A year of drilling has done a lot to advance the Duck Pond base metal deposits, 15 km south of here, from mineral deposits to potential mines.
Joint-venture partners
The Duck Pond deposits were discovered in 1987 by
Thundermin entered the picture in early 1999 when it made a deal with Noranda to take over ownership by spending $1.4 million on the property and paying $500,000 to Noranda. Noranda retains a 2% net smelter return and will get a $3-million payment once production starts.
Queenston got its half-share in exchange for funding Thundermin’s work commitment, and by April of this year the joint venture had spent the required $1.4 million to earn title to the project.
(Should Thundermin and Queenston prove a resource of about 15 million tonnes of equivalent grade to what is known to exist at Duck Pond, Noranda will have the right to change its mind and decide the project really was big enough after all. The major can back in by funding a final feasibility study and financing the two juniors’ share of development costs.)
The Duck Pond deposits are in a 60-km-long volcanic structure southeast of Buchans, called the Tally Pond Belt. The Cambrian-aged volcanic cycle is overlain by Cambrian to Ordovician sedimentary rocks; in a pattern common in the Central Mineral Belt, the sediments are mainly in overthrust contact with the underlying volcanics.
The massive sulphide horizon is at the top of the volcanic sequence, at the thrust contact. The thrusts make for a collection of faulted massive-sulphide lenses, including several large enough to have an economically interesting tonnage.
The Duck Pond deposit proper consists of three such lenses:
Upper Duck carries a 4.6-million-tonne resource with grades of 3.6% copper, 6.6% zinc and 1.1% lead, as well as 69 grams silver and 1 gram gold per tonne.
Lower Duck has 855,000 tonnes running 2.7% copper, 5.3% zinc, 1.3% lead, 58 grams silver and 0.6 gram gold.
The smallest lens, christened Sleeper, is 266,000 tonnes of 1.5% copper, 8.6% zinc, 0.8% lead, 56 grams silver and 0.5 gram gold.
Upper Duck is cut off to the east by the Duck Pond “thrust,” a shallow-dipping normal fault; two other faults, the “Terminator Fault” on the southeast and the “Terminator Splay” on the south, truncate the massive sulphide body on other sides. The lens pinches out to the north and west, grading into barren massive pyrite and then into country rock.
A central early-stage fault, the Backbreaker, separates the northern part of the lens from the southern part, and may have bounded a narrow basin in the north, and a shallow one in the south, both of which controlled the deposition of the sulphides.
At Duck Pond, partly sulphidized lapilli and other rock textures suggest the sulphides may have replaced existing clasts or matrix in a still-consolidating pile of volcanic fragmental material, rather than being a true exhalite.
The footwall volcanics show chlorite and silica alteration, and northwest-plunging pipe-like bodies of chloritized rhyolite occur in the footwall. The rocks immediately below the sulphide horizons show an unusual calcite-chlorite mineralogy. There is some chloritic alteration in the hangingwall rocks as well.
The current feasibility work, by MRDI Canada, will have to consider mining plans for the deposit, which does not lend itself to the easy shaft-drift-and-open-stope approach used so often in the Abitibi. Upper Duck’s gentle southwest dip makes decline mining a reasonable option, but one that might become much less attractive at depth. On the other hand, sinking a shaft would require a large capital cost up front, which might stretch the project’s payback time. A hybrid option — developing by decline, then ultimately raising to surface for deeper production — is also being considered. Cut-and-fill stoping appears to be the most obvious choice as a mining method.
Thundermin and Queenston’s 1999 drill program on the Upper Duck Lens added about 800,000 tonnes to the estimated resource, but its real impact was in converting inferred to measured and indicated resources. About 3.8 million tonnes of the resource now fall into the measured and indicated categories, providing a substantial base for the ongoing feasibility study.
The partners are now deepening several old Noranda holes in the Lower Duck Lens to test downdip from the known mineralization. The Lower Duck Lens dips broadly southward, and, as well as the downdip extension of the horizon, some of Noranda’s widely spaced holes to the east encountered sulphide mineralization.
Duck Pond’s Sleeper zones are a set of faulted slivers of massive sulphide, which lie structurally below the Upper Lens and look as though they are faulted off by the Terminator Splay. The lack of detailed drilling in the Sleeper lenses means they are still only poorly defined. “They’re notoriously hard to correlate,” says Thundermin geologist Gerald Squires, who also worked on the project for Noranda. “They’re more often parallel to structures than to mineralized horizons.”
Resource altered
One telling result of the recent drilling is that the new resource estimate for the property rose (to 6.2 million tonnes from 6 million) even as it decreased in the Lower Duck and Sleeper lenses — radically in the case of the Sleepers, which fell from 676,000 tonnes to 266,000 tonnes (at comparable grades). The smaller resource figures in the poorly known parts of the deposit reflect conservatism, rather than drilling failures; where drilling was tightened up in the Upper Duck Lens, tonnage increased from 3.9 million to 4.6 million without a substantial decrease in grade.
The property’s other deposit, Boundary, is a smaller, near-surface massive sulphide about 5 km to the northeast. It is seen as a front-runner for the Duck Pond project, a low-cost open pit that will bring in early cash flow to help offset the capital cost of a larger mine at Duck Pond.
Three gently northeast-dipping zones of massive and stringer sulphides make up a total of 483,000 tonnes grading 3.8% copper, 3.3% zinc, 0.4% lead, 26 grams silver and 0.3 gram gold per tonne. They are, on average, about 9 metres thick and lie under a thin veneer of glacial overburden and sometimes under a thin tuff unit. “You strip off the overburden and you’re pretty well there,” comments Terry Brace, the project geologist at Boundary.
The deposits sit in the same horizon as the Duck Pond sulphides, but drilling so far suggests they are structurally much less disturbed. Here again, closer-spaced drilling revealed a lot about the deposit. Noranda had made its first resource estimate from widely spaced drill holes, and the joint venture mounted a major program to tighten the information base. The new drilling proved — among other things — that the deposit, which had been thought to dip gently to the northwest, in fact dips the opposite way. Not coincidentally, the resource estimate climbed by about 35,000 tonnes, and moved entirely into the measured and indicated categories.
“For the amount of drilling we did, we got a lot of information,” says Brace.
“And the degree of certainty is a lot higher,” adds Squires.
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