Summary:
Canariaco Project covers a north-easterly 4–5 km long structural trend that hosts three porphyry centres, Cañariaco Norte, Cañariaco Sur and Quebrada Verde, as delineated by geophysics, geochemistry and geological mapping and drilling. The Cañariaco Norte and Cañariaco Sur deposits are considered to be porphyry-copper systems.
In each of these centres various intrusive bodies have been mapped. The host rocks to the mineralized intrusions are Calipuy Group andesite volcanic rocks.
Large, coincident magnetic highs, IP/resistivity lows, and chargeability highs are identified coincident with stream sediment and soil geochemical anomalies and areas of altered rocks that are typical of porphyry deposits.
Cañariaco Norte
The Cañariaco Norte deposit is hosted within a multiphase intrusive–breccia complex approximately 1.7 km in strike extent and 1.1 km wide. The deposit has been drill-tested to a depth of approximately 770 m and remains open at depth. The majority of the copper–gold mineralization is hosted within the intrusive and breccia units, but locally extends for variable distances into the enclosing volcanic units. Intrusive units comprise approximately 55 to 60% of the deposit, breccias approximately 30 to 35%, and pre-mineral volcanic rocks approximately 5 to 10%.
The intrusive units are nested and collectively oval in shape, with older intrusive rocks being cut by successively younger intrusive bodies. In general, the intrusive units are north–south-trending, steeply-dipping bodies. The breccia units cut the intrusive units, are oval to circular in shape, and are steeply plunging. The dykes generally strike northwest– southeast with a steep southwesterly dip.
Mineralization occurs primarily as sulfide disseminations and in fractures, sulfide and quartz veins, faults, and breccias. Fracture density is the single most important factor influencing copper grades and alteration intensity, although breccias and faults can locally be important.
Copper mineralization was introduced as a series of events closely following the emplacement of each of the intrusive units and the polymictic breccia unit. Initially, copper mineralization comprised chalcopyrite and minor bornite, introduced following emplacement of each of the crowded quartz–feldspar porphyry and biotite–feldspar porphyry units, with the greatest amount introduced following emplacement of the biotite–feldspar porphyry unit.
Near surface, the deposit has been intensely weathered, resulting in the formation of a leached cap that contains less than 0.05% Cu, trace pyrite and tenorite, and variable concentrations of limonite, goethite, jarosite, and hematite. The leached cap varies significantly in thickness, ranging from less than a metre to as much as 120 m, averaging approximately 40 to 50 m in thickness. The water table is at, or near, surface.
Cañariaco Sur
The Cañariaco Sur deposit is centred approximately 2 km southwest of Cañariaco Norte and is at an earlier stage of exploration than Cañariaco Norte.
Cañariaco Sur lacks the later stage brecciation event that introduced arsenic into Cañariaco Norte and does not have the other breccias that complicated the copper grade controls at Cañariaco Norte. Cañariaco Sur also has a higher gold content than Cañariaco Norte. A large, coincident magnetic high, IP/resistivity low, and chargeability high was identified coincident with the soil geochemical anomaly and area of potassic alteration. Alta Copper has interpreted the prospect as a porphyry-copper-gold centre dominated by potassic alteration with chalcopyrite–bornite–molybdenite mineralization and anomalous copper–gold–molybdenum grades.
The deposit has a potassic core surrounded by phyllic, silicic and propylitic alteration with a coincident copper–gold– molybdenum soil geochemical anomaly outcropping over 1,400 m x 900 m. The host rocks to the mineralized intrusions are the same as with Norte. Andesite to dacite tuffs and flows belonging to the Calipuy Group volcanic rocks were intruded by an intrusive complex which has similar but less intrusive events than those hosting Cañariaco Norte. Only four intrusive events have been identified which include the CQFP intruded by BFP and followed by CQP then minor amounts of the IBXP breccia. Cañariaco Sur also lacks the later stage brecciation event that introduced arsenic into Cañariaco Norte and does not have the other breccias that complicated the copper grade controls at Cañariaco Norte. Overall drilling to date indicates that the Cañariaco Sur deposit has a lower copper grade, a higher gold content and lower arsenic content than Cañariaco Norte.
Mineralization at Cañariaco Sur is predominantly chalcopyrite and bornite with minor pyrite. The depth of oxidation averages 40 to 50 m and contains copper oxides in the form of copper wads.
Quebrada Verde Prospect
The Quebrada Verde prospect is 3.2 km south of Cañariaco Norte and 1.5 km south of Cañariaco Sur. Strongly anomalous levels of copper and gold in soil samples cover an area of 0.7 km x 0.9 km. A large IP chargeability high centred on a resistivity anomaly and magnetic high, and covering an area of 0.8 x 2.0 km, occurs coincident with the soil geochemical anomalies. Alta Copper staff have interpreted the prospect as a porphyry copper–gold centre. The one historic drill hole did not test the geochemical/geophysical target.
Quebrada Verde host rocks known to date are predominated by a diorite porphyry (BFP) intruding Calipuy Group andesite volcanic rocks. The BFP is exposed on surface in two areas, the largest extending over an area of 1 km x 750 m and a second over 400 m x 400 m approximately 200 m northeast of the larger exposure. In addition, an east–west striking, post-mineralization granodiorite dyke, with dimensions of approximately 1 km x 100 m, intruded the volcanic rocks and the larger BFP diorite porphyry stock.