Alamo

Prospect, Undetermined

Alternative names

Glacier

Commodities and mineralogy

Main commodities Ag; Cu; Zn
Ore minerals chalcopyrite; pyrite; pyrrhotite; sphalerite
Gangue minerals quartz

Geographic location

Quadrangle map, 1:250,000-scale KC
Quadrangle map, 1:63,360-scale D-3
Latitude 55.756
Longitude -130.756
Nearby scientific data Find additional scientific data near this location
Location and accuracy The Alamo (Glacier) prospect is at an elevation of about 200-1000 feet above the north shore of Walker Cove, about 6.3 miles northeast of Hut Point. The prospect is along the northeast wall of a steep, southeast-trending gorge, in section 31, T. 70 S., R. 96 E., of the Copper River Meridian. It corresponds to loc. P-18 in Berg and others (1977, p. 116-120), and to loc. 22 in Elliott and others (1978). The location is accurate within 0.2 mile.

Geologic setting

Geologic description

The area of the Alamo prospect is underlain by a sequence of pelitic and quartzofeldspathic paragneiss, and minor dolomite marble that is part of a large metamorphic roof pendant in Tertiary or Cretaceous foliated granodiorite and quartz diorite of the Coast Range batholith (Berg and others, 1977, p. 117; Berg and others, 1988). The metamorphic sequence represents marine strata that underwent high-grade regional metamorphism in Cretaceous or Tertiary time. The premetamorphic age of the strata is uncertain, but they probably are mainly Paleozoic and may be as old as Precambrian (Berg and others, 1988, p. 26; Gehrels and others, 1990; Crawford and others, 2000).
The deposit is a 75-foot-wide sulfide-bearing zone in paragneiss near the contact of foliated granodiorite (Berg and others, 1977, p. 117-120). The zone strikes northwest and dips northeast, parallel to the regional foliation of the country rocks. At an elevation of about 870 feet, the paragneiss contains a layer of dolomite marble about 18 feet thick. From 0-18 feet above the marble, the paragneiss contains small amounts of pyrite and subordinate chalcopyrite. The next nine feet contain sparse pyrite and a trace of chalcopyrite. The marble appears to be barren. Other parts of the deposit contain seams, patches, and disseminated grains of chalcopyrite and pyrrhotite. The richest material sampled by the U.S. Bureau of Mines in 1972 was a small lens of massive chalcopyrite and other sulfides, accompanied by some quartz and breccia, about 15 inches thick and 30 inches long (Berg and others, 1977, p. 120 and table 11, no. 2P025). Atomic absorption assays of this material showed 10% Cu, 0.2% Zn, 50 ppm Ag, and 0.2 ppm Au. The zinc content in this sample, and the zinc content in several samples collected elsewhere in the deposit, indicate that sphalerite also is present. Twenty-six channel samples at several places along the deposit were collected by the Bureau in 1972 (Berg and others, 1977, p. 117-120). Assays of these samples showed up to 10% Cu and 2.1% Zn, along with as much as 75 ppm Pb, 50 ppm Ag, 15 ppm Mo, and, in one sample, 0.2 ppm Au. The results of this sampling indicate a large body of sulfide-bearing paragneiss containing 0.2%-0.7% Cu.
Geologic map unit (-130.757704371979, 55.7556566463591)
Mineral deposit model Metamorphosed Besshi massive sulfide? (Cox and Singer, 1986; model 24b)
Mineral deposit model number 24b?
Alteration of deposit Locally conspicuous iron-staining.

Production and reserves

Workings or exploration
The deposit was located as the Glacier prospect in 1954 and explored by a small amount of trenching and some core drilling (Berg and others, 1977, p. 116-117). It was restaked in 1969 by another locator as the Alamo group of six claims. Exploration since the restaking included some stripping, several shallow trenches, and 5 diamond drill holes. Four of the holes reportedly were 180 feet long and one was 90 feet long. Two additional claims were located in 1973, but at that time no assay values or logs had yet been released for any of the drill holes. Although results of this private exploration have not been made public, sample values were unofficially reported to range from 0.25%-1.3% Cu in the limited areas sampled. Other unofficial reports described several drill-hole intersections of 18- to 27-foot-long zones containing more than 1% Cu (Berg and others, 1977, p. 120). Continuity of these intersections between holes is uncertain.
Twenty-six channel samples at several places along the deposit were collected by the U.S. Bureau of Mines in 1972 (Berg and others, 1977, p. 117-120). Assays of these samples showed up to 10% Cu and 2.1% Zn, along with as much as 75 ppm Pb, 50 ppm Ag, 15 ppm Mo, and, in one sample, 0.2 ppm Au. The results of this sampling indicate a large body of sulfide-bearing paragneiss containing 0.2%-0.7% Cu.
Indication of production None

Additional comments

Prospect is in Misty Fiords National Monument Wilderness.

References