The Navajo Mine - dragline operation with 2 draglines.
Dragline stripping is the primary mining method used for multiple seam mining operations at the Navajo Mine. The typical sequence for multiple seam mining is as follows:
1. Vegetation and topdressing removal;
2. Overburden drilling and blasting;
3. Overburden removal;
4. Coal drilling and blasting;
5. Coal removal;
6. Interburden drilling and blasting;
7. Interburden removal;
8. Repeat steps 5 through 7 for each minable seam.
The coal seams at the Navajo Mine are exposed in pits that range in width depending on the size of the dragline equipment that is being used to expose them. Pit depths range from 5 to 240 feet, and pit lengths range from 1,000 to 15,000 feet.
Overburden Drilling and Blasting
After all suitable topdressing material is removed, rotary drills are used to drill overburden blast holes. Blast-hole diameters range from 5 to 10 5/8 inches. Blast holes typically are drilled to the top of the coal seam that is being uncovered (until coal is encountered) and then backfilled with 1 to 10 feet of drill-hole cuttings to prevent coal shattering and any accompanying coal loss during blasting. However, some holes may be drilled to a specified elevation of 3 to 7 feet above the coal seam and not backfilled to reduce coal loss due to the movement of the overburden over the coal seam.
Once a set of blast holes has been dr ........
