Adopt a Mine

Heads, Tails, and Decisions In-Between: The Archaeology of Mining Wastes
Paul J. White
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Ore dumps, milling wastes, and other processing residues are ubiquitous features of mining landscapes and often dominate the surface remnants of former operations. While archaeologists have yet to investigate these features systematically, state and federal hazard mitigation programs increasingly target mining and milling wastes for environmental testing and cleanup. This article investigates the extent to which these deposits retain historical information, including differences in ore bodies and technological processes, by reviewing historical and contemporary literature and analyzing rock and sediment samples associated with a small-scale gold mine in Alaska for which an excellent documentary record exists. Results of physical and chemical analyses are tempered by the variability caused by sampling methods, testing techniques, and post-depositional processes, but promising avenues for future studies are also identified.

Introduction

With public opinion polls ranking mining as North America’s least-favored industry, below even that of tobacco manufacturers, mining enterprises have seemingly gained a reputation more for their undesirable consequences than for their desirable products.1 Processing wastes are the likely source for much of this discontent. According to the Environmental Protection Agency (EPA), mining operations in the United States generate some two billion tons of waste material annually, accounting for up to 40 percent of the nation’s solid waste. Approximately three-quarters of mining refuse comes from materials overlying mineral deposits, with the remainder classified as tailings—the discard from milling processes employed to concentrate ore values. Generally speaking, the ratio of waste to product is greatest in the working of precious metals because high commodity prices enable companies to work comparatively poorer outcrops. By recent estimates, the production of a single gold ring now leaves in its wake any-where from 3 to 35 tons of mine waste.2

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There is little need to account for where the bulk of this material ends up. Vast, barren piles of processed rock tend to dominate mining sites, and they also form some of North America’s most dramatic industrial landscapes. Beyond their often-arresting appearance, environmental testing indicates that mining wastes contribute to an unwelcome legacy of contamination, impacting mining regions long after the demise of operations. Indeed, wastes at historic and abandoned mines are thought responsible for a large portion of the total pollution stemming from mining wastes, a reflection of their creation during periods when environmental regulations were poorly enforced, comparatively lenient, or entirely nonexistent.3 To remedy this problem, government programs have increasingly slated wastes at abandoned mines for hazard mitigation over the last three decades.

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The exponential growth of cleanup activity has sparked a proliferation of technical data on the sources, types, and extent of mine waste pollution. That little of this information has found its way into historical analyses is unfortunate and the likely consequence of a frequent communication divide between environmental and cultural resource practitioners.

There are, however, good reasons to explore this area further. Industrial archaeologists generally consider process residues a promising source of information because of their “quantity, usually undisturbed pattern of distribution, and potential for physical analysis.”4 Archaeological investigations of iron-making wastes, among the most studied of industrial residues, have productively linked physical and chemical variances in slag composition to different reduction processes, stages within a process, and, more tentatively, operative efficiency.5

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Mining Wastes as Archaeological Artifact? Prospects and Pitfalls

Processing wastes, at first glance, may appear an unlikely source of information about past mining operations: dumping locations, whether immediately outside mine entrances or downhill of mill sites, suggest little more than a governing economic rationale to dispose of wastes as quickly as possible. Wastes are, however, fundamentally cultural deposits. As environmental historians have frequently stressed, dumping practices have changed over time, and these practices are often in line with prevailing cultural attitudes about the environment.6 Waste deposition required both forethought and continued expenditure, and mining engineers employed different strategies to improve the efficiency of waste disposal. Until the late-19th century, and continuing in remote districts through the 20th century, mining engineers preferred to locate milling facilities along watercourses to expedite waste removal.7
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Local conditions influenced the choice of containment methods. For operations located in rugged terrain, the construction of a retaining wall across the floor of the valley to trap mine wastes might have sufficed. Milling plants located on level or gently sloping ground required other alternatives. Here, the use of size-separating devices, such as classifiers, dewaterers, or perforated launders, enabled engineers to stack tailings and also to construct impoundment dams entirely from tailings material, the larger, sand-size particles forming the embankment behind which finer particles, or “slimes,” were directed.8 Other companies found new uses for wastes, including as fertilizer, road and railroad gravel, concrete aggregate, and fill for mine stopes. Waste storage also opened possibilities for waste reprocessing if improvements to milling technology or mineral prices warranted. In preparation, some companies separated mining and milling wastes according to grade.9

