膏盐在金顶铅锌矿成矿中的作用:硫和锶同位素证据
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国土资源部公益性行业科研专项经费项目(项目号:201211074 )资助


The Role of Halosalt in the Mineralization of Jinding Pb-Zn Deposit: the Evidence from Sulfur and Strontium Isotopic Compositions
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    摘要:

    云南金顶铅锌、天青石、石膏和硫铁矿超大型复合矿床位于兰坪盆地的北缘,矿床中富含沥青和重油等有机质和膏盐类矿物。大部分硬石膏和石膏的δ34SV-CDT集中分布在+12‰~+16‰之间,与三叠纪末期海洋硫酸盐的δ34SV-CDT值+15‰相近;天青石的δ34SV-CDT较为离散,+6‰~+26‰,但在整体上围绕着硬石膏分布。除少部分早期成岩-矿化阶段形成的硫化物具有极低的生物成因特征的δ34SV-CDT以外,大部分金属硫化物的δ34SV-CDT呈现出“两段式”的分布特征,一组δ34SV-CDT集中在-12‰~-20‰区间,与石膏的δ34SV-CDT值相差约30‰;另一组δ34SV-CDT集中在-8‰~-2‰区间,与石膏的δ34SV-CDT值相差约20‰。在200℃的主成矿温度下,硫酸盐与硫化氢之间的硫同位素分馏刚好为30‰,在300℃为20‰,这与金顶矿床中石膏-硫化物之间硫同位素分布规律一致,表明矿床中的大部分硫源自有机质还原三叠纪膏盐所产生的硫化氢。当富含Pb2+、Zn2+、Sr2+等阳离子的成矿溶液与富含有机质、CO2、H2S和硫酸盐的热水溶液在推覆穹窿构造中汇合时,Pb2+、Zn2+与H2S结合生成方铅矿和闪锌矿,Sr2+与SO42-结合生成天青石。另外,矿区天青石、石膏、灰岩角砾和金属硫化物的锶同位素数据表明膏盐类矿床中的锶 (87Sr/86Sr=0.707765~0.710553)可能并非仅来自于三叠纪海相地层(87Sr/86Sr=0.70695~0.70845),而是成矿热液对各个流经地层和蒸发岩的萃取;受成矿热液中高锶同位素组成的混染,灰岩角砾岩的锶同位素组成相对于三叠纪的灰岩有明显增高。膏盐-有机质(油气)-金属硫化物矿床三位一体可能是普遍规律。

    Abstract:

    The Yunnan Jinding Pb-Zn, celestite, anhydrite and pyrite super-large deposits are locate at the northern part of Lanpin basin, which is also rich in organic materials (Bitumen and heavy oil). The δ34SV-CDT values of anhydrite and gypsum are concentrated in +12‰~+16‰, similar to the Triassic marine sulfate (+15‰); The distribution of celestite deposits followed the anhydrite deposits, and its δ34SV-CDT values are ranged of +6~+26‰. Except for some relative lower δ34SV-CDT values which was formed by bacterial sulphate reduction during the primary diagenesis mineralizaion stage, the most of metal sulfides presented a “two-group” distribution characteristic, one group of δ34SV-CDT values is concentrated at -12‰~-20‰, about 30‰ lower than the δ34SV-CDT values of anhydrite; another group of δ34SV-CDT values is concentrated at -8‰~-2‰, about 20‰ lower than the δ34SV-CDT values of anhydrite. When the temperature of the main mineralization stage is around 200℃, the sulfur isotopic exchange level between aqueous sulfates and sulfides is 30‰, while the sulfur isotopic exchange level reaches to 20‰ at 300℃. This phenomenon is consistent with the “two-group” distribution characteristic of Jinding deposit, demonstrate that most of sulfur element involved in the deposit are mainly come from thermochemical sulphate reduction of organic matters in Trassic halosalt minerals. When the ore-forming fluids with cations of Pb2+, Zn2+and Sr2+ encounted hydrothermal solution with organic matters, CO2, H2S and sulphate in the nappe dome structure, the galenite and sphalerite were formed by Pb2+, Zn2+ with H2S, while the formation of celestite is in present of Sr2+ with SO42-. The Trassic marine stratum (87Sr/86Sr=0.70695~0.70845) is not the only source of strontium (87Sr/86Sr=0.707765~0.710553) in the halosalt ore deposits, also extraced from multiple stratums by ore-forming fluids, according to the strontium isotope values of celestite, anhydrite, brecciated limestone and metal sulfides. Because of contamination from the high ratio of strontium isotope in ore-forming fluids, the strontium isotope level in brecciated limestones and metal sulfides are significantly increased. A combination of halosalt minerals - organic matters (or oil gas) - metal sulfides maybe a universal law in economic geology.

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胡古月,李延河,曾普胜.2013.膏盐在金顶铅锌矿成矿中的作用:硫和锶同位素证据[J].地质学报,87(11):1694-1702.
huguyue, Li Yanhe, Zeng Pusheng.2013. The Role of Halosalt in the Mineralization of Jinding Pb-Zn Deposit: the Evidence from Sulfur and Strontium Isotopic Compositions[J]. Acta Geologica Sinica,87(11):1694-1702.

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  • 收稿日期:2012-11-05
  • 最后修改日期:2013-01-05
  • 录用日期:2013-01-14
  • 在线发布日期: 2013-11-05
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