In the Consolidated Virginia mill, the mortars—the huge iron boxes in which the stamps work—do not discharge the pulp or pulverized ore in front, as is usual, but at one side. This gives free access to the mortars in front for the purpose of putting in new shoes and dies. The “shoes” are the heavy blocks of iron or steel fastened to the lower end of the stamp. It is the shoes that fall upon and crush the ore when the stamp is dropped by the cam which raises it. The “dies” are much the same in shape and size as the shoes, and are fitted into the bottom of the mortar in such a position that one is exactly under the point where the shoe of each stamp strikes. Thus it is between the “shoes” and “dies” that the rock is pulverized.
FIRST QUARTZ MILL IN NEVADA.
QUARTZ-MILL—AMALGAMATING ROOM.
A small stream of water is constantly running into the battery among the ore, which water, being strongly churned and agitated takes up and floats all of the finer particles of ore. Across the face of the mortar, just in front of the dies, are the screens, made of the best Russian sheet-iron, punched full of small holes. Through these holes the water and the finely powdered ore pass into a sluice or trough running to the settling-tanks in the amalgamating-room, where the ore, now in the shape of fine sand, is deposited, to be finally shovelled out and placed in the amalgamating-pans. The finer the screens the smaller the quantity of ore that can be put through a battery in a given time.
The roar of Niagara is as a faint murmur compared with the deafening noise of sixty stamps, all in full operation. In the battery-room, and indeed throughout the mill, the noise is such that it is almost impossible to converse. Every word must be shouted into your ear at the top of the speaker’s voice, and in a tone that would be audible at the distance of a mile in the open air. There is little talking done in the battery-room; except when ladies visit the works; then you can see that their lips continue to move, and the presumption is that they are talking right straight along.
Just in front of the battery-room, but having its floor some feet lower, is the amalgamating or pan-room, 92×120 feet in size. Into this room comes the pulp as it runs from the batteries. The pans stand in two long lines, running east and west, and back of the lines of pans are the settling-tanks, while in front of them are ranged the “settlers,” a large kind of pan into which the pulp passes from the pans proper—the amalgamating-pans. On each side of the building, over the settling-tanks, are sluices bringing the pulp (mingled with water) from the batteries. Each sluice brings the pulp from thirty stamps, and supplies one row of settling-tanks—there being spouts leading from the sluice to each tank. There are seventeen of these settling-tanks, and when the pulp has settled in them till it is of the consistency of thick mortar, it is shovelled out upon a platform which runs alongside the row of amalgamating-pans. There are sixteen pans in each row—thirty-two in all—and each pan is five and one-half feet in diameter, and holds a charge of 3,000 pounds of this pulp.
In the bottom of the pans are thick plates of cast-iron called “dies,” while revolving upon these are the mullers, which are furnished with other thick plates of iron called “shoes.” It amounts to much the same thing as the shoes and dies in the batteries, except that in the latter the ore is pulverized by percussion, while in the pans it is done by a rotary motion—by grinding.
When the charge of pulp has been shovelled into an amalgamating-pan, a certain quantity of water is added to thin it to the proper consistency for working, when the mullers are set in motion, and the work of grinding the ore in the pan begins. The pans have covers and double bottoms, and when they are at work, steam is not only let into the pulp, but also underneath, between the two bottoms.