23

be part of the Baker member or may underlie it and be part of the Rain-
bow member. In these uppermost quartzites near their base is a fairly
extensive calcareous horizon. In most places it includes two or three beds
of white limestone each about a foot wide separated by a few feet of grey
calcareous quartzite. No. 3 division also holds a narrow calcareous horizon
which is quite persistent and in one of the places where it was cut it was
replaced by fine-grained pyrite to make an ore-body 8 inches wide.
This horizon elsewhere on the level was a highly silicified calcareous bed.
Near the base of the upper part of No. 2 of Figure 3 are two or three
caleareous argillite beds. These could not be recognized at all places
where this division was crossed, but at least one has been replaced locally to
form a body of replacement ore 18 inches wide. Another narrow limestone
bed occurs near the top of the lower part of No. 2 division. At one place
this bed is white silicified limestone about a foot wide, elsewhere it is
either calcareous quartzite or a fine-grained, soft rock resembling marl.

The rocks have been subjected to two or more periods of fracturing.
There are many transverse fractures and several hundred of these contain
quartz veins. These fractures do not show displacement of the walls and
are not faults. Later than these fractures are faults that strike in three
principal directions. A few faults with very small throw lie along some
of the quartz veins and strike north 60 to 80 degrees east. These faults
are offset by other faults that parallel the strata. These also are mainly at
least of small offset and are apparently all of the normal type. Two faults,
the Rainbow and Lowhee faults, strike roughly north and dip about 60
degrees east. These are of much greater magnitude and are crushed
zones 20 feet or more wide and show horizontal displacement of the strata
of 400 feet and 1,000 feet respectively. In both cases the east side is dis-
placed to the south, suggesting that the faults are of normal type. The rela-
tionship between these and the other faults is not known.

The mineral deposits are of two types:

(1) Gold-bearing, pyritic, quartz veins
(2) Gold-bearing, pyritic, replacement deposits

The veins are of three types, transverse veins that strike north 30
to 60 degrees east and cross the strata roughly at right angles, diagonal
veins that strike north 70 degrees east to east and cross the strata diag-
onally, and strike veins that are parallel or nearly parallel to the strata.
The transverse and diagonal veins appear to be closely related or were
formed at the same time, but the strike veins may have formed at a dif-
ferent time. Many transverse and diagonal veins are commercially valu-
able, but no strike vein is yet known to be of value.

Transverse veins are the most numerous and about seven-eighths of
these are less than a foot wide. The remainder, forty to fifty veins,
range in width from 1 foot to 6 feet and most of these average about 3
feet. They are in general less than 150 feet long and rarely exceed 200
feet. The diagonal veins are less numerous and about three-quarters of
them are narrow and the remainder, fifteen to twenty veins, are more
than a foot wide. These wider veins also average about 3 feet wide,
appear to be somewhat longer than those of the transverse type, but
rarely exceed 300 feet. Both types are vertical or steeply dipping. Both