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Abstract

Goldrush is a Carlin-type sedimentary rock-hosted disseminated gold deposit located within the Cortez mining district on the Battle Mountain-Eureka trend, Nevada, USA. Goldrush is the third giant gold deposit (>310 metric tons Au or 10 Moz Au) discovered in the district after Pipeline (1991) and Cortez Hills (2002), and contains a measured and indicated resource of 59.8 Mt @ 4.35 g/t and an inferred resource of 39.2 Mt @ 4.52 g/t as of the end of 2012. Goldrush is concealed beneath unmineralized Paleozoic rocks as well as Tertiary and Quaternary postmineral tuffs, volcaniclastic sediments, and gravel ranging from more than 100 m to more than 300 m thick. The mineral system is tabular and continuous over a thickness of up to 70 m, a width of up to 250 m, and extends along strike for at least 4,000 m. Gold mineralization occurs within extensive zones of decarbonatization and silicification spatially associated with a stratigraphic horizon containing fossiliferous debris flows in thrust-faulted and folded Devonian carbonate rocks. The system is marked by a large stratiform silicified and sulfidized breccia horizon from 15 to 70 m thick that extends more than 7 km on a north-northwesterly strike; the strike length and continuity of this breccia zone make Goldrush unique compared with other Great Basin Carlin-type gold deposits. Gold occurs as submicroscopic inclusions within fine-grained pyrite, similar to other Carlin-type gold deposits in Nevada. The Goldrush discovery is attributed to a multiyear program utilizing open-pit and field mapping, detailed field, drill hole, and geochemical observations, and relogging of historic drill holes to construct new district- and deposit-scale geologic models. Barrick Exploration management provided strong support via a systematic, model-driven assessment process and funded deep drilling that ultimately resulted in the discovery. Persistence also played an important role as the discovery emerged over several years.

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