ORIGIN AND DEVELOPMENT OE ORE-DEPOSITS. 359 



deep-seated and while a circulating solution of sufficient 

 temperature and pressure was still making its way through 

 it, we might have had here a lode far richer than Dolcoath 

 resulting strictly from lateral (though deep-seated) secretion. 

 It may be that some of our lodes have been thus formed, 

 and even some of the rich Camborne lodes; given then a 

 sufficient cavity, a sufficiently powerful and abundant solvent 

 and '' rock-conditions," capable of causing deposit, and in a belt 

 of country rock charged as that at Mulberry is, and the size of 

 the largest "rich part" in a lode presents no difficulty that 

 cannot be readily met. For we must remember that the most 

 rigid application of the theory of lateral segregation does not 

 forbid us to suppose that the large courses of ore referred to 

 were the results of a local concentration of ore in the fissure 

 itself, while the exhaustion of the country rock would only be 

 proportionate to the average contents of rich and poor parts 

 together. 



The average width of the workable ore of the Great 

 Dolcoath lode would probably not exceed 4 feet for the coppery 

 and 8 feet for the tinny portions, with a general average of 

 perhaps 6 feet. We have not the means of knowing with any 

 degree of accuracy the yield per cubic fathom of the coppery 

 portion of the lode, but we shall probably not be far wrong in 

 taking it at 4 per cent, of copper, while the tinny portions may 

 be taken at 2 per cent, with an equal degree of probability. 

 The values, taking into account differences in the cost of 

 (dressing) preparing for market, would be much the same, so that 

 we may follow out our comparison on the tinny portion alone. 



The 30 fathom belt of tin ground at Mulberry will thus be 

 seen to have yielded, per linear fathom, nearly twice as much tin 

 as the Dolcoath lode, or in other words, if concentrated into a 

 suitable fissure it would have made a lode either twice as large 

 or twice as rich. The similar belt at Great Wheal Fortune in 

 Breage would have supplied a lode four times more productive 

 than that at Dolcoath. The great value of the Dolcoath lode 

 (and equally of the other instances cited by Smyth) consists 

 therefore not so much in the absolute quantity of its metallic 

 contents as in the natural concentration which has brought it into, 

 or into the immediate neighbourhood of, a narrow fissure. 



