There is a romance about the search for gold that communicates itself to the terms used by miners as well as to the places they once gathered. “Gulch placers” and “bar diggings” bring back those red-shirted, full-bearded men whom one may see painted from life in delightful sketches in our Provincial Archives. The type of men who from Australia to Alaska, and from California to the Cariboo sought for gold in many a stampede.
The pan, the cradle, and the long-tom, all primitive tools of the prospector, linger on into this sophisticated machine age. They have a great antiquity behind them, for such were the implements with which the first gold was obtained in Europe, Asia and Africa. The primitive tools and weapons of man are much alike the world over.
To the prospector the question of the likelihood of gold being found in a given locality is of first importance, and of being found in paying quantities. Gold, in spite of its scarcity, is actually one of the widespread minerals of the earth, for much of it is either invisible or in solution. F.W. Clarke, in his “Data of Geochemistry in 1920,” says that “gold is present is present in the ocean in thousands of millions of tons.” Naturally the economic recovery of this marine gold has been the subject of a great deal of inquiry and investigation. But confining ourselves to the terrestrial deposits of gold we find that prospectors realizing that the placers are secondary in time and place have sought the “mother lode.” The term comes originally from Mexico, but it has also been applied to the Great Quartz Vein in California which has been traced for nearly 80 miles, a great dyke-like mass of quartz with a width as great as forty feet and averaging in Mariposa county twelve feet. Generally the source of the gold is found in a number of veins which may be only partially revealed on the surface or may, if large, form conspicuous outcrops or “reefs.” Many prospectors from the South seek occurrences of quartz-porphyry because in Montana, Colorado and Nevada, gold, silver, and lead deposits of great value are found where this rock forms intrusive dykes in limestone.
There seems to be no absolute rule for the identification of the most likely place for gold-bearing rock discovery. The mineral occurs in quartz veins or dykes, but is just as frequently absent. It is not confined to any one type of rock, but has been found in acid ones like granite, in glassy lavas like pitchstone, in lavas like basalt, in sandstones, in limestones and even in coal. Clarke says that assays “suggest a very general distribution of gold in rocks of all kinds.” But the most frequent and and remunerative occurrences are undoubtedly in siliceous rocks, such as granite and the schistose, and other rocks formed from it. It may be added that gold belongs to no particular geological age, its veins are found in rocks ranging all the way from the most primitive to the Tertiary. Today, gold is actually being deposited by certain hot springs, notably those of Steamboat Springs in Nevada, and is has been found that gold along with other minerals is being precipitated from surface water.
From Lode Mining
At the present time, the major part of gold production is from lode-mines, but there is still plenty of room for the placer miner. The placer is pre-eminently the poor man’s mine. In the early days of land settlement in the Edmonton area many of the younger men provided themselves with a little capital for their homesteads by working on the bars of the North Saskatchewan River before the summer freshets began, or later in the season. Others worked not only on the bars but in the gravels of the river cliffs. Good pay dirt was found from above Edmonton to Prince Albert. The best finds were where the swirl of currents had led to the concentration of gold in pockets. This action of water leads us to a consideration of the origin of placers and the place occupied in them by what is known as “black sands” and “ruby sands” respectively.
The primal source of all our gold in common with other metals is in the interior of the earth. But it is brought up into the crust by the movement towards the surface of magma or the intensely heated fluid matter which, when poured out by volcanic craters or by fissures in the crust, cools as lava, but when retained beneath the outer shell, cools and crystallizes coarsely as granite, diorite, or gabbro, and their counterparts. This igneous magma is in its nature a super-heated solution rather than a molten mixture, for water plays a very important place in it. The gold may not only be distributed throughout the cooled rock in minute particles, it may be concentrated in favorable places such as the contact between the intrusive body of a granite and the intruded rock. The circulating waters of the crust, as well as those from unknown depths, play their part here dissolving and then precipitating the gold in fissures and cavities, while at the same time by their action on other rock minerals they make it possible to replace them by the precious metal.
The presence of gold in the sea is an established fact, and exists there in solution. It is known that there are several solvents of gold present in natural waters such as potassium and sodium silicates, and alkaline sulphides. On the other hand, organic matter precipitates gold, of which very interesting evidence comes from British Guiana. There on gold-bearing rocks grow what are known as “ironwood” trees, it has been found by careful analysis, first by Dr. Lungwitz and later by Government Geologist J.B. Harrison, that “the ashes of the trees contain small quantities of gold.” The gold in the ash of the bark yielded one grain per ton, and of the wood, from seven to ten grains. Two things are evident of this. The solubility of gold which could of course only enter the tissues of a tree in solution in the water taken up by the root, and the power of organic matter to precipitate gold. In Dr. Lungwitz’s experiments he found as much as twenty-eight grains to the ton in the upper part of the trunks near the branches.
