THE PRINCIPLES OF METAL MINING.

Otago Witness, Issue 1273, 22 April 1876, Page 16

THE PRINCIPLES OF METAL MINING.

By J. H. Collins, F.R.G., Trxjko.

{Continued.) "heaves," &o.

In following a lode it frequently happens that a cross-vein is reached, after cutting through which the lode is not to be found on the other side. In such cases it is said to be " heaved," and it becomes necessary to drive on the cross-vein in order to discover it again. These heaves are a source of much loss to the miner and his employers, as they are sometimes of great extent, occasionally as much as 70 fathoms ; so that it is a matter of great importance to the miner to be able to say in which direction he is most likely to find it by driving. No rule can be given which has absolutely no exceptions, but a very high degree of probability is attainable.

Direction of Heayes. — Tf the lode is found by driving to the right of the crossvein, it is said to be a right hand heave ; if to the left, a left hand heave. In Cornwall, many more right hand than left hand heaves are known.

It is but seldom that tho lorlo and crnsseourse form an intersection at right angles ; far more frequently a greater angle and a smaller angle are observable. In Cornwall, of 272 cases of intersection recorded by Mr Henwood, 57 Avere unaccompanied by heaves ; and of the 215 remaining, 181, or morethan 84 per cent., were found by drying on the side of the greater angle ; and 34, or less than 16 per cent., on the smaller angle. In other words, by driving on the greater angle, there are five chances to one that the lode will bo met with.

Even this is not all that the study of known intersection teaches. Several other rules will add largely to the chances of success. Thus parallel lodes of similar underlie will be lieayed in the same direction in the great majority of cases. Those with the greatest underlie will mostly be heaves to the greatest extent. Lodes of similar bearings having opposite underlie, v ill not unfrequently be huaved in opposite directions. By studying the bearing and underlie, thereforo, of other lodes intersected by the cross-courso in question, much additional information will be gained. Extent of HeaveSi — Some idea of the extent of tho heave may alao be obtained in many instances, as it has been observed that the heaveß occasioned by large cross-courses are mostly greater than those occasioned by small ones. The science of Geology very fairly accounts for these phenomena in many instances ; but the elementary student of mining had better defer his study of such theoretical matters.

Indications. — The direction of the heave is aometimoa indicated by stains in the crosa-courae, a change in its mineral character, a stream of water, or even by leaders of ore which conDect the two parts of the lode. All such appearances will be carefully sought for and noted by the young miner who wishes to succeed.

Slides are displacements of lodes occasioned by thin veins, often of clay, which have a general bearing similar to that of the hole, but a different underlie. Such slides are by no means so common as heaves.

A kind of reversed slide, which throws up the lode, is not uncommon in the mines of St Agnes, Cornwall. As the disturbing vein contains ferruginous matter, much like the gossan found on the outcrop of many lodes, the slide itself is here frequently called a gossan. As a rule, slides are by no means so common as heaves — and they are often Btill less liked by the miner than heaves. The gossans of St Agnes, however, are in some respects a positive advantage, ?is they bring up the lode nearer the surface, where it can be more easily and cheaply worked.

At a meeting of the promoters of the Mount Eangitoto Silver Mine Company, held inHokitika on the lOtb mot., the prospootus of the proposed Company was submitted and approved. The capital is to be £30,000, in 6000 shares of £5 each. Seven hundred and fifty shares are reserved for Otago.