贵州尾若金矿床载金矿物EPMA分析与原位硫同位素特征
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摘要
尾若金矿位于南盘江盆地西北部,是烂泥沟金矿区外围的小型金矿床,找矿潜力较好。该矿床的黄铁矿按其矿物组合和脉体穿插关系可划分为浸染状黄铁矿阶段(S1)和细脉状石英-黄铁矿阶段(S2)。为了查明该矿床金的赋存状态和硫化物中硫的来源,在金属硫化物组构特征观察的基础上,采用了电子探针(EPMA)和原位硫同位素分析方法,分析了不同金属硫化物中Au、As、S、Fe等元素的含量和δ34S组成。结果表明,尾若金矿床的载金矿物为含砷黄铁矿和毒砂,金主要以纳米级自然金(Au0)形式存在,少部分以固溶体(Au+)形式存在。该矿床的硫同位素值介于10.6‰～14.0‰之间,2个阶段形成的硫化物具有较为相似的硫同位素值,表明2期热液中硫的来源相同,均来自于海相硫酸盐,TSR(热化学还原作用)是尾若金矿床硫酸盐的还原机制。
The Weiruo gold deposit is in the northwestern Nanpanjiang basin. It is a small-scale gold deposit in the periphery of the Lannigou gold orefield with good exploration potential. Based on the mineral association of pyrite and relationship of cross-cutting vein systems in ores, the pyrite of this deposit can be classified into the disseminated pyrite at stage S1 and veining pyrite in quartz-pyrite veinlets at stage S2. Based on the observation of characteristic textures and structures of metal sulfides in the deposit, the EPMA and Nano-SIMS are applied to analyze Au, As, S, Fe contents and sulfur isotopic compositions(δ34S values) of various sulfides, respectively, in order to investigate the occurrence of Au and source of sulfur in sulfides. The results show that dominated gold-bearing minerals of the Weiruo gold deposit include arsenian pyrite and arsenopyrite. The gold occurred in arsenian pyrite in the forms of major nanometer-sized particles of native Au(Au0) and minor gold solid solution(Au+). The δ34S values of studied sulfides vary from 10.6‰ to 14.0‰. The sulfides formed in two stages have similar sulfur isotope values, indicating a same sulfur source in ore-forming fluids of two hydrothermal periods. Our research suggests that the sulfur in sulfides of the Weiruo gold deposit could come from seawater sulfate and the reaction of thermo-chemical sulfate reduction(TSR) may be the mechanism of sulfate reduction for the Weiruo gold deposit.
The Weiruo gold deposit is in the northwestern Nanpanjiang basin. It is a small-scale gold deposit in the periphery of the Lannigou gold orefield with good exploration potential. Based on the mineral association of pyrite and relationship of cross-cutting vein systems in ores, the pyrite of this deposit can be classified into the disseminated pyrite at stage S1 and veining pyrite in quartz-pyrite veinlets at stage S2. Based on the observation of characteristic textures and structures of metal sulfides in the deposit, the EPMA and Nano-SIMS are applied to analyze Au, As, S, Fe contents and sulfur isotopic compositions(δ34S values) of various sulfides, respectively, in order to investigate the occurrence of Au and source of sulfur in sulfides. The results show that dominated gold-bearing minerals of the Weiruo gold deposit include arsenian pyrite and arsenopyrite. The gold occurred in arsenian pyrite in the forms of major nanometer-sized particles of native Au(Au0) and minor gold solid solution(Au+). The δ34S values of studied sulfides vary from 10.6‰ to 14.0‰. The sulfides formed in two stages have similar sulfur isotope values, indicating a same sulfur source in ore-forming fluids of two hydrothermal periods. Our research suggests that the sulfur in sulfides of the Weiruo gold deposit could come from seawater sulfate and the reaction of thermo-chemical sulfate reduction(TSR) may be the mechanism of sulfate reduction for the Weiruo gold deposit.
引文
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[19]Mimaki Y,Nakamura O,Sashida Y.Structures of steroidal saponins from the tubers of brodiaea californica and their inhibitory activity on tumor promoter-induced phospholipid metabolism.china[J].Chem Pharm Bull(Tokyo),1995,43(6):971-976.
[20]Habicht K S,Canfield D E..Sulfur isotope fractionation during bacterial sulfate reduction in organic-rich sediments[J].Geochimica et Cosmochimica Acta,1997,61(24):5351-5361.
[21]Jonathan G W,Jonathan B S,Bogdan P O.Sulfur isotopic composition and the source of dissolved sulfur species in thermo-mineral springs of the cerna valley,Romania-sciencedirect.[J].Chemical Geology,2010,217:31-43.
[22]Machel H G.Relationships between sulphate reduction and oxidation of organic compounds to carbonate diagenesis,hydrocarbon accumulations,salt domes,and metal sulphide deposits[J].Carbonates and Evaporites,1989,4(2):137-151.
[23]DixonI G,Davidson G J.Stable isotope evidence for thermochemical sulfate reduction in the dugald river(australia)strata-bound shale-hosted zinc-lead deposit[J].Chemical Geology,1996,129(3/4):227-246.
