Double Anchor; Alaska State Mines Extension Prospect, Hyder District, Prince of Wales-Outer Ketchikan Borough, Alaska, USA
This page is currently not sponsored. Click here to sponsor this page.
Location: The Double Anchor prospect is in Section 16 at an elevation of about 4100 feet near the top of a south-facing mountainside overlooking Texas Lake, about 0.7 mile south of the lake (Berg and others, 1977, p. 79; Elliott and Koch, 1981, p. 11, loc. 30).
Geology: The country rocks in the area near the Double Anchor prospect are pelitic metasedimentary and minor andesitic metavolcanic strata of the Jurassic or older Mesozoic Hazelton Group; the Triassic Texas Creek Granodiorite, which underlies and locally intrudes the Hazelton; and the Eocene Hyder Quartz Monzonite, which cuts both the Hazelton and Texas Creek rocks (Smith, 1977; Koch, 1996). Buddington (1929, p. p. 98-99) describes the deposit as a subhorizontal shear zone in argillite and graywacke that contains seams and stringers of quartz and sulfides, including sphalerite, galena, pyrite, chalcopyrite, and sparse pyrrhotite. The largest orebody is about 2.5 feet thick and 30 feet long; most individual veins are less than an inch thick. Thick quartz veins nearby are only sparsely mineralized. Berg and others (1977, p. 38-39) describe two quartz breccia zones. One is subhorizontal, up to about a foot thick, and exposed for about 700 feet along strike; the other dips steeply and is exposed for about 160 feet along strike. Both zones contain pyrite, galena, sphalerite, and chalcopyrite. The weighted average of analyses of samples collected by the U.S. Bureau of Mines in 1972 (Berg and others, 1977, p. 79-84) across about a two-foot-width of the main (subhorizontal) orebody is 4.3% Pb, 1.0% Zn, and 3.5 oz Ag and 0.022 oz Au per ton. Lead-isotope studies of galena from the Double Anchor prospect have yielded Jurassic and Eocene ages (Maas and others, 1995, p. 235, 244). The deposit is interpreted to be polygenetic, originating during Jurassic Hazelton island-arc volcanism (Alldrick, 1993), and then partly remobilized or reconstituted as fissure veins during Eocene emplacement of the Hyder Quartz Monzonite.
Workings: Prospect was explored, probably in the 1920's, by pits and short adits. The weighted average of analyses of samples collected by the U.S. Bureau of Mines in 1972 (Berg and others, 1977, p. 79-84) across about a two-foot-width of the main (subhorizontal) orebody is 4.3% Pb, 1.0% Zn, and 3.5 oz Ag and 0.022 oz AU per ton.
Age: Lead-isotope studies of galena from the Double Anchor prospect have yielded Jurassic and Eocene ages (Maas and others, 1995, p. 235, 244). The deposit is interpreted to be polygenetic, originating during Jurassic Hazelton island-arc volcanism (Alldrick, 1993), and then partly remobilized or reconstituted during Eocene emplacement of the Hyder Quartz Monzonite.
Alteration: Local intense iron staining. The subhorizontal quartz breccia zone is oxidized.
Commodities (Major) - Ag, Au, Cu, Pb, Zn; (Minor) - Cu
Development Status: None
Deposit Model: Polymetallic veins
5 entries listed. 5 valid minerals.
The above list contains all mineral locality references listed on mindat.org. This does not claim to be a complete list. If you know of more minerals from this site, please register so you can add to our database. This locality information is for reference purposes only. You should never attempt to visit any sites listed in mindat.org without first ensuring that you have the permission of the land and/or mineral rights holders for access and that you are aware of all safety precautions necessary.
Alldrick, D.J., 1993, Geology and metallogeny of the Stewart mining camp, northwestern British Columbia: British Columbia Department of Mines and Petroleum Resources Bulletin 85, 105 p., 2 plates, scale 1:50,000. Berg, H.C., Elliott, R.L., Smith, J.G., Pittman, T.L., and Kimball, A. L., 1977, Mineral resources of the Granite Fiords Wilderness Study Area, Alaska, with a section on aeromagnetic data by Andrew Griscom: U.S. Geological Survey Bulletin 1403, 151 p. Buddington, A.F., 1929, Geology of Hyder and vicinity, southeastern Alaska, with a reconnaissance of Chickamin River: U.S. Geological Survey Bulletin 807, 124 p. Elliott, R.L., and Koch, R.D., 1981, Mines, prospects, and selected metalliferous mineral occurrences in the Bradfield Canal quadrangle, Alaska: U.S. Geological Survey Open-File Report 81-728-B, 23 p., 1 sheet, scales 1:250,000 and 1:63,360. Maas, K.M., Bittenbender, P E., and Still, J.C., 1995, Mineral investigations in the Ketchikan mining district, southeastern Alaska: U.S. Bureau of Mines Open-File Report 11-95, 606 p. Smith, J.G., 1977, Geology of the Ketchikan D-1 and Bradfield Canal A-1 quadrangles, Alaska: U.S. Geological Survey Bulletin 1425, 49 p., 1 plate.