Las manifestaciones de hierro en skarns del flanco suroriental del cerro Caicayén, Neuquén.

MARTA FRANCHINI; LAWRENCE MEINERT

Revista de la Asociación Geológica Argentina

Asociación Geológica Argentina

Lugar: Buenos Aires; Año: 1991 vol. 46 p. 309 - 324

0004-4822

Iron skarns deposited on the SE slope of cerro Caycayén, Neuquén, occur in a volcanic arc developed on continental crust and they are associated to Early Tertiary subvolcanic igneous rocks. They consist of four lense-shaped bodies with 70% limonites and 30% pyrite, magnetite, chalcopyrite related to skarns and situated in the outer aureole of a porphyry Cu deposit. The skarns and metal concentrations were caused by magmatic-hydrothermal replacement of Jurassic sedimentary rocks which took place at the same time as the emplacement and crystallization of quartz andesite and andesite. The skarns show a zonal pattern according to the rocks they replaced and the distance to the intrusive contact. The dominant silicates and oxides (epidote, clynopiroxene Hd28-60, garnet Ad95-97, quartz, and magnetite after hematite) indicate that hydrothermal fluids were water-rich, poor in CO2 and has high to intermdiate fO2 (log fO2 between -20.5 and -30.5). A pressure below 500 bars for silicates and magnetite formation is estimated like for other epizonal skarns. These anhydrous minerals of the early stage were affected by retrograde reactions: firts they turned into hydrous silicates, magnetite into siderite and then, they were replaced by quartz. The sulfide deposition took place after main skarn formation and synchronous with retrograde alteration. They have pyrite as disseminations and veins in skarns and as massive replacements of marble at the skarns front. Caycayén belong to a variety of skarns genetically associated to a porphyry Cu deposit, but they have Fe as the main metal.