Talk by Carl Nelson: Hot Spring Gold Deposits of the Circum-Pacific Region

Title: Hot Spring Gold Deposits of the Circum-Pacific Region

Lecturer: Carl E. Nelson (Recursos del Caribe SA)

Date: Thrusday October 17th 2013. 11:00A.M.

Place: Room 7

Abstract: There are currently about a dozen gold deposits that exhibit evidence for an origin at or directly beneath the paleo-surface. Collectively referred to as “Hot Spring” deposits, they were first recognized in 1980 with the discovery and recognition of a near-surface origin for the McLaughlin gold deposit (3.2 Moz) in California. Since then, additional discoveries have been made and unequivocal evidence for a hot spring origin has been recognized at other gold deposits in the Circum-Pacific region. Such evidence includes silica sinter, deposited originally as amorphous silica in hot spring pools and terraces, and, aprons of hydrothermal eruption debris which thicken and coarsen toward a central hydrothermal eruption vent. Mineralization typically consists of microcrystalline quartz, minor adularia, several percent pyrite-marcasite and native gold hosted by central, higher-grade, hydrothermal vent breccias and surrounding, lower-grade, quartz vein stockworks. A blanket of advanced argillic alteration, consisting of cristobalite - alunite – kaolinite is superimposed, when present, on ore-bearing sulfidic silicification. Precious metal mineralization in hot spring deposits is the result of shallow boiling of the hydrothermal fluid. Episodes of high fluid throughput steepen the pressure gradient in fossil geothermal systems, raise the boiling level to near grassroots levels and result in shallow precious metal mineralization along with a steeply zoned suite of associated “pathfinder” elements (Sb, Hg, Tl).