PAMOUR: Beats the odds

Take a single paper match and cut a piece from the end just a little shorter in length than the match is wide. This fragment then represents the amount of gold the Pamour mine has in one ton of ore. And, if a one-ton chunk of run-of-mine ore were to be carved into the form of a cube, the cube would have a side just over 2.25-ft. long.

Pamour’s mill-head grade is 0.089 oz. gold per ton, but there are times when numbers need illuminating. They need comprehendable dimensions to bring into focus the feat of management and technology that makes the extraction of such a minute amount of metal not only possible but profitable.

HISTORY

Pamour has always been a low-grade operation, right from the start of milling in 1936. At that time Pamour’s reserve grades were around 0.13 oz. gold per ton. But the McIntyre mine, Hollinger and their numerous neighbours were reporting in the 0.30-0.35 oz. gold per ton range. Indeed, in the early 1940s, the Hollinger wouldn’t deign to consider anything under 0.217 oz. per ton in their formal ore reserves. (The far-distant shareholders, we are sure, would be suitably impressed by this demonstration of exclusivity, a genteel piece of promotion).

The change at Timmins in the past 30 years is the loss of nearly all the famous-name mines of the Porcupine, and, their lesser-known neighbours. Pamour is one of the very few left. It is also the lowest-grade, underground gold mine in the country. So, how then does Royal Oak Inc., Pamour’s owner, manage to make the mine pay? The answer might be — through a well-leavened blend of management skills and technology. And while the technical aspect is straight-forward enough, the management side is far less so. Perhaps the management part of it all boils down to creating and sustaining a collective will to beat the odds. Pamour has been doing just that for over half a century and there’s little doubt it will continue to do so for a good few more years to come.

GEOLOGY

Pamour’s mineable ore’ and `mineralized material’ (Royal Oak’s nomenclature) at Dec. 31, 1992, totalled 9.6 million tons at a grade of 0.086 oz. gold per ton. Nighthawk Lake adds a further 1.6 million tons of `mineable and mineralized material’ at 0.168 oz. per ton.

Royal Oak now owns four miles of strike length on essentially the same ore-making structure. The structure was worked by Hallnor and Broulan Reef mines at higher grades than those that Royal Oak now mines profitably and, consequently, the potential for developing substantial new reserves is positive.

The main Pamour mine is located on the north limb of an overturned syncline. The axis of the syncline dips north at about 70deg and strikes N70degE. The south limb of the fold was faulted away by the Porcupine-Destor Fault; the fault itself is located immediately to the south of the mine property. The contact zone between Keewatin volcanics and Temiskaming sediments is the main feature of the mine.

Approximately 80% of the ore mined has originated from the conglomerates, and to a lesser extent, from the greywackes of the Temiskaming sediments.

Fracture zones, characterized by closely-spaced, quartz-stringers (individually, stringers are up to three-inches wide) make up the ore zones. The zones themselves form ore shoots typically 100-200 ft. high, up to 150 ft. wide and can reach a maximum of 4,000 ft.along the plunge. The shoots plunge 30deg east and dip steeply north. Pyrite and pyrrhotite are the common sulphides and make up to 3% of the mineralization; gold is typically free and often spatially related to accompnaying sphalerite.

Up to five ft. wide, low-dipping quartz veins are commonly found in the volcanics. Quartz veins in the sediments are infrequent. They are usually near-vertical in attitude and often carry significant amounts of arsenopyrite as well as pyrite in the host rocks and the veins themselves.

MINING

Apart from a limited tonnage coming from narrow-vein, underground stopes, Pamour is a bulk-mining operation. Of the 1.22 million tons mined in 1992, 44.5% came from open pits and 55.5% from underground. Average grade for pit ore in 1992 was 0.066 oz. and 0.107 oz. per ton for underground. Total bullion production was 98,898 oz. of which, and suprising for such a low-grade mine, 10% was coarse gold derived from gravity concentrates. Until 1991, a small portion of production also came from heap leaching.

All of the facilities, open pits, mine and mill are in close proximity to Pamour’s main shaft. This is a large-dimension square’ shaft sunk by Noranda in 1935 12 miles east of Timmins adjacent to the main highway.

