Minnova’s patient approach put to work at Seneca project

It has often been said that a patient and persistent approach to exploration is necessary when exploring for polymetallic volcanogenic massive sulphides in the Canadian Cordillera. This appears to be the attitude being taken by Minnova (TSE), a company with considerable experience and expertise in massive sulphide deposits, on the Seneca property some 60 miles from Vancouver.

Minnova optioned the property in 1990 from International Curator (VSE), and can earn a 51% interest by spending $1.6 million on exploration and making cash payments of $300,000 by 1996. A further 9% can be earned by spending an additional $500,000 by 1998.

Three mineralized zones have been discovered to date on the Seneca property, but the current focus is on the Fleetwood zone, a recent massive sulphide discovery which has seen only limited drilling.

Underlain by a prospective package of volcanic rocks called the Harrison Lake Formation, the Seneca property has been explored by several previous operators with the bulk of work completed by Cominco in the 1970s. Previous work was largely focused on the Seneca deposit which was subsequently estimated by Wright Engineers to contain 1.6 million tons grading 3.57% zinc, 0.63% copper, 0.024 oz. gold and 1.2 oz. silver.

Alex Davidson, Minnova’s western exploration manager, cautions that the Seneca deposit doesn’t represent a minable reserve as it is severely block-faulted and broken up into a number of zones. In addition, high-grade fragments of massive sulphides are mixed with volcanic and sedimentary fragments which reduces the overall grade. Minnova is now of the view that the Seneca deposit is transported, as it is not underlain by footwall alteration or stockwork mineralization.

Some previous exploration work was also carried out on the Vent zone — a brecciated, silicified, pyritic area containing zones of sporadic and low-grade base and precious metal mineralization about 1.2 miles from the Seneca deposit. This altered and sodium-depleted zone is considered to have features characteristic of “feeder pipe” mineralization which occurs below massive sulphide deposits. In this case, however, the massive sulphide deposit would have been eroded away.

The area to the northwest of the Vent zone was tested in 1987 by a single hole drilled by International Curator which intersected 9.9 ft. grading 5.68% zinc, 0.43% copper, 1.2% lead, 2.4 oz. silver and 0.02 oz. gold per ton in hole 87-12.

After taking on the property in 1990 and analyzing previous work, Minnova decided to stepout from hole 87-12 during this year’s first-phase drill program. Diamond drill hole 91-10, located 820 ft. west of hole 87-12, intersected 4.4 ft. grading 13.77% zinc, 0.84% copper, 0.42% lead, 0.85 oz. silver and 0.019 oz. gold per ton at a vertical depth of 492 ft. Colin Burge, project geologist, told The Northern Miner and others on a recent site visit that this hole was viewed as significant because the massive sulphide horizon was underlain by an altered and mineralized dacite flow.

This silicified and sodium depleted footwall zone graded 1.54% zinc and 0.14% copper over 62 ft. A lower massive sulphide zone, which occurs about 229 ft. below the upper massive sulphide, graded 10% zinc, 1.66% copper, 0.01% lead, 1.03 oz. silver and 0.012 oz. gold over 1.6 ft.

A more recent hole, 91-16, returned a 3.6-ft. thick baritic massive sulphide layer underlain by a 104.9-ft. zone of stockwork mineralization. The 3.6-ft. intercept graded 5.56% zinc, 0.38% copper, 0.37% lead, 4.73 oz. silver and 0.069 oz. gold per ton, while the underlying stockwork is variably mineralized grading 0.31% copper and 2.06% zinc over the 104.9 ft. (with only slightly anomalous precious metal values). Several other holes encountered sub-vertical dykes, and did not intersect the massive sulphide horizon. So far, the Fleetwood zone has been intersected over a strike length of about 1,500 ft. in three diamond drill holes. This zone, which consists of a bedded massive sulphide layer directly underlain by strong stockwork mineralization, has been tested on broadly spaced 650-ft. centres and is open to the northwest, southeast and south. The Fleetwood zone is about 1.2 miles from the original Seneca deposit.

“This project has good potential and we rate it very highly,” Davidson told The Northern Miner. “But we’d like to see it get thicker and richer.” Davidson said Minnova may continue drilling the project this fall, and a work program is also being planned for 1992. This work will be aimed at continuing exploration of the Fleetwood zone on wide-spaced centres on strike and within the discovery area.

“We’re looking for something big, so we’ll continue with the wide-spaced drilling rather than infill drill the Fleetwood zone,” Burge said during the property visit. “Volcanogenic massive sulphide deposits can suddenly blossom out and that’s what we hope will happen here.”

The Seneca property is accessible by road and located near power and other infrastructure, which is in keeping with Minnova’s strategy of seeking well-located mineral deposits. But as the project geologist pointed out, the nearby power lines make the use of geophysics as an exploration tool difficult. Geochemistry works well, although there is not much exposure on the property, with geology and drilling also considered important exploration tools.