| 北塔山金矿床成矿流体成因及金沉淀机制的探讨 |
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| 引用本文：.1999.A preliminary discussion on the genesis of ore-forming fluids and precipitation mechanism of gold in the Beitashan gold deposit[J].Mineral Deposits,18(3):226~234 |
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| 基金项目:国家“九五”科技攻关项目(96-915-02-06-01) |
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| 中文摘要:北塔山地区金矿床及矿点的含金石英与闪长玢岩、闪长岩及其斜闪煌斑岩等岩脉及小岩体有密切的空间关系，其一般产于岩脉内部及其接触带附近。石英中流体包裹体研究表明成矿流体为近中性低盐度和富CO2的K+-Na+( Ca2+)-Cl-型热液，推测主要属于来自深部的变质流体。金的成矿具有多阶段特征。早期中-高温阶段减压引起CO2和H2S等组分溶解度减小和强烈挥发应是金沉淀的主要机制。晚期中-低温阶段，降温引起成矿流体中[Au (HS)2]-溶解度降低可能是金沉淀的主要机制。 |
| 中文关键词:成矿流体 闪长玢岩 成矿机制 北塔山地区 |
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| A preliminary discussion on the genesis of ore-forming fluids and precipitation mechanism of gold in the Beitashan gold deposit |
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| Abstract:Auriferous quartz veins in the Beitashan gold deposit occur within or near the contact zones of diorite porphyries dikes, small diorite bodies and camptovogesite, suggesting the clost spatial relationship of the ore deposit to those veins and rock bodies. According to study of fluid inclusion in quartz veins, δ18OH2O andδD of ore-forming fluids vary in the range of 4.0‰~9.9‰ and -50‰~-83‰ respectively, and the salinity corresponds to 1.7%~4.2% NaCl. The ore-forming fluid contains rich CO2 phase and CO2 inclusions; the anions in the fluid phase are mainly Cl-, the cations are characterized by K- >Ca2+ > Na+ or K+ >Na+ >Ca2+, the pH value vary in the range of 6.6~ 6.7, and the lgfO2 value calculated on the basis of gas-phase composition is some -39. All these features show that the ore-forming fluid is neutral reductive hydrothermal solution with low salinity, rich CO2 and relatively abundant K+, belonging mainly to the fluid of metamorphic origin. After the emplacement of dikes, the activity of the faults that controlled the emplacement of dikes resulted in the ascending of deep fluid and its material exchange with dikes; as a result, the cations of ore-forming fluids and the hydrogen-oxygen isotopic composition became increasingly close to those in magmatic hydrothermal solution. Gold mineralization has multi-stage characteristics. At the early medium-high temperature stage there existed homogenized gas-rich phase and CO2-rich inclusions, whose homogenization temperature varies in the range of 254~356℃. It is inferred that the immiscible separation and strong volatilization of such components as CO2 and H2S causdd by reduction of solubility during the rapid ascending of high-temperature deep ore-forming fluid to the shallow place might have been the main mechanism for the precipitation of Au at this stage. At the late medium-low temperature stage, the decrase of [Au(HS.) 2]- solubility in ore-forming fluids might have been responsible for the precipitation and mineralization of gold. |
| keywords:ore-forming fluid, diorite porphyrite, ore-forming mechanism, Beitashan area |
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