LE3 .A278 2011

2011

Stanley, Cliff

Acadia University

Bachelor of Science

Honours

Geology

Earth & Environmental Sciences

Most porphyry copper deposits (PCD’s) in Chile have been found because they are/were exposed at the surface. The absence of vegetation in Chile has allowed the use of satellite imagery to successfully locate gossans associated with such deposits, and thus most exposed deposits have already been found. The remaining PCD’s are mostly covered by pediments and ignimbrites, making them difficult to discover. Over the past 15 years, exploration techniques have been developed to more easily locate these buried deposits; one of these techniques involves the use of partial digestion geochemistry. These partial digestions extract only the metals that are loosely bound to the surfaces of soil particles (metals most likely transported from below by circulating groundwaters), and thus produce anomalies with geochemical contrasts that are higher than those obtained using total digestions. In this research, the results of total digestion geochemical methods applied to fine-grained vertical trench profile samples collected from pediment over and adjacent to the Quetena PCD near Calama, Chile are presented. An aqua regia digestion (with ICP-MS finish) was used because it is virtually total for the chalcophile pathfinder elements associated with porphyry copper deposits (e.g., Cu, Pb, Zn). Results illustrate a distinct contamination zone at the surface for many elements, probably due to wind-blown dust from the nearby Chuquicamata PCD, mine, concentrator and smelter. This contamination generally swamps out any anomalies that might exist at the surface related to the underlying Quetena PCD. If contaminated samples (those from less than 50 cm depth) are removed from consideration, subtle geochemical anomalies in samples below 50 depth become evident. The use of lithgeochemical whole rock fusion and aqua regia digestions illustrate that gypsum is the primary mineral to have formed by evaporative saturation, along with minor amounts of calcite and natron. These minerals were formed by precipitation after their saturation in groundwater after they were brought to the surface by capillary action.

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https://scholar.acadiau.ca/islandora/object/theses:772