338
P.I. Lechler
establishment of this area as a US Environmental Protection Agency Superfund
Site in 1990 (S. Hogan, pers. comm.).
Placers from the Silver City/Delamar area (also known as the Owyhee Country)
of southwestern Idaho were discovered in 1863 and led to the pan-amalgamation
milling of lode ores in the Silver CityIDelamar areas, and the release of Hg to
Jordan Creek, until the beginning of the 20 th century (Wells 1983). Jordan Creek
flows out of the Owyhee Range in southwestern Idaho and into the Owyhee River
in southeastern Oregon. After being dammed to form the Owyhee Reservoir in
Oregon, the river flows into the Snake River, which is dammed to form Brownlee
Reservoir. Both fluvial systems are still contaminated with Hg, with concentrations in the range of 1 to 10 ~lg/g total Hg in active channel sediments of the
Carson River, up to 100 ~lg/g in Lahontan Reservoir, and up to 70 pg/g in Jordan
Creek. All of these creeks, rivers, and reservoirs in Nevada, Idaho, and Oregon
contain at least some fish which are contaminated with Hg.
Both mining camps were enriched in Ag relative to Au, and the Ag was largely
present as the sulfide or sulfosalt, which led to the use of the Washoe pan process
for the effective recovery of Ag from these ores (Smith 1943; Wells 1983). The
Washoe pan process was developed on the Comstock as a variation of the
Mexican Patio Process for the extraction of Ag from complex ores. It involved the
treatment of finely crushed (stamp-milled) ore slurry in a large metal pan which
was heated with steam to speed up the process. The Ag sulfides or sulfosalts were
decomposed through the addition of large amounts of salt (NaCl) which
dissolved perhaps 60% of the Ag as a Ag chloride complex. Elemental Hg was
added to the slurry to amalgamate free Au, electrum (Au-Ag alloy), and elemental
Ag which was reduced from its chloride complex through the addition of iron
nails to the mixture.
The form of Hg released to the environment by miners in both areas was
mainly elemental Hg, although some Hg sulfide was released from natural
mineralization in the Jordan Creek watershed as well. Eh-pH diagrams indicate
that the form of Hg stable in these surficial environments is elemental Hg, and Hg
speciation analyses performed as described below indicate that the form of Hg
present in these systems is still dominantly the elemental form. Exceptions to this
exist, however, as explained later. The watersheds of these systems still contain
subaerial mine and mill tailings contaminated with Hg (up to 4600 pg/g total Hg
in tailings in the Carson River watershed, for example) which will remain a
source of Hg to these fluvial systems, ensuring their continued pollution with Hg
for a very long time. Thousands of tons of mine and mill wastes are present on
the flood plains of both watersheds; however, the fine-grained mill tailings
typically generated by historic stamp mills are much more abundant in the
Carson River watershed, Jordan Creek being more impacted by coarser-grained
mine wastes. Niriagu (1994) estimated that 63380 tons of Hg may have been
released from 1820 through 1900 as a result of amalgamation milling of precious
metal ores throughout the United States, and Basham et al. (1996) concluded that
this was probably a reasonable estimate based on their development of a database
of historic amalgamation sites in the US.
The chemical form of Hg present in contaminated systems is important from
the perspective of bioavailability of Hg to humans and the ecosystem. Thus, the
P.I. Lechler
establishment of this area as a US Environmental Protection Agency Superfund
Site in 1990 (S. Hogan, pers. comm.).
Placers from the Silver City/Delamar area (also known as the Owyhee Country)
of southwestern Idaho were discovered in 1863 and led to the pan-amalgamation
milling of lode ores in the Silver CityIDelamar areas, and the release of Hg to
Jordan Creek, until the beginning of the 20 th century (Wells 1983). Jordan Creek
flows out of the Owyhee Range in southwestern Idaho and into the Owyhee River
in southeastern Oregon. After being dammed to form the Owyhee Reservoir in
Oregon, the river flows into the Snake River, which is dammed to form Brownlee
Reservoir. Both fluvial systems are still contaminated with Hg, with concentrations in the range of 1 to 10 ~lg/g total Hg in active channel sediments of the
Carson River, up to 100 ~lg/g in Lahontan Reservoir, and up to 70 pg/g in Jordan
Creek. All of these creeks, rivers, and reservoirs in Nevada, Idaho, and Oregon
contain at least some fish which are contaminated with Hg.
Both mining camps were enriched in Ag relative to Au, and the Ag was largely
present as the sulfide or sulfosalt, which led to the use of the Washoe pan process
for the effective recovery of Ag from these ores (Smith 1943; Wells 1983). The
Washoe pan process was developed on the Comstock as a variation of the
Mexican Patio Process for the extraction of Ag from complex ores. It involved the
treatment of finely crushed (stamp-milled) ore slurry in a large metal pan which
was heated with steam to speed up the process. The Ag sulfides or sulfosalts were
decomposed through the addition of large amounts of salt (NaCl) which
dissolved perhaps 60% of the Ag as a Ag chloride complex. Elemental Hg was
added to the slurry to amalgamate free Au, electrum (Au-Ag alloy), and elemental
Ag which was reduced from its chloride complex through the addition of iron
nails to the mixture.
The form of Hg released to the environment by miners in both areas was
mainly elemental Hg, although some Hg sulfide was released from natural
mineralization in the Jordan Creek watershed as well. Eh-pH diagrams indicate
that the form of Hg stable in these surficial environments is elemental Hg, and Hg
speciation analyses performed as described below indicate that the form of Hg
present in these systems is still dominantly the elemental form. Exceptions to this
exist, however, as explained later. The watersheds of these systems still contain
subaerial mine and mill tailings contaminated with Hg (up to 4600 pg/g total Hg
in tailings in the Carson River watershed, for example) which will remain a
source of Hg to these fluvial systems, ensuring their continued pollution with Hg
for a very long time. Thousands of tons of mine and mill wastes are present on
the flood plains of both watersheds; however, the fine-grained mill tailings
typically generated by historic stamp mills are much more abundant in the
Carson River watershed, Jordan Creek being more impacted by coarser-grained
mine wastes. Niriagu (1994) estimated that 63380 tons of Hg may have been
released from 1820 through 1900 as a result of amalgamation milling of precious
metal ores throughout the United States, and Basham et al. (1996) concluded that
this was probably a reasonable estimate based on their development of a database
of historic amalgamation sites in the US.
The chemical form of Hg present in contaminated systems is important from
the perspective of bioavailability of Hg to humans and the ecosystem. Thus, the