Fernando Guillermo Sardi

Geology and metallogeny of tungsten-bearing ore deposits from central-eastern Famatina System, Argentina.

The different rocks that host the tungsten-bearing quartz veins from central-eastern sector of the Famatina System (La Rioja, Argentina) are part of the crystalline basement of this unit. Petrographic and geochemical studies demonstrate that the emplacement of quartz mineralized veins did not alter the Late Precambrian- early Cambrian metapelites. This can be attributed to their low permeability and little reactivity. The magmatism of the zone took place mainly during the Ordovician and in minor proportion during the Devonian. The granitoids related to the tungsten deposits vary from granodiorites to sienogranites. Geochemically, these range from metaluminous to peraluminous, are calc-alkaline and highly differentiated. The deposits consist of quartz-veins, where the main ore mineral is wolframite, with small amounts of scheelite. The gangue is constituted by quartz and other silicates. The hydrothermal alteration of the different deposits is muscovitization (-sericitization) sometimes related to mineralization, albitization, chloritization, and silicification. The joints in the granitic copula and cleavage in the metamorphic host rocks channelized the W-bearing hydrothermal solutions. The transport of W was essentially as hydroxicomplexes, and fluorine and silica complexes in an acid environment. The precipitation of wolframite may have been caused by reactions of this fluid with ferromagnesian silicates in the granite, decrease of the temperature and/or increase of the alkalinity.