Updated geological model of the Carlin Formation for slope stability purposes at the Gold Quarry mine, Eureka County, NV, An

Abstract

An updated geological model of the Carlin Formation for slope stability purposes at the Gold Quarry open pit mine (Eureka County, NV) has been developed. The Carlin Formation is a sequence of interbedded tuffs, silts, clays, sands, and gravels of variable composition and induration that overlies gold bearing rock at the mine and has undergone numerous failures on the eastern pit slope. The model consists of nine geological cross sections that were constructed using the available drilling information and supplemented with ranges of engineering properties for Carlin Formation sub-units developed from the available testing data along cross section lines. A qualitative assessment of the model consisting of interpreting shear surfaces in cross sections that intersected recent failure zones was also performed in order to evaluate whether the inferred shear surfaces correlated to sub-units with low values for residual strength parameters. The construction of the model showed that although the Carlin Formation may be highly variable and heterogeneous, it is possible to correlate Carlin Formation sub-units between certain drill holes within the study area. Due to the variability in the degree of detail provided in logging descriptions, an iterative construction process was implemented in order to evaluate which combination of drill holes best characterized the Carlin Formation along each section line. Although historically the lower sub-units have been considered the most problematic as related to slope stability at Gold Quarry, the ranges of engineering properties suggest that for parts of the pit, some of the upper and middle sub-units may also have less than favorable engineering properties. This was also illustrated in the qualitative assessment of the model where the base of the inferred shear surfaces repeatedly coincided with the location of sub-units with low residual friction angle values relative to other sub-units.