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Aerial surveying of Wyoming bentonite
ELSEVIER
Applied
Clay Science
I1 (1997)
329-335
Aerial surveying of Wyoming bentonite Thomas A. Thorson Black Hills Bentonite,
Ltd.. Box 9, Mills,
Accepted
28 August
WY 82644.
USA
1996
Abstract Aerial photography is very useful in exploration activities for bentonite deposits found in Wyoming. Significant marker beds are usually evident, which aid in finding specific bentonite formations or host formations of the bentonite. Vegetation is sparse in areas where bentonite is found which allows observation of the surface geology. Aerial photography is also useful with respect to developing mining plans and environmental baseline information. In areas where land surveys are incomplete or lost, aerials are useful in placing mineral deposits in the correct location.
1. Introduction 1.1. Geology Wyoming bentonite is derived from volcanic ash that was deposited in shallow marine seasin the Cretaceousperiod. The ash originated in the Yellowstone Park area and areasfurther west. It was carried eastwardby the prevailing westerly’s to the inland seasthat were present 100 million years ago. Commercial bentonite deposits are found between the Thermopolis and Pierre Formations. This representsa period of approximately 20 million years. Those deposits which fell into marine waters were preserved, while those which fell on land closer to the volcanic sourceswere lost. Alternating and succeedingdepositsof shale and sandstoneburied the volcanic ash under thousandsof feet of sediment. During the Laramide Revolution at the start of the Tertiary period, the volcanic sediments were slowly uplifted as the Rocky Mountains were formed. Progressive erosion over the next 20 million years exposed the volcanic ash along the flanks of the respective uplifts. The ash was then transformed into a clay by alteration processesand ion replacement. Outcroppings of bentonite can be observed in all areas of Wyoming where the Thermopolis, Mowry and Frontier Formations occur. These outcroppings are numerous 0169.1317/97/$ 17.00 Copyright PII SOl6~-l~l7~~6~O~~~~il-~
0 1997 Elsevier
Science
B.V. All rights reserved
330
TA. Thorson / Applied
Clay Science I I (19971329-335
as Wyoming has numerous uplifts. The two most significant are the Black Hills and the Big Horn Mountains. Less significant areas include those near Lander, WY and south of Casper, WY. 1.2. Commercial activity Wyoming bentonite was commercially developed in the late 1880s when it was discovered that the clay had properties valuable to the cosmetic industry. This use was quite small however and it was not until the 192Os, when higher grade deposits were discovered in the Black Hills, that a true industry was born. Steel foundries discovered that Wyoming bentonite imparted superior qualities to molding sands and they became a large consumer. In the 1930s when rotary oil well drilling was developed, the clay was used to develop the drilling muds which were essential in this process. During the early 1950s the iron ore industry identified bentonite as a superior binder for taconite concentrates which were pelletized as a replacement for direct shipments of iron ore. Bentonite began to be used in the 1970s in a variety of environmental applications. Those included slurry trenching, caps over landfills and liners under water based fluids. The latest use of bentonite involves the cat litter industry. This use is environmentally driven since less solid waste is created when bentonite is used as compared to the myriad of materials historically used as litter material.
Fig. 1. Field drying. Hot Wyoming summers allow the bentonite to be partially dried using solar energy. The clay is disked, plowed and then piled adjacent to pit. The dried clay is hauled to the processing plant. This mine is in the Thermopolis Formation.
