Phyllosilicate Variability In The Campana Mahuida Porphyry Cu Deposit, Neuquén, Argentina: Its Exploration Signifigance

MARTA FRANCHINI, AGNES IMPICCINI, ISIDORO B. SCHALAMUK, LAWRENCE MEINERT, AND GEORG GRATHOFF

La Plata

Congreso; 16° Congreso Geológico Argentino; 2005

Comité Ejecutivo y Asociación Geológica Argentina

Fine-grained phyllosilicate minerals are common alteration products in many ore systems such as porphyry copper deposits. However, conventional mapping and petrography during porphyry copper exploration typically does not distinguish fine-grained phyllosilicate minerals or define important compositional variations among them. Fine-grained phyllosilicate minerals are commonly mapped as "sericite" or reported in argillic or phyllic alteration assemblages without determination of the actual phyllosilicate mineralogy, thus missing valuable information that can be used in exploration. This is in spite of studies that have demonstrated the application of illite crystallinity to identify thermal anomalies in sedimentary rocks above hydrothermal Cu deposits (Duba and Williams-Jones, 1983) and the use of illite in metamorphosed phyllite as an indicator of underlying porphyry copper mineralization (Jin et al., 2002). The present study focuses on the identification of clay mineralogy and illite crystallinity in the Campana Mahuida porphyry Cu in order to better understand the fine-grained phyllosilicate alteration in porphyry Cu deposits and to build a general exploration model based upon the observed spatial and compositional variations of these fine-grained minerals.