The U.S. Bureau of Mines, 1943-1944
Aware of the black surface layer, the experienced engineers of the Bureau of Mines avoided remnants and took samplings of undisturbed peridotite. The test included only the diamond-bearing breccia of the southeast slope and a strip of the harder materials immediately west of it. In a preliminary test in April-May 1943, the Bureau used a twenty-six inch rotary bucket drill to put down three holes averaging about thirty-nine feet deep; then in September 1943-January 1944 it took a full-scale sampling from fifty-one holes, using a thirty-inch bucket drill. Two of those attempts hit hard rock near the surface and were abandoned; the others averaged about twenty-seven feet in depth.
Thirty-five tons of peridotite were removed from the preliminary holes and 435 tons from the forty-nine. The preliminary sampling was shipped to the Bureau’s laboratory in Rolla, Missouri, for processing; the main volume was reduced to 21.4 tons of concentrate on site, and that was bagged and transported to Rolla.
Anticipating possible criticism, the Bureau’s field team took various precautions. Safeguards against tampering were at first so strict that even the property manager was barred from the slope, until his protests forced a compromise. The Bureau’s report, including an elaborate flow chart of the test, reflected a cautious approach to processing.
The results were well in line with the Arkansas Diamond Company’s test of the peridotite in 1909. The main sampling yielded an average of slightly less than 2 carats per 100 short tons. The thirty-two diamonds recovered totaled 8.4 carats. About 75% came from a depth of twenty feet or less, but those from below twenty feet were of larger average size than those above. Overall, the thirty-two diamonds matched the historical average weight of about one-quarter carat.
 J. R. Thoenen, et al., “Investigation of the Prairie Creek Diamond Area, Pike County, Ark.,” Report of Investigations 4549 (United States Department of the Interior, Bureau of Mines, November 1949), 10-11, report in Arkansas State Geological Commission Files, Little Rock (the author deposited basic sections in the Crater archive and in the Butler Center, Little Rock). The report commented on the old concentration of diamonds “in the black ground capping the brecciated peridotite,” saying it previously had averaged about 0.5 carat per load (11). When the Bureau’s engineers arrived at the southeast slope, they found spots of original black ground totaling “not over half an acre” (10). John Fuller’s comprehensive mining map of 1931 indicated that almost all the unsluiced soil ran along the top of the southeast slope, at the ridge; when the author began field work at Crater of Diamonds State Park in June 1985, dark coloration was evident only in that area and, to a lesser degree, at a small spot down the slope.
Report 4549 was preceded by a 37-page pre-publication report, distributed in early December 1948. It accompanied a news release announcing the full “manuscript report” would be placed on open file December 15 (Leon W. Dupuy, Chief, Rolla [Mo.] Branch, Mining Division, BM, copy to Harold B. Foxhall, Director, Division of Geology, Arkansas Resources and Development Commission, Little Rock, December 10, 1948, ASGC files).
That full manuscript–completed February 1947–was preceded by a confidential draft report, “Prairie Creek Diamond Area, Pike County, Arkansas,” War Minerals Report (US Dept. of Interior, BM, April 1944), ASGC. A note at the bottom of page 1 explained the document was a progress report for personnel of the BM and was “not to be made available to others, as the data are subject to correction and revision.” The final report, when issued, would be “distributed on a limited basis to officials of the Federal war agencies, the owners or operators of the properties described herein . . ..”
 The sampling was described in Report 4549, pp. 3, 11ff. Figure 2 of the illustrations used the U.S. Geological Survey map (1916) to indicate the grid of bore holes.
 Ibid., 14-18.
 Robert J. Arthur, secretary of the North American Diamond Corporation, Logansport, Indiana, to Solon W. House, Murfreesboro, guardian of the NADC’s property, September 23, 1943, I.P. Arthur suggested they could work out a solution allowing House to continue overseeing the grounds and keeping local visitors from hunting diamonds, while the drilling crew worked at a safe distance.
 Report 4549, Figure 23; details on pp. 14-18. Especially notice the BM’s comment about the grease table: “Salted samples fed to the grease table showed it to be inefficient, owing, probably, to unregulated temperature control of the grease and water suspension and possibly to the type of grease used. However, inefficiency of the grease table would not have altered the final result quantitatively, owing to the small size and quantity of the table feed” (18). Also see the comment on the size of the smallest screen used: “Although the test plant did not include hand sorting of sizes smaller than minus 8 plus 20-mesh, there seems to be no reason why, if smaller stones could be used, they could not be hand-picked down to plus 40-mesh” (ibid.).
 In John Fuller’s test in 1909, 482 loads (1,600 pounds each) of peridotite yielded 25 diamonds weighing a total 9.75 carats, for an average of 2 carats per 100 loads (“Reports and Information,” 36).
 “Results of Concentration,” Report 4549, p. 19. Pages 19-21 provided details for each drill hole on the grid-number of diamonds, weight, depth of recovery, etc. The heart of the volcanic breccia was the richest zone.
George Vitt, now identifying as a consulting engineer in New Haven, Connecticut, issued a nonsensical eight-page critique in March 1946, scoring the property owners as well as the Bureau (Vitt, “Criticism of Bureau of Mines Report on the Murfreesboro Diamond Property,” to John Q. St. Clair, Norman, Oklahoma, March 15, 1946, Parks and Tourism files).