T.A. Thorwn/Applied
Cluy Srienre
I1 (1997)
329-335
331
The industry currently produces approximately 2.5 million tons per year of finished product. The highest production came when oil drilling activity was at its peak in the early 1980s when shipments exceeded 4 million tons annually. 1.3. Mining methods Bentonite is mined using small surface mining equipment. ~verb~den depths of O-30 feet are removed from gently dipping beds with bull-dozers and motor scrapers. No operations use truck and shovel or draglines for overburden removal. The clay is exposed and is often field dried in the hot Wyoming summers to remove 10% of the inplace moisture (Fig. 1). Field drying is performed to reduce transportation costs and the cost of fuel when final processing is done. In situ moisture is usually between 25% and 35%. The clay is then moved to the processing plants by a variety of haulers depending upon the distance and type of road available. 1.4. Processing The clay is dried to a moisture of 7-9% in rotary dryers, milled in Raymond roller mills to 85% minus 200 mesh, or screened to a variety of sizes. The finished product is shipped in a dry crushed form for bulk export, in granular form for a variety of applications and in powdered form for oil field, iron ore and miscellaneous applications. The clay may be bagged in 50 or 100 pound bags, shipped in bulk hopper cars or in bulk bags (super sacks).
2. Aerial surveying Aerial surveying has been available for approximately 30 years since map making activities of the Federal Gove~ment became available for commercial use. This early photography was high altitude and without color. While useful in large scale applications, high altitude photography had little value with respect to mine plans and environmental baseline data. In 1978 a company decision was made to begin low altitude photography of all areas that had potential for exploration, were defined clay deposits or were active mine sites. The principle area to be aerial surveyed for the Black Hills Bentonite Company was near Kaycee, WY on the eastern flank of the Big Horn Mountains. This area consists of a distance of 35 miles north-south and 1 mile east-west. This was the extent of the land either owned or leased for bentonite. The photos were obtained by following the north-south strike of the beds at approximately l/2 mile intervals. Landmarks such as reservoirs or drainages were included in the photographs to aid in the identification of the legal subdivision of the area which had been photographed. By taking the photos in series and then overlapping the coverage it is usually possible to know what property is in the photo. Early in the process difficulty was encountered if landmarks were not visible. There are areas where little relief exists and aerial photos become more difficult to use, because identification of the area flown may be in doubt. The higher the plane flies, the more area is covered. It is advisable to fly the area at 2000 feet or more to obtain coverage that will be helpful
332
T.A. Thorson/Applied
Fig. 2. Clay Spur member in the Kaycee area.
of Mowry
Formations
Clay Science
is highly
visible
II (19971329-335
on right side of photo. This is the marker
bed
when low altitude photos are obtained. The low altitude photos can be matched with portions of the high altitude photos to assure proper location of the respective photos. The Kaycee area contains 5 different minable beds in the formation previously mentioned. The Clay Spur member of the Mowry formation (Fig. 2) is usually the best marker bed. This bentonite. normally crops out in barren shales as a bright yellow band. The beds in the Mowry (Figs. 3 and 4) and Thermopolis Formations are covered by heavy vegetation; however, at the outcrops, small bands of bluish shale are usually visible to identify the extent of the bed. The sequence of the beds are always predictable which allows positive identification of the bentonite versus other beds of shale or non-commercial beds of bentonite. Another area surveyed was located on the west slope of the Bighorn Mountains, near Ten Sleep, WY. This site is approximately 15 miles long and one mile wide on a north-south axis. The results of these surveys made it possible to begin developing detailed mine plans with respect to pit sites, overburden stockpile locations, topsoil stockpile locations and support site areas. These detailed mine plans have been developed without extensive field work, while also avoiding weather delays associated with field activities. All of this work was done with color photography which added details not known before. It is also possible to fly at lower altitudes to further enhance the information being gathered. Aerial photography became extremely useful when exploring areas where no company information was present or where new activities were to begin. The knowledge
T.A. Thorson/Applied
Clay Science II (1997)
329-335
333
334
T.A. Thorson /Applied
Clay Science I I (1997)
Fig. 4. Active mines are in the center of the photo. Land restoration mine. Access road is to haul bentonite to the processing plant.
