Skarn mineralization, both as endoskarn and exoskarn, occurs widespread in the Mexican Altiplano. It is characterized by variable mixtures of calc-silicates formed during contact metamorphism and metasomatism between intrusive bodies and carbonate-rich sedimentary rocks. Polymetallic skarn deposits of prograde or retrograde alteration are hosted in Mesozoic sedimentary sequences following the emplacement of Tertiary intrusive rocks. Disseminated, fracture-controlled, chimneys and mantos are the most common morphologies of the skarn mineralization, with peripheral epithermal veins not uncommon.
Currently eight skarn deposits in the Altiplano have published reserves and resources (all inclusive) for over 2M Oz Au, 280M Oz Ag, 2.0B Lb Cu, 1.2B Lb Pb, and 5.1B Lb Zn.
La Paz Mine owned by Negociacion Minera Santa Maria de la Paz y Anexas has the largest gold resources with over 1.4M Oz Au, 48M Oz Ag, and 757M Lb Cu at grades of 1.56 g/t Au, 52 g/t Ag, and 1.2% Cu, while First Majestic´s La Parrilla has the largest silver resource with over 108.5M Oz Ag, 2,176 oz Au, 469M Lb Pb, and 630M Lb Zn at grades of 211 g/t Ag, 0.02 g/t Au, 1.33% Pb, and 1.79% Zn; and Terrazas of War Eagle Mining has the largest copper resource with over 2.3B Lb Cu and 477M Lb Zn at grades of 0.24% Cu and 1.13% Zn. Other significant deposits are First Majestic´s La Joya with over 524K Oz Au, 78.7M Oz Ag, and 437M Lb Cu at grades of 0.23 g/t Au, 69.80 g/t Ag, and 0.28% Cu, and Sabinas of Peñoles with over 44.6M Oz Ag, 101M Lb Cu, 259.5M Lb Pb, and 447M Lb Zn at grades of 106.1 g/t Ag, 0.35% Cu, 0.90% Pb, and 1.55% Zn.
Charcas and San Martin are a special case regarding resources, as the only source we could get our hands on was the Grupo Mexico’s annual report, and their IMMSA division only states consolidated figures for the resources of all its mining units. Therefore the total resource was divided by the number of mining units to obtain an estimate of the resource.
The table below shows tonnages, grades, as well as gold, silver, copper, lead, and zinc resources (all inclusive) for each of these deposits.