The Anderson-Canyon coal zone, Decker coal field, northern Powder River Basin, Montana: Considerations for future strippable coal resource development

Conference · Thu Dec 31 04:00:00 EST 1998

OSTI ID:349235

Roberts, S; Gunther, G; Taber, T; Ochs, A; Blake, D; Bader, L ^[1]; Wilde, E ^[2]

---

1. Geological Survey, Denver, CO (United States)
2. Montana Bureau of Mines and Geology, Butte, MT (United States)

In 1994, the US Geological Survey (USGS), in coordination with State Geological Surveys and other Federal Agencies, undertook the task of assessing the Nation`s coal resources and initiated a five year National Coal Resource Assessment (NCRA) project to identify the quality, quantity, and distribution of the Nation`s primary sources of coal, including those deposits currently in production or deemed as potential for production in the next few decades. Within this project framework, the Decker coal field in the Northern Rocky Mountains and Northern Great Plains region was designated a priority area for resource assessment in the northern Powder River Basin of Montana. To better evaluate the future potential for surface mine production of coal beds or zones within the Decker coal field in areas not currently under lease, a series of interpretive maps (e.g. isopach and structure contour maps, etc.) were constructed for (1) the Anderson-Canyon coal zone, (2) the Anderson-Dietz coal subzone, inclusive of the Anderson, Dietz 2, and Dietz 3 coal beds and locally, the Kirby bed, (3) the Anderson coal bed in areas where it has not merged with one or more Dietz beds, and (4) the Canyon coal bed. Cumulative, net coal thickness maps for both the Anderson-Canyon zone and Anderson-Dietz subzone indicate that the thickest total coal accumulation in each of these zones occurs in the western and southwestern parts of the coal field, where total net coal thickness values can exceed 100 feet in the Anderson-Canyon zone and 80 feet in the Anderson-Dietz subzone. By comparison, more areally extensive accumulations of relatively thick coal (30--35 feet thick) in the Anderson and Canyon beds are generally found in the central part of the coal field. Future surface mine production of coal resources in the Anderson-Canyon zone will be influenced, in part, by the variable thickness of the coals resulting from the merging and splitting of the beds, as well as overburden thickness throughout much of the coal field. Isopach and overburden maps suggest that better prospects for future strippable resource production within the coal field may be represented by (1) the Anderson-Dietz coal subzone, in the area where the Anderson, Dietz 2 and Dietz 3 beds have merged to a single bed, and to a lesser degree, (2) the Anderson and Canyon coal beds, which are pervasive throughout the coal field. However, although the merged Anderson and Dietz 2 and 3 coal deposit exceeds 80 feet in thickness, calculated stripping ratios (overburden thickness divided by the net coal thickness) within the area of the merged beds are estimated to range from less than 1:1 to greater than 5:1, with the majority of the area comprising stripping ratios of greater than 3:1. Additionally, overburden thickness in areas of thicker coal (30--35 feet thick) associated with either the Anderson or Canyon coal beds can range from 100 feet to nearly 500 feet, with corresponding stripping ratios on the order of 3:1 to well in excess of 10:1. Although coal thickness and overburden are not the only criteria for determining coal resource development potential, these considerations are important and will need to be addressed in order to successfully develop new resource areas of the Anderson-Canyon coal zone in the future.

• OSTI ID: 349235
• Report Number(s): CONF-980985--; ISBN 1-890977-15-2
• Country of Publication: United States
• Language: English

Related Subjects

01 COAL, LIGNITE, AND PEAT
COAL DEPOSITS
COAL RANK
COAL SEAMS
MAPS
POWDER RIVER BASIN
RESOURCE ASSESSMENT
RESOURCE POTENTIAL
SURFACE MINING
THICKNESS