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854
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MINERAL RESOURCES.
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an
elliptical shape with a north and south elongation. It stands about 200
feet above the adjacent slopes and bench lands on the north, east, and
south, and about 75 feet above the spur connecting it with the
Stansbury Mountains on the west. The elevation, as obtained by
barometer, was 5,700 feet. The region is very dry, and water is hauled
16 miles to the mine. It is possible a small supply of water could be
obtained by digging in Hickman Canyon, a mile and a half to the south.
Development work at the mine has not been extensive and consists of
three small open cuts and a crosscut prospect tunnel. The work in the
cuts has not been carried to a greater depth than 8 feet.
The
country rock at the amatrice mine is limestone and quartzite. Hard,
dense, dark-brown, calcareous quartzite forms the summit of Amatrice
Hill. The eastern slope of the hill is composed of beds of siliceous or
sandy and cherty limestone of light to dark gray color and striking N.
20° W. with a dip of 60° W. Typical quartzite outcrops prominently to
the northeast of the hill, with the same dip and strike as the
formations in the hill. On the south side of the hill fossils were
found in the limestone by Mr. Zalinski. They were identified by George
H. Girty, of the United States Geological Survey, as of Carboniferous
age, probably upper Carboniferous, belonging to the Weber quartzite or
upper "Coal Measures" limestone of the Fortieth Parallel Survey. In a
manuscript copy of Mr. Zalinski's report, the occurrence of porphyry
resembling monzonite, about a quarter of a mile southwest of the
amatrice deposit, is mentioned. This porphyry is cut by a set of joints
or fractures corresponding to those in which the amatrice occurs,
showing that the amatrice fissuring was subsequent to the intrusion of
the porphyry.
The
amatrice occurs in the limestone in fissured and brecciated zones,
which strike nearly with the bedding of the limestone and have a
steeper dip to the west. These breccia zones have been strongly
mineralized by the deposition and replacement of chalcedony, chert,
variscite and allied phosphates, and of a small amount of pyrite with
brown limonite stains. In many cases the various minerals have assumed
a concretionary structure, either with one mineral about another, or
with layers of different color in the same mineral. In other cases
seams of one mineral have cemented the fractures of older and crushed
minerals, preserving the brecciated structure. Three amatrice-bearing
streaks have been opened by small cuts. These are known according to
the type of gem material each produces, as the "jade" and "cobweb"
cuts, close together and on the southeast side of the hill, and the ''
apple-blossom " cut about 100 yards east of north of the other two. An
outcrop of good amatrice appears a few yards south of the "jade" cut,,
and loose pieces have been found at several places on the hill. The
deposits appear to be local, however, and no variscite has been found
to the north or south of Amatrice Hill.
Amatrice
owes its attractiveness to the wide variation of colors of the
different constituent minerals, and the variety of combinations and
patterns displayed by these colors. The constituent minerals are
chalcedony, chert, variscite, and probably wardite and allied
phosphates. Brown limonite stains in seams and through the different
minerals form a strong contrast with the variscite. The chalce-
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