In those first few years, almost all consulting geologists thought the surface yield of the eroding volcanic formation reflected a rewarding commercial reserve in the undisturbed matrix below.[1] A rare but prominent yellow flag came from Professor Philip S. Schneider of New York, a leading geologist who studied the pipe in September-October 1907 for the State of Arkansas.
Schneider’s preliminary report, published in Little Rock in late 1907, cautioned that the 160 or so diamonds found so far had come from the base of a slope that had “for centuries received the wash of the three hills to the north, . . . and the gems which are apparently found in such abundance may be the accumulations of a thousand years in this particular spot.” To gauge commercial potential, mining groups needed to evaluate a few thousand loads of fresh matrix.[2]
The ongoing tests of the matrix also offered reason for caution. Only three of approximately 140 diamonds collected by the fall of 1907 were extracted from material below the black surface layer.[3] And later samplings reaffirmed the scarcity. The highest recorded yield ever gotten from the undisturbed peridotite occurred in a test in 1909: an average of 2 carats per 100 loads, far below the 10-12 carats average needed for minimal commercial production.[4]
In those early years, however, such poor results hardly dampened enthusiasm. The surface yield and the stunning size of the formation, then estimated at 60-70 surface acres, combined to overwhelm almost all the experts. The size, per se, inspired awe, for even the famous Kimberley diamond mine of South Africa was initially only 10.37 acres. The largest mine in the original African field, the Du Toits Pan, was 31.79.[5] Because nature typically scattered diamonds at random within such volcanic deposits, it was assumed that commercial-grade hot spots probably would turn up somewhere in the matrix despite disappointing tests at any given time.[6] Test results, however consistent, were easily blamed on inadequate sampling, faulty equipment, incompetent supervision, theft, or perhaps devious intent. John Fuller, himself, never stopped believing that because of “inadequate washing machines,” the company lost about half the diamonds it processed.[7]
Unusually large to begin with, the formation lost very little respect as it became clear that the diamonds were coming from approximately thirty-five acres dominating its east half.[8] That productive “volcanic breccia,” as the U. S. Geological Survey classified it, extended over the big southeast slope and across a high ridge into the northeast corner.[9]
The volume of breccia reserve below the gummy surface was in itself enlivening, for John Fuller and others estimated the rain-softened material extended as much as 60' deep and provided at least 1,500,000 cubic yards that could be “easily and cheaply mined.”[10] Long-hole drilling found the unweathered reserve, the blue ground, still running well below that depth.[11]
[1] As usual, the Nashville News picked up the theme early: “. . . it is thought from this splendid surface indication that the fields are very rich, and will yield many diamonds of rare quality when the mining goes deep enough” (“Four Propositions,” June 12, 1907, p. 1). Evidently, that advice came primarily from Henry S. Washington, the first consultant hired by Reyburn’s group. After studying the pipe for a year, Washington sent Reyburn a final encouraging report in late 1907, and also presented his findings in published articles and at the American Institute of Mining Engineers in February 1908. In the private report, he made a clear, strong statement. It was true, he said, that the diamonds collected since Huddleston’s discovery had come almost entirely from the surface. Nevertheless, there was no doubt the surface diamonds originated in the volcanic matrix below, which was almost the same material as that mined in South Africa, and Reyburn’s deposit was vast. Considering the number of diamonds already found, “the indications” were they “probably” existed in the matrix in remunerative amounts. Washington thought the odds justified “considerable” investment, “with good hopes of financial success under proper management” (Washington to Reyburn, in “Reports and Information,” 8, and passim).
John Fuller was even more optimistic. Referring to one geologist’s caution concerning the surface yield, he said, “I am of the opinion, however, that the underlying peridotite will prove rich enough to be worked at considerable profit and that the surface indications fully justify the expenditure of considerable money to prove this to be so” (Fuller to Loree, in “Reports,” 19).
