Addressing ore formation and exploration

Modeling ore generation in a magmatic context

“…Just remains in the second term of the equation the power law in Péclet number, with the coefficient b, numerically fitted to 1.456 for low Péclet numbers, but to 1.03 for high values corresponding to advection (Huber et al, 2012). The quantification issued from the model indicates an enrichment factor of three orders of magnitude for Au and Cu in porphyry-type magmas (Vigneresse, 2019). The threshold imposed on metal diffusivity in a felsic melt make Pb and As enrichment unlikely in such magmas.…”

“…A full analytical inverse formulation is presently ruled out because of inherent feedback loops between advection and diffusion. The problem of ore generation must be reformulated to address the right questions on the manner and quantity metals are enriched (Vigneresse, 2019). But the answer to such questioning is certainly not simple.…”

“…Nevertheless, the model suffers from the large quantitative uncertainties underlying the diffusivity values and the partition coefficients. First elaborated for porphyrytype (Cu, Mo, W, Sn) deposits (Huber et al, 2012;Vigneresse, 2019), the model uses for simplicity a relative enrichment with respect to one component (Cl) of the MVP. It is the most common situation and best documented case of ore deposits related to granitic intrusions (Hedenquist et al, 2005).…”

“…The metal enrichment factor is bracketed between a minimum value, equivalent to the ratio of metal partitioning between the melt and MVP, and a maximum value. The latter is the preceding minimum value to which terms are added depending on metal diffusion into the melt and melt motion (Vigneresse, 2019). In case of relative enrichment, and for high values of both Péclet numbers (>> 1), the second term of the equation converges toward the ratio of the two Péclet numbers.…”

“…Identifying the causes of metal enrichment is still a matter of debate underpinned by numerous models deriving from field observations, experimental studies or numerical simulations. None of which address the full complexity of the metal concentration process, either during the magmatic stage, nor during the late hydrothermal stage leading to ore deposits (Vigneresse, 2019).…”