DESCRIPTIVE GEOLOGY OF MINES AND PROSPECTS. 205 



SHAFTS ENTIRELY OR CHIEFLY IN LATER AXDESITE. 



HALIFAX SHAFT. 



The Halifax shaft was sunk in the depression lying just north of Golden 

 Mountain in the later andesite, just northeast of a probable fault line which 

 separates the later andesite on the northeast from the white tuffs on the southwest. 

 The shaft was 800 feet deep at the time of the writer's last notes in November, 

 1904, and was entirely in the later andesite. The andesite is very fresh fresher 

 than that examined in any other part of the district. The phases exposed in the 

 upper part of the shaft are very glassy, suggesting that they are near the upper 

 part of a flow, while those in the bottom are also relatively finer grained than 

 the rock exposed for most of the distance down the shaft. Much of this latter is 

 so coarse, with so great a development of phenocrysts compared with the quantity 

 of the groundmass, that it has in the hand specimen almost a granular texture. 

 Nevertheless the different phases all belong to a single mass. 



At a depth of 200 feet in the shaft a drift was run a little east of south for 

 270 feet, and in the opposite direction for 100 feet along a heavy fault, which runs 

 parallel to the drift and dips west at an angle of 45 or steeper. Along this fault 

 plane there is a thick brecciated or ground-up zone 8 or 10 feet thick. The 

 strise indicate that the faulting was normal, the downthrow being on the west 

 side. The same conclusion is suggested by the difference in the texture of the 

 andesite on the sides of the two fault, that on the foot wall side being coarser 

 and almost granular, while that on the hanging wall is finer grained. It is probable 

 that the coarser textured andesite cooled at a somewhat greater depth than the 

 finer grained and, therefore, that this side has been relatively upthrust. 



The shaft stays in this same granular andesite. for 50 feet below this level, when 

 another fault zone comes in, along which is also a clay seam. This dips 60 to 

 the west. Below this, hard and finer grained andesite comes in again and continues 

 downward. 



This is one of the few shafts in the district which have struck a large flow 

 of water. Chiefly below 600 feet in the shaft, water was encountered, which rapidly 

 increased from 10,000 to 30,000 gallons a day, and owing to this the sinking of 

 the shaft was for a long time suspended (see p. 105). Some drifting is being done, 

 from the bottom, north and south, in the later andesite. 



GOLDEN ANCHOR SHAFT. 



The Golden Anchor shaft was started in the center of the later andesite area 

 west of the Midway. When last visited, in the middle of November, 1904, it 

 was 640 feet deep. At a depth of 400 feet a south crosscut runs 510 feet from 

 the shaft, and at a depth of 500 feet a north crosscut runs 463 feet. The upper 



