ENDLicH] GOLD AND SILVER SUNSHINE DISTRICT. 119 



J. Alden Smith did much to bring the district to public notice, and 

 showed, by his inauagemeut of the American mine, the nature and ca- 

 pability of the ores. This region, together with that of Gold Hill, 

 constitutes one of the most interesting and miueralogically important 

 features of Colorado. Instead of finding the precious metals contained 

 in such minerals, classed as "ores" tbat generally carry them in that 

 State, they are in combination with tellurium, and sometimes iodine. 

 TcUurids of gold or silver, or both, constitute the ores that have become 

 justly famous on account of their remarkably high yield of both these 

 metals. Miueralogically, the occurrences in these districts are not 

 equalled in any otber part of the world. In the Sunshine district the 

 ores showed very high pay from the surface down. Decomposition has 

 removed, to a great extent, the tellurium, and we now find either native 

 gold or silver, or an alloy of the two, in the rock. Fiity-five feet was 

 the greatest depth reached (Fair View mine) at the time (October 22, 

 1875) I visited the Sunshine camp. At that depth the decomposed ores 

 were beginning to turn into solid, fresh ones. 



A greater depth has been reached by the Red Cloud and Cold Spring 

 mines at Gold Hill. It may there be observed that the surface-ores soon 

 give way to the undecomposed. Furthermore it is noticeable that with 

 increasing depth other ores, galenite, sphalerite, pyrite, and chalcopyrite 

 set in. These, too, carry very appreciable quantities of the precious 

 metals. Eegarding this in connection with the genesis of an ore- 

 bearing vein, we may be led to some definite inferences. All fissures 

 that now we find to be metalliferous lodes were filtered by infiltration-^ 

 infiltration taken in its widest sense. The constituents, from their char- 

 acter classed as " ores" may have been in hydrothermal or any other liquid 

 solution, or they may have been in a volatile state, gradually condensing 

 as they receded from the source producing their volatilization. In case 

 we follow up this latter view, we will find that it is borne out by evi- 

 dence. Less volatile minerals, pyrite, chalcopyrite, galeuite, and sphal- 

 erite, are found only as we reach greater depth in the vein, while the 

 highly volatile tellurium compounds occur in the greatest quantities 

 higher up. This would place the cause of volatilization at an indefinite 

 depth, but not at the sides of the veins. If we, in addition, take into 

 consideration the fact that the Eed Cloud and Cold Springs lodes are 

 contact veins on either side of a porphyry-dike, this matter is still fur- 

 ther elucidated. Granite is the country-rock, and it is traversed at that 

 point by a porphyry-dike 40 to 50 feet in width. Between this and the 

 granite on either side we find the two veins. It may be observed that 

 whereas small spurs of the veins enter the porphyry from either side, 

 none are found within the granite. It is impossible, therefore, to separate 

 the formation of the lodes from that of the dike. Inasmuch as the 

 material composing the dike was certainly at one time subjected to the 

 action of intense heat, there is no reason why the ores should not have 

 consolidated in the fissures which they reached as vapor. 



All of the metalliferous veins occurring in the regions above men- 

 tioned are found to be within the metamorphic area. Typically, as 

 veins, they show scarcely any differences. They are at times contact- 

 veins, between, for instance, gneiss and granite; and again they run 

 entirely in the one or other rock. As a rule they may be said to be 

 what are popularly termed " true fissure-veins." Presumably this ap- 

 pellation is supposed to convey the idea that they are " persistent " as 

 to downward extension. In some localities veins occur that cannot be 

 classed among them. In this case we find the orebearing body is but 

 a member of the gneissoid or schistose rock, is conformable with it in 



