Frenchie

Prospect, Active

Alternative names

BP Adit

Commodities and mineralogy

Main commodities Au; Cu; Pb; Zn
Other commodities Ba
Ore minerals galena; pyrite; sphalerite

Geographic location

Quadrangle map, 1:250,000-scale PE
Quadrangle map, 1:63,360-scale B-3
Latitude 56.4187
Longitude -132.9548
Nearby scientific data Find additional scientific data near this location
Location and accuracy The Frenchie prospect is at an elevation of less than 100 feet on the south bank of an unnamed creek about one-half mile south of the head of St. John Harbor. It is near the center of the SE1/4, section 8, T. 63 S., R. 80 E. The location is accurate.

Geologic setting

Geologic description

The Frenchie deposit was first described as a gold prospect by Buddington in 1923. In 1978, BP Alaska Exploration staked 34 claims on the prospect, mapped and sampled it, conducted airborne and ground geophysical surveys, did stream sediment and soil geochemistry in the area, and recognized it as a volcanogenic massive sulfide deposit (Brewer, 1979). In 1979, geologists from the U.S. Geological Survey examined the thick layer of pyrite that is the most prominent outcrop of the prospect (Berg and Grybeck, 1980) and recognized as one of the deposits along the Duncan Canal-Zarembo belt of Upper Triassic volcanogenic, massive sulfide deposits. Three holes were drilled in 1984 and five more were drilled in 1966 by Westmin Resources (Rockingham, 1996). As of 2007, the property is again active (Mark Robinson, oral communication, 2007). Buddington (1923) describes a 100-foot adit in the pyrite bed and a shaft that was sunk about 100 feet north of the adit. (The shaft could not be located by Still and others, 2002).
The main massive sulfide layer is up to 6 feet thick and and crops out for at least 600 feet along the creek bank (Brewer, 1979; Berg and Grybeck, 1980; Still and others, 2002). This layer consists of 50-75 percent massive sulfides in a siliceous matrix. The sulfides are chiefly pyrite, accompanied by minor sphalerite, chalcopyrite, and galena that form lenses, bands, and knots in the massive pyrite. The hanging wall of the deposit consists of a thin layer of black phyllite above the massive sulfide layer, about 18 inches of siliceous argillite and chert with up to 10 percent pyrite and sphalerite above that, and then about 13 feet of pyritized argillite and schist to the top of the outcrop in the cliff beside the creek. The footwall consist of siliceous, quartz-muscovite phyllite. All are intruded by Tertiary(?) andesite dikes. The massive sulfide layer is cut by several faults but none dislocates the layer significantly. The deposit disappears under surficial material to the west and it truncated by a fault to the east. Karl and others (1999) map the rocks in the area as part of the Upper Triassic Hyd Group that is the host of many of the massive sulfide deposits to the north along the Duncan Canal-Zarembo mineral belt.
Thirteen samples were collected by Brewer (1979) across the main massive sulfide layer; they averaged 0.047 ounce of gold per ton, 0.42 ounce of silver per ton, 0.55 percent copper, 0.08 percent lead, and 1.48 percent zinc, and 5 to 20 percent barite. Still and others (2002) also sampled the deposit. Eight chip samples across the main layer of massive sulfides contained 0.019 ounce of gold per ton, 0.32 ounce of silver per ton, 0.25 percent copper, 0.16 percent lead, 2.4 percent zinc, and 0.08 percent arsenic.
In 2016, Zarembo Minerals Co. LLC focused on better defining the grade and distribution of gold at the Frenchie deposit by conducting metallic-sieve analyses; results indicate 92 percent of the gold in re-analyzed samples is in the coarser, plus-80-mesh size fraction, which is normally discarded in a standard gold fire assay. A previously sampled, 16-foot-thick section of outcrop now has revised grades of 4.4 grams of gold per tonne, up to 4 percent zinc, and minor lead and silver (Freeman, 2016). In 2017, Zarembo Minerals reprocessed public-domain helicopter electromagnetic and magnetic surveys for the area (Burns and others, 1996), contracted for 3D inversions, and field checked inversion interpretations (Mark Robinson, written communication, 2017).
Geologic map unit (-132.956517903641, 56.4183530468339)
Mineral deposit model Kuroko volcanogenic massive sulfide deposit (Singer and Cox, 1986; model 28a), or Sierran Kuroko volcanogenic massive sulfide deposit (Bliss, 1992; model 28a.1).
Mineral deposit model number 28a or 28a.1
Age of mineralization Late Triassic as part of the Duncan-Zarembo Island mineral belt defined by Berg and Grybeck (1980) and Berg (1981).

Production and reserves

Workings or exploration
The Frenchie prospect was first described as a gold prospect by Buddington in 1923. In 1978, BP Alaska Exploration staked 34 claims on the prospect, mapped and sampled it, conducted airborne and ground geophysical surveys, carried out stream sediment and soil geochemistry surveys in the area, and recognized it as a volcanogenic massive sulfide deposit (Brewer, 1979). Examined by the U.S. Geological Survey in 1979 (Berg and Grybeck, 1980). Three holes were drilled in 1984 and five more were drilled by Westmin Resources in 1996 (Rockingham, 1996). In 2007, the property is again active (Mark Robinson, oral communication, 2007). Buddington (1923) describes a 100-foot adit into the main massive sulfide layer and a shaft that was sunk about 100 feet north of the adit. (The shaft could not be located by Still and others, 2002).
In 2016, Zarembo Minerals Co. LLC focused on better defining the grade and distribution of gold at the Frenchie deposit by conducting metallic-sieve analyses; results indicate 92 percent of the gold in re-analyzed samples is in the coarser, plus-80-mesh size fraction, which is normally discarded in a standard gold fire assay. A previously sampled, 16-foot-thick section of outcrop now has revised grades of 4.4 grams of gold per tonne, up to 4 percent zinc, and minor lead and silver (Freeman, 2016). In 2017, Zarembo Minerals reprocessed public-domain helicopter electromagnetic and magnetic surveys for the area (Burns and others, 1996), contracted for 3D inversions, and field checked inversion interpretations (Mark Robinson, written communication, 2017).
Indication of production None

References

MRDS Number A010320

References

Brewer, N.H., 1979, Frenchie project, Zarembo Island, Alaska: Unpublished BP Alaska Exploration summary report, 49 p. (On file at the Bureau of Land Management, Mineral Information Center, Juneau, Alaska.)
Rockingham, C.J., 1996, Report on the 1996 field work, Frenchy claims, Zarembo Islands, southeast Alaska: Unpublished report by Westmin Resources Limited, 8 p. (Report on file at the Bureau of Land Management, Minerals Information Center, Juneau, Alaska.)
Still, J.C., Bittenbender, P.E., Bean, K.W., and Gensler, E.G., 2002, Mineral assessment of the Stikine area, central Southeast Alaska: U.S. Bureau of Land Management Technical Report 51, 560 p.
Reporters D.J. Grybeck (Port Ludlow, WA); M.B. Werdon (DGGS)
Last report date 8/26/2017