Prospecting Deep Targets Potentially Mineralized with Copper South of the Seival Mines, Camaquã Basin, Southern Brazil

The Seival Mines comprise a group of open-pit copper mines that have been inactive for more than 60 years, located in the municipality of Caçapava do Sul, southern Brazil. In the region, volcanic, subvolcanic, and volcaniclastic rocks of the Hilário Formation crop out; this formation belongs to the Bom Jardim Group, a unit of the Camaquã Basin (450–620 Ma). The Seival area hosts hydrothermal copper sulfide deposits within volcanic rocks of shoshonitic affinity, emplaced in brittle zones controlled by structures with predominant N–NE and NW trends. Enrichment in Cu, Au, and Ag within andesitic dikes suggests that intrusions acted as important conduits for the hydrothermal processes responsible for metallogenesis. Despite Brazil’s high potential for the discovery of new mineral deposits, mineral exploration faces increasing challenges related to the growing scarcity of economically viable outcropping deposits. This context justifies the development of more detailed geological and geophysical studies, combined with the adoption of new strategies and subsurface investigation technologies. In this study, the Transient Electromagnetic (TEM) geophysical method was applied using the WALKTEM 2 system (ABEM). Surveys were carried out in a centre-loop configuration, with a 100 × 100 m transmitter loop and an RC-200 receiver antenna (10 × 10 m), operating in dual-moment mode. Three data profiles were acquired in the study area, totaling 14 electromagnetic soundings spaced at 250 m intervals. Data processing and inversion were performed using the SPIA and Workbench software packages. The resulting electrical resistivity sections reveal significant lateral and vertical variations, with resistivity values ranging approximately from 10 to 2000 Ω·m. In general, an upper unit is characterized by resistivity values exceeding 1000 Ω·m, associated with volcanic rocks of the Hilário Formation, whose thickness varies along the profiles. At depths of around 400 m, subhorizontal layers with resistivity values below 60 Ω·m and thicknesses of up to 200 m are observed. This horizon is possibly related to sandstones and conglomerates of the Maricá Group, the basal unit of the Camaquã Basin. The low-resistivity layer at this interface is a clear indication of the presence of conductive materials, which in the regional context are represented by sulfides hosted within a porous interface during the ascent of hydrothermal fluids responsible for the genesis of the Seival deposits. The identification of this potentially mineralized interface highlights the regional potential for deep copper deposits, based on a relatively rapid and versatile geophysical diagnosis.

Keywords: copper, mineral deposit, transient electromagnetics, resistivity