At the Battery

Korero (AEWS), Volume 2, Issue 8, 24 April 1944, Page 20

At the Battery

You see very little gold in the white quartz. Occasionally there is a rich patch in which the yellow glint of the

metal can be picked up, but normally it cannot be seen by the naked eye. Seventy per cent, of the' gold in the quartz is free gold ; the other 30 per cent, is in the form of arsenical pyrites-black streaks visible in the white surface of the quartz.

When the trucks are brought to the surface they are unloaded into a huge hopper from the base of which a chute feeds the quartz and mullock on to a conveyer belt. The white and grey chunks are deposited into another hopper, where they are roughly broken to about 2 in. size and sent on to a bin holding 600 tons of spoil.

The quartz is next fed into a gigantic cylinder 6 ft. in diameter lined with manganese steel and revolving with a noise that sounds like all hell let loose. The reasons for the uproar are several hundred io lb. balls of manganese steel rolling freely inside the mill and crushing to a powder the quartz and mullock. From this mill the crushed ore passes over a screen, where water turns it to a thin, grey mud. The mud is then pumped up to platforms above the crushers and run over a dozen or so tables called “ strakes ” covered with mats on to which the heavy free gold falls. These mats are changed every two hours and washed in a tub from which the fine gold is collected and amalgamated with mercury in a revolving barrel. But the grey mud still contains the arsenical pyrites and some free gold so

it is passed over a large treadle machine, called a classifier, which, with a gentle paddle motion, separates the fine mud from the coarser lumps. These are recrushed in a mill containing smaller balls and sent through the strakes and classifier once more' Only when the crushed quartz has attained the consistency of a fine face-powder will the classifier allow it to pass on to the next process.

1 his is called the flotation process, and here the chemical side of the goldextraction begins. Pine oil, cresylic acid, and xanthates have been added to the grey sludge in the “ Ball Mill,” and now the combination is mixed in flotation cells by a cylinder of rubber rods revolving at speed. Bubbles form and are strengthened by the chemicals, and to these bubbles the concentrates adhere. Amongst these concentrates are the goldbearing pyrites. The mixture passes through six of these cells, and by the time the last has been reached almost all the concentrates have been floated off on the bubbles. The waste is allowed to escape. The bubbles are collected on two slowlyrevolving vacuum plates and deposit their concentrates, which are scraped off and slowly dried to extract the water. The resultant grey powder is roasted in a huge furnace, driving off the arsenic and sulphur and leaving a red oxide containing iron and gold. To this is added a o-i per cent, solution of potassium cyanide, and the red liquid is stirred in huge agitating vats' for eight days to dissolve the gold. Then the red insoluble iron oxide is extracted by a filter. The gold - bearing solution passes through a clarifier and a vacuum pump to extract the air. Then zinc-dust is added, and in precipitating bags the zinc and gold is collected. The addition of a little acid dissolves the zinc and any copper. Now the amalgam from the barrel and the sludge from the chemical process are mixed with soda and fluxes and retorted. The mercury evaporates, the flux forms a slag, and at long last a shining cone of solid gold appears. Right from the time the quartz was mined not a glimmer of gold has been seen until this last step in all the complicated process.