POSSIBLE CONTENTS OF PORPnYRY BODIES. 



583 



This porpli}-!'}' is assumed to contain 4 per cent, of pyrite (FeS2=4.00). 

 From Table III, Appendix B, its contents of protoxide of lead, as an aver- 

 age of the eight specimens tested, is 0.(02025 per cent, in the soluble por- 

 tion; or, as.suming, from the proportion found in the insoluble portion of the 

 three specimens in which it was tested, that this represents only two-tifths 

 of the entire lead contents, the average contents of the whole rock would 

 be PbO:=: 0.0050625 per cent. From Table IV the average of ten speci- 

 mens assayed for silver is found to be 0.2773 ounce per ton, or, rejecting- 

 tlie richest of these ten specimens as above the normal, the average of the 

 remaining nine specimens is 0.0265 ounce silver per ton of Pyritiferous 

 Porphyry. 



The probable thickness of the porphyr}' sheets it is rather difficult to 

 estimate. The sections as drawn give a maximum thickness of about iifteen 

 hundred feet, and an unknown thickness has been eroded awav. It may 

 not be unreasonable to assume 1,000 feet as the average thickness of the 

 original body. From the above-assumed data would be obtained, as the 

 contents of the present and original areas . of Pyritiferous Porph^-r}-, re- 

 spectively, and on the basis of the two different values for lead and silver 

 given above, the following: 



Contents of Pyritiferous Porphyry. 



Amount of porphyry 



Amount of pyrite, at 4 per cent 



„ , ( at 0.002025 per cent. PhO. 



Amount of g.ilena < .^, ^ 



^ (at 0.0050625 per cent. PbO 



„ ., r at 0.0263 ounce per ton 



Amount of silver <,„„„, 



( at 0.2775 ounce per ton . - 



Designation. | ^ *r„^ °,^ P"**- 



" ent outcrop. 



Tors ' 4,000,000,000 



Tons : 160,000,000 



Tons. 8,675,000 



Tons 21,087,750 



Ounces , 106. 000, 000 



Ounces ' 1, 109, 000, 000 



1 



In area of 

 assumed origi- 

 nal body. 



16, 000, 000, OOO 

 640, COO, 000 

 .34, 700, 000 

 86. 751, 000 

 424, 000, 000 

 4, 436, 000, 000 



To obtain an actual average of the metallic contents of this or any 

 other body of porphyry would have required a systematic sampling of the 

 rock and the taking of specimens at given and equal distances, not only on 

 its surface but through its mass in depth, for the tests already made show 

 that the metals are not evenly distributed, but vary in an apparently arbi- 

 trar}' manner. Such a sampling is manifestly not practicable, nor would 

 the expenditure of labor and time required by it be advisable if it were, 

 since in the present state of explorations in this region it is impossible to 



