Contributions to Geology 10.1

Geologic framework of the Green River Formation in Wyoming

CLAUDIA A. WOLFBAUER Department of Geology, University of Wyoming, Laramie, Wyoming 82071

Pages
3-8

Keywords
Eocene, Green River, Wyoming, Lake Gosiute, Lake Uinta, Fossil Lake

Abstract
One of the most remarkable features of the Eocene epoch in North America was the creation of a string of lakes in the western interior basins of Wyoming, Utah, and Colorado. Among these was a closely related group of lakes in which the Green River Formation was deposited -- Lake Gosiute in the Green River Basin of southwestern Wyoming and northwestern Colorado; Lake Uinta in the Uinta Basin of northeastern Utah and the Piceance Creek Basin of western Colorado; and Fossil Lake in the Fossil Syncline depression west of Kemmerer, Wyoming (Fig. 1).

Geochemical history of Lake Gosiute

JONATHAN H. GOODWIN Department of Geological and Geophysical Sciences, University of Utah, Salt Lake City, Utah 84112

Pages
9-14

Keywords
Lake Gosiute, Green River, Rock Springs uplift, organic, trona, Eocene

Abstract
Studies of authigenic silicate minerals in tuffs of the Green River Formation have made possible the reconstruction of the depositional environments of Eocene Lake Goslute. For much of its history, Lake Gosiute was chemically stratified. The preservation of large amounts of organic matter in the sediments and the presence of sulfide minerals indicate that the lake water and occluded brines commonly had an Eh near -0.4.

Initial filling of Lake Gosiute began during Luman-Tipton time with the formation of a nearly fresh water lake. Because of a climatic change, the lake shrank to its lowest level during Wilkins Peak time. Extensive beds of trona were precipitated from the lake brines and authigenic trona and other saline minerats formed in the sediments during this time. Lake brines and occluded brines became depleted in sodium and caused the formation of authigenic K-feldspar in the tuffs. A second change in climate at the end of Wilkins Peak time prevented further deposition of evaporite minerals. Rapid sedimentation during Laney time filled the Lake basin and ended lacustrine deposition.

Throughout Green River time, the Rock Springs uplift formed a low sill, partially separating brines in the Bridger Basin from fresher water in the Washakie Basin, but allowing relatively free circulation of surface water between the two basins.

Stratigraphy of the trona deposits in the Green River Formation, southwest Wyoming

WILLIAM C. CULBERTSON U.S. Geological Survey, Denver, Colorado

Pages
15-24

Keywords
trona, Green River, Wyoming, correlation, Wilkins Peak, oil shale

Abstract
The Wilkins Peak Member of the Eocene Green River Formation contains about 42 beds of trona in an area of about 1,300 square miles in the southeast part of the Green River basin of Wyoming. Many thin beds of oil shale and tuff, and nine thick blanketlike sandstone-mudstone units in the Wilkins Peak Member are recognizable across hundreds of square miles in cores and geophysical well logs and form a stratigraphic framework that aids in the identification and correlation of the trona beds. Almost all trona beds are underlain by a bed of oil shale ranging in thickness from a few inches to several feet. All except one of the sandstone-mudstone units were deposited directly after deposition of a major trona bed. Three episodes of trona deposition are recognized. Most trona beds deposited during the first episode occupy large areas in the southern and central parts of the trona area, and locally contain large amounts of intermixed or interlayered halite. Trona beds of the second episode mostly occupy small areas in the northwest, and are halite-free. Trona beds of the last episode occupy small areas in the northeast, and also are halite-free.

Wyoming trona deposits

DON L. DEARDORFF and L. E. MANNION Pickands Mather & Company, Denver, Colorado; Stauffer Chemical Company, Richmond, California

Pages
25-38

Keywords
Wyoming, trona, Wilkins Peak, ore

Abstract
In southwest Wyoming, lake deposits of the Wilkins Peak Member of the Green River Formation contain more than 25 extensive trona beds. Eleven of these exceed a six-foot minable thickness and total more than 50 billion tons of trona.

Trona beds tend to be almost monomineralic, although some carry much intermixed halite; other impurities consist largely of rock-forming matter, either dispersed or in layers, and the mineral shortite. It is principally the older trona beds that are salt bearing. They appear to have formed while the ancient lake occupied a rather shallow basin and was undergoing exceptionally strong evaporation. The basin likely had a deeper interior portion separated by gentle rises from more shallow outer basins. Halite represents maximum dessication and is found exclusively in the interior, whereas trona was deposited in both outer and inner basins.

Five trona beds are intersected by mine workings. The FMC and Allied mines both extract ore from the same widespread layer. A younger pair of beds is present in the Texas Gulf Sulphur workings and a still younger pair at the Stauffer mine. In these four beds, solution activity and reorganization of material is particularly evident, including enlarged grain size and secondary redeposition of trona.

