680 IDAHO MINING DISTRICTS. 



RELATION BETWEEN PLACERS AND QUARTZ VEINS. 



The dependence of the gold placers upon the occurrence of gold- 

 quartz veins is very strongly brought out by a study of the occurrences 

 of both. While there are many small quartz seams occurring through- 

 out the granite, some of which may contain a little gold, it is perfectly 

 evident that there are two regions in which quartz- vein deposits are 

 concentrated. These are, first, the Gambrinus mining district, on 

 the ridge between Elk Creek and Moore Creek, continued by the Elk- 

 horn mining district, at the headwaters of Elk Creek; and second, 

 the gold belt extending from the Boise Ridge near Quartzburg to 

 Grimes Pass. Every creek and ravine leading up to these .deposits 

 has been rich, while the watercourses rising in other parts of the 

 range are comparatively barren. It seems clear beyond doubt that 

 most of the gold in the gravels near Idaho City came down the Illinois 

 and Gambrinus gulches; above these Moore Creek becomes compara- 

 tively poor. What gold there is has doubtless been derived from the 

 more distant veins at the very head of Moore Creek, near Summit 

 Flat. In nearly every case an exceptionally rich ravine has been 

 found to lead up to a quartz vein. Thus it is clear that the recently 

 discovered Summit mine, on the ridge between Elk and Grimes creeks, 

 furnished the gold found in Deer Creek and Henry Creek. The only 

 occurrence to which some doubt is attached as to the derivation of 

 the gold is that of the rich angular gravels at the head of Spanish 

 Fork and Willow Creek, but it is probable that they are derived from 

 local seams and veins. 



The headwaters of Grimes Creek furnish a most convincing argu- 

 ment in favor of the derivation of the gold from the quartz belt. 

 Every gulch heading along the line of that belt is rich, while every 

 one not crossing it carries only extremely small quantities of gold. 



The conclusion is that practically all of the placer gold in the dis- 

 trict has been derived from the quartz Veins in these two districts. 



On an average the fineness of the gold in the quartz veins is a little 

 less than that in the placers. This has generally been the experience 

 in most mining districts, and is accounted for by a dissolving of the 

 silver and baser metals from the surface of each grain of gold. The 

 highest grade of quartz gold is found near Quartzburg, and in the 

 gravels of Placerville, derived from the Quartzburg mines, the placer 

 gold is of unusual fineness. 



