The Fairweather property is the most southerly of a group of Teuton properties lying along the southern trend of Jurassic age rocks that host the various gold deposits of Pretium’s Brucejack property.
In 1987 geologist Ken Konkin discovered a pyritic, quartz brecciated conglomerate zone on the Fairweather which was trenched and yielded an average grade of 4.04 g/t gold over 7.0 metres. A similar zone was sampled uphill from this occurrence, returning anomalous gold values of 720, 780 and 1045 ppb (grabs). Exposure in the area was quite poor with deep overburden in places. The next year the site was revisited but limited follow-up work failed to reach bedrock. Although the zone was recommended to be tested by a series of shallow holes, such work is yet to be done. A cluster of soil geochem gold anomalies lies downhill from the occurrence.
It was originally believed that the gold-bearing zone was located within the Lower Jurassic Unuk River Formation. However more recent geological mapping places it in the Triassic (see map). Recently, Jeff Kyba, regional government geologist for the Northwest section of British Columbia, and a co-author with Joanne Nelson of the BC Geological Survey on several seminal papers on the district, has stated his belief that the contact between the Triassic and Lower Jurassic (between the Stuhini and Hazelton group rocks) is an important horizon for locating mineral deposits.
Geologists Jeff Kyba and Joanne Nelson from the British Columbia Geological Survey may have unlocked the secret to world-class porphyry and intrusion related gold-copper deposits in northwestern B.C.
They’ve discovered that most of the major deposits in the region occur within 2 km of a regional stratigraphic contact, and, according to Kyba, there are lithological and structural clues to narrow that window even further.
“The contact represents a period in earth’s history when a lot of deposits in B.C. were forming,” Kyba says during an interview with The Northern Miner. “But no one really knows what controlled their emplacement and where best to look. We’re trying to answer that question, and so far the results are very exciting………….”
Kyba mentions he has an “open-door” policy on the data he uses, and offers explorers a geological map that highlights the prospective contact as a thick red line.
“If you’re near that red line, and there’s a clastic sequence coupled with large-scale faults then you might be in the neighborhood of B.C.’s next big deposit,” he says. “And knowing that is a big game-changer for explorers in the region because it’ll get them closer to making a discovery.” [Excerpted from the May 1,2015 Edition of the Northern Miner]
According to the recent government geological maps, the favourable contact is located both in the eastern and western portions of the property. The westernmost contact is important because it lies close to the southern extension of the Sulphurets Fault.
Kyba believes that the Sulphurets Fault is an important second key to locating mineralization. More of the Northern Miner article, follows:
But a change in lithology across the contact isn’t the only thing Kyba suggests is a useful proxy to finding “nation-building” ore deposits.
Brucejack and KSM are both encased in a large halo of a highly deformed, quartz-sericite-altered host rock. Immediately to the east is a large, Cretaceous-aged thrust fault called “Sulphurets” that caps the altered ore-host.
Kyba reckons that it’s no coincidence the prominent fault is so close to the deposits.
“When the Stikine was compressed, all the prospective structures bounding these old basins were slippery because of the alteration associated with the porphyries. So they were the first to fail, and became reactivated as younger, prominent thrust faults.” [Excerpted from the May 1,2015 Edition of the Northern Miner]