COPPER

The only economic source of copper as yet discovered in Arkansas is the mineral chalcopyrite, or copper pyrites, which is intimately associated with galena in nearly all of the known occurrences of that mineral. There is, so far as is known, no great quantity of copper in Arkansas, although there are many places where traces of it occur in the rocks. Incrustations of azurite, the blue copper carbonate, are common in the black shales, but these are of no commercial importance. In some instances, vein deposits of native copper have been found.

Native copper occurs impregnating a quartz vein near Olsen switch west of Benton. An opening has been made in this vein for the purpose of mining the copper, but because of the irregular distribution of the metal in the vein, and the large amount of gangue that must be handled in recovering the metal, it is probable that this vein cannot be worked profitably at the present time.

A little metallic copper was found at the Rossin shaft, four miles east of Harrison, but not in commercial quantities. A small amount of malachite (hydrous copper carbonate) was mined at the "Tomahawk Mine" in Section 6, Township 16 north, Range 16 west, in Searcy County. Two assays of malachite from this locality gave 39.48 and 39.57 per cent of metallic copper. Small quantities of the same material were shipped from the Big Bear mine near Ferndale, Pulaski County, but the mining of these ores did not prove profitable.

Where copper minerals occur in connection with lead, zinc or other metallic ores, it is often possible to profitably save the copper as a by-product. So far as is now known there are no copper deposits in Arkansas that warrant working for copper alone.

The location of the Tomahawk mine is shown on the map of the zinc and lead district. It lies in a district in which zinc mineralization is common.

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Bibliography of Copper

1888

Comstock, T. B., "Gold and Silver."-Annual Report of the Arkansas Geological Survey for 1888, Vol. I.

1892

Branner, J. C., "Zinc and Lead Region of North Arkansas."-Annual Report of the Arkansas Geological Survey for 1892, Vol. V.

The only locality in North America where diamonds are found in the rocks in which they were formed is in Pike County, Arkansas. The diamonds occur there in dikes of volcanic rock known as peridotite, which closely resembles the material in which diamonds are found in South Africa. Four separate areas of this peridotite, which aggregate about eighty acres, have been found, all but one of which have produced diamonds.

*History-Diamonds were first discovered in Arkansas on August 1, 1906, when two stones were found by John M. Huddleston near the mouth of Prairie Creek, two and one-half miles southeast of Murfreesboro, Pike County. These stones were submitted to the Mermod, Jaccard & King Jewelry Company, of St. Louis, Mo., for identification. Later, stones were sent to Chas. S. Stifft, jeweler, of Little Rock, Ark., for identification, who submitted them to George F. Kunz, gem expert of New York City, who identified them as diamonds. Following this, Messrs. C. S. Stifft, A. D. Cohn, S. W. Reyburn of Little Rock, and J. C. Pinnix of Murfreesboro secured an option on the Huddleston property, which included about fortynine acres of the main peridotite pipe. The remainder of the pipe was made up of the Mauney, tract, which includes about eight acres, and the Austin Q. Millar tract, including about three acres (see accompanying map). Other peridotite areas were later discovered in Sections 14 and 23 (see acompanying map) known respectively as the Kimberlite, American, and Black Lick areas.

Following this the Arkansas Diamond Company was organized,

Historical data largely from U. S. Geological Survey Bulletin No. 735, "Diamondbearing Peridotite in Pike County, Arkansas," by H. D. Miser and Clarence Ross.

which purchased the property. The Huddleston property was then prospected and numerous pits dug and drill holes put down. In May, 1908, the company erected a small diamond washing plant at the southern edge of the area and in August, 1909, increased the size of the plant, which was operated until 1912, after which operations practically ceased until 1919, when the company was reorganized as the Arkansas Diamond Corporation with an authorized capital of $10.000,000. In 1920 a large washing plant was erected near the first one, which contained a No. 3 gyratory crusher, an 8-foot Harginge tube mill, a rotary dryer, two washing pans, jigs, and a grease table. According to John Peay, of the Arkansas Diamond Corporation, this plant operated for a total of nine months and handled approximately 18,000 loads of peridotite, each load containing sixteen cubic feet of material. This plant has not been in operation for some years. The Arkansas Diamond Corporation operates a small power jig from time to time.

