| 焦家式金矿水-岩交换作用——蚀变岩石氢氧同位素组成研究 |
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| 引用本文：.1995.Water-rock exchange in the Jiaojia style gold deposit: Hydrogen and oxygen isotopic study of altered rocks[J].Mineral Deposits,14(3):261~272 |
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| 基金项目:地质行业基金资助项目(89042) |
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| 中文摘要:焦家式台上蚀变岩型金矿地表及浅部绢英岩δ18O值平均在12.5‰，δD值在- 75‰，分别比新鲜原岩花岗闪长岩高出2‰~3‰和20‰。垂向1000 m以下，即沿矿体倾斜方向1500 m以下，绢英岩的δ18O和δD值分别降低为+8‰和-95‰左右，显示出比原岩亏损18O，但是D含量几乎不变。相应地，石英和绢云母蚀变矿物对的δ18O值分别从14‰和12‰左右，降为深部的11‰和9‰左右。综合资料表明，成矿流体是由大气降水与深部中基性岩呈面型淋滤相互作用，温度为350～400℃，有效W/R比为0.001左右时形成的演化大气降水含矿储体热液，随之上升进入破碎带充填呈线型扩散水/岩相互作用，有效W/R比超过5.0，降温的缓冲开放体系中矿化沉积。 |
| 中文关键词:焦家式金矿 水-岩交换 氢氧同位素 缓冲开放体系 |
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| Water-rock exchange in the Jiaojia style gold deposit: Hydrogen and oxygen isotopic study of altered rocks |
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| Abstract:Vertically downward from the surface to the depth of 1000 m in the Taishang deposit, a large-sized Jiaojia style gold deposit, δ18O values of 38 phyllic whole-rock samples decrease from 13.0‰士 to 8.0‰士, δ18O values of 8 quartz and sericite pairs from phyllic rocks decrease from 14.0‰ and 11.5‰ to 11.0‰士 and 9.0‰±, and δD values of 13 phyllic and sericite samples vary from -70‰ to 94‰, averaging (85土7) ‰ or so. These data demonstrate that Δquartz-sericite values vary stably between 2‰ and 3‰, suggesting that quartz and sericite have basically attained oxygen isotopic equilibrium. Nevertheless, δD values of phyllic rocks and sericite are almost equal toδD values of fluid inclusions in vein quartz, implying the existence of hydrogen isotope dynamic fractionation between hydrothermal fluid and sericite, which is probably related to boiling and dehydrogenation. Theδ18O value of ore-forming fluid at the principal ore- forming stage is estimated to be 5‰土. Therefore, the calculated effective W/R ratio should be higher than 5.0 when the temperature decreases from 350℃ at depth to 250℃ at surface. lt is hence concluded that the formation of the Jiaojia style large-sized gold deposit must have experienced two water/rock stages. At the first stage, extensive interaction took place between meteoric water and basic rocks in an high-temperature enwronment at depth; at the second stage, ore-forming fluids produced at depth ascended to the fractured shatter zone, resulting in diffusion, water/rock exchange and mineralization-deposition. On such a basis, a metallogenic model of two stage water/rock exchange in a buffered open system has been established. |
| keywords:Jiaojia Dstyle gold deposit, water-rock exchange, hydrogen-oxygen isotope, buffered open system |
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