FiNLAYSON. — Geology of Quartz Veins of Olago Gold-fields. 81 



they will peter out altogether, and certainly their gold-content will not 

 justify sinking on the outcrop. That they have had their indirect value, 

 however, is undoubted, and they must have helped in some measure to supply 

 the alluvial gold of the drifts. 



Barren Reefs, or Buck Reefs. — These are peculiar types, and correspond 

 to similar occurrences on the Hauraki goldhelds, in California, and in a great 

 many other vein districts. In Otago they consist of very wide, massive, 

 bold outcrops of " hungry " glassy quartz, often traceable for considerable 

 distances. They are practically barren, devoid of pyrite, and composed of 

 quartz throughout. 



A typical buck reef occurs near the Hawksburn Homestead, six miles 

 south of Bannockburn. Several occur at Quartz Reef Point, on the Clutha 

 River, four miles above Cromwell. Another occurs at Nenthorn, and another 

 in the Nokomai district. An interesting buck reef occurs near Waipori, on 

 the road to the Waipori antimony-vein. Where it outcrops it consists of 

 2 ft. of quartz, much of whicli is in very fine pseudomorphs after calcite, 

 and preserves excellently the rhombohedral cleavage. It is, however, not 

 proved that this is a buck reef, as no tests have been made of the quartz. 



General Observations on the Veins. 

 (1.) The Vein- fissures. 



Nature of the Fissures. — The fissures which carry the veins of Otago 

 vary greatly in nature, according to the physical character of the particular 

 zone of schist through which they pass. Where the schist is resistant and 

 quartzose the fissures are simple, being narrow and defined, as at the Carrick 

 and Bendigo ; where the rock is softer the fissures are compound, ill-defined, 

 and longer, and become shear-zones of some width, as at Skipper's and 

 Macetown. Finally, at Macrae's the shear-zones follow the foliation-bedding 

 planes, so that here we have a group of bedded or segregated veins. Thus 

 the division of the veins into groups, first used by Ulrich, is made possible 

 by the above fact — the varying nature of the schist and the consequent 

 varying nature of the veins in different localities. 



Professor Park speaks of the vein-type at Bendigo as a twin fissure 

 containing a band of schist between.* I can see no evidence of this, and I 

 regard such a vein as a single fissure filled by quartz, except where portions 

 of country rock have been detached from the walls of the fissure by sub- 

 ordinate cracks, giving the quartz vein a varying thickness. 



Orientation. — The mean strike of the gold-bearing fissures is west and 

 east, or slightly to the north of west, although locally the strike varies 

 through all points of the compass, as on the Carrick Range. 



Distribution. — The local distribution of fissures as shown on the map 

 is in part more apparent than real, for there is no doubt that the whole 

 goldfield is traversed by veins, even in localities where they have not been 

 located. This is due in part to the absence of prospecting in less inviting 

 districts, and in part to the fact that veins might readily be overlooked in 

 tussocky country where shoots or blocks of quartz did not happen to outcrop. 

 Nevertheless, there is evidence of a localisation of fissures into more or less 

 defined groups. This is probably due to local factors, such as the nature 

 or previous disturbance of the schist, which aided or retarded the fissuring- 

 forces. 



* Park, Bull. No. 5, N.Z.G.S., 1908, p. (i3. 



