Chaucha Mineral Property: Geology

Regional Geology

The Chaucha project area is located within the Western Cordillera (Cordillera Occidental) of western Ecuador, which principally comprises Cretaceous ocean floor basalts of the Pallatanga unit and associated sedimentary units, overlain by Tertiary (principally Eocene) intrusives of the Saraguro Group. The oldest rocks in the locale are Palaeozoic metasediments of the Chaucha terrane.

Local Geology

The project area is dominated by tonalite and quartz porphyry intrusions. The calcalkaline tonalites form the Chaucha batholith (of probable Tertiary-Miocene age) with apophyses found elsewhere in the project area. The quartz porphyries of the Tunas and Gur-Gur sectors are strongly associated with the hydrothermal mineralization of the property, and have a composition similar to the tonalite. The Saraguro volcanic formation of dacite and andesitic lavas is found in the eastern area of the property faulted against the Palaeozoic metamorphosed pelites. A number of occurrences of hydrothermal breccias are also to be found in the project area.

The project area shows the main north-south and northeast-southwest structures of the Andean trend as indicated by the Santa Martha fault to the west and the Ñag fault to the east. Conjugate faulting to the north is represented by the EW and NW-SE Angas and Jerez-Malacatos faults, and to the south by the Rio Pita fault. These faults appear to limit the porphyry intrusions and influence and control the distribution of mineralization and alteration. The various structures represent the dynamic tectonism present in the area during the different phases of development. Secondary tensional structures and NE-SW dilation structures, possibly generated by a dextral movement (strike slip) of the Santa Martha and Ñag faults, contribute to fracture development and act as channels for ascending hydrothermal fluids responsible for the copper-molybdenum mineralization.

Deposit Types

The project area is located in a zone of early-late Miocene subduction related magmatism. The results of past works completed in the project area show that the Chaucha projectarea contains elements of a copper-molybdenum porphyry system. The project area shows a high level intrusion of a tonalitic batholith and quartz porphyry bodies, with copper and molybdenum mineralization found alteration zoning. Gold is also reported related to epi-mesothermal mineralization associated with the porphyry system.

The Ecuadorian porphyry copper and molybdenum deposits are not considered "classical" as compared with those of the American Southwest, and are designated as 'plutonic' or 'volcanic', but with hypabyssal levels of emplacement. Chaucha is considered to be 'plutonic' in this respect.

In general, supergene enrichment within Ecuador tends to be limited due to low sulphide content and/or rapid erosion rates and lowering of the water table such that much of the copper remains fixed in the oxidation zone.

Mineralization

Copper-Molybdenum Mineralization

Copper and molybdenum mineralization is present in quartz veins, quartz vein stockworks and as disseminations related to the phyllic – potassic hydrothermal alteration of quartz porphyry and tonalite intrusions across the property. Copper and molybdenum mineralization is also associated with hydrothermal breccias that developed as part of the intrusive system.

Based on previous exploration work, the project area is sub-divided into six principal zones or sectors of mineralization, as follows: Naranjos, Pita Medio, Gur-Gur/Rio Lanto, Loma de Tunas, Malacatos, and San Gabriel.

At surface the mineralized zones, currently thought to represent the supergene enrichment zone, lie in altered tonalite and in the porphyry. This last is exposed on surface, in drill core, and is inferred to exist extensively below the tonalite. From field evidence in the Naranjos, Rio Lanto and Gur-Gur sectors and examination of drill core from the Naranjos sector, several phases of hydrothermal alteration, typical of a porphyry system, are developed within the tonalite and quartz porphyry. These include:

A core zone of potassic alteration, as observed in drill core, shown by the development of biotite and occasional potash feldspar. This may be overprinted by later phyllic alteration.

Phyllic alteration takes the form of sericitic alteration of feldspar plus development of pyrite, often altered to ‘limonite’ and goethite. Chlorite may be present.

Furthest from the potassic core of the alteration (not shown in the schematic section) a propylitic zone is evidenced by epidote and chloritic alteration.

Silicification is present as moderate to intense amounts of cryptocrystalline silica that occurs in the groundmass of both the tonalite and quartz porphyry, seemingly increasing near shear zones. Calcite is present as a late stage veinlet fill, and argillic alteration is represented by kaolinisation as seen in outcrop and near surface drill core.

The distribution and symmetry of the zones is related to the principal tectonic structures. Primary sulphide mineralization is dominated by chalcopyrite and pyrite, with occasional bornite. Molybdenite may accompany the chalcopyrite in later veins. The sulphides are found in quartz veins and veinlets, in quartz vein stockworks, as fracture coatings, or seemingly disseminated within the host porphyry or tonalite.

The sulphide mineralization is dominantly associated with the potassic and phyllic alteration zones, but may also be observed in quartz veining within the propylitic zone. Stockworks were not extensively developed in the drill core or outcrop exposures observed on the property, but are reported elsewhere, particularly in the underground adits developed in the Naranjos sector. Hydrothermal breccia zones are also reported within the project area, particularly in a 1 km wide belt running parallel to the Nãg fault zone. These breccias are not thought to represent zones of major mineralization, but show enhanced copper values when compared with the alteration zone mineralization. The observed secondary mineralization consisted mostly of copper oxides, although chalcocite and covellite are reported.

Naranjos Sector

The Naranjos sector lies in the north central part of the property, to the north of the Tunas Porphyry. The mineralized zone, thought to represent the supergene enrichment zone, trends northeast-southwest, parallel to the principal regional structures. The approximate dimensions of the zone as defined by diamond drilling are 1100 m by 350 m, with an average thickness of 70 m. Thicknesses range from 9 to 170 m, thickening towards the north. The zone is developed within a larger geochemical copper-molybdenum soil anomaly, also aligned parallel to the principal regional structures. The mineralized zone is apparently structurally controlled, being limited to the north by the Rio Angas fault, to the west by the Jerez-Malacatos fault, and to the south by the Tunas fault. To the east the mineralized zone abuts the metamorphic unit. Density of fracturing increases towards the northern limit of the zone and is associated with the increased concentration of mineralization in this area. It is thought that primary mineralization zones have not been exposed by the historical exploration work.

Pita Medio Sector

The Pita Medio sector is located in the south west of the property, to the south of the exposed Tunas Porphyry intrusion. The mineralized zone occupies an area of approximately 45 ha. Diamond drilling defines three areas of mineralization as being developed within this zone totalling approximately 18.7 ha. Whilst the copper-molybdenum soil anomaly occurs in tonalite, these mineralized areas are probably associated with fingers of the local porphyry intrusion, with one of the zones also associated with the B5 breccia body. The mineralization is again thought to represent the supergene enrichment zone and trends approximately east-northeast to west-southwest. The mineralization lies in an area of overlapping copper and molybdenum soil anomalies that lie parallel to the principal regional structures.

The approximate dimensions of the three areas are 330 m by 200 m, 300 m by 200 m, and 400 m by 300m. Thickness varies between 28 m and 45 m, averaging 38 m. Structural controls of this zone are less clear, although the general orientation conforms to the regional northeast-southwest and east-northeast-west-southwest trends. From the lack of development of phyllic alteration, and the presence of potassic alteration, it is thought that this zone is developed at a high level in the intrusive system, with a density of fracturing suggesting that a favourable environment for enrichment was not well developed in this area.