Study On Metallogenic Regularity Of Copper Polymetallic Deposit In The North Qilian,Qinghai

North Qilian orogenic belt was a part of the northern edge of the Tibetan Plateau in the middle of the Qin-Qi-Kun Central Orogenic System.Because of a different geological periods and environments,it became an important metallogenic belt in western China.The research discusses the tectonic setting in Paleoproterozoic by the study about Beidahe rock group and the adjacent plate in North Qilian.The research indicates that: a.The original rock of Beidahe rock group is series of volcano-carbonate-flysch sediments,which is formed in shallow Marine environment;b.The geochemistry characteristics of volcanic rock in this group shows that the rock belong to calcium-alkaline series,indicating that it was formed in the tectonic setting of the margin of plate;c.The study also indicates that though both continents are formed in the tectonics of the margin of crystalline basement,the tectonics settings of southern and northern continent in North Qilian area are different,indicating that North Qilian is in oceanic settings during Paleoproterozoic.The view is different from others,whose studies indicate that the tectonics setting is klippe or crystalline basement.Systematically Summarizing the evolution of metallogenic system in North Qilian,The research finds that North Qilian Ocean had already existed during Paleoproterozoic.The existence of ocean plateau basalt formed in Mesoproterozoic indicates that North Qilian Ocean is in the stage of mature ocean.The area came into the stage of two-way subduction in the end of the sinian(~545Ma)(at the same time had the northern sucduction and formed back-arc basin),then came into the stage of collisional orogenesis in the end of late Ordovician(~442M),into the stage of inland orogenesis in Hercynian-Indosinian period and into stage of uplift and erosion in Yanshan-Himalayan period.The study shows that the metallogenic effect of the copper polymetallic deposit in th e North Qilian area was closely related to the tectonic evolution in the North Qilian area.The ore-forming effect in the area can be divided into: a.Early Cambrian Period(~ 522Ma),Which was comprised of the tectonic environment of the middle ridge of the oceani c plate in the two-side subduction stage(such as the early period of the Yinaocao copper zinc ore deposit)and post arc extensional tectonic setting(such as the Xiaoshalongzhigou copper deposit),and they controlled the formation of the Cyprus-type VMS deposits;b.Late Cambrian-Late Ordovician Period(482 ~ 442Ma),the two-side subduction stage o f the active continental margin tectonic environment controlled the kuroko-deposit-type VMS deposit(such as Gadaban copper-lead-zinc polymetallic deposit),porphyry deposits(such as the Songshunangou gold deposit,Langlike copper deposit)and hydrothermal ve in deposits(such as Liaobantai lead-zinc deposit,Guomisi Copper-lead-zinc polymetallic deposit);c.The Triassic Period(~212Ma)was the inland orogenic stage,and in this time Alashan plots continually dived below the Qilian block,the lithosphere constantly thicke n,resulting the large-scale delamination of lithosphere,with the upwelling of the mantle material the formation of magmatic deposits(such as the Hongliucao gold-platinum deposit).It is suggested that the structural deformation of the Gadaban copper-lead-zinc polymetallic deposit after ore-forming has played a strong deformation and transformation eff ect on the ore deposit,which leaded to the parallel lateral distribution of the ore body,wh ich is of great significance to guide the mineral exploration work.Based on the study of typical deposits in the area,the genetic types of the deposits in the North Qilian area were redefined,and the geological characteristics,physical and chemical parameters and other data of the typical deposits were systematically analyzed and studied.It is the first time that the Guomisi copper-lead-zinc polymetallic deposit is considered as a mesothermal hydrothermal vein deposit,rather than a hydrothermal exhalative deposit which is considered by the predecessors.The Xiaoshalongzhigou copper mine has a typical "double-layer structure" which is belong to Cyprus-type VMS deposits,rather than to hydrothermal deposits considered by predecessors.It is concluded that the Yinaocao copper zinc ore deposit is a hydrothermal exhalative deposit in the early stage,and superposition of late hydrothermal solution made it to being a superimposed deposit The Gadaban copper-lead-zinc polymetallic deposit is a kuroko-deposit-type VMS deposit;the Langlike copper deposit and the Songshunangou gold deposit are porphyry deposit;the Liaobantai lead-zinc deposit belongs to mesothermal hydrothermal vein deposit;the Hongliucao area has the prospecting potential of the magmatic deposit.There are differences in the eastern and western eruption in the northern Qilian area,the eastern part with minimum denudation depth has good preservation condition for ore deposits,while the western with the biggest eroding depth is difficult to preserve supergene deposit.