Quantitative constraints on the exhumation and preservation of the giant Jinchuan Cu-Ni sulfide deposit

Jinchuan deposit， the world’s 3^rd largest Cu-Ni sulfide magmatic deposit formed in the Neoproterozoic， has been developed as an open pit mine， indicating the impact of exhumation and erosion on the deposit. To evaluate the preservation of the Jinchuan deposit， this study compiles published thermochronological data (zircon （U-Th）/He， apatite （U-Th）/He， apatite fission track) and Monte Carlo inverse thermal modeling results， with the aim to reconstruct <300 Ma time-temperature of the Jinchuan deposit when the deposit was exhumed to zircon （U-Th）/He temperature range. Furthermore， we conduct 2D explicit finite difference inverse thermal modeling and the results suggest that near-surface exposure of the Jinchuan deposit most likely occurred during the mid-Cretaceous （ca. 90 Ma）， which is corresponding to the timing when the Jinchuan deposit entered the apatite （U-Th）/He closure temperature range and is much earlier than a previously suspected Miocene exposure. A total cumulative exhumation thickness of 2.7～6.2 km and 1.8～3.7 km is calculated for time periods since initial exhumation （ca. 300 Ma） and surface exposure （ca. 90 Ma）. It is noted that post-exposure erosion thickness is thicker than the current maximum thickness of the residual ore-bearing intrusion （1.2 km）. Prolonged post-mineralization exhumation facilitates the shallow exhumation and ultimately leads to exposure， partly erosion and a degree of preservation with appreciable economic value for the ancient pre-Cambrian Cu-Ni sulfide Jinchuan deposit.