329-335
has begun
on both sides of the active
developed by low altitude (1000-2000 ft) aerial photography makes it possible to develop predetermined patterns for drilling and the location of drill trails to be used on the surface. Aerial photography was also helpful in final surveying when land markings were difficult to locate. Flying was generally done in the midmorning when the air was calm and low level maneuvers could be done safely. It is advisable to avoid the shadows and unnatural light of the early morning. A single engine, high-wing aircraft was used which did not have a wing strut to obstruct the view. The camera used was a 35 mm with a wide angle lens and date pack. Aerial photography was used extensively to observe areas in southern Wyoming which had not previously been developed commercially. The terrain was quickly observed and determined to offer limited prospects for future development. The beds were steeply dipping and it would have been difficult to gain access due to rugged topography. Wide area bentonite exploration has generally been concluded since all producing outcrops have been located and prospected. Future aerial use will be primarily for
T-A. Thorson /Applied
Clay Science 11 (1997)
329-335
335
environmental considerations. Additional baseline data will be needed on an ongoing basis. It will also be useful in noting the progress of various areas that have been seeded and have been growing a vegetation cover. When it is necessary to obtain ground cover vegetation quality, aerial viewing can quickly identify areas that are successful or may be having problems. Wyoming environmental laws regarding mining began in 1969. The basic premise of the law is that the land should be restored to an equal or greater use. Restoration of premining contours is not a requirement; however, grading must be done to permit the reseeding of all sloping areas. If ponds of water are part of the reclamation plan these must be permitted. It is the practice of this company to develop through drainage in all areas milled to eliminate the development of water reservoirs. Landowners do request on occasion that water be retained and these requests are honored. Wyoming law requires that land restoration be complete within five years, after the land has been affected. This can be a problem where large multiple-cut mines occur; more than live years may elapse. Extensions of time from the state are then required. The reseeded is fenced and must remain under a mining bond for five years before the state can declare the restoration to be complete.
3. Conclusion Aerial photography is an aid in the exploration and development of bentonite deposits in Wyoming. The sparse vegetation allows a complete view of all of the outcropping formations, thus giving a total and complete view of the surface geology. Aerial surveys cannot replace on site drilling to determine depth and quality of the clay reserves but it can reduce the cost of these activities by programming the work to be done. It will have continuing application for environmental uses to document the progress of reclaimed lands and aid in the development of mine plans for newly developed sites.
Applied
Clay Science
I1 (1997)
329-335
Aerial surveying of Wyoming bentonite Thomas A. Thorson Black Hills Bentonite,
Ltd.. Box 9, Mills,
Accepted
28 August
WY 82644.
USA
1996
Abstract Aerial photography is very useful in exploration activities for bentonite deposits found in Wyoming. Significant marker beds are usually evident, which aid in finding specific bentonite formations or host formations of the bentonite. Vegetation is sparse in areas where bentonite is found which allows observation of the surface geology. Aerial photography is also useful with respect to developing mining plans and environmental baseline information. In areas where land surveys are incomplete or lost, aerials are useful in placing mineral deposits in the correct location.
1. Introduction 1.1. Geology Wyoming bentonite is derived from volcanic ash that was deposited in shallow marine seasin the Cretaceousperiod. The ash originated in the Yellowstone Park area and areasfurther west. It was carried eastwardby the prevailing westerly’s to the inland seasthat were present 100 million years ago. Commercial bentonite deposits are found between the Thermopolis and Pierre Formations. This representsa period of approximately 20 million years. Those deposits which fell into marine waters were preserved, while those which fell on land closer to the volcanic sourceswere lost. Alternating and succeedingdepositsof shale and sandstoneburied the volcanic ash under thousandsof feet of sediment. During the Laramide Revolution at the start of the Tertiary period, the volcanic sediments were slowly uplifted as the Rocky Mountains were formed. Progressive erosion over the next 20 million years exposed the volcanic ash along the flanks of the respective uplifts. The ash was then transformed into a clay by alteration processesand ion replacement. Outcroppings of bentonite can be observed in all areas of Wyoming where the Thermopolis, Mowry and Frontier Formations occur. These outcroppings are numerous 0169.1317/97/$ 17.00 Copyright PII SOl6~-l~l7~~6~O~~~~il-~
0 1997 Elsevier
Science
B.V. All rights reserved
330
TA. Thorson / Applied
Clay Science I I (19971329-335
as Wyoming has numerous uplifts. The two most significant are the Black Hills and the Big Horn Mountains. Less significant areas include those near Lander, WY and south of Casper, WY. 1.2. Commercial activity Wyoming bentonite was commercially developed in the late 1880s when it was discovered that the clay had properties valuable to the cosmetic industry. This use was quite small however and it was not until the 192Os, when higher grade deposits were discovered in the Black Hills, that a true industry was born. Steel foundries discovered that Wyoming bentonite imparted superior qualities to molding sands and they became a large consumer. In the 1930s when rotary oil well drilling was developed, the clay was used to develop the drilling muds which were essential in this process. During the early 1950s the iron ore industry identified bentonite as a superior binder for taconite concentrates which were pelletized as a replacement for direct shipments of iron ore. Bentonite began to be used in the 1970s in a variety of environmental applications. Those included slurry trenching, caps over landfills and liners under water based fluids. The latest use of bentonite involves the cat litter industry. This use is environmentally driven since less solid waste is created when bentonite is used as compared to the myriad of materials historically used as litter material.
