Description
A common thread linking the four Jurassic porphyry Cu deposits in the Yerington
district is their relationship with granite porphyry (JGP) dike swarms sourced from
cupolas of the Luhr Hill granite (JPG). The Abacus/Almadex Willow property in the
Buckskin Range to the west covers two zones of high-level alteration in Jurassic volcanic rocks overlying the west-tilted Yerington batholith. The more extensive southern zone is marked by JGP dikes, quartz-veined zones, and chargeability highs, with
Cu and Mo increasing towards the east. Restoration of a long section compiled from
1967-81 drilling showed the dikes are the projection of the JGP dike swarm along the
southern edge of the batholith, where no porphyry center had yet been discovered. A
source cupola of JPG was inferred beneath the southeastern Buckskin Range. An initial three-hole test in 2018 confirmed the concept, intercepting 0.05–0.24% Cu, with
two holes cutting JPG in the subsurface. Highest Cu grades are associated with earlyhalo veins similar to those controlling better Cu at the nearby Ann Mason deposit.
Due to complications drilling through the low-angle faults, two of three holes failed to
reach targeted depths. The target could reach within 100–300 m of the surface, and
will be definitively tested in the near future.
