1. Mineral Resources
  2. Online Spatial Data
  3. Mineral Resource Data System (MRDS)

Pebble Deposit

Prospect in Alaska, United States with commodities Copper, Gold, Molybdenum, Silver
Map
XML
JSON
KML
B
Sections on this page
  1. Identification information
  2. Geographic coordinates
  3. Site location context
  4. Geographic areas
  5. Public Land Survey System information
  6. Commodities
  7. Materials information
  8. Alteration
  9. Mineral occurrence model information
  10. Host and associated rocks
  11. Nearby scientific data
  12. Economic information about the deposit and operations
  13. Mining district
  14. Mineral rights holdings
  15. Land status
  16. Ownership information
  17. Reserves and resources
  18. Links to other databases
  19. Bibliographic references
  20. Reporter information

Geologic information

Identification information

Deposit ID 10258264
MAS/MILS ID 0021030050
Record type Site
Current site name Pebble Deposit
Alternate or previous names Pebble Beach Copper, Pebble Copper

Geographic coordinates

Point of reference Ore Body
Geographic coordinates: -155.2952, 59.8971 (WGS84)
Elevation 350
Location accuracy 100(meters)
Relative position About 2 miles north of locally named Frying Pan Lake (elevation 943 feet) in the headwaters of the Koktuli River. The location is accurate within a few hundred feet for the center of the outcrop area of this large deposit. The drilled mineralization extends underground several thousand feet east of the outcrop.

Site location context

Political divisions (FIPS codes)

Lake and Peninsula(Borough)

Alaska(state)

United States(country)

North America(continent)

Land(continent)

USGS map quadrangles

Iliamna D-7(quadrangle 1:63,360 scale)

Iliamna NW(quadrangle 1:100,000 scale)

Iliamna(quadrangle 1:250,000 scale)

Hydrologic units (watersheds)

Mulchatna River(hydrologic unit)

Nushagak River(hydrologic accounting unit)

Southwest(hydrologic subregion)

Alaska(hydrologic region)

Geographic areas

Country State
United States Alaska

Public Land Survey System information

Meridian Township Range Section Fraction State
Seward 003 S 035 W 21 SW1/4 SE1/4 Alaska

Commodities

Commodity Importance
Copper Primary
Gold Primary
Molybdenum Secondary
Silver Secondary

Materials information

Materials Type of material
Gold Ore
Pyrite Ore
Chalcopyrite Ore
Molybdenite Ore
Bornite Ore
Covellite Ore
Chalcocite Ore
Magnetite Ore
Galena Ore
Sphalerite Ore
Goethite Ore
Biotite Gangue
Diorite Gangue
Quartz Gangue

Alteration

  • (Local) potassic

Mineral occurrence model information

Model code 78
USGS model code 20c
Deposit model name Porphyry Cu-Au
Mark3 model number 34

Host and associated rocks

  • Host or associated Host
    Rock type Plutonic Rock > Granitoid > Tonalite
    Stratigraphic age (youngest) Late Cretaceous
  • Host or associated Host
    Rock type Plutonic Rock > Granitoid > Granodiorite
    Stratigraphic age (youngest) Late Cretaceous

Nearby scientific data

Ore Body (1) -155.2952, 59.8971
ListMap

Economic information

Comments on the geologic information

  • From ARDF
    Pebble Copper is a porphyry copper-gold-molybdenum deposit in the outer part of an Upper Cretaceous (89.7 Ma) tonalite-granodiorite batholith (Detterman and Reed, 1980). The batholith intrudes flysch of Jurassic or Cretaceous age. The west and south parts of the batholith comprise five textural and compositional phases ('the porphyry suite'): biotite diorite, equigranular granodiorite, porphyrytic granodiorite, biotite granodiorite, and intrusive breccia. Breccias appear to have developed with each intrusive phase; the largest breccia body is weakly mineralized (Bouley and others, 1995).

