The Isotopic Composition of Noble Gases in Gold Deposits and the Source of Ore-Forming Materials in the Region of North Hebei, China

摘要

The source of ore|forming materials has long been a controversial focus both in metallogenic theory and in ore|searching practice. This study deals with the helium and argon isotopic characteristics of pyrites from 11 gold deposits and some country rocks in the gold mineralization|concentrated areas within the three mantle|branch structures in the region of North Hebei Province. It is indicated that {}+3He/+4He ratios in the gold deposits are within the range of {0.93×10+{-6}}-{7.3×10+{-6}}, with an average of {3.55} ×10+{-6}; R/Ra={0.66}-{4.93}, averaging {2.53}; {{}+{40}Ar/+{39}Ar} ratios vary between 426 and 2073, with the average value of {}+{40}Ar being {8.32}; and the average of {}+4He/{}+{40}Ar ratios is 2.17. {}+3He/ {}+4He ratios in gneiss and granite in the periphery of the mining district are within the range of {0.001×10+{-6}}-{0.55×10+{-6}}, reflecting significant differences in their sources. {}+3He and {}+4He fall near the mantle, as is shown in the He concentration diagram. Studies have shown that the ore|forming materials in this region should come from the deep interior of the Earth. With the multi|stage evolution of mantle plume, ore|forming fluids in the deep interior were moving upwards to shallow levels (crust). Under such circumstances, there would be inevitably occur crust/mantle fluid mixing, so their noble gas isotopic characteristics are intermediate between the mantle and the crust.