Pamour is Royal Oak’s sole operating property in the Porcupine at the moment. The Schumacher Complex (the former McIntyre mine and 2,700-tons-per-day mill) was closed in 1989. The remaining reserves there are considered sub-marginal at present gold prices. All of the accessible crown-pillar ore at the Hollinger and Delnite mines has been exhausted and the Ross mine, 56 miles east of Timmins, was sold in 1989.

On the other hand, the Nighthawk Lake mine, 20 miles east of Timmins may go into production within the next 24 months, depending on the gold price. The Hallnor mine, contiguous to the Pamour mine to the west, will see renewed underground diamond drilling this year.

Despite Pamour’s main shaft reaching to 3,145 ft. below surface, there is little mine development below the 2,200-ft. level. It is probable the ore-bearing conglomerate continues to make ore below 2,200 ft. There has been speculation the ore-bearing conglomerate may not have the widths and continuity demonstrated on the upper levels, but insufficient drilling has been done to clarify the picture.

However, Royal Oak had just acquired the property. It did not have the lead time to explore and develop this large block of ground. A new source of ore was needed immediately.

Consequently, Royal Oak made an agreement with Falconbridge to exploit the ore on the latter’s Hoyle property, immediately adjoining Pamour to the east. It is the Hoyle property where practically all underground mining is taking place today. Royal Oak pays a royalty of 75 cents for every ton mined, and, so far, the agreement covers only mining in Hoyle’s Temiskaming Series rocks (meta-sediments). The company, however, is now earning the right to work ore in Hoyle’s Keewatin Series volcanics. The property is considered as two parts for negotiating purposes, the steeply-dipping, roughly east-west striking, Temiskaming/Keewatin contact forming the `boundary’ between the two parts. (This agreement also entails an option to Falconbridge of the Vermillion and Errington base-metal deposits in the Sudbury Basin. The Sudbury property is owned by Royal Oak).

The Hoyle mine had its brief five-year life brought to an end in 1943 when fire destroyed both surface plant and mill. Ore reserves were quoted on closure at 1.2 milion tons grading 0.105 oz. gold per ton.

Pamour workings were driven into the Hoyle in 1990 and access was also made by a ramp collared at surface. This is a 10.5-ft.x 16-ft. opening driven at minus 17%. The ramp face is at approximately the 1,100-ft.level and it may ultimately reach beyond the 1,600-ft. level, depending on the continuity of the ore.

The original 1,200-ft. Hoyle shaft primarily provides ventilation, and the intake fans are located at its collar. The shaft will soon accommodate a fuel line delivering diesel fuel directly to a 3,000-gallon tank at the 800-ft. level. “The arrangement will be a boon to us,” said Mine Superintendent Raymond Cloutier. “At the present time, it takes well over an hour for a scoop to run up the ramp, refuel on surface and return underground. On top of that the round trip burns up 20% of the fuel in the process.” The fuel system is fully automated and fitted with fail-safe circuitry. When the fuel drops below a predetermined level in the underground tank it will be replenished automatically from surface. It’s a similar installation to that at Placer Dome’s Detour Lake mine, according to Cloutier.

While the ramp provides service access, broken ore is dropp
ed through an ore-pass system to the 1,400-ft. level and hauled to the Pamour shaft for coarse crushing and hoisting to surface. The rail haul is 6,100 ft. long and the train consists of 17, 120-cu.-ft. Granby cars powered by two, 11-ton trolley locomotives, one at each end of the string of cars.

Underground mobile equipment includes eight diesel Load-Haul-Dump machines ranging in size from two- to eight-cu.-yd. capacity. They are a mix of Eimco, Wagner and Jarvis-Clark machines. There are two, 26-ton and one 13-ton trucks. Development jumbos are single-boom, electro-hydraulic rigs and include two Tamrock, one Continuous Mining Systems (CMS) and one of Montabert manufacture. Two In-The-Hole (ITH) blast-hole drills are both by CMS. There is one CD90 and one CD360. Rockbolting is usually done by the development jumbos. They are fitted with split booms and the changeover to up-hole drilling is done quickly. Services are provided by a variety of farm-type tractors and 4-wheel drive vehicles.

