Kansanshi Copper Mine, Zambia
The Kansanshi mine in Zambia is the eight largest copper mine in the world, with two open pits. The property is located nearly 10km north of the Solwezi town and 180km northwest of the Copperbelt town of Chingola.
The mine is 80% owned by First Quantum Minerals through its subsidiary Kansanshi Mining. The remaining 20% is held by a subsidiary of ZCCM Investment Holdings, a state-owned company in Zambia. The mine began production in April 2005.
A $370m expansion is underway to increase the production at the mine from 250,000t to 400,000t of copper by 2015.
The expansion will be carried out over two phases. The $40m Phase 1 program, slated for completion by the end of 2011, has been designed to increase production to 285,000t.
It will involve capacity enhancement of the oxide circuit by 20% to 8.5 million tons (mt). It will also result in a flexible operation that allows easy switch between mixed and sulphide circuits to suit the mining operations.
The second phase of expansion, scheduled to begin in the second half of 2012, will include construction of a new 25mtpa concentrator. This phase has been budgeted at $350m.
The proven and probable reserves at the mine include 74.8mt of leached ore, 75.10mt of mixed float and 154.6mt of sulphide, graded at 2%, 1.04% and 0.81% copper respectively.
The measured and indicated resources have been estimated at 235.7mt. Resources in the inferred category are 77.8mt, graded at 1.17% total copper.
The deposit is hosted within a wide, northwest trending, closing anticline with a strike length of nearly 12km. The vein-type deposit is concentrated within a tectonised rock complex and has a major mineralisation control.
Geology and mineralisation
The deposit outlines a well mineralised, north-south striking zone. The zone is characterised by complicated faulting, abundant injection vein networks, development of brecciate units and down-dropped rock structures.
Vein-specific copper mineralisation that is either stratiform or concordant is hosted within and directly adjacent to mesoscopic veins, in thin bands and veinlets oriented parallel to rock bedding or foliation. It also occurs as disseminated mineralisation related with albite-carbonate alteration. The main veins and vein swarms plunge sub-vertically, perpendicular to the fold axis.
Mineralisation within the brecciate zones occurs within oxidised and supergene enriched layers. Secondary copper minerals are distributed in a complex manner across these layers. The primary copper sulphide mineralisation is chalcopyrite-dominated and is associated with trace amounts of bornite, minor pyrite and pyrrhotite.
The oxide mineralisation is largely dominated by chrysocolla. It also hosts malachite, limonite and cupriferous goethite. The mixed zone, a combination of both oxide and primary-style mineralisation, also hosts significant amounts of chalcocite, minor local copper and tenorite.
Mining and processing
Mining at the Main and NW open pits is done by conventional open pit methods involving hydraulic excavators and a mining fleet of haul trucks.
Processing of the three ore types, namely leached ore, mixed float and sulphide, is through either an oxide circuit or a sulphide and transitional ore mixed float circuit. Treatment of the sulphide ore involves crushing, milling and flotation to produce copper in concentrate.
A HPL circuit is used to convert the flotation concentrate to final cathode. The HPL circuit processes the copper concentrate in the autoclaves. The operation involves oxidation and leaching.
The circuit residue is treated through a gravity gold circuit that replaced the gold circuit in 2009. Contained gold was originally planned to be recovered into bullion through cyanide leaching and elution, but the gold circuit was not put into operation due to technical problems. In the gravity gold circuit, the efficient gravity concentration is combined with pyro-metallurgical of lower grade gravity concentrate.