Uplift-erosion And Preservation Of Zhunuo Porphyry Cu Deposit In The Gangdese Belt

The Zhunuo mining area is located in the west section of Gangdese.It is a newly discovered large porphyry copper deposit in recent years.In this paper,the Zhunuo mining area and the related rock mass are the research object.Through the system collection of samples,the fission track dating and the thermal evolution simulation are carried out.The erosion rate and the denudation amount of the Zhunuo mining area are quantitatively calculated,the thermal evolution history of the mining area is retrieved,the preservation state of the mining area is analyzed,and the relationship between the uplift erosion process and the regional structure is discussed.The following main understandings are obtained: The apatite track age of the rhyolite porphyry is 7.9Ma~33Ma,the apatite track age of monzonitic granite is 11Ma~13Ma,and the apatite fission track age of the monzonitic granite porphyry is 9.4Ma~13Ma,and the age of granite porphyry apatite track is 3.1Ma~21Ma.The age of the fission track of the ore bearing porphyry apatite is later than or close to the age of the porphyry copper deposit,but it is obviously less than the age of the diagenesis of the ore bearing porphyry,indicating that the rock mass is rapidly cooled to the closed temperature after the mineralization.The fission track length is 12.3±2.4 um~13.8±1.9um m,showing a negative bias single peak distribution,which indicates that the sample is raised and denuded from the bottom of the annealing zone to the surface temperature,and the cooling curve is relatively simple.According to the history of the length of fission track and the history of thermal evolution,there is a rapid cooling event of the rhyolite porphyry at about ~40Ma,which may be caused by the thickening of the crust and the subsequent uplift of the earth's crust.There are two stages of rapid denudation in ore bearing porphyry,8~11Ma and 4~6Ma.Compared with the tectonic events in the Gangdese region,the rapid erosion event of 8~11Ma is caused by the intraplate extensional environment of the middle Miocene Gangdese belt,and the rapid erosion of 4~6Ma may be related to the rapid uplift of the whole Qinghai Tibet Plateau.The denudation of mining area is 2.25~2.63 km,The denudation thickness of the mining area is greater than that of the ore-forming depth,and the mining area has been denuded in different degrees.If the average erosion amount is compared with the ore-forming depth of the mining area,it is known that the mining area has been eroded 1/3.Combined with previous understanding,the deposit has suffered partial erosion since its formation,and no large-scale destruction occurred.The deposit is well preserved.The denudation rate of the mining area obtained by fission track is 0.16~0.202mm/a,which is similar to the denudation rate of the typical Gangdese deposit.The ore deposit formation is related to the Sloan rise event at the bottom of the Gangdese deposit,which is compared with the low temperature geochronological data of the typical Gangdese deposit from the fast cooling stage of the ore deposit and the zircon fission track age of the Zhunuo ore deposit from 13~10Ma.