Preliminary investigation of the source of lead and strontium in deep geothermal brines underlying the Salton Sea geothermal area

A radiogenic tracer study has been made of lead and strontium in deep geothermal brines, salt from brine, and the upper Quaternary rhyolite domes near the Salton Sea in the Imperial Valley, California. The data on the brines and rhyolite glasses are compared to those from Quaternary Colorado River and Tertiary sediments of the area. The brines sampled contain '-'100 ppm Pb, sufficient for consideration as a possible ore-forming fluid. The isotopic data indicate that 80-100 percent of the strontium and 50-100 percent of the lead in these brines were acquired from the associated sediments. The isotopic compositions of lead and strontium in the Quaternary rhyolite glasses are distinctly different from those of the sediments and brines. The strontium data suggest that the rhyolite glasses were derived from basaltic or gabbroic material but may have attained as much as 40 percent of their strontium from upper crustal rocks such as the sediments analyzed.