山东沂南金矿床成矿物质来源探讨

A Discussion on the Sources of Ore-forming Material of the Yi'nan Gold deposit,Shandong Province

矿床宏观特征、矿体产出状态、围岩蚀变、矿石组构及矿物组合特征等,均清楚表明沂南金矿床是一个典型的夕卡岩型矿床。本文通过对矿床铅、硫、碳、氧、氢等同位素特征的研究,探讨了成矿物质来源。矿石铅同位素组成显示异常铅特征,在连续增长模式下,放射性铅同位素源区年龄为2390Ma,与区域花岗-绿岩带固结时间相当。μ值介于9.56～12.17之间,显示金属成矿元素主要源自地壳,少量来自地幔。Th/U值集中在3.30～3.62之间,接近于上地壳Th/U值,表明晚太古代晚期～早元古代壳-幔相互作用形成的花岗-绿岩带(泰山群)是沂南金矿床的主要矿源层。硫、碳同位素特征表明矿石中的硫和碳主要源自深源岩浆。氢、氧同位素组成显示成矿流体主要为岩浆热液,在成矿晚期有不同程度的大气降水混入。

The Yi ＇nan gold deposit can be defined a skarn deposit on the base of these characteristics of macrofeature, occurrence of ore body, wallrock alteration, ore fabric and mineral assemblage et al. Based on the main characteristics of the lead, sulfur, carbon, oxygen and hydrogen isotope of the Yi＇nan gold deposit, the sources of the ore-forming material are discussed in this paper. Lead isotopic composition was characterized by anomalous lead. While in continuous growth model, the age of radioac- tive lead isotope source region is 2390 Ma, being consistent with the consolidation time of granite-greenstone belt, suggesting that ore-forming materials originated from this belt. μvalues varied in the range of 9.56- 12.17, indicating that the metallic ore-forming elements were derived from the crust mainly. Th/U value is concentrated on the range of 3.30-3.62, close to the value of the upper crust. The above-mentioned characteristics imply that the granite-greenstone belt of Yanlingguan Formation, Taishan group, as a result of crust-mantle interaction during the Late Archean to the Early Proterozoic, was the main source of the Yi＇nan gold deposit. Sulfur and carbon isotopic studies indicated that S and C in the ore were mainly derived from the man- tle magma. The ore-forming fluids were mainly magmatic hydrothermal fluids, though some meteoric water might be added during later mineralization stage.