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Zhang Y.-H.,Chinese Academy of Geological Sciences | Zhang Y.-H.,Jinyuan Mining Industry Co. | Zhang Y.-H.,Jilin University | Mao J.-W.,Chinese Academy of Geological Sciences | And 2 more authors.
Jilin Daxue Xuebao (Diqiu Kexue Ban)/Journal of Jilin University (Earth Science Edition) | Year: 2012

The Dahu-Qinnan molybdenum deposit is located in northern belt of the Xiaoqinling gold province and metallogenically belongs to the Xiaoqinling-Waifangshan sub-zone of the eastern Qinling Mo-W metallogenic belt, Central China. Spatially associated with Au-bearing quartz veins, the molybdenite mineralization in the area is characterized by Mo-bearing quartz veins. The occurrences, textures and alterations of Mo-bearing quartz veins in Dahu-Qinnan area have been studied based on the field observation and PIMA instrument analysis. These Mo-bearing quartz veins are friable with cream color, and are of vuggy, cloddy, breccias structure. The breccias in these Mo-bearing quartz veins are mostly gneiss of the Taihua Group and porphyritic granite dyke of Mesozoic with stockwork and disseminated molybdenite mineralization. These breccias are replaced more or less by argillic minerals. Alteration associated with molybdenite-bearing quartz veins is mainly potassium alteration(only in the breccias), alteration to sericite, sillicification (residual silica), alteration to kaolinite, smectite and anhydrite. Based on field evidences, alteration in the area can be divided into 1) Potassium+sericite+sillicification+pyrite+molybdenite in early stage and 2) sillicification (residual silica)+kaolinization+anhydrite in later stage. Molybdenite and other sulfide minerals occur as the infillings in fissures and pore space in molybdenite-bearing quartz veins. The ore-forming temperatures of Mo-bearing quartz veins are from 134°C to 463°C. The δD H2O is from -96‰ to -110‰, and δ 18O quartz is from 10.7‰ to 11.5‰ respectively, revealing a mixing processes of magmatic, metamorphic fluids and meteoritic water. δ 18O value of kaolinite is from 0.1‰ to 2.3‰, also suggesting a hydrothermal origin. δ 34S pyrite is from -5.778‰ to -7.841‰, indicating the involvement of organism in metallogeny. Based on above studies and combined with the geological setting of the deposit, it is suggested that the molybdenite-bearing quartz veins in the area are likely to be porphyry molybdenum orebodies associated with porphyry granite dyke formed probably at ca. 245-211 Ma during the continental-continental collision of the Qinling orogeny. They were leached and enriched by high sulfidation hydrothermal fluids during later gold-forming epoch. Source

Jian W.,Clausthal University of Technology | Lehmann B.,Clausthal University of Technology | Mao J.,Chinese Academy of Geological Sciences | Ye H.,Chinese Academy of Geological Sciences | And 5 more authors.
Economic Geology | Year: 2015

The Dahu Au-Mo deposit is located in the Xiaoqinling region and belongs to the Qinling-Dabie orogen of central China. The quartz vein-style Dahu Au-Mo deposit (31 t Au, average grade: 4.7 g/t; 30,000 t Mo, average grade: 0.13%) formed in four stages, i.e., an early quartz-K-feldspar stage (I), a pyrite-molybdenite stage (II), a sulfide-telluride-sulfosalt-gold stage (III), and a late carbonate-barite stage (IV). Abundant tellurides and sulfosalts occur in stage III: altaite, tellurobismuthite, buckhornite, hessite, petzite, calaverite, aikinite, kupcikite, lindstromite, salzburgite, wittichenite, and tetradymite. The system is characterized by carbono-aqueous fluids of low to moderate salinity and high oxygen fugacity. Total homogenization temperatures of the H2O-CO2 fluid inclusions in stage I and stage III quartz range from 230° to 440° C and 198° to 320° C, respectively. The variation in CO2/H2O ratios and microthermometric data of the H2O-CO2 fluid inclusions results from a combination of fluid unmixing and sequential trapping of fluid inclusions, but also from postentrapment reequilibration. Abundant minerals are present as solid phases in H2O-CO2 fluid inclusions in stage I quartz: Cu1.65S, covellite, chalcopyrite, bornite, molybdenite, pyrite, colusite, anhydrite, and celestine. δ18Oquartz values of stage I quartz range from 10.2 to 12.0‰, with calculated δ18Ofluid values ranging from 5.6 to 7.4‰. The δD values of fluid inclusion waters (thermal decrepitation) in stage I quartz range from -117 to -54‰. The low and scattered δD values reflect a mixture of ore-forming fluids trapped by the H2O-CO2 fluid inclusions at deep crustal levels and postmineralization fluids, possibly meteoric waters, trapped by secondary aqueous fluid inclusions at higher crustal levels during uplift of the Xiaoqinling core complex. Four molybdenite samples yield an Re-Os isochron age of 206.4 ± 3.9 Ma (MSWD = 0.88), suggesting ore formation in the Late Triassic. Metal signature, mineral association, fluid characteristics, and isotope data of the Dahu deposit, together with the tectonomagmatic setting, imply that the ore-forming fluids were derived from an unexposed and oxidized magmatic system, which likely stems from partial melting of enriched lithospheric mantle beneath the North China craton in a postcollisional extensional setting. ©2015 Society of Economic Geologists, Inc. Source

Jian W.,Clausthal University of Technology | Lehmann B.,Clausthal University of Technology | Mao J.,Chinese Academy of Geological Sciences | Ye H.,Chinese Academy of Geological Sciences | And 5 more authors.
Canadian Mineralogist | Year: 2014

The Xiaoqinling vein-style gold district (reserves of >630 t Au) has a very pronounced tellurium signature. The Yangzhaiyu gold deposit is one of the largest gold deposits in this district. The ore-mineral assemblage consists of pyrite, chalcopyrite, galena, bornite, sphalerite, gold, and native tellurium together with a wide variety of telluride and Bi-sulfosalt minerals. The telluride mineral assemblage comprises Phase A, sylvanite [(Au,Ag)2Te4], hessite [Ag2Te], petzite [Ag3AuTe2], calaverite [AuTe2], stützite [Ag5-xTe3], rucklidgeite [PbBi2Te4], altaite [PbTe], volynskite [AgBiTe2], tellurobismuthite [Bi2Te3], tetradymite [Bi2Te2S], and buckhornite [AuPb2BiTe2S3]. The Bi-sulfosalt minerals observed are Phase B, aikinite [PbCuBiS3], felbertalite [Cu2Pb6Bi8S19], and wittichenite [Cu3BiS3]. We observed two unnamed phases: Phase A and Phase B. Phase A, with the empirical formula of AgTe3, occurs in small intergrowth aggregates with sylvanite and chalcopyrite, and locally with bornite, galena, and altaite. Phase A and its associated minerals occur along healed micro-fractures in pyrite. It has a distinctly golden reflection color, without discernable reflectance pleochroism or anisotropy. AgTe3 was synthesized in 1982, but its natural occurrence has not been reported to date. Phase B, with the empirical formula of Cu20FePb11Bi9S37, was observed in an intergrowth aggregate together with hessite, galena, chalcopyrite, bornite, and buckhornite. It has a pinkish grey reflection color, without discernable reflectance pleochroism or anisotropy. The telluride and gold mineralization took place at or below ca. 220 ° C and evolved towards decreasing fTe2. The ore-forming fluids and components of the Yangzhaiyu gold deposit may ultimately stem from refertilized upper mantle, either directly from devolatilization or from a magmatic system resulting from partial melting. Source

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