Potential for shale-hosted massive sulfides in the Permian Dollarhide Formation, south-central Idaho

Abstract

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.

Geology and mineral deposits of the Minnie Moore and Bullion mineralized areas, Blaine County, Idaho

“…The identification of the host rocks at the Snoose mine as Milligen or Dollarhide Formations, has been contentious. Hall (1985) and Wavra and Hall (1989) labeled these rocks as Dollarhide Formation, in contrast to earlier reports. We, however mapped the sheared Milligen-lower Dollarhide contact west of the Snoose mine ( fig.…”

“…There has been disagreement, especially in the wave of exploration of the last fifteen years, about the formation assignment of the rocks in Minnie Moore and Bullion areas (compare our maps with those of Hall, 1985, andHall, 1989). Late in his life, W.E.…”

“…The strata present at the west end of Minnie Moore Gulch are thought to belong to the lower member of the Dollarhide Formation (more than 800 m [2,640 ft] thick) because they contain thick black limestone beds and gray sandstone beds that are nowhere coarser than fine grained, an attribute that distinguishes sandstones of the Dollarhide Formation from the coarse-grained sands of the Cait quartzite in the Milligen Formation. Further, as stated by Wavra and Hall (1989), limestones are uncommon in the upper member of the Dollarhide Formation; thus that assignment is doubtful for the ore hosts in Minnie Moore Gulch.…”

“…In several places in the Wood River area, including Colorado Gulch in the Minnie Moore area, the Milligen Formation contains two generations of folds, an earlier set of small-scale folds probably formed during the Devonian and Mississippian Antler Orogeny and a later large-scale set probably formed during the Cretaceous Sevier Orogeny Otto, 1988, 1995;Burton and Link, 1995). Wavra and Hall (1989) used the presence of a cleavage or foliation as a means to distinguish Milligen Formation. We found, however, that structural fabric in the Milligen is heterogeneous and that the formation does not contain the same structural elements everywhere.…”

“…Hall (1985), in a geologic overview of the central Idaho black-shale mineral belt, assigned the host rocks in both areas to the Middle Pennsylvanian and to the Lower Permian Dollarhide Formation. Wavra and Hall (1989) further restricted this assignment to the upper member of the Dollarhide Formation. Our geologic mapping does not support these assignments; instead we place the Minnie Moore orebodies in the middle part of the Devonian Milligen Formation and the Bullion orebodies in the lower member of the Dollarhide Formation.…”