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The Huashandong W deposit (7.7 Mt @ 0.26% WO3) is a newly discovered Neoproterozoic scheelite-dominated deposit in the world-class Jiangnan tungsten belt, South China. It occurs largely in metasedimentary rocks near the western margin of the Neoproterozoic Jiuling batholith and mainly consists of W-bearing exogreisen, hydrothermal breccias, and quartz veins. Two episodes of Neoproterozoic granite magmatism are identified with zircon U-Pb ages of ca. 830–823 and 807–804 Ma, respectively. According to cross-cutting relationships and mineral assemblages, two periods of hydrothermal alteration and W mineralization, corresponding to the two episodes of granite magmatism, are recognized in the Huashandong deposit. The early period is dominated by greisenization and associated scheelite mineralization whereas the late period is characterized by sericitization, hydrothermal brecciation, quartz veining, and associated scheelite and minor wolframite mineralization. Molybdenite Re-Os dating indicates that the early- and late-period W mineralization took place at ca. 828 and 800 Ma, respectively. Zircon trace element characteristics suggest that the Jiuling granite crystallized from reduced granitic magmas and has the potential for W mineralization. The petrologic and geochemical features of the Jiuling granite, coupled with the zircon U-Pb ages and Hf isotopic signatures and molybdenite Re-Os ages, imply that the Huashandong W deposit is genetically related to two phases of evolved granodiorites in the Jiuling batholith. The magmatic-hydrothermal nature of both metallogenic events is confirmed by H-O isotopes on hydrothermal quartz. [ABSTRACT FROM AUTHOR]

[Display omitted] • Two stages of fluid exsolution are recognized in the Weijia W skarn deposit. • F-rich magmatic fluids are enriched in REEs, Y, Nb, Ta with flat REE patterns. • F consumption is critical for the compositional evolution of F-rich mineralizing fluids. • Combined garnet and scheelite trace elements are powerful in tracking W skarn mineralization. Fluid evolution is an essential subject in the studies of hydrothermal ore-forming processes. Garnet and scheelite prevail in W-bearing skarn deposits and record plentiful information on W skarn mineralization. In-situ LA-ICP-MS trace element analyses have been carried out on the garnet and scheelite from the F-rich Weijia W deposit in South China to constrain the processes of fluid evolution and W skarn mineralization. The Weijia W deposit mainly consists of calcic and magnesian skarns and was formed through six stages of alteration and mineralization. Two stages of fluid exsolution are recognized in the magmatic-hydrothermal system. The earlier exsolved fluids are Cl-rich with rightward-sloping REE patterns and result in pre-ore skarnization. The later exsolved fluids are F-rich with relatively flat REE patterns and are responsible for W mineralization. The pre-ore garnets are LREE-enriched and HREE-depleted whereas the syn-ore garnets are LREE-depleted and HREE-enriched with lower δ Eu values than the former, denoting a transition from wall rock-controlled to magmatic fluid-dominated fluid-rock interaction. Combined with the skarn occurrences, mineral assemblages, and garnet textures, it is revealed that the mechanism of skarn formation shifts from more diffusive metasomatism under lower water/rock ratios to more advective metasomatism at higher water/rock ratios. The advective metasomatism with a high flux of ore-forming fluids is hydrodynamically favorable for the consequent W mineralization. The earliest-formed scheelite is akin to the host granite porphyry in REE patterns and can reflect the features of initial mineralizing fluids. It has high ΣREE (1255–5059 ppm), Y (616–1416 ppm), Nb (585–2629 ppm), Ta (14–248 ppm), Mn (up to 1977 ppm) and low Mo (mostly < 1000 ppm) contents, indicating that the primary F-rich magmatic fluids are reduced and enriched in REEs, Y, Nb, and Ta. The contents of ΣREE, Y, Nb, and Ta in scheelite are decreasing with the evolution of the F-rich mineralizing fluids. The latest-formed scheelites have distinctly lower ΣREE (2.9–140 ppm), Y (0.01–4.1 ppm), Nb (1.7–77 ppm), and Ta (0.04–0.19 ppm) contents and higher (La/Yb) N ratios and δ Eu values. They show 1:1 positive correlation of Eu N vs. Eu N * and have high Mo (up to 129466 ppm) and low Mn (as low as 3.4 ppm) contents, implying involvement of meteoric waters in the evolved ore-forming fluids and an oxidizing condition. Fluid-rock interaction, mineral precipitation, and fluid mixing largely control the process of fluid evolution. Fluorine consumption due to the formation of fluorite and the other F-rich minerals is vital for the compositional evolution of F-rich mineralizing fluids. The decrease of F concentration in fluids will depress the solubilities of REEs, Y, Nb, and Ta and enhance the LREE/HREE fractionation. Greisenization and skarnization induced the neutralization of the acidic W-bearing fluids and the liberation of Ca from the granite porphyry and carbonate strata and then triggered the scheelite precipitation. The carbonate strata contain abundant Ca and the granite porphyry is poor in Ca, and thus the economic W mineralization dominantly occurs in the skarns. [ABSTRACT FROM AUTHOR]