When writing private reports or commenting for the news media, geologists and mining engineers tended to be more openly optimistic. Expressing themselves in professional journals, they sometimes exercised more restraint. For instance, “The Academy of Science of St. Louis,” Science, New Series, 30 (July 23, 1909), 127, a report on the ASSL’s meeting of May 17, 1909, commented on W. E. McCourt’s paper on “Diamonds in Arkansas”: “From these indications this area seems to contain a mass of rock similar to the rock in South Africa. But as to the number of diamonds which may be found deeper in the peridotite, that, said Professor McCourt, is a question which can only be settled by actual mining and testing. The results which have been shown by the more or less spasmodic exploitation, however, seem to indicate a good promise.” McCourt was with the Department of Geology, Washington University.
Of course, John Fuller, Henry Washington, and other professionals almost always included the standard qualifier at some point: Only full-scale testing could finally determine the yield.
[2] Philip F. Schneider, A Preliminary Report on the Arkansas Diamond Field, issued by the Arkansas Bureau of Mines, Manufactures, and Agriculture (Little Rock: Central Printing Co., 1907), 14. Schneider’s study ended October 14, 1907. An expanded work, including historical context, was published in 1908.
Fuller, Report to Loree, June 1908, p. 13, repeated Schneider‘s caveat more tentatively, although Fuller was hardly concerned about the surface accumulation: “As an offset to the above very favorable showing [average yield] attention must be called to the fact that most of the stones so far recovered have been found on the South slope above mentioned, of the volcanic area. This is a place where if any natural concentration of the weathered ground has taken place, the concentrate would naturally collect, so that the underlying peridotite may average lower in value than the excellent surface showing might lead one to expect.” Later in the report, Fuller referred to Schneider’s cautioning, and then offered a more enthusiastic assessment of commercial potential.
[3] Kunz and Washington, “Diamonds in Arkansas,” 173; cf. their “Occurrence of Diamonds in Arkansas,” 1250, which said of the first two diamonds thought to have been extracted subsurface, “This would have settled definitely the question of their source had not some doubt existed through the possible accidental admixture of small amounts of the surface soil with the underlying green earth . . ..”
[4] This was the first subsurface entry in Fuller’s comprehensive report of 1931—“peridotite,” as opposed to “surface” (“Estimate of Unit Value,” in “Reports and Information,” 36).
As a model for analyzing the Arkansas pipe, Fuller used a South African mine he was familiar with, the Jagersfontein, which was profitable at 13 carats per 100 loads (Fuller to ADC, 27).
[5] Fuller, Report to ADC, 24, compared the Arkansas “mine” with those and two others in South Africa: DeBeers, 13.72 original surface acres; Bultfontein, 23.54. Fuller’s “Qualifications,” in “Reports and Information,” 9, indicated he worked at all four mines while in South Africa. Also see the obituary, “John Torrey Fuller,” New York Times, May 19, 1939, p. 21.
[6] This was the assumed nature of diamond-bearing pipes. For instance, E. G. Woodford, Consulting Mining Engineer, to President, Ozark Diamond Mining Corporation [Company], October 28, 1908, p. 3, “Misc.” box, Crater archive: “Large areas of the famous mines have rich and poor quarters, payable and blank layers . . .. A practical diamond miner carefully and exhaustively prospects the whole area of his mine in order to select the rich quarter for his first operations, expecting always to find changes in value and locality as he attains depth” (also a similar comment, ibid., 6). Reyburn and Zimmerman, “Diamonds in Arkansas,” p. 984: “This ‘pipe,’ being similar in every respect to the ‘pipes’ of South Africa, and having the different varieties of peridotite, will, no doubt, contain lean or barren portions with varying diamond content.”
