Copper and gold are not the only commodities being pursued by North American-based companies in Peru. Cominco Resources International (TSE), soon to be merged with its parent company Cominco (TSE), initiated an exploration program in the Pucara zinc belt in 1994.
The belt provides much of Peru’s zinc production and most of the concentrates for Cominco’s newly acquired Cajamarquilla zinc refinery, situated 22 km east of Lima and 37 km from the seaport of Callao. Cominco Resources provided details of its zinc exploration effort at the recent annual convention of the Prospectors and Developers Association of Canada in Toronto, where it displayed drill core from its Tarmatambo property. A diamond drill hole on this property intersected 9.2% zinc over 37.4 metres, including 19.41% zinc over 12.5 metres, about 100 metres below a showing with similar grades.
The company says results of subsequent drilling suggest a limited-size potential, “but are indicative of the excellent regional potential for making additional discoveries.”
The Pucara zinc belt is in central Peru, about 160 km east-northeast of Lima, in the Upper Triassic-Lower Jurassic Pucura basin.
Peru is the world’s fifth-largest producer of zinc (about 665,000 tonnes in 1993), and has three mines among the largest 25 producers.
Most of the major zinc-lead-silver deposits are hosted by the Upper Triassic-Lower Jurassic Pucara group carbonates. Examples of Mississippi Valley Type (MVT), sedimentary-hosted, skarn, vein, manto-chimney and breccia pipe mineralization occur here.
The largest deposit in the belt is the Cerro de Pasco mine of state-owned Centromin Peru, where production plus reserves exceed 80 million tonnes of 10% zinc, 3% lead and 100 grams silver per tonne.
The mineralization is considered to be skarn-type, though Cominco notes that this is debated by some workers.
The San Vicente mine, owned by Minera San Ignacio de Morrococna, is the largest of the MVT deposits and has produced about 20 million tonnes of 10% zinc and 0.7% lead since 1970. Its present reserves are about 4.5 million tonnes at 14.1% zinc and 1.2% lead.
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