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The late Paleozoic tectonic setting of the Zongwulong Belt (ZWLB), a significant unit located in the northern Qaidam margin, Qinghai province, remains uncertain. Diabase dykes in the western part of the Zongwulong Belt offer insights into this issue. Field investigations reveal that the dips of the dykes are almost vertical, and they have sharp boundaries with the host rocks. These dykes consist of plagioclase, clinopyroxene, and opaque minerals exhibiting a characteristic porphyritic texture and massive structure. Zircon U-Pb dating of the dykes yields a weighted 206Pb/238U age of 289 ± 1 Ma. The dykes exhibit relatively high concentrations of TFeO, K2O + Na2O, and TiO2, while the SiO2 and MgO concentrations are relatively low. They display relative light-over-heavy REE enrichment, and lack negative Nb-Ta and Eu anomalies. The dykes underwent negligible crustal contamination, and experienced extensive fractional crystallization of olivine, clinopyroxene, and Fe-Ti oxides. Originating from the spinel–garnet transition zone at depths of approximately 75 km, the dykes result from garnet facies low-degree melting (5%–10%) in a continental rift setting. Combining these findings with regional geological data, we propose that the ZWLB likely experienced a continental rift in the west and exhibited a narrow oceanic environment in the east in the late Paleozoic period, potentially representing the most distant north branch of the East Paleo-Tethys Ocean. [ABSTRACT FROM AUTHOR]

The Bengal Basin is a well‐known foreland basin that archives the tectonic evolution of the Himalayan and Indo‐Burman Ranges (IBR). The Dupi Tila Formation is the youngest among the stratigraphic successions of the Bengal Basin, which witnessed the last phase of the Himalayan uplift. However, there is still controversy regarding sediment provenances since the Himalayan and IBR are in the late Neogene exhumation stage. In this study, the petrographical and geochemical compositions of the Dupi Tila sandstones from the Lalmai Anticline of the Bengal Basin are examined to infer the source rocks, tectonic settings, palaeoclimate and weathering intensity in provenance areas. The detrital modes and geochemical discriminations, as well as Chondrite‐normalized rare earth elements patterns with enrichment in light rare earth elements and nearly flat heavy rare earth elements and negative Eu anomalies (average Eu/Eu* = 0.77) indicate dominantly felsic source rocks. The geochemical data also suggest that these source rocks in provenance areas were influenced by weak to moderate chemical weathering (chemical index of alteration: 65.64–75.62) and multiple recycling under warm and humid to semi‐humid climatic conditions. The detrital zircon ages show three dominant peaks at ca. 100, 500 and 1000 Ma with minor 1700 Ma. The amount of young zircon grains (<120 Ma) is noticeably higher (~18%) in this Lalmai outcrop compared to the Dupi Tila samples from the Sylhet Trough and Chittagong‐Tripura Fold Belt. Results from integrated zircon geochronology and geochemistry indicate that the detritus are likely derived from a recycled orogen provenance related mainly to active continental margin setting with subordinate influence from passive setting. Therefore, the regionally extensive Himalayan Orogen appears to be the primary sediment source, with additional mixing from the IBR and recycled sediments originating from the Gangdese batholith of the Trans‐Himalaya. [ABSTRACT FROM AUTHOR]

Scheelite, one kind of common REE-rich and U-bearing hydrothermal mineral, is extensively developed in various types of gold deposits, which can be used to record nature and timing of metallogenesis. The Zhaishang Carlin-like gold deposit in the Qinling Orogen is a giant Au deposit, hosting 127t of Au @ 2.67 g/t with economic concentrations of tungsten and antimony. The study reports two types of scheelite based on the characteristics of petrography and geochemistry. Sch A shows significant oscillatory zoning with dark gray cathodoluminescence (CL) response, whereas Sch B displays patchy textures with brighter CL response. Systematic LA-ICP-MS U–Pb dating of Sch A and Sch B yields ages of 227.1 ± 3.2 Ma and 226.2 ± 6.9 Ma, respectively. The new dates, constraining the Zhaishang Au–W mineralization to ~ 227Ma, coincide well with the western Qinling magmatism, metallogenic and tectonic events. There are significant variations in concentration, the Sch A has low REE