云南元阳大坪金矿床成矿流体特征及矿床成因探讨  

Discussion on the characteristics of ore-forming fluid and genesis of the Daping Au deposit in Yuanyang county,Yunnan province

作　　者：侯文文 管申进 HOU Wenwen;GUAN Shenjin(School of Land and Resources Engineering,Kunming University of Science and Technology,Kunming 650093,Yunnan,China)

机构地区：[1]昆明理工大学国土资源工程学院,昆明650093

出　　处：《地质找矿论丛》2024年第3期313-325,共13页Contributions to Geology and Mineral Resources Research

基　　金：云南省重大科技专项计划项目(编号:202202AG050014);昆明理工大学自科类人培项目(编号:KKSY201421063)联合资助。

摘　　要：云南元阳大坪金矿床是哀牢山金矿带典型的造山型矿床,但局部又呈现出与浅成低温热液型金矿一致的特性,因而与国外典型的造山型金矿床存在差异,对其成矿作用过程的研究仍然存在较多争议。本文以富CO_(2)流体为切入点,揭示大坪金矿床主成矿阶段成矿流体特性,结合硫化物原位S同位素分析,探讨矿床成因。详细的流体包裹体岩相学观察结果表明,大坪金矿床主成矿阶段的成矿流体,主要由不同CO_(2)/H_(2)O比例的CO_(2)-H_(2)O型包裹体组成,包括含CO_(2)气液两相包裹体(L_(H_(2)O)+V_(CO_(2)))、含CO_(2)气液三相包裹体(L_(H_(2)O)+L_(CO_(2))+V_(CO_(2)))及少量气水包裹体(L_(H_(2)O))。均一温度集中在280℃~360℃之间,w(NaCl,eqv)=6.03%~13.20%,成矿流体为中温、中低盐度的NaCl-H_(2)O-CO_(2)体系。据状态方程估算的成矿深度为3~8 km,具备典型剪切带控制下的中深中温热液金多金属矿床特征。在富含CO_(2)的成矿流体中,金可能主要以硫氢络合物形式迁移,金的沉淀主要与压力骤降条件下发生流体的相分离作用相关。在拉张和强韧性剪切条件下,地幔排气形成的深部地幔流体与下地壳脱水形成的富CO_(2)流体发生混合作用,CO_(2)可导致NaCl-H_(2)O体系在较高的P-T条件下发生相分离,增进了不混溶作用的发生,含矿热卤水沿韧性剪切带上升,且在闪长岩和灰岩地层的构造破碎带中分别形成含金脉。The Daping Au deposit is a orogenic gold deposit located in the Ailaoshan gold ore belt in Yuanyang county,Yunnan province.However it exhibits local characteristics of epithermal low-temperature hydrothermal gold deposit thus differs from the internationally typical orogenic gold deposit and lead to considerable debate over its ore-forming processes.This study is focused on CO_(2)-rich fluids to reveal the ore-forming fluid characteristics during the main mineralization stage.Based on the characteristics and in situ analysis of sulfides genesis of the gold deposit is discussed.Detail petrographic observations of the fluid inclusions show that ore fluid of the main mineralization stage is composed of CO_(2)-H_(2)O with varied CO_(2)/H_(2)O ratios..The inclusion includes CO_(2)-bearing biphasic inclusions(L H_(2)O+V CO_(2)),CO_(2)-bearing triphasic inclusions(L_(H_(2)O)+L_(CO_(2))+V_(CO_(2))),and a minor aqueous inclusions(L_(H_(2)O)).Homogenization temperatures are concentrated in range of 280℃-360℃,the salinities w(NaCl,eqv)is 6.03% to 13.20%,indicating a mid-temperature indicating a mesothermal and moderate to low salinity NaCl-H_(2)O-CO_(2) system.Ore-forming depth estimated from the state equation range from 3 to 8 km,characteristic of mesothermal to epithermal gold-polymetallic deposits controlled by shear zones.Gold likely migrates mainly in the form of thio-complexes in high CO_(2) ore-forming fluids and precipitates primarily with rapid pressure drop and fluid phase separation.Under extensional and strong ductile shear conditions,deep mantle fluids generated by mantle degassing mix with CO_(2)-rich fluids from lower crustal dehydration.CO_(2) can cause phase separation in the NaCl-H_(2)O system under high P-T conditions,enhancing immiscibility.The ore-bearing hydrothermal brines ascend along ductile shear zones,forming gold-bearing veins in tectonically fractured zones of diorite and limestone formations.

关 键 词：大坪金矿 富CO_(2)流体包裹体 原位S同位素 矿床成因 

分 类 号：P618.51[天文地球—矿床学] P597[天文地球—地质学]