Using Remote Sensing and GIS to Better Understand a Copper Porphyry Deposit (Peru)

English Abstract:

This study concerns a copper porphyry which was recently discovered in Central Peru. The overall copper reserves are unknown and cannot be estimated from field inspection alone. The primary objective is to develop new Remote Sensing (RS) and GIS techniques. The second objective is to use these new techniques, along with existing methods, to map and interpret mineral, lithological and structural features.

The two primary RS data types used are medium-resolution ASTER data and high resolution Worldview-2 (WV-2) data. ASTER is a multispectral sensor, which has a broadband coverage (14 bands). ASTER’s 14 bands are divided into three wavelength subsystems, with three bands in Visible and Near Infrared (VNIR), six in Short-Wave Infrared (SWIR) and five in the Thermal Infrared (TIR) portion of the Electro-magnetic spectrum. ASTER’s SWIR has sufficient spectral resolution to be used for lithological mapping and hydrothermal alteration mineral exploration associated with porphyry copper. WV-2 is a multispectral satellite with a high spatial resolution of 1.84m.

The study area is about 2x2km situated in a Cu-Mo porphyry belt in central Peru with a semi-arid climate and has considerable relief. The porphyry is approximately 50 million years old and the Pre-Andes orogeny, in which it is found, originated approximately 30 million years ago. The mineralized Cu-Mo porphyry system is dacitic in composition and intruded into the Cretaceous volcanics and the granodiorites of the Coastal Batholith. Most of the porphyry is phyllic altered and strongly leached with hematite/ferric capping and Cu-oxide occurrences.

Various RS-GIS techniques are used to aid in understanding the movement of copper in this deposit. These techniques include False Color Composites (FCC), band ratios, PCA for alteration minerals, and digital image classifiers for lithology. A Sobel edge fetection filter was implemented in MATlab for lineament mapping. A weighted omnidirectional shaded relief filter model was implemented in ArcGIS for structural mapping. ASTER and WV-2 are utilized in conjunction with SRTM DEM data. Results indicate ASTER is applicable to alteration minerals and lithology mapping, while WV-2 is effective in structural mapping.

Keywords: Copper Porphyry, Exploration Geology, Remote Sensing, GIS, ASTER, WorldView-2, Peru