Denver — In northern Nevada’s Carlin trend,
More than a year ago, definition drilling at Deep Post intersected this mineralization. Measuring thousands of tons at grades of nearly 1 oz. gold per ton, it was too much to ignore.
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To solve the problem, Newmont proposed erecting a buttress, and by the beginning of the year, the company had commissioned contractor Small Mine Development to begin construction of the cement, steel and rock structures. They are on the south wall, 120 ft. below and east of the Deep Post portal.
To create the buttress, Small Mine Development placed chain-link fencing over the top of each bench, then covered that with 8 ft. of cemented backfill, reinforced with steel cables salvaged from old mining shovels.
The company conducted geotechnical analyses and compression tests on the buttress, which miners will be working directly beneath for as much as five years.
Measuring 200 ft. high, the buttress allows miners at Deep Post to reach headings close to the pitwall surface without compromising safety, says Mel Lawson, mine superintendent. “In places, they may be able to mine all the way to the fencing, and I’ve never heard of anyone doing that before.”
Newmont and Barrick have been engaged at Betze-Post under a joint operating agreement since 1992. Barrick mined the material, sending Newmont’s share to its processing facilities. The situation allowed Newmont to post record production in Nevada for 2000.
In May 1999, the two companies agreed to a land swap, whereby Newmont’s Goldbug deposit, near Barrick’s Meikle mine, was exchanged for a corridor of land between the Post deposit and the Deep Star underground mine, a mile to the south. The agreement, which amounted to a total of 4 million oz. gold, had the advantage of consolidating landholdings for both companies.
Accelerated schedule
Development of the Deep Post mine was a direct outgrowth of the land swap. The transaction reduced the capital costs of the original Deep Post project by one-third, allowing the company to put the portal near the bottom of the Betze-Post pit. It also accelerated the schedule by more than two years.
Originally scheduled to begin in mid-year, mining at Deep Post got under way as early as February. Capital costs were US$65 million, including US$1.5 million for the buttress.
So far, the operation has mined 11,000 tons of ore averaging 1.16 oz. per ton from the upper portions of the vertically oriented mine, using underhand cut-and-fill methods. The company is still adding production and maintenance crews.
The material is being shipped to the autoclave at the Lone Tree complex, northeast of Winnemucca, for processing. The autoclave achieves better gold recoveries with the refractory ore than Newmont’s roaster at Carlin.
Mineralization at Deep Post consists of decalcified and brecciated limestones, with as much as 5% sulphides and low carbon, hosted in the Roberts Mountain formation along the Post fault corridor.
At the end of 2000, reserves at Deep Post stood at 3.1 million tons grading 0.81 oz. per ton, equivalent to 2.5 million oz. At full production, Deep Post is expected to contribute 400,000 oz. annually at cash operating costs of US$150 per oz. The company has budgeted production of 166,000 oz. in 2001.
Higher fuel costs
Throughout Nevada, Newmont expects to produce 2.7 million oz. in 2001. Total cash operating costs are projected to be US$215 per oz., slightly up as a result of higher fuel and energy costs.
Although production began early, exploration of the corridor between Deep Post and Deep Star has not stopped. Prior to the land swap, Barrick had drilled several holes from the surface, intersecting encouraging mineralization. Now known as the Gold Margin zone, Newmont has stepped up drilling from underground.
The drilling comes off a recently completed, 5,000-ft. tunnel connecting the two underground mines. The tunnel also serves as a secondary emergency exit for both mines.
Last year’s much-heralded expansion at Gold Quarry has been put on hold. The company had completed open-pit mining from the pit in May of last year, and by the first quarter of this year, it had ceased stripping waste material overlying the expansion project. By deferring the stripping, Newmont will save US$6 million for the year.
The expansion was expected to add 4.6 million oz. from 76 million tons averaging 0.06 oz. per ton. Much of the ore would have been processed through conventional heap leaching and milling. Nearly 40% of the recovered ounces would come through a newly developed bio-milling circuit, which would utilize a reusable heap for bio-oxidation.
Meanwhile, Newmont has shelved plans for expansion at the Twin Creeks and Leeville projects until gold prices improve.
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