Summary:
Tia Maria Project comprises La Tapada and Tia Maria deposits. The La Tapada and Tía María deposits are examples of porphyry copper deposits.
The La Tapada and Tía Maria deposits are within the northwest–southeast-trending Tambo–El Toro structural corridor that appears to be a large dextral shear zone. There are a number of vein-hosted copper–gold–hematite deposits also associated with the corridor, outside our mineral tenure package. Alteration within the project area is associated with the two porphyry systems currently outlined. The only known mineralization is derived from oxidation of low-grade porphyry copper systems.
La Tapada
Deposit Dimensions
The La Tapada deposit is approximately 1,250 m long, 800 m wide, and 630 m thick. Mineralization has been drill tested to a depth of about 630 m. The deposit remains open at depth.
Mineralization
Weathering resulted in three zones of oxidation and mineralization, a leached cap, an oxide zone, and a primary or hypogene zone (Figure 6-6). There is no significant supergene enrichment at La Tapada.
Leached Zone
Leached cap mineralization consists of iron oxides (limonite, goethite, jarosite, and hematite) in fractures. Goethite and specularite hematite predominate over jarosite in some sections of the deposit. This zone is typically barren of copper but locally contains gold grades similar to the grades in unweathered rocks.
Oxide Zone
The economic mineralization at La Tapada is oxide copper consisting of chrysocolla, brochantite, antlerite, and atacamite with minor amounts of malachite and cuprite. Peripheral to this mineralization are veins and veinlets with oxide copper associated with specularite. Molybdenite is infrequent and occurs in veinlets devoid of other sulfides or alteration haloes.
Supergene Zone
Secondary sulfides replacing primary sulfides are primarily chalcocite with minor covellite and digenite. Cuprite and native copper occur rarely. There is no significant supergene enriched zone.
Primary Zone
Mineralization occurs as weak disseminations of chalcopyrite in the host rock matrix and as veins and veins associated with silica, gypsum/anhydrite and to a lesser extent as specularite. At depth, copper mineralization consists of disseminated chalcopyrite and veinlets with a gypsum/anhydrite–chalcopyrite assemblage and chalcopyrite veinlets as thick as 1.5 cm The dominant mineralized veinlets chalcopyrite–gypsum/anhydrite, chalcopyrite, specular chalcopyrite, chalcopyrite–pyrite assemblages, and to a lesser extent, chalcopyrite–bornite veinlets. Magnetite occurs as disseminated grains, but also occurs as veins, occasionally with chalcopyrite.
Tía María
Deposit Dimensions
The Tía María deposit is approximately 1,750 m long, 300 m wide, and averages 300 m thick. Mineralization has been drill tested to a depth of 500 m. The deposit remains open at depth and along the northwest and southeast flanks; however, the open extents are mainly primary sulfide mineralization.
Mineralization
Mineralization of economic interest is primarily copper oxide minerals in the oxide zone. Weathering produced three zones—a leached cap, an oxide zone, and a primary or hypogene zone. There is no significant supergene enrichment at Tía María.
Vein Types A number of vein types are associated with local structures: Stockworks occur throughout the deposit. They are oriented in all directions and are predominantly “A” veins with minor “D” veins and rare “B” veins:
-“A” veins are the most common and occur in all rock types, consisting of quartz veins with no sulfides;
-“B” veins are uncommon, and found deep in the system. They consist of gray quartz with molybdenite;
-“D” veins are irregularly distributed, but most commonly occur near porphyry intrusive units, and comprise gray quartz with K-feldspar halos. Pyrite and chalcopyrite can occur in the halo or in the vein centers;
-Quartz veins composed of predominantly quartz with rare specularite, pyrite, chalcopyrite, and some gold. They are oriented northwest–southeast, and are 3– 50 cm thick.
Leached Zone
Mineralization consists of iron oxides that are common in all leached rock types but occur with the greatest intensity in the gneiss. The most common minerals are hematite, magnetite and specularite with subordinate goethite and jarosite. There are traces of pitch limonite. Within the intrusive rocks, the leached zone is very thin to non-existent. Common minerals include sparse disseminated and fracture-filling goethite and jarosite, traces of hematite and pitch limonite. Specularite occurs in veinlets, and as cavity and fracture fill. The veinlets can approach a weak stockwork.
Oxide Zone
The oxide mineral assemblage is mainly chrysocolla with minor neotocite and malachite at depth. Gneiss is the dominant oxide host. Copper oxides are more common in zones of greater fracturing and along the gneiss–intrusive contact. Specularite in veinlets and as cavity fill is associated with this zone. Minor amounts of hematite and magnetite occur. Quartz veins with gold and copper values occur within this zone. These veins cut through part of the deposit and host minor amounts of green copper oxides restricted to their (very local) environment.
Primary Zone
The hypogene zone includes disseminations and veinlets of pyrite and chalcopyrite with quartz. Traces of molybdenite occur with higher concentrations of chalcopyrite. Some chalcocite developed at the top of the primary zone and is evidence of an incipient enrichment process; however, there is no significant supergene enrichment. Molybdenite occurs in areas of higher chalcopyrite concentration.