Red Lake Gold Mines
Rivals since 1949 when they began pouring gold, the Campbell and the Red Lake mines have at different times each been called the “world’s richest gold mine”. Now a single owner, Goldcorp Inc., is combining the adjacent operations in Balmertown, Ont., reducing costs and nearing its 1-million-oz/year target.
Combining two mines, mills, cultures and workforces that have fostered a rivalry for over 50 years does not happen automatically. Red Lake Gold Mines (RLGM) mine general manager Dan Gagnon said the cultures are melding. “We are slowly growing together. This is a small town of 4,600 people and they see each other at the rink and the bank, so they talk about what is happening and this helps with integration.
“Everything at Campbell and Red Lake used to be done separately and differently. We’ve had to look at everything and choose the best options to go forward, and this by taking the best of both worlds.” The two mines and mills had differing wage and benefit packages, differing approaches to labour (contract vs. full-time employees), and in the warehouse commonality extended to only 11% of the parts and supplies.
Now, as the Red Lake complex and Campbell complex come together under the same management, plans call for gold output to be 786,000 oz in 2007 (70% from Red Lake and 30% from Campbell). By 2011 that number will reach 1.0 million oz, thanks to continuing production efficiencies and the superior exploration potential of the Red Lake camp.
US$26-million exploration budget
Goldcorp has drawn up a US$26-million budget for exploration this year in the area of RLGM. With that investment the company plans to keep 15 rigs busy with 180,000 m of drilling and complete 610 m of underground exploration development. Targets have been chosen in five key areas.
High Grade zone (HGZ) and footwall sulphides in the Red Lake mine
The HGZ is a particular priority because grades are going up as drilling goes deeper. The HGZ above 37 level averages 51.4 g/t (1.5 opt) Au, and between 37 and 47 level averages 115.9 g/t (3.4 opt) Au. Proven and probable reserves at the end of 2006 to the 47 level totalled 1.4 million tonnes grading as high as 99.5 g/t Au. In terms of contained ounces, the HGZ has 3.6 million oz in reserves. Drilling has outlined resources containing 1.4 million oz from 47 to 49 level. And the mineralized zone is known to extend below 51 level.
Parallel to the HGZ runs the footwall sulphide zone interpreted as a group of five separate zones. The sulphides have a geometry ideal for longhole development. Their location between 27 and 37 level will reduce reliance on extremely deep ore sources as mining reaches these zones in 2008 and 2009. Sulphide reserves identified below 30 level total 969,000 t with an average grade of 8.4 g/t Au. Drilling continues from the 34 level.
Deep Campbell (DC) and related zones
The DC zone lies below the 41 level of the Campbell mine. Not only are high gold values being intersected, but the zone is very continuous and open both below 50 level and to the west. Reserves have been calculated in the DC and DCE zones as 390,000 t grading 19.9 g/t Au (0.6 opt) Au, and resources in the PCB and TP zones are 3.7 million t grading 9.9 g/t Au. Between the 41 and 48 levels, these structures may contain over 1.2 million oz of gold. Exploration drilling continues from the 4199 hanging wall exploration drift.
Party Wall opportunities
Combining the Red Lake and Campbell mines under one owner has the obvious advantage of allowing development of the Party Wall area. This is the undeveloped no-man’s-land between the two mines when mining ceased at the property boundaries of the respective owners. The Party Wall will no longer be a data void; Goldcorp is outlining resources in the area in preparation for mining from the Campbell workings.
Drill-testing the Party Wall from 19 to 25 level has outlined a resource of 204,000 t grading 13.4 g/t (0.39 opt) Au in the E and F zones. The drilling program will now test the west extension and down dip to 29 level.
Red Lake Complex (RLC) sulphides
The RLC sulphides, last mined in 1966, lie near the surface and are accessible from the Campbell workings. By reinterpreting the geological model, Goldcorp’s geologists believe the multiple zones include a million ounces of minable gold. From surface to 30 level the zones contain reserves of 620,000 t grading 15.1 g/t (0.44 opt) Au and resources of 1.6 million t at the same grade. Plans are being made to mine these sulphides again, as a means of reducing dependency on extremely deep ore resources. Mining is scheduled to begin in 2008 using mostly longhole stoping methods.
Various surface targets have been chosen between the Reid shaft at the Campbell mine and the No.1 shaft at the Red Lake mine. A previously unknown vein has been drilled and a test pit was worked last summer. The open pit concept will be aggressively tested in 2007, and if a new pit is to be built at the RLGM, this would be a first in the area.
The Red Lake gold mine was the first Goldcorp producer. It operated as the “poor sister” to the extremely high-grade Campbell mine until Goldcorp developed the HGZ at depth in preparation for reopening after a long labour stoppage. And “high-grade” is the name for reserves topping 3.0-opt Au.
The developed area includes a production shaft (No.1) to 1,023 m (1 to 23 level) and an internal winze (No.2) from 23 level to 38 level. No.3 shaft reached its planned depth of 1,924 m in January 2007. The new shaft will provide more hoisting and ventilation capacity, hence increasing the mining rate from 2,350 to 3,100 t/d, of which 40% is ore. A main access ramp connects workings from 21 level to 42 level, and the ramp will eventually reach 50 level.
