Black Mesa Mine (Black Mesa breccia pipe), Black Mesa, Eureka Mining District, Yavapai County, Arizona, USAi

Regional Level Types
Black Mesa Mine (Black Mesa breccia pipe)	Mine
Black Mesa	Mesa
Eureka Mining District	Mining District
Yavapai County	County
Arizona	State
USA	Country

A Cu-Mo breccia pipe deposit with underground workings located on the east side of Copper Creek, less than 1 mile to the north of the Bagdad Mine. Owned by the Bagdad Copper Corp.

Mineralization is a breccia pipe hosted in the Butte Falls Tuff and King Peak Rhyolite. Ore control was faulting and shearing. No alteration noted.

The fragments are largely of quartz monzonite, though some may be of diorite porphyry, but the fragments are so sericitized and silicified that original textures cannot be recognized with certainty in most specimens. The fragments range from 1 inch (2.5 cm) to 1 foot (30 cm) across and they are cemented by irregular vuggy quartz veins to 2 inches (5 cm) wide.

The sulfide minerals are confined largely to the vuggy quartz veins; and pyrite and chalcopyrite crystals nest in the vugs, the smaller grains are embedded in the quartz. Fine, flaky molybdenite crystals are distributed sporadically through the breccia, appearing mostly at the margins of the cementing quartz veins, but a few flakes appear in the vugs. Small veinlets of quartz cut the altered quartz monzonite fragments and carry three sulfides in variable distribution.

The sulfide mineralization is somewhat sporadic; the largest and most abundant chalcopyrite crystals appear at the western margin of the pipe. The only copper carbonate appears where the Hawkeye fault cuts the pipe.

The breccia is heavily coated with chalcanthite along the adit walls for the first 100 feet. A little antlerite was also observed.

Area structures include foliation in metavolcanic rocks that trends N10E to N40E.

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References