The use of soil geochemistry in outlining phosphate deposits, northern and southern Venezuela

Abstract

Phosphate deposits have been outlined in Falcón State (Northern Venezuela) and Táchira State (Southwestern Venezuela) using geochemical soil methods. The phosphate deposits located in Falcón State constitute lenses and masses interbedded with Tertiary limestone and shales. The area is covered by a thick soil with few outerops and the region is characterized by typical tropical rain forest. Soil samples taken every 1000 m across complete stratigraphic sequences were analyzed for P 2O 5 content. An anomalous area with a P 2O 5 content ranging from 3.19% to 9.04% was outlined accompanied by areas with less than 0.83% of P 2O 5. More than 11 million metric tons of commercial phosphatic rock were associated with this anomaly. In Táchira State several stratigraphic sequences of potentially phosphatic rocks with a thick cover of black soil were geochemically investigated. Soil samples taken each 10 m were analyzed for P 2O 5. A sequence of phosphatic rock was outlined showing a P 2O 5 content varying between 7.3% and 9.2%. Apparently the sequence is interbedded with phosphate-poor siliceous rocks showing a P 2O 5 content below 2%. As result of this preliminary investigation, expensive trenching, pitting and drilling works can be carefully planned.