Dalcoath Dike

Prospect, Inactive

Commodities and mineralogy

Main commodities Sn
Ore minerals cassiterite
Gangue minerals arsenopyrite; chlorite; danburite; pyrite; tourmaline; white mica

Geographic location

Quadrangle map, 1:250,000-scale TE
Quadrangle map, 1:63,360-scale B-5
Latitude 65.489
Longitude -167.147
Nearby scientific data Find additional scientific data near this location
Location and accuracy The Dalcoath dike prospect is about 1 mile north of the Lost River Mine (TE048-TE051). It is on the south side of the ridge separating Crystal Creek and the headwaters of Cassiterite Creek, both east tributaries to Lost River in the York Mountains. The surface trace of the dike, which trends N 50 E and dips about 65 degrees north, has been mapped by Sainsbury (1969, plate 1) at elevations of 600 to over 1,000 feet. This location was not identified separately by Cobb and Sainsbury (1972) or Cobb (1975).

Geologic setting

Geologic description

The 2- to 3-foot wide, Dalcoath dike has been mapped for over a mile of length and is highly altered for about 2,000 feet of this length. It intrudes Ordovician limestone and is one of the set of lamprophyre dikes locally present throughout the Lost River area. Faulting has deformed limestone, dike rock, and altered rocks; fault gouge is well developed in some places. The dike may have originally been emplaced along a fault but some movement has post-dated emplacement, alteration, and mineralization. Six-inch wide limestone selvages adjacent to both sides of the dike are recrystallized and contain minor topaz and scattered tremolite. Some tremolite mats are developed along bedding. Cassiterite, intergrown with danburite, is locally abundant in this altered limestone (Knopf, 1908, p. 51). Alteration of the dike includes disseminated replacement by quartz, white mica, tourmaline, arsenopyrite, and pyrrhotite. Arsenopyrite-rich replacement is well developed along the hanging wall contact and small cassiterite grains are disseminated in the highly altered rocks (Knopf, 1908, p. 51). Samples of quartz-tourmaline rock contain up to 1.9% tin but only 3 ppm tungsten (Hudson, 1983).
Layered tactite is well developed on the lower slopes south of the Dalcoath dike. This tactite is also present on the lower part of the west side of the ridge cut by the Dalcoath dike in the area of the Hidden dike prospect (TE053). A positive magnetic anomaly detected by an airborne survey (McDermott, 1983) is developed in the Dalcoath dike area (Hudson, 1983).
Geologic map unit (-167.149722791725, 65.4882262374063)
Mineral deposit model Alteration and mineralization along lamprophyre dike in Ordovician limestone. Deposit analog is not clear; possibly tin vein (model 15b?) or at depth; tin skarn, replacement, or greisen (models 14b?, 14c?, and 15c?) after Cox and Singer (1986).
Mineral deposit model number 14b?, 14c?, 15b?, 15c?
Age of mineralization The age of the mineralization is assumed to be related to the development of tin systems in the Lost River area and therefore Late Cretaceous, the age of the tin-mineralizing granites there (Hudson and Arth, 1983).
Alteration of deposit The strongly altered lamprophyre dike has abundant white mica, arsenopyrite, quartz, tourmaline, danburite in places, chlorite, pyrite, and some topaz.

Production and reserves

Workings or exploration Prospect pits scattered along the dike, a 100-foot long adit, and a 25-foot deep shaft were completed by 1918 (Steidtmann and Cathcart, 1922, p. 76-77). There has been only occasional surface observation and sampling since.
Indication of production None
Reserve estimates Not defined

References

MRDS Number 10308416

References

Hudson, T.L., 1983, Interim report on the Lost River district, Seward Peninsula, Alaska: Anchorage, Alaska, Anaconda Minerals Company internal report (Report held by Cook Inlet Region, Inc., Anchorage, Alaska).
Hudson, T.L., and Arth, J. G., 1983, Tin granites of Seward Peninsula, Alaska: Geological Society of America Bulletin, v. 94, p. 768-790.
McDermott, M.M., 1983, Investigation of the magnetic contact aureoles of the Khotol and Black Mountain granites, Alaska: Anchorage, Alaska, Anaconda Minerals Company internal report (Report held by Cook Inlet Region, Inc., Anchorage, Alaska).
Reporters Travis L. Hudson (Applied Geology)
Last report date 5/10/1998