Dration/Locator asses Theresa

A good deal of religious fervor, including site visitations by priests, was practised by management in an effort to coax profitability from the Theresa gold mine in the early 1950s. The effort was for naught, as the mine was forced to close in 1953 after producing some 4,785 oz of gold from 35,000 tons of mined rock.

Current management of equal partners Duration Mines and Locator Explorations, which acquired the property early last year, have opted for a more traditional approach rather than prayer — such as mapping, sampling and drilling to determine the merits of this property.

During an examination by The Northern Miner of several mineralized zones which were partially developed on the third level at 482 ft, the Theresa’s potential for hosting mineable reserves becomes obvious. The challenge in developing that potential is also equally high.

As with most quartz vein and stringer-associated coarse gold deposits in the Archean, large discrepancies are common between drill hole assays and underground stoped and bulk sampled grades. A result of the erratic distribution of coarse gold grains throughout the deposit and the difference between sample size in drill core and stoped areas, only one solution has ever emerged for evaluating such difficult deposits. Sampling and more sampling, especially from underground.

Faced with such a task, Duration and Locator have dewatered the old mine workings to the 6th level or 1,000 ft. Access is via the No 2 shaft, one of three which were put down on the property. The program is aiming to block out proven reserves this summer. “By June we hope to have 300,000 tons of proven-probable reserves,” William Hill, a mining engineer and director of Duration and Locator told a group of mining analysts on site.

Based on a review of mine production records and old drill logs from 400 holes, Hill feels the property hosts inferred reserves of 540,000 tons grading 0.2-0.25 oz gold per ton from surface to the fourth level at 660 ft. Extrapolating to the lowest level at 1,000 ft, potential reserves swell to 850,000 tons at a similar grade. Calculations are based on 1,000 tons per vertical foot. “The work to date suggests that 1,000 tpvf is quite within our reach,” Hill added. Methodical sampling

However, the need for detailed and methodical sampling of the zones becomes evident after examining old drill logs and comparing this to grades from stoped zones. “If you just looked at the drill logs you would walk away” from the project, Hill explained. “If you look at the stopes, the situation changes. That’s the problem here.” Although numerous holes assayed subeconomic grades, when the same areas were mined out, grades actually assayed closer to 0.18-0.2 oz gold per ton. “From past experience, there will be a factor of several times in favor of underground results,” Hill says.

Gold mineralization is associated with a series of parallel to sub-parallel quartz-filled zones which trace an arcuate concave pattern near the contact margin of a dioritic intrusive and mafic volcanics.

These quartz-bearing fractures were seen underground to pinch and swell — a feature typical of Archean lode-gold deposits. A majority of the mining in the 1950s occurred on two packages of veins known as the 500 and 600 series in the northeast section of the property.

From the third level, it was evident that a majority of the stopes were relatively narrow and focused on the quartz veins, primarily in the search for higher grades. According to Hill and Iain Downie, Duration’s project manager, little evidence of sampling of the foot and hangingwalls of the zones was performed in the 1950s.

Duration and Locator have resampled several stopes and are also testing all wallrocks in drifted zones. To date, the best encouragement is coming from the 800 series veins in the southwest section of the property and more than 1,000 ft from the stoped 500 and 600 series veins.

“Some of our best results are coming from the wall rock adjacent to quartz veins,” Downie said. He was referring to results from the 800 series where drilling is yielding good values. He feels that if two more holes hit, the 800 series will be considered another ore zone.

Another example of sampling surprises comes from a section of 600 series veins, which was examined on the third level by The Northern Miner. Generally uninspiring and displaying little quartz in massive diorite, the zone has yielded strong values from channel samples. Assays across 40 cm channels from one section came in at 1.94, 1.22, 0.4 and 4.62 oz gold per ton. Although over narrow sections, the high grades will alleviate some of the pains which will accompany dilution in narrow sections. More importantly, according to Dr Robert Ginn, a Duration officer and geologist, results such as these underlie the potential exhibited by the multiple zones on the property. Feasibility this summer

By June, the companies plan to have completed 12,000 ft of lateral development and 1,200 ft of raise development. During the site visit, a raise boring station was being commissioned. This work, budgeted at approximately $10 million, will carry the partners to the feasibility stage.

If a production decision is reached, Hill feels another $10 million will be required to place the property into production at a rate of 400 tons per day. At such a rate and assuming a mill grade of 0.2 oz, the Theresa would be capable of producing 25,000 oz of gold per year. Hill also noted that capital financing via a joint venture partner is an option under consideration.

The challenge facing both Duration and Locator at the Theresa is to establish continuity between the multiple series of zones and mine levels and, more importantly, build reserves and improve the confidence limits attached to those mineable reserves. That will take more than just the blessings of St. Theresa, but rigorous sampling, imaginative, capable hands-on-type mine management and a splash of luck.