Geologic map and structure sections of the southwest quarter Willis Quadrangle, Beaverhead County, Montana

Mineral resources in Permian rocks of southwest Montana

“…On this thrust the Quadrant Sandstone (Pennsylvanian), which makes up most of the mountain, has overriden upper Paleozoic strata that are preserved in a long wedge between the thrust and the normal Red Rock fault at the base of the range. Near the north end of this wedge, Triassic strata dip northwest (Lowell, 1949). Because the stratigraphic sequence appears to be uninterrupted, Permian strata can be inferred to underlie the Triassic.…”

“…The geology of the Blacktn.il Rn.nge phosphate area was described briefly by Lowell ( 1949, who mapped the n.rea in detn.il. The following discussion of the geology is based ln.rgely on Lowell's mn.p.…”

“…670.) Geologic descriptions noted herein are based pl,'imarily on the detailed mapping by Lowell (1949 and by Myers (1952).…”

“…Hall (written commun., 1957), Honkala (1949b), Honkala (1953), Karlstrom (1948), Kennedy (1949 andwritten commun., 1952), Klemme (1949), Klepper (1950), Klepper and others (1957), M. R. Klepper (unpub. map compilation of region about Boulder Batholith), Love and others (1955), Lowell (1949), , McMannis (1955), Mann (1950), G. T. Moore (1956), Myers (1952), Peale (1896), E. S. Perry (unpub. map information, Three Forks area, Montana), Richards and Pardee (1926), Robinson (1963), Ross and others (1955), Ross and Forrester (1947), Sahinen (1939Sahinen ( , 1950, Scholten and others (1955), Skeels (1939), Swanson (1951), Theodosis (1955), and Wilson (1934b). rock produced by mining contains mostly phosphorite but may also contain mudstone, sandstone, carbonate rock, or chert that occur in thin layers or lenses within the mined sequence, and these rocks may be poorly to richly phosphatic.…”

“…The description of the geology in the Lima district is based on the detailed map of Lowell ( 1949), on the smaller scale map and accompanying text of· Scholten, J(eenmon, and J(upsch (1955), and on observations made during the phosphate sampling program. The general area is underlain chiefly by thick Carboniferous formations and by broad expanses of thick Tertiary deposits.…”