Inmet Mining drilling to prove up Akie claims

Working under the assumption that sedimentary-exhalative massive sulphide deposits are typically large, Inmet Mining (IMN-T) is drilling the Akie claims in north-central British Columbia. Its goal: to identify a deposit in the range of 50 million tonnes grading 10% zinc.

The Akie, along with the nearby Pie, claims comprise the Gataga joint-venture property, held 60% by Inmet and 40% by Ecstall Mining (EAM-V).

Working with a $1.6-million budget, Inmet has one drill rig testing the main Akie deposit to depth, while a second steps out along strike at 1-km intervals over a distance of 7 km.

The Akie and Pie properties lie in mountainous terrain, 250 km northwest of Mackenzie in the Omineca Mining division. “This is elephant-hunting ground,” Inmet project geologist Paul Baxter told The Northern Miner on a recent site visit.

The properties occupy part of the southern portion of the Kechika Trough, a southerly extension of the Selwyn Basin, which hosts early Cambrian to Triassic sediments deposited off of the western margin of ancestral North America. The basin extends from central British Columbia, north into the Yukon and Northwest Territories. Several significant sedex-type zinc-lead-silver deposits are hosted within the basin, including Howard’s Pass, Faro (Anvil), MacMillan Pass, Driftpile and Cirque.

The Cirque deposit, 25 km northwest of Akie, was once the asset of Curragh.

It is now owned 25% by Teck (TEK-T), 25% by Cominco (CLT-T) and 50% by Korea Zinc.

A prefeasibility study, completed in 1995, examined the viability of an open-pit operation. Minable reserves were estimated at 18.5 million tonnes averaging 8.1% zinc and 2.2% lead, with a stripping ratio of 7.3-to-1.

The capital cost of a 4,000-tonne-per-day operation is pegged at $300 million, with cash costs estimated at 40 cents per lb. zinc. The partners have put Cirque on the back burner until economic conditions improve.

Within the Gataga project area, sulphide mineralization occurs within the Gunsteel formation, a Middle-to-Upper-Devonian-aged sequence of graphitic shales overlying fossiliferous limestones and Silurian-aged calcareous sandstones of the Road River group.

Mineralization is interlayered within the graphitic shales as fine-grained, massive-to-well-bedded pyrite, sphalerite and galena, with appreciable barite.

The Akie and Cirque deposits differ in terms of their mineralization: On the former, the contact between the Gunsteel formation and the underlying fossiliferous limestone is key, while, on the latter, mineralization occurs much higher up, within the Gunsteel formation.

Ecstall’s involvement in this region dates back to the late 1970s, when Christopher Graf (now the company’s president) staked the Akie and Pie claims for Rio Tinto Canadian Exploration. Rio blitzed the properties with soil sampling and initial mapping. In the process, it identified several large, coincident zinc-lead soil anomalies, as well as poorly exposed barite horizons associated with the Gunsteel shales.

Limited drilling was carried out on the Pie claims in 1980. Five years later, Rio, having spent more than $1 million, relinquished the properties to Graf, who subsequently transferred ownership of the claims to Ecstall when he formed the company in 1989.

In 1992, the ground was optioned by Inmet, which spent the next couple of years soil-sampling and mapping to confirm and re-establish the soil anomalies. While traversing the Cardiac Creek as a follow-up to a single anomalous soil sample, Baxter discovered a surface showing that returned a grade of 16% zinc, 2.8% lead and 26% barite over a 0.4-metre interval.

The surface prospect was followed up with significant drill programs in 1994 and 1995. Since 1992, $5 million has been spent on exploration.

To date, the Akie (or Cardiac Creek) deposit has been defined by 12 holes drill holes over a strike length of 1,400 metres and a dip length of 600 metres. The true thickness varies from 10 metres near surface to more than 30 metres at depth, averaging 20 metres.

Ecstall estimates the deposit contains a geologically inferred resource of 78 million tonnes grading 5% combined zinc and lead. Results from four drill holes point to a deeper, high-grade resource of 12 million tonnes grading 8.5% zinc, 1.5% lead and 17.1 grams silver per tonne over widths of 5-10 metres. This zone remains open at depth and along strike.

