GOLD AND SILVER MINERALIZATION EPOCHS AND MINEERALIZA-TION EVOLUTION IN YANSHAN AREA
Wu Zhenhan (Geomechanics Institute, Beijing)
More than one hundred gold and silver ore deposits are distributed in ten gold-silver mineralized districts in Yanshan area. Since the mineralized districts controlled by the Mesozoic tectonic-mag-matic zone,most gold and silver ore deposits are related to Mesozoic rnagmatic activity. The sulfide-bearing quartz vein-type, volcanic-type, altered rock-type, porphyry-type and palaeo-conglomerate-type gold and silver deposits were found in this area. The mineralization epochs are determined by lead isotope multi-stage model dating and altered mineral K-Ar and Rb-Sr dating. The results show that five regional mineralization periods occurred in Yanshan area (Archean to Early Proterozoic and Middle Proterozoic era,Luliangian stage, Variscian to Indosinian stage and Yanshanian stage). Most commercial gold and silver ore deposits were formed in Yanshanian stage, and a few gold oredeposits were formed in the other four periods.