VEINS OF GOLD HILL. 165 



peculiar characteristics of . the .surface andesite, in its lower portion it gradually 

 passes into fresher andesite, more like that of Mizpah Hill, and there is little 

 question that the two phases form parts of the same body. Therefore, it has been 

 concluded that there is here a phase of the earlier andesite which contains biotite 

 rather than hornblende, and which also has a somewhat coarser feldspar crystal- 

 lization. Similar phases can be found on Mizpah Hill, and even very close to 

 the Mizpah vein, and, as stated elsewhere, the rock can be matched in the Fraction 

 and neighboring shafts. 



ALTERATION OF GOLD HILL ANDESITE. 



The alteration of the Gold Hill andesite, as observed in surface specimens, 

 results in the formation of quartz, sericite and secondary orthoclase or adularia. 

 The plagioclase feldspars (oligoclase-albite) alter to orthoclase (adularia) and 

 sericite, or to sericite and quartz. The biotite is usually altered to muscovite . 

 and quartz. Occasional pseudomorphs of secondary minerals after hornblende 

 were detected, consisting chiefly of iron minerals (hematite, etc.). Numerous small 

 crystals of apatite occur. Practically the same characteristics are found in the 

 specimens from the Gold Hill shaft, with rather more pseudomorphs after horn- 

 blende and some chlorite as secondary mineral. 



ENUMERATION OF THE GOLD HILL VEINS. 



Gold Hill differs in an important manner economically from the Mizpah Hill 

 block, in its comparative poverty in mineralization. The veins are shown on 

 the map, but are narrow and weak. The most important outcropping vein may 

 be called the Good Enough vein, from the name of one of the claims. At one 

 point in the upper part of the Good Enough .shaft the vein has a thickness of 

 H feet, but diminishes farther down, and also laterally along the outcrop in both 

 directions, until it splits into diverging and unimportant stringers. This vein has 

 an east-northeast strike with a northerly dip at an angle of about 70. There 

 is a parallel vein 250 or 300 feet to the northwest, which dips in the opposite 

 direction, or to the southeast, at an angle of 70 or 80. This vein has a thickness 

 of 3 to 6 inches and is traceable across the hill. A number of other veins of the 

 same character are found, one of which runs southeastward from the Gold Hill 

 shaft, parallel to and just above the road. It strikes N. 60 W., has an average 

 thickness of <> inches, and is also evidently a weak vein. Veins of the same 

 character, nearly parallel to that last mentioned, occur on the .southwest side of 

 the road, in the same block, as shown on the map (PI. XVI). They are usually 

 several inches thick, but have not been traced far. 



