64 Transact 107}$. 



Art. XV. — The Geology of the Quartz Veins of the Otago Goldfields. 

 By A. M. FiNLAYSON, M.Sc, A.O.S.M. 



Communicated by Dr. Marshall. 

 [^Read before the Otago Institute, \-iih July. 1908.] 



Introductiox. 



The accompanying paper contains the results of investigations into the 

 geology of the veins of the Otago Goldfield. The area is a large one, and 

 the paper is not exhaustive, but the different ty^es of veins have been ex- 

 amined, and the features of every group described and discussed. As most 

 of the mines are now closed down, the district is not an ideal one for studying 

 vein-phenomena, and it is to be regretted that the work was not undertaken 

 many years ago, when Bullendale, Bendigo, and the O.P.Q. workings were 

 accessible. 



I wish to acknowledge my great indebtedness to Professor Park, Dr. 

 Marshall, and Mr. D. B. AVaters, of the Otago School of Mines, for much 

 help and advice, both in the field and in the laboratory ; and to Mr. A. 0. 

 Bishop, of Skipper's, and Mr. R. Mollineaux, of Barewood, who gave me 

 great facilities in examining their mines. 



General Description of the District. 



The Otago Goldfield, as far as veins are concerned, embraces an area of 

 nearly 10,000 square miles, stretching from Lake AVakatipu on the west 

 to the sea-coast on the east, and from Cardrona in the north to La^\Tence 

 in the south. This district is drained chiefly by the Ciutha and Taieri 

 Rivers, and also by the smaller Shag River. 



The country is mountainous, the various ranges running for the most 

 part approximately north-east and south-west, or at right angles to the 

 course of the Kawarau River, while the tributary streams flow between 

 and parallel to the ranges. This disposition is described and discussed by 

 Dr. Marshall in his " Geography of New Zealand."* Professor Park claims 

 that the ranges of Central Otago are block mountains.! 



The climate of the inland districts is much hotter in summer and colder 

 in winter than on the east coast, but the rainfall is generally low. For 

 this reason the hills and valleys are practically barren of vegetation, being 

 clothed only in tussock. Dearth of water and absence of timber are serious 

 hindrances to mining in some parts of the field. 



The goldfield has no centre of population, but "comprises a number of 

 towns which grew up in the roaring days of alluvial mining, for which the 

 district is chiefly noted. The principal towns are situated on the Ciutha 

 River, or in its drainage-basin, and stand as fingerposts indicating the 



♦Marshall, "Geography of New Zealand" (Whitcombe and Tombs, 1905), p. 102. 

 tPark, Bull. No. 2, N.Z.G.S., 1906, p. 7; Bull. No. 5, N.Z.G.S., 1908, p. 9. 



