286 GEOLOGICAL SUEVEY OF THE TEEEITOEIES. 



Mining is carried on pretty mucli upon the same plan of working 

 throughout this section ; therefore mention will be made of it only in 

 concluding the first part of this chapter. 



The Briggs lode is situated between Gregory and Bates Hills, in the 

 gulch parallel to which it strikes, having a course of about east 3^ 

 north. It is a contact- vein, having the granite of Gregory Hill as a 

 south wall, the gneiss of Bates for a north wall. Between walls the 

 distance is about 4 feet at the surface, gradually increasing with depth, 

 so that at 545 feet it is 11 feet wide, while a little higher up it bulges 

 out to 27 feet. This considerable lateral extension, however, is owing to 

 anumberof gneissic "horses" that occurred there, causing a splitting and 

 widening of the vein. Although not disturbed to any extent, the walls 

 appear rough at some i)laces, which is due to the fact that at some 

 points there seem to have been dislocations at one time, whereby por- 

 tions of the wall were broken, and cemented again by quartz. As a rule, 

 it may be said that the south wall is smooth and of a good character. 

 Dislocations of the vein are very rare, scarcely even variations in the 

 almost vertical dip being noticeable. 



Pyrite and chalcopyrite, as usual, form the bulk of the ore, with 

 sphalerite and galenite as accessories. At the depth of 545 feet, a vein 

 of massive pyrite 4 feet in thickness was found. Quartz and feldspathic 

 minerals, together with fragments of granite and gneiss, form the gangue- 

 rock. Minerals found are : Pyrite and chalcopyrite, the former also 

 incrystals ; galenite, sphalerite, gold, dolomite, quartz crystals in small 

 cavities ; quartz, feldspar, and mica in the gangue. The owners of this 

 mine are the Messrs. Briggs, one of whom, Mr. G. Briggs, kindly fur- 

 nished me with some data regarding wages and contracts that will be 

 found at the end of part 1. 



The Mammoth lode, beginning on Gregory Hill and running across 

 westward on Mammoth Hill, has a strike of about east 10° north, show- 

 ing a curve toward the north. A connection between the Bobtail, 

 Mammoth, and Illinois has been sui)posed to exist, and may exist, but 

 not sufficient proof has yet been produced to substantiate the supposi- 

 tion. The very similar character of the ore and the percentage of gold 

 decreasing westward might speak for such a connection. On Gregory 

 Hill this vein runs in granite, coming up very near to the porphyry; 

 while on Mammoth Hill it becomes a contact- vein, between granite on 

 the south and gneiss on the north wall. Along its entire course, the width 

 of this vein between wails is considerable — between 20 to 30 feet — con- 

 taining large quantities of pyrite, with some chalcopyrite, too poor in 

 gold, however, to pay working at present. Its dip is almost vertical, 

 and the walls seem to be clean and well defined. 



The Winnebago lode, opposite the Mammoth, on the north side of the 

 gulch, located on Casto Hill, has a strike of about east 4P north. Gneiss 

 on the south side forms the hanging-wall, while granite borders the vein 

 to the north. Clean walls, at some places almost of a polished appear- 

 ance, characterize this contact- vein : dip to the south of about 8° — 12<=', 

 varying at different depths, strongest at the top. A shaft* has been 

 sunk down on the vein, first inclined, then vertical, following it in its 

 course, and the depth reached is 350 feet. Between walls the lode is 

 from 3^ to 5 feet thick. Near the western end of the Winnebago claim 

 the vein seems to split ; but as it does not split into two equal halves, 

 and the continuation of the vein can be traced westward on the surface, 

 there is reason to believe that this lode connects with Oasto, which is a 

 little farther west, running through granite and gneiss, partially being 

 contact between the two. 



