550 J. T. .Tutsan: 



Tlie Yarra Tunnel Reef was abandoned on account of its bifur- 

 cation, but this does not necessarily prove that it may have 

 met and thickened again lower dowai. 



Secondary enrichment has probably taken place in the reefs 

 here, both in the vadose zone generally and in the sulphide 

 zone at the Caledonia. The geological structure shows the vast 

 amount of silurian strata removed from the surface of the 

 ground at Warrandyte. The reefs must have extended upwards 

 into these rocks, and in the denudation of the latter, the former 

 would be removed, and if gold-bearing, w^ould tend to enrich 

 the undenuded parts of the reefs. There appears to be no 

 doubt, from the general returns, that near the surface the reefs 

 and also the dykes are richer than the lower portions worked, 

 both in the sulphide zone of the Caledonia, and the vadose zone 

 generally. 



So far as can be determined, therefore, the reefs may not 

 maintain their yield at depth, but as the sulphide zone below 

 the oxidation zone is often enriched at or a little below the 

 latter, it is possible that some reefs may have benefited in this 

 way. Apparently the only reefs given anything of a trial in 

 this direction are the Consols and the Yictoiy, and they have 

 not proved payable, so that experience gives no support to the 

 idea. The Caledonia cannot be taken as a fair test of the en- 

 richment of the sulphide zone, as there appears to be so little 

 of the oxidised zone above the former to absorb the gold. 



Again, one of the dykes previously referred to crosses the 

 Yarra close to the Caledonia. It is possible that the gold in 

 the Caledonia may have been leached out from this dyke. The 

 other reefs are some distance from the dyke, and may, there- 

 fore, not have benefited by it. Considering all the evidence, the 

 probabilities are, therefore, against the maintenance of the 

 yields in depth, but this does not exclude the possibility of 

 shoots of gold in some reefs which, if worked with strict 

 economy and care, may be found payable at greater depths than 

 at present worked. 



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