Ericksen-Ashby deposit, Atlin Mining Division, British Columbia, Canadai

Regional Level Types
Ericksen-Ashby deposit	Deposit
Atlin Mining Division	Division
British Columbia	Province
Canada	Country

The Ericksen-Ashby deposit is located on the sharp northern ridge of Mount Ericksen, at the junction of the Unuk and Tulsequah rivers, about 64 kilometres east of Juneau, Alaska, and 130 kilometres south of Atlin, British Columbia.
The following quote is from B.C. Government site “Minfile”- Minfile No. 104K 009, current to 2021:
“The area underlying Mount Ericksen consists of Late Carboniferous to Permian volcanosedimentary strata of the Stikine Assemblage. According to Mihalynuk (Fieldwork 1995), the strata are predominantly pyroxene-phyric andesite or basaltic andesite and gabbro. Near the north end of the ridge, the volcanic strata are interrupted by two interlayers comprised of chert and carbonate. They are approximately 100 metres thick due to folding which obscures the original stratigraphic thickness. The structurally highest sedimentary unit bifurcates northward to envelop andesite of approximately the same thickness. It also includes a thin layer of rhyolite. A subjacent, tabular, porphyritic quartz monzonite, 50 to 100 metres thick (and up to 350 metres thick locally), known as the Ericksen sill, thermally metamorphoses the entire section on Mount Ericksen.
Mineralization occurs within at least thirteen different zones, each of which contains one or more discontinuous lens-shaped bodies of disseminated to massive sulphide (Payne, 1979 (Assessment Report 7707)). The sulphides are mostly a mixture of pyrrhotite, sphalerite, pyrite and galena. The skarn mineralogy typically consists of rhodonite, diopside, tremolite and magnetite. All massive sulphide mineralization of economic interest occurs in the upper sedimentary division (SED-2 of Payne, 1979). Within SED-2, sulphide layers with high zinc, lead and silver contents occur above the discontinuous rhyolite layer. Some sulphide pods and lenses are discordant, clearly related to late skarn alteration and/or remobilization of the stratiform sulphides.”
There is much more information available for the deposit on the British Columbia “Minfile” site, to which interested readers are referred.
Comments by Giles Peatfield regarding some of the minerals reported:
Acanthite?: Gower (1979) reported “argentite” in lenticular massive sulfide pods; Payne (1979) remarked that “argentite” had been reported in earlier studies. In neither case is there any further information, and I would regard this identification as tentative.
Actinolite: Payne (1979) reported actinolite in skarn bodies formed in chert units. I would regard this as valid for the locality.
Arsenopyrite: Although arsenopyrite is not commonly reported here, Bahan (1949) detailed the microscopy of the mineral in polished section. I would regard it as valid for the locality.
Biotite: Mihalynuk, et al. reported biotite in a “quartz porphyry” unit collected for radiometric dating. It is valid for the locality.
Boulangerite: Bahan (1949) described two varieties of a mineral that he identified as boulangerite, one fibrous and the other massive. He described the optical properties in detail, and went on to say that “X-Ray patterns taken of the powder proved the mineral to be boulangerite.” Unfortunately, he did not state which of the two varieties he X-rayed. We can be sure that there is boulangerite at Ericksen-Ashby, but there may be another mineral as well.
Calcite: Payne (1979) reporteded that “Red-fluorescent calcite occurs with some pyroxene bearing assemblages.” Such red fluorescence has been reported at other manganese-rich skarn and metasomatic deposits – for example Franklin and Sterling Hill, New Jersey (Frondel, 1972) and Broken Hill, Australia (Worner and Mitchell, 1982). It seems that the fluorescence is dependent on the manganese content of the calcite; the fluorescent Ericksen-Ashby material is from a manganese-rich skarn assemblage.
Diopside: This was reported by Payne (1979) in skarn assemblages.
Freibergite?: This was reported by Souther (1971); Payne (1979) said it had been identified in earlier studies. I can find no definitive data to verify the identification, and would regard this as tentative.
Garnet: This was reported by Payne (1979) in skarn assemblages, but with no data regarding the specific mineralogy.
Hornblende: This was reported by Payne (1979) in skarn assemblages.
Malachite: This was reported only by Kerr (1948) but not by any subsequent workers. It would be expected in this locality – perhaps other workers did not regard as important enough to mention?
Manganite?: This was reported by Bernius (1963), but in his subsequent detailed mineralography report (1964) he did not mention it, and no other workers reported it. Did he mistake it for another mineral? Manganite is an uncommon mineral in western Canada, with a single occurrence listed on Mindat, from Haida Gwaii (previously known as the Queen Charlotte Islands). I would regard its occurrence at Ericksen-Ashby as unlikely.
Marcasite: This was reported only by Bernius (1964), but he gave a good description of its microscopy details, and I would regard it as valid for the locality.
Meneghinite?: This was reported only by Bernius (1964). He identified it on the basis of microscopy, but interestingly mentioned microchemical tests for Sb and Cu, suggesting that his identification might not be valid. I would regard this as tentative at best.
Rhodochrosite?: Hedley (1966) reported that “Pink manganese minerals are present, including apparently rhodonite and rhodochrosite.” Several other workers have reported rhodonite, but this is the only mention of rhodochrosite. I would regard this as possible, but tentative for the locality.
Sternbergite?: Bernius (1964) tentatively identified sternbergite based on micrography and etch tests, but commented that “This mineral was very difficult to identify. Repeated attempts to get a microchem[ical] test for silver were unsuccessful in spite of the fact that silver assays from massive galena are quite high. An X-Ray analysis was also unsuccessful.” Dr. R. M. Thompson’s comment regarding this identification was “Doubtful”. I would regard it as unlikely for the locality.
Stibnite: This was reported by Hedley (1966) and by Payne (1979), with little supporting data. I would, however, regard it as probable for the locality.
Tetrahedrite: This has been reported by several workers, and was X-ray confirmed by Bahan (1949).
Tremolite: This was reported by Payne (1979) in skarn assemblages.
Wurtzite?: This was reported by Gower (1979), but he gave no supporting data nor did he give the source of his information. No other workers reported the mineral from here, and since it is a relatively rare species, I would regard its occurrence here as tentative.
Zircon: Mihalynuk, et al. reported zircon in a “quartz porphyry” unit collected for radiometric dating. It is valid for the locality.

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Link to British Columbia Minfile:	104K 009

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References