The illustrations, designs, which are described in this issue show the general design and give a fair idea of the machinery required in the best known modern methods of ore treatment. They were designed and fitted out by the F. M. Davis Iron Works Co. of Denver, Colo., and are selected for illustration merely as being fairly typical mills of their kind.
In the 100 ton chlorination mill of The Colorado Ore Reduction Co., Arequa, Colo., the ore is first passed through their private sampling mill where it is crushed to 0.25-inch, sampled and bedded in storage bins.
From these bins the ore is drawn into cars and trammed to the automatic feeders of the revolving dryers. After passing through the dryers the ore falls into the boot of an elevator and is elevated to the sizing screens. The over-size from the screens falls into the feeder hoppers of the fine crushing rolls is fed through the rolls and again elevated to the screens. The ore passing through the screens is conveyed to the finished pulp bins.
From these bins the pulp is drawn into the automatic feeders of a Ropp Roasting Furnace. The ore after being roasted falls into a water jacketed conveyor where it is cooled and conveyed to an elevator which raises it to the storage bins, whence it is drawn into the charging hoppers directly over the barrels.
The Chlorination barrels are cylindrical sheet steel vessels, arranged to be revolved on trunnions. They are lined with sheet lead and provided with an internal filtering diaphragm to separate the gold chloride solution from the pulp after leaching.
The roasted ore is charged into the barrel with sufficient water to make a liquid pulp and the required amount of lime and sulphuric acid added. The barrel is then closed tightly and slowly revolved, thoroughly mixing the whole mass. In from three to six hours the barrel is stopped and the gold chloride solution is drawn off through the filter into lead lined tanks; the filtering being assisted by air or water pressure.
Sulphur dioxide and then hydrogen sulphide gas is passed through the solution, precipitating the gold. The liquor is passed through a filler press, and the gold slimes are finally collected in what is called a sulphide cake, which is dried, roasted and the residue, mixed with suitable fluxes, is melted down into almost pure gold.