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Sand concentrates

Alluvial Gemstone Prospecting

Sand concentrates
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"Alluvial Gemstone Prospecting"
Caption: Sand concentrates
Image by: Allan Taylor

Fossicking for gemstones is an interesting and popular hobby today, as is the cutting and polishing of  any rough gemstones that you might find.

Alluvial gemstone prospecting and mining  can be done by the individual or by a mining company  for various reasons, but the methods are the same.    You need a gold pan with two attached sieves, having coarse (5 mm) and fine (2 mm) apertures.   My gold pan is of black plastic of 34 cm diameter with two aluminum sieves having steel wire mesh  which fit snugly on top.  This I have used for the past 40 years without it being worn out.  It is also useful for general gardening work if you have a vegetable and  herb  garden is a great investment!

To find alluvial gemstones you really have to start out being a gold prospector and know how to pan for gold  in a stream.   You must develop a rapport with rivers and streams and understand how they operate, which will eventually become second nature to you.  The experienced trout fisherman knows  where to cast his fly or spinner to catch the wily trout.  The problems of catching trout or of finding gold, and the finding of  gemstones in a stream,  are all similar in principle.  Observation and learning are the key to success.

You may think that the days of  the gold prospector  using a gold pan  to find riches are long gone being now overtaken by high tech electronic and geophysical prospecting.  This is true up to a point,  but  gold pan prospecting still has its use in mineral and gemstone prospecting today where it may be  called  a   "pan concentrate survey" of  an exploration license area.  This is important in prospecting for diamonds even in the arid countryside of Australia where ancient dry stream beds are prospected.

My experience with pan concentrate surveys for a  mining company  has been in New Zealand where there is no shortage of water.   A large area of several  100 sq. kms can be fairly rapidly surveyed by panning off the heavy residue concentrates from all streams and tributaries using a gold pan with sieves.  Samples are taken and recorded for study back home with a binocular microscope.    To understand what you are looking at you have to be a  geologist, mineralogist or gemologist,  or in other words,  know all about  the physical appearance of  alluvial gemstones and heavy  minerals, such as garnets, zircon, tourmaline, magnetite, ilmenite,  cassiterite, sphene, rutile,  diamond, sapphire, topaz  and of course any gold or ore minerals such as scheelite or sulfides, and be able to recognize them under the microscope.   

The mining company undertaking such a pan concentrate survey of a license area can get a fair idea of what rock types have been eroded and whether there is any sniff of interesting mineralization or gemstones occurring within in the region.

The important gemstones are all  heavy minerals and they will concentrate like gold when washed in a gold pan.  These include diamond,  sapphire, zircon, tourmaline,  garnet, topaz  and many others, except emerald and beryl which have the same density as the ubiquitous quartz and so do not concentrate in alluvial deposits or when panning off.

When you are processing a pan concentrate having jigged every thing up and down in water for awhile and got rid of all the mud and fines, one then up turns the sieve and examines the coarse residue on top of the pile.  Hopefully there will be a rough diamond or sapphire or topaz or zircon awaiting for you to extract and whiz off to your faceting machine.   Don't count on it!

If there is sapphire or zircon etc. in the region where you are prospecting then there will be umpteen more tiny samples of these minerals that have passed through your smallest sieve of 2 mm just waiting for you to be identified by microscope in your final pan concentrate, where there may also be a few gold particles.  

If you can detect tiny sapphires in your pan concentrate then there is a good chance that you will find a larger sapphire on your top sieve.  Hopefully it may be of gem quality and facetable.

It is all like investing some  disposable cash in Lotto.   You will always get tiny returns but  now and then you are lucky to hit the jackpot with a major prize which is like  finding a valuable gemstone when out prospecting.

More about this author: Allan Taylor

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