MINING GOLD

Note: this page is based on the "Browns of Kyeburn Peninsula" by Wally Brown to whom many thanks and added to by myself

Panning

Gold panning is the technique of sorting gold from soil or gravel by weight, gold being heavier than the rest of the material being panned. Wide, shallow pans are filled with sand and gravel that may contain gold. Water is added and the pans are shaken, swirling the water round and allowing it to carry the lighter material over the side of the pan. Gradually only the heavier bits are left, and by skilled manipulation all but the gold is disposed of.
The gravel is usually removed from streambeds, often at a bend in the stream, where the weight of gold causes it to settle out of the water flow. This type of gold found in streams or dry streams are called placer deposits. Alternatively gold-rich (auriferous) gravel may be dug from the ground away from streams and rivers and treated in the same way.
This is most likely to have been the first type of mining undertaken by Moses when he arrived

Hydraulic mining

Hydraulic mining is a type of placer mining used in areas where large amounts of loose gravel and sand or soil are poorly packed and may be washed away with a heavy stream of water. Water cannons are sometimes used to strip away entire hills of loose gravel, which are then run through a sluice box (a wooden trough with ripples). Gold, being heavier, does not move as easily as other material in the sluice.

This is the type of mining which Moses and John introduced to Otago.

Their method was to construct a reservoir at higher level than the area to be sluiced and to pipe the water to the site, using the pressure generated by the weight of water and the fall of over 90 metres from the reservoir. The reservoir was kept topped up by "races" - channels which, like levadas in Madeira, follow the countours at a slight fall and collect springs and small streams on the way. They constructed several of these the longest of which was over 14 mile from the Little Kye Burn to the reservoir, near to Moses' house. Problems used to arise when the tailings from other miner's sites blocked to entrance from the river into the race.

Giant nozzles (known as "directors") made of cast iron and steel with swivel joints for pointing in any direction had to be securely fastened to the ground to prevent the directors from bucking and breaking away from the pipe - they were tipped with brass nozzles from 3" to 4" . The 4" nozzle was known as "Big George" and was said to have enough power to blow a motor car down the road.

One of the favourite tricks when they had a newcomer to the claim was to give him a mug and ask him to fill it from the sluicing nozzle. The water would rip the mug out of their hand!

With the director , fed from the dam by pipes between 8" and a foot in diameter they shifted many hundreds of cubic yards of clay and topsoil to get to the hardpan of old river beds where the paydirt could be found. And in later years they rigged a pelton wheel made of kerosene tins fed by a half inch hose to drive a winch arrangement whic automatically drove the nozzle through a gradual arc. This reduced the number of men needed for the sluicing.

A lot of the ground they worked was too low to allow a natural fall to the sluice box, so they had to use an elevator to lift their tailings. Lining the sluice box some 4 or 5 metres below the top of the elevator were chutes for stones, made of steel, drilled with various size holes and sitting on top of coconut matting which collected the finer particles. The water then travelled into an outlet channel known as a "tail race" and into the nearest water course. After a week or more, depending on the richness of the soil they were sluicing, the chutes and mats were removed and the paydirt was collected - this was known as "washing up the claim". This paydirt was now a mixture of heavy sands and gold which they would wash in their pans to remove the sand.

At the end of the day the reservoir was closed off to allow it to refill; this also enabled the pipes to be drained in winter when frost could burst filled pipes.

Dredging

This system of extraction was also used by Moses and John: the loose gravel and sand was brought up from the bed of the river and then treated in a sluice box in the same way as for hydraulic mining. The photograph below is of the Moses and John's dredge operating on the Kye Burn river in 1918. (The trees in the background are those planted by Moses)



Joseph Fowell was a dredgemaster before he became manager of the Otago Brush Co, and held 1000 £1 shares in the Upper Nevis Gold Dredging Co, which did not succeed because the wash which the dredge found was too hard for the dredge to recover.

Hard rock mining

Hard rock mining is removing rock from the ground, in which miners tunnel and blast into rock, seeking deposits of gold. Veins of gold ore are often found several inches or feet wide in certain rock formations in a volcanic deposit and in certain bed layers in a sedimentary deposit, hence the minerals may be removed, collected, and treated to process the gold and other valuable metals (such as silver) from them. This technique uses the most energy and is typically viable only where exceptional gold grades warrant the associated expense. Deposits where this is the case may have significantly higher grades than those needed to offset the costs and so underground mining can be quite profitable. Hard rock mining produces much of the world's gold.

Typical hard rock mining involves a cycle wherein holes are drilled in the rock to be broken, explosives are placed in the holes then detonated. Rock broken by the explosion is then removed from the area, typically with mechanized equipment. Where ground conditions warrant, rock bolts and other means of ground support may then be installed and the cycle can be begun again with drilling. By this means an advance of some few feet may be achieved.

Cyanide process

Cyanide extraction of gold may be used in areas where fine-gold bearing rocks are found. Sodium cyanide solution is mixed with finely-ground rock that is proven to contain gold and/or silver, and is then separated from the ground rock as gold cyanide and/or silver cyanide solution. Zinc is added to the solution, precipitating out residual zinc, as well as the desirable silver and gold metals. The zinc is removed with sulphuric acid, leaving a silver and/or gold sludge that is generally smelted into a doré that is shipped to a metals refinery for final processing into 99.9999% pure metals.

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