The
outcrop occurs on a hill which, as shown in plate 28, is separated from
the neighboring ridge by erosional depressions on all sides.
Practically all of the country in view in this photograph, which was
taken looking a little east of north, is serpentine, including the
basal portion of the mine hill. The rock mass directly associated with
the veins lies along the top of the hill from a point directly below A
to one directly below B, and is about 520 feet long, and perhaps 400
feet in its widest part.
The
outcrop of the mineralized belt lies entirely on the side of the summit
visible in the photograph and extends along a line determined in the
photograph by the right end of the cut and top of the dump. It is a
zone of veination which consists of a large number of irregular
stringer-veins running along together in the general direction of
elongation of the zone, and connected by many branches and anastomosing
laterals. The rock in the vicinity of the veins is altered by
recrystallization, metasomatosis, and impregnation, in some places
porous from solution of certain constituents, in others tough and
cemented by natrolite impregnation.
EFFECTS OF EARTH MOVEMENT AND PRESSURE.
Considerable
movement has taken place both before and since the mineral deposition,
and it is distinctly concentrated along the mineralized zone. The great
majority of the planes of movement and crushing lie in or near the
plane of strike of the zone of mineralization, but a few are transverse.
The effects of pressure may be tabulated:
In
the first three of these groups the planes lie approximately in the
zone of mineralization. A few of the later fault-planes are transverse
and have displaced the veins and rendered the deposits more or less
discontinuous.
The appearance of schistosity in the massive rocks seems to be limited to the immediate vicinity of the zone of veination
