Johnson River

Region Alaska, Alaska
Mineral systems
Deposit types
Critical minerals
Other minerals

Information leading to the delineation of this focus area

Basis for focus area Known mineral deposit and high prospectivity determined for the Johnson River drainage.
Identified resources Identified resources of copper, gold, lead, silver, and zinc.
Production None recorded.
Status Current exploration.
Estimated resources Johnson Tract: 1.1 M short tons @ 0.75% Cu, 1.13% Pb, 8.32% Zn, 0.293 oz/t Au, 0.22 oz/t Ag.
Geologic maps Statewide geologic map database; Wilson, Hults and others (2015), scale 1:1,584,000.
Geophysical data Mostly (>90%) inadequate aeromagnetic and aeroradiometric coverage.
Favorable rocks and structures Lower Talkeetna Formation which consists of andesite flows and breccia which locally show well-developed pillows in the lower group, the middle group consists of breccias, reworked volcaniclastic rocks, crustal tuffs, and dacite flows.
Deposits Johnson.
Evidence from mineral occurrences ARDF occurrence.
Geochemical evidence Sediment and soil anomalies in pathfinder elements including Cu, Ag, Pb, Zn, Cd, or Co. Additional geochemical evidence comes from pan concentrates containing anglesite, cerussite, chalcopyrite, copper sulfide/oxide, galena, or sphalerite. Heavy Mineral concentrates containing Cu, Pb, Zn or Ag.
Geophysical evidence No data.
Evidence from other sources High prospectivity determined in the Johnson River drainage basin; Karl and others (2016).
Comments This is a small focus area that contains the Johnson River deposit, which contains a defined deposit. The deposit is hosted in the Talkeetna Fm, which is widespread across the region. Despite the prevalence of this formation, most other drainage basins do not exhibit high prospectivity signatures.
Cover thickness and description Unknown.
Authors Douglas C. Kreiner, James V. Jones, III.
New data needs New mapping, geophysics, updated geochemical sampling.
Geologic mapping and modeling needs Mapping at 1:100,000 scale or better.
Geophysical survey and modeling needs Aeromagnetics and radiometrics collected at Rank 2.
Digital elevation data needs IfSAR coverage is complete over entire focus area.