Geological Characteristics Of The Deposits And Analysis Of The Mineralization System Of Qingchengzi Pb-Zn-Au-Ag Polymetallic Ore Field

Qingchengzi Pb-Zn-Au-Ag polymetal deposit is the largest one of Liaotung Main Mineral Belt, and it is also a famous non-ferrous metal deposit in the north of China, which is on the junction of the south slop of Yingko-Caohekou composite syncline and the north slop of Hupiyu composite anticline in the west part of Liaotung Intercontinental Rift. Lots of fults and folds were produced in the ore field. The largest-scal fold which is in connection with mineralization of the ore field is Qingchenzi convolute fold, which is in the south of the ore field and controlled the development of all the Pb-Zn deposits, the core of which is Paleoproterozoic moyite. NNE-trend Qingchengzi fault divides the convolute into two parts---west part and east part. In the east part, majority of the orebodys are layering, and minority of which are veined. In the west part, the orebodys mainly are veined, saccate and featherlike. The largest-scale fault is Jianshan-Baiyun-Zhaijiapuzi geofracture, which controlled development of the Ag-Au deposits. All Ag-Au deposits are distributed along the fracture belt in the adjacent rock’s interlayer fractures.According comparative study of the rule of stratigraphic distribution, under Liaohe formation and underpart of Gaojiayu group of upper Liaohe formation are lost. Paleoproterozoic moyite contact with Gaojiayu group directly. Study of lead isotope, sulfur isotope, mineral fluid inclusion and hydrogen-oxygen isotope of which shows that mineralization stuff came from regional srata and rebuilt by hydrothermal fluid from Mesozoic granite. According to the feature of distribution of regional deposits and geochemical behavior of regional strata, mineralization in Qingchengzi ore field is tightly connected with Paleoproterozoic magmatism and evolution of Liaotung Intercontinental Rift.Liaotung Paleoproterozoic rift is a kind of intercontinental rift in Archeozoic craton. Intensive volcanic action caused the formation of bimodalpattern volcanogenic-sedimentary construction. The volcanic action caused by the evolution of the rift resulted in the high geochemical ground of minerogenic element in Liaohe formation. In the end stage of the evolution of Liaotung Rift, it generally rose and deformed. The Liaohe formation generally suffered greenschist facies-amphibolite facies metamorphism. The Large-scale intrusion of granite which generated from mantel-derived magma resulted in large-scale intensive hybridization in underpart of Liaohe formation. Because lots of fractures formed in the stage of deformation and lots of water went into the magma system in deep ground, the physical and chemical features of the magma system such as pressure, temperature, viscosity, etc. changed greatly, thus, the ability of the Paleoproterozoic moyite assimilating surrounding rock was greatly improved. It assimilated Archean group, under-Liaohe formation, and underpart of Gaojiayu group and differentiated mineral-bearing hydrothermal fluid, which filled up the fracture system in the surrounding rock and formed platelike orebodies in interformational fractures and veined orebodies in insepuent fractures.