Geology of the Campana Mahuida porphyry copper prospect, Neuquén Province, Argentina

Abstract

A geological appraisal of the Campana Mdnfida prospect in Neuquén Province, Argentina has resulted in the recognition of features characteristic of typical porphyry copper deposits. A zonal pattern of hydrothermal alteration—mineralization is centred on a series of small bodies and dykes of andesite porphyry. A core zone of potassium silicate alteration is fringed by a zone of sericitic alteration which passes outwards to propylitic alteration. Hypoqene copper grades in excess of 0.1 % Cu (and reaching 0.3 — 0.4 % Cu) are restricted to potassium silicate alteration and to the immediately adjacent parts of the sericitic zone. Within this area of highest hypogene copper grades, a supergene enrichment zone has formed because of the availability of copper during oxidation: extremely low hypogene copper grades outside this central area have inhibited the enrichment process. The highest—grade enriched ore occurs close to the centre of the potassium silicate zone where hypogene copper grades are highest. Although the orebody outlined at Campana Mahuida appears to be currently uneconomic, both the supergene enrichment blanket (about 40 million tons of 0.5 % Cu} and a larger tonnage of lower - grade hypogene ore within the potassium silicate zone should be considered as future reserves. Should it be decided to mine either of these ore types at a future date, then additional drilling, to a much greater depth in the case of the hypogene zone, will have to be undertaken. It is recommended that a reconnaissance geological examination of the remainder of the area surrounding the Cerros Tree Puntas - Pedreqoso pluton be carried out in the near future, with a View to “locating additional zones of hydrothermal alteration in the Mesozoic sedimentary sequence.