Cut and Fill mining is a method of short hole mining used in narrow ore zones. An access ramp is driven off the main level to the bottom of the ore zone to be accessed. Using development mining techniques a drift is driven through the ore to the defined limit of mining. Upon completion the drift (or "cut") is filled back to the access ramp with the defined type of backfill, which may be either consolidated or unconsolidated. Another drift is driven on top of filled cut. This process continues until the top of the stope is reached.
Drift and Fill is similar to cut and fill, except it is used in ore zones which are wider than the method of drifting will allow to be mined. In this case the first drift is developed in the ore, is backfilled using consolidated fill. The second drift is driven adjacent to the first drift. This carries on until the ore zone is mined out to its full width, at which time the second cut is started atop of the first cut.
Room & Pillar mining is commonly done in flat or gently dipping bedded ore bodies. Pillars are left in place in a regular pattern while the rooms are mined out. In many room and pillar mines, the pillars are taken out starting at the farthest point from the stope access, allowing the roof to collapse and fill in the stope. This allows a greater recovery as less ore is left behind in pillars.
Block Caving is used to effect with large sized orebodies which are typically composed of low-grade, friable ore. The method works best with cylindrical, vertical orebodies. Pre-production mining development work consists of driving accesses underneath the orebody. This includes the formation of "drawbells" by undercutting and blasting. Initially, blasted ore is removed via the extraction level underneath the drawbells until a sufficient area of unsupported ore is formed that the orebody begins to fracture and cave on its own. The eventual aim of the block caving method is that the friable ore needs no blasting and continues to fracture and break up on its own, flowing down the drawbells to the extraction level, where it is removed from the ore chute mouths with loaders and sent off for processing. Eventually the fracturing will propagate to the surface, resulting in subsidence. One of the main hazards associated with block-caving is that fracturing can potentially stop before it reaches the surface unbeknownst to the people in control of the mine. If fracturing stops propagating upwards and extraction continues, a large void can be formed, resulting in the potential for a sudden and massive collapse and catastrophic windblast throughout the mine.
The underground iron mines in Minnesota were shaft mines as opposed to drift mines. Shaft mining refers to the method of excavating a vertical or near-vertical tunnel from the top down, where there is initially no access to the bottom. When the top of the excavation is at the surface, also known as "at ground", it is referred to as a shaft, when the top of the excavation is underground it is called a winze.
Underground Mining Methods
On the surface above the shaft stands a building known as the headframe (also winding tower, or pit head). Depending on the type of hoist used the top of the headframe will either house a hoist motor or a sheave wheel with the hoist engine mounted in the. adjacent engine or winding house. The headframe will also contain bins for storing ore being transferred to the processing facility. If the shaft is used for mine ventilaton a plenum or casing is incorporated into the headframe to ensure the proper flow of air into and out of the mine.
Head frame & engine house of the Mckinley Mine, McKinley, Mesabi Range, St. Louis Co, MN
A mine shaft is generally split into multiple compartments. The largest compartment is used for the cage, a conveyance used for moving workers and supplies below the surface. It functions in a similar manner to an elevator. The second compartment is the skip, used to transport ore to the surface. Smaller mining operations use a skip mounted underneath the cage, rather than a separate device. The third compartment is used for an emergency exit; it may house an auxiliary cage or a system of ladders. An additional compartment houses mine services such as high voltage cables and pipes for transfer of water, compressed air or diesel fuel.
The mine shaft is used to access an underground mining facility. Horizontal workings off the shaft are called drifts, galleries or levels. These extend from the central shaft towards the ore body. The point of contact between these levels and the shaft itself is known as the inset or shaft station.
Main Station, Fayal Mine, Eveleth, Mesabi Range, St. Louis Co, MN
Miners and loaded ore car underground - Fayal Mine
Miners underground in unknown Minnesota iron mine
Miners lighting blasting fuse - Godfrey Mine, Chisholm, Mesabi Range, St. Louis Co, MN
Loading an ore car in an unknown Minnesota iron mine
Underground in an unknown Mesabi Range mine
Underground in an unknown Virginia, Minnesota iron mine.
Notice the dynamite cases on the flat car to the left.