Element mobility above, below, and on the sides of the Ann Mason Cu-Au-Mo Deposit, Nevada, USA

Element dispersion patterns above and on the sides of porphyry Cu-Au-Mo deposits have been studied extensively (e.g. Lowell and Guilbert, 1970; Titley, 1982; Ulrich and Heinrich, 2002; Jago et al., 2014; Halley et al., 2015). Fewer studies have investigated dispersion patterns below porphyry deposits, from the deep parts of the parent magma chamber to the mineralised zone. The Yerington district, Nevada (Fig. 1) provides a unique opportunity to study changes in mineral chemistry with lateral and vertical distance from the centre of a porphyry deposit (Ann Mason) down to nearly 5 km paleodepth. During the Early Miocene (~17 Ma), largescale crustal extension resulted in the tilting of major fault blocks 60 – 90° to the west, exposing vertical cross-sections through several porphyry deposits in the district (Proffett, 1977; Proffett and Dilles, 1984). Rocks that were originally located at 4 km depth within the Ann Mason deposit are now exposed at surface and tilted on their side. This allows for systematic changes in whole rock chemistry around the deposit to be mapped using surface sampling methods, supplemented by drillcore sampling under Tertiary cover.