A strontium and oxygen isotope study of Laramide magmatic and hydrothermal activity near Central City, Colorado

Twelve Laramide intrusions, eleven country rocks, and over thirty hydrothermal minerals from the Central City and Idaho Springs mining districts, Colorado, have been analyzed for Sr isotope compositions. Intrusions have also been analyzed for oxygen isotopes. Precambrian country rocks have an average 87 Sr/ 86 Sr ratio at 59 m.y. ago of ca. 0.73, but with a high degree of local isotopic heterogeneity. Strontium contents and initial ratios in …