Fig. 1. Field drying. Hot Wyoming summers allow the bentonite to be partially dried using solar energy. The clay is disked, plowed and then piled adjacent to pit. The dried clay is hauled to the processing plant. This mine is in the Thermopolis Formation.
T.A. Thorwn/Applied
Cluy Srienre
I1 (1997)
329-335
331
The industry currently produces approximately 2.5 million tons per year of finished product. The highest production came when oil drilling activity was at its peak in the early 1980s when shipments exceeded 4 million tons annually. 1.3. Mining methods Bentonite is mined using small surface mining equipment. ~verb~den depths of O-30 feet are removed from gently dipping beds with bull-dozers and motor scrapers. No operations use truck and shovel or draglines for overburden removal. The clay is exposed and is often field dried in the hot Wyoming summers to remove 10% of the inplace moisture (Fig. 1). Field drying is performed to reduce transportation costs and the cost of fuel when final processing is done. In situ moisture is usually between 25% and 35%. The clay is then moved to the processing plants by a variety of haulers depending upon the distance and type of road available. 1.4. Processing The clay is dried to a moisture of 7-9% in rotary dryers, milled in Raymond roller mills to 85% minus 200 mesh, or screened to a variety of sizes. The finished product is shipped in a dry crushed form for bulk export, in granular form for a variety of applications and in powdered form for oil field, iron ore and miscellaneous applications. The clay may be bagged in 50 or 100 pound bags, shipped in bulk hopper cars or in bulk bags (super sacks).
2. Aerial surveying Aerial surveying has been available for approximately 30 years since map making activities of the Federal Gove~ment became available for commercial use. This early photography was high altitude and without color. While useful in large scale applications, high altitude photography had little value with respect to mine plans and environmental baseline data. In 1978 a company decision was made to begin low altitude photography of all areas that had potential for exploration, were defined clay deposits or were active mine sites. The principle area to be aerial surveyed for the Black Hills Bentonite Company was near Kaycee, WY on the eastern flank of the Big Horn Mountains. This area consists of a distance of 35 miles north-south and 1 mile east-west. This was the extent of the land either owned or leased for bentonite. The photos were obtained by following the north-south strike of the beds at approximately l/2 mile intervals. Landmarks such as reservoirs or drainages were included in the photographs to aid in the identification of the legal subdivision of the area which had been photographed. By taking the photos in series and then overlapping the coverage it is usually possible to know what property is in the photo. Early in the process difficulty was encountered if landmarks were not visible. There are areas where little relief exists and aerial photos become more difficult to use, because identification of the area flown may be in doubt. The higher the plane flies, the more area is covered. It is advisable to fly the area at 2000 feet or more to obtain coverage that will be helpful
332
T.A. Thorson/Applied
Fig. 2. Clay Spur member in the Kaycee area.