    The highest grade parts of the deposit are associated with porphyritic granodiorite in which plagioclase phenocrysts are replaced by potassium feldspar and sericite, and amphibole is replaced by granular greenish biotite. The 'porphyry suite' and the sedimentary country rocks at Pebble Copper are variably mineralized depending on host rock composition and proximity to the center of mineralization. Sulfides occur in stockwork veinlets near the core of the deposit, and are disseminated in peripheral phases. Most of the copper-and gold-bearing minerals occur either in hairline veinlets or in larger veins having well-developed potassic vein selvages. Copper sulfides, chiefly chalcopyrite, also occur as disseminations. Molybdenite occurs in late quartz veinlets that crosscut introduced potassic minerals. Metallic minerals identified at Pebble Copper include pyrite, chalcopyrite, and molybdenite, along with minor bornite, covellite, chalcocite, digenite, and magnetite. Gold is fine-grained, generally only a few microns in diameter, and generally occurs at or near pyrite-chalcopyrite grain boundaries (Bouley and others, 1995). Galena and sphalerite are reported in quartz veins on the periphery of the deposit. Alteration minerals include abundant secondary biotite and potassium feldspar and lesser amounts of ferroan dolomite, albite, and quartz. Characteristic accessory minerals are anhydrite, apatite, and rutile.

    Cross-section 7 of Bouley and others (1995) suggests that the higher grade core overlies a stock or cupola of the porphyritic granodiorite. Mineralized material typically contains 200-300 parts per million of molybdenum: molydenite probably would be recovered as a concentrate in a future mining operation. The deposit is oxidized to a depth of as much as 100 feet. Some secondary chalcocite is developed, but in general the richer ore seems to be related to variations in hypogene rather than supergene mineralization. Gossan of goethite and other oxidized minerals is developed locally, especially over peripheral pyrite-rich parts of the mineral deposit.

    Pebble Copper has been restudied since 2001 by Northern Dynasty Minerals. A regional IP program indicates that it is one of several deposits in an open-ended, 90-square-kilometer (34.8-square-mile) IP/chargeability anomalous area (Youngman, 2003). Northern Dynasty Minerals drilled 68 holes totaling 11,000 meters (about 36,100 feet) in the anomalous area in 2002, and identified new deposits described in records IL002, -003, and -004. The nearby Sill or 25 Gold (IL005) epithermal gold deposit was discovered by Cominco during reconnaissance studies of the area, and has been further explored by Northern Dynasty. The plutonic hostrocks of the Pebble Copper deposit are alkalic (potassic), and are similar to potassium-rich plutons that host copper-gold deposits throughout the world (Bouley and others, 1995; Muller and Groves, 1995).
  • From ARDF
    The dominant pervasive alteration at Pebble Copper is potassic. Secondary biotite has replaced primary mafic minerals and groundmass, and potassium feldspar and biotite have replaced plagioclase (Bouley and others, 1995). Ferroan dolomite, albite, anhydrite, rutile, and quartz were introduced locally. The deposit is oxidized to a depth of 100 feet.

Economic information about the deposit and operations

Operation type Surface
Development status Prospect
Commodity type Metallic
Significant Yes
Discovery year 1989

Comments on exploration

  • From ARDF
    Cominco Alaska Exploration began to explore Pebble Copper in 1986. Early exploration was based on color anomalies observed by local pilots. Drilling started in the 1988 season and continued through 1992, when twelve holes were drilled to further delineate the higher grade porphyry zone found in drilling campaigns between 1988 and 1992. The general objectives were to: 1) define the extent of the porphyry system above a cutoff grade of 0.2 percent copper; 2) delineate the grade and shape of the deposit within the 0.2 percent area; and 3) delineate more precisely the size and grade of the higher grade core. Other work included a limited IP survey, environmental monitoring, and bench-scale metallurgical testing (Bouley and others, 1995).

    After about a decade of inactivity, work was resumed by Canada-based Northern Dynasty Minerals, Ltd., an affiliated company of the Hunter-Dickinson Group. The Northern Dynasty work began by expanding Cominco's IP survey. This work identified an open-ended, 90-square-km area (about 34.8 square miles) with anomalous IP chargeability response. This area includes the Pebble Copper deposit. In 2002, Northern Dynasty drilled about 11,000 meters (about 36,100 feet), partly at Pebble Copper, but mostly elsewhere in the geophysically anomalous area.
  • The Northern Dynasty website as of 7/2010 reports drilling at the Pebble deposit and surrounding exploration lands totaled 886,177 feet in 1,085 holes.
    http://www.northerndynastyminerals.com/ndm/PD_DPR.asp

