The mine extracts thermal coal from the Anderson-Dietz Seam, which averages approximately 80 feet in thickness.

Geology
Strata exposed at the Spring Creek Mine belong to the Tongue River Member of the Fort Union Formation of Paleocene age. The uppermost stratum consists of reddish, clinkered sediments overlying the burned 7 to 15 foot thick Smith coal seam which caps portions of the Central Bluffs and higher topographic areas of the site. The bluffs directly south of the South Fork Spring Creek either have outcrops of the Smith seam or show clinker resulting from Smith seam burn, depending on location. [02/05/2016 Spring Creek Coal conservation plan, p.1]

The 80-foot Anderson-Dietz (A/D) seam is the only presently economic coal seam at SCM. Within the Pits 1, 2 and 3 portions of the mine permit area the A/D seam lies approximately 140 feet below the Smith seam. Within Pit 4 the A/D seam lies approximately 220 feet below the Smith seam. Clinker zones are evident along the outcrop of the Smith seam within the Pit 4 area where natural burning of Smith coal has occurred. A bedrock clinker and partial burn zone for the A/D seam exists near the northeastern and eastern boundaries of the Pit 4 area. Rock units between the Smith and A/D coal seams consist principally of interbeds of gray to dark gray shale/claystone, gray to yellowish gray sandstone and siltstone, and carbonaceous shale. With the exception of the coal seams, the lithologic units are typically lenticular with limited areal extent and change character over short distances. [02/05/2016 Spring Creek Coal conservation plan, p.1]

Two coal seams (Roland and Smith) lie above the Anderson/Dietz (A/D) seam but are limited to areas of higher topography. The upper most seam, the Roland, is very discontinuous and largely oxidized due to its position in the stratigraphy. Where it is present, the seam is thin with ash banding. No quality has been obtained for the Roland. Due to overall thickness and very limited areas where it is found in the current leases, it is not an economic resource. The Smith seam, though a bit lower in the stratigraphic column is also discontinuous and largely oxidized. The Smith seam is not an economically recoverable resource. [02/05/2016 Spring Creek Coal conservation plan, p.2]

There are also three other coal seams (Canyon, Wall, and Carney) below the Anderson/Dietz (A/D) seam. These coal seams are considered to be uneconomical for mining due to their high stripping ratios. [02/05/2016 Spring Creek Coal conservation plan, p.2]

The Spring Creek Mine is located in Montana approximately 20 miles north of Sheridan, Wyoming. The mine extracts thermal coal from the Anderson-Dietz Seam, which averages approximately 80 feet in thickness. The location of the mine relative to the Great Lakes is attractive to our customers in the northeast because of lower transportation costs.

Overburden is removed by a combination of dragline, cast blast, dozer, and truck/shovel methods. Coal is removed by truck and shovel type systems.

Coal Removal
Spring Creek Mine mines coal from a seam averaging 80 feet thick. The coal is blasted using ammonium nitrate and fuel oil explosives and methods similar to what is used for the overburden. The coal is then loaded with shovels and front-end loaders into mining haul trucks. The coal is transported to the primary crusher at the truck dump or to the in-pit crusher for overland conveying. Mining frequently occurs simultaneously at multiple locations across the mine to blend the coal and create a marketable product to meet various customer specifications.

Overburden Replacement
Overburden is placed as backfill in the mined-out pits with a dragline and by cast blasting from the adjacent pit area to be mined, according to ARM 17.24.501 and the General Backfilling and Grading Section of SCM’s approved permit. SCM has estimated up to 35 percent of the overburden volume in some areas can be moved by cast blasting. Overburden can also be transported by truck and placed on backfilled areas to achieve the designed topography.

The coal is transported to the primary crusher at the truck dump or to the in-pit crusher for overland conveying.

The coal from mine is crushed and shipped directly from mine to the customer. [2017, Form 10-K, p.133]