PHOSPHATE MINERAL ASSOCIATIONS IN THE CEMA PEGMATITE (SAN lUIS PROVINCE, ARGENTINA): PARAGENESIS, CHEMISTRY AND SIGNIFICANCE IN THE PEGMATITE EVOLUTION

RODA-ROBLES, E., GALLISKI, M. A., ROQUET, M.B., HATERT, F., DE PARSEVAL, P.

Recife

Simposio; 4th International Symposium on Granitic Pegmatites-PEG2009BRAZIL; 2009

Universidad Federal de Pernambuco

Fe-Mn phosphates nodules are common in the border core unit of the Cemapegmatite (San Luis range, Argentina). Two different complex phosphates associationshave been distinguished in these nodules. One of them is lithiophilite-sicklerite-rich(LS), with varulite and hureaulite as the main secondary products, Fe/(Fe+Mn) valuesin the range 0.37-0.39, and MgO contents always below 1 wt%. The other associationis sicklerite-beusite-qingheiite-rich (SBQ), with varulite and joosteite as the mainreplacement products, higher Fe/(Fe+Mn) values, between 0.46-0.48, and also higherMgO values, up to 2.14 wt%. According to the mineralogical and chemical data, a highertemperature of crystallization is proposed for the SBQ association in relation to the LSone. On the other hand, the important Mn enrichment observed in these phosphates, in apegmatite that is not extremely fractionated, could be explained as a result of the previouscrystallization of other Fe-(Mg-Mn)-rich minerals, such as almandine and schorl, in theborder and externa" zones of this pegmatite. The crystallization of these silicates wouldhave strongly depleted the activity of Fe in the remaining pegmatite melt.