William Gapasin, PhD

The northern extent of the Battle Mountain-Eureka trend contains porphyry, skarn, and distal disseminated deposits of known origin. Marigold, an active producer, and Trenton Canyon Au, which was in production between 1996 and 2001, are sedimentary rock-hosted Au deposits proximal to these magmatic-hydrothermal deposits. As of September 2023, Marigold has recovered 4.7 Moz of gold since 1989. Both deposits share characteristics with Carlin-type gold deposits (CTGDs), such as structural controls, Au deportment, and geochemical signatures of ore zones. However, the majority of mineralization at both deposits is hosted in the siliciclastic Valmy Formation of the Roberts Mountain Allochthon. The ore currently mined at Marigold is oxidized and consists of Au-bearing goethite and hematite. Despite the interpreted timing of the Au deposition as Eocene, the genetic relationship with Eocene hydrothermal activity is not well understood. Marigold's Cretaceous intrusions are mineralized where they intersect with NW-WNW structures, and no Eocene intrusions have been identified. Trenton Canyon, located two kilometers south of Marigold's southernmost deposit, hosts both Eocene and Cretaceous intrusions. The Trenton Canyon and Marigold deposits present an opportunity to compare the role of hydrothermal fluids in sedimentary-rock-hosted Au deposits by defining influential factors involved in fluid evolution and Au deposition. Alteration zonation, mineralogy, illite crystallinity, and the distribution of alteration relative to lithology aid in determining the parameters of Marigold alteration. This contribution presents field data and results of spectral analysis across five fluid conduits located on the primary mineralized trend at Marigold.