OIL-SHALE DEPOSITS

Dominion, Volume 37, Issue 97, 20 January 1944, Page 4

OIL-SHALE DEPOSITS

Investigation In South

Island NEVIS POSSIBILITIES

Wartime demands for fuel oils, with restricted facilities for shipping from the usual overseas .sources, revived interest in the possibility of New Zealand’s being able to secure independent supplies from its own deposits of shale rock.

The director of the geological survey branch of the Department of Scientific and Industrial Research, Dr. G. Henderson, delegate one of his staff, Mr. R. W. Willett, to investigate the Dominion's most extensive deposits, those in Otago and Southland.

The mention of shale immediately brings to mind the name of Orepuki, where there is a field of considerable extent'that has been worked in the past. The location of the field, however, makes it difficult to obtain any reasonably accurate idea of the number of tons of oil-bearing rock existing there, and, in any case, exploitation would involve serious mining engineering problems, as has been proved by the experience of those who have .attempted to work the fields in the past. There are, however, other fields In the district, notably at Nevis, near Cromwell, Cambrian, near St. Batharis, Freshford, near Waikaia, and Waitatl, near Dunedin. It is these fields that Mr. Willett deals with in his report, published by the New Zealand Journal of Science and Technology. From the exploitation point of view, says Mr. Willett, the Nevis deposit offers two great advantages over any other in the Dominion —the enormous quantity available and the absence of overburden, which would permit open-east-mining methods. The deposit occupies an area of 2200 acres, with a minnmum of 90,000,000 tons of rock available above creek level and a probable maximum of 1,898,000,000 tons. Mr. Willett divides the area into five blocks, the first three of which he regards as the most suitable for exploitation because of the relative freedom from overburden. These three blocks contain a probable maximum of 605,619,400 tons of rock, assuming that the shale extends to a depth of 500 to 800 feet below the Nevis River. Of this quantity about 74,518,500 tons is available for immediate extraction, since much of the area is free of even soil and tussock and presehts large bare areas of oil shale.

If exploitation is to be proceeded with, says Mr. Willett, a drilling programme to determine the thickness below creek level and confirm estimated maximums would be advisable. But the amount of shale above creek , level is sufficiently large to commence exploitation without further geological work or drilling. At 500 tons a day such a quantity of rock has a life of about 400 years. The disadvantage.of the Nevis deposit, Mr. Willett says, is its low .oil yield. Eight samples collected at various points over the three blocks gave an average yield of 13.2 gallons of ojl to the ton. the sulphate of ammonia yield. being 16.71 b. a ton. Discussing the other three deposits, Mr. Willett says that Freshford is the only one offering any possibility of exploitation,. and that is dependent on a greater extent of oil-shale than is at present known being proved. The Cambrian deposit. though composed of the richest oil-shale in (New Zealand (55.6 gallons a ton) is too small to warrant exploitation. Available tests at Fresh ford show the average crude oil content of the rock ro be 43 gallons a ton. but Mr. Willett states that, unless drilling revealed further beds of oil-shale extending beyond the present proved area, development of the deposit would be uneconomic.