Geophysical prospection in tin mineral occurrence associated to greisen in granite São Sepé (RS)

Marly Aparecida Silva,Cesar Augusto Moreira,Lenon Melo Ilha,Karolliny Borssatto,Shaiely Fernandes Santos

doi:10.1590/0370-44672017710098

Abstract

Abstract The discovery of new mineral resources involves various research techniques through direct and indirect studies. The geophysical methods are important tools in the detection of deep deposits because they use the contrast between the physical properties of the hosting rocks and the mineralized zone. In this sense, electrical geophysical methods are widely used in the prospecting of sulfide deposits. This work presents and discusses the results of the application of the Induced Polarization geophysical method in the investigation of a tin mineral occurrence associated with greisen, located on the western border of Sao Sepe Granite. The study area is located in the central portion of the Rio Grande do Sul State, in the municipality of Sao Sepe (RS), housed in the metavolcano-sedimentary rocks of the Vacacai Metamorphic Complex. Six lines of electrical tomography were parallel arranged in the N30W direction. The 2D inversion models allowed to identify areas of high chargeability (above 5.0 mV/V), possibly attributed to areas with sulfide accumulation. The areas with low values (below 1.9 mV/V) area associated with soil and rocks absent of mineralization. Through the 3D visualization models, it was possible to identify that the mineralized zone apparently has continuity for more than 36 m. These models also allowed identifying the morphology and the lateral continuity of the sulfide zone. Thus, the results of this work demonstrate the possibility of using Induced Polarization in the research of cassiterite deposits with associated sulfides due to the contrast of physical properties obtained from the high polarizability of the sulfides.

Highlights

Mineral exploration is the first stage in the discovery of new mineral resources and the re-evaluation of mineral occurrences already known
The results presented in this work are based on indirect data and on genetic models of tin mineralization the greisen type in quartz veins
Two sets of quartz veins occur with directions N70E and N30W, related, respectively, to the expansion of the magma chamber and the final phases of intrusive crystallization

Summary

Introduction

Mineral exploration is the first stage in the discovery of new mineral resources and the re-evaluation of mineral occurrences already known. Remote sensing analysis and geochemical studies through the sampling of water, soil, rock and water flow sediment are the most commonly used direct methods in mineral exploration These investigative techniques are limited to outcropping deposits and are little effective in identifying these deposits hosted at great depths (Licht, 1998). The location of subsurface mineral deposits via geophysical methods can be direct; that is, when the response comes from the mineral good being prospected or indirect, when the deposit has insufficient amounts of the mineral sought In this case, the deposit can only be detected if the mineral good being searched is associated with other minerals with contrasting physical properties and with considerable volume or even with some geological structure (Dentith and Mudge, 2014). The probable mineralization occurs inserted in the metasedimentary rocks of the Vacacaí Metamorphic Complex, identified through geochemical studies of the sieving concentrate performed by the Mineral Resources Research Company (Companhia de Pesquisa de Recursos Minerais) (CPRM, 1995)

Area of studies

Materials and methods

Conclusions