Sediment–Hosted Copper Deposits in Mexico

Sediment-Hosted Copper Deposits (SHCD) are known to occur in Mexico with the three most recognized localities in northern part of the country: Las Vigas and Samalayuca in Chihuahua and El Jabalí, in Cuatrociénegas area, Coahuila.

Las Vigas was the first SHCD recognized in Mexico in the 1970´s, initially with Inferred Resources of 200K tonnes of 3% Cu in the three first mantos. It is sited in northeastern Chihuahua and is hosted within a northwest-trending belt of Cu sandstone over 300 km in length, related to a marine transgression (Cuchillo Fm) over a red-bed sequence (Las Vigas Fm). At least ten discontinuous mantos or stratiform lenses are present in Las Vigas at different stratigraphic levels, varying from 1 to 4m in width, and exposed for a strike length of 1,700m. The orobodies are hosted in sandstones that are interbedded with shales and thin limestones. Cu mineralization consists mainly of Cu oxides, chalcocite, chalcopyrite, malachite and azurite.

The El Jabalí in Cuatrociénegas, sited in Central Coahuila, is also a SHCD with Cu-Ag mineralization associated with a redox front developed in the contact of a red-bed sequence (San Marcos Fm) and the overlying limestone (Cupido Fm).

Multiple occurrences of copper-silver bearing mantos are present at El Jabalí, varying in thickness from < 1m up to 20m in thickness, occurrences that can be followed discontinuously for at least a strike length of 50 km. These mantos are in many places partially covered by unconsolidated talus and have down-dip extension in some cases greater than 4km.

The copper mineralization consists of chrysocolla, malaquite, azurite, neotocite, chalcocite, tenorite, brocanthite, argentite, etc., with copper grades ranging from 0.5% to up to 15% Cu and silver from 20 g/t to > 500 g/t.

Other SHCD is Samalayuca, Chihuahua, located about 35 km south of Ciudad Juárez, where the sedimentary unit containing the Cu mineralization is composed of a cyclic sequence of fine-to coarse-grained chloritized sandstones with subordinate phyllitic and conglomerates intervals.

Copper grades at Samalayuca vary from 1 to 10% in 10 to 12m thick stratiform and homogeneous mantos hosted in three green sandstone beds. The copper minerals found there are digenite, chalcocite, covellite, bornite and chalcopyrite. Oxidized copper minerals such as chrysocolla, malachite and azurite are also present as coating and in fractures. Samalayuca contains Inferred Resources for 4.1 M tons of 0.47% Cu and 5.8 g/t Ag.

Northern Mexico and some other areas display favourable stratigraphy and structural settings to contain SHCD of interest.

The picture below shows the Cu-Ag bearing mantos of the El Granizo area in the El Jabalí Valley at Cuatro Ciénegas, Coahuila, Mexico, with average grades of 2.1% Cu and 38 g/t Ag across 8.75m.

cu estratiforme_el granizo_coah

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