Geochemical of exploration in carbonatic and felsic xenoliths associated to

pegmatites (~26є56’S/70є37’W), to the NW of Sierra El Roble, Cordillera

de la Costa, Atacama region, Chile.

DIEGO ALONSO VENEGAS SALGADO

UNIVERSITY OF ATACAMA, CHILE

 

The studied zone is located in Atacama, Third Region, Chile at 38 km to the Caldera Northeastern, by Route 5 North, in Compaснa Minera Estanco S.A. Geology of the western continental margin of Atacama region, mainly in Cordillera de la Costa, is predominated by Devonian-Carboniferous rocks, being metamorphosed in low grade conditions in an accretionary prism and intruded by granitoids of late Permic-Triassic to Jurassic. The activation of the subduction in the early Jurassic caused the emplacement of intrusive bodies, which are defined as variety of tonalites, diorites, granites, and gabbros. Particularly, intrusive bodies of ages from middle Jurassic to lower Cretaceous of the studied zone, are classified as calc-alcaline granitoids I-type, metaluminous, and with initial reasons 87Sr/88Sr 0,07041-0,7059, presenting a great compositional variability. Pluton Sierra El Roble (Jmtd), is an intrusive body with variable composition, which includes melanocratic diorites, amphibole monzodiorites, quartziferous diorites, and tonalites of hornblende and biotite. Quartziferous diorites with phaneritic texture, crystals from subhedral to anhedral, holocrystalline. Tonalitic varieties of hornblende and medium to coarse grain biotite, inequigranular texture, microcrystalline, crystals from subhedral to anhedral, holocrystalline, and poikilitic texture. There are two xenoliths in Pluton Sierra El Roble (Jmtd), one of carbonatic composition and the other of felsic composition associated to post-magmatic processes, Pegmatitic- Neumatolitic stages, where crystals of biotite of approximately 20 cm are identified. According to geochemical of exploration, using a portable analyzer FRX, Bruker S1 TITAN, important concentrations in both xenoliths are recognized, from rare earth elements (REEs), mainly yttrium, lanthanum, and cerium.