of Mowry
Formations
Clay Science
is highly
visible
II (19971329-335
on right side of photo. This is the marker
bed
when low altitude photos are obtained. The low altitude photos can be matched with portions of the high altitude photos to assure proper location of the respective photos. The Kaycee area contains 5 different minable beds in the formation previously mentioned. The Clay Spur member of the Mowry formation (Fig. 2) is usually the best marker bed. This bentonite. normally crops out in barren shales as a bright yellow band. The beds in the Mowry (Figs. 3 and 4) and Thermopolis Formations are covered by heavy vegetation; however, at the outcrops, small bands of bluish shale are usually visible to identify the extent of the bed. The sequence of the beds are always predictable which allows positive identification of the bentonite versus other beds of shale or non-commercial beds of bentonite. Another area surveyed was located on the west slope of the Bighorn Mountains, near Ten Sleep, WY. This site is approximately 15 miles long and one mile wide on a north-south axis. The results of these surveys made it possible to begin developing detailed mine plans with respect to pit sites, overburden stockpile locations, topsoil stockpile locations and support site areas. These detailed mine plans have been developed without extensive field work, while also avoiding weather delays associated with field activities. All of this work was done with color photography which added details not known before. It is also possible to fly at lower altitudes to further enhance the information being gathered. Aerial photography became extremely useful when exploring areas where no company information was present or where new activities were to begin. The knowledge
T.A. Thorson/Applied
Clay Science II (1997)
329-335
333
334
T.A. Thorson /Applied
Clay Science I I (1997)
Fig. 4. Active mines are in the center of the photo. Land restoration mine. Access road is to haul bentonite to the processing plant.
329-335
has begun
on both sides of the active
developed by low altitude (1000-2000 ft) aerial photography makes it possible to develop predetermined patterns for drilling and the location of drill trails to be used on the surface. Aerial photography was also helpful in final surveying when land markings were difficult to locate. Flying was generally done in the midmorning when the air was calm and low level maneuvers could be done safely. It is advisable to avoid the shadows and unnatural light of the early morning. A single engine, high-wing aircraft was used which did not have a wing strut to obstruct the view. The camera used was a 35 mm with a wide angle lens and date pack. Aerial photography was used extensively to observe areas in southern Wyoming which had not previously been developed commercially. The terrain was quickly observed and determined to offer limited prospects for future development. The beds were steeply dipping and it would have been difficult to gain access due to rugged topography. Wide area bentonite exploration has generally been concluded since all producing outcrops have been located and prospected. Future aerial use will be primarily for
T-A. Thorson /Applied
Clay Science 11 (1997)
329-335
335
environmental considerations. Additional baseline data will be needed on an ongoing basis. It will also be useful in noting the progress of various areas that have been seeded and have been growing a vegetation cover. When it is necessary to obtain ground cover vegetation quality, aerial viewing can quickly identify areas that are successful or may be having problems. Wyoming environmental laws regarding mining began in 1969. The basic premise of the law is that the land should be restored to an equal or greater use. Restoration of premining contours is not a requirement; however, grading must be done to permit the reseeding of all sloping areas. If ponds of water are part of the reclamation plan these must be permitted. It is the practice of this company to develop through drainage in all areas milled to eliminate the development of water reservoirs. Landowners do request on occasion that water be retained and these requests are honored. Wyoming law requires that land restoration be complete within five years, after the land has been affected. This can be a problem where large multiple-cut mines occur; more than live years may elapse. Extensions of time from the state are then required. The reseeded is fenced and must remain under a mining bond for five years before the state can declare the restoration to be complete.
3. Conclusion Aerial photography is an aid in the exploration and development of bentonite deposits in Wyoming. The sparse vegetation allows a complete view of all of the outcropping formations, thus giving a total and complete view of the surface geology. Aerial surveys cannot replace on site drilling to determine depth and quality of the clay reserves but it can reduce the cost of these activities by programming the work to be done. It will have continuing application for environmental uses to document the progress of reclaimed lands and aid in the development of mine plans for newly developed sites.