The gold-vanadium-tellurium association at the Tuvatu gold-silver prospect, Fiji: conditions of ore deposition

The Tuvatu gold - telluride prospect is one of several epithermal gold systems along the > 250 km northeast trending Viti Levu lineament, Fiji, which are genetically associated with alkalic magmatism. Vein structures contain a variety of sulfides, native elements, sulfosalts, and tellurides. Calaverite is intimately associated with various vanadium-bearing minerals: roscoelite, karelianite, vanadian muscovite, Ti-free nolanite, vanadian rutile, schreyerite, and an unnamed vanadium silicate. Thermodynamic calculations for the systems V - Al - K - Si - O - H (Cameron, 1998) and Au - Te - Cl - S - O - H at estimated conditions of formation of the telluride-native gold stage at Tuvatu ( similar to 250 degrees C, Sigma Au = 1 ppb, Sigma Te = 1 ppb, Sigma S = 0.001m, Sigma V = 0.0001 m, and a(K) = 0.01), show that the stability fields of calaverite, roscoelite, and karelianite converge in pH-fO(2) space near the hematite - magnetite buffer and at neutral to slightly acid conditions. Thermodynamic and textural data suggest that these minerals were deposited together at Tuvatu and likely explain the common coexistence of roscoelite and calaverite in epithermal gold systems elsewhere. The presence of magnetite with up to 0.7 wt.% V(2)O(3) in the Navilawa Monzonite is consistent with the derivation of V from the alkalic intrusive rocks, which are also considered to be the source of Au and Te in the Tuvatu deposit.