strongly
and forms rugged hills. The outcrop of the decomposed silicified
porphyries are often rough, with projecting quartz veinlets and seams
or hard silicified portions standing above the softer feld-spathic
material. The latter has been removed from the surface by erosion in
some places, leaving cavities between the quartz veinlets and masses.
In places the rocks are much stained by limonite, both along joints and
seams of quartz or turquoise. The brown limonite stains evidently come
from formerly existing iron sulphides, and in one place remains of the
sulphide were still visible along a badly stained turquoise veinlet.
The rock is more or less stained blue and green with copper, especially
where altered and kaolinized. It appears that some of the turquoise may
have formed directly from kaolin by the addition of phosphate and the
copper stains, for specimens are found that show a gradation from good
turquoise to soft semitur-quoise and to copper-stained kaolin, and,
furthermore, balls or patches of material, which may have once been
feldspar phenocrysts, are found that range from kaolin to semiturquoise
to turquoise. In one of the mines the semiturquoise, about 4 in
hardness, contained a good deal of
p
hosphate, with alum
and copper sulphate through it. It appeared to have formed from kaolin
and had assumed a nodular form. Portions contained large amounts of
free alum and small amounts of free copper sulphate. The color of this
semiturquoise was a beautiful dark turquoise blue in places and
lighter shades in others. Evidently much of the turquoise has been
deposited from solution, for it occurs in seams, veinlets, and veins,
and in patches or streaks in quartz seams and veinlets occupying
original joints or fissures in the rock. Occasionally there is a
tendency for nuggets or nodules to develop, especially in the larger
veinlets, or veins, or in masses of kaolinized feldspar. The turquoise
in the veinlets and seams does not often assume a nodular form, as is
common in the deposits in the Burro Mountains of New Mexico.
The
principal work of the Aztec Company has been on the Monte Cristo claim,
on the southeast end of Ithaca Peak, near the top; the Queen claim, on
the south side of the west end of Ithaca Peak; the Peacock claim, on
the north side of Aztec Mountain; and the Aztec and Turquoise King
claims, on the south side of Aztec Mountain.
The
Monte Cristo claim extends N. 85° W. over the top of the southeast end
of Ithaca Peak. Below and to the southwest of the top of the mountain
two openings have been made on the precipitous slopes. At the west end
of these a 15-foot tunnel has been driven in from a small open cut. The
rock is decomposed, silicified quartz porphyry, containing many quartz
seams. Some good, pure turquoise has been obtained in this opening,
chiefly in the quartz seams. Nodules and nuggets of semiturquoise
saturated with alum and a little copper sulphate were associated with
the turquoise in the rocks. This material desiccates and cracks open
where exposed to the dry air. The other cut on the southwest side of
the ridge is large and has yielded much good turquoise. E. J. McNulty,
superintendent of the mine, states that about 2 tons of selected rough
turquoise has been shipped from this cut in the last six years. This
work encountered large seams of good turquoise, one ranging from 0 to 8
inches in thickness. A tunnel is being driven through the top of the
ridge N. 15° E. from the open cut. This tunnel was 140 feet long at the
time of the visit and was to be carried 25 feet farther through to rich
turquoise
