Marble in the Precambrian of South Dakota, USA. (geology hammer for scale)

This rock is in a small, very old marble quarry in the Black Hills of western South Dakota. It was operated in 1901 by the Black Hills Porcelain Clay & Marble Mining Company.

The quarry walls consist of about 9 feet worth of section (in-situ outcrop). The rocks here are marbles with amphibolite above - both lithologies are metasedimentary (= metamorphosed sedimentary rocks). The marbles are very weathered, gray-colored, and often lichen-covered, but fresh crack surfaces are grayish-white to off-white, often with speckled green minerals (these include forsterite olivine, serpentine, and chlorite). Observed lithologies in outcrop samples and loose samples derived from here include marble, muscovitic marble, serpentinic marble, muscovitic serpentinic marble, chloritic marble, and forsteritic marble. The "original" forsterite olivine component in the marble has often been retrograde metamorphosed into serpentine.

This marble is part of a large carbonate inlier in Harney Peak Granite, a large, late Paleoproterozoic granite pluton in the Black Hills (dated to 1.695-1.715 billion years old). The pre-existing inlier rocks were caught up & incorporated into the Harney Peak Pluton and intensely altered by contact metamorphism. The protolith, or precursor, of the marbles here was probably impure (argillaceous) dolomitic limestone or high-magnesian limestone or dolostone (see Kernaghan & Garske, 1968).

Some scheelite has been identified in the marbles at this site, just below the marble-amphibolite contact near the top of the quarry wall. Scheelite is a tungsten mineral, CaWO4 - calcium tungstate.

In addition to marble and amphibolite, skarn is also present here. Skarn is a coarsely-crystalline, polyminerallic, contact metamorphic rock. Skarn samples at this site are light greenish in color and are composed of calc-silicates, pyoxenes, amphibole, scapolite, sphene/titanite, apatite, and scheelite (Kernaghan & Garske, 1968).

This site is documented in Kernaghan & Garske (1968) and in Lufkin et al. (2009) (as stop 8).

Locality: Black Hills Porcelain Clay & Marble Mining Company Quarry ("old marble quarry"), just south of the Needles Highway, Custer State Park, Black Hills, western South Dakota, USA (GPS: 43° 49.638' North latitude, 103° 31.539' West longitude)

References cited:

Kernaghan & Garske (1968) - Marble and tungsten in the southwestern portion of the Harney Peak "Dome", Custer County, South Dakota. pp. 173-176 in: Wyoming Geological Association 20th Annual Field Conference Guidebook.