The mine is expecting a new 26-ton truck and a six-cu.-yd.loader to be delivered this year replacing aging equipment. In this vein, Mechanical Superintendent Chris Pollard gave an example of how Pamour continues to beat the odds. “Some time ago,” Pollard said, “we heard that the Kidd Creek mine was about to retire ten, 8-cu.-yd scoops to the light-duty circuit. Well, we were able to negotiate an acceptable price and back here in our yard we transformed the ten tired machines into three sprightly new ones — and we have enough spare parts for the next half dozen years.”

Bulk-mining practice at Pamour’s Hoyle mine is conventional. Stope blocks are 100 to 150 ft. long and 350 ft. high. Ore widths average 50 ft. and dips vary from 70deg to 75deg. Rib pillars, 25 ft. wide, separate the stopes along strike.

A centrally located drift splits the block into an upper and lower section to ensure the majority of blastholes are no more than 160 ft. long. The three drifts: upper drill drift, central drill drift and the lower mucking sill are slashed to ore widths and back support installed. Seven-foot Swellex’ bolts on a 4-ft.x 4-ft. pattern are the norm in drifts, while five-foot grouted rebar is frequently used at draw points.

Cloutier is pleased with the performance of `Swellex’ bolts. “Many of these bolts have been in place for seven years and they are still sound at a 17-ton pull,” he said. “Other newer installations have been tested to 20 tons, but we don’t usually take them beyond that to the break point.”

Hangingwall control is maintained by fans of bird-cage-type cable bolts. Fans are drilled at ten-ft. centres (horizontally) and the fans are slewed 70deg to 80deg from the centre-line of the drift to catch the cleavage of the rock at right angles. Each fan consists of three to four, 50-ft.-long holes drilled at angles of plus 10deg to plus 50deg. The pattern is repeated on each of the three drifts making up the stope development.

Typically, stope walls stand well. Many stopes have been drawn out for up to two years with little wall slough in evidence. Dilution is quoted in the 5%-10% range, only occasionally reaching as high as 15%

In-The-Hole (ITH) blast-hole rigs drill 6.5-inch-diameter down-holes on a nine-foot (burden) by 11-ft. pattern. Hole deviation is generally less than 2% (about three feet on a 160-ft. hole). Redrilling has been reduced to 5% through the early detection and elimination of machine slop and the use of laser hole spotters.

Stopes are blasted in 20-ft. lifts. Amex is the commonly used stoping explosive but higher-powered, aluminized slurries are needed for taking the slot.

Interestingly, the first use of a Roger raise borer was being made at the time of The Northern Miner Magazine’s visit. It is expected that slot development via a 30-inch-diameter raise will eliminate much of the blasting-hammer presently experienced from conventional drop raises employing the usual clusters of 6.5-inch-diameter holes. What this means in practice is that the slot will be blasted in 20-ft. lifts rather than the present 9.5 ft. It will save time and reduce blast vibration.

Two men are employed on the raise borer. One is on the upper level attending the ITH drill rig which provides the borer’s pull-force; the second changes and sharpens drill bits and disposes of the borer’s cuttings on the lower. This particular raise borer (there are now 27 Roger machines in use worldwide) came from the company’s Hope Brook mine, Newfoundland.

While management strives to pare costs through improved organization and by the introduction of ever more productive equipment, Pamour is fortunate in having a degree of leverage over the grade of ore delivered to the mill. Namely, by the mining of high-grade ore.

High-grade ore shoots have a strike length of 100-150 ft. They are carried by narrow, flat-dipping veins, the vein structures themselves ranging up to 1,500 ft. in length. Oreshoots are erratic and dips are variable. Shoots are mined in panels 33 ft. along the strike with an 8-ft. rib pillar along the dip separating adjacent panels. Typically, a panel stope is opened by a raise driven through to the upper level, a distance of about 140 ft. on the slope. The raise is then slashed to design width.

