NORTH RIM NICKEL; INCO’s Lower Coleman and East McCreedy orebodies

Not much has changed here in at least the past 10 years, and it certainly doesn’t look like a boom town. Nevertheless, Levack, Ont. is the hot-bed of mine building in Canada today. More money is being spent developing mines here than anywhere else in the country. Three projects, budgeted at a total of $510 million, lie within 10 km of this quiet, unassuming town nestled in the rolling hills of the north rim of the Sudbury Basin.

Situated within the regional municipality of Sudbury, Levack was built by Inco Ltd. in 1900 as a bedroom community for employees of the Levack mine, one of five mines now operating on the north rim. Nothing is really new in town. (As they have for years, the same two restaurants serve a regular out-of-town clientele at lunchtime.). Yet over the next five years, hundreds of millions of dollars worth of mine equipment will be pouring into the new mines in Levack’s backyard.

Three new producers will ensure the flow of run-of-mine nickel/copper ore that travels south by rail every day to two milling and smelting complexes in Copper Cliff and Falconbridge, 40 km away. (Inco operated a mill at the Levack mine for about 20 years, but it was closed in the early 1970s.)

Two companies (Inco and Falconbridge, the former controlled by Noranda and Trelleborg) have had a monopoly on the checkered pattern of properties here on the north rim since the turn of the century. (Actually, Inco controlled all the ground until the 1950s when Falco began acquiring claims.)

Over the next four years, Falconbridge plans to spend $280 million to develop the 16.5-million-ton Craig orebody, which averages 2% nickel. It is next door to that company’s Onaping mine. And Inco has budgeted a total of $180 million to develop the 50-million-ton East McCreedy orebody (1.7% nickel and 0.8% copper) as well as $51.5 million for the 6-million-ton Lower Coleman orebody (1.99% nickel and 1.3% copper). The two new Inco mines are situated on both sides of Falconbridge’s Strathcona mine. The total level of capital spending on mine development activity is more than the amount spent on the Williams and David Bell mines in Hemlo, Ont. to 1985 (which totalled about $336 million in 1985 dollars, or $400 million in 1990 dollars).

In mid-January, Inco’s Levack area manager John Smith and capital projects manager Meno Friesen showed us the beginnings of the Lower Coleman mine, which will not be operating for another two years. Riding in the shaft bucket, we inspected the 3090 level (levels are numbered by Inco according to the number of feet the level is below surface), where ventilation fans will eventually be installed to draw air into the workings yet to be excavated. Then we climbed down the shaft ladders to the 3290 level where two declines are being driven to intersect the Lower Coleman orebody, 900 metres to the south.

The Lower Coleman is a stringer-type, copper/nickel orebody that has been on the books for about 22 years. Now, on the heels of two of the most profitable years in its history (US$753 million in 1989 and $735 million in 1988), Inco has decided to go after the 5.5-million-tonne, flat-lying, saucer-shaped “plum.” Surface drilling on the property started in the 1940s; the Coleman orebody was discovered in 1954; the No. 1 shaft was sunk in 1966 and the mine operated for 10 years from 1971 to 1981.

“The Lower Coleman orebody was drilled on 200-ft. centres in 1964,” mine geologist Greg Greenough said. Senior engineer Friesen recalls looking at the geological sections when he started with the company in 1967. Since then, countless feasibility studies have been done to determine whether mining would pay off.

“Today, there is a stack of studies a metre high,” mine engineer Rick Godin said.

Last year, Inco conducted an extensive diamond drilling program from the 2750 level of Falconbridge’s Strathcona mine, drilling the Lower Coleman orebody on 100-ft. (30-metre) centres. That information was compiled by geologist Greenough in about three months on a personal computer using Data mine software, developed by Toronto-based Kilborn Ltd. Compiling the data without the aid of a computer would have taken twice as long.

Inco has 360 million tonnes of proven, probable and possible ore reserves in the Sudbury Basin. But this new mine and another (the 45.5-million-tonne East McCreedy orebody, 760 to 1,800 metres farther to the southeast) are Inco’s last large, known, undeveloped nickel/copper deposits in the Sudbury Basin. Reserves in the two mines will furnish ore for 25 years of production. But when fully developed in 1992 and 1996 respectively, they will not add to the company’s flow of ore. Rather, they will supplant ore now coming from two operating Inco mines on the north rim — the 3,800-tonne-per-day Levack and the 2,800-tonne-per-day McCreedy West mines. Those mines now contribute about 20% of the 12 million tonnes of ore treated by the company in Sudbury every year.

(The company’s other large undeveloped ore reserves are in the deep reaches of the Creighton mine and in the idle Garson mine, both on the south rim of the basin. Inco is looking closely at reopening Garson.)

Expanding ore production is not Inco’s ambition. The company couldn’t treat more ore even if it had the mine capacity. A ceiling of 265,000 tonnes of SO per year from the Copper Cliff smelter by 1994, imposed by the provincial government, will dictate how much ore the company treats in its smelter. In the 1990s, the amount of acid-rain-causing gases that go up the stack will determine how much ore the company treats — not how much ore the company has developed, ready to bring to surface. That’s why Inco is spending $500 million to rationalize the milling system in the Ontario division and to construct two oxygen flash furnaces in Copper Cliff (see separate story).

