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The occurrence of gold in hydrothermal sulfide at Southwest Indian Ridge 49.6°E

Acta Oceanologica Sinica 2012年第6期31卷 72-82页

作者： YE Jun SHI Xuefa YANG Yaomin LI Naisheng LIU Jihua SU Wenchao Institute of Oceanology Chinese Academy of SciencesQingdao 266007China First Insititute of Oceanography State Oceanic AdministrationQingdao 266061China Graduate University of the Chinese Academy of Sciences Beijing 100049China National Oceanographic Center Qingdao 266071China State Key Laboratory of Ore Deposit Geochemistry Chinese Academy of SciencesGuiyang 550002China

Massive sulfide precipitates found in the Southwest Indian Ridge （SWIR） 49.6°E hydrothermal field are enriched in gold. Here, the mineralogy and mineral chemistry of these massive sulfides to constrain the process of gold precipitation were studied. sulfide samples in this field include lower- temperature Zn-rich sulfides and relative higher-temperature Fe-rich sulfides. Zn-rich sulfides are dominated by sphalerite-pyrite-chalcopyrite assemblages, with concentrations of gold ranging from 9.08 to 17.0 μg/g. Fe-rich sulfides consist mainly of pyrite-marcasite-isocubanite assemblages, with gold concentrations from 2.17 to 3.79 μg/g. The significant enrichment in gold within the lower- temperature Zn-rich sulfides and the effective separation of Zn and Fe in hydrothermal precipitates at the surface of this field are here interpreted to reflect the strong temperature dependence of gold transportation and deposition within the sulfides. In Zn-rich samples, large amounts of isolated native gold grains were identified. They were found mainly as inclusions up to 8 μm in diameter, occupying porous cavities in sphalerite or in the elevated iron content rim of sphalerite. The fineness of the gold ranged from 810 to 830. Unlike previously published results on other hydrothermal fields, these data show a low gold fineness values in SWIR 49.6°E. The FeS content of sphalerite associated with gold grains ranged from 3.2 mole % to 18.9 mole %. This was higher than in other fields, indicating that the sulfur activity is relatively low during the gold precipitation process and that sulfur activity may be one of the main factors affecting gold fineness in the SWIR 49.6°E hydrothermal field. Evidence regarding gold fineness and sulfur activity suggests that gold was quite likely transported as AuHS° rather than as a Au（HS）2- complex.

关键词： hydrothermal sulfide Southwest Indian Ridge occurrence of gold mineralogy

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Ga isotopic fractionation in sulfides from the Yuhuang and Duanqiao hydrothermal fields on the Southwest Indian Ridge

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Geoscience Frontiers 2021年第4期12卷 122-130页

作者： Yuxu Zhang Shili Liao Chunhui Tao Hanjie Wen Haifeng Fan Jing Wen Weifang Yang Wei Li State Key Laboratory of Ore Deposit Geochemistry Institute of GeochemistryChinese Academy of SciencesGuiyang 550081China Key Laboratory of Submarine Geosciences Second Institute of OceanographyMinistry of Natural ResourcesHangzhou 310012China University of Chinese Academy of Sciences Beijing 100049China

This study examines the Ga isotopic compositions of sulfides in the Yuhuang and Duanqiao hydrothermal fields on the Southwest Indian Ridge,mid-ocean ridge basalts(MORB),and calcareous sediments around the hydrothermal ***δ^(71/69)Ga_(NIST-994) values of theMORB samples vary little(+1.20‰to+1.23‰,with an average of+1.22‰)and are consistent with the δ^(71/69)Ga_(NIST-994) values of two standard basalt samples(BCR-2 and BHVO-2),indicating that Ga isotopes may either not fractionate or fractionate only slightly under high-temperature geological processes;therefore,the δ^(71/69)Ga_(NIST-994) value of oceanic crust may be+1.22‰.The sediments(+1.28‰to+1.47‰,with an average of+1.38‰)are rich in heavier Ga isotopes than the basalts,and the Ga present in the sediments may have originated from soluble Ga present in the seawater that was adsorbed by(Mn,Fe)oxides/*** Ga contribution of basaltic debris to the sedimentswas almost ***,wespeculate that theδ^(71/69)Ga_(NIST-994) value of seawater in the study area fell within a range from+1.92‰to+2.36‰.Theδ^(71/69)Ga_(NIST-994) values of the sulfides in the Yuhuang hydrothermal field range from+0.99‰to+1.57‰,with an average of+1.25‰,and theδ^(71/69)Ga_(NIST-994) values of the sulfides in the Duanqiao hydrothermal field range from+0.93‰to+1.55‰,with an average of+1.19‰.Theδ^(71/69)Ga_(NIST-994) ranges of the sulfides in the Yuhuang and Duanqiao hydrothermal fields are similar,with the Ga isotopic fractionation reaching 0.58‰and 0.62‰,*** averageδ^(71/69)Ga_(NIST-994) values in the sulfides are close to those in the *** suggests that Ga within the sulfides in the Yuhuang and Duanqiao hydrothermal fields mainly originated from MORBs,with seawater and sediments making only small *** Ga isotopic fractionation in the sulfides may be related to processes associated with the formation of sulfides,such as rapid precipitation or the admixture of different stages of *** st

关键词： Ga isotope hydrothermal sulfide Yuhuang Duanqiao Southwest Indian Ridge

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