Distribución de las alteraciones en la manifestación de hierro del skarn de Vegas Peladas, sudoeste de la provincia de Mendoza

PONS, M. J., FRANCHINI M. B. Y ETCHEVERRY R. O

Buenos Aires

Congreso; VI Congreso de Mineralogía y Metalogenia, (Eds. Brodtkorb y Kourskha) p.345-351; 2002

Universidad de Buenos Aires

The Vegas Peladas Fe  skarn  is located in the Main Cordillera of SW Mendoza, in the Malargüe Thrust Belt.  Mineralized skarn exposures show similarities with typical oxidized Fe skarn deposits worldwide.  Skarn formation has particularly affected silstone  intercalated with mudstone and calcareous sandstone of Cerro Puchenque Formation (lower Jurassic) in the contact with  diorite and gabbro-diorite stock (Los Molles Group; Eocene- upper Miocene). Diorite and gabbro-diorite stock margins exhibit  different grades and types of alterations: magmatic  amphibole,  and feldspar  patchy and vein replacement by amphibole ± chlorite ± calcite  ± titanite ± magnetita and  ortoclase ± epidote ± calcite ± clay. Along the contacts, replacement of diorite by quartz ± orthoclase ± epidote pervasive endoskarn overprints the above alteration and may result in complete destruction of the original igneous texture. The earliest alteration preserved in the sedimentary protholiths involve recrystallization of the siltstone, mudstone and calcareous sandstone to fine-grained  pyroxene-rutile hornfels,  and subordinate biotite-rutile hornfels;  both  are pyrrhotite rich. Hornfels are overprinted and veined by zoned exoskarn of irregular distribution.  An inner garnet-rich zone is exposed at the porphyry contact,  followed  by an intermediate pyroxene> garnet rich zone; these prograde skarn zones are magnetite and sulfide barren. The  early retrograde assemblage  epidote ± amphibole  envelopes magnetite-rich veins and pods that cross cut early hornfels and skarn zones. Later epidote ± quartz  ± ortoclase± pyrite are also present in minor amounts as late cross cutting veinlets and alteration products of hornfels and skarn.