Date of Award

Spring 2020

Document Type

Open Access Dissertation

First Advisor

James N. Kellogg

Abstract

T

he goal of this study was to calibrate and test geophysical methods for the detection of geological structural and disseminated sulfides in the area of the four largest gold deposits in the Southern Appalachian of South Carolina. The Coastal plain sediments, vegetation and saprolite covering the mining areas remain the most challenging in this region. The work focused on the calibration of high-resolution gravity, and helicopter electromagnetic (EM) and magnetic data provided by OceanaGold over the Haile and Brewer Mines; then calibrating the regional gravity and aeromagnetic data over the four gold mines in South Carolina. Observed geophysical fields are correlated with rock properties: resistivities, susceptibilities and mineral concentrations are measured for 40 samples from 16 drill holes, as well as densities and mineral concentrations for 49,183 samples from 448 drill holes in the Haile ore zone. While high resolution potential field data (gravity and magnetics) has not been proven to be effective at small scales in exploration for disseminated sulfides, there is a strong regional correlation between high amplitude gravity and magnetic anomalies and the most productive gold mines in the Carolina terrane. Helicopter EM methods have been shown to be effective in distinguishing sedimentary from volcanic-dominated sediments in the metamorphic rocks of the Carolina terrane. The interpretation of the gravity and magnetic data utilized tilt derivatives, vertical derivative, reduced to pole anomalies (RTP), shaded relief, frequency spectrum, 3-D Euler deconvolution, core drilling and 2-D forward modeling. The most surprising result was that over the Haile Mine, the residual gravity vi anomalies, tilt derivatives, and vertical derivative show positive anomalies correlated with the location of a disseminated ore body. The gravity field over the ore body can be interpreted as produced by 4% pyrite and molybdenite. Electromagnetic (EM) anomalies are spatially associated with the Haile ore bodies. The edges of a granite pluton are clearly illuminated by the shaded relief, tilt derivative, and Euler deconvolution of the potential fields. The magnetic fields do not show correlations with the mineralized zones but are instead dominated by granitic and gabbro plutons and northwest trending diabase dikes. The integration and interpretation of the results indicate that metamorphism and hydrothermal alteration destroy magnetite and cause demagnetisation anomalies for the Carolina terrane. East-northeast trending linear anomalies have been sampled and dated as Alleghanian lamprophyre dikes providing the first magnetic map of these intrusions at Haile. Finally, we calculated the probability of detecting a geophysical anomaly of the required minimum dimensions with a given survey spacing over the Haile mine area to reduce the risk of missing the target anomaly.

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