Geological and other Reports
It will be remembered in my previous reports, that with the exception of finding gold beneath the tertiaries of the westward of the Province, I had reduced the districts in which gold might be found, to the inclined rocks of the main range of Rimutaka, Tararua, and Ruahine, and its outliers at Cape Palliser and the Kaimanawa range, and to the “drift” derived from them.
Now that we have some slight evidence as to the age of these rocks, it remains to consider its bearing upon the gold question.
The highest authority in these matters, Sir R. Murchison, lays down as follows:—
“Appealing to the structure of the different mountains, which at former periods have afforded or still afford any notable amount of gold, we find in all a general agreement. Whether referring to past history, we cast our eyes to the countries watered by the sources of the Golden Tagus, to the Phrygia and Thrace of the Greeks and Romans, to the Bohemia of the middle ages, to tracts in Britain which were worked in old times, and are now either abandoned or very slightly productive, or to those chains in America and Australia, which, previously unsearched, have, in our times, proved so rich, we invariably find the same constants in nature. In all these lands gold has been imparted abundantly to the ancient rocks only, whose order and succession we have traced, or their associated eruptive rocks. The most usual original position of the metal is in quartzoe veinstones that traverse altered, Palæozoic slates, frequently near their junction with eruptive rocks. Sometimes, however, it is also shown to be diffused through the body of such rocks, whether of igneous or of aqueous origin. The stratified rocks of the highest antiquity, such as the oldest gniess and quartz rocks (like those for example of Scandinavia and the northern Highlands of Scotland), have very seldom borne gold; but the sedimentary accumulations which followed, or the Silurian, Devonian, and Carboniferous, (particularly the first of these three) have been the deposits which, in the tracts where they have undergone a metamorphosis or change of structure by the influence of igneous agency, or other causes, have been the chief sources whence gold has been derived.”
You will perceive from the above quotation that, supposing our old rocks to be even as high in the scale as Carboniferous, Sir Roderick holds out a hope of finding gold in them.
I may give a still more favourable opinion on the authority of Mr Jukes, whose work on geology is perhaps the most useful and practical manual extant on the science. He states,—
“The supposed relation between mineral veins and the age of the rocks they traverse is probably an accidental one only. Mineral veins may be expected in all highly indurated and greatly fractured rocks, whatever may be their geological date. Neither page 7 does the connection between mineral veins and the occurrence of igneous rocks appear to be better founded, than on the probability that igneous rocks will be most likely to be found in the same indurated and fractured districts which we have seen to be essential for the production of mineral veins.”
Having thus, on the authorities of Sir R. Murchison and of Mr Jukes, shewn that there was a prima facie case for the search for gold in our old rocks, I will proceed to point out why we need not expect alluvial or “drift” diggings among them, and will then consider the chances of finding gold in the rock itself.
The main reason why we need not expect to find gold diggings in, or derived from, our Palæozoic rocks, is simply from the result of experiment.
As in careful washings of the gravels of the Hutt, the Wai-o-hine, the Ruamahunga, and the Otaki, (performed under my inspection in March last), no trace of gold was found, it would seem absurd to expect any payable “diggings” within the same ranges of mountains which are traversed by these rivers.
Next, although Sir Roderick Murchison includes the Devonian and Carboniferous groups within those in which gold may be found; yet, practically, no payable gold has been worked, at all events in the Southern Hemisphere, that is not in, or has not been derived from Silurian rocks, perhaps I may say from lower Silurian only; and if our rocks should prove to be higher in the scale than these, our chances of workable gold are reduced.
It is however certain that the rocks in the immediate vicinity of Wellington contain some gold, although hitherto not found in payable quantity. I need hardly instance that found at Terawiti.
As it appeared a difficult point to decide whence the little gold there obtained in the gravel was derived, I took advantage of a similar discovery on the Karori road, close to this town, to send some of the underlying rock to Sydney for analysis, and have received the following report from the Sydney Mint, shewing that there is some gold in the rock itself.
“Assay for Gold of three samples of rock received from Rev. W. B. Clarke.
“These samples all bore the No. 68.”
“The first sample tried, being the softest and lightest colored, contained a minute trace of gold, but not exceeding a few grains to the ton.”
“Second sample tried contained no. gold.”
“Third sample tried contained no gold.”
These results are not encouraging, but still they tempt to further investigation. As the indications of gold are principally in the immediate vicinity of Wellington itself, enquiry is comparatively easy; the rocks are ready of access and tolerably soft, and a small per centage of gold might yield a profitable return.
What is wanted for this enquiry is not a “prospector,” but a good analytical chemist, assisted by a competent miner. In this investigation no powerful quartz lodes need be expected, but sundry rocks will be found seamed with thin quartz veins, and it is just possible that these rocks may contain a notable quantity of gold diffused through them. Towards the central part of the range, the rocks that are in sight, are less crystalline, and less likely for gold than those nearer Wellington.
I have before pointed out that the grand gold bearing rocks of the Middle Island are the micaceous schists lying to the westward of the Eastern ranges; and I must again repeat, that, considering the general parallelism of the old rocks of New Zealand, analogy would lead one to expect to find the gold rocks, the above mentioned mica schists, towards the west of the Province, where, however, on account of the great thickness of tertiaries, it is impossible to determine, without sinking, what may lie beneath. I would not however advise a neglect of the few gold indications of the Eastern ranges, but, I consider a chemical investigation, as above recommended, ought finally to exhaust the subject.page 8