Interpretation of geophysical data obtained near Lumberton, North Carolina suggests the presence of a granitic pluton buried beneath Slate Belt-like rocks. A 239 m drill core retrieved from a hole 7.5 km southeast of the city of Lumberton consists of interlayered felsic and mafic volcanics of lower amphibolite grade metamorphism. Dipping reflections in a nearby 16. 5 km long seismic reflection line are believed to be from these volcanics, which are interpreted to be 3.5 km or more in thickness. Below these volcanics is an acoustically transparent zone which is interpreted to be caused by a granitic pluton. This hypothesis is supported by gravity data, which show a -35 mgal Bouguer gravity anomaly, and the relatively high heat flow of 63.4±5 mW/m² obtained in the drill hole, both of which are characteristic of Hercynian granitic plutons in the southeastern United States. Gravity modeling suggests that the body is nearly circular in shape, about 45 km in diameter, and nearly 14 km in thickness. Deep, nearly horizontal reflections in the 5 to 7 sec time range are interpreted to be from the base of the granitoid at a depth of about 17 km. One possible explanation for these reflections is that the granitoid is allochthonous; emplaced elsewhere and then transported to its present position along a sole thrust. The high heat flow suggests that the body is unmetamorphosed and the thrusting, which may post-date or be coeval with the intrusion, would thus be late Paleozoic in age. / M.S.

Interpretation of aeromagnetic anomalies to find the subsurface extent and attitudes of multiply deformed stratigraphic units near Roxboro, North Carolina is complicated by effects of regional metamorphism on rock magnetism. Anomaly amplitudes diminish markedly to the WNW near the onset of amphibolite facies. Thus, for similar lithologic mixes in this area, at higher metamorphic grades, magnetic susceptibility contrasts are markedly reduced. Modelling was done to determine the subsurface configuration of a magnetized greenschist facies metasedimentary unit in the faulted core of the Virgilina synclinorium. Magnetic anomalies appear to be caused by the entire fold structure in some locations and by only the upper limbs of the structure in others. Two alternative explanations are proposed: (1) the deeper part of the fold may have been displaced by thrusting, (2) metamorphic grade may increase with depth so that magnetic susceptibility contrasts diminish near the amphibolite facies boundary. The latter explanation is favored because it is consistent with surface data in the region. The study indicates that magnetic modelling has utility in complex metamorphic terrains to determine subsurface structure and subsurface configurations of metamorphic isograds. / Master of Science

The Virgilina District, which occurs in the Carolina Slate Belt of Virginia and North Carolina, produced over 300,000 tons of copper and significant amounts of silver and gold between 1852 and 1916. A detailed examination of the ore and gangue mineralization from the district reveals that the ores display two stages of hypogene deposition and a significant phase of supergene alteration. Hypogene mineralization, in decreasing order of consists of bornite, chalcocite/djurleite, an ilite, digenite, chalcopyrite, pyrite, magnetite, ilmenite, rutile, hessite, and gold (fineness 850). Supergene mineralization, in decreasing order of abundance is malachite, covellite, cuprite, digenite, hematite, chalcopyrite, chalcocite/ djurleite, azurite, spion kopite, and yarrowite. This represents the first reported occurrence of djurleite, anilite, hessite, spionkopite, and yarrowite in the area. Lamellar intergrowths of anilite and djurleite on their close packed planes, myrmekitic intergrowths of bornite and chalcocite/djurleite, coexisting chalcocite and djurleite, and gradational transitions from an-ilite to digenite were determined to have formed by secondary hypogene reactions that removed iron and sulfur from the bornite and increased the copper: sulfur ratio, which shifted the Cu-S binary phases towards copper and produced the described textures and intergrowths. The nature of the source of ore fluids and the timing of the mineralization are not known precisely. Fragments of wall rock contained within the veins with schistosity at an angle to the regional schistosity constrain the veins to be post-Taconic, and the metals are likely derived in part from the metamorphosed mafic volcanics in the area. / Master of Science