THE GEOLOGY OF MINES AND MINERALS.

Otago Witness, Issue 2499, 5 February 1902, Page 70

THE GEOLOGY OF MINES AND MINERALS.

Et Pkofessoe Pakk,

Chapter YH.

PROSPECTING.

Scope of Prospecting. — Surface prospecting means the search for -i d .itions of a mineral. In a new distiiet tlie prospector will naturally confine his operations at first to a search of the gravels and sands in the bed of the streams, and afterwards to an examination ox all conspicuous rocks, outcrops, dyke.-, and escarpments. The locating of a gold-bearing vein from the trail of " colours "' of gold found in the bed of a stream is a work often requiiing much patience and perseverance.

A lode or «cam is more ea§ily located in a broken, rocky country than in a flat-lying or undulating area. In the former, the narrow rocky defiles and gorges form natural cross-cuts, which often serve to expose the character of the country for many hundreds of feet below the origin level. In low-lying country, the outcrops of veins and seams are frequently obscured by a heavy overburden of soil, clay, or gravel, which renders prospecting slow, expensive, and, to a certain extent, uncertain.

The search for alluvial gold or stream tin is confined to an examination of the sands and gravels in the bed, banks, and terraces of streams. The discovery of rough gold with, adhering particles of quartz indicates the proximity of a gold-bearing vein. In this case the trail is followed up by frequent examination of the alluvia by panning and washing in the ordinary miner's prospecting dish. Sometimes the tiail will lead up a side stream, which is, in turn, followed, until the vein shedding the gold is discovered. A lode of tin should be located in the same way.

The indications -which guide the experienced prospector are

(1) Form of Ground. (2) Colour of ground. (3) Decomposed outcrops. (4) Presence of springs. (5) Character of vegetation. (6) Old workings and ruins, and the native names of places.

Form of Ground. — When the mineral is harder than the surrounding country, it will form projecting outcrops in the way that hard rocks form ridges and escarpments and soft rocks are cut into hollows.

The great Mother Lode of California has a conspicuous outcron forming the crest of ills, so thai it can be seen for milet.

The great Premier lode at Te Aroha can be traced for miles on the flanks of the mountain, standing up conspicuously like a great dyke.

The Waiotahi lode at Thames can be traced for miles along its outcrop, its blanched quartz forming a prominent object in the distance.

The great Tokatea lode at Coromandel presents a wall-like outcrop traceable by the eve for mile«.

The Broken Hill lode at Silverton in New South Wales was traceable for 14 miles by the outcrop of huge black crags of ferruginous quartz, associated with ironstone, pyrolusite and other minerals.

Colour of Ground. — The presence of iome ores imparts a characteristic colour to the adjacent rocks or soil. When Gamier was exploring in New Caledonia in 1863 he found that the green colour of the rocks was due to coatings, veins, and lumps of a hydrous silicate of nickel and magnesium, whicu -was afterwards largely worked.

Copper minerals produce green, blue, and red stains on rocks. Iron gives a red or brown colour ; manganese, a black colour, often with ; bluish tinge ; cobalt, a pink ; and cinnabar a bright red or vermilion.

Decomposed Outcrops. — By long-con-tinued exposure to atmospheric agencies and the action of descending waters, the outcrops of iron, copper, and silver sulphide lodes are often oxidised by removal and replacement, and so altered as to bear little resemblance to the unaltered product which vrill generally be found at a greater depth. The iron sulphides are oxidised first to sulphates and then to oxides, while the copper is removed by water in the form of soluble sulphates, or is oxidised to caibonates, which stain the rocks green and blue. Silver sulphides are altered to the chloride near the surface.

In most sulphide lodes, iron is the predominating constituent, and its oxidation generally results in the outcrop assuming a porous, honey-combed appearance, the removal of the sulphide leaving cavities ■which are only partially filled with, oxide. The ferruginous solution flowing from the outcrop stains and discolours the burroundmg rocks and soil.

Such iron-stone outcrops aie knenra as " gozzan "in Cornwall, " iron-hat " in Germany, and " ironstone blows " in Australia. The nature of a gozzen varies, with the

character of the original sulphide ore^ody.

If much quartz be present, the result is a cavernous and cindery, rod or browncoloured rock ; but if the vein or ore-body be composed principally of iron pyrites, the gozzen will consist mainly of ochre and brown hematite, often in botryoidal and stalactitic xorms.

The oxidation and leaching of lode-mat-ter has often proceeded to a depth of 500 ft below the surface outcrop, in some cases far below the present ground water-level. Sometimes there is a sharp line of demarbetween the oxidised and unaltered portions of a lode, but more often the passage is gradual, the sulphides making their appearance at first in detached nodules, bunches, and small lenticular masses, which gradually become more abundant "with, increasing depth.

A gozzan is always an indication of a lode below, and, for this reason, forms a valuable guide to the prospector.

