Textures and In Situ Chemical and Isotopic Analyses of Pyrite, Huijiabao Trend, Youjiang Basin, China: Implications for Paragenesis and Source of Sulfur

摘要

Many Carlin-like Au deposits occur within the late Paleozoic and Triassic Youjiang basin of southwest China. The Huijiabao trend in Guizhou Province contains over 300 metric tons (t; 10.6 Moz) of Au at an average grade of 7 to 18 g/t in a narrow corridor that is about 20 km long and 5 km wide. Petrographic and SEM studies of pyrite in barren host rocks and high-grade orebodies led to the recognition of four stages of pyrite. Pyl consists of fine-grained framboidal crystals in black muclstone. Py2 is comprised of coarser grained euhedral-subhedral clusters that are spatially related to organic matter. Py3 is coarse grained, euhedral, and occurs as overgrowths on Pyl and Py2. Py3's porous texture, inclusion of randomly oriented detrital minerals, and association with quartz recrystallization suggest it was deformed during Late Triassic orogenesis with Pyl and Py2. Py4 generally occurs as rims on Pyl to Py3 and is intergrown with arsenopyrite.