The Akie claims are accessible by helicopter from the Finbow airstrip, situated 35 km southwest in the Finlay River Valley.

Inmet is using the Fletcher forestry camp at the airstrip as its base, though core logging is carried out at the property site.

Inmet project geologist Paul Baxter is drill-testing the Akie deposit on the premise that the source of the mineralization is preserved at depth. He points to an increasing grade and width downdip, as well as the development of a hangingwall zone, which he feels could be significant. Also downdip is what appears to be a thickening footwall breccia zone.

The deep drilling program on the Akie deposit has not been without hardship.

The 1996 program began with the continuation of hole 95-19, which was stopped at an 850-metre depth last November owing to poor weather conditions. The hole was completed to a depth of 1,192 metres, but the zone apparently was faulted out. (This despite the fact that a 2.9-metre interval of hangingwall mineralization averaged a grade of 1.34% zinc.)

Baxter said that where the hole was expected to enter into the Main zone, it instead passed through a clean fault that contained no stringer mineralization, before cutting the underlying footwall and Road River formation. Hole 19 was a stepout 600 metres north of hole 95-18, which intersected 18.6 metres grading 5.1% zinc and 0.9% lead (including a 6.3-metre interval grading 9.2% zinc and 1.4% lead).

The next deep hole to be drilled was 96-21, which was collared on the footwall side of the massive sulphide horizon and designed to intersect the zone about 400 metres directly downdip of hole 95-18. At a depth of 601 metres, drilling was suspended because the hole was deviating northwards away from the target area back to hole 19. The deviation occurred even though Inmet is employing a directional drilling system.

The deep drilling rig has been moved farther south and is currently drilling hole 96-28. The planned 1,200-metre-long hole is targeted to test a 400-metre downdip extension of the deposit between holes 95-16 and 18.

While still in the early stages, the geology of the deposit and the topography in the area suggest the deposit could be developed from a 2-3-km-long decline driven horizontally from the valley floor at an approximate 800-metre elevation.

A second smaller rig has drilled six exploratory holes comprising 1,800 metres to date. The rig is stepping out at 1-km intervals north and south of the Akie deposit over a distance of 7 km. “We are looking for something large,” Baxter said, which justifies the size of the stepouts. He is encouraged by results and believes the northern end of the property has great potential.

Hole 96-24 was drilled 2.8 km north of the Akie deposit and intersected more than 10 metres of laminated sulphides interlayered with shale. At the base, a 0.8-metre massive sulphide interval assayed 11.6% zinc and 9% lead.

Baxter said this massive sulphide section differs from the mineralization previously encountered in that it is more granular and coarse.

The massive sulphides overlie a narrow breccia unit, and Baxter believes it is possible they are still on the fringe.

Holes 96-25 and 26 were drilled 400 metres south along strike and updip of hole 24. The holes are 2 km north of the nearest hole in the Akie deposit.

Hole 96-25 intersected 12 metres of interbedded barite and shale without massive sulphides, which is consistent with a sedex model of a barite fringe zone around a deeper-seated massive sulphide deposit. Faulting prevented hole 96-26 from intersecting the target horizon.

Holes 96-20, 22 and 23 were drilled a respective 2, 3 and 3.8 km south of the Akie deposit. The zone was faulted out in hole 96-20, but a 1.5-metre interval still averaged 3.59% zinc and 1.54% lead.

Hole 96-22 encountered fringe-style mineralization intersecting 4.6 metres of laminated massive sulphides, of which a 1.7-metre interval averaged 1.36% zinc. Hole 96-23, drilled on the southern side of the Akie River, cut 2 metres of laminated sulphides but no significant base metals.

A deeper follow-up hole, 96-27, was collared between holes 96-20 and 22 and has a targeted depth of 600 metres. The hole had advanced more than 300 metres at the time of The Northern Miner’s visit.

Ecstall has 6.4 million shares outstanding, or just under 8 million shares fully diluted.