When geologist Howard Stockford thinks about the major new copper-zinc discovery made by Aur Resources in Val d’Or, Que., a broad smile breaks across his face. It’s not hard to appreciate why. The Aur geologist is basking in the limelight of the biggest base metal discovery of his career, and quite likely the base metal find for years to come.
After nearly 30 years as a geologist, 13 of which were spent at Falconbridge, the 48-year-old Stockford is experiencing the excitement of discovery, the shear thrill that comes with finding an elephant — a huge base metal deposit of the type most geologists conjure only in dreams. And no matter how a lawsuit between Aur’s partner in the find, Societe Miniere Louvem, turns out, Stockford’s role in the discovery should be assured.
Stockford graduated with an honors degree in mining geology from London’s Royal School of Mines in 1962. After landing his first job as a junior geologist at a Quebec gold mine, he immigrated to Canada. Since then, his professional career has taken him to mining projects in Botswana, Canada, Finland, Guatemala and Norway. In the 1960s, he worked at various gold and base metal mines in the Malartic and Bachelor Lake areas of Quebec, and joined Falconbridge in 1970, becoming chief geologist for Canada-wide exploration in 1981. He left Falconbridge to take up his present post as vice-president of Aur Resources in 1983.
The highlight of Stockford’s career so far is his role in the Aur/Louvem discovery. There is no current base metal production at Val d’Or, although there were four previous copper-zinc producers — the East Sullivan, Manitou Barvue, Dunraine and Louvem mines. The rock formations around Val d’Or are better known for the gold bullion they turn out than for the copper and zinc they contain.
So last summer’s announcement of the Aur/Louvem discovery caught many in the industry by surprise. “This new discovery will change the mining image of the Val d’Or camp,” Stockford told The Northern Miner Magazine. He added that many companies already have begun to re-orient their exploration efforts in the area towards base metals. Discovered in mid-1989 by Aur’s exploration team of four geologists, the Louvicourt Twp. find is big, probably the biggest of its kind found in central Canada since Kidd Creek in the mid-1960s. However, Stockford cautioned: “It’s very difficult to rank our discovery right now. We don’t have any holes below 2,500 ft. and we’re still at a very early stage.”
The deposit, at depths of more than 2,000 ft., is on the southern half of a property shared 50/50 by Aur and disputing partner Louvem. The partners are embroiled (as this publication goes to press) in a legal battle over the project, while senior companies Noranda (a Louvem shareholder), Teck and Cominco (Aur) now hold major stakes in both juniors.
Legal squabbles aside, the Aur discovery offers a classic exploration “case history” and clearly illustrates how geological concepts guided by high-tech exploration tools can lead geologists to modern mother lodes. With the exception of Aur’s recent work, no significant exploration for base metals had occurred in the Val d’Or area since the Louvem mine closed in 1981. Preliminary estimates for the Louvicourt deposit exceed the combined tonnage mined previously from Val d’Or’s four past-producing base metal mines. Collectively, the mines extracted more than 30 million tons of copper-zinc ore, with the East Sullivan and Manitou Barvue mines accounting for most of it.
Aur estimates the Louvicourt deposit contains at least 36 million tons averaging 3.11% copper, 1.34% zinc, 0.55 oz. silver and 0.025 oz. gold per ton, using a 2% copper or 4% zinc block cut off and tonnage factor of nine cubic feet per ton. If grade proves to be higher than expected, then using a 4% copper or 6% zinc block cutoff and a tonnage factor of eight cubic feet per ton, there are 17.4 million tons at 5.64% copper, 2.27% zinc, 1.05 oz. silver and 0.044 oz. gold per ton. These calculations are based on widely spaced drill intersections (in about 30 holes) and obviously are not proven mining reserves, yet. Additional infill drilling and exploration below the 2,500-ft. horizon is planned.
For comparison, the prolific Noranda camp hosted massive sulphide deposits totalling about 114 million tons with an average grade of 2.14% copper, 1.37% zinc, 0.59 oz. silver and 0.12 oz. gold per ton. That tonnage came from 19 deposits, 85% of them situated within 16 km of the big Horne deposit.
“It’s a very moving experience to find a major deposit of this size,” Stockford said. But he’s quick to spread credit for the discovery to other members of Aur’s exploration team. “I’d like to emphasize that this discovery was a team effort.” Stockford gives special praise to the company’s team of geologists in Val d’Or, including Don Bubar (now exploration vice-president) and George Mannard (senior project geologist). “Jim Gill (Aur president) and I also like to think we played a small part,” he added.
Geologists Bubar and Mannard were both on site when the discovery holes were pulled from the ground last June. Bubar says he will never forget June 1. On that afternoon, he and Mannard decided to visit the drill site to see if the target zone (now called the Aur horizon) had been reached. “Spectacular copper sulphides glittered in the summer sunlight as we peered into the open box of drillcore,” he recalled. The core had just been pulled from deep below surface.
