Geologic description
Nokleberg and others (1992 [MF]; 1992 [Open-File]) map the rocks in the area as undivided gabbro, diabase, and metagabbro on their regional 1:250,000-scale geologic map. Ragan and Hawkins (1966) and Bittenbender and others (2007), who examined the geology in more detail, identified a nearly horizontal thrust fault under the occurrence. The upper plate rocks consist of highly deformed, quartz-biotite schist cut by dikes and plugs of Triassic(?) gabbro, pyroxenite, and peridotite. About 300 feet away, the schist has been intruded by Cretaceous(?) granodiorite. The mafic and ultramafic rocks are strongly altered. Peridotite is serpentinized; clinopyroxene is replaced by hornblende, biotite, and chlorite; and plagioclase is sericitized. The rocks in the lower plate are relatively undeformed basalt and fine-grained gabbro. Bittenbender and others (2007) collected several samples of copper stained peridotite from a small plug in the metamorphic rocks of the upper plate. They did not note any specific ore minerals but this occurrence is similar to ARDF site MH375 about a mile to the southwest, where chalcopyrite, pyrrhotite, and pentlandite are present in similar mafic and ultramafic rocks. A representative sample of peridotite from the southern portion of the occurrence contained 50 parts per billion (ppb) platinum, 56 ppb palladium, 12 ppb gold, 330 parts per million (ppm) copper, and 1,500 ppm nickel. A select sample of iron-stained rubble in the middle of the occurrence contained 409 ppb platinum, 414 ppb palladium, 17 ppb gold, 1,500 ppm copper and 1,880 ppm nickel. |