The amount of sulphur in the ore is key to the amount of ore the company handles. Pyrrhotite, a magnetic iron sulphide, is the villain. All ore mined in Sudbury contains more waste pyrrhotite than valuable nickel or copper sulphides. Less pyrrhotite in the ore means more ore can be treated while operating within the limits of SO emissions set by government. On average (in Inco’s Ontario division), the ratio of pyrrhotite to nickel is 14:1. But in the Lower Coleman and East McCreedy orebodies the ratio is slightly higher, at about 16:1. That’s bad news for Inco. But higher-than-average nickel grades should take up the slack. Compared with the 1970s when the company was milling ore averaging 0.7% nickel, millhead grades now average about 1.3% nickel. Nickel grades in the two new mines average 1.9% to 2% nickel. Ore from 10 Inco mines around the Sudbury Basin will eventually all be treated at the Clarabelle mill near Copper Cliff. About 40% will enter a huge new 9.8-metre-diameter, semi-autogenous grinding mill.

Current Development

For now, MacIsaac Mining & Tunnelling is driving two ramps to the Lower Coleman. Access to the development headings is provided through the existing Coleman No. 1 shaft. In 1987-88, MacIsaac extended the shaft to a depth of 1,050 metres from 695 metres. By the mid-1990s, up to 9,000 tonnes of ore will be coming up the 5-compartment passage every day. Active development headings consist of two ramps — one for men, equipment and fresh air plus a smaller one for an ore-handling system. The new openings will service both the Lower Coleman and the East McCreedy orebodies.

“Access, ventilation, compressed air and ore-removal systems will all be shared by the two mines,” explained Art Lauzon, project superintendent for MacIsaac.

The Lower Coleman orebody is 900 metres south of the No. 1 shaft. The East McCreedy deposit lies between depths of 1,100 and 1,400 metres and is 760 metres to 1,800 metres southwest of the Lower Coleman orebody. That geometry together with the checkered pattern of mine properties in the area dictated the layout of mine development.

From the 3090 level, a straight decline measuring 4.9 metres square is being driven by MacIsaac’s mining crews at a grade of 20%. Simultaneously, a much larger decline measuring 7.6 metres wide and 5.3 metres high is being driven (again on a straight azimuth) at a near flat grade of 1.3% from the 3290 level. The two declines intersect at a distance of about 450 metres from the shaft. When MacIsaac mine captain Bill Bardswich gave us an underground tour, the larger access ramp had been advanced about 60 metres past this so-called crossover point and his crews were maintaining an advance rate of about 17 metres per day. Their equipment included two Gardner-Denver 2-boom jumbos (an MK 35 and an MK 120), two Wagner Scooptrams, a JDT 426 truck and two scissor-lift trucks.

“It takes about two hours to muck out an 11-ft. (3.3-metre) round in the big ramp,” Bardswich said.

These openings, which are being driven in hard granodiorite rocks in the footwall of the orebody, should service the mine for about 25 to 30 years. Because of this relatively long service life, only rebar and resin bolts provide ground support, as opposed to end-anchoring friction bolts. Also, galvanized steel wire mesh screen is being installed to Inco specifications. The opening (one of the largest in any Canadian hardrock mine) has been excavated with skill and precision. “Ground control has been good and the opening has good arching,” said Friesen. “It’s a good job.”

Ventilation System

Four 190-kw ventilation fans will be installed on the 3090 level to draw 236 cubic metres of fresh air per second down the No. 1 shaft. A series of ventilation doors and regulators will direct the air down the large cross-sectional access ramp. Another 472 cubic metres of fresh air per second will be supplied through a 5.8-metre- diameter fresh air raise, to be collared this spring. When we toured the mine site in mid-January, Aurora Quarrying and Thyssen Mining Construction of Canada were scheduled to begin the fresh air shaft in May. That opening will be collared on a small hill overlooking Falco’s Strathcona mine. A crew was also drilling and blasting the side of another hill to create a flat working area where the return air shaft will be collared in early 1991. Both of these openings will be sunk by conventional shaft-sinking techniques. The two fresh air streams combined (totalling 708 cubic metres per second) will exit the mine through the return air shaft. The entire system should be operational by 1996.

An Alimak raise, 15 metres in diameter, is also planned; it will provide an escapeway into existing mine workings in the Upper Coleman mine.

Mining Methods

The Lower Coleman orebody measures 360×240 metres and is situated between 995 metres and 1,025 metres below surface. The thickness of the orebody averages 20 metres, and it is as thick as 30 metres in places. Where thicknesses exceed 20 metres, vertical retreat mining (vrm) will be used in a single pass (no pillars). Elsewhere, “longhole uppers” will be used to mine the ore. The split between the two methods should be about 60% vrm and 40% longhole. About 85 operaters and staffers will be employed to produce at the planned capacity of 2,700 tonnes per day in January, 1992.