content (mean = 41.3 ppm), negative Eu-anomaly with slightly positive Ce-anomaly, whereas Sch B, with small negative or positive Eu-anomaly, has higher REE content (mean = 247 ppm) and higher positive Ce-anomaly. The positive correlation of EuN and EuN* records oxidizing condition during the whole W mineralization event. Additionally, Sch B intergrown with selenides with an increase in the Ce-anomaly supports that the latter has higher oxygen fugacity environment. The Sr isotope signature for scheelite supports that ore-forming metals mostly inherited the host rock component, while the proportion of magma-derived Sr increased in the Sch B. Fluid–rock interactions co-precipitated Au and W caused by the release of Fe and Ca cations and the increase of pH. The study highlights that scheelite as a recorder can help in deciphering the nature and timing of metallogenesis of the studied Au–Sb–W deposit, and thus other similar Au–W deposits. [ABSTRACT FROM AUTHOR]

The influence of the paleo-Tethys or paleo-Pacific oceanic plate subduction on Early Triassic South China has long been debated. We have studied the zircon U-Th-Hf isotopes, trace elements, and whole-rock geochemistry of Early Triassic peraluminous granitoids in the Qinzhou Bay area, South China Block. LA–ICP–MS zircon U–Pb dating has revealed the Jiuzhou granodiorites and Dasi-Taima granite porphyries formed between 248.32 ± 0.98 and 246.6 ± 1.1 Ma. These rocks are characterized by high K2O and Al2O3, and low MgO, CaO, and P2O5 contents with A/CNK = 1.06–1.17, showing high-K calc-alkaline S-type affinities. The Early Triassic intrusive rocks and adjacent silicic volcanic rocks in the Qinzhou Bay area were found to be comagmatic and derived from a common magma pool, detached in an undifferentiated melt instead of indicating remarkable crystal—melt separation. Although the analyzed granitoids have highly enriched zircon Hf isotopic compositions (εHf(t) = −23.9 to −7.8), they cannot originate solely from metasedimentary protoliths. Source discrimination indicators have revealed enriched lithospheric mantle-derived magma was also an endmember component of the S-type silicic magma, which provided a heat source for the crustal anatectic melting as well. We inferred the studied Early Triassic granitoids formed under the paleo-Tethys tectonic regime before the collision of South China and Indochina blocks, as the oceanic plate subduction would have created an extensional setting which further caused the mantle-derived upwelling and volcanic eruption. [ABSTRACT FROM AUTHOR]

[Display omitted] • Hongqiling Sn-W polymetallic deposit is a product of granitic magmatism in Late Jurassic. • The elemental composition of primary cassiterite is controlled by the compositions of ore-forming fluid and the rate of crystallization. Hongqiling deposit is one of the most typical hydrothermal vein type Sn-W polymetallic deposits in the Dongpo ore field, southern Hunan. It is an ideal object to study the Sn-W mineralization in the Nanling metallogenic belt and even in the whole South China Block, and to reveal the regional metallogenetic regularity. Based on the detailed investigation of the deposit geology, this paper discusses the mineralization age and processes of the Hongqiling hydrothermal vein type Sn-W polymetallic deposit by LA-MC-ICP-MS in-situ U-Pb dating and trace element geochemistry of cassiterite from the quartz vein type Sn-W ore body. Cathodoluminescence (CL) imaging shows that cassiterite in Hongqiling deposit can be divided into two generations. primary cassiterite (Cst-I) and altered cassiterite (Cst-II). The LA-MC-ICP-MS in-situ U-Pb age of the two groups of Cst-I samples are 158.9 ± 0.7 Ma and 158.4 ± 0.8 Ma, respectively, which are well consistent with the mineralization ages of most Sn-W deposits in the Nanling metallogenic belt, and are also consistent with the ages of middle to late Jurassic magmatic activity represented by the Qianlishan intrusion. This indicates that the Hongqiling deposit, like many Sn-W deposits in the Nanling metallogenic belt, is genetically related to the regional Middle to Late Jurassic granitic magmatic activities. LA-ICP-MS trace element analysis shows that trace elements such as Na and Cs are mainly distributed in fluid inclusions in cassiterite, while the major elements such as Mg, Al, and Si are mainly distributed in the mineral inclusions, and other elements such as W, U, Zr, Hf and Ti are mainly distributed in the cassiterite by isomorphic substitution. The