Mississippi valley-type Pb-Zn deposits formed by episodic fluid migration in the fold-and-thrust belts of the Tibetan Plateau

Mississippi Valley-type (MVT) Pb-Zn deposits are typically found in the foreland basins and fold-and-thrust belts of orogens, and they form under low-moderate temperatures and high salinities. Deposits in thrust belts typically form in folded strata during strike-slip or extensional stages following early collision, indicating different hydrologic and tectonic controls from deposits in foreland basins. On the basis of the Tanggula thrust belt and the Duocaima deposit, we established a 2D simplified model and employed the finite element method (FEM) to investigate how topographic gradient and faults control fluid migration and temperature changes. We further discuss the implication and prediction of simulation results for MVT mineralization in thrust belts, such as the duration of mineralization, the source-transport-convergence processes of ore-forming fluid, and the factors controlling the metallogenic location and scale. The results indicate that the fluid that migrates from the orogen toward the basin is driven by topographic gradient. Throughout this process, the fluid migrates along the detachment fault and central faults to the surface. The fluid does not stabilize in the central belt but migrates toward the front belt. When the ore-forming fluid reaches the front belt, it ascends rapidly along faults, enters the shallow structure and mineralizes. The temperature variations at the monitoring points indicate episodic upwelling of the fluid. The simulated temperatures correspond to the metallogenetic temperatures. Assuming that structural conditions remain constant, mineralization may be completed within 240-550 kyr, and the calculated fluid volumes are 1.4 x 106-2.8 x 106 m3. High-permeability faults gather high-temperature and high-velocity fluid, acting as conduits that provide the necessary heat and flow for mineralization, thus limiting the metallogenic range and time of MVT deposits. This simulation study provides a good indication for the prediction of the distribution and scale of mineralization of MVT deposits.