Characterization of San Martín pluton and associated tungsten deposits, Valcheta Department, Río Negro Province

Abstract

The San Martín pluton is formed by abiotitic granite border facies, a leucogranite central facies and cogenetic granitic dykes and aplites. This pluton is a I-type metaluminous granite. It was seated in high crust levels in the middle Upper Permian (262 ± 5.2 Ma). The pluton rocks show a textural evolution from medium grained hypidiomor phicbiotitic granites to fine grained allotriomorphic leucogranites, porphyriticdykes and miarolitic aplites, which suggest magma undercooling, water saturation and exsolution of magmatic volatiles to favor tungsten removal and transportation. There are two vein types in the San Martín pluton: 1) pre-tungsten mineralization veins, and 2) tungsten-bearing veins. The paragenetic sequence began with the first hydrothermal sterile stage (stage I), which formedpre-tungsten mineralization veins and generated potassium alteration in thewall rock. The second hydrothermal stage (stage II) formed the tungsten-bearingveins and deposited quartz, alkali feldspar and wolframite followed by quartzand wolframite. At the end of the stage II, quartz, sulphides, base and precious metal sulphosalts and fluorite were deposited. A magmatic-hydrothermal system model is proposed where the San Martin pluton is the wall rock of the hydrothermal veins whose source is a highly differentiated granite intrusion located below. The granite intrusion would be a late stage of the granitic system of San Martín pluton.