Treasure Maps

Bill James (Australia) writes:

If you have done the job properly, the gem material should be concentrated in a small circle in the center of the sieved gravel. Pick the stones out, using tweezers if necessary, and place them in your collecting bottle. Many things happen in the history of a river, the life cycle of which is accomplished only when it has cut its bed down to the level of that lake or sea into which it flows. Even then it may occur that some earth movement raises the land or the sea level falls so that the river is rejuvenated and flows rapidly again.

Rivers often change their course, destroying part of their former deposits and creating new ones. The stream may leave gravels on terraces high above its present bed or its course may be swallowed by a flow of lava—which is what happened to the ancient riverbed now forming the New England diamond fields of Copeton and Bingara. Miners call these prehistoric deposits of buried gravel deep leads.

Alluvial mining for gems on a commercial scale in Australia is now mechanized, with bulldozers stockpiling the gravel for treatment in pulsators. At Copetown, for instance, a revolving screen was used followed by pulsator treatment before hand sieving for diamonds.

Australian methods of alluvial sapphire mining vary according to water supplies, miners in some areas having to rely on dry screening and hand sorting. Fossicking or noodling on mine dumps may call for both the quarter-inch sieve and 3 lb hammer, as no rock of any size should be left unsplit. The golden rule mine dumps is to look for the place where the grass and weeds have been left undisturbed and dig there.

Another tip, as far as the smaller and older type of disused mine is concerned, is to look around for any large rock fragments that may have been scattered in the bush by blasting. They are worth cracking open, too. Old mine workings have a fascination for rockhounds. Normally sensible people are irresistibly lured into these gloomy, damp tunnels although they must be well aware that time, rust and white ants have made everything thoroughly unsafe.

Shafts and underground workings are often filled with carbon dioxide gas, a quick and stealthy killer of people unaware of it. The presence of the gas can be discovered by testing with a naked light, which the gas put out, but my advice is: Steer clear of the old mine workings altogether.

Certainly never go off on your own to work rockfaces or investigate mine tunnels. In fact, it is sound policy never to go off on your own on any long trips, and on short trips always to make a point of telling someone where you are going. If you are going into arid or rough country make sure you take extra food and petrol and at least five gallons of extra water for each person in the party.

Look out for snakes, spiders, ticks and, most of all, sunburn. Buy yourself a shady hat, some tough mittens and boots stout enough to protect your ankles and steel-capped to guard your toes. Don’t forget a rucksack to carry the tools and spoils. Among the extras you will find useful are electric torch, a pocket lens of jeweler’s loupe and a bottle of bromoform or methylene iodide, to enable on-the-spot identification of gemstones through their specific gravity.

It works this way: topaz (specific gravity around 3.5) sinks in bromoform (specific gravity 2.9), while quartz (specific gravity 2.65) floats. Other test liquids such Klein’s, Sonstadt’s and Retger’s solutions are difficult, dangerous or messy to use and best left to the laboratory.

One of the most rewarding ways of opal-hunting is to speck or noodle the dumps on abandoned—make sure it is abandoned—claims at Lightning Ridge or any of the other famous opalfields. The best time for this is just after a heavy shower of rain when gems washed to the surface catch the sunlight.

Many good stones were overlooked in the old days and remain in the dumps, which are now being gone over with mechanical sieves or puddling machines. Without a doubt many deposits of precious opal have yet to be found and worked in the west of Queensland and New South Wales, where lack of water beat the old-time gougers. The same can be said of the north-west of South Australia, where it is officially regarded as ‘quite possible’ that important discoveries remain to be made.

Little more than the surface has been scraped off most of Australia’s gemstone deposits. Sapphires, zircons, topaz—almost every gem in the alphabet—lie scattered in a bed of gravel between a few inches and 50 ft thick over an area of 350 square miles at Anakie, Central Queensland. Although the easily accessible areas are largely worked out, much of the ground is still almost untouched.

This is one of Australia’s richest gemfields; but the picture is typical. Gemstone mining is everywhere an individual effort, crippled by lack of capital. The only full-time miners on many fields are pensioners, picking up little more than the price of their smokes.

While they seem to offer little return for financial investment, the wonderful variety and widespread nature of Australia’s gemstone deposits are now being recognized in the growth of the gemseeking as a most fascinating and rewarding hobby.