Thayer Lindsley entering production

Subject to environmental permitting, the Thayer Lindsley (TL) project in the Sudbury, Ont., area is expected to be a producer in the near future.

Though long known to Falconbridge, it wasn’t until recent years that the TL orebodies justified the major capital expenditure required for shaft sinking and underground development.

Primary reasons were the limited reserves, the moderate grades of the then known three zones of mineralization and no more than average metal prices. The zones had been located by drilling downdip from Inco’s (TSE) outcropping, Blezard deposit. (This deposit has been drilled off, though not mined, inferring either too low a grade, too few tons or both.)

All the mineralization, Inco’s included, was within the traditionally productive lower-intrusive (norite) contact zone of the Sudbury basin. Then, in 1986, a drill hole intersected high-grade values in the granite footwall 100 metres below the contact. The intersection expanded into what is now designated the No. 4B zone and it is the one now being developed for mining. Falconbridge is not publicizing reserves or grade of the new find; but according to Paul Biney, senior geologist, the assays announced in the 1991 annual report, if not representative of the zone as a whole, are indicative of its richness.

A crosscut on the 1,310-metre level returned 2.4% nickel, 5.3% copper, 0.13% cobalt and 14 grams of platinum group metals per tonne over a length of 56 metres. And, with a declared production rate of 500 tonnes per day and a projected life of four years, the estimated reserve is in excess of half a million tonnes.

Published mineral inventories of all the zones so far located are 6.4 million tonnes grading 1.58% nickel, 1.51% copper and unspecified precious metals, indicating no more than modest grades for the three original sulphide discoveries.

With nickel prices in the basement, Falconbridge clearly views the TL mine as a precious metals-copper producer, at least for the next few years. It will also serve as an excellent underground base for future exploration. “The TL is quite a vast project,” says Eric Belford, general manager of Sudbury operations. “It will require substantial amounts of money to explore the whole property and the mining of this small orebody will help underwrite the cost of further exploration.”

As noted, the TL has had a long history. The first drilling was initiated in 1941, followed by a second exploration phase in 1956 resulting in the discovery of zone 1. Shaft sinking started in 1970 but didn’t go beyond 100 metres before the project was put on hold. Diamond drilling nevertheless continued and zone 2 was discovered in 1974.

Exploration resumed in 1986. Undoubtedly, Falconbridge’s persistence was spurred by the proximity of two of Inco’s major producers — the Stobie and Little Stobie, 2 km and 1.5 km distant to the west — and one of Falconbridge’s earlier operations to the east, the McKim mine. Persistence paid off with the discovery of zones 3 and 4 in 1987 and 1988 and shaft sinking got under way in March, 1989.

Sinking was slowed by the cutback of 1991 but the 1,638-metre shaft finally bottomed in May, 1991. Drifting on two levels, comprising 1,350 metres and 38,000 metres of drilling, is part of the $40-million exploration program and the mine is poised to proceed with stope development.

“Production awaits the successful conclusion of environmental permitting and this process is now at an advanced stage,” said Norman Girard, TL project manager.

Understandably, and following typical Falconbridge form, the mine will employ post cut-and-fill to ensure minimum dilution and maximum extraction of this small but outstandingly valuable orebody.