G. Furniss et al., Radiocarbon-dated ferricrete provides a record of natural acid rock drainage and paleoclimatic changes, ENVIR GEOL, 37(1-2), 1999, pp. 102-106
Ancient deposits of ferricrete (stratified iron oxyhydroxide or elastic sed
iment cemented by stratified iron oxyhydroxide) are present in headwater st
reams draining an historic mining district in the Rocky Mountains, USA. The
se deposits, which form under conditions of low pH and high metal concentra
tions, are present in streams draining many other mineralized areas. Radioc
arbon dating of wood fragments entombed within the ferricrete indicates dat
es of deposition as old as 8840 +/- 50 years before present (b.p.). The fer
ricrete deposits provide evidence that natural, metal-rich acid rock draina
ge has been occurring in this mineralized region for thousands of years, du
e to the weathering and oxidation of exposed or near-surface massive sulfid
e ore deposits. The dating and chemical composition of the ferricrete depos
its have applications to the environmental remediation of historic mining s
ites and to environmental issues related to natural background chemistry. I
n addition, the radiocarbon dates of the ferricrete deposits correlate clos
ely with warm-wet periods in the Holocene record, showing that ferricrete d
eposits may represent a previously untapped source of paleoclimatic informa
tion.