Disseminated gold deposits along the Carlin Trend are hosted in Paleozoic age (250 to 541 million year old) sedimentary rocks. These rocks were deposited beneath the ocean surface on the continental shelf and slope on the western edge of the North American continent. Preferred host rocks are limestone with or without quartz silt grains, making for a reactive and permeable rock. Other sedimentary rock types host gold where permeability is enhanced by fracturing due to faults, folding or dissolution of the rock.
Three distinct periods of igneous intrusive activity are documented on the Carlin Trend. Intrusive rocks ranging in composition from rhyolite to diorite have been dated from the Jurassic (145-201 million years old), Cretaceous (66-145 million years old) and Tertiary (Eocene 34-56 million years old). These igneous rocks occur as stocks, dikes and dike corridors, and sills. Four distinct magmatic centers are recognized on the Carlin Trend – each center focusing multiple pulses of magma that produced igneous-cored domes with hornfelsed halos (Ressel and Henry, 2006). From northwest to southeast on the Carlin Trend these magmatic centers / domes include: the Richmond Dome, the Maggie Creek Dome, the Rain Dome, and the Railroad Dome on Gold Standard’s Railroad-Pinion Project. Importantly, host rocks occur at the surface or shallow depths within and marginal to these domes. Based on extensive age dating of igneous rocks and hydrothermal alteration, and observation of cross-cutting relationships, the age of gold mineralization on the Carlin Trend best correlates with Eocene age igneous activity.
Although volumetrically minor, lamprophyre dikes have been identified within and proximal to many gold deposits along the Carlin Trend, including some of the gold deposits on Gold Standard’s Railroad-Pinion Project. Lamprophyre dikes are indicative of deep tapping faults that may have served as conduits for gold mineralization. The presence of lamprophyres serves as a link between the Carlin Trend and other large gold belts around the world.
Similar to the igneous activity, the Carlin Trend has been the subjected to multiple structural deformation events including emplacement of the Roberts Mountains thrust; two contractional phases that produced north, northwest, west-northwest and northeast trending folds; and, moderate to high-angle normal faults (Rhys et. al., 2015). Gold mineralization occurs in structural culminations and intersections produced by convergence of folds, faults, and favorable, reactive lithologies (Rhys et. al., 2015). Gold bearing fluids flowed upward into these favorable structural settings and were commonly trapped beneath or against an impermeable rock type or fault, much like a trap in an oil field. At the deposit scale, collapse and hydrothermal breccias can be an important control on gold mineralization.