, such as pyrite, arsenopyrite, wolframite, scheelite, and apatite. Mineral paragenesis and pyrite trace element signatures suggest the ore fluid is characterized by elevated fO2, low pH and high temperature in S1, decreased fO2, medium pH and medium temperature in S2, and elevated fO2, high pH and low temperature in S3. The evolution of the physicochemical condition may be induced by penetration of multipulse ore-forming fluids and the transition of the ore-forming mechanism from fluid-rock interaction in S1 and early S2 to phase separation in late S2 and S3, as suggested by textural and LA-ICP-MS analyses. This study highlighted that coupled dissolution-reprecipitation reactions might facilitate the association of the Au-Sb-W elemental that successively mineralized and co-enriched in the Woxi deposit.