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地壳中流体的大规模流动系统及其成矿意义

马东升   

  1. 南京大学内生金属矿床机制研究国家重点实验室
  • 收稿日期:1998-09-20 修回日期:1998-09-20 出版日期:1998-09-20 发布日期:1998-09-20

LARGE-SCALE FLUID FLOW SYSTEMS IN THE CRUST AND THEIR IMPLICATIONS FOR METALLOGENESIS OF HYDROTHERMAL ORE DEPOSITS

Ma Dong-sheng   

  1. State Key Laboratory for Mineral Deposits Research, Nanjing University, Nanjing, 210093
  • Received:1998-09-20 Revised:1998-09-20 Online:1998-09-20 Published:1998-09-20

摘要: 地壳中的水量相当于海洋体积的水量,已确定的水溶液活动深度可达20km,根据驱动力的不同,地壳中主要存在三大流动系统,即重力,浮力和应力驱动系统。本文评述了当前国际上有关大规模流体运移研究扩要进展和发展趋势,介绍了有关流动系统的模式和运动机制,并简要论述了其成矿意义。文章指出,目前区域古流体场地球化学背景问题已成为区域规律和热液成矿理论中一个不容回避的关键课题,地壳中大规模流动系统将成为今后地质流体研究的重要方向之一。

Abstract: In the late 1980s, the study on geochemistry of gold and Au deposits in the northwestern Hunan, China revealed gold depletion up to more than one thousand km2 around the Woxi Au- Sb deposit in the Proterozoic strata which contro1 most Au(Sb)deposits in region. Together with other evidences, such as regional distribution patterns of Sb, Sr and Hg in the strata, it was explained as a result of large- scale fluid flow leaching the ore- forming materials from the strata and focusing them into the fossil fluid pockets and now expressed as gold deposits. Actually, the researches on the large- scale or regional scale fluid flow have made considerable progress in the world since 1980s. It has be determined, hydrogeo1gists as pioneers in this field, that groundwater and oil- gas can transfer up to several hundreds and even to thousand km, and several numeric models for genesis of hydrothermal ore deposits have be developed in which large- scale fluid flow is emphasized. Present paper reviews recent advances and tendencies in research of large- scale fluid flow through the continenta1 crust, discusses the models and mechanisms of the flow systems and their implications for metallogenesis of hydrothermal ore deposits. The reservoirs of total aqueous fluids in the crust are very close 1o the ocean in volume, and the uppermost ten km of the continental crust is ubiquitously saturated with aqueous fluids having high activity. According to driven forces, three flow systems occur in the crust: the gravity-, buoyancy-, and stress- driven system. The last two can be divided into four subtypes or subsystems, respectively, the therma1 and density- differential convection- driven, and the tectonic and compactional stress- driven. The large- scale fluid flow not only has a long distance, but also bears impressive quantities of fluids to form hydrothermal ore deposits. Via studies of Woxi Au-Sb deposit and Xikuangshan Sb deposit in Hunan, it is conservatively estimated that the mass of fluid 1o move the tonnage of gold and antimony (which equals the known reserves) to the deposit would be at lest of the order of 10^16 g. and that to form the regiona1 gold- depleted zone around Woxi Au-Sb mine be 5.2 × 10^18g. Therefore, 1arge- scale fluid flow with high flux and high water/rock ratio should play an important role to form hydrothermal ore deposits, especially for those elements with 1ow abundance and concentrated under 1ow temperature such as Au, Sb, Hg, As etc. The paper suggests that the regional geochemical background of palaeofluid field involving large- scale fluid flow might be a key link to integrally understand hydrothermal ore-forming processes, and research of large- scale fluid flow in the crust wil1 become one of the main currents of geologic fluid study in the future.