This study documents the geochemistry of sulfide ores of the Tudun Cu–Ni sulfide deposit, located at the western end of the Huangshan–Jing'erquan ore belt in the northern part of eastern Tianshan. The ores have been classified as (1) disseminated sulfide ores, (2) net-textured sulfide ores, and (3) massive sulfide ores. The geochemistry of barren rocks shows Ni and Cu contents ranged 889–1330 ppm and 145–253 ppm, respectively. The rocks generally contained ~ 0.10 ppb Rh, Ir, Ru and Os, and ~ 1 ppb Pt and Pd, as well as high Cu/Pd ratios (133–246). The contents of Cu, Ni and PGEs in sulfide ores were calculated on a 100% sulfide basis. Total PGEs on a 100% sulfide basis ranged from 13.2 ppb to 443 ppb (average = 144 ppb), which were lower than the values in the Huangshandong deposit (average = 186 ppb) in the eastern Tianshan ore belt, one order of magnitude lower than the Jinchuan deposit, and two orders of magnitude lower than the Noril'sk–Talnakh deposit. The R factor value ranged from 168 to 1810 in sulfide ores of the Tudun deposit, indicating Cu and Ni enrichment, although PGEs enrichment did not reach recoverable grades. In the Tudun deposit, the Pd/Ir ratio of sulfide ores was less than 100, showing weak hydrothermal fluid alteration. The massive sulfide ores exhibited less primitive mantle-normalized PGEs patterns, which are depleted in PPGEs and different from PPGEs-rich intrusions, as well as disseminated and net-textured sulfide ores. In addition, the massive sulfide ores exhibit a strong negative Pt anomaly. This may be due to fractionation of Pt–Fe alloys in the magma batches prior to its intrusion into the staging chamber. It could also be caused by selective Pt leaching from the sulfides by hydrothermal fluids during remobilization within the Tudun chamber.
Abstract: The Fengshan porphyry‐skarn copper–molybdenum (Cu–Mo) deposit is located in the south‐eastern Hubei Province in east China. Cu–Mo mineralization is hosted in the Fengshan granodiorite porphyry stock that intruded the Triassic Daye Formation carbonate rocks in the early Cretaceous (∼140 Ma), as well as the contact zone between granodiorite porphyry stock and carbonate rocks, forming the porphyry‐type and skarn‐type association. The Fengshan granodiorite stock and the immediate country rocks are strongly fractured and intensely altered by hydrothermal fluids. In addition to intense skarn alteration, the prominent alteration types are potassic, phyllic, and propylitic, whereas argillation is less common. Mineralization occurs as veins, stock works, and disseminations, and the main ore minerals are chalcopyrite, pyrite, molybdenite, bornite, and magnetite. The contents of palladium, platinum and gold (Pd, Pt and Au) are determined in nine samples from fresh and mineralized granodiorite and different types of altered rocks. The results show that the Pd content is systematically higher than Pt, which is typical for porphyry ore deposits worldwide. The Pt content ranges from 0.037 to 1.765 ppb, and the Pd content ranges between 0.165 and 17.979 ppb. Pd and Pt are more concentrated in porphyry mineralization than skarn mineralization, and have negative correlations with Au. The reconnaissance study presented here confirms the existence of Pd and Pt in the Fengshan porphyry‐skarn Cu–Mo deposit. When compared with intracontinent and island arc geotectonic settings, the Pd, Pt, and Au contents in the Fengshan porphyry Cu–Mo deposit in the intracontinent is lower than the continental margin types and island are types. A combination of available data indicates that Pd and Pt were derived from oxidized alkaline magmas generated by the partial melting of an enriched mantle source.
The Tongshankou skarn deposit in the Edong ore district is a typical metasomatic deposit associated with adjacent granodiorite porphyry and carbonate rocks. Using comprehensive microscopic observations, mineralogical and geochemical analysis, scheelite grains in the skarns can be classified into three major types, showing multi-stage mineralization characteristics. In the redox fluid environment, scheelites that occur with garnets usually have affinity to garnets, while in later skarn phases others exist with oxides and sulfides. They can be subdivided by trace elements, such as Nb and Eu, to discuss the detailed ore-forming process. Scheelites have three typical substitution mechanisms including: 2Ca2 + ⇌ REE3 + +Na+ (1); Ca2 + + W6 + ⇌ REE3 + +Nb5+(2); and 3Ca2 + ⇌ 2REE3++ □Ca (□Ca = Ca site vacancy) (3). Plagioclase or various hydrothermal stages can cause Eu anomalies to fluctuate from positive to negative, and these processes can cause particular zonation in W and Mo contents in scheelites. This study highlights the use of texture and geochemistry of scheelites in skarn deposits, depicting the W mineralization processes.
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