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Mining literature also indicates that wastes contain internal information of import to daily operations. Ore bodies were rarely homogenous and often changed with depth—and the profitability of mining ventures hinged upon the ability to keep apace of these changes. Mine operators accomplished this by regularly sampling ores and host rock. Inside milling plants, too, the comparison of mill heads, concentrates, and tailings enabled millwrights to calculate the efficiency of the plant and of individual machines.10 Supporting the textbook dictum that “a millman is not progressive who is content with his flow sheet,” mining treatises and journal articles abound with case studies identifying minor improvements to extractive efficiency. Some common adjustments included altering grinding size, varying the chemical agents used in recovery equipment, rerouting the flow of ore through the mill, or adding and removing machines from the circuit.11

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Discussion and Conclusion

Chemical analysis indicates that mining and milling deposits retain a range of historical information. Ore samples taken from the mill resemble those from a particular mine; recovery processes such as amalgamation (and gravity concentration to a lesser degree) leave traces in the elemental composition of milling sediments; ore reduction stages leave signatures in particle size. More tentatively, milling wastes also furnish some qualitative indicators of operative efficiency, particularly with regard to mercury loss. All told, if results from Bremner represent the most detailed information ascertainable from abandoned mining wastes, then the outlook for future archaeological studies holds promise, albeit with qualifications. Realistically, researchers could glean much of this information from written records and site surveys, without the need for extensive laboratory analysis.

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Substantial limitations exist, then, in using environmental characterization studies to also serve the purposes of historical inquiry. Arguably, however, some restrictions could be overcome (or at least better controlled) if incorporated early into the design of waste characterization programs. Data taken primarily from the upper levels of waste deposits (as at Bremner) or strategies that mix different sampling locations to form an overall composite (another common technique) mask the internal variability of deposits.

Sampling from vertical profiles would enable researchers to observe leaching and oxidation processes in greater detail and potentially enable the assessment of changes over time. An analytical strength of this approach is that it provides a firmer basis for interpreting whether element concentrations are the likely consequence of leaching and oxidation processes or whether the variation is due to other factors. Historical interpretations would benefit also from combining qualitative and quantitative approaches, analyzing mineral phases together with an assessment of concentration ranges for a given element. Other analytical techniques may also be of service. For cases where valued metals such as gold are identifiable in waste materials in sizable amounts, optical microscopy might usefully distinguish gold not recovered from gold not recoverable by milling techniques.

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As this suggests, archaeologists and historians need not pursue these lines of inquiry independently of environmental research. Indeed, environmental characterization programs remain imperative to historical studies of wastes because they determine the susceptibility of specific deposits to acid generation and leaching. Moreover, environmental testing programs show signs of increasing compatibility with archaeological methodologies. Recent procedures for characterizing mine wastes, for instance, stress three-dimensional sampling to better account for the internal heterogeneity of deposits, one environmental testing handbook noting, “If a tailings pile has several levels, each level represents a different time period and must be sampled separately.”59 Lastly, and arguably most critically, environmental researchers will continue to examine historic and abandoned mining wastes in the foreseeable future—and archaeologists and historians ought to be involved in this process.

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Notes
1. Roper Research on the public favorability of industries, 1992 and 1994, cited in Sharon Prager, “Changing North America’s Mind-Set about Mining,” Engineering and Mining Journal 198, no. 2 (1997): 36–44.
2. Robert L. Hoye and S. Jackson Hubbard, “Mining Wastes” in Standard Handbook of Hazardous Waste Treatment and Disposal, ed. Harry M. Freeman (New York: McGraw-Hill, 1989), sec. 4, 48–49; gold ring estimates derive from the Mineral Policy Center, a nonprofit organization dedicated to reducing the destructive impacts of mines on communities and the environment.
3. Hoye and Hubbard, “Mining Wastes,” sec. 4, 49 (see n. 2).
4. George A. Teague, “The Archaeology of Industry in North America” (PhD diss., Univ. of Arizona, Tucson, 1987), 205.
5. See, for instance, Hans-Gert Bachmann, The Identification of Slags from Archaeological Sites, Institute of Archaeology, Occasional Publication 6 (London: Institute of Archaeology, 1982); Jerzy Piaskowski, “Distinguishing between Directly and Indirectly Smelted Iron and Steel,” Archaeomaterials 6 (1992): 169–73; W. Rostoker and James Dvorak, “Wrought Irons: Distinguishing between Processes,” Archaeomaterials 4 (1990): 153–66; Robert B. Gordon, “Material Evidence of Ironmaking Techniques,” IA: Journal of the Society for Industrial Archeology 21, no. 2 (1995): 67–80, and “Process Deduced from Ironmaking Wastes and Artifacts,” Journal of Archaeological Science 24 (1997): 9–18; Robert B. Gordon and David Killick, “The Metallurgy of the American Bloomery Process,” Archaeomaterials 6 (1992): 141–67; David Landon, Patrick Martin, Andrew Sewell, Paul White, Timothy Tumberg, and Jason Menard, “‘… A Monument to Misguided Enterprise’: The Carp River Bloomery Iron Forge,” IA: Journal of the Society for Industrial Archeology 27, no. 2 (2001): 5–22.
6. For an excellent account of the mining industry’s changing disposal practices and their environmental consequences, refer to Duane A. Smith, Mining America: The Industry and the Environment, 1800–1980 (Lawrence: Univ. Press of Kansas, 1987).
7. F. E. Marcy, “The Enrichment and Segregation of Mill Tailings for Future Treatment,” Transactions of the American Institute for Mining Engineers 58 (1917): 178.
8. Arthur F. Taggart, Handbook of Ore Dressing (New York: John Wiley and Sons, 1927), 1284.
9. Marcy, “Enrichment and Segregation,” 178–83 (see n. 7); Otto Ruhl, “Mine Tailings, the Basis for a Growing Industry,” Mining and Engineering World 35, no. 16 (1911): 733–35; R. S. Handy, “Treatment of Tailing and Ore in the Sweeny Mill,” Mining and Scientific Press 30 (August 1919): 289–94; “Tailings Disposal Innovations,” Engineering and Mining Journal 131, no. 6 (1931): 275; John B. Huttl, “Re-Treating Complex Tailings at Ophir, Utah,” Engineering and Mining Journal 141, no. 5 (1940): 52–53; Taggart, Handbook, 1287–88 (see n. 8).
10. Robert S. Lewis, “Milling Calculations,” Chemical and Metallurgical Engineering 20, no. 5 (1919): 224–33; A. L. Engel, “Some Aspects of Ore-Dressing: General Observations on the Conduct of Daily Operations in the Plant, Made from the Viewpoint of an Operating Engineer,” Mining and Metallurgy 12, no. 298 (1931): 447–49. The regular testing of mill sediments seems to have been a late-19th-century development. Arthur Taggart notes, for instance, that for the typical mill in the 1870s, “Head assays were substantially unknown. Feed tonnage was ‘guesstimated’ … Moistures were agreed upon, often in the Russian sense. Tailings were similarly manhandled.” Taggart, “Seventy-Five Years of Progress in Ore Dressing” in Seventy-Five Years of Progress in the Mineral Industry, ed. A. B. Parsons (New York: American Institute of Mining and Metallurgical Engineers, 1947), 118.
11. Robert H. Richards and Charles E. Locke, Textbook of Ore Dressing, 3rd ed. (New York: McGraw-Hill, 1940), 355. There are copious examples of milling modifications, but for a sense of some different possibilities, refer to tables in Charles F. Jackson and J. H. Hedges’s “Metal Mining Practice,” U.S. Bureau of Mines Bulletin 419 (Washington, DC: GPO, 1939), 404, 406–19, which detail the circuits of 28 gold mills.
