TEXTURAL AND MINERALOGICAL ANALYSIS OF PORPHYRITIC ANDESITES OF SABANA GRANDE, PUERTO RICO

This investigation focuses on two large igneous deposits in Sabana Grande. The purpose of this project is to study the nature of these deposits and to see if they are related with the previously studied Tea dikes in San Germán, P.R. as they are mapped. They have not been studied in any detail and are described only in general terms. The main hypotheses of this project are: 1) these larger bodies are plutons, sills or dikes parallel to the surface and 2) these deposits are related to the Tea dikes. Field studies were done to confirm the existence of these deposits and hand samples were collected to compare them with the Tea dikes. Textural and mineralogical analysis from hand samples and thin sections were made to determine the mineral abundances. It was confirmed that these deposits from Sabana Grande are of igneous origin; they are porphyritic andesites composed of plagioclase and hornblende. In addition, the two deposits from Sabana Grande are plutons that are very similar and they could be the same formation. However, the Tea dikes and the deposits of Sabana Grande are different in texture and mineralogical composition meaning that they are not probably related.