Lost Lake

Prospect, Active

Commodities and mineralogy

Main commodities Ag; Ba; Pb; Zn
Other commodities Au
Ore minerals galena; pyrite; sphalerite
Gangue minerals quartz

Geographic location

Quadrangle map, 1:250,000-scale PE
Quadrangle map, 1:63,360-scale C-4
Latitude 56.5734
Longitude -133.059
Nearby scientific data Find additional scientific data near this location
Location and accuracy The Lost Lake prospect is on the north bank of the small lake, locally named 'Lost Lake' on northwestern Woewodski Island (lake '175' on the USGS 1:63,360-scale topographic map). The deposit is about 25 feet north of the lake; it extends extends east and west of a small creek that flows to the north from about the center of north shore of the the lake. Drilling pads and landing sites were visible in 1996 at the prospect and there was additional drilling in 2004. The prospect is near the center of section 22, T. 61 S., R. 79 E. The location is known to within 100 yards and easily located.

Geologic setting

Geologic description

This prospect was found in the late 1970s and has been explored or examined by a number of companies since, including Cominco Exploration, Colony Pacific, Amselco, and Kennecott Exploration. In 1996, it was held by Westmin Resources Limited, who had other properties on Woewodski Island. In 2008, the prospect is held by Bravo Ventures Group. The deposit consists of massive sulfide layers that are covered by only a thin layer of vegetation at several outcrops beside the lake. They have been sampled several times in shallow pits but most of the area is covered by muskeg and vegetation. Several drilling sites were obvious at the prospect in 1996 (D. Grybeck, personal observation) and at least 16 holes are said to have been drilled by then. Four more holes were drilled in 2004.
A resistant layer of cream- to light-gray colored schist about 10 feet thick dams in the north side of Lost Lake. The foliation strikes about N 80 E to S 75 E, i.e., roughly parallel to the north side of the lake, and dips about 70-85 S. The schist contains at least two layers of massive sulfides 8 inches to 16 inches thick that consist mainly of sphalerite with moderate amounts of pyrite and sparse galena (D.J. Grybeck, unpublished field notes, 1996). Analyses of a number of samples of similar(?) schist sampled nearly by Newberry and Brew (1989) indicate that: 1) the schist is probably hydrothermally altered basalt, 2) the schist is geochemically analogous to schist at the Greens Creek mine on Admiralty Island, and 3) the deposit is probably Triassic in age.
Still and others (2002) sampled surface exposures of the bands of massive sulfides exposed at the surface. A 4.4-foot chip sample at one outcrop contained 153.8 parts per million (ppm) silver, 5,519 ppm lead, and 11.5 percent zinc. A 7.5-foot sample across another outcrop with two narrow bands of mineralization contained 83.9 ppm silver, 5,180 ppm led, and 4.5 percent zinc. A third outcrop that exposes a 1.1-foot-thick band of pyrite, sphalerite, and galena in schist contained 282 ppm silver, 2.79 percent lead, and 24.15 percent zinc.
Bravo Ventures Group (2008) reported that high grade zinc mineralization was intersected in two of the three holes drilled in 2004. Samples contained up to 70 grams of silver per ton and 13.6 percent zinc across 1.3 meters and 21 grams of silver per ton and 4.5 percent zinc across 5.9 meters.
Westmin Resources (1997) cited a 'geologic reserve' for the Lost Lake deposit as approximately 500,000 tonnes grading 8.1 percent zinc, 0.6 percent lead, and 77.76 grams of silver per ton.
Geologic map unit (-133.060722299414, 56.5730540670795)
Mineral deposit model Barite facies of a Kuroko volcanogenic massive-sulfide model (Cox and Singer, 1986; model 28a). Alternatively a barite facies of a volcanogenic Sierran Kuroko model (Bliss, 1992; model 28a.1).
Mineral deposit model number 28a or 28a.1
Age of mineralization Probably Triassic based on geochemistry of the host rocks (Newberry and Brew, 1989), and the deposit's similarity to other deposits in the Triassic, Duncan Canal-Zarembo belt of massive sulfide deposits defined by Berg and Grybeck (1980) and Berg (1981).
Alteration of deposit The schist that host the massive sulfide layers is probably hydrothermally altered basalt.

Production and reserves

Workings or exploration This prospect was found in the late 1970s and has been explored or examined by a number of companies since, including Cominco Exploration, Colony Pacific, Amselco, and Kennecott Exploration. In 1996, it was held by Westmin Resources Limited, who had other properties on Woewodski Island. In 2008, the prospect is held by Bravo Ventures Group Several drilling sites were obvious at the prospect in 1996 (D. Grybeck, personal observation,) and at least 16 holes are said to have been drilled by then. Four more holes were drilled in 2004. Still and others (2002) sampled surface exposures which expose bands of massive sulfides.
Indication of production None
Reserve estimates Westmin Resources (1997) cited a 'geologic reserve' for the Lost Lake deposit as approximately 500,000 tonnes grading 8.1 percent zinc, 0.6 percent lead, and 77.76 grams of silver per ton.

References