The fine alluvial gold dust travels farther down to the flat country, where the force of the water is not great; and it is found there amongst the sand on the banks of the river.

Again, alluvial deposits appear on terraces, on the sides of mountains, or on plateaus, where the more recent auriferous formation decomposes and is floated away, leaving the heavier particles behind.

Having found an alluvial patch, the principal thing is to ascertain whether the wash is sufficiently rich in quality and quantity to cover all expenses connected with transport, water courses, ducts, &c. Local circumstances have much to do with making it remunerative.

The porous nature of the gravel makes it easy to work with pick and shovel; but the large boulders usually met with increase expenses, as it is necessary to use dynamite for blasting them.

As before mentioned, one meets on the bed-rock gravel mixed with clay. Often, through ignorance of its soapy and sticky nature, much gold may be lost; for the lumps of clay, which do not disintegrate as quickly in water as the gravel, will be carried away with all their contents (see Sluicing). Therefore, in washing this particular compound, it should be rubbed between the hands, so that the clay runs away in the form of muddy water, and the heavy gold settles to the bottom.

The most easily-worked alluvial deposit is where the wash is shallow, and where generally a non-auriferous black surface soil overlies it. This must be first removed. The process is called stripping."

When the payable deposit is laid bare, the work of sluicing can go on uninterruptedly. Again, deep-lying alluvial deposits are found where, in many cases, the stripping process is impossible to perform on account of the presence of hard overlying beds.

To reach it, shafts and drives must be used, and the payable ore brought to the surface, where the sluice-boxes are erected.

2. Proving Alluvial Deposits. In testing the contents of the alluvial deposits, one generally employs the method of panning. Special prospecting pans are made for this purpose, stamped from a piece of sheet iron of a smoke black colour, in order that the yellow gold may be more easily seen. By much use the smoky colour of the pan disappears, but can be renewed again by placing it over a fire, preferably over one made with brown paper as the fuel.

The pan itself generally measures 8 to 10 inches across the

bottom, and 12 to 14 at the top; it has grooves running round it, as shown in Fig. 3.

Fig. 3.-Prospecting pan.-The heavy metal accumulates in a, upper groove, and b, lower groove.

These grooves catch the heay gold, which sinks to the bottom, while all the lighter matter is washed away.

3. Panning. In working, the following method is adopted:— Fill the pan about a quarter to one-half full with earth, the remainder with water, then stir the whole together with the hand. Pour half the muddy water very slowly away. Refill with water and repeat this process, using the while a sifting motion, by which the heavy substances settle to the bottom and the water becomes nearly clear.

When this point is reached, tilt the pan slightly and allow some of the light substance to flow out slowly with the running water. Continue refilling with clear water and pouring off, till nothing remains in the pan but the heavier metal. According to the results of the panning and the quantity of ore washed, experienced prospectors can judge very closely the value of the ground.

In panning alluvial deposits the large pebbles or stones should be removed after first carefully washing them in the pan, and the fine substance treated as described above.

It is advisable, for convenience sake, to have a tub or bucket close at hand in which to pan valuable deposits. Many mistakes are made by inexperienced men in filling the pan too full of earth. This makes the sifting process difficult to perform, and the gold, consequently, does not accumulate round the bottom of the pan, but is washed out with the other substances.

In panning, the gold is often noticed floating on the water; the reason of this is that the fine particles of gold are flat or covered with a soapy substance which formed its matrix.

By sprinkling it with water it will sink to the bottom.

4. Sluicing.—In treating large quantities of alluvial ore, one must resort to the more practical arrangement of sluicing in preference to the primitive form of panning.

For the purpose of ordinary field work, sluices are made in two parts, each consisting simply of three planks of wood, formed trough-like, through which runs a constant flow of water to wash away the sand, clay, or sediment (Fig. 4).

Fig. 4. Trough-like sluice box.

The soil is shovelled into the higher end of the trough, and stirred if it is not carried away freely.

