202 



THE PROBLEM OF THE METALLIFEROUS VETlsrS. 



Per cent 

 by anal- 

 ysis. 



Pounds 

 per ton. 



Copper 0. 009 



Lead (galena ) . 



Zinc (zincblendi' i 

 Silver (argentite). 

 Gold 



.coil 



.008 



. o;:i4 



. 004,S 

 .009 

 . 00007 

 . 00016 

 . 00002 

 . 00004 



0.18 

 .022 

 .16 

 .08 

 .096 

 .180 

 .0014 

 .0032 

 .0004 



Pounds 

 chalco- 

 pyrite. 



0.52 

 .025 

 .186 

 .002 

 .128 

 .240 

 .0016 

 .0037 

 .0004 

 .0C08 



Volume 



(cubic 



inches). 



3.42 



.092 



.700 



.340 



.90 

 1.60 



.006 



.014 



. 00065 



. 00130 



Ratio of 

 probn- 

 bility. 



1/6 



1/20 



1/10 



1/13 



1;12 



1/V 



l;49 



138 



i;i04 



1/83 



From the table it is evident that the chances vary from a maxi- 

 mum in the case of copper of 1 in C through various intermediate 

 vahies to a minimum for gold of 1 in over 100. This is equivalent to 

 saying that with cracks whose total width bears the same relation to 

 the width of the rock mass as is borne by the diameter of the particle 

 of ore, the chance of crossing a particle varies from 1 in 6 to 1 in 100. 

 Or we may say that with cracks of this spacing from one-sixth to one 

 one-hundredth of the contained metallic mineral might be leached 

 out." When, therefore, as is often the case in monographs upon the 

 geology of a mining district, inferences are drawn as to the possibil- 

 ity of deriving the ore of a vein by the leaching of wall rocks whose 

 metallic contents have been proved by assay, the total available con- 

 tents ought to be divided by a number from 6 to 100, if the above 

 reasoning is correct. 



This diminution will tend to modify in an important manner our 

 belief in the probability of such processes as have been hitherto 

 advocated. We may justly raise the following questions: How 

 closely set, as a matter of fact, are the cracks wdiich are large enough 

 to furnish solution waterways in the above rocks, and can we reach 

 any definite conception regarding their distribution? Some quanti- 

 tative idea of the relations may be obtained from the tests of the 

 recorded absorptive capacity of the igneous rocks which are employed 

 as building stone. G. P. Merrill in his valuable work on Stones for 

 Building and Decoration, page 459, has given these values for 33 

 granites and 4 diabases and gabbros. They vary for the granites 

 from a maximum of one-twentieth to a minimum of one seven-hun- 

 dred-and-fourth. I have averaged them all and have obtained one 



o With regard to the flow of waters through crevices and the relation of the 

 flow to varying diameters or widths, a very lucid statement will be found in 

 President C. R. Van Hise's valuable paper in the Transactions of the Ameri- 

 can Institute of Mining Engineers, XXX, 41, and in his Monograph on 

 Metamorphism. 