Numerous marker beds, including tuffs and oil shales, permit detailed stratigraphic correlation in the upper Wilkins Peak. Notable are the persistent thin beds associated with trona and the indication of rapid trona accumulation with vitually no laterally equivalent rock strata.

The mining of Wyoming trona

ROBERT J. STEEL Mine Superintendent, Stauffer Chemical Company of Wyoming, Green River, Wyoming

Pages
39-42

Keywords
trona, Wyoming, Stauffer, soda ash, production

Abstract
Trona, a natural sodium sesquicarbonate, was initially discovered in southwestern Wyoming prior to 1940. Development of this vast natural resource was not rapid, but by 1962 the production of soda ash from trona ore was being conducted at two separate locations. One of these producers was Stauffer Chemical Company of Wyoming's Big Island Mine and Refinery located seventeen miles northwest of the town of Green River.

Stauffer's exploration program was initiated in 1959 and resulted in the construction and development of a 200,000 ton per year soda ash plant and mine by the summer of 1962. Two expansions have increased this production capacity to approximately 1,000,000 tons per year at the present time.

Access to the lower of the two Big Island ore bodies is gained by two vertical shafts reaching to approximately 830 ft. below the surface. Mining is accomplished by utilizing conventional coal mining equipment in a room-and-pillar mining method. Present refinery capacity is equivalent to 1.75 million tons of ore per year. Ore is transported underground by roof hung conveyor belts and hoisted to the surface by an automatic hoisting system.

Future mine expansion will proceed into the essentially untouched area to the east of the present shafts and include the mining of the upper ore bed in this location.

Processing of Wyoming trona

W. R. FRINT FMC Corporation, Inorganic Chemicals Division, Box 872, Green River, Wyoming 82935

Pages
43-48

Keywords
trona, Wyoming, ore, oxide, deposit

Abstract
The trona ore as it comes from the mine is processed into an item of commerce, although it could conceivably be used "as is." Wyoming trona is an important natural resource, as a source of sodium oxide (Na2O). The ore as it comes from the mine contains only 38% Na2O, along with 33% carbon dioxide, 19% water, and about 10% of various water insoluble minerals, with calcium and magnesium carbonate compounds predominating. Pure sodium oxide is difficult to produce and handle, so it is normally supplied and used in the form of sodium hydroxide (NaOH) called caustic soda, or sodium carbonate. The remaining 37.5% consisting of the carbon dioxide, water, and insolubles has very little economic value. The trona deposit is remote from sodium oxide consuming locations, so it is desirable to upgrade the sodium content at the mine site and remove the worthless materials before incurring transportation charges.

Origin and deposition of trona

HANS P. EUGSTER Department of Earth and Planetary Sciences, The Johns Hopkins University, Baltimore, Maryland 21218

Pages
49-56

Keywords
trona, precipitation, deposits

Abstract
Trona deposits pose a number of challenging problems with respect to occurrence and mechanism of precipitation. Though we have reasonably good insight into some aspects of their origin, much remains to be clarified.

Authigenic minerals of the Green River Formation

CHARLES MILTON Research Professor, Department of Geology, George Washington University, Washington, D. C.

Pages
57-64

Keywords
species, Green River, minerals, Utah, Colorado

Abstract
Over 70 authigenic species have been found in the Green River Formation of Utah, Wyoming, and Colorado; these are listed with indication of their abundance, and each is briefIy commented on; with, for many, references to recently published data.

Early and Middle Eocene faunas of the Green River Basin

PAUL 0. McGREW Department of Geology, University of Wyoming, Laramie, Wyoming 82071

Pages
65-68

Keywords
trona, Wyoming, lacustrine, fluvial, Wasatch, Bridger, Green River, Eocene, fauna

Abstract
The trona deposits of Wyoming occur in a very complex sequence of lacustrine and fluvial sediments involving sub-units of the Wasatch, Green River and Bridger Formations. Gross relationships of these units are well known but there is still much to be learned about details.

A summary of authigenic silicates in the tuffaceous rocks of the Green River Formation

RONALD B. PARKER and RONALD C. SURDAM Department of Geology, University of Wyoming, Laramie, Wyoming 82071

Pages
69-72

Keywords
Green River, silicates, Wyoming, Lake Gosiute, oil shale, trona

Abstract
The tuffaceous rocks in the Green River Formation show extensive alteration to aluminosilicates, specifical1y montmorillonite, clinoptilolite, mordenite, analcime, and potassium feldspar. The distribution, both horizontally and vertically, of these authigenic minerals shows a regular pattern which is related to paleosalinities and paleoalkalinities in Lake Gosiute. Clay and zeolites are associated with freshwater facies with high yield oil shales whereas potassium feldspar is associated with the saline alkaline trona-bearing facies. Analcime reflects intermediate salinities and alkaiinities.