NON-PEGMATITIC BERYL RELATED TO CARBONIFEROUS GRANITIC MAGMATISM,VELASCO RANGE, PAMPEAN PROVINCE, NW ARGENTINA

HEIMANN, A.; GROSSE, PABLO; SARDI, FERNANDO GUILLERMO.

ANDEAN GEOLOGY

SERVICIO NACIONAL GEOLOGIA MINERVA

Lugar: Santiago de Chile; Año: 2016 vol. 43 p. 86 - 104

0718-7092

The specialized leuco-monzogranite of the La Chinchilla Stock is a small Carboniferous stock located in the center of the Velasco Range, Pampean Province, La Rioja, Argentina. It is highly evolved and locally F- andBe-bearing, and has the potential for hosting U mineralization. Three different facies can be identified in the granitoid: border, porphyritic and equigranular facies. In all three facies the main minerals are quartz, microcline, plagioclase, biotite, and muscovite. Accessory minerals present in all facies include fluorite, zircon, and apatite. In addition, monazite, rutile, and uraninite occur as accessory minerals in the equigranular facies. Secondary minerals are muscovite, sericite, kaolinite, and opaque minerals. Secondary uranophane occurs in the equigranular and border facies. In localized areas,the equigranular facies contains small, green idiomorphic crystals of beryl (Be3Al2Si6O18) as accessory mineral. One of these beryl crystals was chemically analyzed for major and minor element contents using an electron microprobe andthis information, along with fractional crystallization models and comparison with compositions of non-pegmatitic beryl from the literature, were used to understand the degree of evolution of the granitic melt. The chemical formula of beryl from the La Chinchilla Stock can be written as: C(Na0.014-0.033, K0.001-0.002, Ca0.001-0.004) T(2)(Be2.978-2.987, Li0.016-0.022) O(Al1.889-1.967,Fe0.045-0.103, Mg0.001-0.007, Mn0.001-0.007) T(1)(Si5.994-6.040O18). The alkali contents are low (Na2O