The best way to address the differences in mining techniques used at the Scrub Oaks and Washington Mines is to quote the aforementioned Alan Wood Steel publication. Here is the entire text from the "Mining Division" section:
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MINING DIVISION
Iron ore is one of the basic raw materials necessary in the manufacture of iron and steel. Alan Wood Steel Company derives nearly 60 per cent of its present ore supply from its own mines at Scrub Oaks, Dover, N.J. and Washington, Oxford, N.J. The mines have been operated by Alan Wood since 1929.
Most iron ore minerals are oxides, such as hematite, limonite, and magnetite. The latter is being mined at Scrub Oaks, considered to be the largest known magnetite iron ore body in the State of New Jersey.
The Scrub Oaks Mine has a 3,200-foot shaft which penetrates the Earth at an angle of 55 degrees and levels extending out at 300-foot intervals. It has already been mined out down to the fifth level and active mining is now taking place on the 5th, 6th, 7th, and 8th levels. Development work has been started on the 9th and 10th levels.
On each level, a main drift or tunnel is run from the shaft to the ore body, and from this drift, raises or shafts are run to the level above. About 30 feet above the main level there is a sub-level, which is called the grizzly sub. The sub-level, runs along the footwall of the ore, and is kept about 75 feet in advance of the haulage drift. From the grizzly subs, 300-foot-long shrinkage stopes are started with chutes located at 60-foot intervals. The ore body in each stope is undercut with stoper drills and pulled down into the grizzlies.
Development work for shrinkage stoping includes a haulage level, driven into the footwall about 10 feet from the ore, and grizzly raises at 40-foot intervals. Stope preparatory work consists of a sub-level, 30 feet above the haulage level, driven in the ore at the footwall, short crosscuts from sub-level to grizzly chambers cut out over the tops of the chute raises, and, from each grizzly chamber, two draw raises put up to the ore. In beginning a stope, these draw raises are belled out and widened until they meet, and the ore is completely undercut. Then mining progresses by taking down successive slices from the back of the stope, drawing off only sufficient broken ore to leave convenient room for the miners.
The grizzlies, which are level, consist of heavy steel billets, six by eight inches, laid over a raise and firmly locked in place. The bars are spaced 20 inches apart to allow much of the ore to fall through as it comes from the stope. Chunks too large to go through the grizzly are broken up by hammer or blasting by the grizzlymen. The ore slips through the grizzlies into the chutes.
Chutes are of steel-lined timber construction, with undercut arc gates worked by double acting air cylinders. Cars are loaded in a minimum of time, and with little dangers of spills. The chutes are 4-foot, 6-inches wide and about 3-feet, 6-inches high in the clear.
Trolley locomotives haul the ore to the shaft in trains. The ore is crushed before hoisting. At the shaft, the car dumps automatically into pockets above the crushers. The crushers, in turn, discharge into pockets directly over the shaft, from which it is automatically loaded into the skip car and hauled to the surface.
In the mill, the ore is crushed and barren material cobbed out by running the ore over magnetic pulleys. Because the ore contains some martite, which is non-magnetic, a gravity system of concentration is also used. The crushing process is continued until the ore is reduced to fragments of abort one-eighth inch diameter. It is then processed through magnetic separators, jigs, and tables. The waste tailings are conveyed to the sand piles; the concentrates go by conveyor belt into railroad cars, ready for shipment to the Blast Furnace.
A part of the concentrates at Scrub Oaks are processed on tables and a high-grade concentrate is made for special purposes. Some of the high-grade concentrates are dried and shipped to our iron powder plant for further treatment. The remainder of the high-grade concentrate is shipped directly to customers.
The Washington Mine at Oxford, N.J., consists of two ore bodies. Washington No. 1, ore body is an old working, which pinched out at about the 15th level. Near it is located the Washington No. 2 ore body, which is now being worked. It is reached from the 15th level of the old shaft, which has been sunk to a depth of approximately 1,500 feet at an angle of 69 degrees.
A different method of mining is employed here than is used at the Scrub Oaks Mine. The system is called “long hole drilling”. Instead of blasting the ore down from the back of the stopes, holes up to 60 feet long are drilled in a ring pattern, radiating from a tunnel which has been driven above and parallel to the drift level. These rings of drill holes cut off slices of ore 6 feet thick, 30 feet wide, and 60 feet long.
These huge blocks are then broken up and pulled through the grizzlies into chutes below where the ore is loaded into skips and hoisted to an ore pocket on the 15th level. It is dropped into a jaw crusher below this pocket which reduces the ore size to six inches diameter or less.
A conveyor belt then takes the ore to the main shaft of old No. 1 ore body, where it is hoisted in four-ton skips to the mill where all concentration of this relatively high-grade ore is done magnetically. The ore is easily crushed and concentrated, resulting in a simplified and economical operation.
In addition to ore mined, a large tonnage of by-products such as sand, stone and grit for chickens and turkeys are produced and sold by the Sand and Stone Division.
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I hope that this sheds some light on the techniques used at these mines. Similar methods were employed at Mount Hope and elsewhere.
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