[24]Bo B J,Mai F I,Halger W J.Bacterial sulfate reduction above 100°C in deep-sea hydrothermal vent sediments[J].Science,1992,258(5089):1756-1757.
[25]顾雪祥,章永梅,吴程赟,等.黔西南卡林型金矿床与古油藏的成因联系:有机岩相学证据[J].地学前缘,2013,20(1):9
[2]陈懋弘,吴六灵,Phillip J.Uttley,等.贵州锦丰(烂泥沟)金矿床含砷黄铁矿和脉石英及其包裹体的稀土元素特征[J].岩石学报,2007,23(10):2423-2433.
[3]黄庆文,刘苏桥,丁龙.我国右江盆地与美国“大盆地”卡林型金矿对比研究[J].矿产与地质,2009,23(3):193-203.
[4]陈懋弘,毛景文,陈振宇,等.滇黔桂“金三角”卡林型金矿含砷黄铁矿和毒砂的矿物学研究[J].矿床地质,2009,28(5):539-557.
[5]张弘弢,苏文超,田建吉,等.贵州水银洞卡林型金矿床金的赋存状态初步研究[J].矿物学报,2008,28(1):17-24.
[6]周天成,孙祥,郑有业,等.藏南查拉普金矿床载金矿物特征与金的赋存状态[J].矿床地质,2015,34(3):521-532.
[7]毛世东,杨荣生,秦艳,等.甘肃阳山金矿田载金矿物特征及金赋存状态研究[J].岩石学报,2009,25(11):2776-2790.
[8]张燕,陈翠华,顾雪祥,等.贵州三都苗龙金-锑矿床金赋存状态初步探讨[J].中国地质,2014,41(5):1620-1635.
[9]夏勇.贵州贞丰县水银洞金矿床成矿特征和金的超常富集机制研究[D].贵阳:中国科学院地球化学研究所,2005.
[10]丁俊,张洪信,罗建均,等.贵州省册亨县尾若金矿点地质特征及找矿方向[J].山西科技,2014,29(4):48-51.
[11]ZHANG J C,LIN Y T,YANG W,et al.Improved precision and spatial resolution of sulfur isotope analysis using NanoSIMS[J].Royal society of chemistry,2014,29:1934-1943.
[12]Reich M,Stephen E.K,Satoshi U,et al.Solubility of gold in arsenian pyrite[J].Geochim Cosmochim Acta,2005,69(11):2781-2796.
[13]陆建军,王鹤年,沈渭洲,等.河南金矿同位素地质研究[J].地质找矿论丛,1990,5(1):84-92.
[14]Zhang X C.The Geology and hydrothermal evolution of sediment-hosted gold deposits in southwestern Guizhou Province,PRC[D].London:Imperial College(Doctoral thesis),1997.
[15]Zhang X C,Baruch S,Christopher H,et al.Sediment-hosted disseminated gold deposits in southwestern guizhou,prc:their geological setting and origin in relation to mineralogical,fluid inclusion,and stable-isotope characteristics[J].International Geology Review,2003,45(5):407-470.
[16]Chen M H,Zhang Z Q,Santosh M,et al.The carlin-type gold deposits of the“golden triangle”of SW China:Pb and S isotopic constraints for the ore genesis[J].Journal of Asian Earth Sciences,2015,103:115-128.
[17]Zheng Y F,Jochen H.Effects of mineral precipitation on the sulfur isotope composition of hydrothermal solutions[J].Chemical Geology,1993,105(4):259-269.
[18]Canfield D E,Teske A.Late proterozoic rise in atmospheric oxygen concentration inferred from phylogenetic and sulphur-isotope studies[J].Nature,1996,382(6587):127-132.
[19]Mimaki Y,Nakamura O,Sashida Y.Structures of steroidal saponins from the tubers of brodiaea californica and their inhibitory activity on tumor promoter-induced phospholipid metabolism.china[J].Chem Pharm Bull(Tokyo),1995,43(6):971-976.
[20]Habicht K S,Canfield D E..Sulfur isotope fractionation during bacterial sulfate reduction in organic-rich sediments[J].Geochimica et Cosmochimica Acta,1997,61(24):5351-5361.
[21]Jonathan G W,Jonathan B S,Bogdan P O.Sulfur isotopic composition and the source of dissolved sulfur species in thermo-mineral springs of the cerna valley,Romania-sciencedirect.[J].Chemical Geology,2010,217:31-43.
[22]Machel H G.Relationships between sulphate reduction and oxidation of organic compounds to carbonate diagenesis,hydrocarbon accumulations,salt domes,and metal sulphide deposits[J].Carbonates and Evaporites,1989,4(2):137-151.
[23]DixonI G,Davidson G J.Stable isotope evidence for thermochemical sulfate reduction in the dugald river(australia)strata-bound shale-hosted zinc-lead deposit[J].Chemical Geology,1996,129(3/4):227-246.
[24]Bo B J,Mai F I,Halger W J.Bacterial sulfate reduction above 100°C in deep-sea hydrothermal vent sediments[J].Science,1992,258(5089):1756-1757.
[25]顾雪祥,章永梅,吴程赟,等.黔西南卡林型金矿床与古油藏的成因联系:有机岩相学证据[J].地学前缘,2013,20(1):9