Tonto tackles Goldstream improvements

The Goldstream mine, jointly owned by Bethlehem Resources (TSE) and Goldnev Resources (VSE), is located on the Goldstream River, a 69-mile drive up the Columbia River Valley from railhead at Revelstoke, B.C.

The area plays host to more than just mining. Canadian Mountain Holidays runs helicopter skiing tours in the winter out of an old but considerably upgraded bunkhouse a short distance downstream from the mine. Skiers appear willing to share this beautiful valley with both the mine and the logging companies whose clear-cuts appear in a patchwork up the valley. The deposit is in a north-facing hillside. The ore zone dips to the north at 30-35 degrees and plunges to the northeast at about a 50 degree rake. The zone consists of a continuous bed of massive and disseminated sulphides with an average thickness of about 10 ft. and a lateral extent of up to 1,200 ft. in the uppermost ore block.

Noranda reached the ore zone with a number of adits into the hillside and developed the deposit by ramping down it to establish main development levels at about 160-ft. vertical intervals.

The ore between the developed levels was to have been mined out by driving a series of connected sublevel drifts with pillars left for support. Bethlehem, the operator at Goldstream, contracted mining operations to Tonto Mining. Tonto is using the revised mine plan which utilizes sublevel drifts as well, but spaced on about 25-ft. vertical centres. The ore between the sublevels, equivalent to about 36 ft. along the dip of the ore zone, is mined out by what might be described as a drift-and-slash method.

To begin slashing operations, a drop raise is opened between sublevels to create space for blast holes to break into. A fan of holes is drilled to the sublevel below, one hole along the top of the ore zone, one along the bottom, plus one or more holes in-between depending on the thickness of the zone. The fans are drilled on 4-ft. spacings. Tonto is currently experimenting to determine how many fans can be blasted at one time but is typically blasting one or two at once.

A 10-ft.-wide pillar is left on 115- to 165-ft. centres. Wherever possible, Tonto tries to position pillars at locations where the ore zone pinches making them essentially “free.”

Depending on the thickness of the ore zone (typically about 10 ft.), a portion of the lower corner of each sublevel is in footwall waste. The slashing operation, therefore, reduces the amount of dilution created by Noranda’s mining method.

Tonto has four 4-yd., one 6-yd., and two 2.5-yd. LHDs on site. Ore haulage is handled by two 30-ton and four 15-ton trucks. The mine utilizes underground primary crushing before ore is conveyed into the mill on surface. Ed Yurkowski, president of Tonto, noted that there is no coarse ore stockpile since crushing operations are located underground. For this reason, he said it is important to have six or seven working areas.

Ore grades can vary from 2.5% copper up to 7% copper and the additional working areas allow the company to blend the high- and low-grade ore. Head grades are currently running at about 4.05% copper and although Noranda did operate a zinc circuit, the mill is producing only a copper concentrate while metallurgical studies are completed on zinc recovery.

Head grades are expected to increase to over 4.5% copper as the relative amount of slashing increases.

To date about 66,000 tons of development ore have been mined while slashing has amounted to about 29,000 tons. Ultimately, the mine is expected to produce equal amounts of drifting and slashing ore.

The mill utilizes a rod mill and a ball mill for secondary grinding coupled with standard flotation and a re-grind circuit.

Bethlehem is installing column cells in order to increase copper recoveries to 91% from the current 89%, as well as increase copper concentrate grade to 26% from an average of 23% to 24%.