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Los Pilares, Nacozari

Sonora, Mexico

Main commodities: Cu
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The Los Pilares porphyry copper deposit is within the Sonora Basin and Range Province of the Nacozari District, Sonora State, in northern Mexico, 10 km to the west of the La Caridad deposit (#Location: 30° 20' 2"N, 109° 37' 58"W).

The surrounding country rocks include andesitic, dacitic and rhyolitic tuff, with granodiorite and quartz monzonite intrusions. The deposit is associated with a breccia pipe cutting early Tertiary (53 Ma) sub-aerial latite flow breccia and underlying andesite flow breccias and dolerite dykes. The pipe has a diameter of 650 m and is known to a depth of at least 750 m. The breccia is apparently a result of collapse, with an original 20% open space prior to mineralisation. Post ore andesite porphyry dykes cut the breccia pipe (Sillitoe, 1976).

Mineralisation is preferentially developed in the marginal parts of the breccia pipe, principally as breccia fill. K silicate alteration is not recorded, while phyllic alteration is represented by an assemblage of quartz, sericite, pyrite, chalcopyrite, specularite, calcite and scheelite, with lesser sphalerite and barite. A propylitic zone is also present with chlorite, epidote, calcite, specularite and pyrite. Silicification is also recorded.

The deposit was worked intermittently as an underground operation between 1909 and 1949, to produce 19 Mt @ 2.6% Cu, and had an associated 44 Mt @ 0.8% Cu reported in 1976. Supergene enrichment was recorded to a depth of 100 m, overlain by an oxidised zone which contains jarosite, goethite and hematite, with lesser malachite (Sillitoe, 1976). The USGS (Singer et al., 2008) quotes a resource of 147 Mt @ 1.04% Cu.

The most recent source geological information used to prepare this summary was dated: 2008.    
This description is a summary from published sources, the chief of which are listed below.
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Los Pilares

  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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