worked, and the gravels over part of the flats contain angular to subangular debris of porphyry, tuff, and conglomerate.
The
porphyritic tuff is composed of feldspar and glassy quartz phenocrysts
in a fine slate-gray matrix with inclusions of quartzite and other
material. The inclusions observed range from an inch or two down in
size, and the phenocrysts average about one-sixteenth of an inch
across. The conglomerate at the sapphire deposits is composed of
pebbles of quartz, red, brown, and gray sandstone and quartzite, gray
and black chert, and a serpentine-like material, with a siliceous
cement, the whole containing decomposed feldspar fragments throughout.
The pebbles range in size from about 2 inches down. About a mile to the
east of the mine is a bed of very coarse conglomerate forming cliffs 60
to 70 feet high along the north side of the West Fork. The pebbles of
this conglomerate are composed of sandstone, quartzite, siliceous
slate, and chert, with a compact, hard, red, jaspery matrix. These
pebbles are well rounded and range in size up to 10 and 12 inches in
diameter. While a number of them are very similar to those of the finer
conglomerate at the sapphire mine, the frequent quartz pebbles of the
latter seem to be lacking. There are pebbles and fragments of
light-yellowish and greenish-gray to green serpentine-like mineral
included in the coarse conglomerate to the east of and in the
conglomerate and tuff at the sapphire mine. Large blocks of apparently
the same material were found on the flats at the mine. The latter
consisted of a fine-grained greenish-gray matrix with translucent
dark-green blocks, resembling crystal fragments, included in it. Both
the matrix and the inclusions were soft and like serpentine. In thin
section the greenish inclusions were seen to be very fragmentary with a
light, porous, kaolin-like looking material between the fragments. The
latter were composed of many small, doubly refracting particles and
fibers extinguishing at all angles.
The
gravels in Anaconda Gulch vary from 30 to 100 feet in width and from a
few inches to 8 or 10 feet in thickness. At the bends and in some of
the hollows along the gulch gravel bars extend up the hillsides short
distances. On portions of the flats along the gulch gravel beds occur,
and good deposits of sapphire are reported to exist in channels leading
to the gulch. At one place on the flats the gravels, and probably also
the decayed tuff or conglomerate, have been washed for sapphires over
an area of a number of feet square. The gravels in Meyer Gulch are from
30 to 40 feet wide in the lower part and from 100 to 200 feet wide
farther up the gulch. In thickness they vary from a foot or two up to
8 or 10 feet, and are probably as much as 5 feet thick over a large
portion of the area.
The
gravels in both Anaconda and Meyer gulches are sluiced down with small
hydraulics. The first part of the sluice is over bed rock and from this
portion the bowlders and coarse debris are forked out. The finer
material is then washed down through board sluices over cross riffles.
The latter are removed and cleaned up each day. In Meyer Gulch the
tailings from the riffles are carried through several hundred yards of
wooden sluice to remove the waste from the gulch near the workings.
This sluice has riffles with bars parallel to its length, largely to
protect the boards of which it is constructed, though partly to catch
sapphires that have washed over the cross
