Na-Fe-Ca Alteration and LREE (Th-Nb) Mineralization in Marble andGranitoids of Sierra de Sumampa, Santiago del Estero, Argentina

摘要: The Jasimampa area in the Sierra de Sumampa Santiago del Estero, Argentina, contains light rare earth element (LREE: Th-Nb) mineralization associated with several stages of carbonates and widespread fenitization of marble, granite (496 ± 2.9 Ma), alkaline siliceous igneous comendite dikes (U/Pb zircon age 390 Ma) derived from fractionation oceanic island basalts. This is third discovery LREE mineralization Argentina and marks a new intracontinental magmatic event Devonian age. Albite (Ab 97-99 ) + aegirine (Ae 70-92 Ja 1-11 Q 6-19 )± hematite Mg-arfvedsonite fluorine-rich apatite late Ca-Fe-Mn carbonates monazite pyrochlore overprint crosscut and comendite outcrops 15 km 2 area; locally, Na-rich assemblage is pervasive results total destruction host rocks. Na-Fe metasomatism near comendite produced 86-91 1-8 6-11 minor albite 98-99 adjacent marble, with multiple Ca-Mn-Mg-Fe associated iron and manganese oxides, hematite, traces sulfides (sphalerite, pyrite, galena). Monazite-(Ce) main LREE-bearing mineral occurs minor ferrocolumbite, pyrochlore, strontiopyrochlore, a second generation fine-grained barite, celestine. Structural controls on Na-Fe-Ca alteration granitoid marble protoliths include brittle-ductile shear zones, brittle fracture systems, a series monolithologic heterolithologic breccias hydrothermal aegirine, carbonate, chalcedony matrices that occur at granite-marble-comendite contacts. Fragments breccia types within indicate multiple episodes brecciation, alteration, mineralization. fluid responsible for early was aqueous-carbonic CO relatively high density (between 0.85 and 0.95 g/cm 3 ), salinity near 9 wt percent NaCl equiv, minimum temperatures range 250° to 280°C. Pervasively altered and granite have REE content (1,750 ppm 2,126 ppm, respectively), mainly LREE. Early banded mottled arfvedsonite replacements of marble absolute abundance (2,513–4,663 ppm) compared the least marble (476 ppm). Subsequent hydrothermal carbonates, hematite, pyrolusite, monazite, subordinate celestine barite caused alteration was accompanied by an increase REE abundance, up 15.45 percent, Sr (10.5 %), Th (4,390 ppm), and Ba (1.8 %). Alteration are result late-stage carbonatitic magma exsolution. indicated the strongly character composition the hydrothermal carbonates, apatite, LREE-Sr- Ba-rich minerals, the chondrite-normalized patterns showing strong enrichment without Eu anomaly, replacement assemblages very Ba, Th, LREE, Sr, K, Zr, Ti depletions. style and mineralization similar giant Fe-LREE-Nb deposit Bayan Obo other deposits hosted carbonatites China.