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Tin-Midway

Prospect in Alaska, United States with commodities Silver, Copper, Lead, Zinc, Cadmium, Cobalt
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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. Nearby scientific data
  10. Economic information about the deposit and operations
  11. Mining district
  12. Links to other databases
  13. Bibliographic references
  14. General comments
  15. Reporter information

Geologic information

Identification information

Deposit ID 10307853
Record type Site
Current site name Tin-Midway
Alternate or previous names Tin Creek #1

Geographic coordinates

Geographic coordinates: -153.65284, 62.41948 (WGS84)
Relative position The Tin Creek-Midway deposit is exposed in a canyon of a major tributary of Tin Creek, about 2.4 kilometers northwest of the north end of Veleska Lake at an elevation of 2,250 feet (685 m) in the NE1/4 sec. 24, T. 27 N., R. 24 W., of the Seward Meridian. The reporter visited the site in 1981 and 1983.

Site location context

Political divisions (FIPS codes)

Yukon-Koyukuk(Census area)

Alaska(state)

United States(country)

North America(continent)

Land(continent)

USGS map quadrangles

McGrath B-2(quadrangle 1:63,360 scale)

McGrath SE(quadrangle 1:100,000 scale)

McGrath(quadrangle 1:250,000 scale)

Hydrologic units (watersheds)

Upper Kuskokwim River(hydrologic accounting unit)

Southwest(hydrologic subregion)

Alaska(hydrologic region)

Federal lands

Cook Inlet Region, Incorporated(ANCSA Region)

ANCSA Region NTVPIC(Type of land area)

NTVPIC(Federal land areas administered by NTVPIC)

Geographic areas

Country State
United States Alaska

Commodities

Commodity Importance
Silver Primary
Copper Primary
Lead Primary
Zinc Critical Primary
Cadmium Secondary
Cobalt Critical Secondary

Materials information

Materials Type of material
Arsenopyrite Ore
Chalcopyrite Ore
Galena Ore
Pyrite Ore
Marmatite Ore
Amphibole Gangue
Calcite Gangue
Epidote Gangue
Garnet Gangue
Quartz Gangue
Pyroxene Gangue
Johannsenite Gangue

Alteration

  • (Local) Late epidotization of prograde skarns.

Mineral occurrence model information

Model code 60
USGS model code 18c
Deposit model name Skarn Zn-Pb
Mark3 model number 22

