How To Prospect for Minerals and Gold

How To Prospect for Minerals and Gold 

  A great lesson from 1933 by DR. L. Stolfa, only the equipment has changed and he gives some great description and tests for detecting Minerals. 

(Placer prospecting) Having arrived at the scene of your intended prospecting activities, what mode of initial attack will you select, what will be your opening move in playing the game? Ordinarily it will make little difference whether you are searching for a placer or a gold vein. You will look for a definite clue, and when found, you will follow it to its successful termination. The most reliable clue is “float”, a term applied to small, sometimes minute pieces of gold and other vein material found in sand and gravel of the streams, in detritus of canyons and gullies, at base of mountains, in sand of the desert, etc.

Originally gold was contained in a vein higher up in the mountains. In the course of long periods of time the surface part of the vein, called outcrop, was slowly eroded by water and wind and gradually disintegrated by complicated chemical agencies with the result that gold was gradually separated from the other component parts of the vein and set free. 

These particles of metallic or native gold were subsequently picked up by water during rains and transported for variable distances until finally, when the stream slowed down sufficiently to allow these particles to settle down, they were deposited on mountainsides, in gullies, canyons, in beds, banks and bars of either constant or intermittent streams where they formed deposits, which are, so to say, samples of the materials contained in the higher reaches of the drainage zone. 

The following metals may occur in paying quantities in placers: Gold, platinum. silver, iridosmine, all of which have distinct metallic luster. Besides that the following minerals with non-metallic luster may be found: zircon, monazite, tin stone (cassiterite), cerium, uraninite (pitchblende) source of radium, yttrium, rutile, diamond, etc. Repeated erosion, separation, transportation and deposition produced layers of gold containing sands’ and gravels, sometimes many feet in thickness, called gold placers. The placers that were formed many ages ago are called “ancient placers”. They may be even several hundred feet in thickness. 

It is well to remember that in these ancient placers the upper layers usually carry lower values than the deeper ones, which is the value of gold per cubic yard of the material increases with the depth, though not at a uniform rate. Because of long continued exposure to chemical action produced by seeping-in water, in presence of iron, lime and other minerals, those deposits often became cemented together into a form of conglomerate. Some of the rivers that produced these placers changed subsequently their course due to changes in the elevations of earth surface or because the flow of lava in their upper course blocked the stream. Thus it happens that gold is found not only in the sands of presently flowing rivers (modern rivers), but also high up above the present streams in benches, that is, terraces, that ages ago formed the banks of the rivers, also in ancient river beds, on some hills and in deserts far away from any stream flowing now. Some of the ancient placers were subsequently buried by lava flow and others cut across by new rivers, thus forming modern placers by eroding, transporting and depositing material from the ancient placers. 

Since the gold particles settle down wherever the stream slows down sufficiently, the gold is most likely to be found wherever there is a change in the direction of the stream as for example on the concave side of the stream, also in holes and pockets in the river beds, on the downstream side of rocks and boulders, in the river bars, banks that were submerged during high water, around the roots of grass and trees growing on the banks, etc. It is always advisable to dig several feet down to what is called “hardpan”, a name applied to a hard layer of gravel and sand or clay, or to the bedrock under the gravel. Black, rusty, yellow, red or any other conspicuous color is often a very favorable, though not infallible, sign of the presence of gold. 

Rich deposits occur in those places of the stream where a sudden change of direction occurs, where the tributaries empty into the main stream. Larger pieces of gold are usually found in the vicinity of the vein from which they came, while finer gold may be found many miles away from the lode deposit. Coarser gold is found with coarser gravel and finer particles with finer sand. Wherever black sand and other iron minerals accumulate, gold is liable to accumulate also, because both of these metals are quite heavy, Potholes are not favorable places for deposition of gold. Bars of rock running across the stream collect considerable amount of gold on their downstream side. 

From its hiding places gold is dug out and separated from the admixture of worthless matter by the process designated as panning. This consists of mixing with water the gold containing sand, gravel or dirt in a pan made especially for this purpose and agitating the mixture in such a way as to allow the gold, that is heaviest, to settle down at the bottom of the pan, while the lighter particles of the soil, sand and other worthless ingredients are washed over the rim of the pan and discarded. 

Since mastering the art of panning is essential to your success, you should study carefully the directions given below and -then practice and practice until you acquire a high degree of skill in handling the gold pan. 

Following are the directions for panning: 

1. Fill the pan about two-thirds full with “dirt” (gold bearing sand and gravel), immerse in water and holding it horizontally, soak its contents well, then with fingers crush under water all lumps and mix the contents thoroughly into thin, uniform mash. 

2. Holding the pan with one hand on each side and still keeping it horizontal under the water, rotate it briskly in circles slightly larger than the pan itself, swinging the arms freely, the motion being more in the shoulder and elbow joints than in the wrists. Pick the larger pebbles out of the pan and discard them. By this time the coarser gravel and the lightest particles (dust, clay) should have been removed and the water in the pan is much clearer than at the start of panning. 

