Phosphate anomalies in the Nico Pérez terrane

geology's contribution to agronomy development

Abstract

The CONICYT 3014 project's objective is to achieve prospection criteria for phosphates in the Arroyo del Soldado Group (marine - continental platform sedimentary sequence ofVendian to Cambrian age after GAUCHER et al., 1996). In the basement rocks of this unit two phosphate anomalies were identified, mapped and studied. These anomalies are located into the medium-grade rocks of the Metamorphic Grenvillian Complex (CAMPAL y SCHIPILOV, 1999) and were subsequently transformed by intense and extensivc contact metamorphism that overprint mineralogica1 and textura! patterns.
Petrographic features of the apatite bearing rocks (up to 30% of calcium hydroxi-fluor-phosphate) are discussed, and two main prospection criteria are exposed. The first one is related to the spatial position in the sequence, between broad quartzites strata and impure limestones. Toe other tentative criteria implies the recognition of particular botanic associations which reflect the anomalous concentration of phosphate in soils developed over the mineralized rocks.