Newmont opens heap-leaching JV in Uzbekistan

Standing atop the Muruntau pit in this former Soviet republic, the mind boggles at the immensity of the operation. Indeed, the excavation is on record as being the largest ever created for a mining operation, measuring 3 by 4 km in surface area and extending to a depth of 300 metres.

“You’ll definitely need a wide-angle lens for this one,” said Marcel DeGuire, vice-president of project development for Newmont Gold (NYSE), as The Northern Miner prepared to photograph the canyon-like vista.

Discovered in 1958, the mine did not open until 1967. It has been producing 1.8 million oz. gold per year ever since, and, to date, more than 200 million tonnes of non-mill-grade ore have accumulated beyond the far side of the pit.

It was this huge pile that caught the eye of senior Newmont geologist Joseph Kowalik when he arrived on a field trip in October, 1990. Kowalik was in Moscow for a conference and, after some difficulty, managed to recruit two other geologists to visit the mine — the first ever by Westerners.

Kowalik recounted the mine’s recent history at the grand opening of a joint venture aimed at heap-leaching the stockpiles. The partners include Newmont and Uzbek-based Zarafshan, the operator.

The opening, which featured speeches, ribbon-cutting and plenty of picture-taking, brought together almost 200 visitors, many of them bankers, analysts and journalists, from around the world.

Kowalik, whom Newmont recently made its regional manager of exploration in Peru, continued recounting the mine’s history for The Northern Miner: “Over many toasts of vodka, I told them (the Uzbek operators) that if they ever wanted to do something with the stockpiles, they should give us a call because Newmont has the technology to process low-grade ores.” Six months later, in April, 1991, the Uzbeks did just that. Negotiations followed quickly, and in February, 1992, a 50-50 deal was hammered out between Newmont and the newly independent Uzbek government. Newmont was required to import its heap-leach technology, developed over nearly 30 years at its mining operations in Carlin, Nev., in order to begin processing the stockpiles.

The Uzbek partners include the State Committee of Geology and Mineral Resources of Uzbekistan (25%) and the Navoi Mining and Metallurgical Combinat (25%), which together make up Zarafshan.

The stockpiles contain 60 million tonnes of low-grade ore at 1.59 grams gold per tonne, plus another 130 million tonnes of material grading 1.09 grams per tonne. Also included is an option on another 30 million tonnes, grading 1.09 grams per tonne, which brings the total to a staggering 220 million tonnes of rock, with grades and tonnes guaranteed by the Uzbek partners.

At a capital expenditure of US$225 million, the operation is expected to produce 5 million oz. gold over 17 years. Production for the remainder of 1995 should amount to 180,000 oz., reaching a peak of 450,000 oz. annually for the first few years, and about 250,000 oz. annually thereafter.

Operating costs are estimated at US$150 per oz.

To process the stockpiles, Newmont has designed a 4-stage crushing operation. In the first stage, an immense mobile jaw crusher moves over the stockpiles, reducing larger fragments. Conveyors then carry the rock through a second-stage MP1000 standard cone crusher, two more MP1000 crushers in the third stage, and then on to a final stage, which employs 14 vertical shaft impact crushers. The rock comes out at minus-6 mesh, or about 3 mm. The circuit will crush 37,800 tonnes per day, or 13.8 million tonnes per year.

The material is then transported to the leach pad, where it is placed on eight lifts, each of which measures 10 metres high. Initially, the size of the pad will be 950 by 600 metres, but this will eventually be expanded to 2,225 by 950 metres.

The higher-grade material will have a 65% recovery on the heap, compared with 50% for the lower-grade ore. The leach cycle lasts 49 days.

The pregnant solution is pumped into a gold recovery plant, where dore is produced using the Merrill-Crowe process. Silver is present in the dore, but in variable degrees.

All gold produced from the operation can be refined in Uzbekistan before being sold on the international market.

The project, which began construction in October, 1993, required 41,000 tonnes of machinery, equipment and steel. Material from the U.S. was shipped to Finland where it was placed on the Russian railroad for transport to Uzbekistan. Bulldozers and other large earth-moving equipment were flown in on Russian-made cargo planes, despite difficulties with refueling and short runways. Steel was shipped across the Trans-Siberian railroad from Korea, and pipe from South Africa was trucked across Iran.

The transportation of goods across Asia was fraught with logistical problems. Special, heavy-duty seals were required for containers, for example, and armed guards were hired to discourage robbery and vandalism.

The plant was designed and built to American and Uzbek environmental standards. The environmental plan includes 31 monitoring wells upstream and downstream of the plant, covered conveyors for dust control, double-lined solution ponds, total solution recycling, and a strategy for reclamation.

At full production, the operation will employ 325 people, most of whom will be locals.