Chinalco Mining Corporation International is focusing on developing the Toromocho Project through Minera Chinalco Peru S.A., a wholly-owned subsidiary of the Company in Peru.
CMC was delisted from the Hong Kong Stock Exchange on 15 March 2017.
Since 2017, CMC is a wholly-owned subsidiary of Aluminum Corporation of China Overseas Holdings Limited (“COH”).
Operator - Minera Chinalco Peru S.A.
Summary:
The Toromocho ore body lies within the central copper zone of the well-zoned Cu/Pb-Zn/Pb-Ag polymetallic Morococha district. The ore body forms the center of a skarn and breccia associated with 7 million year old mineralisation, alteration, and granodiorite and porphyry intrusions.
Geology of the Toromocho Deposit is complex and with a high degree of variability. Copper is in primary sulphide and skarn material. Skarn represents 50% of the material that contain copper mineralisation. High percentage of fluorine and MgO has been noted with skarn ores as alterations in form of talc, phlogopite and chlorites that are considered as problematic at the time of floatation in both reducing copper recovery and causing high concentration of MgO and fluorine in the concentrate that attracts undesirable heavy penalties.
The Toromocho ore body outcrops on the surface. The copper ore body extends downwards to a flat “bottom” 500 to 600 m below the surface. The highest grade part of the ore body lies within a 1.0 km × 2.0 km body of brecciated skarn, surrounding a cupola-like 7 million year old feldspar porphyry and granodiorite intrusive, and underlies on the west side, the older regional andesitic/dioritic intrusive exposed on the surface.
The primary ore body is over-printed by late-stage, pyritic primary mineralisation, clay and serpentine alteration, and supergene chalcocite and covellite enrichment. Spotty and structurally controlled, moderateto weak, chalcocite enrichment extends from the surface and from the top of dominant sulphides, downward to the bottom of enrichment, 200 to 400 m below the original topographic surface. A sulphate zone containing anhydrite disseminations and veinlets occur several hundred meters below the bottom of enrichment. A significant portion of the original leached capping above the enriched zone was probably stripped by Pleistocene glaciation. The upper half of the enriched zone in many places contains more than 50% leachable copper by sequential analyses. The lower half of the enrichment blanket above the bottom of enrichment and the top of the primary zone is generally only weakly enriched and contains from 15 to 50% leachable copper by sequential analysis.
In the Morococha District the major structure is Morococha anticline, an asymmetric fold with the axis of the anticline running at a strike of N20°W south of the district, and N40°W to the north of the district, plunging between 10 and 15° to the north. There are two secondary anticlines along the east and west flanks of the Morococha anticline, respectively.
At least two important reverse faults are noted parallel to the general strike of the sedimentary rocks. These faults are the west-dipping “Potosi” fault on the east flank of the north-west portion of the anticline; and the east-dipping “Gertrudis” fault on the west flank. The dip of the two reverse faults varies between 45 and 70° and is opposed.
A number of other faulting shears of interest including the Huachamachay and the San Gerardo Faults in the central eastern part of the ore district and the San Antonio 2 and 8 Vein faults.
There are several relatively small mineralised polymict and monomict hydrothermal breccias in the Pucará sediments. These breccias are generally located along reverse fault zones or along their projections, as well as along the disconformity between the limestone and the Catalina Volcanics, and along the contacts of the Morococha intrusives or Montero basalt.
The most abundant primary ore minerals in the deposit are chalcopyrite, tetrahedrite, enargite, sphalerite and galena and occur in three main forms.
- Veins: The strongest mineralised veins were emplaced along tension fractures. The shear faults, with abundant gangue were only weakly mineralised, making small ore shoots. Tension fractures and veins are well developed in the intrusive rocks. These are relatively continuous in length and depth, with generally uniform mineralisation. The veins in skarns and hornfels are less continuous and generally do not extend to depth. These are irregular in thickness and grade, and tend to form horse-tail structures along contacts with granodiorite and feldspar porphyry. The veins have been formed chiefly by fracture filling, but in skarn host rocks formed by both filling and irregular replacements of the skarn wall rocks.
- Mantos (massive sulphide) and Clustered Orebodies: In general, the mantos are irregular and both follow and cross-cut the stratification. The clustered orebodies are small, very irregular, and located chiefly along the hanging wall of major veins. These orebodies are the horizontal extensions of the veins along the stratification, with local irregular replacements of the adjacent wall rocks.
- Contact Orebodies: These orebodies are irregular and have been formed by replacement of the skarn. The mineralisation is mainly finely disseminated but also massive, and in coarse pods. The adjacent granodiorite and feldspar porphyry can also contain finely-disseminated mineralisation.