小秦岭文峪金矿床流体包裹体研究及矿床成因

Fluid inclusion characteristics and ore genesis of the Wenyu gold deposit, Xiaoqinling gold belt

文峪金矿位于小秦岭矿田南部,其产出受脆-韧性剪切带控制,赋矿围岩为太华群变质杂岩。根据脉体穿切关系和矿物交代关系,可以将文峪金矿流体成矿过程分为早、中、晚三个阶段,其热液石英中发育CO2-H2O型、纯CO2型和H2O溶液型三种类型流体包裹体。早阶段石英中原生包裹体主要是CO2-H2O型和纯CO2型,其成分为CO2+H2O±N2±CH4,均一温度集中在290～330℃,盐度为1.02%～9.59%NaCleqv;中阶段为主成矿阶段,该阶段石英中包含了所有3种类型的包裹体,其中以CO2-H2O型包裹体为主,获得CO2-H2O和水溶液包裹体均一温度集中在250～290℃,盐度为0.02%～12.81%NaCleqv;晚阶段石英仅发育水溶液型包裹体,具有较低的均一温度(114～239℃)和盐度(4.18%～8.95%NaCleqv)。根据CO2-H2O型包裹体计算早、中阶段压力分别为130～178MPa和85～150MPa,对应的成矿深度分别为4.7～6.5km和3.1～5.5km。总体而言,文峪金矿的初始流体具有中高温、富CO2、低盐度的变质流体特征,晚成矿阶段流体演化为低温、低盐度水溶液流体,流体的不混溶导致了主成矿期矿质的大量沉淀,文峪金矿为中浅成的造山型矿床。

The Wenyu gold deposit, Henan Province, is located in the southern part of the Xiaoqinling gold belt. It is controlled by a brittle-ductile shear zone and hosted in the Taihua Group metamorphic complex. The crosscutting relationships and mineral assemblages suggest that the ore forming process includes the early, middle and late stages. Three types of fluid inclusions （FIs） in the quartz of Wenyu gold deposit are identified as CO2-H2O, pure CO2, and H2O-solution. The early-stage quartz contains primary pure CO2 and CO2-H2O with homogenization temperatures clustering at 290~330℃ and the salinity of 1.02%~9.59% NaCleqv. Vapor bubbles are composed of CO2＋H2O±N2±CH4. The middle-stage quartz trapped all the three types of FIs. The CO2-H2O FIs is the majority one, and the homogenization temperatures of CO2-H2O and H2O-solution FIs cluster at 250~290℃, and the salinities are 0.02%~12.81% NaCleqv. Fluid inclusions in late-stage quartz are H2O-solution with low homogenization temperatures （114~239℃） and low salinities （4.18%~8.95% NaCleqv）. Minimum trapping pressures estimated from CO2-H2O inclusions are 130~178MPa and 85~150MPa for early and middle stages, respectively, corresponding to the ore-forming depth of 4.7~6.5km and 3.1~5.5km, respectively. In general, the ore fluids in the early and middle stages are characterized by meso- to hypothermal, CO2-rich and low salinity, which are considered as the nature of metamorphic fluids, whereas the late-stage fluids are low temperature, low salinity and CO2-poor. Fluid immiscibility caused gold precipitation in the middle-stage. The ore-forming fluid-system of the Wenyu gold deposit is the same to that of the orogenic-type. The Wenyu gold deposit is a mesozonal to epizonal orogenic gold deposit.