GOLD SURVEY

Rotorua Morning Post, Volume 2, Issue 543, 29 May 1933, Page 2

GOLD SURVEY

IN CENTRAL OTAGO work of geophysicists .> in assessing . prospects f - " BURIED RIVER GUTTERS. One of the purposes of the • geophysical survey which has just been carried out in Central Otago has been to aid the prospector and miner to .sort 'out likely gold-bearing country from parts not so likely to yield gold. Mr. H. F. Baird, of the Christchurch Magnetic Observatory, a member of the survey party, returned home on Saturday evening iafter five months in Central Otago. He was wqrking with Mr. E. O. Macpherson, Government mining geologist, Mr. N. Modriniak, geophysicist, of the Department of Indu,s'trial and Scientific Research, while assistance was given by students from -the University of Otago. The party worked mostly about the Cromwell district. Mr. Baird said that when considering the position of the gold-mining industry in New Zealand as compared with the same industry in other eountries one saw striking similarities in the occurrence of gold. Phenomenally rich strikes of gold have so far been easily obtained by very shallow working. That gold seemed to have eome from deeper leads. The old workings did not strike those deep leads to any great extent, alth'ough some of the successful dredging- operations probably did get many of their rich returns. from such deep leads . as pre-sent-day river courses uncovered. It was reasonable to assume that some old river courses carried alluvial gold, but owing to various changes in neighbouring topography those old courses had been abandoned by the stream and covered over by drift so effectively that it was not possible even to guess where their meanderings had been from the present appearance of the land surface. The recent effects of earthquakes such as that at Murchison went to show to a minor degreej one way at least in which streams h'ad been bloclced, and even lakes formed. There seemed little doubt that over a period of thousands or even millions of years such processes went on in Central Otago. Provided such old streams had suitable bottom it would be easy for them t0 retain such a heavy metal as gold and to a lesser degree other heavy substances such as black sand. The Government geologist attached to the party carried out a reconnaissance over such old river courses. By certain electrical properties Mr. Madriniak was able to follow these gutters or t)la.cers in some localities.

Black sand or magnetite had very strong magnetic properties. Owing to its weight, light gold was clifficult to scour away. By means of modern magnetic instruments Mr. Baird was able to trace out areas of strong magnetic anomalies. Much work was done to show up those anomalies that could be attributed to old buried river gutters. By still another method known as the seismic method the underground structure was studied. Explosives were fired, and elastic waves were picked up by microphones spread out along suitable profiles. In the schist rocks so conimon the waves travelled much faster than in quartz conglomer^tes and g?ravels overlfcring them Gold apparently came from the quartz from which the conglomerates had their origin. To know the depth of the schist or rock bottom was an important economic factor. Dr. M. A. F. Barnett was associated with that branch of the survey. Mr. Baird said that he saw some remarkably rich washes in some of the claims. All round Central Otago one saw a great many tents. In them were honsed unemployed men from ia,ll parts of New Zealand. The weather was extremely cold, and the men deserved any succe'ss they got as the reward of their hardihood. The U nemploy ment Board was doing usefuj work in the area.