Mineral resources of the Rainbow Lake Wilderness Area and the Flynn Lake Wilderness Study Area, Bayfield County, Wisconsin

Abstract

The Rainbow Lake Wilderness Area contains a low-grade identified resource of copper in thin sedimentary beds that are no more than 1.5 feet thick and that contain grades no higher than 0.5 percent. The beds are restricted to a single stratigraphic horizon, dip 5° to 30° N., and are present only at great depth in much of the area. The area also contains about 210,000 short tons of commercial-quality peat and a great amount of sand and gravel (fig. 1). An abundance of similar material in the region closer to transportation and consumption centers makes these deposits unimportant. The Flynn Lake Wilderness Study Area contains about 300,000 short tons of commercial-quality peat and large amounts of sand and gravel, but these, like similar deposits in the Rainbow Lake Wilderness Area, are not economically important. Basalt and andesite lava flows are bedrock beneath the glacial drift in the southern part of the area and dip northward 30°. Consequently, the lava flows are present in the subsurface of both the Flynn Lake and the Rainbow Lake areas. Little is known of these rocks because of the lack of exposures, but, on the basis of regional geologic relationships and a theory of how native-copper ores were formed, they are believed to be favorable for such deposits. Because native-copper ores in Michigan are presently unecon9mic to mine, little interest in exploration for native copper is found in Wisconsin. The study area could prove promising, however, if copper prices inerease.