THE GOLDFIELDS OF NEW ZEALAND.

Otago Witness, Issue 1921, 14 September 1888, Page 12

THE GOLDFIELDS OF NEW ZEALAND.

Professor Hutton read a paper on ° The Goldfields of New Zealand " at the meeting of the Philosophical Institute at Christchurch, and from the report of the Lyttelton Times we make the following extracts : — , The Professor said he proposed to speak of the subject purely from a scientific point of view. The great gold-bearing districts of New Zealand were three in number — tbe Otago goldfields, the Westland and Nelson goldfields, and the Hauraki or Thames goldfields in Auckland. There was also a small goldfield at Orepuki, in Southland, and another small one in Marlborough, but of those it was not worth while to treat. THE ORIGIN OF GOLD. Before proceeding to describe the goldfields of the colony, he would give a general outline of the present scientific theory of the origin of gold. Gold in minute quantities was very widely diffused — firstly, in the augite, hornblende, and mica of volcanic or igneous rocks, in which we must look for its original source; secondly, in sea water, together with a number of other metals — silver, lead, copper, and zinc. The gold in the sea was derived, like othercmineral constituents of the oceau, from the igneous rocks, which were decomposed by the action of air and water. ExceediDgly small quantities of gold were found in the sea, whence- being added to as the gold in the ocean must be continually, it was evident that sea water could not hold much gold in solution. Ifc was therefore deposited precipitated at the bottom of the sea along with mud, &c. We should expect to find gold distributed through slate rock— hardened mvd — almost universally, but at [present we could not detect it. Gold, to be worked to pay, must have been concentrated, as it was in the reefs or lodes of goldfields. It would be well to consider, therefore, what were the conditions necessary to the concentration of gold. Speaking broadly, there were three kinds of geological structures, or rock masses, in which goldfields occurred — firstly, (■chiafcs, foliated cryhtalline rocks; secondly, elates, but always when they are in close proximity to igneous rocks, granite, &c. ; thirdly, I certain volcanic rocks. One necessary condition of the formation of all goldfields was heat, not necessarily great, but extended ' over a long period of time. The reefs were always formed in fisßures — the rocks were split, and the material of the reef introduced. It was generally accepted now by geologists that these fissures had been formed bit by bit. The rock had been opened a little, and a little of the material of the reef forced in, if below sea level, by the waters of the ocean. The process was repeated till the reef, even if large, formed, without the rock ever having been very widely opened. The rocks, therefore, must have been continually split by earthquakes; .and there could, be no goldfields without earthquakes on the surface. Goldfields were found either in mountainous districts or in districts which had once been mountainous, but in which the rocks forming the mountains had been decomposed. The filling of the fissures had been accomplished by the means of water— heated, alkaline, or acidulated waters. THE OTAGO GOLDFIELDS. In describing the three fields he would begin with the oldest, that of Otago, in which the rocks were schistose. The gold in these schists occurred principally in two different ways. First, iv the schists themselves. Mica schist was a rock which consisted of little layers or bands. At one place, at Alexandra, the gold was found in these layers in such quantities that when the stone was crushed it yielded 6dwt to the ton. The quantity of stone, however, was not great.. Again, the gold was found in lodes or reefs. Thete lodes were of mullock, iv which were scattered pieces of quartz, anil the gold was found in both quartz and mullock. Of this character were the auriferous deposits of the Arrow, the Carrick Range, and the Bendigo. Iv some of the lodes the mullock and quartz were founds iv bands lying longitudinally in the reef. The reefs of Lawrence, Tokomairiro, and VVaipori were of this description. The Marlborough goldfield wa3 of the same character as those of Otago, WEST COAST AND NELSON. The goldfields of the West Coast and Nelson were composed of slates and granite. Two bands of granite formation ran through the country. Between these bands were slates, and in these slates, which probably belonged to the carboniferous period, were found the goldbearing reefs. These reefs were very little known to the scientific world as there was no scientific report on them. So far as he had seen they were very different from the Otago reefs. The quartz very largely predominated over the mullock — iv fact the reefs were often nearly pure amorphous quarts — whereas in Otago the mullock predominated over the quartz. The golil, iv both the Otago and Westland fields, was of the same character, very pure, with occasionally a small admixture of silver and copper.

THE AUCKLAND GOLDFIELDS.

The Hauraki, or Thames, goldfields were much smaller in extent than the others. In them there were large areas of slate, covered with volcanic rocks, which were of the tertiary age, aud had evidently been formed over the slate in a melted state. The gold was in the volcanic rocks and not in the slates, though slates were of tbe same kind as those which bore gold on the West Coast. A peculiarity of the gold-bearing volcanic rocks at the Thames, was that thehornblende and augite had been altered — changed into another; mineral called chlorite. The same thing had happened to the volcanic rocks of the Comstock in North America, and to those of Transylvania in Hungary. The presence of chlorite seemed a necessary condition of the presence of gold in volcanic rocks. Gold occurred in the rocks of . the Haur,aki goldfields in four ways — first, in thin quartz veins, the smaller the more irregular ; secondly, in quartz lodes, tolerably regular, the greatest of which was 14tt in width ; thirdly, in what were called segregation lodes, in which the whole rock was infiltrated with quartz; and fourthly, in what were known as brecciated lodes. The gold differed from that of the West Coast of Otago, being largly alloyed with silver.

ALLUVIAL GOLDFIELDS.

Alluvial goldfields were derived from the breaking down of the reefs. The alluvial goldfields in Otago were unusually large, though the reefs were not very numerous. A large proportion of the gold found in the alluvial goldfields in Otago probably came from the quartz layers to whioh he had alluded. In Otago there had been a great deal of denudation of the rocks, as

.there had also been on the West Coast, where the alluvial gold came fromu the quartz reefs. At Hauraki there had not been much denudation. This must always be the case in a tertiary field, and consequently there was but little alluvial gold there. Beach gold had been simply carried from the goldfields to the sea by the rivers. VALUE OF SCIENCE TO THE MINER. In referring to the value of scientific knowledge to the gold miner, the professor stated that Sir Roderick Murchison's prediction that gold would be discovered in Australia was a mere fluke. Sir Roderick had seen gold only in the Ural Mountains, where he saw it in slate. He was shown a piece of 3late from Australia, and said, " That's like the slate from the Ural ; there'll be gold there." Science could not tell exactly where gold would be found, as might be seen on considering the fact that the rocks of Cornwall and of Westland were similar in character; but tbe one produced copper and tin, with no gold, the other gold and little else. Geology, however, could say where gold would not be found— i.e., not in volcanic rocks without chlorite, not in undenuded regions, not in denuded regions in which no heat had been developed in the neighbourhood. Gold would not bo found in great quantities on this side of the Southern Alps, the eastern sides of which had not been denuded. The prospector, however, practically came before the geologist, and while the latter was making his necessarily careful and long examination the alluvial geld was discovered and revealed the presence of the goldfield. In answer to Mr E. Ford, Professor Hutton said that the Blue Spur deposit was an old alluvial deposit which had been preserved by falling into a 'lake. It now stood up as a ridge, because it had been denuded. In answer to another question Professor Hutton said the three conditions in which gold was found in New Zealand were identical with those under which it was found in other countries. He knew of no other conditions. No geologist now believed in the fuded quartz theory.