Geochemistry: Exploration, Environment, Analysis; May 2002; v. 2; no. 2;
p. 185-202; DOI: 10.1144/1467-787302-022
© 2002 Geological Society of London
Elemental mercury in copper, silver and gold ores: an unexpected contribution to Lake Superior sediments with global implications
W. Charles Kerfoot1,
S. L. Harting1,
Ronald Rossmann2 and
John A. Robbins3
1 Lake
Superior Ecosystem Research Center and Department of Biological
Sciences, Michigan Technological University, Houghton, MI
49931, USA (e-mail:
WKERFOOT{at}MTU.EDU)
2 United
States Environmental Protection Agency, Mid-Continent Ecology Division,
Large Lakes Research Station,9311 Groh Road, Grosse Ile,
MI 48138, USA
3 NOAA
Great Lakes Environmental Research Laboratory, 2205 Commonwealth Blvd,
Ann Arbor, MI 48105, USA (e-mail:
ROBBINS{at}GLERL.NOAA.GOV)
Mercury
and copper inventories are low in central Lake Superior and increase
markedly towards the Keweenaw Peninsula. Total copper flux to Lake
Superior sediments averages
5.0 ± 2.5 µg cm2 year1
(mean ± 95% confidence limits), whereas mercury
flux averages
7.5 ± 4.2 ng cm2 year1.
In the Keweenaw Peninsula region, copper, mercury and silver
inventories are elevated and highly correlated. High copper, silver and
mercury inventories can be traced back to shoreline stamp sand piles,
the parent ores and to smelters. Mercury occurs in elemental form,
probably as a natural amalgam, in native metal (copper, silver, gold)
deposits and was liberated as volatile Hg0
during on-site copper smelting. Stamp mills discharged at least
364 Mt of stamp sand tailings, whereas smelters
refined 5 Mt of native copper, liberating together at least
42 t of mercury. The Keweenaw situation is not unique, as
mineral-bound mercury is commonplace in US and Canadian Greenstone
Belts and is of worldwide occurrence in massive base metal
ores.
KEYWORDS: natural
amalgam, mercury, metal ores, copper
smelting, sediments
Copyright © 2009 by Geological Society of London