NUMERICAL MODELING OF ORE-FORMING MAGMATIC-HYDROTHERMAL PROCESSES

Ore formation can take place in various parts of magmatic-hydrothermal systems. Steep temperature-pressure gradients in crystallizing magma stocks may facilitate the formation of porphyry copper deposits from complex magmatic fluids. Phase separation leads to the formation of a high-salinity, high-density brine phase with limited mobility and a buoyant low-salinity vapor phase. The latter may rise to shallower parts of the system but its potential to carry ore-metals from the magmatic to the epithermal domain strongly depends on the exact temperature-pressure-composition path.

Numerical simulations of fluid flow are a key to understand the dynamics of these systems. It has been shown that both the fluid properties and the physical laws that govern fluid flow must be treated without major simplifications in order to obtain meaningful simulations. Frequently used simplifications such as the Boussinesq approximation will obscure or even completely suppress the true dynamics and evolution of the simulated system. Results obtained so far seem to indicate that the non-linear dependence of fluid properties on temperature, pressure, and composition severely limits the possible evolution paths that a system can take in a given geological setting. Comparison with well-documented field observations shows that numerical simulations naturally “predict” all first-order features found in major ore-forming natural systems. This will be discussed in some detail for an epithermal Pb-Zn system of Oligocene age from Madan, Bulgaria. In addition, our current knowledge on the hydrology of porphyry copper systems and the potential link to some types of epithermal systems will be summarized.