Mineralization & Geology
Cobre del Mayo controls a portfolio of 30 titled mining concessions encompassing an area of ~57k hectares, including one recently acquired titled concession covering ~52k hectares. CDM owns 25 of the 30 concessions, the other 5 concessions are owned by Grupo Rexgo, S.A. de C.V. (“GR”). CDM exploits the concessions it does not own pursuant to an agreement between CDM and GR executed in March 1997.”
Two types of hypogene alteration styles host copper mineralization in the Piedras Verdes copper porphyry deposit. Potassic alteration is the earliest copper-mineralizing event. This style of alteration is indicated by the presence of secondary biotite and potassium feldspar. Disseminated chalcopyrite and bornite constitute the most abundant copper minerals in this alteration type. Potassic alteration is hosted in the batholithic intrusive rocks, metasediments and quartz feldspar porphyry.
The second, cross cutting, copper bearing alteration event is defined by sericitic-illite-chalcocite alteration. This alteration type also cross cuts all earlier alteration styles including potassic alteration. Sericite-illite-chalcocite alteration ranges from incipient to intense, with the intense phases resulting in complete destruction of the host lithology. Chalcocite occurs as disseminations, coatings on fractures, and veinlets. In hand samples of potassicaly altered rocks that have been over printed by the sericite-illite-chalcocite mineralization, chalcocite is seen rimming existing sulfides such as chalcopyrite and pyrite.
Oxidation of hypogene and secondary sulphides generated supergene chalcocite, chrysocolla, neotocite/tenorite, limonite copper mineralization, cuprite, native copper and minor amounts of malachite, brochantite, libethenite, and azurite. The mineralization model generated for the resource estimate utilized three different mineralization categories, oxide, secondary and hypogene. The oxide category is modeled on the complete absence of copper sulfide minerals as logged in the core and reverse circulation drill holes. The secondary category is the occurrence both supergene and hypogene chalcocite, the hypogene mineralization category is indicated by the presence of chalcopyrite as the primary copper bearing mineral.
Where chalcocite is logged as an overprint on hypogene mineralization, this occurrence would be modeled as secondary.
Secondary copper mineralization at Piedras Verdes shows the effects of in-situ oxidation, as well as leaching and supergene enrichment. More than one episode of leaching is indicated. Following early episodes of oxidation and enrichment, there was considerable remobilization of copper, both vertically and laterally, along faults.
Mineralization is predominantly hosted within Triassic-Jurassic metasedimentary units and various intrusive phases ranging in composition from granodiorite to quartz monzonite and an aphanitic, porphyritic quartz feldspar porphyry. Supergene copper mineralization is present as azurite, neotocite, tenorite, chrysocolla, native copper, cuprite and chalcocite. Hypogene copper mineralization consists of chalcocite, chalcopyrite and bornite as the main copper minerals.
Major northwest trending dextral strike slip shear zones and northeast-trending sinistral strike slip shear zones controlled the emplacement of the intrusive rocks and the copper mineralization. Younger north striking normal fault zones cut across the deposit and have had repeated movements. The latest displacements on some of the faults occurred subsequent to supergene enrichment. A leached and oxidized cap demarcates the surface expression of the deposit with a characteristic reddish-brown color caused by iron oxides.