Characteristics of gold mineral in Gengzhuang gold deposit and its significance to metallogeny

Based on earlier works, the genesis of gold deposits in Gengzhuang was studied in depth via systematical observations on the characteristics of the gold mineral . An assay was made for the composition of the mineral with an electron probe to determine the fineness of gold. It was found that in the minerals the electrum is the major part with small amount of natural gold and the fineness of gold mineral is 508~896 with an average assay 673. Observations on the shape and the size of the minerals indicated that the gold minerals are mainly in irregular brecciform and most of them are medium-grained or fine-grained, which are found mainly in the cracks and intracrystallines of sphalerite, pyrite, galena and other metallic sulphides. Combining the occurrence characteristics with ore-forming geological conditions, the forming conditions and ore genesis of Gengzhuang gold deposit are discussed, and it is revealed that the gold deposit experienced long-term metallogenic epoch and many genetic stages, i.e., the mesothermal-hypothermal ore-forming stages of which the hypothermal stage was dominant. The deposit is of hypabyssal or ultra-hypabyssal epithermal genesis.