In advancing the Carosue Dam gold project to feasibility,
Situated 110 km northeast of Kalgoorlie in the Eastern Goldfields of Western Australia, Carosue Dam is host to a 2.2-million-oz. resource contained in 40.1 million tonnes grading 1.7 grams gold per tonne. A prefeasiblity study determined a probable open-pit reserve of 16.5 million tonnes grading 1.96 grams, equivalent to just over 1 million oz. The study shows the economic potential for a 1.5-to-2-million-tonne-per-year, stand-alone carbon-in-leach processing plant that would yield 120,000-150,000 oz. annually over a mine life of 8-10 years. Capital costs are projected at $38 million.
A comprehensive bankable feasibility study is expected by year-end. Pending a positive outcome, construction could begin as early as March 2000, leading to production in the fourth quarter of that year. PacMin has reached agreement with all native title claimants and been granted mining leases.
PacMin purchased the Carosue Dam project and various gold assets from
The other assets included a half-interest in the Pungkut project in Indonesia and a 60% interest in the Irwin Bore joint venture in Western Australia. Western Metals acquired these gold projects through a $285-million hostile takeover of Aberfoyle Resources in 1998.
The Carosue Dam project, along with 800 sq. km of exploration tenements, cover a significant portion of the Pinjin area along the Keith-Kilkenny fault. Pinjin is an underexplored region that PacMin believes has the potential to be a new major gold province. Carosue Dam is about 200 km southeast of PacMin’s Tarmoola open-pit mine, which produces 200,000 oz. per year.
When PacMin first reviewed the Carosue Dam project, Aberfoyle had outlined an inferred resource of 12.8 million tonnes grading 2.8 grams, equivalent to 1.2 million contained ounces.
During a recent site visit, The Northern Miner learned from PacMin’s chief geologist, Arndt Brettschneider, that it had taken Aberfoyle less than a year to establish a resource in excess of 1 million oz. Only 3.5 km of the favourable 15-km strike length had been tested by some 69,000 metres of reverse-circulation (RC) drilling.
North of Carosue Dam are the Monty Dam and Twin Peaks gold deposits, both of which are held by Goldfields (gld). Monty Dam contains a resource of 1.3 million tonnes grading 3.6 grams; Twin Peaks, 770,000 tonnes at 4.5 grams.
Most of the ground has been covered by soil geochemical and rotary-air-blast (RAB) drilling, though follow-up RC drilling has been limited. Brettschneider said about a dozen prospects in the immediate Carosue Dam area require further testing.
In Carosue Dam, PacMin also recognized metallurgical characteristics similar to those of Tarmoola. Carosue Dam contains a significant component of free coarse gold, and PacMin felt that previous sampling and assaying techniques may have led to the grade’s being underestimated.
All of Aberfoyle’s resource work was based on fire-assaying, which PacMin has been comparing to bottle-roll leach assays on the suspicion that an upgrade could be warranted. However, results to date have been inconclusive, says Brettschneider.
Concerns that the RC samples may have been contaminated by water at a certain depth prompted PacMin to twin a number of the exceptionally higher-grade holes with core drilling. The company found that the RC results were replicable, giving confidence in the RC work.
The Carosue Dam project is hosted in a volcaniclastic sequence of the Gundockerta formation, on the western limb of the regional Yilgangi syncline. The volcanic sequence is bounded to the southwest by a younger sedimentary sequence along an interpreted structural contact, marked by a zone of shear sericitic volcanics.
Gold mineralization is largely confined to quartz stockworks and breccia in the volcaniclastic sandstones and is associated with albite, K-feldspar, silica, hematite, carbonate and pyrite alteration assemblages.
The current resource comprises three deposits: Karari, Whirling Dervish and Luvironza. The deposits are concealed by 8-30 metres of transported cover, comprising colluvium-alluvium, lacustrine clays and quartz sands. Beneath the cover, laterite occurs to depths ranging from 10 to 60 metres.
In February, PacMin began extensive infill drilling, having, to date, completed 29,400 metres of RC and 6,900 metres of core work. This led to the revised resource of 2.2 million contained ounces, representing an 84% increase over the previous estimate.
The infill program identified a previously unrecognized supergene gold component in the laterites. At the Luvironza deposit, the supergene gold occurs within 10 metres of surface and averages about 15 metres in thickness. This significantly lowers prestripping requirements and is expected to provide early economic benefits.
The closer-spaced drilling has had the effect of upgrading the resource, owing to the significant coarse gold component. “We find there is more upside than downside with the tighter drilling,” said Brettschneider.
Luvironza is the smallest and northern-most deposit, with a resource of 6.3 million tonnes grading 1.6 grams. It has been drilled on a 25-by-25-metre spacing and lies at, or close to, surface. Brettschneider expects it will be mined first, as there is “not much prestripping.”
To the south is Whirling Dervish, weighing in at 12.4 million tonnes at 1.7 grams gold. The deposit is covered by up to 60 metres of overburden and will be mined last. It has been drilled on a 25-by-25-metre pattern above 120 metres of depth, and, because of problems with water, PacMin elected to use core drilling below this depth on a 25-by-50-metre pattern.
