Geochemistry of K‐feldspar and Muscovite in Rare‐element Pegmatites and Granites from the Totoral Pegmatite Field, San Luis, Argentina

Abstract

The geochemistry of K-feldspar for K, P, Sr, Ba, Rb, Cs, Ga, and of muscovite for the same elements plus Nb and Ta, was used for proving the parental relationships of S-type granites and LCT (Li, Cs, Ta) rare-element pegmatites in the southernmost pegmatitic field of the Pampean pegmatite province in Argentina. The variation of K/Rb-Cs, K/Cs-Rb, K/Rb-Rb/Sr, K/Rb-Ba in K-feldspar from the granites and pegmatites show that they form an association with the evolutional sequence: granites → barren-to transitional pegmatites → beryl type, beryl-columbite-phosphate pegmatites → complex type of spodumene subtype pegmatites → albitespodumene type → albite type pegmatites. This sequence reflects the regional distribution of the different magmatic units. The Ta-Cs diagram for muscovite reveals that none of the studied pegmatites exceed the threshold established in previous studies for being considered with important tantalum oxide mineralization. The granites and pegmatites constitute a rare-element pegmatitic field in which different magmatic units form a continuous fractionation trend, extended from the less evolved granitic facies to the most geochemically specialized pegmatites

Mixing of magmatic-hydrothermal and metamorphic fluids and the origin of peribatholitic Sn vein-type deposits in Rwanda

“…Furthermore, it was observed that Ba in pegmatitic muscovite shows a positive correlation with the K/Rb-ratio (figures 6a). Crystallization of feldspars and micas has been reported to result in progressive depletion of Ba and Sr (Jolliff et al, 1992;Oyarzábal et al, 2009;Roda-Robles et al, 2012;Vieira et al, 2011).The Ba-data are thus likewise in accordance with an evolution that can be attributed to fractional crystallization. This is not the case for Sr, as a positive…”

“…K/Rb versus Cs in muscovite has been reported to be a reliable indicator of pegmatite evolution (e.g. Černý et al, 1985;Jolliff et al, 1992;Oyarzábal et al, 2009;Roda-Robles et al, 2012;Vieira et al, 2011). During fractional crystallization, bulk incompatible elements get enriched in the residual melt, while bulk compatible elements get depleted.…”

Morphology and mineral chemistry of monazite–zircon-bearing stream sediments of continental placer deposits (SE Germany): Ore guide and provenance marker

“…The surrounding gneisses pertain to the cordierite-sillimanite facies indicative of temperatures slightly higher (650°C) than the temperature determined for the pegmatite itself (500 to 600°C) (Holdaway and Lee, 1977). Examples from the pegmatite in northern Norway, from Malawi and the San Luis pegmatite province, NW Argentina, corroborate this idea of types III and IV zircon to be used as an ore guide to and within a pegmatite province (Dill, 2007;Oyarzábal et al, 2009;Pedersen et al, 1989;Roberts et al, 2006) (Fig. 9).…”

The anatomy of an albite-type granitic pegmatite from the Totoral pegmatite field, San Luis, Argentina

“…The plot of K/Rb vs. Cs for K-feldspars from Cerro La Torre granites and the intermediate zones of the pegmatites shows a linear fractionation trend (Fig. 2, Oyarzábal et al 2009). This, together with the known ages for the granites and pegmatites of the Totoral pegmatite field (centred at ~455 Ma, von Quadt and Galliski 2011), supports the interpretation that all of them are cogenetic (Galliski 2013 …”

“…Beryl-columbite-phosphate subtype pegmatites containing beusite-lithiophilite phosphate assemblages occur near the granite and pass eastwards to albite-type pegmatites very near to the transition from mica schist to phyllite (Oyarzábal et al 2009). The beryl-type pegmatites are disharmonically folded showing evidence of strong deformation.…”