Williams mine running on track ure by

During the first half of this year cash production costs averaged $210(US) per oz, Leathley said. The average mill-head grade is 8.1 g per tonne. The proven a nd probable reserve is 33,992,000 tonnes grading 6.2 g per tonne (as of January, 1989), with another approximately six million tonnes grading 4.1 g in the possi ble category.

Underground, three main mining blocks yield the tonnages that make this mine the biggest gold producer in Canada. The topmost block, centred near th e approxim ately 300-m deep A Zone exhaust raise, can provide 750 to 1,000 tonnes of muck p er day.

This block will be mined out in another one to two years, according to mine engineer Stewart Brown, although a sill pillar underneath this block wi ll take a f ew more years to mine.

The second block, between the 9450 level (890 m below surface) and 9555 level (785 m underground), contributes the bulk of the daily tonnage and also contains the highest grade section of current operations. (To understand the level sequencing, keep in mind that the shaft was collared at the 10340 eleva tion.)

A portion of this second mining block contains higher grade material spanning at least 100 vertical m with a horizontal strike length of 200 m. It runs in the range of 3-4 g above the average grade. This richer pocket is believed to exten d across the Williams/Golden Giant boundary.

Right now, that rich section of the Williams second block is mined at a daily 2,500 tonnes.

The third mining block, between 9240 (1,100 m below surface) and 9345 (995 m) levels, produces from 2,100 to 2,200 tonnes per day. Once the upper A Zone ore i s depleted, Corona will rely on ore below 9240.

Meanwhile, the long-term future of the mine (that is, beyond the 20 years or so already more or less assured) lies to the west of the current wor kings. Corona /Teck are driving an exploration drift into this zone from the 9175 level (1,165m below surface) of the existing workings (the main shaft bottoms at the 9030 level).

Diamond drill stations are being established as drifting advances. And by year-end, some initial core assays will be available to the mine geolog y department. This should begin to disclose, in rough fashion at least, the grades and widths awaiting miners perhaps two decades from now.

Next year, diamond drilling from this level will be completed and the results in, which undoubtedly will generate some excitement. There simply isn’t enough i nformation now even to guess at the average grades and widths in this western po rtion of the Williams deposit.

And with an exploration drift proposed for the 9975 level (365 m below surface ) west of the main shaft, it will be interesting to see how the C Zone open pit to the west, with its series of east/west- striking lenses, relates to the rest of the Hemlo orebody. “Everybody is wondering where they join,” said Chief Geolo gist Al Guthrie. Exploration at this level has yet to be entered into the 1990 b udget. “Nothing has been finalized,” said General Superintendent Rory Mutch. “It won’t be for the next month or month and half.”

The underground orebody is a continuous tabular body running anywhere from 3 to 40 m in width. Below current workings, gold mineralization extends t o at least 1,300 m below surface, said Guthrie.

The C Zone open pit is not regarded as an orebody by the mine operators. Rather, this “quarry” provides backfill material and, occasionally, a b onus of low gr ade ore mill feed when production drills bite into gold-mineralized sections.

Up to now, underground exploration has taken a back seat to development and production. The contested ownership and ensuing LAC/Corona trial had no thing to do with this, however.

“Our whole emphasis was to get up to certain production levels,” said Mutch. ” If we drive an exploration drift, we’re losing 3,000 tonnes per day in the mill, because we would be hoisting that much waste up the shaft every day.”

While nominal mill capacity is 6,000 tonnes per day, achieved last year in an expansion from 3,000 tonnes per day, the mine is running at 5,500 tonnes, accord ing to year-to-date figures.

“We need 10 producing stopes to give us 6,000 tonnes per day,” said Brown. “Right now we have eight or nine stopes.” Mutch said the 6,000-tonne fi gure should be attained some time in the fourth quarter of this year. The mine uses longhole , open stoping with delayed backfill.

While the mill nameplate capacity is 6,000 tonnes, it has been run as high as 8,400 tonnes to test its upper limit. The mill incorporates two semi-autogenous (SAG) mills, primary and secondary ball mills, a leach cycle, a carbon-in-pulp c ircuit and pressure stripping vessels. The gold is electrowon and put through an induction furnace.

Mill recoveries averaged 94.9% to the end of July and the mill head grade was 8.1 g gold per tonne (0.23 oz gold per ton). By the end of July, the operation h ad produced 269,692 oz of gold. “Even at 7,000 tonnes per day, the mill coast s very well,” Mill Metallurgist Robert Raponi told The Northern Miner.

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