Igneous geology of the Carlin Trend, Nevada; development of the Eocene plutonic complex and significance for carlin-type gold deposits.

Abstract

The Carlin trend contains the largest concentration of Carlin-type gold deposits in the world. Two major controversies about these giant gold deposits have been their age, which is now firmly established as Eocene, and the source of heat, fluids, and metals, which remains debated. We present data that demonstrate an intense period of Eocene magmatism coincided in time and space with deposit formation and was arguably the primary heat source. Geologic studies over the last 40 years have emphasized the stratigraphy and structure of Paleozoic sedimentary rocks, which are the major ore hosts. However, four igneous episodes affected the Carlin trend, in the Jurassic, Cretaceous, Eocene, and Miocene. A Jurassic diorite-granodiorite laccolith and related dikes were emplaced at about 158 Ma in the northern Carlin trend. A Cretaceous granite intruded the north-central part of the trend at 112 Ma. Abundant Eocene dikes intruded along most of the trend and were accompanied by lavas in a large volcanic field along the southwest edge of the trend between approximately 40 and 36 Ma. Miocene rhyolite lavas erupted just west of and across the southern part of the trend at approximately 15 Ma. Exposed Eocene rocks consist predominantly of silicic to intermediate dikes, lavas, and epizonal intrusions, which we interpret to be sourced from a large Eocene plutonic complex underlying the Carlin trend. Eocene dikes are present in most deposits, are generally altered, but, with a few exceptions, were poor ore hosts. Distinct Eocene igneous suites, which are restricted to specific areas of the trend, are from north to south

70 samples from this reference