If Seven is a lucky number, imagine how lucky Triple Seven can be. It was drill hole No.777 that first intersected the orebody that gave Hudson Bay Mining & Smelting Co., Limited (HBMS) new life in Flin Flon, Man. It was lucky that the discovery was made near the copper and zinc plants and at a time when other nearby orebodies were nearing depletion. While luck certainly has its place in finding mines, it is sound management and a clear vision that results in a successful development.
The 777 mine, owned 100% by HBMS, is the final piece of a much larger project. The company committed five years and over Cdn$400 million to the 777 Project. The plans called for an expanded concentrator, environmental improvements for the copper smelter, throughput and productivity improvements at the zinc refinery including a new state-of-the-art cellhouse, and the development of two new mines–Chisel North and 777(see sidebar).
Production on time and budget
Commercial production at the 777 mine was reached in January 2004, several months ahead of schedule and on budget. Development costs of this 1.0-million- tonne per year copper and zinc mine was approximately $200 million.
The 777 deposit lies near the metallurgical plant in Flin Flon. It consists of two massive sulphide lenses and associated stringer mineralization overlying a thick rhyolite package. These lenses extend 600 m along strike and lay between 850 and 1,500 m below surface. Minable reserves total 14.3 million tonnes, and drilling is expanding that amount. The average ore grades 5.3% Zn, 2.5% Cu, 2.2 g/t Au, and 31.2 g/t Ag. The 777 deposit lies beneath the town, close to the existing Callinan orebody and the original Flin Flon deposit.
The vertical shaft was collared in 2000, about 500 m from the current mining areas of the existing Callinan mine. J.S. Redpath was awarded the approximate $60-million contract for shaft sinking and lateral drifting on the 690-, 1082-, 1262- and 1412-m levels as well as the 1508-m level ramp to shaft bottom at 1,534 m. The shaft is concrete-lined, 6.7-m in diameter, and contains two ore skip compartments, a compartment for a double-deck main cage, and a Mary-Anne auxiliary cage for occasional personnel use. The shaft has been designed so that it can be deepened to 2,000 m.
There was an “interesting” aspect that HBMS’s projects superintendent, Carlos Morao, told CMJ. Since certain drifts intersected the orebody, prior to completion of the underground crushing facilities, the company developed a plan to extract early ore concurrent with the development activities. A portable surface crusher was installed and approximately 60,000 tonnes were mined during a six-month period before the underground ore-handling facilities were completed, allowing for an early cash flow from the mine.
HBMS adapted a method of cantilevered shaft conveyance supports developed by Anglo American, HBMS’s parent company. Rather than having all horizontal steel beams anchored in the shaft walls, only the main cage members are attached. The members holding the skip guides are cantilevered from the main beams, stopping short of the wall. This is the first time this method of cantilevered guides and steel sets with 6-m spacing has been used in North America (see also CMJ June/July 2002). The shaft steel was assembled using a huck bolt system allowing for a quicker assembly, and HBMS believes that this connection system is also a first for North America. The supplier of the shaft steel was Mine Steel Fabricators.
The placement of the shaft, close to the Callinan underground workings, also allows ore from that deposit to be hoisted up the 777 shaft. The existing Callinan ore deposit, which will be exhausted in a few years, provides 25% of the total ore hoisted at the 777 mine.
The mining method of choice initially is cut-and-fill, with blasthole stoping and delayed fill being also used as the mine develops. Faces are drilled using Atlas Copco two-boom jumbos and blasted with a special emulsion from Western Explosives that reduces the risks associated with sulphide dust ignition. A fleet of six Toro 1400 6-m3 load-haul-dumpers transports the muck to the ore passes. Where haul distances dictate, 40-tonne Toro trucks are used for both ore and waste hauling. Mining rates are currently at 3,000 tonnes per day from the combined Callinan and 777 deposit.
The automated ore-handling system went into service on Dec. 1, 2003. All phases of ore movement are integrated, from the ore passes, through the 1,200- x 1,500-mm Birdsboro-Buchanan jaw crusher manufactured by PR Engineering, across a conveyor to a loading pocket and into a pair of 16-tonne skips, hoisting, and dumping to a surface bin. A Modicon control system oversees the ore-handling. From the surface bin, ore is trucked approximately 3.0 km to the concentrator. The production and service hoists were built by Hepburn Engineering and originally installed at the Stanleigh uranium mine in Elliot Lake, Ont. The skip hoist is a 5.0-m-diameter, 4,100-kW unit, and the cage hoist is 4.25-m in diameter with a 1,300-kW motor.
Satellite maintenance shops and permanent fuelling stations have been established on the 1262- and 1412-m levels.
