FiNLAYsoN. — Geology of the Reefton Gold-veins. 



91 



further concentrate movement and shattering into a comparatively narrow 

 zone in the slates. 



The absence of veins in the Devonian rocks is not surprising, as they 

 would not be amenable to extensive Assuring, more especially as the relief 

 of strains would be readily effected by faulting of the weaker slates. More- 

 over, Assuring and faulting would take place where the stress due to folding 

 was greatest — that is, in the apex of the main syncline of the slates. 



Throughout the width of the zone of disturbance there are places where 

 more defined fissuring has taken place, giving access to thermal solutions. 

 It is in these places that the veins proper occur, and the position of the 

 chief veins is indicated by the position of the mining claims. 



Turning to the individual veins, if they can be so regarded, a vein con- 

 sists of a series of lenses of quartz, with constriction of the vein -walls 

 between. The lenses follow each other more or less continuously to 

 considerable depths, with short barren patches of " vein-formation " be- 

 tween the lenses. The vein, as indicated by its walls and the included 

 band of crushed slate which contains the lenses, conforms as a rule to the 

 bedding of the country rock, though frequently it may cut across it. 



The lenses vary considerably in dimensions in different parts of the 

 field, the smallest occurring at Boatman's and the largest in the Inkerman 

 Mine. In most cases they show a steep pitch to the north along the strike 

 of the vein. The gold, of fineness 960, and worth over £4 an ounce, is free- 

 milling, and varies from coarse to fine. The former is caught on the battery- 

 tables, and the latter recovered by cyaniding the tailings. It is scattered 

 for the most part through the lenses, though occasionally it lies in shoots 

 on the walls. Of sulphides, auriferous pyrite is always present, the pyritic 

 concentrates being worth approximately £20 per ton. "Stibnite is also 

 very frequently present, some veins carrying a notable proportion of it. 

 It is mostly low grade, and mingled with quartz. When present in quantity 

 it occurs in seams and bunches. As an accessory it is scattered sporadically 

 through the stone, and greatly increases the consumption of cyanide. To 

 remedy this, the Keep It Dark Company now treat their tailings with a 

 solution of caustic soda previous to cyaniding. 



Metasomatic Action. — The results of analyses made of the fresh and 

 altered slates show a considerable loss of silica and alkalies ; the effect of 

 the ore-bearing solutions on the slate has been sericitization, with a decrease 

 of specific gravity. The effects are thus quite analogous to those which 

 I have described in the case of the veins of Otago.* Both Reef ton and 

 Otago, it may be noted, carry a very similar class of vein and ore 

 throughout, although most of the Otago veins cut across the bedding of 

 their country rock. 



Features of the Mines. 



w 



?« //(// 



_8od^ 



' Welcoi?te^ 



^[ Fieri/ CfVAs 



(1.) Boatman s Group. 



The veins of this group were 

 characterized by quartz blocks of 

 small size and high value, but at 

 greater depths they became less 

 frequent and too small to extract 

 with profit. The position of the 

 different mines is shown in the 



Fig. 3. — Sketch-plan of Boatman's Veins, sketch-plan. 



* This volume, p. 82. 



