BLOCK 14. The first plant was erected at Broken Hill, on the Broken Hill Proprietary Block 14 company's mine, in 1903, to treat middling from the lead-concentrator. Aside from the small amount of zinc concentrate produced by the Sulphide Corporation by magnetic concentration, this marks the beginning of the Broken Hill zinc industry. The first machines installed were of the Goyder & Laughton type, which were of complicated design and low capacity. In 1904 the Delprat pan (Figs. 23 and 25) was introduced instead. After 1905 this plant was shut down owing to lack of material for treatment. Fig. 25A is a flowsheet of this plant.
PROPRIETARY. Concurrently with the above plant, in 1903, the Broken Hill Proprietary installed the Delprat process, the inventor G. D. Delprat being the general manager of the mine. This plant in 1904 was treating 3,500 tons per week, which was increased to 5,500 tons in 1905. During 1906 the plant treated 235,000 tons, and a system was installed whereby the material from the dumps was first sent to tables to recover some lead, deslimed to provide material for sintering, and then re-ground for the flotation process. Litigation had begun between Potter and Delprat, but was settled in 1907. By the end of 1907 this plant had produced 180,000 tons of zinc concentrate. The plant worked steadily during 1908, and produced 65,000 tons of concentrate. For five months of 1909 it was idle because of the strike, but in the remaining time produced 52,000 tons of concentrate. In 1910 the production was 70,000 tons, and in 1911 92,000 tons. The total production has been 459,000 tons of concentrate from over 2,000,000 tons of tailing treated.
Figs. 26 and 27 are photographs which give some idea of the magnitude of the operations. The concentrate assayed nearly 46% zinc, 8% lead, and I3oz. silver per long ton. During the first half of 1910 the plant was re-modelled at a cost of 8,000 by the introduction of cast-iron flotation-boxes, presumably of the same design and principle as those shown in Figs. 23 and 25, and by the introduction of conveyors from the heaps and steamshovel excavators.
For several years it was not possible to treat slime by this method, but an ingenious idea of E. J. Horwood has solved the difficulty. He found that as the slime contained a large amount of finely ground calcite, the carbon dioxide gas was generated too rapidly, and the bubbles grew too fast to effectively attach themselves to the sulphides. He therefore introduced a centrifugal pump between each two of a series of separating boxes for the purpose of mechanically breaking the bubbles to small size. This violent agitation also, no doubt, assisted in coagulating the slimed sulphides ; this, together with the breaking up of the bubbles, enabled the frothing to proceed on this material as easily and perfectly as upon any other class. A plant is now in operation which produces about 1,000 tons per month of concentrate from material 90% of which will pass a 200-mesh screen.
ZINC CORPORATION. In 1905 this company began its operations by an installation of the Potter process on the British mine, where they had purchased a large dump of tailing and middling. This plant was intended to treat 2,000 tons per week. The plant ran intermittently through 1906, with many alterations, and finally the process was abandoned.
GILLIES. The Gillies company purchased a large dump on the Block 10 mine, and erected a plant in 1906 with an estimated capacity of 2,000 tons per week. In 1907 this plant produced 7,700 tons of concentrate during the periods when it was being altered, but finally the Potter process was abandoned, and after a short trial of the Minerals Separation process the plant was dismantled and the tailing sold.