[Display omitted] • The Sanxianba granite is originated from the partial melting of the Banxi Group metasandstone. • Tungsten and volatiles are concentrated and form a W-rich evolved melt during fractionation. • Exsolved fluids from the evolved melt react with granite, forming veinlet-disseminated scheelite mineralization. Whole rock geochemistry combined with spatially resolved geochemistry of zircon, apatite, biotite and plagioclase allows us to uncover the magmatic processes leading to ore formation at the Muguayuan deposit. The Sanxianba granite, associated with the Muguayuan veinlet-disseminated scheelite deposit, is located in the middle of the Jiangnan Orogen. Whole rock Sr and Nd isotopes, and zircon Lu-Hf isotopes suggest it might originate from the Neoproterozoic Banxi group strata. The Rb element modeling shows that, after ~35% of partial melting, the Banxi group metasandstone can generate the primary Sanxianba melt with 164 ppm Rb and 21 ppm W. The intra-/intercrystal texture and compositions of zircon and plagioclase indicate that W and other elements such as HREE, Th, U, Nb, Ta, and P increase in the melt during fractional crystallization. The water content in the early Sanxianba magma, calculated through the plagioclase-hydrometer, is ~4.4 wt%, and its enrichment in the melt is reflected by the increasing water content in biotite with fractionation. F content in the early apatite is relatively high and invariable but further elevated in the late apatite. Chlorine, LREE and Na contents in the early apatite also present an enrichment trend. When H 2 O and Cl start to be saturated with the magma fractionation in the deep magma chamber, Cl-, Na-, and LREE-rich but W-poor fluid exsolves from the melt, resulting in the albitization and chloritization of feldspar and biotite phenocrysts, respectively. The subsequent decrease of Cl, Na 2 O and La 2 O 3 in the late apatite record this first fluid exsolution. Fluorine, P, H 2 O and W continue to enrich in the evolved melt with fractionation after the Cl-rich fluid exsolution. These fluxing components reach oversaturation during the shallow-ward emplacement of the magma, forming the F-, P- and W-rich fluids. The apex of the intrusion cools and forms a solid barrier, which prevents the escape of fluids. The exsolved fluids from the underlying magma continuously supply upward and react with the apex along fractures, resulting in greisenization and phyllic alteration. During alteration, Ca is released from calcium-rich plagioclase and combines with tungsten in the fluids to form scheelite mineralization. Magma evolution leading to the tungsten mineralization may be also the general scenarios in the other granite-related veinlet-disseminated scheelite deposits. [ABSTRACT FROM AUTHOR]

The Late Triassic Muguayuan W deposit is located in the middle of the Jiangnan Orogen, South China. This deposit is characterized by veinlet-disseminated W mineralization that developed in the Sanxianba granitic porphyry stock. The ore minerals are mainly scheelite with minor molybdenite and wolframite. Scheelite mineralization was closely related to greisenization and phyllic alteration, and took place in two stages. Stage I involved scheelite ± wolframite ± molybdenite + quartz veinlet and disseminated mineralization, whereas Stage II resulted in scheelite + quartz + sericite veinlet mineralization. Sulfide and quartz + calcite ± pyrite veinlets formed during the post-ore stage. Scheelites from the two mineralization stages have different textures and compositions. Cathodoluminescence (CL) images of Stage I scheelites reveal two generations of growth (I-a and I-b). Stage I-a scheelite is dark under CL with oscillatory zoning, and has light rare earth element (LREE)-enriched chondrite-normalized patterns, negative Eu anomalies, and high total REE contents. Stage I-b scheelite forms rim overgrowths on Stage I-a scheelite, is bright under CL, and shows positive Eu anomalies and relatively low REE contents. Although Stage II scheelites are