GOLD IN NEW ZEALAND.

Evening Star, Volume VII, Issue 1956, 12 August 1869, Page 2

GOLD IN NEW ZEALAND.

At a meeting of the New Zealand Institute, held at the Colonial Museum, Wellington, on the 24th July, the following speech was delivered by Dr Hector, the Colonial Geologist, on the above subject. We quote from the Wellington Independent :—

Dr Hector said he had been asked to explain the geological conditions under which gold had been found in the North Island. At the meeting of the Philosophical Society, on Saturday last, he had made a communication of a somewhat similar character, and without detaining the meeting longer than he could avoid, he 'would endeavor to convey to them in a concise form the information he himself possessed on the subject. In doing so, he must first briefly refer for the purpose of comparison to the conditions under which gold has been so abundantly found in the South Islands during the last seven years. He would confine his remarks entirely to the description of what had been observed by himself and others in New Zealand, and avoid the charge of indulging in theories—a charge which was too frequently cast upon scientific men by those who believing themselyes to be practical in their views were in fact relying only on limited and imperfect observation and vague assump- ] tions. i

In the province of Otago the alluvial gold is obtained on the denuded surfaces of metamorphic schists, and originally came out of some of these rocks. Metamorphic rocks are those which, originally sedimentary, have, during a long course of geological periods, been subjected to chemical agencies, and have, as a result, acquired a very different structure. All rocks deposited as sediments consist of the fragments

of other rocks aggregated in the form, of conglomerate sand or impalpable mud. Metamorphic action has had the effect of re-arranging the component parts of these rocks in the form of simple minerals. In the South Island wherever a large area of these rocks is axposed, in every depression or ravine gold may be found sometimes in enormous quantities, and without there being any distinct lodes or reefs to which its origin can be traced except in a few cases. In the district of Westland the alluvial gold has been found in the western slope only of the dividing range of the Island, and on this slope are found all the varieties of metamorphic rocks. The absence of gold on the eastern slope, where unaltered palaeozoic rocks are chiefly to be found, except in a few localities where there is a local re-ap-appearancs of the metamorphic rocks, has a remarkable significance. In the western district of the Nelson Province we find that the gold occasionally occurs under conditions which differ both from those in Otago and in Westland, being derived from rocks which are never auriferous in the south, but which have been locally metamorphosed by being involved in complicated dislocations of this part of the earth’s crust, accompanied by the injection of a variety of igneous rocks, and we are entitled to infer that the gold and other metals found in this rich mineral district have been introduced through their agency. Turning now to the North Island, we find an extensive area, about one-third of the whole, occupied by the unaltered paheozoic strata, which overlie the metamorphic rocks of the South. He then pointed out on a geological map the distribution of these rocks, indicating those portions of the map derived from actual observation. The rocks comprise sandstones and slates, frequently much indurated and jointed, but np trace of true metamorphic rocks have yet been discovered in the North Is» land. Gold has been found at tire Thames district, and in the neighborhood of Wellington, which are almost at the two extremities of the Islands, and doubtless many other intermediate places will yet be discovered. He then described the structure of the Colville Peninsula, on the western side of which the goldfields are situated, and exhibited a map showing the position and comparative area of each, calling attention to the very insignificant portion of the country which had as yet been tested by the miners. The rocks found in the Peninsula consist of lofty ridges of the slate rocks iuterbedded with which occur strata formed from very ancient eruptive rocks. Enveloping these ridges to a height above the sea of many hundred feet, are deposits of tertiary tufa, a stratified rock consisting of volcanic asli intermixed with ejected fragments of recent geological date. This tufaceous rock presents a marked variety in its character, in some localities forming a grey fine grained rock containing a large quantity of auriferous pyrites dispersed through its substance. This is the characteristic rock in which all the richest lodes have been found at the Thames. In all the auriferous areas yet examined igneous dykes occur, the j composition of which shows that they are allied to those found accompanying ! the dislocations previously ajhjdod as occurring in the South Islands ; and which no doubt account for the presence in these superficial rocks. He then proceeded to describe the hills between Wellington harbor and Cape Terawiti, in which district alluvial gold has been found in small quantities, and showed that they consist of the slate and sandstone rocks, and {hqt ye have neither the metamorphic rogks, of the South, nor the igneous dykes of the North to account for the occurrence of this gold; in every case, however, where gold has been found, it is associated with a peculiar variety of slate rock, patches of which occur in li ics not agreeing with the stratification. This rock is a friable cherty slate of the dee]) indigo blue color, traversed by innumerable" thread-like veins of quartz. In the neighborhood of this rock the sandstones are highly indurated and infiltrated with silica, so that in some cases hand specimens have been mistaken by good authorities for fine grain granite. We have, therefore, an indication of a chemical change in these rocks, and from observation it is found that the patches of rock so altered conform to lines of dislocation parallel with those which are found to occur ip the area. From the foregoing consider tious we find that in the south, when the gold is most widely spread we have the metamorphic rocks on the surface; in Nelson, dislocations, igneous dykes, and rocks locally metamorphised; at the Thames, igneous dykes; and at VV ellington, dislocations : so that in the three latter cases we have evidence that the existence of a communication between deep seated and chemically altered rocks and the surface is the essential accompaniment of the gold, lie mentioned, in conclusion, that

thermal waters escaping by such lilies of communication are generally admitted as sufficient to effect the transport of any metal.