High Horse

Prospect, Undetermined

Alternative names


Commodities and mineralogy

Main commodities Au
Other commodities Zn
Ore minerals gold; pyrite; sphalerite
Gangue minerals quartz

Geographic location

Quadrangle map, 1:250,000-scale KC
Quadrangle map, 1:63,360-scale B-4
Latitude 55.367
Longitude -131.181
Nearby scientific data Find additional scientific data near this location
Location and accuracy
The High Horse claim is in section 18, T. 75 S., R. 94 E., of the Copper River Meridian. It straddles Gokachin and Sea Level creeks, just upstream from their confluence. The map site represents the approximate center of the claim as shown in Wright and Wright (1908, fig. 12). The site corresponds to loc. 98 in Elliott and others (1978). The location is accurate within about 0.25 mile.
Also see Additional comments.

Geologic setting

Geologic description

The country rocks in this part of Revillagigedo Island are marine, interbedded, andesitic and basaltic metavolcanic rocks and subordinate pelitic metasedimentary rocks that are intruded by stocks, sills, and dikes of Cretaceous feldspar-porphyritic granodiorite (Berg and others, 1988). The strata and some of the granodiorite were regionally metamorphosed to greenschist grade in Late Cretaceous time. These regionally metamorphosed rocks subsequently were locally remetamorphosed to hornblende hornfels near the contacts of Cretaceous granodiorite plutons that were emplaced after the regional metamorphism. The premetamorphic age of the strata is uncertain. Berg and others (1988) assign them a Mesozoic or (late) Paleozoic age. Berg (1982) and Crawford and others (2000) assign them to the Gravina belt, of Late Jurassic or Cretaceous age, or to the Taku terrane, of late Paleozoic to Late Triassic age. The metamorphic and intrusive rocks locally are overlain by basalt and andesite lava flows of Quaternary or Tertiary age.
Brooks (1902, p. 68) describes the Monster (subsequently relocated as High Horse) deposit as a 12- to 20-foot-wide pegmatite dike that contains abundantly disseminated pyrite, but very low gold values. The dike cuts diabase schist, which also carries considerable pyrite near its contact with the pegmatite.
According to Wright and Wright (1908, p. 147-148), the High Horse prospect is an [auriferous] quartz fissure vein 6 inches to 3 feet thick that strikes N55E and dips 75SE. The vein is hosted by schists that strike N50W and dip 80NE. The ore consists chiefly of pyrite and sphalerite, and, reportedly, carries low values in gold.
The foregoing descriptions, although scanty, suggest that the High Horse vein is similar in character and geologic setting to other auriferous quartz fissure veins in the Sea Level mine area (see KC095-098).
Maas and others (1995, p. 215) note that the quartz in the veins in the Sea Level mine area is not recrystallized; the veins thus are probably younger than most or all of the Late Cretaceous regional metamorphism.
Geologic map unit (-131.182693813744, 55.3666601333301)
Mineral deposit model Low-sulfide Au-quartz veins (Cox and Singer, 1986; model 36a)
Mineral deposit model number 36a
Age of mineralization Maas and others (1995, p. 215) note that the quartz in the veins in the Sea Level mine area is not recrystallized; the veins thus are probably younger than most or all of the Late Cretaceous regional metamorphism.
Alteration of deposit Most of the principal veins in the Sea Level mine area are bordered by a hydrothermally altered zone up to three feet thick, characterized by generally fine-grain, light-gray to bluish-gray, massive, carbonate- and sericite-bearing rock that commonly contains cubic pyrite crystals up to an inch across (Maas and others, 1995, p. 215). Maas and others (1995) interpret this zone as hydrothermally altered mafic metavolcanic rock. Early miners called this altered rock 'blue porphyry,' which they interpreted as crosscutting altered dikes that predate the quartz veins, but are closely associated with some of the orebodies (Brooks, 1902, p. 65; Wright and Wright, 1908, p. 143). Gold content of these pyritic altered zones is high adjacent to the quartz veins and diminishes away from them. Weathered altered rocks have a reddish-brown, oxidized rind up to three inches thick.

Production and reserves

Workings or exploration The deposit was explored in the early 1900s by opencuts and a short prospect tunnel.
Indication of production Undetermined

Additional comments

The High Horse claim is a relocation of the original Monster claim (Wright and Wright, 1908, p. 147).


MRDS Number A012351


Reporters H.C. Berg, USGS
Last report date 7/4/1999