Petrology of the lithologies, hydrothermal alterations and mineralizations of the Tineo Formation north of San Juan.

Abstract

The research was based on the collection of samples for subsequent analysis; the stages that made up the research project are described below. In the collection stage, a compilation was made of articles from scientific journals, books, theses, technical reports, web pages, among others, with the purpose of identifying all the geological knowledge about the study area, as well as understanding the petrological and petrographic characteristics of the upper unit of the Tireo Formation. After compiling all the information on the study area, detailed mapping at a scale of 1:5000 was carried out using topographic sheets (Juan de Herrera 5972-I, Pedro Corto 5972-IV, Lamedero 5973-II, and Arroyo Limón 5973-III). In this step, coordinates were taken with a GPS, structures (strike and dip) were measured with a Brunton compass, and two layers of tracing paper were used over the topographic map on which outcrops, structural features, alterations, and mineralization (where present) were drawn. All data obtained in the mapping were processed and interpreted using Geographic Information Systems (TrackMaker, MapInfo, and ArcGIS). After locating the study area, sampling was carried out during mapping of all lithological units outcropping at the surface. All rocks were considered, whether altered with mineralization or not, in-situ outcrops and boulders. Samples weighed approximately 3 to 5 kilograms. A description in a field notebook secured the data on the samples collected. Petrographically, the rocks of the Toribio and La Escandalosa projects are composed mainly of andesites with semi-porphyritic to porphyritic textures, rich in feldspar and amphibole phenocrysts. The felsic rocks (dacites-rhyolites) have a porphyritic texture, with plagioclase as the abundant phenocryst. The basic rocks have a seriate diabasic texture. Rocks of ultrabasic composition have a seriate granular texture. The minerals are altered, most notably olivine, which alters to serpentine and antigorite.

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