Numerical Modelling of Coupled Interactions of Magmas, Fluids and Rocks in the Formation of Porphyry Copper Deposits

New discoveries of ore deposits are essential to secure our future demand on raw materials. Exploration for major hidden ore deposits at depth requires novel exploration concepts based on mineral system analyses beyond the deposit scale. Such approaches seek to develop a fundamental understanding of the process chain of coupled physical and chemical interactions between magmas, fluids and rocks that lead to the formation of large ore deposits. Numerical models will play a key role in bridging spatial and temporal scales varying by orders of magnitude. In this contribution, we present new numerical constraints on the formation of porphyry Cu-Mo and epithermal Au-Ag deposits. The model can simultaneously resolve both magma (Navier‐Stokes) and hydrothermal (Darcy) flow. It further uses realistic non-linear properties of crystallizing magmas and saline fluids, dynamic permeability feedbacks including fault structures, and proxies for metal transport.  The simulations describe the interplay of episodic sill emplacements, magma convection, focused volatile degassing, hydraulic fracturing, fluid phase separation and mixing. The model further simulates the fate of chemical components like salts and metals, considering fluid-melt and vapor-brine partitioning, as well as precipitation and remobilization. The simulation results show that the coupled physicochemical interactions of all of these processes can self-organize into the accumulation of voluminous hydrous magma reservoirs, distinct stages of degassing and ore precipitation by interaction with groundwater convection in typical porphyry ore shells (e.g. Gruzdeva et al., 2024). The modelled temporal and spatial evolution of the magmatic-hydrothermal system successfully reproduces and explains many observations at porphyry and epithermal deposits worldwide. Combining these first-order constraints from simplified numerical models with geochemical and geophysical data provides a promising avenue for the development of multi-method approaches to develop robust exploration criteria for future discoveries of critical mineral deposits.

Gruzdeva, Y., Weis, P., Andersen, C. (2024): Journal of Geophysical Research: Solid Earth, 129, 7, e2023JB028433. https://doi.org/10.1029/2023JB028433