Named for productive iron-formation exposed at the Riverton mine at Iron River, southern Iron Co, northwest MI in the Lake Superior region. Is part of Paint River group (new) of Animikie series. Visible in walls of caved workings of the old mine. Small exposures are widespread in eastern part of Iron River-Crystal Falls district. Is host rock for ore bodies composed of interbedded chert and siderite, and ranges in thickness from less than 100 ft in western part of district to about 500 ft in eastern part. Locally, upper part eroded beneath overlying Hiawatha graywacke. Overlies Wauseca pyritic member (new) of Dunn Creek slate (new). Stratigraphic sequence chart; location map. Is Middle Precambrian in age.

Source: GNU records (USGS DDS-6; Denver GNULEX).

Pg. 2845 (fig. 2, stratigraphic chart compiled from Leith and others, 1935; James, 1958; Gair and Thaden, 1968). Riverton Iron-Formation of Paint River Group of Marquette Range Supergroup (new; replaces †Animikie series of James, 1958, south of Lake Superior, in Michigan and Wisconsin). Present in Iron River-Crystal Falls district, northwestern Michigan. Overlies Dunn Creek Slate and underlies Hiawatha Graywacke, both of Paint River Group. Age is middle Precambrian.

Source: Publication.