Genesis of Platinum-Group Minerals in the Las-Aguilas Mafic- Ultramafic Rocks, San-Luis Province, Argentina - Textural, Chemical and Mineralogical Evidence

MOGESSIE, A; HAUZENBERGER, CH; HOINKES, G; FELFERNIG, A; STUMPFL, E F; BJERG, E A; KOSTADINOFF, J

MINERALOGY AND PETROLOGY

Sringer

Lugar: Viena; Año: 2000 vol. 68 p. 85 - 114

0930-0708

Palladium bismuthotellurides (merenskyite-michenerite-moncheite-melonite) of variablecomposition and platinum arsenides (sperrylite) are documented in several drillcores of the Las Aguilas ma®c-ultrama®c intrusion, San Luis province, centralArgentina. The ma®c-ultrama®c rocks ranging in composition from harzburgite todunite, lherzolite, norite, and gabbro, intruded an amphibolite facies basement causinglocally granulite facies metamorphism. The platinum ± group minerals (PGM) identi®edin these rocks occur in (1) unaltered orthopyroxene-rich, plagioclase- and spinelbearingrocks which carry abundant base-metal sulphides (BMS), such as chalcopyrite,pentlandite, and pyrrhotite; and in (2) serpentinized olivine-rich zones along cracks, butalways associated with BMS, spinel, serpentine, and secondary magnetite. Texturalevidence suggests a primary magmatic origin as well as late-stage hydrothermalremobilization, transport, and deposition of the PGM. Geophysical exploration andgeological ®eld work have delineated the extent of the Cu-Ni sulphide mineralization inthe ma®c-ultrama®c intrusion underlain by a crystalline basement of Ordovician age. Itis estimated that platinum-group-element (PGE) ± enriched zones of several metersthickness could be present at depth in the ma®c-ultrama®c intrusion. Chondrite ±normalised plots reveal that the ultrama®c rocks have a similar PGE fractionation trendas the Bushveld and Stillwater layered complexes. This contrasts with the ophiolitetypeultrama®c associations of the Sierras Pampeanas in Cordoba Province, whichoccur about 400 km to the northeast of the study area.