nearly uniform under CL, they can be subdivided into two generations according to their REE systematics. Stage II-a scheelite yields middle REE (MREE)-enriched chondrite-normalized patterns, with negative Eu anomalies, whereas Stage II-b scheelite has MREE-depleted patterns with positive Eu anomalies. Minor amounts of apatite formed in both stages of mineralization. Stage I apatite contains 1370–1930 ppm Mn and 97.7–127 ppm Sr, whereas Stage II apatite has lower Mn (111–158 ppm) and higher Sr (2170–4690 ppm) concentrations. The distinct trace elements compositions of the scheelite and apatite from the two stages identify two ore-forming fluids that had different origins and compositions. The ore-forming fluids in Stage I-a were relatively reduced magma-derived fluids with high Mo, Mn, Nb, and Ta, and low Sr. Fluid modeling shows that the initial fluids of Stage I-a were LREE-enriched with negative Eu anomalies, similar to the Sanxianba granitic porphyry. Precipitation of early apatite and scheelite, as well as plagioclase decomposition, altered the fluid composition and led to relative depletions in REE, Nb, and Ta, and increases of Eu and Sr in the Stage I-b fluids. Cooling of these fluids and the addition of recycled meteoric water led the fluids to become relatively oxidized and Sr-rich; Stage II scheelite precipitated from these fluids. Precipitation of Stage II-a scheelite resulted in the Stage II-b fluids becoming progressively MREE-depleted. Extensive alteration, especially greisenization and phyllic alteration, led to plagioclase decomposition, which provided the Ca necessary for scheelite mineralization. This process was important in generating the W mineralization in the Muguayuan deposit, and perhaps for other granite-hosted, veinlet-disseminated scheelite deposits in the Jiangnan Orogen. [ABSTRACT FROM AUTHOR]

Veinlet-disseminated and vein-type tungsten deposits are important tungsten resources in South China and show remarkable diversity in dominant tungsten minerals. To better understand their genesis, scheelite from the Shimensi veinlet-disseminated deposit and wolframite from the Xihuashan and Piaotang vein-type deposits were selected to conduct in-situ laser ablation-inductively coupled plasma-mass spectrometry trace element analyses. The Shimensi tungsten mineralization occurs in intensively altered granitic rocks and is characterized by scheelite. Two generations of scheelite in a single grain can be identified by cathodoluminescence (CL) imaging. The early scheelite (dark domains in CL images) is characterized by nearly flat chondrite-normalized REE (REE N ) patterns with significantly negative Eu anomalies, whereas the late one (bright domains in CL images) shows light rare earth element (LREE)-enriched REE N patterns and obviously positive Eu anomalies. The former has higher REE, Na, Nb and Ta and lower Sr contents than the latter. The Xihuashan and Piaotang wolframite-quartz veins are developed in greisenized granite (type I) and metasedimentary rocks (type II). Both types of wolframite show LREE-depleted patterns, but type I exhibits strongly negative Eu anomalies and type II positive Eu anomalies. Type I contains higher REE, Nb and Ta concentrations, and lower FeO/MnO ratios than type II. Variations of Eu anomalies and trace element compositions in both scheelite and wolframite can be used to decipher the origin and processes of tungsten mineralization. Both the early scheelite and wolframite (type I) display significantly negative Eu anomalies and have high REE, Nb and Ta contents, suggesting that the initial ore-forming fluids were of magmatic origin. Precipitation of tungsten minerals and alteration would effectively modify the composition of ore-forming fluids. Deposition of the early tungsten minerals would lower REE, Nb and Ta in the mineralizing fluids, leading to depletion of these elements in the late ones. Although both the type I and II wolframite have different REE contents and Eu anomalies, they show similar left-dipped REE N patterns, implying that compositional variation of fluids is likely driven by crystallization of wolframite during the processes of fluid evolution. In contrast, the elevated LREE/HREE (heavy rare earth element) ratios, δEu (Eu N /Eu N ∗ ) values and Sr abundances in the late scheelite are possibly caused by the decomposition of plagioclase and K-feldspar. Alteration plays an important role in the formation of veinlet-disseminated scheelite deposits. It can be concluded that vein-type wolframite mineralization is mainly formed by filling and that veinlet-disseminated scheelite mineralization is associated with metasomatism. [ABSTRACT FROM AUTHOR]