12. Handy, “Treatment of Tailing,” 289 (see n. 9).
13. See, for instance, Robert G. Eppinger, Paul H. Briggs, Danny Rosenkrans, and Vannesa Ballestrazze, “Environmental Geochemical Studies of Selected Mineral Deposits in Wrangell-St. Elias National Park and Preserve, Alaska,” U.S. Geological Survey Professional Paper 1619 (Washington, DC: GPO, 1999), 34.
14. Roger P. Ashley and Charles N. Alpers, “How Mineral Deposits Interact with the Environment,” Abandoned Mine Lands Preliminary Assessment Handbook, State of California, Environmental Protection Agency, Department of Toxic Substances Control (State of California, 1998), Appendix B, 1–2; Robert B. Vaughn, Mark R. Stanton, and Robert J. Horton, “A Year in the Life of a Mine Dump: A Diachronic Case Study” in Tailings and Mine Waste ’99 (Rotterdam: A. A. Balkema, 1999), 475–84.
15. Michael Trinkley, “Archaeological Investigations at the Reed Gold Mine Engine Mill House (31CA18**1): Reed Gold Mine State Historic Site, Cabarrus County, North Carolina,” Chicora Foundation Research Series 6 (Columbia, S.C.: Chicora Foundation, 1986), 28, 40, and “Additional Investigations at the Reed Gold Mine Engine Mill House, Reed Gold Mine State Historic Site, Cabarrus County, North Carolina, 31CA18**1,” Chicora Foundation Research Series 12 (Columbia, S.C.: Chicora Foundation, 1988); George A. Teague and Lynnette O. Shenk, “Excavations at Harmony Borax Works: Historical Archaeology at Death Valley National Monument,” Western Archaeological Center, Publications in Anthropology 6 (Tucson: National Park Service, 1977), 172–77, 192.
16. Charles V. Baltzer, “Developing Mineral Waste Sampling Plans for Reprocessing Studies,” Hazardous Materials Control Research Institute, Monograph Series: Sampling and Monitoring 1 (Silver Spring, Md.: Hazardous Materials Control Research Institute, 1991), 104. Custom mills processed ores from different companies, with prices varying by tonnage, complexity of the operation, and stipulations for the final product.
17. For an introduction to the legislative background of Superfund, refer to Richard Stanford and Edward C. Yang, “Summary of CERCLA Legislation and Regulations and the EPA Superfund Program” in Standard Handbook of Hazardous Waste Treatment, sec. 1, 29–45 (see n. 2). The EPA currently lists 88 mining sites on its National Priority List, with the total cost of cleanup estimated at $2.8 billion. EPA projects encompassing extensive mining regions include the Bunker Hill Mining and Metallurgical Complex, and Stibnite/Yellow Pine Mining Area in Idaho, the Oronogo-Duenweg Mining Belt, Missouri, and, in Montana, the Basin Mining Area, Barker-Hughesville Mining District, Upper Tenmile Creek Mining Area, and Carpenter Snow Creek Mining District. USEPA, Abandoned Mine Lands Team, Reference Notebook (Sept. 2004) <http://www.epa.gov/superfund/programs/aml/tech/amlref.pdf>.
18. U.S. Bureau of Land Management, Abandoned Mine Lands Task-force, Abandoned Mine Land Inventory and Remediation: A Status Report to the Director (1996); see also U.S. Geological Survey, “The USGS Abandoned Mine Lands Initiative: Protecting and Restoring the Environment near Abandoned Mine Lands,” U.S. Geological Survey Fact Sheet 095–99 (Reston, Va.: U.S. Geological Survey, 1999).
19. Bill to Provide for the Reclamation of Abandoned Hardrock Mines and for Other Purposes, HR 504, 108th Cong., 1st sess., Congres-sional Record, 149, (29 January 2003): H244. [HR 504 is currently awaiting executive comment from the Department of the Interior.]
20. Donald L. Hardesty, “Issues in Preserving Toxic Wastes as Heritage Sites,” The Public Historian 23, no. 2 (2001): 19–28; Fredric L. Quivik, “Integrating the Preservation of Cultural Resources with Remediation of Hazardous Materials: An Assessment of Super-fund’s Record,” The Public Historian 23, no. 2 (2001): 47–61.
