Both experiment and empirical observation contributed to advances in
knowledge about the geochemistry of metalliferous hydrothermal fluids.
Hemley et al. [1992] studied the solubility of Fe, Pb, Zn and Cu
sulfides in chloride solutions that were rock-buffered in pH, fS
and
fO
from 300-700
C and 0.5-2.0 bars (5 x 10
to 2 x
10
Pa). Hemley and Hunt [1992] applied the results to conclude that
for quasi-adiabatic transport conditions, the pressure effect on
rock-buffered solubilities compensates for the temperature effect,
allowing metal transport over long distances from deep-seated
crystallizing plutons. The outward Cu-Zn-Pb zoning typically seen
around mineralized plutons forms in a complex manner dictated by the
intersection of transport pathways with metal sulfide saturation surfaces,
caused by thermal and chemical changes and their temporal variations.
Hemley and Hunt [1992] also present an insightful discussion of
paragenesis and zoning in space and time that should be read by
everyone interested in ore genesis.
Other experimental studies of hydrothermal base
[4]
metal solubility and
speciation include those of Seyfried and Ding [1993] on the relative
solubilities of Fe and Cu in Na-K-Cl fluids and Ohmoto et al.
[1994] on the solubility of pyrite in Na-Cl solutions, and references cited
therein. Platinum-group elements and gold were the focus of
experimental studies by Wood et al. [1994], Berndt et al.
[1994] and references cited therein.
As a complement to experimental studies, McKibben et al. [1990] described similar dissolved concentrations but contrasting precipitation mechanisms of gold and PGE in boiling hot brines within geothermal wells, thus providing empirical evidence for significant differences in the transport mechanisms of these two metals in natural hydrothermal brines. Peters [1993] described the connate origins and Au-Ag-Hg-hydrocarbon contents of hot spring waters in the California Coast Ranges, and related them to the genesis of hot spring precious metals deposits such as McLaughlin.