CFD MODELLING OF HYDROTHERMAL TRANSPORT IN THE EARTH'S CRUST: IMPLICATIONS FOR THE FORMATION OF ORE BODIES

Computational Fluid Dynamics (CFD) modeling (via Finite Element Methods) of hydrothermal flow in the earth’s crust provides invaluable insight to the development of temperature and flow regime fields in rock hosting ground water, information vital to understanding the formation of ore bodies and the distribution material within them. Calculation of distances that hydrothermal flow may be mobilized by magmatic heat indicate flows can be readily driven at least as far as 100km in the horizontal through zones of relatively permeable rock (e.g.,10^–13 m²). Even tighter units can host flow which can involve considerable transport over geological time frames. Depending on the orientation of aquaclude to aquifer, a host of flow patterns are obtainable. There may be either return flow along the bottom of a closed end aquafir set in tight rock or the formation of a series of convecting cells along the conduit itself. If the aquafir extends in an open ended fashion, recharge will occur through tighter rock above and below into the conduit with no need for return flow within the conduit itself. CFD modeling has strongly demonstrated that the geothermal gradient clearly cannot be neglected in these computations and the geothermal gradient alone is capable of generating convection cells of hydrothermal flow, a phenomenon that seems not to have been noted until recently. Computational results do not show significant departure from the configuration of ore bodies reported in the literature and lend support to “light bulb” models of porphyry deposits:, replicating distributions seen in Palabora and Cripple Creek. The modeling also supports speculations that a number of sources of precious metals are derived from hydrothermal circulation in crustal rocks rather than from partial melts associated with subduction.