high Fe and W contents in both primary and altered cassiterite indicate that the ore-forming fluid of Hongqiling deposit is mainly derived from granitic magma. The fluctuating variation of Fe, V, Sc, Ti, Zr, Hf, Nb and Ta in the primary cassiterite with the crystalline bands indicates that there are two large-scale pulses of magmatic hydrothermal fluid during the mineralization process, while the altered cassiterite is relatively depleted of Ti, Sc, Zr and U elements, and enriched in Pb which may represent the compositional characteristics of the late-stage fluid. In summary, the Hongqiling hydrothermal vein type Sn-W polymetallic deposit was formed by the pulsating exsolution of magmatic hydrothermal fluid of late Jurassic granitic magmatism. The trace elemental compositions of primary cassiterite are generally controlled by the compositions of ore-forming fluid and the rate of crystallization. [ABSTRACT FROM AUTHOR]

Representative CL images showing the texture of the Yangla scheelite and corresponding variations in the REE patterns throughout the evolution of the oreforming fluids. [Display omitted] • Three types of scheelite are identified based on their microstructure. • Tungsten mineralization age is significantly later than the Triassic Cu mineralization in the Yangla district. • Source and evolution ore-forming fluids were constrained by scheelite texture and geochemistry. The Yangla Cu-polymetallic deposit is the largest skarn Cu deposit in the Jinshajiang suture zone. Recently, an new W orebody was identified in the depths of the Cu orebodies. However, the genetic relationship between W and Cu orebodies, along with the tungsten ore-forming processes, remains unclear. This study delves into the careful investigation of three types of scheelites focusing on microstructure, trace element compositions and Sr isotope geochemistry. The aim is to elucidate the source and evolution of ore-forming fluids and ore genesis in the multi-episodic metallogenic systems. Primary scheelite (Sch-I) generally displays oscillatory zoning in CL images with the lowest REE (3.8–142 ppm) and highest Sr (604–1480 ppm) contents. Secondary scheelite (Sch-III), commonly precipitated as overprinting rims on primary crystal, has the highest REE (145–1071 ppm) and lowest Sr (376–793 ppm) contents. In contrast, Sch-II represents a transitional stage from primary to secondary, with REE and Sr contents at intermediate levels. Sch-I is characterized by LREE enrichment and a positive Eu anomaly in the chondrite-normalized REE patterns, whereas Sch-III shows MREE-rich patterns with a weak positive Eu anomaly. Scheelite U-Pb dating (30.3 ± 1.5 Ma) indicates that the W mineralization is not genetically related to Triassic granitoids in the Yangla district. Instead, it is likely associated with magmatic activities and tectono-thermal events in the Jinshajiang fault zone during the Cenozoic. The high initial 87Sr/86Sr ratios (0.71771–0.72229) in the scheelite, significantly higher than those of Triassic granites and ore-hosting marble, suggest that the geochemical features of Sch-I are inherited from the parental ore-forming fluids. These fluids are likely derived from the mixed hydrothermal fluids involved by the Neoproterozoic strata and/or concealed magmatism. [ABSTRACT FROM AUTHOR]

Schematic diagram of textural characteristics, formation process and hydrothermal spatial evolution of garnets at different locations in the Huanggangliang Fe-Sn deposit. [Display omitted] • U-Pb dating of garnet constrains the onset of hydrothermal activity and the formation of skarn. • The hydrothermal physicochemical conditions of the Huanggangliang garnets are constrained. • Garnet trace elements are important in distinguishing different mineralization conditions. • Tin-rich garnet can be used as an indicator mineral for exploration of skarn-type tin deposits. Cu-Fe (Au), W-Sn (Mo), Pb-Zn (Ag) and other element assemblages are common in many skarn deposits, but examples of Fe and Sn coexistence in nature are relatively rare. The Huanggangliang deposit in the southern Great Xing'an Range is the largest Fe-Sn polymetallic deposit in northern China, and there are five main mining areas (SK Ⅰ–SK Ⅴ) distributed along a SW–NE trend. SK Ⅰ and SK Ⅲ are the two larger mining areas in the Huanggangliang deposit, and their mineral assemblages and wall-rocks are significantly different: cassiterite and metal sulfides are duncommon in SK Ⅰ (andesite), while they are widely distributed in SK Ⅲ (marble). Garnet is widely distributed in SK Ⅰ and SK Ⅲ mining areas, and provides a good opportunity to explore the mechanism of Fe-Sn assemblage differentiation. Three types of garnet are distinguishable (Grt 1, Grt 2 and Grt 3) based on their mineral associations, textures and locations, and they mainly belong to the andradite-grossular solid solution series. The LA–ICP–MS U-Pb ages of the garnets from SK Ⅰ and SK Ⅲ are 136.0 ± 1.2 Ma (n = 25, MSWD = 1.9) and 136.2 ± 2.6 Ma (n = 37, MSWD = 1.8), respectively, suggesting that magmatic-hydrothermal activity in these two mining areas began at the same time. Grt 1 (located deep in SK Ⅰ and SK Ⅲ) and Grt 2 (located shallowly in SK Ⅰ) are mainly andradite, while Grt 3 (located shallowly in SK Ⅲ) is mainly grossular. They are all enriched in high field strength elements (HFSEs) and depleted in large ion lithophile elements (LILEs), and their REE patterns are enriched in light rare earth elements (LREEs) and depleted in heavy rare earth elements (HREEs). However, Grt Ⅰ-1a and 1b (deep garnets in SK Ⅰ) exhibit obvious positive Eu anomalies, while the other garnet types exhibit negative or no obvious Eu anomalies. Additionally, Grt 3 has high contents of V, Sn, U, Th, Zn and Y, and low contents of W and Mo. This pattern implies that the garnets in deep SK Ⅰ may have formed under oxidizing conditions with high temperatures, high oxygen fugacity (f O 2) and weak acidity, while the garnets in shallow SK Ⅲ formed under reducing conditions with moderate temperatures, moderate f O 2 and near-neutral pH. The garnets in shallow SK Ⅰ and deep SK Ⅲ may have formed under weak oxidation–reduction conditions at moderate to high temperatures, moderate f O 2 and weakly acidic to neutral pH conditions. Our newly reported field geological, mineralogical, and geochemical data from garnet suggest that the ore-forming fluids of the Huanggangliang were magmatic-hydrothermal fluids mixed with slightly acidic external fluids, chloride complexes may have been the main transport ligands of REEs. The metallogenic environment may be an important factor leading to the difference of mineral assemblages in the Huanggangliang deposit. [ABSTRACT FROM AUTHOR]

The subduction of the Pacific Plate led to asthenospheric upwelling and thus partial melting of the metasomatized mantle occurred. The REE-bearing initial alkaline magmas were evolved to generate the subsequent exsolution of carbonate melts and REE-rich hydrothermal fluids which existed at relatively shallow depth. Notably, two kinds of REE mineralization occur in the Weishan REE deposit: 1) quartz–barite–carbonate vein type and 2) disseminated and veinlet type. [Display omitted] • Zircon U-Pb dating indicates that the alkaline rocks intruded at ∼ 120 Ma; • Molybdenite Re-Os dating corroborates the mineralization age of ∼ 120 Ma; • Ore-forming magmas were mainly derived from an enriched lithospheric mantle; • Asthenospheric upwelling during craton destruction led to the mantle partial melting. The Weishan REE deposit is one of the largest LREE deposits in China, which is hosted by the Weishan alkaline complex (WSAC) and late Archean gneisses. Two types of mineralization including vein-type and disseminated-type occur in this deposit, of which the former is characterized by large quartz-sulfate-calcite-REE mineral veins cutting all kinds of wallrocks, while the latter is featured by REE minerals disseminated in the alkaline rocks. The vein-type mineralization commonly occurs at shallow depths and has been numerously studied. The disseminated-type mineralization typically occurs at deeper depths, which was newly discovered by drilling exploration and has been poorly studied. In this contribution, zircon U-Pb dating and Hf isotopic analysis as well as whole-rock geochemistry and Sr-Nd isotopic analyses were conducted on the deeply drilled alkaline rocks, combined with molybdenite Re–Os dating on the disseminated ore, with the aim to unravel the petrogenesis of the alkaline rocks and their contributions to the REE mineralization. Zircon U–Pb dating suggests an intrusive age of 119.9 ± 0.9 Ma for the WSAC, which is quite consistent the Re–Os age of 120.0 ± 1.8 Ma for the disseminated ore, corroborating their close genetic correlation. The studied alkaline rocks show enrichment of LILEs, depletion of HFSEs and strong fractionation between LREEs and HREEs, indicating a crustal involvement in the magmas or a metasomatized mantle source. They are characterized by higher Hf (εHf(t) = -6.7 