Water Plays A Part
Water again plays an important part when the metallic ores become subjected to rain or melted snow as it enters the soil and rocks. The effects of this water may be seen from the account of Father Pierre Fontanel in his “Le Sol Canadien.” When permitted to visit the scene of operations during the construction of the Mount Royal tunnel, he was a little surprised to see and feel rain falling upon him. Yet the rock overhead was hard and compact. The water had filtered through the rock for several hundred feet. At the surface, water attacks the veins containing gold, along with metallic sulphides such as pyrite, galena and arsenopyrite. These are dissolved and either carried away or redeposited at lower depths. The gold, however, is a more difficult solution and is left behind.
In addition to the chemical action of water as a solvent, is its mechanical operation. The weathered and disintegrated rocks are carried away by streams, varying in size from the tiniest trickle to the mightiest river. Evidence of this may be seen in the Sooke hills, where the weathered particles of rock are carried over the edge of a slightly sloping bed and come to rest as a scree or talus below. In streams, the largest fragments the water and slope will carry are dropped first. Often they are broken by the violent pounding against each other. Anyone who has prospected along the Fraser River in summer has heard the thunder from submerged boulders as they are forced down in the raging torrent. Boulders are found all down the steepest part of a water course, but among them there is an increasing amount of gravel and sand. Different stages of the water will vary the material of the bed according to volume and velocity, and thus in the lower reaches of a rivers beds of gravel, sand and clay may be found alternating or intermingled.
In Gravel And Sand
The gravel and sand are composed of the weathered and disintegrated rocks and of the minerals they contain. Naturally as the load carried by the running water drops the heavier materials, these materials tend to arrange themselves gravitationally, the heavier at the bottom, the lighter on top. Any metallic ores that have been brought down through escaping chemical erosion in the bedrock are further subjected to this in the stream-bed, the gold still remaining intact or even being freed from some of its host rock. The free gold, because of its high specific gravity, 15.6 to 19.3, sinks through the porous gravels and sands and finds its resting place on the surface of the bedrock of the stream-bottom, or where this is roughened by schistose or a slaty structure in the crack and crevices. The coarser gold is thus found in the upper parts of stream valleys, while the finer particles are carried onwards by the current. Eventually these finer particles come to rest in the deposits of stream-bed layers of clay or closely compacted sand which produce a false bottom. Whether on bedrock or other compacted layers that does not allow the gold to pass through, the resting place is known as a “pay streak.”
Gold is not the only material with a high specific gravity. It is equaled by platinum, which is similarly deposited in the sands and gravels. Nearly all platinum is derived through placer mining. At one time, the basin of the Tulameen River produced a larger amount of platinum than any other part of North America. Another important mineral with a high specific gravity is magnetic iron, or magnetite. With a specific gravity of a little over 5, it also passes downward and will be seen by a conspicuous dark band. This is what is known by prospectors as “black sand.” It is obvious that where gold has been carried down by a stream, its resting place will also be where the magnetite or “black sand” is located, and is known as the “finder” of gold. However, not all black sand contains gold. If the waters of a stream are not fed by gold-bearing rock, it stands to reason there won’t be gold.
Veins Of Black Sand
The heavy concentrations of black sand in the Nechako River near Prince George, as well as the sands of Wreck Bay, contain flake gold. In addition, these sands also carry small pink garnets. This brings us to another type of colored sand known to prospectors as “ruby sand,” but in reality it is composed of garnets. The specific gravity of garnet is less than that of magnetite, but it is greater than the ordinary components of sand and gravel. In addition to the evidence of black sand concentrations, these ruby sands are also important because gold-bearing rocks often contain garnet.
The Earlier Levels
Gulch placers are those which are worked in the narrow valleys which head up in the mountains or hills, and where the first deposits of gold are laid down, close to its point of origin. In addition to the placers worked in stream valleys and on bars, there are those on the terraces or benches that mark previous and earlier levels of the water. On the Leech River, the stream-bed placers were worked first, then the benches, where some mining is still going on today. The Fraser River is another great example. The old-timers retrieved million of dollars in gold from the bars. Today, all the “easy” gold is gone, leaving only the uneconomic remains scattered amongst the rocks. There still remains a considerable amount of gold along the Fraser, but it lies in the terraces and benches, not along the river’s edge.
Another form of placer mining has been carried on with some degree of success. This consists of working the contents of the potholes in streams such as those found between Otter and Sherringham Points, where some good finds have been made. The gold must come from the glacial drift forming the cover of the coastal strip. The potholes are in the Sooke sedimentary rocks.
All placers are not so recent as those which are usually worked. Some of the richest date from Tertiary times, when they were covered with lava and sealed up. Many of the richest placers of California were of this kind. Others have been described as “fossil placers,” for their gravels, older than the Tertiary, have been converted into conglomerate and so involved in the effects of earth movements and mountain-making that they have lost all traces of their original topography and are recognized only by their water-worn boulders and pebbles. Some of these conglomerates can reach a thickness of 500 feet, lying below Cambrian beds and above Archaean gneisses and schists, and seemingly are auriferous throughout. Its gold has been explained as the result of the chanical concentration on the shores of a pre-Cambrian Ocean.