Santo Tomas

Sinaloa, Mexico

Main commodities: Cu
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The Santo Tomás porphyry copper deposit is developed within the western margin of the Sierra Madre Occidental in Sinaloa, western Mexico (#Location: 26° 43' 0"N, 108° 13' 59"W).

Mineralisation is associated with a Paleocene (60 Ma) quartz-monzonite (adamellite) porphyry sill intruding a larger, probably genetically related phaneritic pluton of granodioritic composition and lower Cretaceous lutite and limestone.

Mineralisation is associated with an alteration pattern comprising a core K-silicate assemblage of quartz, K-feldspar, biotite, pyrite, chalcopyrite and epidote, fringed by a propylitic zone with chlorite, epidote and pyrite, but lacking an intervening phyllic zone. Calc-silicate alteration within the adjacent limestone is also reported. Mineralisation is present both as a stockwork and as disseminations.

Supergene oxidation with goethite, malachite and chrysocolla is reported, with only minor supergene enrichment below. Exotic copper mineralisation is present as talus cemented by malachite, chrysocolla and 'wad'. The deposit is overlain by younger rhyolite tuffs and lavas and red fanglomerates (Sillitoe, 1976).

Published reserves include:
>80 Mt @ 0.55% Cu (Res., 1975, Sillitoe, 1976).

The most recent source geological information used to prepare this summary was dated: 1976.    
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd.   Unauthorised copying, reproduction, storage or dissemination prohibited.

Santo Tomas

  References & Additional Information
   Selected References:
Valencia-Moreno, M., Ochoa-Landin, L., Noguez-Alcantara, B., Ruiz, J., and Perez-Segura, E.,  2007 - Geological and metallogenetic characteristics of the porphyry copper deposits of Mexico and their situation in the world context: in Alaniz-Alvarez, S.A. and Nieto-Samaniego, A.F., (Eds.), 2007 Geology of Mexico: Cele brating the Centenary of the Geological Society of Mexico: Geological Society of America,   Special Paper 422, pp. 433-458.

Porter GeoConsultancy Pty Ltd (PorterGeo) provides access to this database at no charge.   It is largely based on scientific papers and reports in the public domain, and was current when the sources consulted were published.   While PorterGeo endeavour to ensure the information was accurate at the time of compilation and subsequent updating, PorterGeo, its employees and servants:   i). do not warrant, or make any representation regarding the use, or results of the use of the information contained herein as to its correctness, accuracy, currency, or otherwise; and   ii). expressly disclaim all liability or responsibility to any person using the information or conclusions contained herein.

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