河南省内乡县银洞沟银矿床流体成分研究

Compositional study on ore fluid of the Yindonggou silver deposit in Neixiang county,Henan province,China

河南省内乡县银洞沟银矿床是产于东秦岭北部二郎坪地体中的断控脉状矿床,主要赋矿围岩为二郎坪群小寨组绢云石英片岩。流体包裹体的气相、液相和稀土元素研究表明,成矿流体的 CO_2含量为12.829%～22.172mol%,属于 CO_2-NaCl-H_2O 体系,与世界造山型流体成矿系统一致。成矿流体系统在早阶段主要为来自赋矿地层改造-变质脱水作用的深源变质水,经中阶段沸腾,向晚阶段大气降水热液演化。在早阶段,Ag 等成矿元素通过与 Cl^-等离子络合而被萃取、富集到成矿流体中,并被搬运;流体沸腾导致大量金属成矿物质在中阶段快速沉淀。而不同深度、不同阶段的流体包裹体中 Mg^(2+)、Ca^(2+)、REE 等含量差异可由围岩的热液蚀变所致。

The Yindonggou silver deposit is a fault-controlled lode deposit, occurring in the Erlangping Terrane, the northeastern Qinling Orogen. It is hosted in the sericite-quartz schist of the Xiaozhai Formation, Erlangping Group. In this paper the deposit is determined to be of orogenic-type in terms of a systematic study of the molecular, ion and rare earth elements compositions of fluid inclusions. With CO2-content ranging 12. 829% -22. 172mol% , the fluid inclusions are dominated by CO2-NaCl-H2O composition, which characterizes the orogenic-type fluid-systems worldwide. The ore-fluids were mainly derived from metamorphic devolatilization of marine carbonate-containing lithologies in early stage, and boiled in middle stage and evolved into a meteoric water-dominated fluidsystem in late stage. The ore metals, such as Ag, through coordinating with Cl^ - and other anions anions, were extracted and enriched into fluids and then transported in early stage. Fluid-boiling probably caused rapid precipitation of ore metals in middle stage. Differences in contents of REE, Mg^2＋ , Ca^2＋ and other ions in fluid inclusions between different levels and/or metallogenic stages can be related to hydrothermal alterations of wall-rocks.