安徽铜陵凤凰山铜矿床成矿流体特征研究

Mantle-derived ore-forming fluids of the Fenghuangshan Cu deposit,evidences form microthermometric and isotopic studies

本文以凤凰山矽卡岩型铜矿床为例,通过对成矿流体特征研究以及碳、氢、氧、硫、铅同位素分析,探讨成矿流体性质、成矿流体来源以及成矿物质来源。凤凰山铜矿床透辉石、石榴子石、石英和方解石中普遍发育流体包裹体,其类型为液体包裹体、气体包裹体和H2O—CO2三相包裹体。气液固相成分的激光拉曼探针分析,流体包裹体液相以H2O为主,气相以为CO2、H2O、N2、CH4为主。流体包裹体的均一温度和盐度显示成矿流体演化经历了的3个不同阶段,反应了成矿流体从高温度、高盐度向低温度、低盐度的持续演化过程,与成矿作用阶段基本对应,降温、流体沸腾是导致流体中巨量铜元素卸载的主要因素。石英和方解石中的氢、氧同位素组成表明成矿流体以岩浆热液为主,成矿晚期混有少量大气降水。黄铁矿中的硫同位素(1.8‰～2.9‰)具有幔源硫的特征。方铅矿中的铅同位素具有岩浆热液特征,表明凤凰山铜矿床中成矿元素来自上地幔。

The Fenghuangshan is a large Cu skarn deposit in the Low—Middle Yangtze metallogenic province. Based on microthermometric and isotopic （C,H,O,S,and Pb） studies,we discuss ore-forming fluids evolution and metal origin （s） of the Fenghuangshan Cu deposit. H2O—CO2 type fluid inclusions,which can be classified into liquid-rich,vapor-rich and daughter crystal-bearing subtypes,are ubiquitous in diopside,garnet,quartz and calcite. Laser Raman spectroscopic analysis indicates that liquid phase of fluid inclusions is H2O,and vapor phase is dominant by CO2,N2 and CH4. Homogenization temperature （Th） and salinity of fluid inclusions suggest three-stage history of ore-forming fluids,reflecting an evolution process from high-temperature and salinity at mineralization stage to low-temperature and salinity at post mineralization stage. Temperature decreasing and fluids boiling may be responsible for precipitation of large quantity of metals. Hydrogen and oxygen isotope of quartz and calcite indicate that magmatic fliud was dominant during the ore-forming stage,whereas a small quantity of meteoric fluid mixed with original magmatic fluid at post ore-forming （or late） stage. Narrow variation range of pyrite δ^34S （1.8‰- 2.9‰） suggest that sulfur was from a relatively uniform reservoir,substantially from mantle. Pb^206/Pb^207 values of ore-forming stage pyrite present magmatic hydrothermal characteristics,which further suggest metals of the Fenghuangshan Cu deposit were from mantle.