A prominent geological feature in Yukon is the Selwyn Basin, a late Precambrian-Devonian depositional basin characterized by offshelf deep water shales in a basin bounded by platform carbonates to the northeast. The Tintina Fault truncates the basin on the southwest.
The area is well-known for lead-zinc silver sedimentary-exhalative (SEDEX) massive sulphide deposits, which have been discovered in Cambrian (Faro or Anvil), Silurian (Howards Pass), and Devonian (Macmillan Pass) shales. Although known primarily for SEDEX deposits, the geographic extent of the Selwyn Basin also contains several other deposit types. Exploration activities have outlined tungsten skarn (Mactung), stratiform barite (Tea), intrusion-related gold systems, silverlead vein (Keno Hill), stratiform nickel (Nick) and volcanogenic massive sulphide (VMS, e.g., Marg) occurrences and deposits.
Mining of Faro deposits has occurred intermittently since 1969. The Faro district was discovered in 1953 and was the world’s third largest zinc mine during its operation. The combined pre-mining mineral resource was 120 million tonnes grading 5.6 percent zinc, 3.7 percent lead and 45 to 50 grams/tonne silver.
The Grum, Grizzly, and Swim deposits still contain a geological resource of 67 million tonnes, including some mineable reserves and drill-indicated resources. The prospective contact remains locally untested, even close to known deposits, opening up the potential for new discoveries.
Deposits of the Anvil camp are road-accessible and are served by the town of Faro. Other deposits such as Tom, Jason, Clear Lake, and Howards Pass remain undeveloped.
In the Macmillan Pass area, the Tom claims were staked in 1951. Published mineable reserves for the Tom East and West zones are 9,283,700 tonnes grading 69.4 grams/tonne silver, 7.5 percent lead and 6.2 percent zinc using a 7 percent combined zinc+lead cutoff grade.
The Jason deposit was staked in 1974 and is located at the same stratigraphic level as the Tom deposit. It contains an indicated mineral resource of 14.1 million tonnes of 79.9 grams/tonne silver, 7.09 percent lead and 6.57 percent zinc, using a cut-off grade of 8 percent combined lead+zinc. The Tom and Jason deposits are accessible from the North Canol Road and by an airstrip located between the two deposits.
Active exploration for lead and zinc in the late 1960s and 1970s led to the staking of the Howards Pass district in 1972. The drill-indicated geological resource for the XY and Anniv deposits total 86.6 million tonnes of 4.93 percent zinc and 1.73 percent lead; inferred reserves are in excess of 215 million tonnes, making this potentially the largest zinc deposit in the world.
