Los fosfatos en el Ordovícico del Norte Argentino

After four decades of the preliminary phosphates prospecting programm carried out by the Argentine Geological Survey, new prospections are started following lingula beds sequences in the north of Argentina. These Ordovician deposits show a temporal and a spatial distribution of phosphate-bioclastic accumulations linked to the paleogeographic basin evolution. In this paper we present, describe and discuss the results of systematic sampling and geochemical prospecting of discontinuous lenses from 10 to 60 cm thick of lingula-bearing coquinas outcropping in the Mojotoro Range. Six phosphogenic intervals with good biostratigraphic controls are detected in intercalated levels of Floresta Fm. (early to late Tremadocian shales), Áspero Fm. (late Tremadocian sandstones), San Bernardo Fm. (latest Tremadocian-Floian shales), Mojotoro Fm. (Dapingian-Darriwilian sandstones) and Santa Gertrudis Fm. (late Darriwilian-Sandbian shales). Because of the sixteen analyzed samples, two are classified as phosphorites (19% and 21% P2O5), seven as phosphate rock (8% - 18% P2O5) and seven slightly phosphatic rocks (<8% P2O5), and additionally,all samples exhibit significant enrichment Y, Sr, La, Yb, U, Pb, Zr and rare earth elements (REE), we suggest andencourage further exploration focusing on the eastern flank of the Eastern Ranges and the Subandean Ranges.