Abstract

MARTINEZ, Viviana A  and  GALLISKI, Miguel Angel. Geology, Mineralogy and Geochemistry of Las Cuevas pegmatite, San Luis. Rev. Asoc. Geol. Argent. [online]. 2011, vol.68, n.4, pp.526-541. ISSN 0004-4822.

The present study deals with the description and interpretation of the geology, mineralogy and geochemistry of the Las Cuevas pegmatite, Conlara pegmatitic district, Sierra de San Luis, Argentina. This ore deposit belongs to the Rare-Element class, REL-Li subclass, complex type, spodumene-subtype of granitic pegmatites. it is a tabular bodie trending to the northwest, with dips ranging from vertical to subhorizontal. The host-rocks of the pegmatite are usually quartz-micaceous schists. The depth of emplacement was in the ductile to brittle transition domain, possibly ranging between 7 and 12 km. The intrusion of the pegmatite was forced, producing secondary folding in the host rock and enclosing metric-sized xenoliths. The emplacement took place during the Eopaleozoic, shortly after the regional metamorphic peak of the Famatinian Cycle. The pegmatite and its host-rock were deformed by the late tectonism belonging to the Ocloyic phase. Eight zones of different mineral association, texture and setting have been identified in this pegmatite. The mineralogy comprises: quartz, microcline, spodumene, albite, muscovite, apatite, beryl, schörl, zircon, garnet, columbite-(Mn), tantalite-(Mn), pyrochlore and microlite group minerals, ambligonite-montebrasite, triphylite-litiophilite, elbaite, eucriptite, lepidolite, bismuthinite, pyrite, huréaulite, phosphosiderite, beraunite, rockbridgeite, stewartite, bismutite, ferric oxides, manganese oxides, and mitridatite.The processes of pegmatitic differentiation, indicated by the chemical composition of trace elements in K-feldspar and muscovite, are comparable and do not differ from the known paths of similar world- and argentinian- pegmatites of this type showing lineal fractionation trends. Besides, the individual analysis shows a lineal differentiation, in some cases with an overprint between the samples of different zones, resulting from changes in the physico-chemical conditions of cristalization. Based on the muscovite geochemistry, Las Cuevas has an interesting but limited potential for tantalum mineralization.

Keywords : Spodumene-subtype; Rare-Element pegmatite; Geochemistry; Ta-ore minerals; Conlara pegmatitic field.

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