[7] Fuller, trying to encourage new investment in the ADC in 1909, immediately decried the company’s previous “haphazard experimental tests” with “inadequate washing machines.” The “chances are,” he wrote in the Engineering and Mining Journal, “that as many diamonds were lost in tailings as were recovered” (Fuller, “Diamond Mine in Pike County, Arkansas,” 154). He refrained from mentioning that few of the diamonds, recovered or lost, came from the undisturbed peridotite, the essential commercial reserve. Nor did he mention the problem of processing the black gumbo soil. Fuller was still expressing such criticism as late as 1931 (“Public Statement of John T. Fuller on April 7, 1929,” in “Reports and Information,” 33-34; “John T. Fuller’s Estimate of Unit Value in Carats per Load, 1931,” ibid., 35).
Also notice Fuller’s statement to the Nashville News in December 1910: “Engineer Fuller, who is in charge of the work [on the ADC’s property], states that only a portion of the stones are being found under the present method of working the dirt, and that it will all be worked over when the [new] machinery is installed, and that he expects to find as many more as he has already secured, at the second working” (“Washing for Diamonds in Pike County,” December 10, 1910, p. 1).
[8] Soon, those in the field distinguished between the easily weathered ground on the slope, “being at least 35 acres in extent,” and the much tougher dark peridotite dominating the west side of the pipe—material similar to the “hardebank” of South Africa (sometimes spelled “hardibank”) and classified by the USGS as “intrusive peridotite.” John Fuller, with experience in South Africa, quickly drew the distinction in his reports, and consistently estimated that the softer “volcanic breccia” covered about thirty-five surface acres (“Diamond Mine in Pike County,” 154).
At first, the hardebank was merely deemed too difficult to treat economically. Fuller to Loree (1908) 12: “. . . no amount of exposure to the atmosphere will have any practical effect on its disintegration. . . . Its economical and successful method of treatment has not yet been successfully solved.” Fuller to ADC, 23: the hardebank was “equal to the hardest quartzite” and would have to be “crushed by powerful gyrating crushers and crushing rolls.” Reyburn and Zimmerman, “Diamonds in Arkansas,” 984, 986, said of the ADC’s operations to date, (1920): “Owing to lack of proper facilities, none of the harder portions of the peridotite including the ‘hardebank’ were tested.”
Gradually, it became apparent the hardebank, as well as the companion light-blue peridotite tuff, was either diamond-free or so poorly endowed that diamonds escaped notice. Evidently, the first to acknowledge this was Austin Q. Millar, who reported that hardebank on the small northeast slope of the pipe contained no diamonds (infra, “Northeast Slope-Kimberlite Company“).
Basically, experts have theorized that any diamonds in the original hardebank magma disintegrated (“resorbed”) under intense heat and attrition. For instance, petrographer S. A. Williams’s statement in Charles L. Fair, “Progress Report #3,” to Neal Potts, General Earth Minerals, April 4, 1969, in Crater of Diamonds file, Department of Parks & Tourism, Little Rock.
Whatever the theories, this author’s extensive field work at the Crater of Diamonds, 1985-1993, reconfirmed the extreme rarity or apparent non-existence of diamonds originating outside the volcanic breccia (as the USGS identified it). State-sponsored tests of the Crater in the mid-90s pointed to the same conclusion (infra, “Final Test”).
[9] The USGS map, Plate 10, delineated the breccia as it appeared at the time.
[10] This is Fuller’s estimate of the weathered reserve, in “Diamond Mine in Pike County, Arkansas” (1909), 154. Estimates of depth varied, with Washington the most conservative; as usual, the experienced Fuller got closer to the average eventually established.
[11] At least three drill holes were completed in 1907, to depths of 205’, 186’, and 80’ (Kunz and Washington, “Diamonds in Arkansas,” 171; cf. their “Occurrence of Diamonds in Arkansas,” 1248, written earlier and mentioning “drill holes” to only 30’). The USGS map, Plate 10, located four drill holes—three in the field of volcanic breccia and one at the center of the pipe (the numbers correspond to discussion in the USGS reports).