Mitridatita derivada de la alteración de pirita y apatito de la pegmatita El Criollo, Cerro Blanco (Córdoba, Argentina).

COLOMBO, FERNANDO

Río Cuarto

Congreso; 10º Congreso de Mineralogía y Metalogenia; 2010

Universidad Nacional de Río Cuarto y Asociación Geológica Argentina

Mitridatite occurs replacing pyrite interstitial to apatite crystals which occur rimming a large triplite mass in one of the intermediate zones of a pegmatite at Cerro Blanco, near Tanti, Córdoba Province (31º 21´ 24.5´´ S, 64º 39´ 13.4´´ W). This phosphate is found as porous microcrystalline masses of dirty olive green color, or as blackish brown spherules with radiating internal structure. Only Ca, Fe, P, O and traces of Si were detected by EDS. Unit-cell dimensions, refined using the Rietveld method, are a 17,540(2), b 19,359(4), c 11,238(2) Å, b 95,61(2)º, V 3798(1) Å3. Other secondary phases present in the same association are hematite, goethite, dufrénite, phosphosiderite and strengite.   They originated by a low-temperature (<200ºC, and possibly less than 100ºC) hydrothermal decomposition of apatite and pyrite under oxidizing and acidic conditions. Precipitation of secondary phases probably occurred under non-equilibrium thermodynamic conditions. The chemical composition of the secondary phases reflects the very local environment.