to −12.2) and Nd (εNd(t) = -8.8 to −9.7) isotopic compositions compared with those of the contemporaneous subcontinental lithospheric mantle (SCLM). Based on the above features, it is inferred that the parental magmas of the WSAC were mainly derived from an enriched SCLM with some involvement of asthenospheric mantle-derived materials. The mantle source was likely metasomatized by the subducted Paleo-Pacific oceanic plate, leading to the enrichment of REE and carbonate. Rollback of the oceanic slab during the early Cretaceous resulted in an extensional setting in the study region, which was favorable for partial melting of the metasomatized mantle and thus generated the REE-rich alkaline magmas. [ABSTRACT FROM AUTHOR]

[Display omitted] • Garnet U-Pb dating constrains the age of the Lazhushan deposit at ca. 150 Ma. • Fe skarn mineralization in the Edong district started earlier than previously thought. • The Th/U ratio of garnet is a potential redox indicator of ore fluids. Garnet is ubiquitous in skarn deposits. It is a sensitive recorder of physiochemical conditions and also a powerful geochronometer. In this study, we use garnet trace element geochemistry and U-Pb geochronology as well as sulfur isotopes of sulfides to constrain the age and mineralization process of the Lazhushan Fe skarn deposit. Garnets in the Lazhushan Fe skarn belong to the andradite-grossular solution series and yield a compositional range from Adr 47.2 Gro 50.7 to Adr 97.4 Gro 0.9. There are strong correlations between La N /Yb N ratios and andradite contents in garnet, indicating that garnet major element composition exerts a strong control on the REE fractionation. The decrease of HFSEs (Nb, Ta, Zr, Hf, and Ti) and Co, V, and Mn concentrations from prograde to retrograde garnets may reflect increasing water/rock ratio and decreasing temperature during skarn evolution, respectively. Co-precipitation with magnetite may be responsible for the low concentration of V in the retrograde garnets. The Th/U ratio increase from endoskarn garnet to exoskarn counterparts, probably reflecting an increase of fluid f O 2 due to interactions with evaporate sulfate from the wall rocks. The sulfides in this deposit are enriched in δ34S (up to 13 ‰), conforming the involvement of evaporate sulfate during Fe skarn mineralization. The incursion of evaporate sulfate may have played an important role in magnetite mineralization for the Lazhushan deposit by increasing fluid f O 2 and facilitating the oxidation of Fe2+ to precipitate magnetite. LA-ICP-MS U-Pb dating of garnets from 4 garnet-bearing samples yielded ages of 150.8 ± 6.8 Ma (2σ), 150.9 ± 5.3 Ma (2σ), 150.2 ± 7.9 Ma (2σ), and 150 ± 11 Ma (2σ), which are consistent with zircon weighted mean U–Pb ages of 150.1 ± 2.0 Ma (2σ) and 150.5 ± 1.0 Ma (2σ) of the ore-related intrusion. Combined with previously published metallogenetic ages of skarn deposits in the Edong district, we suggest that the Lazhushan deposit may represent the initiation of Fe skarn mineralization for the Edong district during the Late Mesozoic. [ABSTRACT FROM AUTHOR]

[Display omitted] • The Xiaolonghe and Lailishan Sn deposits in the Tengchong-Lianghe tin belt formed in oceanic subduction and continental collisional settings, respectively. • The Sn-related granitoids from the two deposits have very similar magma sources, melting temperatures, evolution processes, redox states, and volatile contents. • The specific mechanism triggering mantle upwelling could be the most significant difference between the formation of Sn-related granitoids in subduction versus collision processes. Magmatic-hydrothermal Sn deposits can develop in both subduction and collision settings. However, a systematic comparison of the geochemical fingerprints and petrogenetic evolution of Sn-related granitoids from both settings is still lacking. The Tengchong-Lianghe tin belt hosts numerous Sn deposits but of different metallogenic ages, such as the Xiaolonghe and Lailishan Sn deposits, which provide an ideal study area for addressing this issue. Zircon U–Pb dating suggests that the Xiaolonghe and Lailishan Sn-related granitoids were emplaced at 74.2–75.5 and 50.0–51.1 Ma, respectively. Given the initial India-Asia collision commenced at ca. 65–60 Ma, these ages, consistent with available Sn metallogenic ages, suggest the formation of the Xiaolonghe and Lailishan Sn deposits in subduction and collisional settings, respectively. New zircon and apatite compositions, and apatite Sr