Mining is mostly cut-and-fill, both overhand (37%) and underhand (40%). Other ore sources are pillar recovery (8%) and longhole stopes (15%). Muck is hauled to ore passes on 34 and 37 level with load-haul-dumpers (LHD) ranging in size from 0.75 to 2.7 m3. Ore is hauled on 38 level by train to the bottom of No.2 shaft, hoisted to 23 level, and skipped to the surface using either of two 5.5-t skips in No.1 shaft.
The Campbell gold mine is a recent addition to Goldcorp’s list of producers. Goldcorp bought the mine in 2006 from Barrick Gold as part of the Barrick takeover of Placer Dome and its subsequent sell-off of selected assets.
The Campbell shaft has been deepened four times, reaching 1,316 m and servicing 27 levels. In 1999 construction began on the Reid shaft 150 m to the west. It was sunk to 1,819 m and opened up deep ore sources including the DC zone. A ramp has been driven from the 39 level at the bottom of the Reid shaft to the 45 level and provides a drill drift from which the ultimate depth of the DC zone is being tested.
A variety of mining methods are used in the Campbell mine. Down to the 27 level, a combination of mechanized diesel equipment and tracked haulage is practised on every level. Below 27 level all mining is trackless. This year plans call for mining 532,000 tonnes of ore from longhole (65%), cut-and-fill (30%) and development (5%) stopes. Ore is hoisted through the Reid shaft.
Combined hoisting capacity for the two mines will rise to 8,100 t/d in 2008 from 6,000 t/d this year.
Along with two mines, Goldcorp operates two mineral processing plants. Both are built around conventional crushing, grinding, gravity recovery and carbon-in-pulp (CIP) flowsheets.
The original Red Lake mill was built in 1948 and was replaced by a new facility in 2000. Throughput at the new mill is ramping up to 1,250 t/d by the end of July 2007. The mill consists of three distinct parts: two-stage crushing; gravity and CIP circuits followed by electrowinning or autoclaving; and a paste backfill plant.
The gravity circuit (a ball
mill, two Knelson concentrators and Diester table) recovers about 55% of the gold, making a 75%-Au concentrate that is directly smelted. The CIP circuit recovers approximately 34% of the gold. Slurry is leached in four tanks, passes through the CIP circuit, and the pregnant solution reports to a pair of electrowinning cells. The precipitated gold-bearing sludge is directly smelted.
The Red Lake mill also produces a bulk sulphide concentrate using a conventional flotation circuit. It is shipped to the Campbell mill to be autoclaved. About 9% of the gold is recovered from this portion of the ore.
The Campbell mill treats both free milling and refractory gold ore at a rate of 1,850 t/d. Run-of-mine ore is crushed in three stages to 19 mm and then enters a two-stage rod and ball mill circuit. The slurry is pumped to a bank of eight cyclones, the overflow going to the flotation circuit and the underflow going to the ball mill. A pair of Knelson concentrators and shaking tables recover approximately 40% of the gold by gravity means.
The cyclone overflow reports to a bank of seven Denver DR-500 rougher cells, and the resulting concentrate enters a bank of four Denver DR-100 cleaner cells. Cleaner tails are recycled back to the roughers at the head of the circuit. Flotation tails are thickened, with the underflow being sent to the leaching circuit and the overflow to the process water tank.
Thickened flotation concentrate feeds the pressure oxidation circuit. Pressure oxidation replaced the antiquated roaster circuit in 1991. After pre-treatment, the slurry flows by gravity through five chambers in the autoclave. This is a 2.8-m-long by 12.2-m-diameter vessel that operates at 2,100 kPa and 190C sustained by the exothermic nature of the chemical reactions. Designed slurry retention time is two hours.
Depressurized and slightly cooled slurry leaving the autoclave passes through a two-stage CCD wash circuit. The CCD second wash underflow is transferred to the carbon-in-leach (CIL) circuit. The oxidized slurry undergoes cyanidation and carbon adsorption in a pair of tanks, each having a retention time of 48 hours.
The leached concentrate from the second CIL tank is combined with thickened flotation tails and further treated in a carbon-in-pulp (CIP) circuit. It consists of six tanks, each having a slurry retention time of 50 minutes. After the carbon is stripped, the pregnant solution enters the electrowinning cell.
In the refinery, gravity concentrate and EW sludge are melted together in an induction furnace. The dor bars average 92% Au and 6% Ag.
Combined capacity for the Red Lake and Campbell mills will be 3,100 t/d by mid-year. Recovery rates are approximately 97% of the gold in the Red Lake plant and 95% in the Campbell mill.
With the one-million-oz/year target clearly within range, Goldcorp’s RLGM is exhibiting the best of both worlds: the high-grade (45.0 g/t Au), low-tonnage Red Lake mine and the high-tonnage, lower-grade (12.0-15.0 g/t Au) Campbell mine. The company is fortunate to have two proven producers and a host of exploration potential in one of Canada’s richest gold camps.