Auriferous hydrothermal precipitates on the modern seafloor

Abstract

Submarine hot springs were probable sources for gold enrichment in a variety of rock types which host mineable gold deposits. These include iron formations, mixed chemical and clastic sediments, tuffaceous exhalites, and disseminated or massive sulphides in both volcanic-and sediment-dominated sequences. Gold-bearing iron formations and interflow metalliferous sediments associated with seafloor hydrothermal activity also have been implicated as potential source rocks for some nonstratabound gold deposits in ancient greenstone belts (Foster and Wilson, 1984; Keays, 1984). Recent studies of gold in volcanogenic massive sulphides indicate a strong genetic relationship between gold and sulphide mineralization in seafloor hydrothermal systems (Hannington and Scott, 1989; Large et al., 1989; Huston and Large, 1989). The total past production and current reserves of gold in massive sulphides world wide amount to nearly 2900 t Au and indicate that modified seawater is capable of transporting and depositing significant amounts of gold. In addition, the discovery of gold-rich sulphides actively forming at hydrothermal vents on the modern seafloor has confirmed the existence of gold-bearing fluids in submarine hot springs and supports a seafloor hydrothermal origin for gold in many preserved deposits now on land. The documentation of fluid chemistry at active vents also has served to constrain the conditions of gold mineralization on the present-day seafloor. In this chapter, we describe the occurrence and distribution of gold in modern hot spring deposits and discuss aspects of gold transport and deposition in seafloor hydrothermal systems with reference to possible implications for the origin of gold deposits in auriferous chemical sediments.