Colquijirca (Tajo Norte)

Tajo Norte is an open pit operation that exploits zinc-lead-silver ores in the District of Colquijirca, Province of Pasco, Region of Pasco. The mine forms part of the Colquijirca Production Unit, property of Sociedad Minera El Brocal (61.43% BVN), a subsidiary of Buenaventura.

Geology: The Colquijirca deposit (Tajo Norte) is structurally located within asymmetric synclines and anticlines, whose flanks are Principal-Mercedes-Chocayoc-La Llave-La Pampa; and stratigraphically located in the Calera Formation (Lower Tertiary-Eocene), middle and upper members. The base metal zone (Zn + Pb-Ag) is the outermost halo of mineralization (cordillera-type) and, by volume, the zone of greatest economic importance. Its mineralogy consists of sphalerite and galena as vein ores, which occur as fracture filling and cavities, disseminations, and massive replacements. The gangue consists of pyrite, specular hematite, magnetite, kaolin, barite, siderite, ankerite-dolomite, and fluorite, less commonly. All of them occur as fracture filling and cavities. Native silver as filigree in cavities, and in association with siderite, has been observed near the transition zone. It is also possible to observe the occurrence of chalcopyrite-galena-dickite as filling in fractures and replacement zones.

Mining: The drills make boreholes measuring 6.5 m deep and 6.74 m in diameter, in a 5 x 5 m grid. Once the terrain has been drilled, the explosives are placed, carrying out the blasting process to stir up the rock. An excavator allows for better selectivity of the ore to be transported to the concentrating plant, 8 km away, using dump trucks with a 35-MT payload. For loading, a power shovel with a bucket capacity of 10 m3 is used. The barren material is transported to the waste or waste ore deposit located 1.8 km away, using trucks with a 50-MT payload.

Metallurgy: The ore from Tajo Norte is treated at Plant 2, which uses the selective flotation process to achieve the concentration of the economic mineralization. It includes the crushing, washing, sorting, milling, conditioning, flotation, and filtering processes, as well as the respective tailings storage yards. Given the equipment characteristics and layout, the plant has the ability to beneficiate silver, lead, and zinc ores. It has direct access to a railway, which it uses to transport the concentrates to the port of El Callao.

Treatment capacity: The El Brocal processing plant, located in Huaraucaca, has a capacity of 20,000 TMD, which is shared by the Marcapunta and Tajo Norte mines.