The following description of the operation of the Rutherford mines is typical of all the workings in the vicinity.
The Rutherford tunnel is 6 feet high and 600 feet long. The gangways are driven along the foot-wall of the cement side, 6 feet high, and are heavily timbered and lagged at the top and on the clay side. The sets of timbers are 3½ feet apart, and usually of 9-inch timber. The width at the top is 3½ feet, with a spread of 5 feet at the bottom, the extra width being cut from the clay. Where the cement-rock is firm, the collar is hitched 6 inches into it and supported by a leg on the clay side. The cost of the timber is 54 cents (2s. 3d.) per set, including the lagging. The monkey gangway, which carries the air along the top of the breast from the air-shaft, is 2½ feet high, 1½ feet wide at the top, with a spread of 2½ feet at the bottom. Wooden rails with a gauge of 18 inches are spiked to the cross-ties.
The gangway is not driven continuously, but after being driven about 55 feet on either side of the shaft, the breasts are started 25 feet from the shaft, a pillar being left to protect it. The breast is then opened up to the face of the gangway, and when one ore-breast is worked out, the gangway is driven ahead about 30 feet, and a new breast is opened and worked out before commencing a third. The air-hole is first driven to the surface, then the breast is opened to its full width of 6 feet. The thickness of the bed of ore here varies from 4 to 6 feet, depending upon the thickness of the partings of clay and slate. The clay and slate are left on the bottom, which is made sloping to allow the ore to roll down to the shute; this is 6 feet wide and 4 feet long and heavily timbered. Small props or sprags are hitched into the cement, and wedged with a lid on the clay side to prevent falls of rock.
The holes are drilled by hand in the clay-partings. They vary in depth from 1 to 4 feet, and the charge of dynamite is varied correspondingly, according to the amount of ore it is desired to throw down. The loose ore is wedged down with crowbars and picks, and is then freed from any adhering clay and thrown down the shute. It is there loaded into boxes holding about half a ton each, which are pushed to the shaft on a truck. The ore-boxes have four rings at the corners, to which are attached four chains, suspended from the wire hoisting-rope. At the top of the shaft the boxes are detached and placed on a truck, which is run to the dump. Thirty cars, averaging 15 tons, are extracted in a day of two shifts, the day-shift working nine hours and the night-shift eleven. The pay of the miners is 5s. per shift. The cost of mining the ore averages 7s. per ton.
The ore, as it comes from the mines, is free from refuse, great care having been taken to separate slate and clay from it in the working places. It is hauled in 2-ton wagons to kilns, which are situated on a hill-side for convenience in charging. The platform upon which the ore is dumped is built from the top of the kiln to the side of the hill. The ore is first spalled to fist-size and freed from slate, and is then carried in buggies to the charging-hole of the kiln.
The slate, when burned, has a light yellowish colour, which would change the colour of the product. [Figs. 30 to 32] represent a front elevation of the kiln and two sections at right angles to each other. The kiln is 22 feet high and 16 feet square on the outside. The interior is cylindrical, 5 feet in diameter, with a fire-brick lining a of the best quality. The interior lining slopes from the fire-place b to the door c, by which the charges are withdrawn; this facilitates the removal of the calcined ore. The casing d is of sandstone, 5½ feet thick, and tied together with the best white-oak timber e. When charged, a kiln holds 16 tons of ore, and the kiln is kept constantly full. The heat passes from the fire-places b—of which there are two, placed diametrically opposite each other—through a checker-work f of brick into the centre of the charge. The charge enters at g and is withdrawn by a door c in the front wall, 2 feet long and 18 inches high. The ashpit is at i. The fire is kept at a cherry-red heat, and about one cord of wood is burned every twenty-four hours.
The kiln works continuously, calcined ore being withdrawn and fresh charges made without interruption. The ore is subjected for forty-eight hours to the heat, which expels the moisture, sulphur and carbon-dioxide. About 1½ tons of calcined ore are withdrawn every three hours during the day. The outside of the lumps of calcined ore has a light brown colour, while the interior shows upon fracture a darker brown. Great care is necessary to regulate the heat
Figs. 30, 31, 32.—Rutherford and Barclay Kiln.