Alder Island arsenic-gold occurrence, Haida Gwaii, Skeena Mining Division, British Columbia, Canadai

Regional Level Types
Alder Island arsenic-gold occurrence	Island
Haida Gwaii	Group of Islands
Skeena Mining Division	Division
British Columbia	Province
Canada	Country

The Alder Island arsenic-gold occurrence is located on Alder Island, immediately north of Burnaby Island, southern Haida Gwaii, 104 kilometres south of the village of Daajing Giids (previously known as Queen Charlotte), British Columbia.
There is a brief description of the geological setting for this property on the British Columbia “Minfile” site, current to 1989, as quoted below:
“Alder Island is underlain by complex geology, including folded limestone and argillite of the Jurassic to Triassic Kunga Group, Middle Jurassic Yakoun Group volcanics, Lower Cretaceous Longarm Formation sandstones, Tertiary Masset Formation basalts and granitoid dikes related to the Middle to Late Jurassic Burnaby Island Plutonic Suite.
An intense fault-mylonite zone extends the entire east side of the island. The mylonite is composed of shattered country rock, which is mainly Yakoun volcanics in the south and skarn, variably developed in Longarm sandstones in the north. A silicified, chilled contact occurs between a hornblende monzonite and sheared greenstones to the east.
The massive to poorly bedded garnet-actinolite-diopside-zoisite skarn is interbedded with baked cherty siltstone and layered carbonate. Massive pyrrhotite pods with accessory chalcopyrite, molybdenite and magnetite occur along the skarn and fault-mylonite zones. Allemonite [sic – allemontite, now stibarsen] is associated with calcite veins and the pyrrhotite mineralization, which is sometimes nickeliferous.”

Giles Peatfield comments:
There has been no production from the property, and there is no mineral inventory. Note that this very small island is part of the large Gwaii Haanas National Park Reserve and Haida Heritage Site. Mineral collecting would presumably only be possible with the permission of Parks Canada and the local Haida Nation – neither of which would likely be granted.
The Pacific Museum of Earth at the University of British Columbia holds a large collection of specimens from early collections from the locality.

Comments on Minerals Reported:
Amphibole Supergroup: Shearer (1980a, 1980b) reported ‘actinolite’ in skarn.
Antimony: This was reported in polished section by Chamberlain (1951), as fine exsolutions in arsenic – this is the only report of antimony for the property.
Arsenic: This was reported from this locality by Johnston (1915) as from “Alden [sic] island, Queen Charlotte islands (Pr. Com. T. L. Walker).” It is not clear whence Johnston acquired this material. Palache, Berman and Frondel (1944) reported arsenic from Alder Island. Chamberlain (1951) described it in polished section. Traill (1970, 1983) repeated Johnston’s observation. The Pacific Museum of Earth has a total of eight specimens labelled arsenic from Alder Island, of which seven are listed as coming from W. J. Sutton as part of the original Sutton Collection; it seems likely that this is the material listed by Sutton (1889) as coming from “Queen Charlotte Island”. Interestingly, Sutton (1889, p. 325) also lists arsenopyrite from “Queen Charlotte Island”, but no subsequent workers have reported it here and there is no specimen for Alder Island in the Pacific Museum of Earth catalogue, so it must be regarded as tentative at best.
Baryte: The Pacific Museum of Earth has a single specimen of arsenic with ‘barite’, donated by H. T. James. James was the ‘Resident Mining Engineer’ for the North-Western Mineral Survey District (No. 1), in the late 1920’s. I can find no other reports of baryte from Alder Island.
Clinopyroxene Subgroup: Shearer (1980a, 1980b) reported ‘diopside’ in skarn.
Garnet Supergroup: Shearer (1980a, 1980b) reported ‘garnet’ in skarn, but gave no further details.
Gold: Shearer (1980a, 1980b) reported visible gold “. . . within a mass of resistant, s[i]licified, thin bedded, black limestone.”
Magnetite: Reported by Sutherland Brown (1968) as an accessory in skarn.
Molybdenite: Shearer (1980a, 1980b) reported molybdenite in massive pyrrhotite pods, with chalcopyrite.
Pyroxene Group: Sutherland Brown (1968) reported ‘pyroxene’ in skarn.
Sphalerite: Shearer (1980b) reported that “Minor sphalerite was noted in recrystallized limestone.”
Stibarsen: This mineral was historically known as allemontite, named for the type locality at Allemont, France (Palache, Berman & Frondel, 1944). The earliest record I can find for the mineral in Canada is by Sutton (1889), who reported “Arsenical Antimony (likely Allemontite)” from “Queen Charlotte Island.” The Pacific Museum of Earth has two specimens now labelled stibarsen from Alder Island, that are listed as coming from W. J. Sutton as part of the original Sutton Collection; it seems almost certain that this is the material listed by Sutton (1889) as coming from “Queen Charlotte Island”. One specimen is described as “with feldspar” and the second as “with arsenic”. Johnston (1915) did not list the mineral; Traill (1970, 1983) list allemontite from the Engineer Mine on Tagish Lake in the Atlin District, but since the Engineer was not discovered until 1899 (Cairnes, 1913) this is obviously not the location for Sutton’s material. Walker (1921) described “allemontite” from the Engineer Mine, but did not mention Alder Island – see, however, Johnston’s attribution above for arsenic. Palache, Berman & Frondel (1944) listed Alder Island as one of two Canadian localities, the other being the Engineer Mine. Chamberlain (1951) completed a photomicrographic study of arsenic-antimony alloys (as he called them) – many of his photos were of sections from Engineer material, but one was listed as Alder Island. He described it as antimony and arsenic, with a central area that by inference was thought to be originally “allemontite”; whether it still is that phase is open to question. The whole subject of what stibarsen really is, is beyond the scope of this review – interested readers should consult, inter alia, Holmes (1936) and Bayliss (1991). Finally, Back (2022) lists stibarsen as Sb0.5As0.5. In my opinion, Alder Island is the first documented locality for stibarsen in Canada.
Zoisite: Shearer (1980a, 1980b) reported zoisite in skarn.

Giles Peatfield
BASc. (Geological Engineering) University of British Columbia 1966.
PhD Queen's University at Kingston 1978.
Worked for Texas Gulf Sulphur / Texasgulf Inc. / Kidd Creek Mines - 1966 to 1985.
Vancouver based consultant 1982 to retirement in 2016.

Other Databases

Link to British Columbia Minfile:	103B 017

Other Regions, Features and Areas containing this locality

References