Final decisions on equipment selection have not yet been made, but mine engineer Godin says most of the main drilling equipment will be electric/hydraulic (6 1/2-inch diameter ith drills and 2 1/2-to 4 1/2-inch-diameter up-holes) and scoops and trucks will all be electric.

For backfill, Inco plans to refurbish the Coleman backfill plant, which shut down in 1981. It is the company’s most modern backfill plant. Gravel will be mixed with cement slurry on surface, delivered underground via a 0.6-metre-diameter borehole and dewatered underground using hydro-cyclones.

Ore-handling System

Ore from the two orebodies will be brought to surface in a unique way. Inco has decided to use at least one long cable belt conveyor, and possibly two (rather than conventional belt conveyors) to bring the ore to the storage bin above the loading pocket. Cable belt conveyors are new to hardrock mines in the Sudbury Basin. The first of two conveyors has been purchased from Cable Belt of Camberley, Surrey County, England. The unit, which is the first in the manufacturer’s pvl’s Series 1000 line of conveyors, is 1,200 metres long. By September, 1990, it will bring development muck up the 20% grade at a rate of about 900 tonnes per hour. (A 70-tonne capacity, unmanned, electric trolley truck, being developed by Inco, is scheduled to go underground for tests at the Little Stobie mine, on the south rim of the Sudbury Basin sometime this year. It will not be proven in time to be used at Lower Coleman.)

When muck starts coming from the Lower Coleman, it will first be dumped into a 1,400-tonne storage bin above the crusher station on the 3480 level, then crushed to minus 20 cm by a refurbished Trayler jaw crusher. The size of the feed opening on this unit measures 96×110 cm. Crushed ore will then fall into a 1,400-tonne storage bin below the crusher and will be conveyed to a 2,300-tonne storage bin to be excavated near the shaft. The conveyor will operate on 1,308 KVA electric power, unique to Inco’s mines. Canadian General Electric is the supplier of the 895-kw DC drive system. Like the new friction hoist, it is equipped with thyristor armature supply.

In selecting the cable belt conveyor, Inco looked at operating units in other mines, such as a 5,200-kw unit in Dofasco’s iron mine in Wawa, Ont. That unit has been carrying fine siderite iron ore to surface since 1976. Cable belt conveyors have their advantages — no idlers, little spillage, little carry-back. In addition, they are fast and may save energy, and the belt will not run backwards if it breaks as it is not in tension (only the cables it runs on are in tension).

The belt will travel at a rate of about 3.8 metres per second and has a carrying capacity of 82 kg of material per metre of belt. Line stands will be installed in the back of the conveyor ramp every seven metres. This compares favorably with conventional belt conveyors, which require idlers every one to 1.2 metres. (The two mines require two access ramps, one for the conveyor and one for men, materials and ventilation; this is because mining law in Ontario dictates that conveyor drifts cannot be used for access.) Inco will also be using new cable technology on the cable belt conveyor. A new Triton cable, galvanized and coated with plastic, has been selected.

“Cable belt conveyors are competitive with conventional belt conveyors for lengths of up to 1,500 metres,” Godin said.

The second cable belt conveyor, which will bring ore from East McCreedy mine up to the crusher, will be even longer (1,430 metres). It is still in the feasibility stage, so the company has not decided whether it will be a cable belt or a conventional belt conveyor. But it should be operating in 1992.

The concrete- and steel-lined No. 1 shaft will be equipped with two 17.5-tonne skips (manufactured by Sala Machine Works of Mississauga, Ont.) operating in balance from the 3220 level. A new 2,900-kW friction hoist with thyristor armature supply, manufactured by Canadian General Electric, has been installed to operate from the greater depths. To take ore south to the mill, a spur line from the main rail line that now terminates at the Levack mine will be constructed to the Coleman headframe and a loadout facility will be erected.

Computerization

Mine offices in the Coleman complex are already highly computerized. But more computerization is planned. Four mine planners now use Lotus and AutoCAD programs on Compaq 386 personal computers with a Hewlett Packard Draftmaster II plotter. A personal computer program called Timeline, marketed by U.S.-based Symantec, was used for critical path and other project management functions. These office computers, and several new ones yet to be added, will all be linked up eventually, Godin said.

Ground control specialist James Willan uses a 3-dimensional numerical modelling software package developed by Inco’s mines research department to model stress concentrations around planned excavations before they are actually excavated. The computer package allows Willan to model the openings in three dimensions then permits him to select a plane at any location and orientation. Stress concentrations and factors of safety on that particular plane are calculated by the computer and these values are displayed on the computer screen in color-coded graphics. If stress concentrations are unacceptable, the design is changed.

By 1992, computerization will extend underground as well. A sophisticated monitoring system will watch a plethora of underground operations, as is done at the Creighton mine. The hoist, skips, conveyors, crusher, pumps, ventilation fans and doors and even the sandfill system will all be fitted with programmable “logic controllers” connected to the fibre optic “data highway” and monitored and controlled by a master computer on surface. This technologically sophisticated mine management system should make the Lower Coleman/East McCreedy operation one of the most productive and safe mines in Inco’s Ontario division.