宁夏卫宁北山金场子金矿床流体来源及矿床成因:来自流体包裹体和C⁃H⁃O同位素证据

卫宁北山地区是宁夏境内最有望实现找矿突破的多金属矿成矿区之一,已发现众多Au、Ag、Cu、Pb、Zn、Fe、Co等矿点或矿化点.金场子金矿是该地区已发现的最大的金矿床,矿体主要赋存在前黑山组及中宁组内的层间断裂破碎带中,呈东西向带状分布,产状与地层近乎一致.区域上除少量闪长玢岩脉出露外,岩浆岩不发育.为了探讨金场子金矿...

Source of Fluid and Genesis of Jinchangzi Gold Deposit in Weiningbeishan,Ningxia: Evidence from Fluid Inclusions and C-H-O Isotopes

The Weiningbeishan area is the most promising polymetallic ore target area in Ningxia, where numerous Au, Ag, Cu, Pb, Zn, Fe, Co, and other ore occurrences have been found. The Jinchangzi gold deposit is the largest gold deposit found in the area, and the ore bodies are mainly hosted in the intra-layer fault fractures, with an east-west distribution and near-uniform with the bedding. Magmatism is weak in this district, with several diorite porphyrite having been identified in exposures adjacent to the gold veins. In order to explore the nature, source and genesis of the ore-forming fluid of the Jinchangzi gold deposit, the fluid inclusions and C-H-O isotopes in the study area were studied. The ore-forming hydrothermal period of the deposit can be divided into 4 metallogenic stages, from early to late, they are sericite-pyrite-quartz stage (Ⅰ), pyrite-barite-quartz stage (Ⅱ), polymetallic sulfide-carbonate-quartz stage (Ⅲ) and pyrite-carbonatite stage (Ⅳ), of which stage Ⅲ is the main metallogenic stage. There are four types of fluid inclusions in the mineralization stage, which are aqueous solution inclusions, pure CO₂ inclusions, CO₂-H₂O inclusions and multiphase inclusions containing daughter crystals. The completely homogenous temperature of the ore-forming fluids is between 171-396℃, the salinity is between 1.30%-10.99% NaCl equiv, and the density is 0.24-0.78 g/cm3, which are CO₂-H₂O-NaCl systems with medium-low temperature, low salinity, low density, CO₂ rich, and a small amount of N₂. The δD value of hydrothermal quartz is -66.0‰ to -32.0‰, and the δ18O_V-SMOW value is (+19.7‰)-(+22.6‰), indicating that the ore-forming fluid is metamorphic and the magmatism is not obvious. The C isotope shows that the δ13C of calcite and siderite in the late stage (stage Ⅳ) is between -2.540‰ and -0.736‰, indicating that C in the ore-forming fluid has the characteristics of mixed sources. The fluids formed by the metamorphic dehydration of Ordovician-Carboniferous terrigenous clastic rocks and carbonate rocks may be the main source of gold ore-forming fluids. During the ore-forming process, the fluids had an obvious immiscibility phenomenon, which was an important factor causing gold precipitation. The genetic type of the deposit is an orogenic gold deposit.