LOS SKARNS DE Fe DE VEGAS PELADAS: CARACTERÍSTICAS GEOLÓGICAS, MINERALÓGICAS Y DISTRIBUCIÓN DE LAS PARAGÉNSIS MINERALES

PONS, JOSEFINA; FRANCHINI, MARTA; IMPICCINI, AGNES

Revista Asociación Geológica Argentina

Asociación geológica Argentina

Lugar: Buenos Aires; Año: 2009 vol. 64 p. 329 - 351

0004-4822

The Vegas Peladas iron prospect is hosted in the marine Jurassic sedimentary silicoclastic (Puchenque F.) and calcareous (Calabozo F.) rocks affected by Andean magmatism (15.19 ± 0.24 Ma) and tectonism. Four intrusive events were identified associated  with hydrothermal alteration and mineralization. Two of them are metasomatic in origin  (Fe skarn). The most important is an Fe skarn associated to the diorite pluton that contains  an aureole of hornfels and marble and a zoned prograde skarn with an oxidant mineralogy rich in garnet (And31-100Py 0.34-0Grs68-0) and subordinate clinopyroxene (Di24-70 Jo4.1-0.7Hd72-29.3). The diorite margins have incipient (actinolite ± chlorite ± calcite ± orthoclase ± epidote) alteration and a thin massive orthoclase + quartz envelope. Retrograde assemblages replaceearly alterations and are rich in epidote and amphibole. In the diorite and in the inner exoskarn zones, the mineralization consists of magnetite (83 y 88 % de Fe2O3 total) whereas in  the intermediate and outer exoskarn zones. hematite and mushketovite (93.5 y 95 % de Fe2O3 total) dominate.  Iron oxides are in equilibrium with retrograde minerals. The mass balance  calculations show a hugh increase of the total Fe2O3 in the exoskarn during the skarn formation. The second metasomatic event  is associated with the granite. It formed a zoned skarn rich in scapolite (Me25-36), garnet (And10-81 Py0.72-0 Gr89-19) and pyroxene (Di42-93 Jo2.6-1.7 Hd54.8-5.1) with superposed retrograde alteration and scarce iron mineralization, probably remobilized from the early skarn. The distribution and composition of the mineral assemblages in the Vegas Peladas district can be useful guides for the exploration of other SW Mendoza regions with partial outcrops of the  alteration-mineralization or where they remain blind.