Here we have shafts sunk on the reef at B, and levels driven right along the course of the lode, where rises (D) and winzes (E) have been driven and sunk, whilst in some places the winzes and rises (F ) have met. The shaded portions show where the ore has been stoped out and taken to the surface, and the unshaded where the lode is still intact and still to be stoped out.
Some reefs, as we know, run through a mountain, and when this is the case the company is a fortunate one, for such a reef can be mined much more cheaply than in the ordinary case, for here we can reach it much more easily and less expensively than in sinking shafts, whilst the cost of haulage is not anything like so great. These lodes are worked by means of adits, which are tunnels driven into the side of the mountain or hill, from which the usual levels are driven, by means of which the property is developed in the usual way. The following gives an illustration of this:
A shows us the outcrop of the lode on the top of the hill, and how it dips through the hill. B is the side of the hill from which the adits, or tunnels, C, D and E, have been driven to intersect it. F is the barren country rock.
Sometimes in a report we are told that they have come across a rich shute or patch of rich ore, and this is undoubtedly of frequent occurrence, especially in Western Australia. The following shows a reef in which there are two of these shutes in the reef, the shaded portions being these shutes, and the unshaded the poorer portions of the reef:
When rich shutes or pockets of this kind are encountered, dishonest directors and managers work them for all they are worth, in order to send up the prices of the shares on the market. It is called 'picking out the eyes of the mine,' and this is what is done to enable the directors and their friends to speculate in the shares for a time, until the rich shutes have been worked out. Then the manager has to work the poorer portions, the monthly returns fall off, and the price of the shares declines, and there has been another scandal added to the long list of those of which mining directors have been guilty. When levels have been driven right across this lode, some parts of the levels will, of course, be in rich ore, and others not. The ends of them, which are driven through the shutes, will, on the other hand, be in the unshaded portions given in the above illustration, or in poor ore, thus making clear the common expression in managers' reports, that the ends of the levels are in poor ore. Therefore, from this we may generally conclude that a rich shute or shutes are being worked.
If, on the other hand, two shafts have been sunk, each one on these rich shutes, we should naturally have an exaggerated idea of the richness of the lode, concluding that it was all as rich from shaft to shaft, whereas the subsequent drivings of the levels would prove it to be poor for some distance between both shafts. Again, if the shafts happen to be sunk on the poorer portions of the reef, we may conclude that it is a very poor reef, until the levels prove that there is richer ore lying on one or both sides of it. Thus, it will be seen that, when driving on a formation of this kind, it is only after several crosscuts have been put in at various points, proving it in breadth from the hanging wall (which is the part of the lode lying next to the country rock immediately above it) to the footwall (which is that part of the lode lying nearest to the country rock below it), that we can get anything like a fair idea of the value of the reef - that is to say, whether it is likely to prove payable or not.
Sometimes we read of parallel reefs being found in a property, and the meaning of this is so self-evident that it hardly needs any explanation. However, the following illustration will show how they often occur:
A, B, and C are parallel reefs traversing a property, and D are two shafts sunk, from which cross-cuts (E) are driven to prove their value. Often, instead of sinking shafts to prove a reef at depth, the less expensive method is employed of sinking boreholes, as is now being done in West Africa.
Often we hear of a fault having thrown the reef in another direction, and, therefore, of the reef being lost. This is the effect generally of some volcanic upheaval, and in many cases it means a great expenditure of capital and labour to find it again. The following illustration will show how a reef has been thrown a considerable distance from its original dip:
Here the shaft A has been sunk to strike the reef, say, at 200 feet, but a few feet lower it finds that the reef is lost. Hence levels have to be driven in the direction the manager thinks it will be found. Here we find it to be an upthrow (B), and the manager may guess successfully where it is likely to be. But if it happened to be a downthrow instead of an upthrow, he would make a most expensive miscalculation, for which the shareholders would have to pay. But as it would not be his fault, but Nature's, the shareholders could lay no blame upon him, and would have to bear their misfortunes as patiently and as philosophically as they could. Such faults as these are, of course, not confined to any particular field or formation. They are met with everywhere, and have been somewhat common on the Rand. All this adds greatly to the speculative nature of mining. A company may for many years be very fortunate in striking rich ore, and then suddenly the rich reef which it has been working may be lost altogether, and the shareholders may have to wait many years before it is found again. The expense incurred in this way may be so great as to nullify the earlier successes. The company may have to be reconstructed several times before the reef is found again, and then when it is found the risk has to be faced of finding it as rich as where it was intact.
This, of course, is no reason why mining should be condemned, or why so beneficial an industry should be handicapped for the lack of means to carry it on. There are just as great risks to be run in other ventures, and perhaps, on the whole, they may even be greater. An invention may come out to-day which may revolutionize a certain trade or industry, and it may accordingly be an enormous success. But that success maybe shortlived, for a better invention still may come out and bring heavy losses upon the company that exploited the original invention. The onward march of science puts a great many flourishing undertakings in perilous positions, so that mining may not be more risky, if we take the proper precautions, than many other phases of industry. I advise everybody, therefore, to take those precautions, and if they are taken then I shall feel that I have not written this book in vain.