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Report on the Geology & Gold Fields of Otago

Technological Museum, Melbourne, April 1875

page 155

To His Honor the Superintendent of the Province of Otago.

Technological Museum, Melbourne, April 1875.

Sir,—

I have the honor to submit herewith for your consideration the observations I made during my recent journey of inspection through the quartz mining districts of Otago. The instructions contained in your letter of the 21st December, 1874, were, that I should devote myself principally to an examination of the quartz workings, with the view of reporting generally on their geological relations, and more particularly in regard to any improvement I might be able to recommend in the mode of mining, crushing, or amalgamating, as would come within the scope and means of private enterprise; and further that, if not unduly trenching upon the time required for such examinations, I should pay attention to and afford information on the known occurrences in different parts of the Province of copper ore, cinnabar, antimony, and other minerals that came under my notice.

In obedience to these instructions, and mostly under the valuable guidance of Mr. D. MacKellar, the Secretary for the Goldfields, I have visited all the principal quartz mining localities of the Province, viz., Tokomairiro, Tuapeka, Waipori, Bendigo, and the Carrick near Cromwell, Arrow, Skipper’s Creek, the Rough Ridge, Macrae’s Flat, Shag Valley, Green Island, and Portobello, and besides examining most of the quartz reefs in work or opened, and the crushing mills existing in each district, I also made observations in certain localities on the auriferous drift deposits, and on the occurrences of copper ore, cinnabar, grey antimony, and on some of those—for Otago most important ones—of brown coal. Finding that in merely working out the copious notes taken during these inspections, very frequent repetitions would be unavoidable, more especially in my recommendations touching the working of the mines, crushing, and amalgamating, prospecting, etc, I thought it best to embody the principal observations and recommendations in a general report, throwing into appendices the special description of the mines, and certain information I have to afford on a profitable mode of burning brown coal for boilers, in a fireplace of novel construction, invented in Germany. Having, in forming my opinion on the reefs of the Province in their various stages of development, and more especially page 156with regard to their chances of carrying payable gold in depth, taken those of Victoria as my principal standard of comparison I think it but fair to state my reasons for so doing. It will be remembered that a celebrated, perhaps the best, authority on the occurrence of gold in matrix in the older rocks—the late Sir Roderick Murchison—propounded in the third edition of Siluria, when speaking of the Victorian goldfields, the hypothesis that the gold in quartz reefs would gradually decrease in quantity downward, and ultimately run out, or at least become unpayable to work at a limited depth. His reasons for this prognostication were solely based upon mining experience in other gold mining countries. Nevertheless, the miners of Victoria worked courageously and successfully deeper and deeper, and thus in later years it was incontestably proved that gold occurred there in payable and even large quantities at depths which certainly did not deserve to be called "limited," Sir Roderick, in his last edition of Siluria, fairly withdrew from his original standpoint, acknowledging that the results of quartz-mining in Victoria put former general experience at fault, and inferring that quartz reefs of similar character and geological relations might offer similar chances of success in depth.

In more recent years the results of deep mining in Victoria have still more fully established the downward extent of the gold, and several reefs are there at present being profitably worked at depths approaching 1000 feet. Considering all former experience in gold mining in the matrix in other countries (California excepted), everything concerning mineral character, structure and behaviour of the auriferous quartz reefs of Victoria in depth, is therefore new to miring science, presenting, as it were, a new experience, fairly applicable in judging of the chances of similar quartz-reef occurrences elsewhere. And as I found the reefs of Otago to exhibit this resemblance—in many respects a very close one—to Victorian reefs, I shall, I think, be considered justified in basing my opinion of their prospects upon certain features exhibited by the latter in similar stages of development.