Modern Mercury Contamination from Historic
Amalgamation Milling of Silver-Gold Ores in the
Carson River, Nevada and Jordan Creek, Idaho:
Importance of Speciation Analysis in Understanding
the Source, Mobility, and Fate of Polluted Materials
P.]. LECHLER
Approximately a century after peak mining and milling activities at two historic mining camps in the
western United States, Hg pollution persists in the Carson River, Nevada, and Jordan Creek, Idaho.
Active channel sediments in these streams are still enriched in Hg at levels of 2 to 4 orders of
magnitude above regional background.
The dominant form of Hg is still elemental Hg, the form historically released to the environment
(although some Hg sulfide was released from natural mineralization in the Jordan Creek watershed).
However, in more-anoxic reservoir sediments and deep soil horizons at the Carson River Superfund
Site, significant proportions of Hg sulfide have been formed where total sulfur exceeds 0.05 to 0.10
weight percent. Eh-pH diagrams describing Hg and S forms in a variety of surficial environments
agree with the Hg speciation results for elemental and sulfide species obtained in this study using a
combination of published methods.
1
Introduction
Prior to the introduction of cyanidation technology at the beginning of the 20 th
century, mercury-amalgamation of precious metal ores was common practice
throughout the western United States. Amalgamation is the alloying and
collection of fine gold-silver (Au-Ag) particles in puddles, droplets, or coatings of
mercury (Hg). The Hg is then collected and heated to evaporate the Hg away
from the precious metals; the Hg is recondensed in a retort and saved for reuse.
Some loss of Hg (and associated precious metals) is attendant in the many steps
in this metallurgical process.
This western US mining era began with the discovery of gold in California in
1848 and the Californian gold rush ofI849 (Fisher and Holmes 1968). Placers from
the Comstock lode in Nevada were discovered in 1859 and pan amalgamation of
these ores, mainly between 1860 and 1895, released approximately 6.4 x 10 6 kg of
Hg to the Carson River/Lahontan Reservoir system (Smith 1943; Ansari 1989). It is
also estimated that 3 x 10 6 troy ounces of Au and 64 x lO6 troy ounces of Ag were
lost along with the Hg. These tremendous amounts of Hg, Au, and Ag now reside
in mill tailings and the channel sediments and flood plain deposits of the Carson
River, largely along the no-km stretch between Carson City and Fallon, Nevada.
Approximately 100 mills processed Comstock ore at one time or another during
the peak mining period. Recognition of the magnitude of this pollution led to the
Environmental Science
Mercury Contaminated Sites (ed. by R. Ebinghaus et al.l
© Springer· Verlag Berlin Heidelberg 1999
Amalgamation Milling of Silver-Gold Ores in the
Carson River, Nevada and Jordan Creek, Idaho:
Importance of Speciation Analysis in Understanding
the Source, Mobility, and Fate of Polluted Materials
P.]. LECHLER
Approximately a century after peak mining and milling activities at two historic mining camps in the
western United States, Hg pollution persists in the Carson River, Nevada, and Jordan Creek, Idaho.
Active channel sediments in these streams are still enriched in Hg at levels of 2 to 4 orders of
magnitude above regional background.
The dominant form of Hg is still elemental Hg, the form historically released to the environment
(although some Hg sulfide was released from natural mineralization in the Jordan Creek watershed).
However, in more-anoxic reservoir sediments and deep soil horizons at the Carson River Superfund
Site, significant proportions of Hg sulfide have been formed where total sulfur exceeds 0.05 to 0.10
weight percent. Eh-pH diagrams describing Hg and S forms in a variety of surficial environments
agree with the Hg speciation results for elemental and sulfide species obtained in this study using a
combination of published methods.
1
Introduction
Prior to the introduction of cyanidation technology at the beginning of the 20 th
century, mercury-amalgamation of precious metal ores was common practice
throughout the western United States. Amalgamation is the alloying and
collection of fine gold-silver (Au-Ag) particles in puddles, droplets, or coatings of
mercury (Hg). The Hg is then collected and heated to evaporate the Hg away
from the precious metals; the Hg is recondensed in a retort and saved for reuse.
Some loss of Hg (and associated precious metals) is attendant in the many steps
in this metallurgical process.
This western US mining era began with the discovery of gold in California in
1848 and the Californian gold rush ofI849 (Fisher and Holmes 1968). Placers from
the Comstock lode in Nevada were discovered in 1859 and pan amalgamation of
these ores, mainly between 1860 and 1895, released approximately 6.4 x 10 6 kg of
Hg to the Carson River/Lahontan Reservoir system (Smith 1943; Ansari 1989). It is
also estimated that 3 x 10 6 troy ounces of Au and 64 x lO6 troy ounces of Ag were
lost along with the Hg. These tremendous amounts of Hg, Au, and Ag now reside
in mill tailings and the channel sediments and flood plain deposits of the Carson
River, largely along the no-km stretch between Carson City and Fallon, Nevada.
Approximately 100 mills processed Comstock ore at one time or another during
the peak mining period. Recognition of the magnitude of this pollution led to the
Environmental Science
Mercury Contaminated Sites (ed. by R. Ebinghaus et al.l
© Springer· Verlag Berlin Heidelberg 1999