Oxygen and hydrogen isotope geochemistry of the Coeur d'Alene mining district, Idaho

The current hypothesis concerning the origin of mineralization in the Coeur d'Alene district is based on remobilization of vein material from Belt metasediments by fluids generated during low-grade metamorphism. This hypothesis is based on geologic observation and fluid inclusion evidence. The primary objective of this project is to use oxygen and hydrogen isotopes to characterize the water(s) involved in the mineralization and to evaluate this information with respect to the current hypothesis.; Eighty-five oxygen isotope analyses of vein quartz were obtained along with 12 analyses of Belt rocks and three analyses of igneous rocks. Sixteen D/H analyses were obtained from quartz inclusion fluids. Oxygen extractions were performed using standard techniques with ClF{dollar}sb3{dollar}. Water for the D/H analyses was obtained by crushing. Results are reported in standard {dollar}delta{dollar} notation relative to SMOW.; The {dollar}rmdeltasp{lcub}18{rcub}Osb{lcub}QTZ{rcub}{dollar} values range from +9.48 to +18.04{dollar}perthous{dollar} (mean = 14.51{dollar}perthous{dollar}; s.d. = 1.07{dollar}perthous{dollar}) and approximate a normal distribution. Contoured mean {dollar}rmdeltasp{lcub}18{rcub}Osb{lcub}QTZ{rcub}{dollar} values for each mine reveal isotopic lows offset by about 20 km across the Osburn fault. Mean {dollar}rmdeltasp{lcub}18{rcub}Osb{lcub}QTZ{rcub}{dollar} values for each of the three productive intervals of the Belt range from 14.93{dollar}perthous{dollar} (middle Prichard) to 14.45{dollar}perthous{dollar} (Revett-St. Regis). Twenty-six analyses of vein quartz from the Star-Morning mine reveal a decrease in {dollar}rmdeltasp{lcub}18{rcub}Osb{lcub}QTZ{rcub}{dollar} toward deeper mine levels.; Hydrogen isotope compositions of quartz inclusion fluids range from +43 to {dollar}-{dollar}105{dollar}perthous{dollar}. Positive values are attributed to H{dollar}sb2{dollar}O-CH{dollar}sb4{dollar} exchange. Mean {dollar}delta{dollar}D values for the middle Prichard and Prichard-Burke are +25{dollar}perthous{dollar} and {dollar}-{dollar}15{dollar}perthous{dollar}, respectively. The presence of positive {dollar}delta{dollar}D values and reduced hydrocarbon species in fluid inclusions from these intervals suggests relatively reduced ore fluids derived from formation waters in the Pritchard. The mean {dollar}delta{dollar}D for the Revett-St. Regis is {dollar}-{dollar}68{dollar}perthous{dollar}. Inclusions in quartz from these veins contain CO{dollar}sb2{dollar}, suggesting the ore fluids are a mixture of formation waters and oxidized meteoric waters.; The {dollar}deltasp{lcub}18{rcub}{dollar}O values of regionally metamorphosed Belt rocks range from +12.35 to +16.81{dollar}perthous{dollar} (mean = 13.64{dollar}perthous{dollar}). The values of contact metamorphosed Belt rocks and igneous rocks range from +7.15 to 8.90{dollar}perthous{dollar}.