Geoenvironmental significance of spectral IP anomalies at two rock cuts along the new TransCanada Highway, central New Brunswick

Abstract

The oxidation of aggregate containing even small sulphide concentrations in combination with a water source can produce sulfuric acid and in turn pollute aquatic life and local ground water systems. The adverse environmental impact and high cost of remediating affected areas provide motivation for engineers to identify areas at risk for sulphide oxidation during the highway planning stage. By identifying these zones, they can be avoided or the sulphide-bearing fill can be disposed of in an environmentally friendly manner. Butler and Al (2002) preformed geophysical field trials at two sites along the new TransCanada Highway, and large IP/ resistivity anomalies were seen. The principle objective of this report was to determine if the shape of IP decay curves, as described by spectral IP parameters, "m", "Tau" and "c", could be used as a basis for discriminating the type of mineralization responsible for observed anomalies, especially graphite versus sulphide. The methods used in this investigation included magnetic susceptibility, IP and resistivity measurements. It was determined that the chargeability "Mx" is highly influenced by the sulphide concentration, and in particular, pyrite mineralization. Ilmenite and pyrrhotite were found to produce high magnetic field peaks while the "Tau" parameter was influenced by the total graphite content and specifically the grain size.