The petrologic, mineralogical, and chemical data are used to put constraints on the temperature and pressure history of the rocks and fluids. The petrologic, chemical, and radiogenic isotope data are used to quantify the elemental mobility that took place in a hydrothermal or metamorphic system. The approach described above has lead to a number of conclusions. Ore deposits are small parts of very large hydrothermal systems. Fluids circulate to at least 30 kilometers into the earth's crust.
Fluids carry a great deal of material from one site to another within the earth's crust.
We have been able to demonstrate that although these fluids were derived from the surrounding metamorphic rocks they have oxygen isotopic signatures completely controlled by the plagioclase in the Bushveld Complex. This finding implies that the fluid flow system evolved from pervasive flow in the inflow region of the system to fracture controlled flow in the outflow region of the system. Furthermore, much of the fluid flow that occurs along fractures appears to be transitory. As minerals undergo isotopic exchange at different rates, we have been able to use the disequilibrium systematics to estimate the amount of time fluid was present in a vein system. We have also been able to determine the fluid fluxes in both the metamorphic rocks and in the veins.