The Carlin Trend is northwest alignment of sedimentary rock-hosted gold deposits in north-central Nevada that extends for approximately 80 km from Gold Standard’s Dark Star deposit in the southeast, to the Arturo-Dee deposit in the northwest. More than 40 separate oxide and refractory gold deposits have been delineated along the Carlin Trend, and more than 26 open pit and underground mines have been developed (Teal and Jackson, 2002). Since the discovery of micron-size, disseminated gold mineralization in 1961, more than 84 million ounces of gold have been produced from the Carlin Trend (Muntean, 2016). The Carlin Trend hosts one of the largest gold concentrations in the western hemisphere. Resources and reserves on the Carlin Trend exceeded 31 million ounces of gold as of 2015 (Barrick, 2016 and Newmont, 2016).
Gold continues to be found on this productive trend. Recent developments in the northwest and central parts of the trend include the discovery of the Arturo deposit, significant expansion of the Leeville and Turf deposits, development of the Exodus and Pete Bajo deposits, and expansions of the Genesis and Gold Quarry deposits1. At the southeast end of the trend, recent work includes development of the Emigrant deposit1; and Gold Standard’s discoveries at the North Bullion and North Dark Star deposits, and expansion of the Pinion and Main Dark Star deposits2. Gold deposits occur in clusters and have a periodicity with respect to certain geological features – some of which are described below.
Since the inception of mining at the original Carlin Mine in 1965 to the early 1990’s, gold ore mined from open pits was processed at oxide mills or heap leach facilities. The mid 1990’s was a transitional period where open pit mining for oxide and refractory mineralization continued concurrently with the development of underground mines from shafts or declines extending outward from existing open pits. Underground development targeted higher-grade, typically carbon-sulfide refractory gold ore. To process the refractory ore, two whole-ore roasters were constructed – one at the Gold Quarry mining operation (Newmont) and the other at Goldstrike (Barrick). Both companies blend multiple refractory ore types from a variety of gold deposits to enhance efficiencies within the roasting process. Currently a large variety of ore types from across the Carlin Trend are processed via conventional heap leaching, thiosulfate heap leaching, milling, roasting and autoclaving.