Mining is by jackleg and muck is moved to the level below by slusher. In the specific instance of the 300-ft.level, panel-stope muck is loaded onto trucks by an LHD (there are no chutes as such) and hauled directly to surface for stockpiling.

A panel stope seen by The Northern Miner Magazine on the `35′ vein at the 300-ft. level (335-136 panel stope) showed a mining width of 4.5 ft. Footwall dip was 40deg. Quartz and pyritic mineralization varied from 2-3 inches to 18 inches within a 60-ft. stretch along the dip.

The branching of veins and the concomitant inclusion of lenses of country rock are frequent features of vein ore shoots, as are rolls in the footwall and small-throw faulting. Despite these vagaries, panel stopes produced 8% of Pamour’s total bullion at a mill-head grade of between 0.3 and 0.4 oz. gold per ton.

A novel development is planned for the Hoyle 400-ft. level. A 40-ft. thickness of ore is to be bulk-mined above the level, but at the same time leaving a substantial crown pillar to ensure stability of the highway right-of-way which traverses the general area. The novelty in the proposal is to use modified, 50-ton Caterpillar trucks to haul the stope muck to surface. The existing drift is provisionally scheduled to be slashed out to accomodate the vehicles next year.

OPEN PIT

Pamour has worked crown-pillar ore at a half-dozen sites by open-pit methods and the largest of these is the combined No.1 and No.3 pits. Open-pit reserves at the December, 1992, totalled 1.95 million tons of mineable ore’ and mineralized material’ grading 0.065 oz. gold per ton. The No.1/No.3 pit is 1,500 ft. long, 900 ft. wide, 300 ft. deep and in close proximity to the mill. Stripping ratio is approximately 0.5:1.0.

Equipment consists of 50-ton, Cat 773B trucks, a new, 10-cu.-yd. Hitachi EX 1000 hydraulic shovel and a mix of Montabert and Ingersoll-Rand air-track drills. There are also a number of Cat loaders for light duty and a fleet of standard service vehicles.

Three-and-a half and 4.5-inch-diameter holes are drilled on a nine foot by nine foot pattern. Amex is the blasting agent.

MILLING

The first mill at Pamour turned over in 1935 at 700 tons per day (tpd). Capacity was rapidly increased to 1,600 tpd. In 1992, the mill averaged 3,355 tpd. It is one of the very few Counter-Current-Decantation (CCD) gold mills remaining in North America and most of the CCD equipment is vintage hardware. Overall gold recoveries are in the 89%-90% bracket.

Ore is ground to 55% minus 200 mesh in two, closed-circuit stages. A bulk sulphide flotation product is made by three Maxwell cells followed by six Galigher Agitair 150 scavenger cells. Final tailings from the scavengers assay 0.0060 oz. gold per ton.

The bulk concentrate is cleaned in Denver Sub-A cells which produce a final concentrate assaying five to six oz. gold p
er ton. The concentrate is ground at the rate of 50 tpd to 98% minus 325 mesh, subjected to 16 hours pre-aeration to oxidize pyrite and pyrrhotite and then passed to CCD. Overall retention time in the cyanide circuit is 54 hours. Gold is recovered by standard Merrill-Crowe zinc precipitation and the precipitate shipped to the Schumacher refinery (McIntyre) for smelting and casting into bullion.

Heavy sulphides and free gold are caught in hydraulic traps located at the coarse ball-mill discharge and the resulting rough concentrate is cleaned up on a single Deister table. Some of the gold is surpringly coarse, up to 0.4-inches long and it finds a ready market in Timmins in the form of tie pins and brooches.

Gold has also been recovered by heap leaching. A total of 700,000 tons has been treated since 1987, accounting for a recovery of 12,549 oz. metal.

Extraction rate is 65% and production to date shows a recovered grade of 0.018 oz. per ton. No new ore has been placed since 1990, but the plant has been maintained and is available should leaching grade ores again become available. Depending on the gold price, leaching ore generally grades from 0.01 to 0.035 oz. gold per ton. The re-usable pad is a few hundred feet from the mill.