Diamond
Hill Quartz Prospect As
Featured In Rock & Gem Magazine Geology of Diamond Hill by: Read Miner Geologically, South Carolina is comprised of two distinct geologic environments. Sedimentary rocks are found in a series of seaward dipping layers in the southeastern half of the state. In the northwestern half of the state, metamorphic rocks are found. The contact between the sedimentary and metamorphic terrains is sometimes referred to as the fall line and is oriented in a northeast-southwest direction (parallel to the coast of SC) and goes through the state capital of Columbia, SC. Northwest of the fall line, the metamorphic rocks are divided into several geologic belts each oriented in a NW-SE direction parallel to the axis of the Appalachian Mountains. From the fall line, the geological belts include the Carolina Slate Belt, the Charlotte Belt, the Inner Piedmont belt, and the Blue Ridge. The Inner Piedmont is separated from the Charlotte Belt by the Lowndesville Sheer Zone. As one moves from the fall line, each respective geologic belt increases in metamorphic grade as a result of the higher temperatures and pressures closer to the core of the Appalachian Mountains. The Diamond Hill Quartz Prospect is located in the Inner Piedmont Belt of SC just outside the northern edge of the Lowdesville sheer zone. The prevailing rock type around in the Diamond Hill Quartz Prospect is a granitoid gneiss. Rb/Sr isochron age dating of multiple rock samples in this area have yielded ages between 385 and 415 million years old. This age represents the time during which the rocks were last subjected to temperatures and pressures high enough to cause partial melting of the rock. Partial melting of the parent rock resulted in the formation of migmatites, that have been observed at the Diamond Hill Quartz prospect. Migmatites can be simply described as a coarsely crystallized pegmatite formed during the metamorphism of the parent rock. During metamorphism, the partially melted viscous rock is squeezed into irregular lenses that typically follow the layering of the parent rock or planes of weakness such as faults. The rock at Diamond Hill has been significantly broken up or brecciated. Slickensides (commonly coated with a manganese oxide) are commonly seen in the saprolite and many of the quartz veins are fault breccias. The formation of slickensides and fault breccias are believed by the author to be similar in age to fault movement in the nearby Lowndesville Sheer Zone. Brecciation of the quartz veins at the Diamond Hill Quartz prospect resulted in the development of large open cavities. Later, hydrothermal water that were likely generated at deeper depths moved through the open cavities and deposited silica in the form of plates of drusy quartz crystals. A later change in composition of the hydrothermal water resulted in the deposition of amethyst and smoky quartz crystals over the drusy crystals. Reference: Griffin, Jr., Villard S., 1979, Geology of the Abbeville East, Abbeville West, Latimer, and Lowndesville Quadrangles, South Carolina. South Carolina Geological Survey MS-24. |