Geology and Genesis of the Superlarge Jinchang Gold Deposit, NE China

The superlarge Jinchang gold deposit is located in the joint area between the Taipingling uplift and the Laoheishan depression of the Xingkai Block in both eastern Jilin and eastern Heilongjiang Province.Wall rocks of the gold deposits are the Neoproterozoic Huangsong Group of metamorphic rocks.Yanshanian magmatism in this region can be divided into 5 phases,the diorite, the graphic granite,the granite,the granite porphyry and the diorite porphyrite,which resulted in the magmatic domes and cryptoexplosive breecia chimney followed by large-scale hydrothermal alteration.Gold mineralization is closely related to the fourth and fifth phase of magmatism. According to the occurrences,gold ores can be subdivided into auriferous pyritized quartz vein, auriferous quartz-pyrite vein,auriferous polymetallic sulfide quartz vein and auriferous pyritized calcite vein.The ages of the gold deposit are ranging from 122.53 to 119.40 Ma.The ore bodies were controlled by a uniform tectono-magmatic hydrothermal alteration system that the ore-forming materials were deep derived from and the ore-forming fluids were dominated by magmatic waters with addition of some atmospheric water in the later phase of mineralization.Gold mineralization took place in an environment of medium to high temperatures and medium pressures.Ore-forming fluids were the K~ -Na~ -Ca~(2 )-Cl~--SO_4~(2-)type and characterized by medium salinity or a slightly higher, weak alkaline and weak reductive.Au in the ore-forming fluids was transported as complexes ofAu (HS)_2]~-,AuCl_2]~-,Au(CO_2)]~-andAu(HCO_3)_2]~-.Along with the decline of temperatures and pressures,the ore-forming fluids varied from acidic to weak acidic and then to weak alkaline,which resulted in the dissociation of the complex and finally the precipitation of the gold.