Rio Tinto Patino S. A. - Cerro Colorado Mine – Spain

The Rio Tinto - Cerro Colorado operation was the first major cyanide plant built out of South Africa since the Carlin and Corte mills came on-stream in 1965 and 1969. Its flowsheet was presented in the original monograph, "Gold and Silver Cyanidation Plant Practice, " published in 1975, with a brief description of the plant but without the operating costs. The authors have recently received these data and it was believed worthwhile to present them in this volume along with the aforementioned flowsheet. The Cerro Colorado ore deposit is located at Minas de Rio Tinto in the province of Huelva, Spain, approximately 88 km (55 miles) north- west of Seville. The previously mined copper ore bodies lie on either side of the deposit which is mainly copper ore. The crest of the deposit is a capping of "gossan" containing hematite, limonite, gold, and silver. Separate facilities for primary crushing, concentration of copper ores and cyanidation of gold-silver ores are provided. Fine crushing is common to both ores. The run-of-mine open-pit ore is fed from a stockpile via a surge bin and apron feeder to a jaw crusher. After crushing to minus 150 mm (6 in. ), the ore is washed in a rotary scrubber to remove the clay material ahead of fine crushing. Minus 6 mm (1/4 in. ) screen undersize is pumped directly to the grinding circuit with the screen oversize being crushed to minus 19 mm (3/4 in. ) for feed to the primary ball mill; this is followed by two subsequent stages of ball mill grinding to 80% minus 43 microns (325 mesh). Grinding is with water only; no cyanide is used. After thickening, lime is added to the first two of seven Pachuca tanks for conditioning ahead of cyanide addition in each of the five remaining Pachuca tanks. This flowsheet indicates rapid cyanide consumption and the need to maintain a high strength cyanide solution for silver extraction. Agitation for dissolution of the gold and silver is followed by standard CCD practice employing four 67 m (220 ft) washing thickeners in series, with repulping between each thickener. A departure from American and Canadian practice is the use of Stellar filters developed in South Africa for pregnant solution clarification and recovery of zinc-gold-silver precipitates. The precipitate is treated with acid for zinc removal, the sludge filtered in presses, dried, calcined and smelted to produce dore bullion of 900 fineness containing 12% gold and 78% silver.