The nature of the gold is to sink, or to rest against obstacles; therefore, in the first part of the box, obstructions are made by long and cross bars of wood, with a sieve or screen at the lower end (Fig. 5, a) to catch all the heavier metal.

The fine gold dust will be carried farther; consequently the second box has appliances for catching it, arranged as follows:Narrow cross bars (c), and at the end a rough blanket (d) (Fig. 5, 6).

Fig. 5.-Obstacles on the bottom of the sluice box.

Many ways are adopted for arresting the gold, such as false bottoms; but this greatly depends on the individual and on the financial position of the prospector.

In any case it must be arranged that the box can be raised or lowered at one end, according to the nature of the earth washed, the usual slope being 8 inches in 12 feet (1 in 18). In washing soil containing fine gold, the sluices are made longer, and mercury is added, for the purpose of catching the gold, which blends with the mercury and forms "Amalgam."

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The nuggets and fine gold are collected and cleaned in the pan. The amalgam is first cleaned in water, more mercury is then added, and the whole is squeezed through chamois leather.

By heating the amalgam the mercury evaporates and the gold appears as a spongy mass, called "Retorted gold" (see p. 26). The value of this can be ascertained by assaying and weighing.

5. Reef Prospecting. As previously explained, veins are located by means of the signs in old river-beds, valleys, strata exposed in kloofs, creeks, or deep-cut waggon roads.

On finding loose pieces of ore-bearing rock, the first step is to search for the ore in situ. The clues for this abound, especially in a mountainous country, where ranges and long stretching outcrops attract the attention at once. The reefs exposed on the surface are called "Outcrops."

It is not to be expected that the outcrops of any reef will be equally manifest along its whole course, as it may be disturbed by variations in the dip, slips, by being pinched to nothing, or by being divided into many small leads ("leads," a term used to describe small strings of ore leading to the main body.)

Some are decomposed and are hence easily overlooked, while others occur as very large conspicuous outcrops with weathered and porous rock, looking like a melted mass of milky quartzite and reef matter. Then, again, outcrops appear running along and across the strike.

Faults will often divert the strike (i.e., the direction of the outcrops of a stratum) to the right or left from its ordinary course. In their mineral contents also, many variations are found. It often happens that an outcrop contains gold in one place, and farther on none at all; but, on closer examination, sometimes one finds the gold in the casing ("casing" means the formation next to the usual gold-bearing body).

Often outcrops cannot be noticed, because they are entirely oxidised and appear to be red clay, though it carries the gold. There are many reefs which bear no gold. In prospecting, it is advisable to take as little lumber as possible in the field, as the main object should be to examine as much ground as possible and to get a knowledge of the value of all the different outcrops.

The richest outcrops will naturally be dealt with in detail prospecting, in regard to its value in depth, which will be described later.

Prospecting of new ground should be done by walking, for to search properly one must climb and pass places where no roads nor thoroughfares are made.

In testing outcrops, one must be provided with a number of small canvas bags in which to gather the samples; these should be taken at every 5 feet along the strike of the exposed reef. Number the bags 1, 2, 3, and so forth. At the same time a sketch should be made of the situation of the ground, marking the reefs and spots whence the samples are obtained, so that the number on the bag will correspond with the sketch in the notebook. Afterwards take the various samples to the water, where pestle and mortar (Fig. 6) should be used.

b

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Fig. 6.-a, Pestle; b, mortar.

Fig. 7.- Gash vein.

Crush the different samples, one after the other, to a fine powder, and pass them through a fine sieve into the pan. Pan each sample in accordance with the number in the notebook, and write the result against it. When the results of any sample are favourable, it is important to return and examine those places more closely, and to collect further samples without picking or selecting any particular specimen.

It must especially be noticed if the lode (or reef) strikes across or along the strata. The former is of less value than the latter and is generally called a "Gash" vein (Fig. 7), because it usually ends in short depths tapering to nothing. They are very numerous in the auriferous fields and often contain good gold, as the gash veins are formed by reef matter filling fissures in the rocks.

On the other hand, the lode running along the strata is