A survey of 24 elements in North Dakota lignite (Fort Union Group, Paleocene) and possible geologic implications
Date of Award
Master of Science (MS)
Calystone, carbonaceous shale, lignitic shale, and lignite samples were collected from western North Dakota for element analysis during May 1978, April 1979, and August 1979. Lignite was collected from the Sentinel Butte Formatlon--Hagel Bed (Oliver and McClean Counties), Beulah-Zap Bed (Mercer County), Lehigh Bed (Stark County)-- and from the Bullion Creek Formation--Harmon Bed (Bowman County). Claystone samples were also collected from clay partings present in the Hagel Bed and Harmon Bed. Control samples were collected from an outcrop of the marine lower middle Cannonball Formation (carbonaceous shale) south of Mandan, North Dakota and from an outcrop of the brackish oyster lignite and oyster bed (lignitic shale) of the Slope Formation north of Marmarth, North Dakota.
The samples were analyzed for 24 major, minor, and trace elements using an Inductively Coupled Argon Plasma (lCAP) Spectrometer. Generally Cd and high concentrations of Na occurred at the top of a seam. Concentrations of V and Zn were usually higher at the top and bottom of a seam, whereas other elements were equally dispersed throughout the seam. The position of high concentrations in a seam indicate that: Cd and Na may be deposited by groundwater; that V and Zn may be influenced by groundwater; and that most of the other elements occur as the result of primary deposition.
The five elements used to attempt to differentiate between the Beulah-Zap, Lehigh,, Hagel, and Harmon beds were As, Ba, Ca, Co, and Sr. Considering average values, it appears that the Beulah-Zap Bed may be generally characterized by high concentrations of Ba (630 ppm) and As ( 170 ppm), moderate concentrations of Sr (660 ppm), and low concentrations of Ca (0.5%) and Co (5 ppm). The Lehigh Bed may be characterized by high concentrations of Sr (1170 ppm), Ba (620 ppm), and Ca (0.9%) and moderate concentrations of As (110 ppm) and Co (30 ppm). The Hagel Bed may be characterized by low concentrations of As (5 ppm), Ba ( 290 ppm), and Sr (340 ppm) and a high concentration of Ca (0. 9%) and Co (170 ppm). The Harmon Bed is characterized by moderate concentrations of As (60 ppm), Ba (410 ppm), Ca (0.7%), and Co (40 ppm) and low concentrations of Sr (410 ppm).
Elemental concentration may indicate relative rate of basin subsidence. The higher the concentration the slower the rate of subsidence. A comparison of lignites from North Dakota (Williston Basin) and coals from the Powder River Basin indicate that North Dakota lignites have a higher inorganic element concentration. Therefore, the Williston Basin may have subsided at a slower rate than the Powder River Basin.
Cr, Ga, Ni, and V may be indicative of the salinity of the depositional environment of a lignite. The samples of the marine lower middle Cannonball Formation are higher in Cr, Ga, Ni, and V than are the samples of brackish oster bed (Slope Formation). Values for these elements for the Beulah-Zap and Hagel Bed lignites (Sentinel Butte Formation) are irregular.
A low K/Li ratio for noncoalified material is indicative of a higher salinity environment. The Beulah-Zap and Lehigh Beds had no clay partings, so K/Li ratios could not be determined for these beds. The Harmon bed and oyster bed K/Li ratios are similar, whereas the Hagel Bed K/Li ratio is two orders of magnitude higher than the oyster bed, indicating lower salinity.
Zimmer-Dauphinee, Susan A., "A survey of 24 elements in North Dakota lignite (Fort Union Group, Paleocene) and possible geologic implications" (1983). Theses and Dissertations. 336.