21. For examples of the landscape approach, see Richard V. Francaviglia, Hard Places: Reading the Landscape of America’s Historic Mining Districts (Iowa City: Univ. of Iowa Press, 1991); Donald L. Hardesty and Barbara J. Little, Assessing Site Significance: A Guide for Archaeologists and Historians (Walnut Creek, Calif.: Altamira Press, 2000); Bruce R. Noble and Robert Spude, “Identifying, Evaluating, and Registering Historic Mining Sites,” National Register Bulletin 42, revised ed., National Park Service, Interagency Resources Division, National Register of Historic Places, 1997.
22. A troy ounce is 1/12 of a pound (compared to the usual 1/16) and was used regularly in the assaying of precious metals.
23. See Ernest Patty, “The Airplane’s Aid to Alaskan Mining,” Mining and Metallurgy 18, no. 362 (1937): 92–94. For a general history of mining in the Copper Basin, refer to William Hunt, Mountain Wilderness: Historical Resource Study for the Wrangell-St. Elias National Park and Preserve (Anchorage: National Park Service, 1991).
24. Indicating the improved conditions for precious-metal mining, the number of mines producing gold and silver in the United States rose from approximately 1,200 placer and 2,000 lode operations in 1929 to, respectively, 7,400 and 4,650 in 1935, with gold production rising from 689,403 fine ounces to 3,222,116 fine ounces. J. P. Dunlop, “Gold and Silver” in Minerals Yearbook 1930 (Washing-ton, DC: GPO, 1933), 817, 827, and “Gold and Silver” in Statistical Appendix to Minerals Yearbook 1935 (Washington, DC: GPO, 1936), 337; Chas. W. Henderson and J. P. Dunlop, “Gold and Silver” in Minerals Yearbook 1936 (Washington, DC: GPO, 1936), 92. See also Charles W. Miller, The Automobile Gold Rushes and Depression Era Mining (Moscow: Univ. of Idaho Press, 1998).
25. J. C. Roehm, “Preliminary Report of the Bremner Mining Company, Hanagita-Bremner Mining District,” Alaska Territorial Department of Mines Property Examination 87–3 (1936), Bureau of Land Management, Alaska Resources Library, Anchorage, PE 87–3.
26. Higher metal prices and the ability to reduce gold ore to bullion cheaply were likely factors behind a noted trend that gold-mining operations tended to construct milling plants earlier in mine development than the mining of base metals. E. D. Gardner and C. H. Johnson, “Mining and Milling Practices at Small Gold Mines,” U.S. Bureau of Mines Information Circular 6800 (Washington, DC: GPO, 1934), 4. The cost of milling equipment at the Lucky Girl mill is provided in “Yellow Band Gold Mines, Inc. Balance Sheet, 31 December 1939,” MS 36–1–10–8, Asa C. Baldwin Papers, c. 1907–1942, Alaska State Library, Juneau (hereafter cited as Bald-win Papers).
27. A number of gold-recovery methods more efficient than amalgamation and gravity concentration were in existence by the 1930s. Flotation and cyanidation, for instance, were both capable of working poorer, more refractory ores. Amalgamation and gravity concentration methods nevertheless remained popular among small-scale operators for several reasons. For one, small-scale mines tended to work less-complex deposits, to which these techniques were best suited. These methods were also comparatively cheaper, required fewer man-hours to operate, and could be run by less-skilled operators—of particular benefit to smaller operations where labor resources were often limited. Refer to Gardner and Johnson, “Mining and Milling,” 19–28 (see n. 26).
28. The arrangement of the milling circuit derives from field observations and a detailed description in Roehm, “Preliminary Report,” 4 (see n. 25).
29. J. C. Roehm, “Investigations: McCarthy, Nizina River, Bremner and Chisana Mining Districts: Summary Report and Itinerary of J. C. Roehm,” Alaska Territorial Department of Mines Itinerary Report 195–14, p. 8 (1936) Bureau of Land Management, Alaska Resources Library, Anchorage.
30. Fred Moffit, “The Lower Copper River Basin, Alaska: The Taral and Bremner Districts, The Chitina District,” U.S. Geological Survey Bulletin 520-C (Washington, DC: GPO, 1912), 10, and “Geology of the Hanagita-Bremner Region, Alaska,” U.S. Geological Survey Bulletin 576 (Washington, DC: GPO, 1914).
31. Asa Baldwin, “Yellow Band Gold Prospect, Golconda Creek, Bremner District, Alaska” (1935), and “To the Unitholders [sic] in Yellow Band Gold Option,” MS 36–1–10, items 1 and 3, Baldwin Papers, 10 March 1937, p. 2; Fred Moffit, “Recent Mineral Developments in the Copper River Region,” U.S. Geological Survey Bulletin 880-B (Washington, DC: GPO, 1937).
