14 Colorado Gold Mines* [January, 



and matter for exaggeration so abundantly that American 

 brokers were enabled to form, in the cities of the east, no 

 less than 1S6 public gold-mining companies. The com- 

 panies generally possessed capital enough to build a mill, 

 but before the mill was running it in many cases happened 

 that the surface rock, which yielded its gold to mercury, 

 was exhausted, and after a few experiments the mill was 

 stopped ; and mill and mine have remained closed ever 

 since. A few mines, however, rich enough to bear the loss 

 of from three-fourths to two-fifths of their produce in the 

 mill, have remained open, to testify to the extraordinary 

 richness of the district. As the mills existed they have 

 continued to be used, despite the defects of their work ; but 

 unless some better system be introduced mining must lan- 

 guish, for no mines can long sustain such waste. 



The present article is a contribution towards the solution 

 of the question, which, as it involves the saving or loss of 

 several million dollars' worth annually of gold, silver, and 

 copper, is well worthy the attention of metallurgists. So 

 abundant is the ore that were mining conducted systematic- 

 ally, and the product of the mines utilised, Gilpin County 

 would probably yield more value in mineral than any district 

 of equal size in the world. 



The country rock is granitic, with some gneissic varieties. 

 The lodes have a general E. and W. course, and dip almost 

 vertically. They are very free from faults, and many of 

 them can be traced, running with remarkable regularity, for 

 long distances ; but the productive portion rarely exceeds 

 4000 feet. The deepest shaft in any of them is only 700 

 feet, and there are few others deeper than 500 feet : it is 

 therefore impossible to predict what their character will 

 continue to be, and whether the gold yield will be perma- 

 nent ; and the changes which have taken place in certain of 

 the lodes, at different depths, are too inconsistent with one 

 another to allow of any deductions being drawn from them. 

 The structure of the lodes is very characteristic of fissure- 

 veins. The walls are usually distinct, and marked often 

 with well-polished schlicken sides. A clay sewage, then a 

 band of almost pure iron and copper pyrites, intermixed 

 with small quantities of blende and galena, or of blende and 

 galena alone, or of all these sulphurets mixed in almost 

 equal proportions, occurs on one or both sides, while the 

 centre of the lode is composed — where the lode is rich — of a 

 gangue of decomposed quartz or felspar, carrying more or 

 less of the same sulphurets. The solid sulphurets of iron 

 and copper, known as No. I., or smelting ore, usually yield 



