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GEMS AND PRECIOUS STONES. 1041
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weighing about one-fourth of a carat. Mr. Richard states that this discovery has been proved authentic.
C. H. Gordon's map 1 of
this part of Texas shows a large part of Foard County to be covered by
the Seymour formation of Pleistocene age, consisting of sands and
gravels overlain by fine silts. The valleys contain outcrops of Clear
Fork and Double Mountain formations of Carboniferous (Permian) age.
Recent alluvium is shown in. some of the valleys. In places the later
conglomerates, called "upland gravels," probably in part belonging to
the Seymour formation, are cemented by lime into hard masses which have
in some cases been mistaken for the Permian gravels.2 M. J.
Munn, of the United States Geological Survey, suggests that possibly
some of the unconsolidated gravels in the region east and northeast of
Foard County, in Texas and Oklahoma, are of more recent age than the
Seymour. The presence of more than one gravel formation in the region,
some of which resemble one another, makes difficult the placing of the
reported diamond in its proper stratigraphic position. Mr. Richard
refers it to the Clear Fork formation, but there is a possibility of
its having come from gravels of the Seymour formation or from later
gravels.
The
nearest outcrops of eruptive rocks lie some 60 miles northeast of Foard
County in the Wichita Mountains, Okla. They have been described by J.
A. Taff 3 in four general classes as gabbro and related
anoithosite, granite and associated aplite, granite porphyry and
associated aporhyolite, and diabase. These rocks are considered older
than Middle Cambrian and probably of pre-Cambrian age.
AFRICA. UNION OF SOUTH AFRICA.
Cape Colony.—The production of diamonds during, the fiscal year 1912 by the De Beers Consolidated Mines 4
amounted to 2,087,392 carats, as compared with 2,180,856 carats in
1911. Actual sales during the year amounted to 2,058,397 carats at
£5,524,475 ($26,-884,858). The total production of blue ground in 1912
amounted to 7,950,442 loads, as compared with 8,105,138 loads in 1911.
The total quantity of blue ground and tailings washed during 1912 was
7,995,953 loads, as compared with 9,219,192 loads in 1911. The yield in
carats of diamonds per load of blue ground wash increased from 0.28 to
0.31 at the De Beers and Kimberly mines, from 0.27 to 0.29 at the
Wesselton mine, from 0.38 to 0.41 at the Bultfontein mine, and
from'0.21 to 0.23 at the Dutoitspan mine. The De Beers mine has not
been reopened since it was closed in 1908, but a small amount of
prospecting was carried on. The main shaft at the Kimberly mine is
3,601 feet deep, and hoisting is now done from the 3,520-foot level.
The value per carat of the diamonds obtained from the different mines
was as follows: De Beers and Kimberly 53s. 11.47d., Wesselton 45s.
3.12d., Bultfontein 40s. 8.24d., and Dutoitspan 83s. 0.13d.
1
Geology and underground waters of the Wichita region, north-central
Texas: Water-Supply Paper U. S. Geol. Survey No. 317, 1913, PI. I.
1
Udden, J. A., and Phillips, D. McM.: A reconnaissance report on the
geology of the oil and gas fields of Wichita and Clay counties, Texas:
Bull. Univ. Texas, No. 246, 1912, p. 107.
Geology of the Arbuckle and Wichita mountains in Indian Territory and Oklahoma: Prof. Paper U. S. Geol. Survey No. 31,1904.
' Twenty-fourth Ann. Eept. De Beers Consolidated Mines, for year ending June 30,1912.
10424°—it k 1912, pt 2------66
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