Other
Scientific paper
Mar 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993gecoa..57.1093p&link_type=abstract
Geochimica et Cosmochimica Acta, vol. 57, Issue 5, pp.1093-1104
Other
3
Scientific paper
D and 18 O enriched waters of several weight percent salinity issue from hot and cold springs in Franciscan Complex and Great Valley Sequence rocks in the northern Coast Range Mountains of California. Although these waters have been described separately in the past and called "metamorphic," "connate," and "serpentinizing fluids," this study shows that the hot and cold springs are all fed by one source of water--trapped Cretaceous seawater modified by a variety of reactions. The district is an example of the complexities of subsurface waters and their importance for our understanding of metamorphic fluid sources, oil-field waters, and ore transport problems. The subsurface waters have a range of 34 S values, including some near marine sulfate values (+20%.), and 13 C near marine calcite values (0%.). Strontium isotopic signatures in the spring waters are derived from the Great Valley Sequence ( 87 Sr / 86 Sr values near 0.705). The most saline spring pool is lined with serpentine phases found together as a fine white precipitate and has a pH of 11. One portion of the subsurface water is heated and reduced; it transports Au, Ag, Sb, As, and Hg to the surface (gold grades of the hot spring precipitates range from less than 1 ppm to over 10 ppm). These heated waters are chemically and isotopically similar to the fluids which formed Au mineralization at the nearby McLaughlin gold mine. The hot springs precipitate pyrite and native sulfur and are supersaturated with respect to calcite. Other springs are less saline and are oxidized, cooler, and diluted versions of the hot spring fluid. They do not carry ore metals but they are supersaturated with respect to silica and calcite. 3 He / 4 He ratios of the springs gases are all above atmospheric values and indicate a possible magmatic component, consistent with the presence of Quaternary Clear Lake Volcanics. 129 I data yield a minimum age of 60-80 Ma for the source of the iodide in the waters, consistent with the connate nature of the source fluid (FEHN et al., 1992).
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