Horacio Echeveste

Geoelectric Exploration of the Purísima-Rumicruz District, Jujuy Province, Argentina

Purisima-Rumicruz district consists of several polymetallic veins, rich in copper and lead. The veins have a breccia texture and are located in shear bands, with locally high concentrations of sulfides in a carbonatic gangue. The host rock of the veins consists of a black shale sequence with thin levels of fine sands, with a low degree of metamorphism, and corresponds to the Acoite formation (Lower Ordovician). The depositional environment was an open clastic platform where storm processes prevailed. An exploratory program using induced polarization and resistivity with the dipole-dipole method was carried out with the objective of establishing geoelectric anomalies in depth, which would permit the identification of exploratory targets. The group of veins was divided into three sectors: Purisima, El Brechon, and La Nueva. Low-resistivity values correspond to faulty zones, some of which are related to surface veins. The presence of diagenetic pyrite in the shales of Acoite formation considerably increases background chargeability (induced polarization) values. However, small chargeability anomalies associated to low-resistivity values represent exploratory targets for the Purisima-Rumicruz district.

Geology of the Manantial Espejo epithermal district, Deseado Massif, Patagonia Argentina

ABSTRACT The silver–gold epithermal mining district, Manantial Espejo, is located southwest of the Deseado Massif, Patagonia. The district is set into Jurassic volcaniclastic rocks of the Bahía Laura Group. A geological map of the district, at a scale of 1:50,000 drawn over a base map prepared from the fusion of satellite imagery and aerial photographs, is included. A suite of andesitic to rhyolitic eruptive units was identified, with prevailing high-grade rhyolitic ignimbrites. Travertine levels show the beginning of a hot-spring system in the region. Quartz veins, with typical crustiform–colloform banded structures, fill WNW, sub-vertical, normal faults, originating from extensional tectonics. The silicification of travertines, tuffs and breccia is the most common hydrothermal alteration.