Samatrosum mine opens producing silver, zinc plus copper, lead,

Keith Hendrick, chairman of Minnova and president of Noranda Minerals, snipped the ceremonial red ribbon to mark the opening of the small, high grade silver and base metal mine. But the moment was shared by Minnova President Ian Bayer, Rea Gold President Larry Reaugh, and by visiting dignitaries and company officials.

Bayer told the crowd gathered at the mine site that the successful start-up of Samatosum was the result of an initiative to apply Minnova’s “eastern” massive sulphide expertise to the Cordillera. The mine is the first to be developed in Western Canada by the Toronto-based company which also has an extensive land package in the surrounding area.

“We expect to be here a long time,” he said. Bayer is also president of Kerr Addison Mines (TSE), which acquired control of Minnova (then known as Corporation Falconbridge Copper) in 1986. Kerr Addison in turn is controlled by Noranda Inc. (TSE).

The $30.3 million mine, 70%- owned and operated by Minnova, was completed within budget and 20 days ahead of schedule. Construction began in early October of last year, production was 100% achieved in July, and the operation is generating a positive cash flow.

Rea Gold has a 30% interest plus a 5% net smelter return royalty. The company optioned the property in October of 1983 from prospector Al Hilton on the strength of a promising gold-bearing massive sulphide showing.

David Watkins and Alex Davidson of Minnova are credited with having secured a deal with Rea Gold the following month. Subsequent exploration work by Minnova led to the discovery of what is now the Samatosum deposit in July of 1986.

This deposit will be mined by open pit methods for the first two- and-half years, followed by a transitional year to underground, and ending with one-and-half years of underground mining (most likely trackless cut and fill).

Diluted mine reserves were reported (July, 1989) as 766,682 tonnes grading 833 g (24.3 oz) silver, 1.6 g (0.05 oz) gold, 1.1% copper, 1.4% lead and 3% zinc.

Since the beginning of July, the mill has operated at its nominal capacity of 422.5 tonnes per day. More than one million ounces of silver — the prime economic metal — were shipped in 5,000 tonnes of concentrates by the end of September. Other payable metals, in order of importance, are zinc, gold, copper, lead and antimony.

The mine produces three products. Lead concentrates are trucked in bulk to Asarco in East Helena, Mont. Zinc concentrates are trucked to Cominco in Trail, B.C., and copper-silver concentrates are bagged and shipped to Belgium and Japan.

Minnova’s 1990 production forecast is for 8,000 tonnes of copper concentrate, 9,000 tonnes of zinc concentrate and 5,500 tonnes of lead concentrate. These concentrates will contain 6.25 million oz silver and 10,500 oz gold. So far, mining and milling costs are reported to be in line with Minnova’s expectations.

The Samatosum ore zone consists of both a quartz vein and massive component, rather than a typical massive sulphide deposit. Both ore types contain tetrahedrite, sphalerite, galena, chalcopyrite, and electrum.

The zone undulates, pinches and swells and is structurally altered, but Minnova said it has proved to be remarkably continuous. Down- dip the deposit straightens out into a flat, plunging tabular orebody averaging 6x500x80 m.

“This orebody is a little more folded and a little more faulted than we thought initially,” said Bob Friesen, chief geologist. “But the grade and continuity was established with the drilling and it’s holding up very well.”

Minnova awarded a contract for open pit mining to Ledcor Industries early this year. The Vancouver- based contractor built 1.5 km of haulroad connecting the pit and the plant, hauled the first overburden by the end of March, and the first ore in early May.

About four million tonnes of waste and 70,000 tonnes of ore have been removed from the pit to October 18. The over-all strip ratio is expected to average 18.4:1 tonnes waste to tonnes ore over the life of the pit.

Mine superintendent Brad Thiele noted that all mining schedules have been met and the company is pleased with the performance of Ledcor. Mining currently involves 45 people, working five days per week on two 10-hour shifts per day.

The decision to use contract miners was primarily based on the relatively short mine life at Samatosum. No capital outlays were required to buy equipment, Thiele pointed out, and the company has the advantage of skilled operators and flexible use of equipment. Ledcor is paid on a unit basis which varies depending on whether the contractor is working in waste or in ore.

“We pay a higher unit price when Ledcor is working in the ore zone,” said mine manager John Purkis. “This is where our engineers and geologists take control. We pay a premium to achieve that control, but in our opinion it’s worth it.”

Ore mining — which involves handling low volumes of very high grade material — is carried out on shallow 2.5 m bench heights with all activities under the direct supervision of a Minnova mine technician.

“This operation does differ from most open pit mines where you typically have large amounts of lower grade disseminated ore,” said Bob Friesen. “Ours is a high grade and predominantly vein-hosted orebody. So even though it’s open pit we have to use underground techniques to identify the ore.”

Typically, this involves tight- spaced drilling, assaying, plus constant supervision during mining for grade control. Areas with high lead (over 5%) are set aside, as metallurgical problems develop in the mill when the lead to copper ratio exceeds 3:1. Purkis said blending from stockpiles is necessary to reduce grade variability and provide a smooth mill feed.

Waste material at Samatosum is predominantly non-acid generating, and this material is used to buffer the maximum 10% of waste that has acid-generating potential.

The milling process at Samatosum is, as might be expected, a rather complex process. Ore is fed to the crushing circuit and crushed to 3-inch size. This material is then screened and product oversize is carried to a shorthead crusher which reduces the ore size to 1/2 inch.

Ore is drawn from the fine ore bin by two variable speed conveyors to feed a 8×10-ft ball mill which grinds the ore down to a separation size of 60% minus 200 mesh.

This slurry reports to the copper- silver, lead roughers at 38% solids and sulphur dioxide is added to depress the zinc. Collectors and frothers are added to float the copper-silver/lead concentrate which goes through one cleaning stage.

The copper-silver/lead float from the cleaner stage goes to reverse flotatio n where the lead is depressed and the copper-silver is removed by flotation. The zinc is activated by copper sulphate and cleaned in a separate zinc flotation circuit.

The concentrates are fed to three thickeners as copper-silver concentrate, lead concentrate and zinc concentrate. As they thicken, they are transferred to stock tanks and then individually fed to a filter press for moisture reduction to 7% level.

October mill head grades (to Oct 23) averaged 1.01% copper, 2.66% lead, 5.19% zinc and 808 g silver per tonne. Minnova said head grades, metallurgical results and operating costs are now in line with expectations.

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