FERGUSON MINE. 
97 
marked foliation at the contact of the two rocks or just within the amphibolite. The result 
is a band of exceedingly schistose rock of light-green color and lustrous surface, composed 
very largely of sericite but containing also quartz and epidote. It seems probable that 
this product is the outcome not only of the shearing but of the action of the vein solutions. 
This zone outcrops noticeably on the surface southwest of the shaft and is reached under- 
ground at the bottom of the shaft. 
The Ferguson ore deposit lies principally in l he porphyritic tuff. It would at first be taken 
as a representative of the fissure-vein type, and so it is; but it is more than that. By the 
deposition of quartz as a filling of space it represents the fissure veins and by the impregna- 
LEGEND 
Li 
F 
Altered volcanic tuff 
c 
% 
Quartz 
Scale of feet 
l 
Pyrite 
Fig. 11.— Sketch of vein, vertical section, Ferguson mine, winze, looking northeast. 
tion of the fissure walls by the ore-bearing solutions it stands as a close link to the replace- 
ment deposits. In fact, if the quartz lenses could be completely removed, there would 
remain a small and low-grade replacement deposit, similar in character to those of the Haile 
and Colossus mines. The ore is thus of two kinds — vein quartz carrying good values and 
adjoining wall rock (cf. pp. 59-61) carrying just about enough gold to pay for milling what 
is broken rather than sorting it out. -The quartz ore from the vein carries only a slight 
amount of free gold where it is unoxidized;a but the proportion of pyrite is rather large, 
averaging about 10 per cent. The pyrite occurs plentifully within the quartz, but shows a 
marked tendency to segregate near the vein walls and in many cases it occurs in the wall 
rock just outside the quartz. Fig. 1 1 is a sketch of one side of the winze which is being sunk 
a Mr. Frank informed the writer that he had never seen a particle of native gold in the undecom- 
posed ore from this mine. Amalgamation tests have yielded $1 per ton. 
Bull. 293—06 7 
