Types of Metal Detecting Activities, page 32

GOLD NUGGET HUNTING & Electronic Gold Prospecting

General Info, Tips, Accessories & Metal Detectors Required

Gold Nugget Hunting

Metal Detecting for Gold Nuggets - Gold Nugget Hunting or Gold Nugget Shooting, is about detecting gold as small as a half a grain.

The greatest advantage of gold nugget hunting over non-electronic gold prospecting (panning, sluicing and dredging gold) is that it does not require water that is necessary for most non-detecting methods of gold prospecting/placer sampling (placer or placer deposit is an accumulation of valuable minerals formed by deposition of dense mineral phases in a trap site). And if you are an avid gold prospector, by using a gold metal detector, you can easily search areas that are far from water, such as dry locations or deposits located away from the stream.

Also the gold metal detectors are used effectively to find shallow free-milling gold pockets and pay streaks within both dry placer and hardrock gold districts.

Forms & Natural Areas of Gold Occurrence
Gold is commonly found in its elemental form, with varying amounts of silver, copper and iron as impurities. Based on natural size and nature of appearance, gold occurs in six main forms, of which only first two are available to electronic gold prospecting with metal detectors:

1) Pieces of free gold of 2mm and larger in size that are known as nuggets.

2) Large grains of gold embedded in quartz and ironstone and derived from quartz reefs (continuous quartz veins) and lodes (other large primary deposits) are known as specimens.

3) Coarse to fine grains of gold 2mm to 150 microns that are visible to the unaided eye as either embedded in gangue (quartz, ironstone, etc.) in primary deposits or loose grains within secondary deposits. Machinery is required to separate gold grains from unwanted material.

4) Microcrystalline gold 150 to 0.8 microns in size, i.e. only visible with a microscope, is common within primary deposits. Grains of gold are disseminated and embedded in a quartz gangue or locked within sulfide minerals such as Fool's Gold, which is a pyrite. Coarse grains can be liberated by crushing and grinding followed by concentration using gravity concentrators. If the ore consists of very fine grains, extraction with sodium cyanide or amalgam is necessary.

5) Submicrocrystalline particles of gold occur in the crystal lattice of certain sulfide ores. Sulfide minerals cannot be concentrated by gravity methods due to their low specific gravity. Froth flotation (separation of valuable minerals from waste gangue) is common, followed by treatment with sodium cyanide to remove the gold. Such mining methods are expensive and can only be used on large deposits.

6) Gold also occurs in compounds of gold and/or silver with tellurium. The tellurides, calaverite and sylvanite are mined for their gold content and quite rare.

Now you can see that electronic gold prospecting or gold metal detecting deals only with nuggets and specimens which can be recovered as alluvial, eluvial, and supergene gold. Hydrodynamically accumulated alluvial gold can be found in the small lakes and seasonal streams that cut through the surface-gold-producing districts.

Alluvial gold placer deposits will also occur in the abandoned channel bases (dry washes), point bars (formed on the inside of a bend in rivers and streams), immediately adjacent grounds, natural hollows, at the break of slope on a stream, at the base of an escarpment, waterfall or other barrier, and within sand dunes, beach profiles or gravel beds, and in deep leads - ancient stream channels that are deeply buried.

Eluvial gold can be found on low hills, rises and flat lying areas adjacent to the above locations. These are often covered with quartz and ironstone rubble. Rainfall assists by carrying the surface material containing gold downhill, that is why eluvial deposits are concentrated at a change in gradient, such as the base of a hill.

Supergene gold is found on low hills or flat lying areas that have developed laterites over bedrock. Laterite is a surface formation rich in iron and aluminum (nearly all laterites are rusty-red because of iron oxides), formed in hot and wet areas. It develops by intensive and long-lasting weathering of the underlying parent rock. Weathering is the breaking down of Earth's rocks, soils and minerals through direct contact with the planet's atmosphere. Weathering should not be confused with erosion, which involves the movement of rocks and minerals by water, ice, wind, and gravity.
Chemically altered and physically transported primary grains and nuggets are derived from the original body of ore, occur in the surface and near surface with the secondary deposits, and are the main targets for nugget hunters.

Where to Find Gold Nuggets
In the US, the gold-bearing areas extend from Northern Alaska down to the lower Southwestern deserts of Nevada, California, Arizona, and the Mexican border. Besides watercourses and residual deposits where the gold-bearing veins or lodes have decayed, gold nuggets are also found in the tailings piles of previous mining operations, especially those left by gold mining dredges.

Arid desert regions in the Southwest are prime targets for today's electronic gold prospectors because that was where the most gold prospecting took place in the past (Gold Rush). Due to a high specific gravity of gold and millions of years of erosion and concentration, gold nuggets found the lowest possible places to rest. Most of the time, these areas were drainages.

The old-timers used insufficient methods such as dry washing and screening to speed up the recovery process. But due to faulty equipment design, inconsistent air flow, overloading and operational errors, more than 50% of the gold they processed was left in drywasher tailing piles. Since the miners in the past were not able to see the gold hidden inside rocks, they would discard them. Many sizable gold nuggets can now be easily recovered with modern metal detectors in both drywasher tailings dumps and tailing piles of old mines.

It is possible to find even a gold vein or lode by a metal detector if to use it along the walls, roofs and floors of old mine tunnels. The original gold prospectors did not have electronic means to discover the gold veins that were just a few centimeters deep. Now, with a metal detector, it is easy to locate a rich vein that was overlooked in the past.

Other great locations for profitable gold nugget detecting can be found alongside the Pacific Coast where a lot of beach placers have been discovered. Their occurrence can be explained by the action of shore currents and waves on the material that has been broken down from the cliffs and washed into the ocean by the streams.

Gold nugget hunting can be done only in gold-bearing regions. Do not expect to find gold where it has never been found. Make sure you know whether your area has gold or not before you decide to buy a metal detector especially designed for finding gold!

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Source: en.wikipedia.org