Emplacement Depth Of The Granitic Complex,Post-ore Change And Preservation Of The Duobaoshan Prophyry Cu(Mo) Deposit, Heilongjiang Province,China

The Duobaoshan large porphyry Cu-Mo deposit in Heilongjiang,which is located in the northeastern part of central Asia-Mongolian-Hinggan orogenics belt in northern margin of North China Landmass,is one of the most important porphyry Cu-Mo deposit in the eastern part of Central Asia Orogenics Belt(CAOB).The predecessors have done a lot of research work and gained considerable results.However,the depth at which the mineral deposit forms,and the change and preservation after the formation haven't been studied.In this paper,the Duobaoshan Cu mineral deposit is taken as the research object.By using methods such as petrology,fission track and geothermobarometer,the diagenetic depth and thermal structure geochronology of porphyry copper ore-bearing rock-body will be studied.Thermal history simulation shows the uplift time of Mesozoic-Cenozoic in this region,the rate and the processes of uplift and denudation.The condition of change and preservation of mineral deposit will be discussed,which will offer theoretical basis for evolution history of thermal structure in regional orogenic belt and deep prospecting.According to the research result of geothermobarometer,the diagenesis pressure of the Duobaoshan granodiorite porphyry is about(1.69-1.78)×10~8Pa,the temperature is about 650-710?,and the diagenesis depth of rock mass is6.36-6.69Km.The diagenesis depth corresponding to the diagenesis pressure is the emplacement depth of rock mass.Nowadays,as the mineral deposit crops out,the diagenesis depth refers to denudational depth since diagenesis.Therefore,average denudational depth of the whole Duobaoshan granitic complex is about 6.36-6.69km.Based on thermal structure study of the apatite fission track,since the late Cretaceous,the uplift and cooling of ore-hosting rock-bodies in Duobaoshan mining area has experienced three stages:basic stability,rapid uplift,basic stability.The rate of uplift of ore-hosting rock-bodies is about 0.2201mm/a,and the depth of uplift and denudation is 3.28Km,which is much lower than the depth of mineralization.As a result of that,the preservation of mineral deposit is good.The track age of ore-hosting rock-bodies is about 55Ma,and that of the country rock is about 74Ma.That is to say,the uplift of the mineralize rock body is late,while the uplift of the country rock is relatively early,which is related to ore body locating in the core of the syncline with double anticline,syncline of north west direction.Mining compression uplift due to both sides of the squeeze pressure makes both sides with respect to the core uplift faster,which means that uplift of ore-forming rock body is late while the uplift of country rock is earlier.All of that provides favorable geological conditions for the change and preservation of mineral deposit.According to the tectonic evolution of the mining area and the evolution process of the uplift and cooling of the ore bearing rock,since Yanshan period,with the influence of the Yanshan movement,the mining area has both the function of the compression structure and the extension of the structure.At that time,this mining area run through the obvious rapid uplift and denudation,until the Eocene rock body was being stability.Through the research,it is found that average depth of denudation after mineralization is 6.525Km,while the denudation depth of rock body after Yanshanian period is about 3.28Km,which mainly occurred in the late Cretaceous to Eocene.From Caledonian to Yanshanian period,the uplift of rock body is about 3.245Km,mainly in Indosinian period,which is relevant to collision and closing of the paleo Asian Ocean.