FALCONBRIDGE IN SUDBURY: FRASER: STILL A CONTENDER

It has always been the case at the Sudbury operations of Falconbridge that one mine bore the brunt of the production load. It was so in the beginning with the original mine at Falconbridge, where the smelter and the first concentrator were situated. And it has been the case through the intervening years. The Strathcona mine, for example, was the production mainstay through the late 1970s and early 1980s. Then came the Fraser mine on the northwestern rim of the Sudbury Basin, which, at 970,000 tonnes per year, is still the biggest single nickel-copper ore producer for Falconbridge. But, like its predecessors, the Fraser will soon be eclipsed by a new production leader, the Craig mine (see preceding story). Nevertheless, Fraser still has a decade or more ahead of it.

The Fraser mine sits between two Falconbridge producers — the Fecunis/North mine, now mothballed, and the Strathcona. However, Inco claims are immediately adjacent to Fraser, which has led to co-operation between the two nickel miners.

For example, Fraser production is extracted from two distinct areas. The first is called the Fraser Exchange, which lies on the Fecunis side to the northwest. The second is Fraser Depth, situated on the Strathcona side to the east. The Fraser Exchange (also known as Nos. 1 and 2 zones) is the up-dip portion of Inco’s McCreedy East deposit. An ore exchange was negotiated with Inco in the late 1970s to facilitate mining of this deposit. Falconbridge mines everything above the 34 level, while Inco mines the Fraser Exchange ore below 34. A horizontal (rather than vertical) split meant less development and, therefore, cost savings on both sides of the boundary. Inco inspects the timber mat on 3400 to ensure it conforms to its specifications. The Fraser Exchange, which is strictly in a pillar recovery mode now, dips 80deg south along a strike length of 390 metres and is up to 120 metres wide. Roughly 60% of total production originates above 34 level.

Because of its proximity to existing shafts, the Fraser has never enjoyed a true production shaft of its own. Originally sunk for exploration and development, the 1,600-metre (5,250-ft.) Fraser No. 1 shaft in use today provides man access and services. Its 10-tonne skip also hoists waste rock to surface. Back in the early 1980s, most of the production was trammed west along the 3600 level to Falconbridge’s Fecunis shaft about 4,500 ft. (1,372 metres) away. “That served us well until mining had reached 3600,” said mine captain James Nerpin, who along with planner Wayne Jeffkins, conducted an underground tour for The Northern Miner Magazine. However, Fraser Exchange ore and muck from several zones in Fraser Depth are now fed through orepasses to 4600 level and trammed about 6,000 ft. (1,830 metres) east to the Strathcona shaft. The 10-cubic-metre ok cars dump off a monorail.

The train of 11 cars that haul along 36 level to the ok dump is pulled by two 13-tonne Goodman locomotives. Because of slave/master controls on the locos, one person can operate both locos from the lead loco during loading. Airram rockbreakers by Kent Air are on the 34 and 44 levels. Falconbridge plans to install three or four breakers, all controlled remotely by one operator whose visual contact will be cameras and a video screen.

During our visit, the main orepass linking the 46 level with the western mining zones above 36 level was being rehabilitated. The orepass cuts through the hangingwall norites, which generally pose ground control problems, said Ian Clegg, ground control supervisor. “This rock has an unravelling tendency with weak joints,” he said. “There is no cohesion.” Added mine geologist David Owen: “The norite is fractured, jointed and blocky. The late granite breccia in the footwall is high in quartz and will store energy. So you can get violent releases under stress, which is typical of Sudbury North Range orebodies.”

When deterioration in the orepass was first detected, Falconbridge built a 4-wheel aluminum buggy outfitted with two video cameras and a range finder. Clegg sent the remote-controlled contraption down the orepass for a visual inspection. The repair was effected by “bird-cage” cable bolts. Intermittent bulges resembling bird cages bind the grouted cable to the rock.

Mine production is split between cut-and-fill and blasthole. Above the 36 level in the Fraser Exchange, transverse blasthole stoping, mechanized cut-and-fill, and the occasional long-hole stope provide a continuous flow of ore from a short ore strike length. The transverse stopes were designed 10 metres (33 ft.) wide, with 8-metre (26-ft.) pillars. Sub-levels are typically 20 to 25 metres (66 to 83 ft.) apart. The bulk of blasthole production now derives from secondary and tertiary stopes (pillars). The remaining 25% comes from “longitudinal” and longhole upper stoping.

A new Tamrock Datasolo drills both 4-inch uppers and downholes on a 2.5-metre-square pattern. The Datasolo is accurately drilling up to 24 metres. “It took a little while for us to get used to the machine,” said Nerpin, adding that they are not yet fully utilizing the machine’s automated drilling capabilities. “But the Datasolo was definitely the way to go.” The Datasolo was chosen not only for its automated tube handling, but also for its accuracy and reach, allowing operators to collar holes in back heights of up to five metres.

Mechanized Ramp Access

One Ingersoll-Rand ITH drill still remains from the old fleet. It is used when required to fulfill scheduled blasthole tonnages. Both Tamrock and Gardner-Denver longhole machines drill 2-inch holes for cable bolts. Development work is done by Gardner-Denver 2-boom electric hydraulic jumbos drilling with HPR-1 drills. In about three years, all the ore amenable to blasthole methods will have been removed.

The four mining zones below 36 level are mined entirely by cut-and-fill (as are two of the lower ore zones above 36). The method employed is formally called “mechanized ramp access, post-pillar cut-and-fill.” It allows for selectivity and flexibility, two vital characteristics in mining these erratic ore zones that dip anywhere from 0deg to 35deg in the lower levels. For ground support, the stopes are pre-pinned. For example, after the sill cut, cable bolts are inserted up to Cut No. 4. When the third cut is mined out, cable bolts are secured up to Cut No. 6 and so on.

The entire range of load-haul-dump machines at Fraser and other Falconbridge mines is under review. An aging fleet at some of the mines prompted the study, which will try to define which sizes and makes are best for which applications. This is occurring at Fraser and the other mines. At Fraser, the mine has several Jarvis Clark JS-800s and JS-500s, a JCI 6-cubic-yard LHDS and several Tamrock Toro 500Ds. Operators have also been impressed with the speed and manoeuvrability with which an Elphinstone scoop loads trucks.

Cross-cutting Fault

The cut-and-fill ore zones are intersected by a major fault, which runs through the main ore zones at Fraser, blasthole stopes included. “It is a large, cross-cutting fault,” said Clegg. “We call it No. 2 fault. It has been active from surface to depth.” In the cut-and-fill zones, 11-metre-wide panels and slots with 5-metre-square post pillars have been incorporated. This is modified to a 9-metre-wide panel with a 5-metre-wide rib pillar when mining advances to within 10 metres under the fault.

Throughout the mine, ground support is prevalent. All backs are screened and bolted, as are the walls, to about six to eight feet down from the back. Falconbridge has initiated an in-house project undertaken to design a system that can bolt and screen without exposing the operator to an unsupported back.