Kansas Geological Survey, Bulletin 187, pt. 1, originally published in 1967
Originally published in 1967 as part of "Short Papers on Research in 1966," Kansas Geological Survey Bulletin 187, part 1, p. 13-14. This is, in general, the original text as published. The information has not been updated.
A study was made of the copper content of the Ninnescah Shale and the Milan Dolomite Member of the Wellington Formation in south-central Kansas. Five east-west sampling traverses were made across the outcrop in a four-county area. Channel samples numbering 411 were analyzed by X-ray spectroscopy for copper. The copper, as the mineral malachite, was found to be the highest (6.65 percent Cu as the metal) in the Runnymede Sandstone Member of the Ninnescah Shale in Harper County, Kansas.
Geologists who have worked on the Permian red beds in south-central Kansas have reported malachite (CuCO3 • Ca(OH)2) associated with dolomite and with some of the shales and sandstones in the area (Swineford, 1955; Norton, 1939; Moore, 1951, p. 40). More recently Ham (1964) has reported commercial reserves of copper-bearing shale in a geologically higher unit (Flower-pot Shale) of the Permian red beds in southwestern Oklahoma.
The Milan Dolomite Member, which is the topmost bed of the Wellington Formation (Permian), is the lowest unit studied. The Milan is approximately 52.7 feet thick at the type locality in sec. 30, T. 32 S., R. 3 W., and is composed of five thin, shaly dolomite beds 1-9 inches thick separated by 4-42.3 feet of banded and mottled red and gray-green blocky shale. Malachite is usually found on the laminations of the gray shale found under each thin dolomite bed and in the vugs and cracks in the basal part of the dolomite bed. This is the only copper mineral identified to date in the outcrops investigated.
The overlying Ninnescah Shale is predominantly red shale with gray-green spots and cracks, but it also contains discrete beds of red and gray-green shale. Secondary deposits of gypsum are found as crack fillings and as thin laminae that weather out differentially along the bedding planes of the shale. At some locations gypsum geodes and septarian concretions are relatively abundant. Locally, a thin discontinuous dolomite is found in outcrops of the Ninnescah Shale. The upper member of the Ninnescah Shale is the Runnymede Sandstone described by Norton (1939), who reported malachite in this unit in the vicinity of Runnymede, Harper County, Kansas. The Runnymede is a gray to white shaly, silty, sandstone that is often powdery on weathered outcrops.
Five east-west traverses were made from the outcrop of the Milan Dolomite Member across the Ninnescah Shale to the Runnymede Sandstone Member (Fig. 1), and samples were taken from available outcrops. Where no outcrops were available samples were augered from exposed bedrock, which permitted fresh samples to be taken from a depth of 2-2.5 feet in shale from relatively flat graded road cuts.
Figure 1--Sampling traverses across the Ninnescah Shale and the Milan Dolomite Member of the Wellington Formation in south-central Kansas.
Samples were taken on the basis of vertical footage and change of lithology from the outcrops. Lithology changes could not be clearly seen in the auger samples and here samples were taken on a footage basis only. Of the entire suite of samples most were representative of lithologies less than 1 foot in vertical thickness. Thicker units in the shale were broken into 12-inch channel samples.
The 441 samples taken were dried, crushed, and ground to pass a 250-μ screen and analyzed for copper content on a GE XRD-6 X-ray spectrograph using a LiF analyzing crystal and tungsten target X-ray tube. The X-ray spectrograph was made available for this study through the courtesy of the Geology Department of the University of Kansas. Copper standards were made up with both dolomite and clay matrices in order to simulate the range of geologic materials likely to be encountered. Plots of the standards in both matrices were linear and nearly superposed in the range from 0.05 to 10.0 percent Cu, indicating no major interferences resulting from the matrix differences.
The field observations and analytical results rapidly delineated several facts: (1) Copper was not present in concentrations exceeding 0.05 percent in any of the red, oxidized parts of the shales of the Milan Dolomite Member or of the Ninnescah Shale. Copper concentrations exceeding this value were found only in some of the gray-green shales, some of the dolomites, and in the silty, shaly Runnymede Sandstone Member; (2) The gray shales in the Ninnescah Shale were found to contain < 0.05 percent Cu; (3) The emplacement of the malachite is controlled by porosity, and it is deposited in the cracks and parting planes of the shales associated with dolomite beds and in cracks, vugs, and parting planes of the basal part of the dolomite strata; (4) The Cu has been carbonate precipitated from solution in the shale, dolomite, and sandstone; (5) Low porosity dolomite strata are usually very low in Cu content; (6) As pointed out by Swineford (1955), strontianite is also associated with the malachite in the Milan Dolomite Member; (7) The lower carbonate strata that overlie a shale sequence usually contain the highest amounts of Cu.
The anomalously high Cu in this area is concentrated in the outcrops of the Milan Dolomite Member and the Runnymede Sandstone Member. The highest concentrations found in percent by weight of copper as the metal are:
Significantly high concentrations of Cu (up to 6.6 percent in one sample) are present at least surficially in the lower Milan Dolomite Member and Runnymede Sandstone Member of the lower part of the Permian red beds. Additional investigation of the copper-rich zone both on the outcrop and in the subsurface appears warranted. If the copper-rich zones identified have sufficient areal extent with a favorable overburden ratio, they may warrant commercial exploitation.
Ham, W. E., and Johnson, K. S., 1964, Copper in the Flower-pot shale (Permian) of the Creta area, Jackson County, Oklahoma: Univ. Oklahoma, Circ. 64, 32 p.
Moore, R. C., Frye, J. C., Jewett, J. M., Lee, Wallace, and O'Connor, H. G., 1951, The Kansas rock column: Kansas Geol. Survey, Bull. 89, 132 p. [available online]
Norton, G. H., 1939, Permian red beds of Kansas: AAPG Bull., v. 23, no. 12, p. 1,751-1,819.
Swineford, Ada, 1955, Petrography of upper Permian rocks in south central Kansas: Kansas Geol. Survey, Bull. 111, 179 p. [available online]
Kansas Geological Survey, Short Papers on Research in 1966
Placed on web July 25, 2011; originally published in Feb. 1967.
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