Unnamed, near Lime Peak Pluton (Rocky Mountain)

Prospect, Inactive

Commodities and mineralogy

Main commodities Sn
Other commodities Ag; Cu; Mo; U; W; Zn
Ore minerals cassiterite; chalcopyrite; molybdenite; pyrite
Gangue minerals chlorite; fluorite; quartz; sericite; topaz; tourmaline

Geographic location

Quadrangle map, 1:250,000-scale CI
Quadrangle map, 1:63,360-scale C-6
Latitude 65.635
Longitude -146.7
Nearby scientific data Find additional scientific data near this location
Location and accuracy The location given is the approximate center of tin mineralization within the Lime Peak pluton. It is about 1.6 mi due east of VABM Mascot. Lime Peak, also identified more recently as 'Rocky Mountain' is approximately 58 miles northeast of Fairbanks in the White Mountains. There is no road access to the area. The Steese Highway is located 30 miles to the southeast and existing winter trails extend from it into the area.

Geologic setting

Geologic description

The Lime Peak pluton is one of five lower Tertiary and/or Upper Cretaceous plutons exposed in the White Mountains (Foster and others, 1983). The Lime Peak pluton is a composite intrusion comprising at least three plutonic phases cut by two sets of north-trending dikes (Burton and others, 1985). The most abundant rock type is medium- to coarse-grained, equigranular to porphyritic, biotite granite that contains approximately 35 percent smoky quartz, 40 percent orthoclase, 20 percent albitic plagioclase, 5 percent biotite and trace to minor amounts of fluorite, apatite and zircon. Plagioclase, quartz and biotite occur as subhedral, embayed crystals surrounded by larger anhedral orthoclase phenocrysts. This unit commonly forms tors that line ridgetops in the Lime Peak area. The second most abundant intrusive phase is leucocratic, fine-grained, hypidiomorphic granular, seriate biotite granite that is found along the margins of, and in scattered outcrops within, the Lime Peak pluton. The third unit is a small body of moderately coarse-grained equigranular muscovite granite composed of approximately 40 percent smoky quartz, 30 percent albitic plagioclase, 25 percent orthoclase, 4 percent muscovite, up to 2 percent tourmaline, and minor amounts of fluorite. This third unit outcrops at the southwestern end of the Lime Peak pluton. The Lime Peak pluton intrudes metasedimentary rocks, dominantly quartzite and argillite, of Precambrian and/or Paleozoic age (Burton and others, 1985). Wilson and Shew (1981) obtained a K-Ar age of 56.7 m.a. for the granite, which intrudes sandstone, shale, and slate. The intrusion is exposed over 2500 vertical ft, and forms abundant rubble above 3500 ft elevation.
High tin values are concentrated in intensely altered biotite granite. Numerous occurrences of fault-controlled, tin-bearing greisen have been identified. The greisen is composed of quartz, chlorite, sericite, and minor amounts of fluorite, tourmaline, topaz, pyrite, chalcopyrite, and molybdenite; samples contain between 60 and 1560 ppm tin (Burton and others, 1985). Seven samples from separate occurrences along the ridge in section 3, T. 9 N., R. 5 E. (Warner and others, 1988) contained an average of 610 ppm Sn and 2.36 ppm Ag with values ranging from 220 to 1000 ppm Sn and 0.37 to 4.84 ppm Ag. Warner and others (1988) also collected samples of greisen in the Lime Peak area that contain up to 7100 ppm Sn, as well as locally anomalous concentrations of arsenic, beryllium, boron, columbium, copper, gold, iron, lead, lithium, manganese, silver, strontium, tungsten, uranium and zinc.
Geologic map unit (-146.702504569044, 65.634603165945)
Mineral deposit model Sn greisen (Cox and Singer, 1986; model 15c).
Mineral deposit model number 15c
Age of mineralization Mineralization is related to Tertiary and/or Upper Cretaceous granitic plutons.
Alteration of deposit Deuteric: tourmalization; hydrothermal: chloritization, sericitization, silicification.

Production and reserves

Workings or exploration Surface samples taken.
Indication of production None

Additional comments

The name 'Lime Peak' has been changed to 'Rocky Mountain' on recent topographic maps; however, most literature refers to the peak as 'Lime Peak'.


MRDS Number A012245


Reporters C.J. Freeman, J.R. Guidetti Schaefer, A.S. Clements (Avalon Development Corporation)
Last report date 6/22/1998