Highway 51 Quarry, Magnet Cove, Arkansas:
An alkali intrusive equivalent of alpine mineral veins?
The Highway 51 Quarry, operated by Mid-State
Construction, is located near the southern rim of the Magnet Cove alkalic intrusive. In
recent years the quarry has approached to within 0.5 kilometer of the intrusive contact.
The quarried rock at this point is a highly altered and fractured Stanley Shale that
contains numerous veins, dikes and recrystallized faces along fracture zones. As the
quarry has moved near to the Magnet Cove intrusive, the degree of mineralization has
increased dramatically.
There are four main types of mineralization found at the Highway 51 Quarry:
1) fracture fillings and faces on open fractures that contain: quartz, hematite, amphiboles, chlorites, pyrite (octahedrons to 10mm), fluorite, sphalerite, barite, albite, anatase, rutile, micas, calcite, ankerite and kolbeckite.
2) carbonate veins, some probably carbonatites, that contain: calcite, fluorite, quartz, micas, rutile, pyrite, barite and amphiboles.
3) quartz-albite veins that contain: quartz (smoky crystals to 6 cm), albite, amphiboles, anatase (to 6mm), apatite, pyrite and green sphalerite.
4) altered lamprophyre dikes that contain: diopside, amphiboles, pyrite and chlorites.
The hematite/quartz/pyrite specimens with amphiboles and chlorites are particularly reminiscent of alpine veins with the hematite forming "iron roses". Anatase in both dipyramidal and tabular crystals is locally abundant, and along with rutile forms quite attractive micro specimens. Mineralization in the quartz veins is generally embedded in massive smoky quartz, but where found in open pockets has very nice examples of anatase crystals and apatite. Smoky quartz crystals are found in pockets of iron stained albite and, while quite clear internally, are etched on the surfaces.
The quarry will eventually penetrate the rim of Magnet Cove and begin mining the border syenites; however, the mining plan calls for operations to simply skirt the intrusive for at least several years. This means continued exposure of the altered zones and the potential for continued collection of good specimen material.