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GEOLOGY, MINERALIZATION, ALTERATION, AND STRUCTURAL EVOLUTION OF THE EL TENIENTE PORPHYRY Cu-Mo DEPOSIT—A DISCUSSION

M. Alexandra Skewes and Charles R. Stern

Department of Geological Sciences, University of Colorado, Boulder, Colorado 80309

Corresponding author: e-mail, Skewes@colorado.edu

The first 20% of the full text of this article appears below.

Sir: In their paper concerning the geology, mineralization, alteration, and structural evolution of the El Teniente Cu-Mo deposit in Chile, Cannell et al. (2005) concluded that El Teniente, despite its anomalously large size, is a typical porphyry Cu-Mo deposit with regard to its alteration and sulfide assemblage zonation and the genetic association of mineralization with dacite intrusions.

We do not agree that the dacite porphyries were the causative intrusions for copper mineralization. Instead, most of the mineralization was emplaced in conjunction with the formation of multiple hydrothermal breccia pipes and their associated veins that were derived from a large, deep magma chamber (Skewes et al., 2002, 2005; Stern and Skewes, 2005), and this deposit should be classified as a megabreccia rather than a porphyry deposit.

At El Teniente most Cu mineralization (80%) is intimately associated with biotitized mafic intrusive rocks (Camus, 1975; Cuadra, 1986; A. Arévalo, R. Floody, and A. Olivares, unpub. report for CODELCO-Chile, 1998, 76 p.). Cu mineralization occurs disseminated in the biotitized mafic rocks, in different generations of highly visible anhydrite and quartz veins, in less visible but abundant biotite veins, and also in the matrices of the multiple hydrothermal breccia complexes that occur in the deposit. A significant proportion of high-grade (>1%; Fig. 1) hypogene Cu mineralization at El Teniente was emplaced both within and in veins around these multiple hydrothermal breccia complexes in direct genetic association with their formation.

View larger version (69K):   FIG. 1. Copper grades between levels Teniente 4 and 5 in the El Teniente mine (Skewes et al., 2002, 2005). Copper grades surrounding the Teniente Dacite Porphyry dike north of the Braden pipe are enhanced by supergene enrichment (diagonally lined area) that penetrated below level Teniente 5 in this area of the mine. Grades in the central . . . [Full Text of this Article]

This article has been cited by other articles:

				C. R. Stern, C. R. Stern, J. A. Funk, M. A. Skewes, and A. Arevalo MAGMATIC ANHYDRITE IN PLUTONIC ROCKS AT THE EL TENIENTE Cu-Mo DEPOSIT, CHILE, AND THE ROLE OF SULFUR- AND COPPER-RICH MAGMAS IN ITS FORMATION Economic Geology, November 1, 2007; 102(7): 1335 - 1344. [Abstract] [Full Text] [PDF]

				J. Cannell, D. R. Cooke, J. L. Walshe, and H. Stein GEOLOGY, MINERALIZATION, ALTERATION AND STRUCTURAL EVOLUTION OF EL TENIENTE PORPHYRY Cu-Mo DEPOSIT--A REPLY Economic Geology, September 1, 2007; 102(6): 1171 - 1180. [Full Text] [PDF]