Geological and other Reports
Wellington, November 30th, 1861
Sir,—I have the honor to submit the foling theory for the discovery of gold in this Province, with the facts and reasoning on which it is founded; and which, whether of value or not, will, I hope, prove of interest.
A few days ago, I rode to the Karori and Waireka valleys near Cape Terawiti, and, although the men who had been at work at the diggings there were absent, and I was therefore unable to obtain various details, yet I found an inspection of the valleys, highly suggestive as to the direction in which a search for gold should be prosecuted.
There is nothing new in the mineral character of the rocks in the Terawiti district—they seem to consist of a slaty rock, laminated with veins of quartz; of the usual hard green crystalline sandstone, veined with thin threads of quartz; some hornstone or chert, indicating probably the no great distance of plutonic rocks; some serpentine; and a slaty rock containing iron pyrites, which may possibly belong to the first named stratum, but which seems to me identical with specimens of the bed rock of Tuapeka, which I have seen. All the above named rocks are repeated at various points of the Rimutaka and Tararua ranges, and therefore, if gold be found at one point, the inference is that it may be expected in others. The same rocks, or some of them, may be seen near the printers' flat in Makara, at various points on the Karori road, between Ngahauranga and Pitone, on the Rimutaka road, and elsewhere. One schistose rock which I have not previously observed, is exposed in the cutting of the new Makara road; it appears to be near the top of the series and looks a likely rock to search for fossils.
As a general rule, the lower the bed of rock and the nearer to the central fires, the more the rocks seem to be rendered crystalline, traversed by veins and possibly transfused with gold. It would seem as if the force of the plutonic rocks had been sufficient to act so far, but not to force themselves to the surface.
It is evident that the semi-metamorphic range, which here constitutes the main range of the Island, and which we must be content to call grauwacke, until the discovery of fossils shall enable us to assign to it a definite geological age, does contain some gold. Gold is found in it at Terawiti, in the Upper Hutt, and in various other quarters, and therefore, after all, it may be an auriferous range—discovery also may soon show that it answers Sir Roderick Murchison's description of gold constants, viz., silurian rocks, broken up by granites, porphyries or greenstones, inasmuch as I have found the eruptive rocks in the East Coast country, and I hope before long to find them in the main range itself; added to this we find serpentine in many parts of the range, and although few if any well defined quartz reefs or lodes are found, yet irregular veins of quartz, large and small, are very common. On the other hand, the quantities of gold yet found are small.
In considering the geological aspect of the district one inquires where is the most likely place to look for gold in quantity, and one naturally turns to the enormous development of “drift” gravel on both sides of the range, and in some of the valleys within it. After observation here and in the Middle Island, and duly considering the inadequacy of any other force to produce the effect, I am bound to suppose the existence of large glaciers, in every valley of our main range, during the glacial era, and at a time when the plains were submerged and the mountains stood as islands in the ocean. The moraines, the floating ice islands depositing their loads as they melted, have doubtless formed the mass of drift, which lies horizontally on the West Coast from Wainui to Rangitikei and beyond; and the sea has there spread the gravel regularly and evenly. The drift comes to the surface at Otaki and Rangitikei, and probably underlies the alluvium and the sand hills at the Manawatu, the lower part of the Rangitikei, and elsewhere. It will be found in small and irregular quantities in the different narrow valleys, including those of Waireka and the Karori stream, but denuded in places by the action of the streams. The Upper Hutt and Pakuratahi valleys have their deposits of drift, and probably in the Lower Hutt it will be found below the alluvium of the page 4 river; and in the Wairarapa this deposit is of immense extent and uncertain depth. It will be necessary to discriminate between the gravel of the drift and that which underlies the tertiary limestone; the former, in the Wairarapa, probably shows its Eastern limit where it rests on the grauwacke rocks, on Mr. Bidwell's run, while crossing the Ruamahanga the latter is seen resting on the tertiary shale. At the glacial epoch, when the gorges of the mountains were filled with ice, it is natural to suppose that the summits of the mountains were covered with snow, and I should therefere attribute the apparent alluvium of Karori, Porirua-road, and other table lands of the mountain range to a drift from melting snow.
There appears to be this difference between the drift of New Zealand and that of Europe, that in the former we have not yet found those large blocks of granite and other rocks, transported from their original locality for great distances, sometimes hundreds of miles, and of which the granite boulders used for building purposes in St. Petersburgh, and one of which forms the pedestal to the statue of Peter the Great, are good examples.
Considering therefore the enormous degradation and wearing away of rock, equal to the work of any number of quartz crushing machines, which is indicated by the drift of this district, it is evident that if the rocks acted upon contained any gold, that gold must be looked for at the bottom of the drift. From its specifing gravity it would be sure to find its way down until it found the bed rock to rest upon. For these reasons I would suggest that it is desirable that the drift should be bottomed in various places, to ascertain whether gold does or does not exist there;—this may be a serious undertaking and one requiring both capital and skill, for the chances are that the miners would have to contend with much water; but on the other hand, should the search prove successful, the results would probably be enormous and lasting, from the great extent of ground covered. What the depth of the drift may be, can be best proved by sinking a shaft; in some places, as at Rangitikei, it is evidently of great thickness; in others it may not exceed many feet.
Although I have been unable to get any details as to the quantity of gold found at Terawite, I have yet seen enough of the metal to show that it certainly exists in some quantity, and moreover, the specimens I have seen are of a heavier and more nuggety description than is usual in New Zealand diggings. The holes have been sunk in the drift, and I am given to understand, that in consequence of the quantity of water, the miners have never as yet been able to bottom their holes, and that consequently the ground has not had a fair trial. Whether it would not be wiser to sink through and bottom the drift in more open localities than the Waireka gully, is a question which I should like to hear answered by a practical miner.
I have lately expressed a doubt as to gold being found in any quantity in the grauwacke rocks of the Canterbury Province, which are identical with those of this range. An inspection of the Terawiti valleys, leads me to suspend my judgment on this point. In conclusion, I arrive at the following results:—
That gold in this Province is to be sought for at the bottom of the drift, where it rests on the older rocks.
That a search in the direction indicated offers a fair and reasonable prospect of success.
I have the honor to be,
Your most obedient servant,
James C. Crawford.
P.S.—It is to be supposed that the drift extends northward into the Province of Hawke.