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1038 MINERAL RESOURCES, 1912.
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The second area was described by A. H. Purdue,1
but prospecting has developed further points of interest. It is 3 miles
S. 75° E. of Murfreesboro, in sec. 14, and is held by the American
Diamond Mining Co. The exposures of the peridotite and its weathered
products are on a steep north hill slope. Prospecting has been carried
on by shallow pits, trenches, cuts, a shaft, a tunnel, and drill holes.
The peridotite exposures occur within an area of 2-1/2 acres,
but the drill holes show that this rock is much larger under and near
the surface. Dikes extend outward from the mass of peridotite, or large
bodies of the country rock are included in it, or probably both
conditions exist.
On
the property of the Kimberlite Diamond Mining & Washing Co., about
one-fourth mile northwest of the American Diamond Mining Co.'s tract,
in sec. 14, peridotite has been exposed in pits, trenches, and drdl
holes. The apparent form of intrusion, judging from present exposures,
is that of a crescent-shaped dike with a northeast-southwest strike.
This dike is at least 700 feet long and possibly 100 feet wide at the
surface, but may be found wider after further prospecting.
There
are two exposures of peridotite on the Grayson-McCloud Lumber Co.'s
tract, about half a mile southwest of the American Diamond Mining Co.'s
property. One of these is at the "Black Lick" near the northwest corner
of sec. 23 and the other is about 900 feet to the east. Two test pits
were made at these places by Mr. Miser, in which the greenish earth was
found to retain the original texture of the peridotite. These two
exposures may be on the same mass of peridotite. Hand specimens from
these pits closely resemble the decomposed peridotite on the American
Diamond Mining Co.'s property, in section 14.
The
nature of the peridotite and its products from weathering are similar
at the four areas discovered. The fresh peridotite is dark-greenish to
brownish-black and in places presents a porphyritic texture. Altered
phases become rather more greenish with an earthy appearance and grade
into greenish and yellowish soil. A dark to black "gumbo" soil results
from the presence of vegetable matter. Numerous inclusions occur in the
peridotite, among which black shale, baked by the heat of intrusion,
are common.
The
rocks of this part of Arkansas are chiefly sedimentary and are of
Ordovician, Carboniferous, Cretaceous, and Quaternary age. The
Ordovician and Carboniferous rocks, consisting of shales, sandstones,
novaculites, and cherts, outcrop a few miles north of the area in which
the peridotite has been found. The peneplaned surface of the
Carboniferous rocks is overlain by the Trinity formation, of the Lower
Cretaceous, consisting of intercalated beds of marly clay, sand,
gravel, and limestone. The Trinity formation is unconformable overlain
by the Bingen sand, of the Upper Cretaceous, consisting of
intercalated beds of gravel, sand, and clay.
The
peridotite cuts the Trinity formation, the clays of which were baked to
a hard semivitrified rock by the heat of the intrusion, but is overlain
by the Bingen sand. At one place, near known peridotite areas, the
gravel at the base of the Bingen sand contains altered grains of
serpentine and fragments of peridotite. The age of intru-
l A new discovery of peridotite in Arkansas: Econ. Geology, vol. 3,1908, pp. 525-528.
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