The Constancia open-pit copper- molybdenum mine is located in the Chumbivilcas Province of Peru. Image courtesy of Craig Dietrich.
The concentrator at the Constancia processing facility has a throughput capacity of 90ktpd with a 94% physical availability. Image courtesy of Ausenco.
Constancia is one of the lowest cost open-pit sulphide copper mines in South America. Image courtesy of Jonathan Zander.

Constancia is an open-pit copper-molybdenum mine by Canadian mining company Hubay Minerals in the Chumbivilcas Province of Peru. It is one of the lowest cost open-pit sulphide copper mines in South America.

The exploration activities date back to the 1980’s with the exploration activities conducted by Mitsui at the San José Prospect which is now part of the Constancia mine. Rio Tinto subsequently commenced exploration activities in December 2003 and entered into a partnership with Norsemont in early 2005, while Hudbay became the 100% owner of the Constancia project by acquiring all the outstanding shares of Norsemont in March 2011.

Hudbay completed the construction of the Constancia mine in 2014 and commenced commercial operations in April 2015.The mine produced 113,825 tonnes (t) of copper in 2019 and its operational life is expected to extend until 2036.

Project location and geology

The Constancia copper mine is located in the south-eastern Andes, in the Chumbivilcas province of Peru, approximately 600km southeast of the capital city of Lima and approximately 80km north-west of Yaur. The project encompasses a total of sixty-six concessions covering approximately 43,536ha.

The Constancia deposit is a porphyry copper-molybdenum system with copper-bearing skarn mineralisation dominated by a sequence of sandstones, mudstones, and micritic limestone of the Cretaceous age intruded by multiple phases of monzonites and monzonite porphyry.

The Pampacancha deposit occurs as a porphyry Cu-Mo-Au related Skarn system with an Oligocene unmineralised basement diorite intruded by the diorite porphyry.

Mineralisation and reserves

The mineralisation at the Constancia deposit is divided into five distinct mineral associations. The first is a hypogene, porphyry-style mineralisation associated with disseminated, quartz-vein stockwork, and fracture-controlled chalcopyrite-molybdenite mineralisation.

The second mineralisation type is associated with Hypogene chalcopyrite, rare bornite, galena and sphalerite in skarns, while the third type is associated with Supergene digenite-covellite-chalcocite mainly hosted by intrusive rocks lying below the leach cap.

The fourth type is characterised as the transitional mineralisation associated with secondary copper sulphides/chalcopyrite in the monzonite, while the fifth mineralisation style occurs as oxide copper in the forms of cuprite and tenorite.

The Constancia deposit was estimated to hold 486.3 million tonnes (Mt) of proven and probable reserves grading 0.28% copper and 83g/t molybdenum as of January 2020. The proven and probable reserves at Pampacancha were estimated to be  39.9Mt grading 0.60% copper and 177g/t molybdenum.

Mining methods

The open-pit mining method involving drill and blast operations are employed at the Constancia mine. The mining fleet comprises two 27m3 Hitachi EX5600-6 shovels and a 19m3 CAT 994H loader to excavate the blasted materials. The ore and waste materials are handled by 240t CAT 793F haul trucks.

Mining operations are currently being carried out at the Constancia pit with an average daily mill feed of 86,000t.

The ultimate pit design at Constancia will measure approximately 1.8 km east to west, 1.6 km north to south with a maximum depth of approximately 660m. The Pampacancha satellite pit will measure approximately 0.6km east to west and 1km north to south with a maximum depth of approximately 300m.

Mineral processing

The concentrator at the Constancia processing facility has a throughput capacity of 90ktpd with a 94% physical availability. The run-of-the-mine (ROM) ore undergoes crushing in a gyratory crusher to reduce the ore size to less than 125mm. The grinding circuit consists of two units, each equipped with a semi-autogenous grinding (SAG) mill and a ball mill operating in closed circuit.

The ground ore is fed into the copper flotation circuit to produce a copper/molybdenum concentrate which reports to a copper/molybdenum feed thickener to reduce the carryover of reagents from the copper flotation circuit into the molybdenum flotation circuit. The molybdenum flotation circuit recovers molybdenum into a molybdenum concentrate while rejecting the copper concentrate tailings.

The molybdenum concentrate is thickened to 60% solids and pumped to an agitated molybdenum surge tank. The slurry is then introduced into a pressure filter to produce  filter cake with 15% moisture which is further dried to produce a molybdenum concentrate with 5% moisture.

The copper concentrate tailings report to a copper concentrate thickener to produce a filter feed which is pumped to one of the two LAROX horizontal plate pressure filters to produce a filter cake which is then stored and made ready for transport to the Port of Matarani for shipment to customers.

Infrastructure facilities

The Constancia mine is accessible by air from Lima via Arequipa or Cusco from where  paved and gravel roads connect to the mine site. The primary road to the site is a 65km-long compacted dirt road from Coporaque.

The power supply requirement for the Constancia mine is supplied by the south national energy system via a 220kV transmission line from Tintaya to Constancia. The process water is sourced by recirculation from the tailings management facility while the fresh water is sourced through the dewatering wells at the mine site.

Contractors involved

Ausenco was engaged for the design, construction and commissioning of the process plant at Constancia.