Helena limestone (MTpCAh;0)

State	Montana
Name	Helena limestone
Geologic age	Proterozoic \| Mesoproterozoic
Original map label	pCh
Primary rock type	carbonate
Secondary rock type	meta-conglomerate
Other rock types	quartzite
Lithologic constituents	Major Sedimentary > Carbonate (Bed)Weakly metamophosed limestones and dolomites. Incidental Metamorphic > Metasedimentary > Metaclastic > Quartzite (Greenschist) Metamorphic > Metasedimentary > Metaclastic > Metaconglomerate (Greenschist)Weakly metamorphosed conglomerates.
Map references	Ross, P.R., Andrews, D.A., and Witkind, I.J., 1955, Geologic map of Montana: U.S. Geological Survey, 2 sheets, scale 1:500,000.
Unit references	Ruppel, E.T., O'Neill, J.M., and Lopez, D.A., 1993, Geologic map of the Dillon 1o x 2o quadrangle, Idaho and Montana: U.S. Geological Survey Miscellaneous Investigations Series Map I-1803-H, scale 1:250,000. [http://pubs.er.usgs.gov/publication/i1803H] Tysdal, R.G., Ludington, Steve, and McCafferty, A.E., 1996, Mineral and energy resource assessment of the Helena National Forest, west-central Montana: U.S. Geological Survey Open-File Report 96-683-A, 322 p., 6 plates. [http://pubs.er.usgs.gov/publication/ofr96683A] Fox, J.E., 1993, Stratigraphic cross sections showing electric logs of Upper Cretaceous and older rocks, Powder River basin, southeastern Montana and northeastern Wyoming: U.S. Geological Survey Oil and Gas Investigations Chart OC-135 to OC-138, [http://pubs.er.usgs.gov/publication/oc135] Harrison, J.E., Whipple, J.W., and Lidke, D.J., 1998, Geologic map of the western part of the Cut Bank 1° x 2° quadrangle, northwestern Montana: U.S. Geological Survey Miscellaneous Geologic Investigations Series Map I-2593, scale 1:250,000. [http://pubs.er.usgs.gov/publication/i2593] McGill, G.E., and Sommers, D.A., 1967, Stratigraphy and correlation of the Precambrian Belt Supergroup of the southern Lewis and Clark Range, Montana: Geological Society of America Bulletin, v. 78, no. 3, p. 343-351. Harrison, J.E., 1972, Precambrian Belt basin of northwestern United States--Its geometry, sedimentation and copper occurrences: Geological Society of America Bulletin, v. 83, no. 5, p. 1215-1240. Whipple, J.W., Connor, J.J., Raup, O.B., and McGimsey, R.G., 1984, Preliminary report on the stratigraphy of the Belt Supergroup, Glacier National Park and adjacent Whitefish Range, Montana, in McBane, J.D., and Garrison, P.B., eds., Northwest Montana an Earhart, R.L., Mudge, M.R., and Connor, J.J., 1984, Belt Supergroup lithofacies in the Northern Disturbed Belt, northwest Montana, in McBane, J.D., and Garrison, P.B., eds., Northwest Montana and adjacent Canada--Montana Geological Society 1984 Field Con
Geographic coverage	Jefferson - Lewis and Clark - Powell