Geology of the Farmville Metagranite and Associated Units as Exposed at the Notasulga Quarry, Notasulga, Alabama

Abstract

Predicting the locations and thicknesses of aggregate-affable lithologies (ore units), interburden (non-ore material between ore-units), and overburden (overlying soil/saprolite) on a local level is critical for developing a cost-effective aggregate stone mine. This research thesis investigates a tectonic sequence of meta-sedimentary and igneous lithologies that have been metamorphosed under amphibolite-facies conditions yielding both a tectonically and lithologically complex deposit within a historically problematic group of Inner Piedmont rocks. Temporal, geometric, and lithologic control over the Farmville Metagranite and its encapsulating units at the Vulcan Materials Company Notasulga Quarry, Notasulga, Alabama, was achieved through geologic mapping, diamond drill core logging, petrographic analysis, electrical resistivity, seismic refraction, and geomorphologic methods. Five rock packages (RPs), or units, were recognized within the immediate area of mining operations. From structurally lowest to highest these include: 1) RP1, a metasedimentary package consisting of paraquartzite, quartz-plagioclase paragneiss, and garnet-muscovite schist; 2) RP2, an ore unit, characterized as an augen gneiss with persistent concordant pegmatite layers; 3) RP3, a metasedimentary package predominantly composed of quartz-biotite schist with common leucosomal pegmatitic boudins; 4) RP4, the primary ore unit, a metagranite with gneissic margins corresponding to the Farmville Metagranite; and 5) RP5, a relatively pure muscovite quartzite marking the uppermost structural layer encountered within the mining area. Electrical resistivity was found to be an effective method for delineating RP3, a local interburden unit that affects the quality of stone produced from the mine operation if incorporated into the production mix. Estimation of overburden, which is costly to remove, was achieved through a seismic refraction survey. It is demonstrated that the overburden/rock interface can be found through this non-invasive technique at a fraction of the cost of drilling. Field mapping of joints and foliations and their geomorphologic relations provide technical information for enhancing mine design. Analyses of boudinage structures and metamorphic conditions aided in explaining the morphology of rock packages and contributed to our understanding of the tectonic and metamorphic evolution of the Opelika Complex. Computer-generated rock solids were used to model the five rock packages utilizing Gemcom GEMS 6.2®. These were used in the creation of an accurate geologic map that can guide future exploration programs and mine design.