Geologic Overview of the Martin Marietta Hickory Quarry
Catawba County, North Carolina
September 2006
Report by Mike Streeter
(Important note: definitions and explanations of key geologic terms and phrases in the
the report may be seen and read by clicking on those that are
red and underlined).

Martin Marietta Hickory Quarry
(click on the above picture to enlarge)

The geology of the Martin Marietta Hickory Quarry, an aggregate producer in Catawba County, North Carolina, has not been mapped in detail. However, regional mapping shows that the quarry is contained in what is known as the Walker Top Granite, an igneous intrusion that was emplaced into the Cat Square Terrane about 366 million years ago (Ma) (Giorgis, Mapes & Bream, 2002). The Cat Square may be an accretionary prism in front of the Carolina Terrane to the east and behind the Tugaloo Terrane to the west. The aluminous schist and biotite gneiss of the Cat Square are believed to be a metamorphosed sequence of immature deep-water sandstones and pelites that were probably deposited in the remnants of the Theic Ocean until post-430 Ma. (Hatcher, Jr., 2004).

The Walker Top Granite consists predominately of plagioclase, potassium feldspar, quartz, biotite, and muscovite. Lesser amounts of myrmekite, garnet and opaque minerals are present with trace amounts of sphene, zircon and apatite. In outcrop and hand sample, the Walker Top is characterized by 1 cm to 8 cm-long potassium feldspar megacrysts that tend to be randomly oriented, although some appear to be highly oriented. The matrix consists of medium-grained (less than 4 mm) quartz, biotite, muscovite and two feldspars.


Since the Walker Top intrusion took place during the Acadian orogeny (410-330 ma) and before the Alleganian orogeny (325-280 Ma), the rock was subjected to regional compression, thus causing some metamorphic fabric including foliation. Portions of the Walker Top resemble the Henderson Gneiss (~490 Ma) in appearance and bulk chemistry. However, the different crystallization ages distinguish the two and the geologists who identified the Walker Top have suggested that its foliation looks more like an igneous flow pattern than deformational foliation (Giorgis, Mapes & Bream, 2002).

Prominent fractures cut the quarry walls and mineralized slickensides have been identified on some of them and loose boulders. Breccia and gouge evidence brittle faulting. Faulting, fracturing and mineralization may have occurred during multiple events associated with the Alleganian orogeny and Mesozoic regional extension (Garihan, Preddy & Ranson, 1993). Fracture-filling quartz, calcite and stilbite are thought to be the result of precipitation by hydrothermal events during Paleozoic and Mesozoic tectonic events. A wide variety of secondary minerals, including many zeolites, are present in the faults, fractures and voids. Secondary minerals identified by rock and mineral collectors include chalcopyrite, pyrite, rutile, fluorite, quartz, ankerite, calcite, fluorapatite, siderite, babingtonite, epidote, laumontite, prehnite, allanite, chabazite, & stilbite. Although the sources of these minerals have not been specifically identified, certain minerals from pre-existing sedimentary rocks may have been brought into solution and recrystallized during hydrothermal events. Metamorphism may have also played a role as zeolites and prehnite can form under relatively low pressure and temperature metamorphic conditions.

A small sampling of collectable minerals is pictured on the following page.

Report continued . . . . . . .

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