486 MmmG industey. 



They present the characteristic features of true fissure veins and many of them 

 are rich in gold, silver, copper, and lead. 



The relative association and method of distribution of these metals are 

 very interesting, and although the subject has, thus far, been too little studied 

 to aiford data for much generalization, these lodes will, in future, furnish an 

 instructive field for the student of vein phenomena. The gold-bearing veins of 

 Colorado differ in many respects from those of California. The latter have gen- 

 erally a gangue of clear white quart.z carrying free gold, with a comparatively 

 small proportion of iron pyrites ; those of Colorado are usually filled with a 

 gangue rock composed of quartz and feldspar, sometimes porphyritic in char- 

 acter, and associated with a seam of ore which consists chiefly of auriferous 

 copper pyrites and iron pyrites. Very little of the gold is free in the quartz, 

 but is mostly combined or intimately associated with the pyrites ; and, accord- 

 ing to general observation, the copper pyrites is a much richer gold ore than 

 the iron pyrites. Nearly all the gold-bearing veins carry some silver. The 

 proportion of this latter metal is variable, but is seldom less than one ounce 

 of silver for each ounce of gold, and oftentimes very much more. 



While the gold-bearing veins almost always, if not invariably, carry some 

 silver, the richest silver-bearing veins, as, for instance, those about Greorge- 

 town, are usually wanting in gold. The ores of these veins generally consist 

 of argentiferous galena, mixed with comparatively little pyrites and enriched 

 by the presence of true silver minerals in sulphureted and antimonial forms. 

 In the several groups of veins one or the other of these types usually pre- 

 dominates. Those in the Gilpin County region, of which Central City is the 

 center, the lodes are pre-eminently auriferous ; although in the immediate 

 vicinity there are veins that are strictly silver-bearing, and, so far as the 

 writer is informed, entirely without gold ; of such the Coaley lode, a half mile 

 or a mile below Black Hawk is an example. Advancing in a southwesterly 

 direction from Central City toward Georgetown, the gold veins become 

 notably richer in silver, and, according to the observations of some, a gradually 

 increasing proportion of silver may be discerned, until, ariving at the George- 

 town district, the veins become entirely argentiferous in character and are 

 almost, if not quite, without perceptible traces of gold. 



The relations of these veins to each other, as regards their position, age, 



