BLACKMON MINE. 93 
The schist has always been described as a talc schist, and its appearance certainly war- 
rants such a description; but chemical examination shows that only a slight amount of 
magnesia is present, and the material is therefore sericite. The rock is more or less soft, 
decidedly fissile, and varies in color from dull gray to pinkish, bluish, and green. It is 
made up largely of shreds of sericite or fibrous mica, with a little quartz, numerous tiny 
red and black garnets, a little magnetite, and a few small fragments with high polarization 
colors whose identity is unknown. Where cut by the diabase dike the folia are much 
crumpled. It is probable that this rock is of sedimentary origin. The porphyritic rock, 
while fairly massive on the whole, is somewhat foliated near the contact with the schist, 
indicating probably that the intrusion took place just before the cessation of the shearing 
or folding movements which produced foliation. The contact is not sharp and simple; 
the schist was probably injected near the main porphyry mass by narrow dikelets of the 
porphyry, and the subsequent foliation has produced a mingling of the two rocks. In its 
present somewhat decomposed condition the rock consists of a fine-grained mosaic of quartz, 
sericite, epidote, and some zoisite, in which are imbedded large phenocrystic grains of 
quartz and of turbid feldspar, both orthoclase and oligoclase. A little biotite was probably 
present, but is now decomposed. This rock may be designated a quartz-monzonite 
porphyry, and is probably closely related to the tuffs which occur at the Haile and Colossus 
mines. The diabase is doubtless much later than either of the other rocks. Granite is 
known on the surface about one-fourth mile to the north. 
The ore of the Blackmon mine is a zone of sericite schist occurring at the contact with 
the quartz-monzonite porphyry. Small siliceous lenses between the folia of the schist, 
averaging one-eighth inch wide and one-half inch long, have been formed, partly by filling 
and partly by replacement. Where this silicification is most marked the grade of ore is 
best. A small amount of pyrite accompanies the quartz and may carry gold, but the 
principal value is as free gold usually in tiny grains or flakes. In this ore zone the schist has 
a bright, vivid appearance — the colors are striking, ranging from delicate grays and pinks, 
resembling mother-of-pearl, to beautiful brilliant greens — and the rock is lustrous. Pass- 
ing into the hanging wall to the more normal rock, the bright colors fade to dull grays and 
the hardness decreases. Narrow bands of quartz, true veins of filling, occur here and there 
in the ore body. They carry a little pyrite, but practically no gold. As in the case of all 
the mines thus far described, these barren quartz veins appear to be of a little later forma- 
tion than the silicification which produced the ore. Between the ore body and the fairly 
massive porphyry there is a zone perhaps 5 to 20 feet thick, which forms the foot wall. In 
appearance it resembles the dull or "dead" schist of the hanging wall, but it is found to 
pass gradually into the unfoliated porphyry, and the microscope shows that it is of the 
same composition. It is pretty thoroughly impregnated with small cubes of pyrite, but 
carries only slight gold values. The density of the schist and the stability of its composi- 
tion have resulted in excluding surface waters from the greater part of the ore body and the 
sulphides are in general unoxidized. But along certain fracture planes decomposition has 
converted the sericite into kaolin, the so-called "talc" of the miners. As a consequence 
great masses of ore, bounded by and resting on these sheets of soft and exceedingly slippery 
material, are continually tending to slide in and wreck the workings, and it is only by the 
strongest timbering that some portions of the workings are maintained. Another serious 
obstacle to economical mining which arises from the character of the ore is the difficulty 
of obtaining good results from blasting. The rock is so schistose that drilling can be done 
practically only at a large angle to the plane of foliation. A water Leyner drill has been 
put in and in this rock works far better than hand drills or ordinary machine drills. But 
even when the holes are obtained, it is almost impossible to get the powder to do more than 
shatter and loosen great slabs of the schist, which are still left wedged in place almost as 
firmly as before. Time and experience may disclose some more efficient manner of placing 
or loading the holes than has yet been discovered. 
The ore body is a zone of altered schist parallel to the dip and strike of the schist of the 
region and to the contact with the quartz-monzonite porphyry. Measured horizontally, 
