FiNLAYSON. — Geology of Quartz Veins of Otago Goldfields. 



79 



Alteration of the Wall-rock. — The country rock is little altered, except for 

 about 2 ft. from the vein-walls, where the alteration is considerable, the rock 

 being soft and " muUocky." There is, further, frequently found on the 

 walls a type of greasy yellowish rock, devoid of pyrite, and very similar to 

 the corresponding rock described above in the Nugget and Cornish Mine. 

 It accompanies the brecciated ore, the payable seams being well developed 

 in No. 3 level and the winze. 



The following analyses indicate the alteration of the normal rock : — 



100-68 100-92 75-78 + 2-85 



—27-75 



1. Unaltered rock. 



2. Altered rock. ^ -24-90 



3. Altered rock, recalculated on a basis of constant alumina. 



4. Gains and losses. 



The alteration in this case is more intense than at Skipper's, although 

 more local, and the loss of material greater. It is, however, of a similar 

 nature — namely, sericitic. 



Analyses made of the yellowish or bleached variety of wall-rock show 

 that, like that at Skipper's, it is a kaolinized type of the ordinary sericitic 

 rock, evidently formed by the action of descending waters. 



Ore-shoots of Primary Origin. — The characteristic hanging-wall and foot- 

 wall seams described above doubtless originated during the primary de- 

 position of the gold, through the influence of the wall-rock. 



Ore-shoots of Secondary Origin — Secondary Sulphide Enrichment. — A 

 number of facts indicate that the No. 3 level winze has encountered a zone 

 of enriched sulphides (pyrite and stibnite). These are as follows : (1.) The 

 occurrence of the gold in the free state, and its frequent rusty colour. (2.) The 

 occurrence of stalactites of pyrites. (3.) The peculiar siliceous concretions, 

 probably due to solution and redeposition by subsequent leaching j)rocesses. 

 (4.) The brecciation, signifying subsequent movement, would give readier 

 access to descending solutions. (5.) The kaolinization and bleaching of the 

 yellowish wall-rock, and the absence of pyrite in it, are evidently due to 

 descending surface waters, and it is notable that it occurs associated with 

 the brecciated ore and with the richest seams. (6.) Finally, the impoverish- 

 ment in the upper levels, supported by the above data, points to the work 

 of secondary enrichment, which has largely leached the gold out of the 

 upper levels and redeposited it with sulphides in the zone now being opened 