Ground conditions in the 777 mine vary but are generally good, said Morao. The worst conditions occurred in the 1412-m level drift for approximately 100 m where 100% screening and shotcrete were applied in addition to the standard ground support of resin rebar; cable bolting was also required. There have been no major problems with water. Results from a probe hole drilled the length of the proposed shaft were examined to check rock stability and presence of water during engineering before shaft sinking began. The water that accumulates in the mine is removed in two stages–from the 1508-m level to the 690-m level and from 690 to surface using Mather & Platt pumps. Slimes are collected in cones at the 1465-m level and processed using a filter press, with the dry cake being fed into the fine ore bin.
The underground facilities were designed by McIntosh Engineering. The engineering of the headframe and hoisthouse were provided by GL Tiley.
HBMS has chosen paste backfill for the 777 mine to achieve high ore extraction by eliminating pillars. Stope cycle times are also improved, facilitating high production tonnage. Partially cycloned mill tailings are mixed with portland cement and pumped into the mine at a rate of 80 m3/hour. The paste backfill plant was designed by AMEC.
The ventilation of the 777 mine is “straightforward”, noted Morao, based on the levels of diesel equipment exhaust dilution required in the drifts and headings. Fresh air enters the shaft through two Alphair 260-cm vane axial fans at a combined rate of 330 m3/second. The exhaust fan is a single Davidson 4.3-m centrifugal model.
All considered, the 777 mine development created an economical source of ore for HBMS’s Flin Flon copper and zinc plants. But it is more than that. It is also the culmination of a farsighted strategy that is going to pay dividends to employees and investors for many years to come.
The 777 Project
The 777 mine cannot be viewed in isolation. It is only the last and key part of the larger $400-million-plus 777 project. The project encompassed two new underground mine developments, a 15% increase in zinc production, reduced environmental discharges, reduced operating costs, labour stability, and a business plan through 2016. When the green light was given for the 777 project in the fall of 1999, it marked the start of a remarkable turnaround for a company that would have otherwise faced closure before 2004.
HBMS decided to provide direct management of the project using its own project control systems except for the zinc plant expansion, which was awarded to SNC-Lavalin on an EPCM basis. Engineering of other sub-projects were performed by specific firms as was construction, which involve
d both local Flin Flon area contractors and major construction companies.
Chisel North Mine. The Chisel North zinc deposit is located near the reopened Snow Lake concentrator, 225 km east of Flin Flon. Three ore zones are reached by decline, built by a team of HBMS employees who bid on and won the development contract. Production began in 2000 and is now at 800 tonnes/day. Ore is recovered by cut-and-fill, then trucked to the surface in 50-tonne trucks. Reserves are estimated at 3.0 million tonnes (sufficient for production until 2013) at grades averaging 8.4% Zn.
Flin Flon Concentrator Expansion. Capacity at the Flin Flon concentrator was expanded 20% to 2.18 million tonnes from 1.81 million tonnes per year. Work was done to modify ore receiving and storage, to boost crushing capacity, to rationalize the grinding circuit including the addition of a new Nordberg ball mill, and to expand flotation capacity. Two high-capacity Westech thickeners were also installed separately from the 777 Project to replace the conventional thickeners that had been in service since the 1930s. SNC-Lavalin was the engineering contractor for the concentrator expansion project.
Zinc Plant Expansion. To boost zinc production to 114,000 tonnes of cast metal annually required building a new electrolytic cellhouse. The technology of Asturiana de Zinc was chosen for the first time outside Spain. Asturiana supplied automated electrode cranes and cathode stripping machines (both manufactured by Aisco) and a ventilation system and solution cooling system (both supplied by Desom). At 3.6-m2 the cathodes (from Limpact) and anodes (from Asturiana) are the largest ever installed. Relatively minor changes were made to the two-stage zinc pressure leach plant and solution purification. Full eventual capacity of the plant will be 128,000 tonnes of zinc annually. PCL, Alto and Empire Iron Works were the main construction contractors.
Copper Smelter Spill Gas Project. Ground-level fugitive gas from the reverberatory furnace and converters has been cut 90% from the amount released before the 777 project began. The temperature of converter off-gases is reduced by passing the gases through new water-cooled (Drummond) hoods followed by adiabatic water spray chambers. Both converter and furnace gases pass through a new electrostatic precipitator (supplied by Environmental Elements) before discharge through the existing 256-m stack; the maintenance-intensive baghouse was eliminated. HG Engineering performed engineering for the project.
777 Project Infrastructure. The big-ticket item of the infrastructure project was a new 90-MVA electrical substation (by ABB) that supplies the 777 mine and the new cellhouse.
777 Mine. This is the new 1.0-million-tonne per year copper/zinc mine developed near the Flin Flon metallurgical plants. This project also included a 2,000-m3 office/changehouse complex.
These projects provide the foundation of HBMS’s business plan that it hopes to extend from 2016, based on currently known reserves and resources, to 2027 and beyond.