514 EEPORT — 1887. 



lurgy have diminislied the rate of loss, and from these improvements an 

 increased yield of gold may be looked for. 



Under this head of vein-gold should be classed the gold occurring 

 with the ores of other metals in sufficient quantity to be worth extracting. 

 In much of the silver ore of the Comstock, &c., the gold occurs to about 

 one-third the total value. 



Gold is widely distributed in iron pyrites, especially when this occurs 

 in lode-like masses traversing the older rocks. Sometimes it is sufficiently 

 abundant, either alone or in association with other metals, to pay well for 

 extraction. Often, however, it is in too small a quantity to pay by any 

 process at pi-esent known. 



The pyrites at Rio Tin to contain from 8 to 11 grains of gold, and 

 fi'om ^ oz. to 1 oz. of silver per ton. This ore is essentially iron pyrites 

 with a little copper pyrites. With the exception of small quantities ob- 

 tained from some of the copper at Swansea, Widnes, and in Germany, 

 this gold is entirely lost ; yet Mr. J. H. Collins states that the pyrites 

 raised yearly in the Sierra Morena contains a ton and a half of gold, or 

 a money value of about 150,000^. 



There are other important mineral masses which must be classed with 

 lodes, but which are extremely irregular in their mode of occurrence, and 

 are very likely to diminish in productiveness in depth. There are the 

 • Bonanzas,' and similar rich masses of ore, which have yielded such 

 vast quantities of silver and gold in the United States. In the Comstock, 

 which is in many respects an exceptional area, the Bonanzas are enlarge- 

 ments of a quartz-lode along the junction-planes of eruptive rocks. 

 As a matter of experience, it is found that these become less frequent and 

 important at great depths. 



Of diffisrent origin from these Bonanzas, but resembling them in con- 

 taining large quantities of ore, are the chambers or pockets in calcareous 

 rocks from which the greater part of the silver of the United States is now 

 obtained. These are produced in the first instance by the action of atmo- 

 spheric water dissolving away the limestone ; into the hollows thus formed 

 metallic ores have been subsequently introduced. Such chambers will 

 therefore be unlikely to occur below the level to which surface waters have 

 circulated. Sometimes, as in Nevada and Utah, there is no special relation 

 between the country rock and the metallic contents of these chambers ; 

 but in other places, as at Leadville, in Colorado, the ores only occur 

 where the limestone is overlain by eruptive rock. 



The important bearing of these considerations on our present subject 

 is this, that although it is not unlikely that great and irregular masses of 

 rich silver or silver-lead ores may be again discovered, which may even 

 for a time rival the past productiveness of the United States, yet it is 

 improbable that any such rich districts will continue to be productive for 

 a long period of time. 



The opinion held in the eai'ly days of Californian mining, that lodes of 

 gold-quartz diminish in production in depth, has been abundantly dis- 

 proved. All lodes vary in productiveness in different places, and when 

 in working downwards the lodes became impoverished, the workings were 

 abandoned, and the miners transferred their energies to other lodes at 

 the sni'face. But it is now known that such impoverishment is in most 

 cases only local. If the lode be followed it generally regains its average 

 productiveness. At the Adelong mine, New South Wales, payable 

 quartz is raised from a depth of 1,030 feet. But it is in Victoria that the 