Noise from the drill rig made conversation impossible, but they both knew the copper-rich rock in front of them was about to change their lives. “We were sure we had a big deposit on our hands,” recalled Bubar.
Assays from the copper-rich section of hole 42 confirmed Bubar’s visual inspection by yielding 29 ft. grading 11.8% copper. The high-grade section occurred within a 117-ft. interval averaging nearly 5% copper. Some individual samples from that hole assayed as high as 21.9% copper. Incidentally, the discovery hole in 1968 from the former Louvem copper mine, (one mile west of the Aur discovery) assayed 6.5% copper over 110.3 ft. The Louvem mine closed in 1981 after a 10-year production life.
Meanwhile, far from the swamps of Val d’Or, Stockford, who was soon to gain fame for a base metal find, was at an investment gold show in Boston. Bubar later reached him at his Toronto home with news of the copper-rich drill core. Stockford arrived in Val d’Or as excitement of the new discovery grew. More spectacular drillcore rolled in from hole 44 and assays confirmed a major deposit was in the making.
“Hole 42 got the ball rolling, and hole 44 really convinced us we were on to something big,” explained Bubar. Assays from the latter hole yielded an impressive 141.5 ft. grading 2.8% copper, 5.7% zinc, 2.04 oz. silver and 0.10 oz. gold per ton. The company officially announced the discovery assays on June 12, 1989 and, predictably, share prices of Aur and Louvem quickly headed skyward on the Montreal and Toronto stock exchanges.
Both Bubar and Stockford say neither of them could think of much else in that first week of June except drill core, assays, and the new discovery. With the initial discovery period behind them, the geologists are now working to drill off the deposit and come to grips with its geometry. So far, Aur has determined that the deposit lies along a newly recognized “exhalite” zone (called the Aur horizon), 600 ft. south of the past-producing Louvem mine horizon. Although the mineralization is highly conductive, the Aur deposit was too deep to be easily detected by surface or airborne electromagnetic survey methods.
Aur’s sulphide zone, which locally exceeds 300 ft. in thickness, exhibits classical metal zonation common to most major base metal deposits. “The geological setting of the deposit is typical, in many ways, of the classical Noranda or Kuroko-type deposits,” Stockford explained to a Toronto meeting of the Canadian Institute of Mining and Metallurgy late last year.
Based on scientific research, geologists have developed sophisticated models which help ex
plain the origin of most volcanogenic massive sulphide orebodies. Base metal deposits like Aur’s are thought to have formed billions of years ago around active felsic volcanic centres. During formation, hot metal-laden springs from submarine vents spewed on to ancient seabeds while hydrothermal fluids altered the surrounding rocks. The ore deposits were later “capped” by subsequent volcanic flows. A somewhat similar modern-day process operates at oceanic “black smoker” sites, where the Earth’s major tectonic plates meet.
According to Stockford, the Aur zone is hosted by a unit of fine ash tuffs and laminated cherty tuffs, exhibiting strong chlorite alteration. The zone dips at an average of 70^o (deg) to 80^o (deg) to the north. “Our knowledge of the geology of the new deposit is steadily improving, but many of the details remain to be worked out,” Stockford explained. Ongoing exploration work is focusing on tracing the down-plunge easterly extension of the deposit. He noted that while the discovery came as a surprise, the base metal potential of the Louvicourt Twp. property had been recognized by Aur as early as 1987. The property’s previous production history and favorable felsic volcanic rocks in the area were strong clues. During first-phase exploration, Aur’s geologists realized that the former Louvem mine horizon below 1,500 ft. was a blank. No one had explored there.
“A review of the data for the Louvem mine area revealed that no deep drilling had ever been done to test the depth potential,” said Stockford. The data review involved exhaustive compilations of previous work and included updating the geophysical information by magnetic and electromagnetic surveys over the entire property.
Since the Aur horizon doesn’t outcrop at surface, the new deposit is considered a “blind discovery” found through systematic exploration. Of particular importance was Gill’s willingness to commit money for expensive, 2,000-ft. drillholes based solely on a geological concept. In interviews, none of the four Aur geologists would take sole credit for devising the initial plan to do risky deep drilling. They all agreed it was a group decision. “We knew we needed to find a large deposit to make money at 2,000 ft. or more below surface,” Stockford said. “The 1,000-ft. spacing between the holes ensured we wouldn’t miss an elephant.”
As part of the phase-2 work, the geologists conducted systematic testing of the former Louvem mine horizon at depths of 2,000 ft. with holes spaced 1,000 ft. apart. Lithogeochemical analysis of core was carried out to study alteration patterns, and, where possible, the holes were logged geophysically with borehole induced polarization or pulse electromagnetic surveys to locate off-hole sulphide zones. An important breakthrough came during the phase-2 program, completed in February, 1989. This breakthrough was the identification of a large alteration zone in hole 30, drilled beneath the former Louvem No. 6 zone.