3. Holding the pan in the same way under water, shake and rotate it with motions closely resembling those of sifting. Repeat several times. 

4. Now begin to incline the pan slightly in such a way that the rim away from you remains under water, while the one close to you barely emerges above the water level. In this position shake and rotate the pan with sifting-like motions, allowing always little of the contents to wash over the depressed rim. 

5. Remove from water and rotate in such a way as to produce a wave of water travelling around the sides of the pan from the depressed rim upwards and then sideways down towards the lower rim and carrying with itself over the lower rim always a little more of the lighter materials in the pan. This phase of the work has to be done gently and smoothly without jerking, in order to save as much of the fine gold as possible. Keep always enough water in the pan, repeated~ ly adding, as necessary, and continue this washing until about a teaspoonful or less of clean, sandy material is left in the pan. If gold is present, this residue will be chiefly gold sand or gold dust and “black sand” which is composed of minute dark grains of various minerals, chiefly iron minerals (magnetite, ilmenite, chromite), tinstone (cassiterite), tourmaline, etc. 

6. When about a teaspoonful or even less of the material is left, the pan is given a sliding motion which is arrested with a sudden jerk. This procedure partially separates the worthless sand from the gold. In this residue look for “colors” that is deep orange yellow specks with metallic luster. Use a magnifier if you see no colors with unaided eye. The orange yellow material, if found, has to be subjected to some of the previously described tests in order to differentiate gold chiefly from yellow mica, which is usually sharply angular and flattened, and pyrites, and establish its positive identity. 

It is impossible to separate completely black sand from gold by mere panning. If magnetic, the black sand may be removed by a magnet after previous drying of the residue left in the pan. The gold may also be extracted by amalgamating it with mercury (quicksilver) which method will be described later. While, as a rule, the main component part of the black sand is worthless, being made of iron minerals, there are several other, chiefly very valuable minerals, that lag behind in the residue after the removal of its magnetic component. 

These minerals may be divided into two groups according to whether they have a metallic or non-metallic luster. The following are the minerals with metallic luster that may remain with the black sand, and that are valuable: 

Platinum, This is pale steel gray or silver white in color, streak the same, harder and heavier than gold, infusible, soluble only in aqua regia, malleable easily into thin sheets and giving no odor on heating. 

PALLADIUM. This is steel gray to silver white, often with bluish tarnish, scratched with glass, as heavy as lead, dissolved in nitric acid, flattens under hammer, no odor on heating. 

IRIDOSMINE. Steel gray or silver white, scratches glass and is scratched by quartz, gives off peculiar odor when heated. 

WOLFRA1\UTEl Dark grayish black, aiS heavy as steel, hard to scratch with a knife. 

URANINITE (Pitchblende). Black or brownish, easily scratched with knife, very heavy. Its luster is not typically metallic, sometimes almost non-metallic. Being a source of radium it is a very valuable ore. 

The following valuable minerals without meta11ic luster remain with the black sand: 

CASSITERITE (tinstone). Black or brownish black, not scratched with a knife, but scratched with quartz, three times as heavy as quartz. 

SCHEELITE. White, cream, yellow, brownish, red­ dish, will not scratch glass, scratches copper coin, streak white. 

CORUNDUM. Blue, gray, red, yellow, cannot be scratched by anything else, but diamond, \will scratch quartz easily. Pure variety is sapphire and red variety ruby. Both are very valuable gems. 

DIAMOND. It may be colorless, white, red, blue, orange or even black. Will scratch even corundum and cannot be scratched by any mineral. Is heavier than quartz, briskly rubbed (wben dry) will flasb light ill tbe dark, becomes electric on rubbing. 

Topaz. glassy, pale yellow and other shades, sel’Ht!’hes glass, is scratched only by corundnm and diamond. 

If you find anything that gives the above tests, or closely resembles some of the above described minerals; take several samples and have them thoroughly tested in a laboratory. Since the find may be even more valuable than the gold itself. with an amateur it takes about 15 minutes to properly work one pan, while an experienced man is able to do it in 10 minutes or even less. Start with at least 15 minutes and gradually, as your skill increases, shorten the time of working. Especially towards the end of the process, when only a small quantity of material is left in the pan, the amount of waste washed out by water with every movement should gradually be smaller and smaller and the work should proceed more carefully. 

Before starting on an actual prospecting trip get outdoors and near some stream practice panning, as follows: 1. Half fill the pan with soil and mud and try to wash the heavier particles of sand clean. 

2. Repeat the same operation with sand, separating the lighter from the heavier particles. 

3. Get some fine shot, preferably No. 12, count them and then mix thoroughly with sand and try to recover all of them by panning. 

4. Mix some clean (not oily) iron filings and recover them by panning. To measure the degree of your efficiency, weigh filings before mixing and weigh the filings recovered, after preliminary thorough drying. 5. Get some gold filings from your dentist, weigh them, mix with sand and then try to recover by panning. 


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