At operating open-pit gold mines the characterization of ore-controlling features is a challenge typically addressed through geological pit mapping by mine geologists. An additional source of data in mines with a pronounced structural control of mineralization is the blasthole sample assay results created during routine mining. The Lone Tree mine, a structurally controlled gold deposit in Palaeozoic-age sedimentary rocks of north-central Nevada, is a good example of where blasthole assay results can be used to delineate details of structural features that might not be evident from periodic pit mapping. The Powerline fault, a north-trending compound fault zone, is the most important ore host at Lone Tree. The close association of ore-in particular, higher-grade material (>3 ppm gold)-with brecciation in the fault zone allows significant structural interpretations to be produced from the outlines of higher-grade ore obtained from blasthole assay results. The location, morphology and internal structure of the Powerline fault, including such features as fault segments, stepovers and internal horses, can be recognized when geological pit mapping is combined with the 4-m spacing of blasthole assay results. Mines, such as Lone Tree, that exhibit a strong structural control of mineralization can achieve better structural interpretations, which lead to improved ore-reserve estimation, by supplementing routine geological pit mapping with geological interpretations based on blasthole data.