The hole intersected bands of pyritic sulphides over a width of about 100 ft, followed by a broad interval of stringer chalcopyrite mineralization accompanied by intense black chlorite alteration containing 0.84% copper over 386 ft. (Current geological theory recognizes that such chlorite alteration zones were created by ore- producing events.) Aur geologists immediately recognized the significance of hole 30. The hole intersected a large alteration pipe which could be a feeder to a massive sulphide body somewhere in the area. It was like following smoke to find the fire.
Here’s where two other important discovery tools enter the picture. “A borehole pulse em survey in hole 30 indicated strong, off-hole conductivity in the lower part of the hole accompanied by an unusually strong lithogeochemical alteration signature,” Stockford explained. Rock geochemical trends accompanied the intense alteration. Magnesium and potassium were found to be enriched, while sodium and calcium showed depletion. Strong enrichment of alumina was also a characteristic, he said. “The alteration indicated that a major new hydrothermal vent system was present in the area around hole 30.”
Armed with those encouraging signs to follow up, a phase-3 program was launched in April last year. The first couple of holes hit extensive copper stringer mineralization and convinced them to focus more attention on the Aur horizon as a top-priority target. Holes 42 and 44 finally intersected 117 ft. of 11.8% copper, and 141.5 ft. of 2.8% copper with 5.7% zinc. “This confirmed that we had a major discovery on our hands,” Stockford said.
Reviewing the discovery process, he emphasized three key tools used in the company’s systematic approach to exploration at Louvicourt Twp:
* Deep drilling based on sound geological reasoning. Incidentally, each deep hole cost about $50,000, according to Aur. The hole spacing (1,000 ft.) was arrived at by considering the size of deposit necessary to make a profit at 2,000-ft. depths.
* Down-hole geophysical surveys such as borehole pulse (em) were used to locate anomalies caused by sulphide zones not yet intersected by the drill holes.
* Lithogeochemical studies and analysis detected alteration haloes representing feeder zones to the massive sulphide body.
“Drilling made the Louvicourt discovery, but the other tools gave our geologists the confidence they needed to continue through three phases of exploration work,” said Stockford. How much did the three phases of exploration work cost? A total of $2.5 million has been spent since the first phase was started in 1987. When asked what particular attribute best accounts for the success of Aur’s geological team, Stockford stressed a combination of factors, but the role played by people took prominence. “The team of exploration people assembled by Aur was most important,” he said. “The company’s senior management are all dedicated geologists.”
Bubar agrees: “We are all geologists who like to do a lot of drilling.” Having worked previously for companies such as Kidd Creek Mines, and Falconbridge (now units of Noranda and Trelleborg), both Stockford and Bubar gained extensive experience in massive sulphide exploration. Under Gill’s guidance and financial savvy, the team systematically developed a “vision,” which ultimately lead them to the orebody.
“None of us wanted to be just finders of deposits for big companies,” said Bubar. Before joining Aur as a senior geologist in 1984, Bubar worked in the Northwest Territories for Texasgulf Inc. (of Kidd Creek fame) and helped discover the Gondor massive sulphide deposit in 1981 in the Slave Province of the Northwest Territories. While working on gold exploration projects in the Back River, N.W.T., area, he met project geologist George Mannard in 1982.
Mannard later joined Aur in 1985. Born in the East African diamond fields and raised in various mining centres throughout Canada, Mannard is a second-generation geologist, son of the late Dr George Mannard who studied under the late Dr. James Gill (grandfather of Aur’s current president).
It was more than 30 years ago, at high school in England, that Stockford acquired his early love of geology. The first seeds of his distinguished career were sown by former geology teacher and mentor John Allchin who left a lasting impression on the young Stockford. “He (Allchin) was a really exceptional high school teacher who devoted himself to his students,” recalled Stockford. “Others in his class also went on to become geologists.” Stockford remembered travelling on various geological field trips and fossil-hunting excursions in localities ranging from Wales to Scotland in the late 1950s. Nearly 20 years later, while working for Falconbridge in Winnipeg, Stockford sat on various education committees lobbying for more geology programs at high schools.
Aur’s management believes in employee share ownership. “That’s the carrot,” according to Stockford. “It’s the knowledge that if you make a discovery, you have a nice nest egg to build on.” Many Aur employees have made down payments on their homes as a result of the company’s success. As an added bonus, both
Stockford and Bubar were promoted. Stockford became executive vice-president while Bubar was elevated to vice-president of exploration.
Such are the rewards of a big base metal find in the perhaps iraptly named Val d’Or — the Valley of Gold.
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