Geochemistry of the Villisman granite, associated aplite-pegmatites and surrounding Li-pegmatites, Sierra de Ancasti, Argentina

MARANGONE, S.; SARDI, F.; ALTENBERGER, UWE; GRIFFIN, K.; CISTERNA, C. E.; SCHLEICHER, A.

JOURNAL OF SOUTH AMERICAN EARTH SCIENCES

PERGAMON-ELSEVIER SCIENCE LTD

Año: 2020 vol. 103

0895-9811

The Villisman ´ pegmatite group belonging to the Ancasti district of the Pampean Pegmatite Province is geologically formed by banded schists of the Ancasti Formation which are intruded by the homonymous granitic stockand Li-pegmatites. It is located in the northern sector of the Sierra de Ancasti, Catamarca province, Argentina.The Villisman ´ stock -VG- is a small, sub-rounded in shape two-mica-syenogranite. The VG hosts felsic aplitic andpegmatitic dykes -FDVG- with muscovite, black-tourmaline (schorl) ± garnet as main accessory minerals. The Lipegmatites contain giant crystals of spodumene and are classified as of the Rare-Element class (REL) and REL-Lisubclass pegmatites and belong to the LCT (Li?Cs?Ta) pegmatite family. They are more or less symmetricallyzoned with outward zones composed of felsic aplite and coarse-grained to very coarse-grained granite -OZLiP-.The minerals of OZLiP are quartz, feldspars (secondary albite ?cleavelandite? predominant over K-feldspar),muscovite and scarce black-tourmaline (schorl), garnet and F-apatite. The VG, FDVG and OZLiP have high andsimilar SiO2 concentrations (72?78 wt %). They are peraluminous (ASIVG 1.10?1.16; ASIFDVG 1.23?1.77, ASIOZLiP1.00?1.14). The VG has subalkaline-calc alkaline character with K2O > Na2O. Ferromagnesian elements(included Ti) and CaO have low concentrations in VG and the FeOt/FeOt + MgO ratio is low (0.80?0.82) classifying it as magnesian granite. High Rb/Sr (FDVG ~16; OZLiP ~19) and Rb/Ba (FDVG ~41; OZLiP ~ 7) and lowK/Rb (FDVG ~107; OZLiP ~56) ratios clearly indicate that aplites and pegmatites are geochemically moreevolved than the Villisman ´ Granite (Rb/SrVG ~ 3; Rb/BaVG ~ 0.8; K/RbVG ~ 161). The Zr-saturation temperaturein the granites, as expected, is higher than in the dykes and the outward zones of the Li-pegmatites. The VG is apost-orogenic granite developed in the easternmost sector of the Ordovician Famatinian active arc. All geological, mineralogical and geochemical features of the VG are comparable to typical S-type granites, probablyoriginated from partial melting of the metasedimentary rocks of the Ancasti Formation. FDVG could have beenformed by fractional crystallization from the VG parental-magma.