Geophysical study of the abandoned Gullbridge Mine Tailings Management Facility, central Newfoundland

Blagdon, Andrew Gordon (2021) Geophysical study of the abandoned Gullbridge Mine Tailings Management Facility, central Newfoundland. Masters thesis, Memorial University of Newfoundland.

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Abstract

As part of an ongoing dam monitoring study, this research aims to assist in the closure of the Gullbridge Tailings Facility in Central Newfoundland using geophysical survey methods. Centered over a volcanogenic massive sulfide ore deposit, the Gullbridge mine produced 94,000 tonnes of copper concentrate from 2.8 million tonnes of ore from 1967-1972. The facility deploys an earth-filled dam separating a valley impoundment reservoir containing 1.8 million m3 of subaqueously deposited copper tailings from an adjacent wetland. Historical seepage of tailings water through the embankment is concerning as it poses a risk of seepage related erosion, a likely failure mechanism which, combined with poor dam foundations, contributed to a breach in December 2012. Relevant variations in the material properties of the dam can be detected by geophysical methods. Spontaneous-potential (SP), direct-current resistivity and ground-penetrating radar and magnetics were deployed for surveying the embankment, particularly over a known seepage location. SP data points to irregular seepage of tailings water through the embankment in the known seep area and in the northern part of the dam. DCR surveys indicate there is a 1-2 m thick dry layer, thickening northward, over the main seep. GPR data suggests flow of tailings water through the embankment is constrained to poorly compacted core materials surrounding an historic inlet channel, the location of which is indicated by magnetic data. As a secondary focus, an adjacent wetland was surveyed using an electromagnetic ground conductivity meter. The conductivity data delineate areas of elevated copper resulting from the distribution of tailings sediment along a dammed stream bed and along a discharge channel where water exits the reservoir and into the wetland via a spillway.

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