Karari, the southern-most deposit, contains 21.3 million tonnes grading 1.7 grams, based on a 25-by-50-metre drill spacing. PacMin has since completed an additional 23,500 metres of RC drilling on a 25-by-25 metre spacing to bring Karari into a measured status. An updated resource estimate is expected sometime before year-end.
Karari measures 800 metres long, 400 metres wide and 200 metres deep, and remains open at depth, the deepest hole being 400 metres. “We still have high-grade intersections at that sort of depth, which gives us confidence in the downdip extensions of the deposit,” said Brettschneider.
A 5-hole program of diamond drilling demonstrated that higher-grade mineralization extends at least 100 metres farther beneath previously defined mineralization. Results included:
- 9 metres grading 6.73 grams starting at a downhole depth of 269 metres in hole 10;
- 7.7 metres of 3.66 grams at 336 metres of depth, plus 7 metres of 4.97 grams at 366 metres, in hole 9; and
- 7 metres of 4.93 grams at 290 metres downhole, plus 9 metres of 3.16 grams at 323 metres, in hole 13.
Recent infill drilling at Karari has identified a series of enriched high-grade supergene-mineralized zones in a broader supergene halo. These zones trend to the northeast and typically show higher grades over increased thicknesses. The supergene zones are up to 100 metres long and 30 metres wide. Intercepts of up to 20 metres grading more than 15 grams have been recorded.
Meanwhile, the company has begun a program of tighter drilling at 15-by-15-metre spacing. Because of their high grade, these zones could potentially have a significant impact in the economics of the overall project, says PacMin.
As part of the feasibility work, PacMin has been carrying out resource modeling, metallurgical tests, infrastructure design, hydrogeological studies and an extensive progra
m of sterilization drilling on areas that will be covered by waste dumps and infrastructure. The sterilization work was based on a 400-by-100-metre RC drilling program that tested to the bedrock interface.
A series of anomalies defined by a 100-parts-per-billion gold contour have been defined and will require follow-up drill-testing. The most significant result was an 8-metre interval grading 1.83 grams gold.
Elsewhere, PacMin is enjoying some exploration success with the high-grade Chariot gold discovery at the Tennant Creek joint venture in Australia’s Northern Territory. PacMin holds a 33% interest in the joint venture, with the remainder held by
This past summer, PacMin encountered high-grade gold mineralization from close to surface to a depth of 250 metres. The best results included:
- 14 metres grading 66.2 grams gold (including 9 metres of 100.6 grams) in hole 31;
- 3 metres of 39.5 grams in hole 34;
- 15 metres of 9.66 grams in hole 19;
- 4 metres of 21.7 grams in hole 23;
- 10 metres of 12 grams in hole 25; and
- 11 metres of 10.1 grams in hole 28.
The mineralization remains open at depth and along strike.
The intersections occurred in a 6-to-11-metre-thick, steeply dipping hematite-magnetite-chlorite ironstone. The grade and style of the Chariot discovery are said to be typical of previously mined high-grade deposits in the Tennant Creek area.
The Tennant Creek district has produced 5.4 million oz. gold from small-but-high-grade deposits. Normandy’s White Devil mine, which ceased mining operations in August after 12 years of operations, produced 1.7 million tons at 14.4 grams grade, from which were extracted about 743,000 oz. at a cost of less than $190 per oz. The Juno deposit has produced 455,000 tonnes grading 57 grams, equivalent to about 840,000 oz.
Chariot is the first significant find in the area since 1985. The discovery was made 50 km south-east of Normandy’s Warrego carbon-in-pulp process plant, which is currently treating the remaining stockpiles from White Devil.
Exploration resumed at Chariot late in September, following PacMin’s decision to fund the next $2.85 million of exploration. The first hole of a planned 17-hole diamond drill program tested the western margin and intersected 3 metres of 13.3 grams at a downhole depth of 136 metres. The second hole is reported to have hit visible gold. A resource estimate is expected early next year.
On the Indonesian island of north-central Sumatra, PacMin can earn a half-interest from Western Metals in the Pungkut gold project through a 3-year earn-in agreement. Pungkut is a seventh-generation contract of work covering a well-mineralized portion of the Trans-Sumatra fault zone. A Carlin-type, sediment-hosted gold prospect has been traced over 3 km of strike length. The mineralized horizons are up to 25 metres thick and have returned an average of 5.3 grams in initial chip samples.
A recent 18-hole program of diamond drilling tested the main geochemical anomaly at the Sihayo 1 North prospect. Stepping out on 100-metre centres, PacMin has established a significant zone of mineralization over an area of 800 by 200 metres, with thicknesses of up to 27 metres and grades of up to 4.1 grams. The zone remains open in three directions and lies within 100 metres of surface.
A follow-up program of geophysical surveying and soil sampling is under way over an expanded grid covering the untested Sihayo 1 and 2 prospects. Drilling is expected to resume in the new year.
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