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 has fully paid all claim license fees and taxes both for concessions owned and otherwise under its control. 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.
The PV Mine utilizes conventional truck and shovel mining methods. Three alternative process options are utilized for copper recovery:
I. ROM heap leach;
II. Crushed ore heap leach; and
III. Crushing, grinding, and froth flotation.
Copper is produced as LME Grade A cathode from the SX/EW process and in concentrate from the flotation plant.
Ore is mined using conventional open pit methods, 24 hours per day, 365 days per year. Mining follows a traditional drill, blast, load haul dump sequence of mining. Ore and waste are hauled out of the pit. Currently waste is hauled to dumps located north and northeast of the current pit configuration. These dump areas will continue to be active for the foreseeable future. As areas within the pit footprint are depleted, waste material will be backhauled and placed within in-pit dumps. Ore material is hauled to selected areas depending on its grade and physical characteristics. Lower grade oxides and supergene material is hauled directly to the ROM leach area where it is stacked in 5m high lifts prior to irrigation. Higher grade oxides and supergene material is hauled to the primary crusher or stockpiled depending on daily grade and alteration constraints.
The PV Mine is located in Sonora, one of Mexico’s safest states with a long history of copper mining. Sonora also represents Mexico’s most important state in terms of mining production and in particular, copper production. Piedras Verdes is the third largest copper mine in Sonora and in Mexico. The PV Mine is located 20 km from the town of Álamos (population 9,000), and 50 km from the town of Navojoa (population 160,000).
Piedras Verdes is an elongated porphyry copper deposit that, based on exploration to date, is 5 km long in an east-west direction and over 1 km wide in a north-south direction. Mineralization is predominantly within Triassic-Jurassic metasedimentary units and various intrusives phases of the batholithic scale, granodiorite to quartz monzonite intrusives and an aphanitic, porphyrytic quartz feldspar porphyry. Supergene copper mineralization is present as azurite, neotocite, 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 northwest trending sinestral strike slip shear zones control the emplacement of the deposit. Younger north striking normal fault zones cut across the deposit and have had repeated movements. The latest displacements on some 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.
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 potassic altered rocks that have been overprinted 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.
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.