MINING NEWS.

Alexandra Herald and Central Otago Gazette, Issue 371, 18 June 1903, Page 5

MINING NEWS.

The Davis Bend Co.'s No 2 dredge (late Old Dunstan) commenced dredging on Wednesday of last week, near the upper oml of the Ciirnrauir claim. Tho No 2 dredge is at preacnt, for the purpose of some necessaiy repairs effected. We clippie folk fling from the "Cromwell Argus'".—The grabs for the Rising Sun are being made ; the extra buckets are on the road, and the elevator will be quite finished and on the road this week.—The Electric I has got on to good gold on a blue clay bottom on which the big returns are generally got. Once fairly going into this kind of country the dredge may be expected to uphold its old prestige.— The Junction 1 had some trouble last week with a crack in oie of the gantry posts necessitating a strengthening of , it. The bottom worked upon is partly coaL The gold is coarse. Her returns are improving. '

In an article on gold dredging in New Zealand byC Edward Turner, which appears in the February number of the " New Zealand Mines Record," the writer says there is ample room for improvement in the gold-saving appliances on dredges. The wear and tear on screens is enormous; on a steadyrunning machine from six to twelve months is about the length of Ufa Efforts are being made to relegate them to the background and to introduce shaking-tables, or even to make the elevator do the screening as well as the elevating. In proportion to the amount and weight of matter in motion the screening area of the revolving screen is very small. When there are 16ft of perforations in a sft diameter screen there might be 28 square feet actually screening, whereas a shakingtlble screen of similar length and only 30in wide would give 40 square feet screening, besides depositing the fine gravel more evenly over the matting on the screen-table. Much of the fine gold is not able to reach the matting after leaving the revolving screen, because the fines are deposited all on one side of the table. It is comparatively easy to lift a large quantity of wash and to elevate it after screening; but it is by no means so easy to separate and save a reasonable percentage of gold. It is an acknowledged fact among gold dredging men that the design of the gold-saving apparatus is not all that can be desired. A plant that will save 90 to 98 per cent in one place, if removed to a place a mile away might re-deposit 50 per cent of the gold contents among the tailings. The dredgemaster, therefore, has to be constantly on the alert in order to adjust his apparatus to any changing conditions which may present themselves. With heavy, shotty gold the tables are often narrow—24in or less—and with the maximum pitch. This gives a minimum of space for a maximum of wash treated. But the practice is reprehensible, as fine light gold often accompanies the heavier sample, and must necessarily be carried overboard. In the best-observed practice the tables were so pitched that the particles of leavy black sand accompanying the gold were just kept moving in as small depth of water as would carry away the fine gravel of the wash.