Thompson Knolls

Region West, Southwest
Mineral systems
Deposit types
Other minerals

Information leading to the delineation of this focus area

Basis for focus area Outline of the Kings Canyon mining district from Krahulec (2018b). This district includes the Road Canyon and Crown disseminated Au-Ag deposits and the recently discovered Thompson Knolls Cu porphyry.
Identified resources Identified resources for gold and silver.
Production None.
Status Current exploration.
Estimated resources Southwestern Road Canyon area could contain a resource of approximately 6 Mt at an average grade of about 0.7 ppm Au and 13 ppm Ag. The Crown deposit contains an estimated 7.3 Mt at an average grade of about 0.93 ppm Au using a 0.34 ppm cut-off (Krahulec, 2011a). No estimate currently available for the Thompson Knolls porphyry.
Geologic maps Hintze and Davis (2004, 2006), scale 1:100,000.
Geophysical data Inadequate Rank 4 aeromagnetic coverage.
Favorable rocks and structures Massive, very thickly bedded, Upper Devonian Guilmette Formation forms cliffs on the west side of the Confusion range and most of the recognized surface expression of the known Au deposits occurs within this unit (Krahulec, 2011a). The underlying Middle Devonian Fox Mountain Formation is a poorly mapped and understood carbonate solution breccia/karst cave-fill unit. Most of the recognized Au deposits occur in or near the Fox Mountain Formation. The Fox Mountain is underlain by thickly bedded, ledge-forming, Middle Devonian Simonson Dolomite and the underlying Lower Devonian Sevy Dolomite with a few Au prospects farther east in these units (Krahulec, 2018b). The Thompson Knolls porphyry is a blind Jurassic porphyry intersected under 300 ft of alluvial cover.
Deposits Road Canyon Au-Ag, Crown Au-Ag, Thompson Knolls Cu.
Evidence from mineral occurrences UMOS (Utah Geological Survey, 2021).
Geochemical evidence Road Canyon is a Ag-dominant system with weakly anomalous Sb, Hg, and Cd. The Crown zone is a Au-dominant system weakly anomalous in As, Sb, and Tl. Mineralization at Boobs Canyon is Ag-dominant with a strong base metal (Pb-Zn-Cu) signature and associated Sb, As, Bi, and Hg (Krahulec, 2011a).
Geophysical evidence Thompson Knolls blind porphyry was discovered by drilling an aeromagnetics anomaly.
Evidence from other sources Krahulec (2018b).
Comments This area is included due to the recent blind discovery of a Jurassic porphyry intrusion under 300 ft of pediment cover. The intrusion was drilled based on an aeromagnetic anomaly, and other intrusives of similar age (for example, Gold Hill) often have a small but high grade, critical mineral-enriched mineralization signature. The Thompson Knolls porphyry only has reported weak Cu grades but may not be getting assayed for the full critical mineral suite. The Fox Mountain Formation underlying the Guilmette is known for solution breccias and karst cave fill, which are ideal mineralization sites.
Cover thickness and description Jurassic porphyry under 300 ft of pediment alluvium, disseminated Au-Ag exposed or shallow under Paleozoic basement.
Authors Stephanie Mills.
New data needs Regional aeromagnetics to detect further blind intrusions, which is how the porphyry was first detected; detailed mapping particularly on the Fox Mountain Formation and for further evidence of intrusive activity.
Geologic mapping and modeling needs 1:24,000 scale mapping.
Geophysical survey and modeling needs High-resolution, Rank 1 aeromagnetic and radiometric surveys.
Digital elevation data needs Lidar inadequate.