Descripción: In this paper the mineralogy and fluid inclusion of the upper sector of an epithermal manganese deposit are described. The study area comprises the central sector of a bigger mineralised zone where non-ore mineral are the most common ones and are composed of barite, calcite and opal with fewer amounts of chalcedony, quartz and manganese oxides. Their textures and their assemblages allow us to determine several events of precipitation. The open spaces between barite crystals were filled by calcite and opal which are commoner species toward the end of the mineralization process. Chalcedony and quartz only occur inside a few small cavities. Fluid inclusions were studied in barite, calcite and quartz samples. They are composed of H 2O, NaCl and fewer amounts of CaCl 2 and MgCl 2. Calcite and barite samples have an average salinity of about 4.18 %wt NaCleq., meanwhile quartz evidences salinities around 5.26%wt NaCleq. Homogenization temperatures are also different for each species: quartz shows an average temperature of about 148°C, meanwhile barite and calcite seem to be a little higher (184° and 171°C respectively). All the data compiled in this paper suggest that this district represents one of the uppermost sectors of the ore deposit. The high amount of non-ore minerals evidences that this area, in contrast with the others ones, was especially active during the end of the mineralization process.

Descripción: El Infiernillo Mining District is located in the San Rafael Block (34°38'20";68°47'37"), province of Mendoza, Argentina. It is a porphyry Cu (Mo) type deposit which is hosted by a volcaniclastic sequence. It develops an alteration halo with a concentric pattern consisting of a central quartz neck surrounded by a potassic alteration zone and outwards a phyllic halo and small polymetallic veins. The potassic halo has a paragenesis of K-feldspar-quartz-(biotite). Three silicification phases are related to this alteration stage, one of them (with temperature between 550° and 390°C and salinity between 35 and 47 %) genetically linked to the copper mineralization. The phyllic alteration consists of quartz-illite-(rutile) with minor albite. The albitization process points out to an early phase of this phyllic stage. The fluid inclusions together with the textures of the quartz neck suggest the shallowing of the active hydrothermal system. The disseminated ore paragenesis consists of bornite, chalcopyrite-molibdenite, pyrite, (galena-sphalerite). The presence of molibdenite-quartz veins indicate the transition from the potassic to the phyllic stage while the pyrite-quartz ones point out to a transition to a fragile deformation regime during which the polymetallic veins, with a paragenesis of chalcopyrite- sphalerite, pyrite, (Ag) tetrahedrite, galena were formed. The petrologic characteristics of the volcaniclastic host rocks reveal that they correspond to the lower section of Choiyoi magmatic cycle. The magmatic and structural controls constrain the age of this ore deposit to the Early-Middle to Late Permian.

Descripción: Towards the northeast of the Sierra de San Luis several wolfram ore deposits occur. In San Martín district they are divided into three groups: Los Avestruces, La Esperanza and Cerrito Blanco. The geology of this area is formed of the Conlara metamorphic complex composed of schists (with a strike of 300° north), granitoids and pegmatites. In the same area subsaturated chalco-alkaline lamprophyres also appear as subvertical bodies with NW-NE strikes. Toward the boundaries of these rocks, the amount of biotite rises gradually from 80 to 90% developing a biotitite rock due to metasomatic processes and the superimposed deformation. This biotitite is rich in K, Rb and W among other elements. The scheelite mineralization (with quartz, biotite and tourmaline as non ore minerals) occurs in veins that are usually hosted between the lamprophyres and the wall rocks. Scheelite also appears between the schist planes of the biotitite rocks as well as disseminated crystals in quartz aggregates. This mineralization took place from fluids with XH2O: 0.87/0.82 - XCO2: 0.11/0.16 - XNaCl: 0.015/0.013 - (CH4) meanwhile the scheelite, according to the fluid inclusions studies, precipitated from unmixing processes below 320°C and 2.3 kb. Achaliana orogeny and the intrusion of Las Chacras-Piedras Coloradas batholiths (Devonian-Carboniferous) were the responsible for the slight rise of the fluids from the basement, the generation of fault structures through which they rose, the metasomatism and the mineralization.