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Lucky Four

Prospect in Alaska, United States with commodities Copper, Gold
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Sections on this page
  1. Identification information
  2. Geographic coordinates
  3. Site location context
  4. Geographic areas
  5. Commodities
  6. Materials information
  7. Alteration
  8. Mineral occurrence model information
  9. Host and associated rocks
  10. Nearby scientific data
  11. Economic information about the deposit and operations
  12. Mining district
  13. Links to other databases
  14. Bibliographic references
  15. General comments
  16. Reporter information

Geologic information

Identification information

Deposit ID 10001567
MRDS ID A012316
Record type Site
Current site name Lucky Four
Alternate or previous names Hump Island

Geographic coordinates

Geographic coordinates: -131.75872, 55.5228 (WGS84)
Relative position This prospect is on Hump Island, which is in Clover Passage about 13 miles northwest of Ketchikan. The island is about 0.9 mile long and 0.2 mile wide, and is in sections 20, 21, and 29, T. 73 S., R. 90 E., of the Copper River Meridian. The site corresponds to loc. 41 in Elliott and others (1978), and to loc. 264 in Maas and others (1995, p. 277 and fig. 5). The location is accurate within a hundred or so feet.

Site location context

Political divisions (FIPS codes)

Ketchikan Gateway(Borough)

Alaska(state)

United States(country)

North America(continent)

Land(continent)

USGS map quadrangles

Ketchikan C-6(quadrangle 1:63,360 scale)

Ketchikan NW(quadrangle 1:100,000 scale)

Ketchikan(quadrangle 1:250,000 scale)

Hydrologic units (watersheds)

Ketchikan(hydrologic unit)

Southern Southeast Alaska(hydrologic accounting unit)

Southeast Alaska(hydrologic subregion)

Alaska(hydrologic region)

Federal lands

Tongass National Forest(National Forest)

National Forest FS(Type of land area)

FS(Federal land areas administered by FS)

Geographic areas

Country State
United States Alaska

Commodities

Commodity Importance
Copper Primary
Gold Secondary

Materials information

Materials Type of material
Chalcopyrite Ore
Molybdenite Ore
Pyrite Ore
Quartz Gangue

Alteration

  • (Local) Locally intense silicification, argillization, and sericitization. Local iron-staining and oxidation of copper minerals.

Mineral occurrence model information

Model code 53
USGS model code 17
Deposit model name Porphyry Cu
Mark3 model number 4

Host and associated rocks

  • Host or associated Host
    Rock type Metamorphic Rock > Schist

Nearby scientific data

(1) -131.75872, 55.5228
ListMap

Economic information

Comments on the geologic information

  • Geologic Description = The country rocks on and near Hump Island consist chiefly of flyschlike metasedimentary rocks and subordinate andesitic and basaltic metavolcanic rocks that are intruded by Cretaceous feldspar-porphyritic granodiorite stocks, sills, and dikes (Berg and others, 1988). The strata were regionally metamorphosed to greenschist-grade phyllite and semischist in Late Cretaceous time (Brew, 1996, p. 27). Near some of the granodiorite contacts, the phyllite and semischist were subsequently contact metamorphosed to hornblende hornfels (Berg and others, 1988). The premetamorphic age range of the strata is unknown; Berg and others (1988, p. 17) note that they closely resemble Upper Jurassic and mid-Cretaceous marine flysch and volcanic rocks nearby on Gravina Island.? Hump Island consists largely of intensely hydrothermally altered and locally sulfide-bearing rocks. Maas and others (1995, p. 277) describe the island as a small, foliated, Cretaceous quartz diorite or quartz monzonite pluton that intrudes Jurassic or Cretaceous mafic to felsic volcanic rocks and interbedded pelitic sedimentary rocks. Weak porphyry copper mineralization accompanied emplacement of the pluton, along with silicic and argillic alteration of the surrounding country rocks. The east side of the island is underlain by felsic volcanic rocks that have been altered to quartz-sericite-pyrite schist with a high silica content. The west side is intensely argillized pelitic schist. ? the deposit consists of pyrite, chalcopyrite, and minor molybdenite that form veinlets and disseminations in the hydrothermally altered rocks. Locally, chalcopyrite, and possibly other sulfides, occur as small masses in quartz veinlets (Maas and others, 1995, p. 278). Assays of samples of sulfide-bearing veins and altered country rocks collected in the early 1990s by the U.S. Bureau of Mines ranged from 806-3080 ppm Cu (average: 2064 ppm Cu) and 6-236 ppm Mo (average: 69 ppm Mo), along with as much as 3.6 ppm Ag, 3837 ppb Au, 172 ppm Bi, and 11 ppm Te (Maas and others, 1995, p. 278 and fig. 73). Other samples of sulfide-bearing altered rocks contained up to 2.0% Cu, 10 ppm Ag, 30 ppm Mo, and 500 ppm Co (Elliott and others, 1978, loc. 41). Maas and others (1995, p. 278) classify the prospect as a metamorphosed porphyry Cu deposit, and note that it is the only one known in the Ketchikan district.
  • Age = Probably Late Cretaceous.

Economic information about the deposit and operations

Development status Prospect
Commodity type Metallic

Mining district

District name Ketchikan

Comments on the workings information

  • Workings / Exploration = Assays of samples of sulfide-bearing veins and altered country rocks collected in the early 1990s by the U.S. Bureau of Mines ranged from 806-3080 ppm Cu (average: 2064 ppm Cu) and 6-236 ppm Mo (average: 69 ppm Mo), along with as much as 3.6 ppm Ag, 3837 ppb Au, 172 ppm Bi, and 11 ppm Te (Maas and others, 1995, p. 278 and fig. 73). Other samples of sulfide-bearing altered rocks contained up to 2.0% Cu, 10 ppm Ag, 30 ppm Mo, and 500 ppm Co (Elliott and others, 1978, loc. 41).

Reference information

Bibliographic references

Comments on the references

  • Primary Reference = Maas and others, 1995

General comments

Subject category Comment text
Deposit Model Name = Metamorphosed porphyry Cu deposit (Cox and Singer, 1986; model 17)

Reporter information

Type Date Name Affiliation Comment
Reporter 30-JUN-1999 H.C. Berg U.S. Geological Survey

Beyond USGS

Supplemental information added by qvyshift.com. Not part of the original USGS MRDS record.

Maps centered on this site

Authoritative Alaska resources

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