Sources of high-pressure fluids involved in the formation of hydrothermal deposits

Abstract

Available fluid inclusion data on hydrothermal deposits, deep seated xenoliths, magmatic and metamorphic rocks were used to generalize the determinations of physicochemical parameters (temperature, pressure, and compositions) of natural fluids. It was established that fluid pressures during formation of hydrothermal deposits often exceeded lithostatic loading (250-270 bar/km) of the overlying rocks. Fluids from deep seated xenoliths, magmatic and metamorphic objects are considered as the possible sources of high pressure fluids. Data on temperatures, pressures, and fluid composition are generalized for each object.

Vein intersection zones and host rock composition as controlling factors in polymetallic ore shoots genesis: insights from the Southern Arburèse five-element (Ni-Co-As-Bi-Ag) vein system (SW Sardinia)

“…The "five element" vein type (Ni-Co-As-Ag-Bi) (Halls & Stumpfl, 1972;Kissin, 1992) is a class of hydrothermal ore deposits originated by low-temperature, very high-salinity fluids and characterized by complex mineral assemblages, represented by native elements (Ag, Bi), Ni-Co arsenides and base metal sulfides/sulfosalts in quartz and carbonate gangue. Several models have been proposed to explain the precipitation of the ore shoots: 1) dilution and cooling through mixing of different fluids (Essarraj et al, 2005;Kissin, 1993;Marshall & Watkinson, 2000;Marshall et al, 1993); 2) interaction of the fluids with the wallrock (by leaching and by natural fracking of carbon-rich litologies) (Naumov et al, 1971;Markl et al, 2016;Burisch et al, 2017) or with Fe 2+ bearing minerals (Robinson & Ohmoto, 1973;Ondrus et al, 2003;Kreissl et al, 2018). Host rock chemistry and rheology, but also intersections with former hydrothermal systems seem to play a critical role, since they control the development and geometry of the veins, and they may act as sources of elements or as redox barrier.…”