Platinum-group mineral formation: Evidence of an interchange process from the entropy of activation values

The possibility of PGM formation from the direct reaction of free metals with sulfur would be inconsistent with the estimated entropy of activation values (ΔS≠ ∼ 0) at various temperatures. In the cases of PGMs of known r, the formation temperatures can be estimated, and then the free energy of activation obtained, applying 2.5ln(r) + ln(T) versus 1/T (straight line). From that value, the entropy of activation can be calculated [ΔS≠ = −R + (Eact − ΔG≠)/T], and an interchange mechanism is proposed. Furthermore, applying the relation of 2.5ln(r) + ln(T) versus 1/T on PGM grains of known r and T, an interchange mechanism for their formation can be suggested if they fit the above line.