Gozzan outcrops should be carefully sampled and assayed, as they may contain valuable minerals whose presence cannot be detected by panning.

The valuable gold and silver-bearing lodes of the Hauraki goldfields in Auckland give no indication of their value by crushing and panning. The gold exists in such a finely-divided state that a colour is rarely seen in the ore, and the value can only be ascertained by careful sampling and fire a,«say. The rich, unoxidised telluride ores of Western Australia possess no physical feature of a striking character to indicate their great value, and when tested by the prospector's ready method of rough crushing and panning would appear valueless.

Each mineral possesses certain characteristic indications peculiar to itself, and .must be considered separately. Thus an iridescent film or layer of oil on a pool of water, or emanation, of carburetted hydrogen, has directed attention to the •existence of' petroleum in the vicinity. Brine springs point to deposits of salt, and chalybeate springs to iron, though not necessarily of commercial value. Puffs of I steam or the smell of sulphuretted uydrogen in a volcanic region may point to the existence of sulphur. At Rotorua and White I&land in New Zealand extensive deposits of sulphur are found around the numerous fumeroles, both active and extinct, and at both places the odour of sulphin*etted hydrogen is plainly perceptible long before the deposits are reached.

Character of Vegetation.— Different plants require different kinds of food, and to a certain eitent the composition of the soil determines the character of the vegetation Thus, the Nelson mineral belt, which con&ists of olivine and serpentine, supports only the scantiest vegetation. It stretches in a . continuous line from Dun Mount to Red Hill, a distance of over 30 miles, and from any commanding position its course can be traced through the densely-wooded country as a treeless, barren, dim-coloured belt, resembling a strip of country blighted by lightning.

Dr Raymond says that the calamine pansy of Rhenish Prussia, known to botanists as "Viola calaminaiia," is peculiar to the calamine-beanng hills of Aix-la-Cha-pelle. Analysis has revealed the presence of zinc in the plant and in the sap.

The lead plant, "Amorpha canescens," is a low shrub from lft to 3ft high, covered ivith a hoary down. It is most abundant in Michigan, Wisconsin, and Illinois, and it is believed to flourish best in soil containing lead.

Prospectors in Estramadura are guided in the search for phosphorite by a creeping plant named " Convolvulus althaeoides."

Shoading. — Loose pieces of lode-stuff found about the surface are known in Cornwall as shoad-stones ; and shoading is the term given to the process of tracking them to their source.

Spearing or Piercing — Kauri gum in New Zealand and phosphatic nodules occurring in clay in South Carolina are found by stabbing with a steel rod, called a spear. When a piece of gum is located it is dug out with a spade.

Springs. — The layer of clay, or flucan, on the •walls of a lode is often impervious to "water, ■which thus accumulates behind the lode, and escapes by rising to the sur-face-outcrop. A lodgment of -water on the course of a lode is of common occurrence in mme c , and when driving a cro&scut a flow of water is often an indication of the proximity of a lode, or ore-body.

O^d Native Workings. — Old -workings, spoil heaps, -»nd ruins have often led to the discovery of valuable minerals, and <tre always worthy of a careful examination. -l ne discovery of ruins in Mashonaland containing smelting furnaces led to the finding oi ancient gold mines, some of which have developed into productive mine?. M The gold ornaments worn by natives have sometimes led to the discovery of gold.

On the other hand, new processes may be the means of enabling an abandoned mine to be profitable. The inlroduction of the cyanide process has enabled many mines working at k loss to pay jteadgr

dividends; and many large accumulations of tailings at mines in New Zealand, Victoria, Queensland, and United States are now being worked at a profit.

Dipping Needle. — In the case of magnetic iron ore, this is a safe guide. It is used in Sweden to locate deposits of this ore, even when covered by some thickness of drift or depth of water.

The needle is suspended, so as to dip in any direction.. The greater the mass of magnetite, the steeper is the dip of the needle.

Qualifications of Prospector. — In addition to a knowledge of geology and rocks, the prospector should be able to distinguish; all the common valuable minerals and their ordinary associates, and be able to apply tests in the field to confirm his opinion.

Coal Prospecting. — The prospector for coal by boring requires a general knowledge of the geology 01 the country, and a special knowledge of the distinctive \features and fossils of the coal measures. The prospector, should be provided with the best geolfljical maps obtainable.

Bering. — If surface examination fail to give a trace of mineral sought, and there remains a reasonable expectation of nnding it at a depth below the surface, drJYing, sinking, or boring may be undertaken. The two former are- more expensive, but safer guides than boring, which is rarelyemployed as a searcher for a mineral, but merely to confirm indications presented at the surface.

