Uplift-cooling Evolution Of The East Longshou Mountain And Its Influence On Denudation And Preservation Of The Jinchuan Deposit

Regional uplift and denudation are important factors affecting the preservation of the deposit.Systematic and comprehensive anatomy of uplift and denudation in the East Longshou Mountains is of great research value for studying the changes that occurred in the metallogenic late stage of the Jinchuan sulfide-type copper-nickel(platinum group)deposits and the preservation status of the deposit.In this paper,we applied LA-ICP-MS apatite fission track thermalchronology technique to recover the thermal history of East Longchou Mountain including Jinchuan deposit,reveal the uplift and denudation history of East Longchou Mountain since Mesozoic,elucidate the preservation status of Jinchuan deposit,and predict the next location of ore search.The test results show an obvious difference in ages of apatite fission track between the Jinchuan ore district and its surrounding area as well as the more distant southwest region clastic rocks.The ages of the fission track in the Jinchuan ore district are located are 71.9 ± 7 Ma,62.3± 3 Ma,71.7 ± 10.8 Ma,79.8 ± 5.6 Ma,and 83.1 ± 5.5 Ma;the ages in the area around the ore district in the central part of the study area are 132 ± 15.1 Ma,127.1 ± 15.3 Ma,135.4 ± 7.8Ma,and 98.7 ± 5.5 Ma;The ages of the fission track in the southwest part of the study area are197 ± 10.2 Ma and 214.7 ± 14 Ma.There is a correlation between the ages and elevation within the above three areas,and the distribution of the confined track lengths of all samples shows a single peak with slightly wider and lower characteristics,and the Dpar values range from 1.0-2.2 μm.The thermal history of regions was simulated with a multivariate annealing model utilising the thermodynamic parameter Dpar.The inverse thermal history models indicate that the area where the Jinchuan ore district is located experienced rapid cooling from the early of the Late Jurassic(～160 Ma)to the end of the Early Cretaceous(～100 Ma),slow cooling from the end of the Early Cretaceous(～100 Ma)to the middle of the Miocene(～15 Ma),and intense cooling since the middle of the Miocene(～15 Ma),with cooling and denudation rates of 1.33 °C/Ma,0.25 °C/ Ma and 2 °C/Ma;28.10 m/Ma,7.41 m/Ma and 57.14 m/Ma,indicating that the Jinchuan deposit was exposed to the surface no earlier than the Miocene(～15 Ma).The central part of the study area experienced rapid cooling from the early Early Jurassic(～200 Ma)to the end Early Cretaceous(～100 Ma)and slow cooling since the end Early Cretaceous(～100 Ma),with cooling and denudation rates of 1.25 °C/Ma and 0.33 °C/Ma,35.71 m/Ma and 9.52 m/Ma,respectively.The southwestern region of the study area experienced two cooling events: slow cooling from the early Early Jurassic(～200 Ma)to the end Early Cretaceous(～100 Ma)and relatively rapid cooling since the end Early Cretaceous(～100 Ma),with cooling and denudation rates of 0.25 °C/Ma and 0.33 °C/Ma,7.14 m/Ma and 9.52 m/Ma.The uplift and denudation in the above three regions are under an increasing trend from southwest to northeast,and each region has a certain similarity.Based on the depth of mineralization obtained by previous authors,combined with the simulation and calculation results of this study,it is known that most of the Jinchuan deposit may still be retained at depth,and the interface between Jinchuan II and I ore zones may be a favorable location for the next step of mineral search exploration.