The Cerro Matoso deposit is located to the south of Cordoba and north of Antioquia provinces, where three peridotite bodies are present in a north-south orientation, referred to as the Cerro Matoso nickel belt. The peridotites are associated with a Cretaceous ophiolite complex, located along the northern extension of the regional NNE–SSW-oriented Cauca-Romeral fault system. Tertiary age argillaceous sediments with local coal horizons surround the peridotites.

The peridotites are present in the following areas:
- Cerro Matoso mine area, comprising the current mine and possible extensions below sedimentary cover;
- Planeta Rica License area, located 40 km north of Cerro Matoso mine; and
- Uré License area, located 15 km south of Cerro Matoso mine.

The local geological setting of Cerro Matoso is characterised by a complex set of rock types that have been grouped into a number of major rock sets.

This geological basis for the rock type grouping is critical, as the local laterite profile is characterised not only by the evolutionary products of a typical tropical laterite weathering profile, but by several unique lithologies that also occur, including tachylite and very dark (black) saprolite units.

The resulting vertical layering is based on common physical and chemical features and from top to bottom consists of four zones – a sedimentary cover, a limonitic zone, a saprolitic zone and fresh peridotite bedrock.

The principal mineralisation types consist of Saprolite containing Serpentine and Ni-bearing Smectite as well as Ni bearing Goethite. The bulk of mineralisation at Cerro Matoso is found in the low MgO green Saprolite. Mineralisation is also present in high MgO green Saprolite, black Saprolite, brown Saprolite and Saprolitised Peridotite. Other lithologies have lesser amounts of mineralisation.

Mineralisation in the form of fracture filling garnierite (with locally very high Ni grades) is also present in veins in the lower lithologies of the profile such as in green Saprolite and Saprolitised Peridotite.

In the upper levels of the weathering profile the basement structures have not played a major part in the mineralisation controls with the sub horizontal weathering being dominant. Recent bench mapping has defined the rock types in the exposed faces and floors resulting in a detailed picture of the influence of the structures on the weathering and rock type. These structures are significant as they are capable of extending partially weathered Ni mineralisation up to 100 m or more below the current pit floor bedrock where present. The reduced influence of weathering and the increased influence of the structure on the rock type variability at the current pit floor is a major factor in the reconciliation issues experienced in recent years.

The Cerro Matoso nickel operation is a well-established open cut mining operation. Its business model is predominantly owner-operator. The Main Pit is broken into a number of pit areas. The trucks, loading units, blasthole drills, blasting units and ancillary equipment are owned by CMSA. Some of the maintenance operations, such as drill maintenance, are completed by specialty contracting services.

Cerro Matoso uses a traditional truck-and-shovel mining approach. The operation is a mix of selective and bulk mining areas in both ore and waste. The pit design is relatively shallow from ground level (~60 masl), (approximately 70 m to the base of Pit 6 (-7 masl); however, the original hill height was approximately 200 m above the surrounding surface level (260 masl) The mining operation is constrained by the Uré River which has a water level of approximately 44 masl.

Due to the lateral extent of the orebody and the trend of Ni grade lowering with depth, the Cerro Matoso pit has generally been mined in a “top-down” method – which is appropriate for this style of orebody. The mining method is traditional truck-and shovel utilising shovel, excavator and front end loaders (FELs) as required for both primary digging and stockpile rehandle. The excavator in backhoe configuration is the primary loading unit in ore, while shovels and FELs are used in bulkier materials or stockpile reclaim.

Mining activities include removal of any growth medium (topsoil), free-digging, drilling, blasting, loading, hauling and mining support activities. Approximately 10% of the material mined is classed as free-dig (not requiring blasting). Approximately 12% of the ore can be sent directly to the crusher. The remaining ore is sent to the ROM fingers or the off-specification stockpiles near the waste dump, and later rehandled to the crusher as required to achieve the required blend.

The mine is designed in 7 m benches, mined as two (nominal) 3.5 m flitches in selective ore and a 7 m bench in bulk ore and waste. There will be multiple ore faces available at any point in time to achieve a blended feed to the ROM pad, while minimising shovel/ excavator movements. If critical short term ex-face blending is required, the FELs are used as FELs are more mobile than the track-mounted equipment. CMSA has used a volume of 4 m (X) x 4 m (Y) x 3.5 m (Z) as the SMU. This SMU is aligned to the capacity of the CAT 777 dump truck.

Ore mined is blended with ore from stockpiles before it is passed through a two-stage crushing sequence. The two stages of crushing reduce the size from a nominal minus 600 mm to minus 50 mm.

Cerro Matoso is a major producer of nickel contained in ferronickel which is used to make stainless steel. Ore mined is blended with ore from stockpiles, which is then dried in rotary kilns and smelted in two electric arc furnaces where ferronickel is produced.

Description
After crushing, the ore is mixed and homogenised before it is partially dried in two rotary driers. An upgrading process is then undertaken whereby lower nickel grade is removed. After the upgrading process, the dried ore is then blended with a reductant agent (locally bought coal) and calcined in two rotary kilns.

Calcined ore is then transferred to two 75 MW electric furnaces where ferronickel is tapped at around 1,460° C. The crude metal is transported to the refinery where impurities are removed. The refined metal is granulated and packed.

Cerro Matoso has a water management system which allows it to recycle 95 per cent of the water used in operations. The remaining 5 per c ........