Mining district

District name Bristol Bay

Mineral rights holdings

Type of mineral rights Located Claim

Land status

Ownership category State

Ownership information

  • Type Operator
    Owner Cominco Alaska Explorations Ltd>
    Home office Alaska
    Year 1994
  • Type Owner
    Owner Cominco Ltd.
    Interest 100
    Home office Canada
    Year 1994
  • Type Owner
    Owner Northern Dynasty Minerals Ltd and Anglo American
    Interest 100
    Year 2010
    First year 2001

Reserves and resources

  • Type In-situ
    Estimate year 1991
    Indicated 181500000mt ore
    Demonstrated 181500000mt ore
    Total resources 181500000mt ore
    Commodity Subtype Grade units Group Importance Year
    Gold Au 0.41 g/mt Gold Minor 1991
    Copper Cu 0.4 wt-pct Copper Major 1991
  • Type In-situ
    Estimate year 2010
    Indicated 5414000000mt ore
    Remarks Pebble East and West Indicated, 0.3% CuEQ cutoff\nNorthern Dynasty PR 2/1/10
    Commodity Subtype Grade units Group Importance Year
    Molybdenum 0.0257 wt-pct Molybdenum Secondary 2010
    Copper 0.43 wt-pct Copper Primary 2010
    Gold 0.35 g/mt Gold Primary 2010
  • Type In-situ
    Estimate year 1991
    Indicated 90720000mt ore
    Commodity Subtype Grade units Group Importance Year
    Gold Au 0.41 g/mt Gold Minor 1991
    Copper Cu 0.04 wt-pct Copper Major 1991
  • Type In-situ
    Estimate year 2010
    Measured 527000000mt ore
    Remarks Pebble East and West Measured, 0.3% CuEQ cutoff\nNorthern Dynasty PR 2/1/10
    Commodity Subtype Grade units Group Importance Year
    Molybdenum 0.0178 wt-pct Molybdenum Secondary 2010
    Gold 0.35 g/mt Gold Primary 2010
    Copper 0.33 wt-pct Copper Primary 2010
  • Type In-situ
    Estimate year 2010
    Inferred 4835000000mt ore
    Remarks Pebble East and West Inferred, 0.3% CuEQ cutoff\nNorthern Dynasty PR 2/1/10
    Commodity Subtype Grade units Group Importance Year
    Molybdenum 0.0215 wt-pct Molybdenum Secondary 2010
    Gold 0.26 g/mt Gold Primary 2010
    Copper 0.24 wt-pct Copper Primary 2010
  • Type In-situ
    Estimate year 1992
    Inferred 219000000mt ore
    Total resources 219000000mt ore
    Commodity Subtype Grade units Group Importance Year
    Gold Au 0.4 g/mt Gold Minor 1992
    Copper Cu 0.4 wt-pct Copper Major 1992
  • Type In-situ
    Estimate year 1994
    Demonstrated 420000000mt ore
    Total resources 420000000mt ore
    Commodity Subtype Grade units Group Importance Year
    Gold Au 0.4 g/mt Gold Minor 1994
    Copper Cu 0.35 wt-pct Copper Major 1994
  • Type In-situ
    Estimate year 2010
    Total resources 10776000000mt ore
    Remarks Total Measured and Indicated Resources plus\nTotal Resources Containing Inferred\nNorthern Dynasty PR 2/1/10
    Commodity Subtype Grade units Group Importance Year
    Molybdenum 0.0234 wt-pct Molybdenum Secondary 2010
    Gold 0.31 g/mt Gold Primary 2010
    Copper 0.34 wt-pct Copper Primary 2010
  • Type In-situ
    Estimate year 1996
    Demonstrated 420000000mt ore
    Total resources 420000000mt ore
    Commodity Subtype Grade units Group Importance Year
    Gold Au 0.4 g/mt Gold Minor 1996
    Copper Cu 0.35 wt-pct Copper Major 1996

Reference information

Bibliographic references

Reporter information

Type Date Name Affiliation Comment
Reporter 16-JUN-97 Ges U.S. Bureau of Mines
Reporter 02-JUN-03 Hawley, C.C. U.S. Geological Survey ARDF reporter.
Editor 06-JUL-10 Schruben, Paul U.S. Geological Survey Merged ARDF record.

Beyond USGS

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

External references

Maps centered on this site

Authoritative Alaska resources

These are landing pages for further research — the state agencies don't currently expose per-mine deep links.