W. R. Henkle, R. E. Hague, R. Zimmerman
Coal mining was started at the Navajo mine in 1964. Exploration and related activities started in the mid 1950s. Single-seam strip mining is practiced in the northern areas of the lease. Multiple-seam operations are mining two seams in the southern part of Block 2. As mining operations proceed south, additional seams appear both in the subsurface and in outcrop. Blocks 3, 4, 5 contain as many as 10 minable coal seams. Multiple-seam mining operations are scheduled for this part of the lease.
Subsurface correlations, geologic mapping, and seam-outcrop mapping of Blocks 3, 4, 5 have shown that pinchouts and mergers of coal seams are common in the Fruitland Formation. Major pinchouts are on the flanks of stratigraphic rises in the Pictured Cliffs Sandstone. Minor pinchouts are in nondepositional areas which were present in the coal swamps. These nondepositional areas generally are unrelated stratigraphically to the underlying Pictured Cliffs Sandstone.
The lower Fruitland Formation intertongues with the Pictured Cliffs Sandstone. Thick sandstone units are common above minable coal zones. This occasionally results in exploration holes being too shallow and missing underlying seams. Cutouts by sandstone units also cause confusion in correlation of coal zones. Field mapping has helped to define the lower limits of coal deposition.
AAPG Search and Discovery Article #90979©1975 AAPG – SEPM Rocky Mountain Sections Annual Meeting, Albuquerque, New Mexico