Nearby scientific data

(1) -153.65284, 62.41948
ListMap

Economic information

Comments on the geologic information

  • Geologic Description = The Tin Creek-Midway deposit (southern extension is known as Tin Creek #1) is perhaps the best-studied silver-base metal skarn deposit in the Farewell Mineral belt. It consists of a series of sulfide-skarn deposits that occur along contacts between dikes and carbonate sedimentary rocks, along faults, and as bedding replacements of calcareous units in siliciclastic rocks (Lu and others, 1992). The mineralization occurs where a composite, northwest trending dike and sill swarm (averaging granodiorite in composition) cuts highly deformed siliciclastic and carbonate sedimentary rocks of the mid-Silurian Terra Cotta Mountains Sandstone, a unit of the Dillinger subterrane (Bundtzen, Harris, and Gilbert, 1997). . The sedimentary rocks have been transformed into marble, garnet-banded marble, banded hornfels, and sulfide-rich, calc-silicate skarn. Volcanic units of the Latest Cretaceous (65 Ma) Veleska Lake Volcanic Field (Bundtzen, Harris, and Gilbert, 1997) cap the section immediately south of the Tin Creek-Midway Skarn deposit. Three sets of faults are present: (1) N30E high angle faults; (2) N50E-trending low angle reverse or thrust faults; and (3) younger west to northwest trending high angle faults that cut the earlier, northeast trending faults (Szumigala, 1986, 1987; Lu and others, 1992). These latter faults apparently controlled the northwest-trending granodiorite dike and sill swarm. Practically all of these dikes contain endoskarns; i.e., the dikes were apparently intruded prior to skarn mineralization. Several granodiorite dikes in the prospect area have been radiometrically dated at 25-30 Ma (Szumigala, 1987; Solie and others, 1991). Mineralized areas explored by Anaconda Minerals Company (Reed, 1982) were designated the MW (Tin Creek- Midway) and TCI (Tin Creek #1) zones. Although both endoskarn and exoskarn occur at the Tin Creek-Midway deposit, only exoskarn contains significant silver-base metal mineralization (Lu, 1988). The Tin Creek-Midway skarn system is zoned from a predominantly garnet skarn with abundant chalcopyrite and stockwork quartz veining in the northern MW zone to a pyroxene (johannsenite) skarn dominated by iron-rich sphalerite (marmatite) and minor galena in the southern TCI zone (Lu and others, 1992). Microthermometric, isotopic, and microprobe data collected by Szumigala (1985,1987), Lu (1988, 1989), and Lu and others (1992) all indicate the Tin Creek-Midway skarn can be described as a low temperature (<250 degrees C), lead-zinc skarn in the southern TCI zone that zones into a higher temperature (>280 degrees C), copper-base metal skarn in the northern MW zone. A plutonic heat source is indicated near the northern MW mineral zone. Using the FeS mole fraction in sphalerite, Lu (1988) calculated that skarn formation took place at about 300 bars, or in a very shallow, subvolcanic environment . Six drill holes penetrated the Tin Creek-Midway deposit. Channel sampling from the various sulfide horizons average 0.7 percent copper, 4.7 percent zinc, and 40.4 grams/tonne silver over sample widths ranging from 1.5 meters to 23.0 meters (Brewer and others, 1992). Surface grab samples summarized by Bundtzen and others (1997) contain 0.35 percent copper, 0.17 percent lead, 5.55 percent zinc, 0.05 percent cadmium, and 13.0 grams/tonne silver. Based on subsurface exploration work completed by Anaconda Minerals Company (Reed, 1982; Rob Kell, written communication, 1984), at least 353,000 tonnes of semi- to massive-sulfide mineralization is inferred in the Tin Creek-Midway skarn deposit.
  • Age = Not dated; inferred to be 25-to-30 Ma, based on ages of granodiorite dike swarm (Solie and others, 1991).

Economic information about the deposit and operations

Development status Prospect

Comments on exploration

  • Status = Inactive

Mining district

District name McGrath

Comments on the reserve resource information

  • Reserves = Based on Anaconda Minerals Company exploration work, which included some limited diamond drilling, about 353,000 tonnes of semi- to massive-sulfide mineralization (of unstated grade) can be inferred at the Tin Creek-Midway deposit (Noklebeg and others, 1987).

Comments on the workings information

  • Workings / Exploration = The Tin Creek-Midway skarn was investigated by the Alaska Division of Geological and Geophysical Surveys in 1980 (Bundtzen, Kline, and Clough, 1982). During 1981 and 1982, the Anaconda Minerals Company explored the deposit with surface sampling and 6 diamond drill holes (Reed, 1982; Brewer and others, 1992). Channel sampling of the various sulfide horizons average 0.7 percent copper, 4.7 percent zinc, and 40.4 grams/tonne silver over sample widths ranging from 1.5 meters to 23.0 meters (Brewer and others, 1992). Grab samples collected by Bundtzen, Harris, and Gilbert (1997) contained 0.35 percent copper, 0.17 percent lead, 5.55 percent zinc, 500 ppm cadmium, and 13.0 grams/tonne silver. Based on the Anaconda Minerals Company exploration work, about 353,000 tonnes of semi- to massive-sulfide mineralization (of unstated grade) is inferred at the Tin Creek-Midway deposit (Nokleberg and others, 1987). However, no official grade and tonnage data has been formally released (Reed, 1982; Brewer and others, 1992; Rob Kell, written communication, 1984).

Reference information

Bibliographic references

Comments on the references

  • Primary Reference = Szumigala, 1987

General comments

Subject category Comment text
Deposit Model Name = Low temperature lead-zinc skarn deposit (Cox and Singer, 1986; model 18c).
Deposit Other Comments = See Tin Creek-North (MG041), Tin Creek-South (MG046), Bowser Creek Northeast (MG067), and Bowser Creek-Main deposits (MG068).

Reporter information

Type Date Name Affiliation Comment
Reporter 06-DEC-98 T.K. Bundtzen Pacific Rim Geological Consulting

Beyond USGS

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

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Authoritative Alaska resources

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