The Mauney tract mentioned above and shown on the accompanying map was operated by M. M. Mauney on a small scale for several years prior to 1912, when the Kimberlite Diamond Mining and Washing Company obtained a lease on the mine and began the erection of a washing plant three-quarters of a mile from the mine. This was completed in 1913 and was in continuous operation until January 13, 1919, when the plant was burned. The plant was equipped with a concentrating pan, screens, jigs, and a grease table. The plant has not been rebuilt and the mine has not been operated since 1919.

The Austin Q. Millar tract shown on the accompanying map was the first worked by the Ozark Diamond Mines Corporation, in 1912. At that time the company constructed a washing plant near the mine and operated it for a few months. Approximately 5,000 loads, each containing sixteen cubic feet of decomposed material, were washed in the plant. In December, 1914, this plant was sold by a receiver to the Kimberlite Diamond Mining and Washing Company and was operated by that company until the first part of 1919, when the plant was burned and it has not been rebuilt. Between 800 and 900 diamonds are reported to have been recovered.

The Kimberlite area in Section 14, which is owned by the Kimberlite Mining and Washing Company, was prospected to a small extent, but no washing for diamonds has been done, although several stones have been reported to have been found on the surface there. The American area in Section 14 was originally owned by the Pike County Diamond Mining Company, which was succeeded in 1908 by the American Diamond Mining Company, which was in turn succeeded in 1914 by T. E. Flournoy, who purchased the property from the receivers of this last organization. A small amount of prospecting has been done and twenty-four diamonds are reported to have been found, one of which is reported to have weighed 3 11/16

carats.

The Black Lick area in Section 23 has been little prospected and no diamonds are reported to have been found in it.

Geology. There are three general types of peridotite in the volcanic areas. There are (1) the porphyritic intrusive peridotite, (2) the volcanic breccia, and (3) the tuffs and fine grained breccias.

The porphyritic intrusive peridotite makes up much of the Prairie Creek area and also the Kimberlite area in Section 14, Township 8 south, Range 25 west. On fresh surfaces this rock is a dull green, brown or black, and is very hard, known to miners as "hardebank." The weathered rock is usually pitted and a dull gray green in color. Only a few diamonds have been found in this material. The volcanic breccia is composed of strongly cemented fragments composed largely of the porphyritic type of peridotite, together with fragments of shale and sandstone very probably derived from deep seated Carboniferous rocks. It covers a fairly large area in the Prairie Creek dike and makes up the American area, the Black Lick area, and has produced nearly all of the diamonds found. On exposure to the air the breccia weathers to a yellowish green and is known as "green ground" or "blue ground." The tuffs and fine-grained breccias occupy the smallest portion of the peridotite in the Prairie Creek district. The rocks have a bluish tinge and a medium hardness and vary considerably in texture. They contain a considerable proportion of shale and some fine-grained sandstone. No diamonds have been found in this material so far as is known.

The peridotite areas occur about six miles south of the northern edge of the Coastal Plain area of southwestern Arkansas. According to H. D. Miser, the peridotite is probably the same age as the Tokio member of the Bingen formation (Upper Cretaceous), since the lower beds of the Bingen contain fragments of peridotite. As a portion of the Bingen beds actually overlies a portion of the peridotite in the American and Black Lick areas, the age of the intrusion is not older than Bingen times.

The peridotites found in the different areas are quite similar in general character and were probably all formed during a single period of volcanic activity. It is probable that the peridotite was intruded from a great depth, penetrating deep-seated sedimentary beds, including the Carboniferous and a portion of the Lower Cretaceous. After the intrusion of the peridotite, explosions took place which ejected portions of the intruded mass and carried with them some deep-seated shale and sandstone of Carboniferous age. This ejected material probably formed a crater in the Prairie Creek area with sloping sides and also eventually cemented into a peridotite breccia. A second series of explosions were perhaps responsible for the formation of the fine grained breccia and volcanic tuff.

Character of Diamonds.-The following statement concerning the character of the diamonds found is taken from U. S. Geological Survey Bulletin No. 735, "Diamond-bearing Peridotite in Pike County, Arkansas," by H. D. Miser and Clarence Ross: