Un Nuevo Prospecto de Tierras Raras Livianas en la Sierra de Sumampa (29°18´LS, 63°36´LO), Santiago Del Estero, Argentina,

FRANCHINI, M., LIRA, R., MEINERT, L., RÍOS, F., POKLEPOVIC, M., IMPICCINI , A. Y MILLONE, H.,

La Plata

Congreso; 16° Congreso Geológico Argentino; 2005

Comité Ejecutivo y Asociación Geológica Argentina

Abstract The Jasimampa area in the Sierra de Sumampa of  Santiago del Estero, Argentina, contains rare earth element (Th-Nb) mineralization associated with widespread fenitization of marble, granite (496 ± 2.9 Ma), and comendite dikes (U/Pb zircon age of 390 Ma). This is the third discovery of LREE mineralization in Argentina and marks a new alkaline intracontinental magmatic event of Devonian age. Albite (Ab97-99) + aegirine (Ae70-92Ja1-11Q6-19) ± hematite ± Mg-arfvedsonite ± fluorine-rich apatite with multiple stages of late Ca-Mn-Mg-Fe carbonates ± iron and manganese oxides, and LREE-bearing minerals overprint and cut granite, comendite, and marble outcrops in a 15 km2 area. Monazite (Ce>La) is the main LREE-bearing mineral and occurs mainly in altered marble with minor ferrocolumbite, pyrochlore, strontiopyrochlore, and apatite associated with a second generation of fine-grained hematite, barite, and celestine. Altered marble contains up to 15.45 wt percent REE, and high Sr (10.5 wt %), Th (4,390 ppm), and Ba (1.8 wt %). Alteration and mineralization at Jasimampa are the result of late-stage carbonatitic magma fractionation and fluid exsolution. This is indicated by the strong alkaline character of early alteration, the composition of the carbonates, apatite and LREE-Sr-Th- Nb and Ba-rich minerals, and the replacement of marble by assemblages with significant K, Zr, and Ti depletions.