Fission Track Analysis And Thermal History Simulation Of Tongcun Mine Area In Zhejiang Province

Molybdenum(copper) deposit of Tongcun locates in the southwest of Jiangshan-Shaoxing structure zone, and lies in Qinzhou-Qiantang juncture zone adjacent to Jiangnantai anticline, locates in eastern part of Qinzhou-Hanghzou metallogenic belt.On the basis of field work and investigaton, this essay conducts a systematical summary of geologaical characteristics of mine lot and ore body, combines with apatite and zircon fission track and simulate thermal history to study the uplifting and exhumation of Tongcun deposit. finally receiving some achievements as follows:Mining area mainly has granite, granite diorite, and hornfels, occasional quartzite; The ore bearing rocks are mainly altered granite and hornfelsed, and mineralization of molybdenite, pyrite and chalcopyrite. Enrichment of ore bearing quartz veins, the alteration zone of the mine area is composed of potassic, propylitization(sericitization) and kaolinization from the center of the rock mass outwards, in which the propylitization(sericitization) is mainly alteration type and has more developed quartz veins.According to apatite fission track lengths data(AFTLD), the average lengths range from 11.9±2.4μm to 13.2±2.0μm, relatively concentrated, the histogram of AFTLD has two types, the deep samples are unperturbed basement type, the top samples are double peak type, which shows that apatite samples of Tongcun deposit under the influence of thermal events presents two kinds of distribution, the whole rock under the effect of two stages thermal events, but the core of rock samples is shown as simple cooling process. The zircon fission track ages range from 109 Ma to 143 Ma, the apatite fission track ages range from 109 Ma to 143 Ma, their main peak age is 137 Ma and 22 Ma respectively.with the help of He FTy software, temperature-time evolvement curves is obtained. Apatite samples have similar cooling trajectory. First advanced into the cooling period, and then slowly cooled, finally entered the period of accelerated cooling. Zircon and apatite(named "the mineral pair") fission track ages are used to calculate the cooling and uplifting rate. The rock formed in Late Jurassic, and it can be elicited that from Early Cretaceous to the Neogene, the average exhumation rate of the Tongcun Deposit is 0.0238km/Ma, the exhumation and unroofing thickness is over 2.732 km. From the Neogene to the Quaternary, the average exhumation rate is 0.0383 km/Ma, the exhumation and unroofing thickness is over 0.842 km. During 45~25Ma and 15~0.1Ma, the rock has two uplifting process, their main cooling rate of rock is 3.75~5℃/km and 3.21~6.67℃/km respectively. From 137 Ma to today, the exhumation and unroofing thickness of the Tongcun rock is 3.579 km. The rock mass of the exhumation and unroofing is conformity with the south China block regional tectonic action.