Securing Title. — Having located a mineral deposit of a promising character, the prospector should secure a legal title to the ground. In the United States two classes of claim are granted — namely, placer and vein. The difference in the grants in the two cases, besides a question of acreage, is that the mining of ore within placer ground is confined to the vertical planes through the boundaries of the claim ; while vein deposits may be followed along their dip throughout the entire depth, even if they depart from the perpendicular so as to extend outside the vertical side lines of the claim. The miner's right is determined only by the vertical planes through the end lines, which should, therefore, be properly pegged at the corners and intersections.

Iv the United States, locations 1500 ft in length along the line of lode are granted to the discoverer of .the lode, and in different States the surface right of from 25ffc to 3uoft on each side of the lode, to give access to the claim, and for convenience of working. There is no rent or labour obligation, but from year to year after the registration of the location certificate, the prospector must expend annually a sum of £40 as evidence of mining intent and occupation. A number of claims contiguous or otherwise may be pegged out by the same prospector, so long as he shows intent to mine by sinking a discovery shaft 10ft deep on each claim, and after the first year shows the necessary assessment work. New Zealand Titles.— ln New Zealand and most of the Australian colonies, there are three classes of claim — namely, prospecting licenses for minerals other than gold, gold-mining claims, and alluvial claims.

Classes of Claims. — Claims are divided into the following classes, according to size : — 1. Ordinary claims. 2. Extended claims. 3. Special claims. Each class of claim is sub-divided as follows, according to the nature of the ground and of the operations: — 1. Alluvial Claims : Meaning claims worked in alluvia, not being dredging or river 'claims. 2. River Claims : Meaning claims worked in the bed or on the banks of watercourses, not being alluvial or dredging claims. 3. Dredging Claims : Meaning claims worked by dredges. 4. Quartz Claims : Meaning claims worked on quartz or other lodes', or ■ements or other deposits by means of crushing, roasting, or chemical process. 5. Sea-beach Claims : Meaning claims on the sea-beach, arid* extending seawards, however worked. Areas of Claim?. — The area of alluvial claims shall not exceed: — 1. Ordinary Claim — One acre, if held under license, and 10,000 square feet if held otherwise than under li-

cense. 2. For an Extended Claim — Five acres. 3. For a Special Claim — One hundred acres. The area and form of dredging and river

cljims are as follows : — 1. For ordinary claim the area shall not exceed one acre, and not comprise more than three chains of the course of the watercourse. 2. For extended claim, not more than five acres in area, and not more than 15 chains on course of water-oaurWb

' ' ~Z. Tor a special claim, area not exceeding t 100 acres-, nor more than a mile on course of water-course. The area and dimensions of a quartz claim are as follows: — 1. Ordinary Claim. — One acre in area, and not more than 200 ft on length of supposed lode. 8. Extended Claim.— Five acres in area, and not more than 500 ft on line of lode. 3. Special Claim. — Area shall not exceed 100 acrea. Marking of Claims. — At every angle or corner of each boundary line and at points not more than 500 ft apart shall be erected pegs of substantial material, standing not less than 3ft above the ground, and being not less than 3in square or less than 3in in diameter. Starting from each peg and extending for not less than sft there shall be cut a trench not less than 6in wide and deep. I Cairns of stones or mounds of earth may be used where timber is not available, having in each case a height of 2ft and diameter of 18in. _

The peg or cairn or mound shall bear some distinctive letter or mark, together with the initial letters of the mining privilege — i.e., 0.C., for ordinary claim; E.C , for extended claim, and S.C., for special claim. Beach claims need not be marked below water mark. Labour Regulations. — For the purposes of Section 85 of " The Mining Act, 1898," the number of workmen to be employed by the holder of a claim shall be in the proportion of not less than one workman -for every complete six acres of area during the first year ; and one workman for every complete four acres for the second year ; and one workman for every complete three acres thereafter Rents. — The rent for extended and special claims, other than Native land, is as follows : — First Year — 2s 6d per acre, or fraction thereof. Second Year — 5s per acre, or fraction thereof. Third Year — 7s 6d per acre, or fraction thereof. For Native land the rent is Is per acre, or fraction thereof ; but the licensee shall take out a £1 miner's right in respect to every person employed on. the claim. Duration of Title.— The claims Te granted for 42 years, and can generally be renewed on application to the Warden's Court. Prospecting Licenses for Gold. — There are two classes of license, known as ordinary prospecting licenses and tunnel prospecting licenses. Ordinary prospecting licenses are granted over areas up to 100 acres, at an annual rental of Is per acre. A tunnel license shall not exceed 150 yards on each side of the proposed tunnel for its whole length. Title for two years, and may be renewed from year to year afterwards ; fee, £1. Mineral Licenses. — These are granted to prospectors for minerals other than gold. The area shall not exceed 520 acres. Annual rent, 2s 6d per acre. Miner's Rights. — When prospecting on Native land the prospector should be provided with a £1 miner's right, and when on Crown lands with a 10s right.