WEED.] 
ORES AND VEINS. 
13 
of tin ore and quartz which resembles a course granite and corre- 
sponds to the greisen ore of European tin deposits. Pyrite occur- 
rarely in the eastern exposures of the vein, but appears to constitute 
the bulk of the metallic contents in exposures seen in the westernmost 
openings. These ores occur in well-defined veins, which run up the 
slopes nearly at right angles to the direction of the range, the strike 
being approximately east-west and the veins dipping steeply to the 
north. Three veins have been discovered, all of which have been 
exposed by open-cut work and by pits for several hundred feet in 
length. The most northerly vein is traceable along the surface for a 
distance of about 1,200 feet, The middle vein lies about 300 feet south 
of the east end of the northern one, but apparently converges west- 
ward toward the northern vein. The southern vein, which is the 
smallest of the three, lies about 000 feet farther south. 
The veins exhibit the usual characters of the European tin veins. 
notably those of Cornwall, England, their clearly defined fissures 
showing a central core or lead of coarse 
quartz, sometimes containing tin ore. and 
Hanked on either side by altered rock in 
which the tin ore replaces the feldspar of 
the granite. Where this metasomatic re- 
placement is complete the ore shows a 
mixture of cassiterite, with or without 
wolframite and quartz. Where the re- 
placement is only partial the greisen ore 
fades off into the unaltered granite. A 
cross section of the veins shows, there- 
fore, the same phenomena seen at Corn- 
wall. The diagram, tig. 2. shows an ideal 
representation of the conditions existing 
in the veins, and has been drawn from sketches made in the field. 
The central mass of quartz corresponds to the "leader" of the Cornish 
veins. It is composed of massive, coarsely crystalline quartz, some- 
times showing comb structure, and it is clearly the result of the tilling 
of the open fissure by quartz. The adjacent ore-bearing material is 
a replacement deposit in which the mineral solutions have substituted 
ore for the feldspar of the granite by metasomatic action; in other 
words, the main mass of the ore occurs alongside of a quartz vein, and 
is due to the alteration of the granite forming the walls of the fissure. 
In general, the ore passes into the granite by insensible transition and 
there are no distinct walls. 
A thin section of the greisen ore has been examined by Mr. Lind- 
gren, who furnishes the following notes: 
The thin section of the tin ore shows it to be a quartz-cassiterite rock. It is a 
coarsely granular rock consisting of anhedral quartz, with which is intergrown 
grains of slightly brownish cassiterite. The quartz is full of fluid inclusions and makes 
Fig. J.— Section of tin vein exposed 
in open cut (north vein). 
