Ore-bearing quartz-carbonate veins of the Coeur d'Alene mining district yield 87Sr/86Sr ratios of 0.74 to >1.60 for low-Rb/Sr, carbonate gangue minerals, similar to current ranges measured in Middle Proterozoic, high-Rb/Sr rocks of the Belt Supergroup. Stable-isotope and fluid-inclusion studies establish a genetic relationship between vein formation and metamorphic-hydrothermal systems of the region. These extraordinary 87Sr/86Sr ratios require accumulation of radiogenic 87Sr in a high Rb/Sr system over an extended period prior to incorporation of Sr into the veins by hydrothermal processes. Evaluation of the age and composition of potential sources of highly radiogenic Sr indicates that the ore-bearing veins of the Coeur d'Alene district formed within the last 200 Ma from components scavenged from sedimentary and metasedimentary rocks of the Belt Supergroup, the primary host-rocks of the district. These results are consistent with a Cretaceous or Early Tertiary age for these veins. Pb-Zn deposits that yield Pb isotope, K-Ar, and Ar-Ar results indicative of a Proterozoic age probably formed during deposition or diagenesis of the Belt Supergroup at 1350-1500 Ma, possibly as Sullivan-type syngenetic deposits. K-Ar and Rb-Sr apparent ages and 6l80 values of Belt Supergroup rocks decrease southward from the Coeur d'Alene district toward the Idaho batholith, normal to the trends of metamorphic isograds, fold axes, foliation, and the major reverse faults of the district. Isoclinal folding, thrust faulting, high-temperature metamorphism, granitic plutonism, and regional-scale metamorphic-hydrothermal activity is documented in the region between 140 Ma and 45 Ma, but no similar combination of events is recognized for Late Proterozoic time. Combined with Sr P results from the veins, the evidence strongly favors formation of the ore-bearing carbonate veins of the district by fluids related to a complex metamorphic-hydrothermal system during Cretaceous and/or early Tertiary time. Proterozoic Pb-Zn deposits were probably deformed, remobilized along younger structures, and incorporated into the younger hydrothermal deposits during this event.

The upper member of the Permian Dollarhide Formation is a discrete tectonostratigraphic unit within the "Idaho Black Shale Belt" as defined by W.E. Hall in 1985. It can be traced approximately 20 miles from the town of Bellevue to Dollarhide Mountain. Along this trend more than 20,000,000 ounces of silver and associated base metals have been recovered from epigenetic fault-controlled veins. The upper member is highly carbonaceous, hosts many silver-lead-zinc veins, and is associated with a syngenetic barite horizon. These relations suggest a high potential for undiscovered massive sulfide deposits exists in the upper member. Southwest of Bellevue, the northeasttrending Hailey Gold belt intersects the northwest-trending zone of Ag-Pb-Zn epigenetic veins in the upper member of the Dollarhide Formation. This area has potential for undiscovered gold deposits.

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