Hemlo grades decline at depth

This section runs at least 100 vertical m with a horizontal strike length of 200 m in the Williams mine. It grades in the range of 3-4 g above the a verage gra de of the Williams mine. This richer pocket seems to extend across the Williams/ Golden Giant boundary. (Another isolated, higher grade pod has also been found i n the David Bell mine — another Corona/Teck collaboration — to the east of the Golden Giant.) But this richer zone does not extend at depth.

“The theory (of richer grades at depth) is a generality that I don’t see in our workings specifically,” said Al Guthrie, chief geologist at the Wil liams mine. “And I don’t see it as a trend in all three mines put together.”

In the Williams mine, for example, three deep holes from surface intersected some gold mineralization below the 9175 level (1,130 m below surface), but the gr ades were less than mine average. Guthrie expects that a planned diamond drill p rogram from the 9175-level drift next year will confirm the results of prelimina ry holes put down some years ago.

Gil Leathley, Corona’s senior vice-president operations, agrees that in the Williams and David Bell mines grade does not improve with depth. But th e orebody d oes widen.

“I think what is true is that the orebody gets a little thicker the deeper we go,” he said.

At the neighboring Golden Giant mine — The Northern Miner recently visited both operations, but not the David Bell — mine geologist Peter Brown hesitates to make any generalizations about the orebody. It is true that in the deeper portions of the quarter claim, owned jointly by Golden Giant and David Bell and in th e eastern section of the Golden Giant mine above the 4500 level (821 m below sur face), grades were higher.

But uncertainty prevails over the grades and thicknesses to be encountered below that level.

“We’ve had local areas (in current workings) that have been pinched right down to five metres wide,” said Brown. Golden Giant’s stopes can be was wide as 30 m.

“They’re still mineable, but we’ve had to do a lot of work in shaping our stopes. And as rapidly as it pinches out, it balloons back up to the or iginal width.

“That’s the difficulty in trying to develop any generality. It’s not only the grade you have to take into account, but the thickness as well.”

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