isotopic data, combined with previously reported whole-rock geochemical results, all indicate that the Xiaolonghe and Lailishan Sn-related granitoids share similar magma sources, evolution processes, redox states, and volatile contents. The presence of hornblende, high apatite Nd N /Nd N * (mostly > 1), and whole-rock evolutionary trends, together indicate that they represent fractionated I-type granites. Distinctly elevated apatite 87Sr/86Sr ratios (0.70988–0.71430) suggest that they originated from an ancient lower crust. Subsequently, they underwent an extensive fractional crystallization dominated by feldspar, as revealed by whole-rock, apatite, and zircon elemental variation trends. The low zircon Ce N /Ce N * (mainly < 200) and ΔFMQ (–1.9 to 1.7), together with elevated apatite F content (2.30–3.69 wt%), reveal that they crystallized from reduced and F-rich magmas. The relatively high whole-rock zircon saturation temperatures (mainly > 800 ℃) and Ba/Pb ratios imply that they were produced at a higher temperature by biotite-dehydration melting, which requires additional heat from the mantle. The specific mechanism that triggers mantle upwelling (oceanic slab subduction or break-off) could be the most significant difference between Sn-related granitoids formed during subduction and collision processes. [ABSTRACT FROM AUTHOR]

[Display omitted] • This study is the first attempt of a systematic horizontal skarn profile in Beiya. • Two types of garnet have been distinguished in endoskarn and exoskarn. • The conditions and compositions of hydrothermal fluid in different environments vary. • The skarn mineralization age is restricted by crystallization age of garnet. Garnet is one of the most typical minerals in skarn deposits, and its texture and composition is a proxy for the changing physicochemical conditions. Thus, mineralogical and geochemical characterization of different garnet types can provide important information on the nature and evolution of ore-forming fluids. The Beiya gold-polymetallic deposit is China's largest skarn-type Au deposit with Au reserves of >380 t. Although several studies have addressed the skarn formation mechanism and nature of fluid evolution, a systematic study on the changes in the composition and texture of garnet from wall rocks to ore-related intrusion has not yet been attempted. In this work, we carry out a systematic investigation along a horizonal profile in the open pit of the Beiya deposit. Our results show that the garnet in the profile belongs to grossular-andradite solid solution series with all grains showing well-developed fine oscillatory zoning. The garnets are of two types: the first type (Grt I) formed within the endoskarn, is reddish to red with euhedral-subhedral megacryst structure (>10 mm) and has altered surfaces. The second type (Grt II) occur in the proximal exoskarn, is red to brown–red, euhedral-subhedral, with medium- to fine- grained structure (0.3–4 mm) and displaying oscillatory zoning. Unlike Grt I, hydrous minerals occur in the pores among Grt II garnets, such as calcite, quartz, epidote and chlorite. Also, calcite-chlorite vein, quartz vein and quartz-chalcopyrite-pyrite vein cuts the Grt II garnets. Grt I is dominantly grossular (Adr 14.88-43.58 Grs 55.25-82.87), depleted in the large ion lithophile elements (LILE), relatively enriched in high field strength elements (HFSEs) and enriched in heavy rare earth elements (HREEs) with negative Eu anomalies. Grt II is mostly andradite (Adr 62.18-98.91 Grs 0-36.22), depleted in the LILE and HFSE, enriched in light rare earth elements (LREEs) with slightly positive Eu anomalies. Here we selected Grt II for in-situ LA-ICP-MS U-Pb dating, since Grt I contains negligible uranium. The results yielded a lower intercept 206Pb/238U age of 35.3 ± 1.8 Ma (MSWD = 0.68, n = 23). The calculated oxygen isotopic compositions of hydrothermal fluids in equilibrium with two types of garnets range from 6.46 ‰ to 8.56 ‰ (average 7.89 ‰), which are within the range of values for magmatic fluids. We infer that the physicochemical conditions of the hydrothermal fluid changed from relatively reduced, nearly neutral, and low water/rock ratios to slightly oxidized, slightly acidic, and high water/rock ratios. The chlorine content in the fluid increased during garnet growth. The fluctuating compositions of garnets in the skarn suggest multistage ore-fluid activities and the fluid evolution provide insights into the ore-forming process. [ABSTRACT FROM AUTHOR]