Granitic pegmatites and Nb-, Y-REE- and F-mineralization in the Las Chacras Batholith,Argentina

ALTENBERGER, U; TRUMBULL, R.; RIBACKI, E.; LÓPEZ DE LUCHI, M. G.

Munsters

Conferencia; GeoMunsters 2019; 2019

Deutsche Geologische Gesellschaft ? Geologische Vereinigung (DGGV ? The German Geological Society) and the Deutsche Mineralogische Gesellschaft (DMG ? The German Mineralogical Society)

The Devonian Las Chacras Batholith of the Sierra de San Luis in central Argentina intruded into an Ordovician basement, composed of metasediments and S-type granitoids. The batholith is composed of nested granitic intrusions emplaced within a pull-apart structure controlled by major strike slip fault systems (Siegesmund et al., 2004). Coeval intrusions of stocks and syn-plutonic dikes of lamprophyres demonstrate a strong mantle component in the Devonian magmatism. The intrusions show a north to south directed increase in themagmatic differentiation and crustal contamination, as indicated by radiogenic Sr/Nd-isotope ratios (López de Luchi et al., 2017). Intra-granitic pegmatites occur in all units of the batholith but are most abundant in the south. Some of the pegmatites reveal NYF-type mineralization (Nb-, Y-, REE-, F-rich phases; Lira et al., 2012). In contrast, the pegmatites of the Ordovician basement contain LCT-type mineralization (Li, Cs, Ta). The present work investigates the mineralogical and geochemical composition of the pegmatites and their granitoid hosts and sources to provide new insights into the evolution of the magmatic system and the development of the NYF mineralization. The focus is on the emplacement and the evolution from primary melts at different structural levels within the crust to a differentiated residual melt as a carrier for high-technology elements. In order to compare the different sources, melt contamination and fractionation processes, suchas assimilation and mingling, major and trace element analyses as well as boron isotopes on tourmalines are used. First field and geochemical evidences point to a strong influence of the syn-magmatic mafic mantle-derived melts.