陕西柞山地区穆家庄铜矿床成矿流体来源的氦氩氢氧同位素示踪

最近,在秦岭柞山地区泥盆系中又发现了穆家庄铜矿,矿体明显受层间破碎带控制,矿石主要产在铁白云石-石英脉中,其后生成矿现象非常明显.文章利用的黄铁矿流体包裹体He-Ar同位素和氢氧同位素,来探讨这类矿床的成矿流体的来源.穆家庄铜矿床矿石矿物黄铁矿流体包裹体的3He/4He比值为0.322～0.889R/Ra,小于1.0R/Ra.3He/4He比值远远低于地幔流体的比值,与地壳流体的比值在相同的数量级上.穆家庄铜矿成矿流体的40Ar/36Ar比值为377～569,平均470,显然偏离大气氩的同位素组成.穆家庄铜矿成矿流体的40Ar/4He比值为0.09～0.23,平均值为0.164.很显然,该矿床的成矿流体的40Ar/4He比值接近地壳.根据以上分析,柞山地区的穆家庄铜矿床的成矿流体是壳源的.氢氧同位素分析表明穆家庄铜矿的氢氧同位素则落入原生岩浆水范围内,表明穆家庄铜矿的成矿流体为岩浆水.综合对比分析后认为,穆家庄铜矿的成矿流体是由壳源岩浆驱动并参与的岩浆流体提供的.

He-Ar, H-O ISOTOPES TRACING FOR ORE-FORMING FLUIDS IN THE MUJIAZHUANG COPPER DEPOSIT

Mujiazhuang copper deposit is a newly found middle scale deposit the southern Qinling Devonian metallogenic belt. The ore bodies were controlled by fracture zones in stratum layer, and ores are located in ankerite-quartz-pyrite-chalcopyrite veins. Ore-forming fluids and ore genesis are discussed through analyses of He-Ar isotopes of pyrite in ores and H-O isotopes composition of fluid inclusions. ~3He/~4He ration of fluids in the Mojiazhuang copper deposit is 0.322~0.889 R/Ra (under 1.0 R/Ra). This value is smaller than the mantle fluids and is almost near to the crust fluids. ~(40)Ar/~(36)Ar ration of fluids is 377~569 with average 470, far away from Ar isotopes composition of atmosphere. ~(40)Ar/~4He ration of fluids is 0.09~0.23 with average 0.164, equal nearly to crust's or lower than crust's fluids. He-Ar isotope composition shows ore-bearing fluids came from crust. H-O isotopes composition of fluid inclusion in quartz shows that the ore-forming fluids came from magma water.