Na-Fe-Ca alteration and LREE (Th-Nb) mineralization in marble and granitoids of Sierra de Sumampa, Santiago del Estero, Argentina

The Jasimampa area in the Sierra de Sumampa de Santiago del Estero, Argentina, contains light REE (LREE: Th-Nb) mineralization associated with several stages of carbonates and widespread fenitization of marble, granite (496 + or - 2.9 Ma), and alkaline and siliceous igneous comendite dykes (U/Pb zircon age of 390 Ma) derived from fractionation of oceanic island basalts. This is the third discovery of LREE mineralization in Argentina and marks a new alkaline intracontinental magmatic event of Devonian age. Albite + aegirine + or - hematite + or - Mg-arfvedsonite + or - fluorine-rich apatite and late Ca-Fe-Mn carbonates + or - monazite + or - pyrochlore overprint and crosscut granite and comendite outcrops in a 15 km (super 2) area; locally, the Na-rich assemblage is pervasive and results in total destruction of host rocks. Na-Fe metasomatism near granite and comendite produced aegirine + or - Mg-arfvedsonite and minor albite in adjacent marble, with multiple stages of late Ca-Mn-Mg-Fe carbonates associated with iron and manganese oxides, hematite, and traces of sulphides (sphalerite, pyrite, galena). Monazite-(Ce) is the main LREE-bearing mineral and occurs with minor ferrocolumbite, pyrochlore, strontiopyrochlore, and apatite associated with a second generation of fine-grained hematite, baryte and celestine.