Abstract:

The analysis of the micro-petrography and element geochemistry, combined with electron microprobe and SEM, shows that the extremely fine, black opaque materials in the ores consist mostly of super-microcrystalline quartz, silicate, sulfide, carbonate and the liquation of rutile, scheelite and specularite (magnetite). These materials are distributed in intergranular space, along the cracks in minerals or along amphibole cleavage. They are associated with silicification, carbonation and sulfidation in the wall rocks, mineralized rocks and gold ores in the Laowangzhai gold deposit. The special petrographical texture characters of thees black opaque matters as coexistence of liqutation and precipitating cocrystallization reveal the transitional features of the mineralizing fluid between the magmatic melt and the hydrothermal fluid. Combined with REE composition of the host rocks and ores, we suggest that these super-microcrystalline solid, black opaque materials under the transmitted-light microscope are the direct microcosmic manifestations of metasomatism of mantle fluids which are thought to be of the characters of melts and supercritical fluids. During the metasomatic alteration, the mantle fluids were transformed into thermal fluids from magmatic melts. Their simultaneous contaminations by hybridization of mantle-derived and crust-derived materials in the deep geological processes were favorable for gold metallogenesis in the area.

Key words: micro-petrography, super-microcrystalline solid, deep processes, geochemistry, hybridization of , mantle and crust, Laowangzhai gold deposit