32. The Sheriff claims were formerly known as the “Nelson Prospect,” but the name evidently changed upon its acquisition by Yellow Band Gold Mines. Asa Baldwin, “Notice of Special Meeting of Stockholders” (1938), and “Yellow Band Gold Mines, Inc. President’s First Annual Report to Stockholders” (1938), MS 36–1–10, items 4 and 5, Baldwin Papers.
33. Asa Baldwin, “Journal of the Yellow Band Gold Mine, 1940–41,” entry 4 July 1941, MS 36–1–2–4, Baldwin Papers.
34. Baldwin, “Yellow Band,” (see n. 32); Asa Baldwin, “Annual Report 1939″ and “Annual Report 1940,” MS 36–1–10, items 7 and 9, Baldwin Papers.
35. The contract for Yellow Band, rewritten just prior to the purchase of the Bremner Gold Mining Company holdings, allowed the Baldwin to pay royalties of 25 percent to the original claim-holders for any ore from the Yellow Band taken to the mill, with a minimum cash payment of $1,500. Baldwin, “Yellow Band,” 2, 6 (see n. 32).
36. Asa Baldwin, “Assay Map, Sheriff Claims, Yellow Band Gold Mines, Inc., Golconda Creek, Alaska,” MS 36–1–8–28, Baldwin Papers.
37. Baldwin, “Annual Report 1939,” 4 (see n. 34); Baldwin, “Journal,” entry 4 October 1941 (see n. 33).
38. Baldwin, “Journal,” entry 23 July 1941 (see n. 33). The Bremner Gold Mining Company may also have suffered a similar problem with the concentration circuit, mine inspector J. C. Roehm noting, “Very little concentrate is collected on the [Wilfley] table since most of the mineralization is oxidized and passes off in the tails.” Roehm, “Preliminary Report” (see n. 25).
39. Asa Baldwin, “Annual Report 1941,” 3–4, MS 36–1–10–11, Baldwin Papers; also “Journal,” entries 30 April to 1 June 1941 (n. 33).
40. C. E. Needham, “Gold and Silver,” Minerals Yearbook 1942 (Washington, DC: GPO, 1944), 80–81.
41. Claude Stewart to Mrs. Asa C. Baldwin, 10 November 1946, 15 March 1948; and Paul Fretzs to C. F. Taplin Jr., 9 January 1960, MS 36–1–11, items 13, 16, 18, Baldwin Papers.
42. Paul Fretzs to Sylvia (Baldwin) Johnson, 26 March 1975, 17 April 1978, MS 36–1–11, items 22 and 24, Baldwin Papers.
43. For a complete description of sample methodology, sample size, and analytical techniques, refer to Robert G. Eppinger, Paul H. Briggs, Danny Rosenkrans, Vannesa Ballestrazze, José Aldir, Z. A. Brown, J. G. Crock, W. M. d’Angelo, M. W. Doughten, D. L. Fey, P. L. Hageman, R. T. Hopkins, R. J. Knight, M. J. Malcolm, J. B. McHugh, A. L. Meier, J. M. Motooka, R. M. O’Leary, B. H. Roushey, S. J. Sutley, P. M. Theodorakos, and S. A. Wilson, “Geochemical Data for Environmental Studies of Mineral Deposits at Nabesna, Kennecott, Orange Hill, Bond Creek, Bremner, and Gold Hill, Wrangell-St. Elias National Park and Preserve, Alaska,” U.S. Geological Survey Open-File Report 99–342 (Washington, DC: GPO, 1999); Eppinger et al., “Environmental Geochemical” (see n. 13).
44. For testing methodology, refer to Eppinger et al., “Geochemical Data,” 8–9 ( n. 43).
45. These techniques come with different methods. Laboratory analysis employed ICP-AES using total digestion and 10-element partial extraction, and trace- and major-element scan methods, cold-vapor AAS for mercury, and graphite-furnace AAS for determining gold concentrations. For a fuller description of these techniques and other analytical techniques employed, see Eppinger et al., “Geochemical Data,” 10–13 (n. 43).
46. Geochemical studies at other sites indicate that leachate tests do approximate the initial waters flowing from waste piles prior to their dilution by adjacent streams. Eppinger et al., “Environmental Geochemical,” 34 (see n. 13). For a detailed description of the leaching methodology employed, refer to Eppinger et al., “Geochemical Data,” 10 (n. 43).
47. Eppinger et al., “Environmental Geochemical,” 15 (see n. 13).
48. The preservation of milling equipment and mill floors indicates that it is unlikely that these boulders derived solely from slide debris but probably resulted from the blasting necessary during the mill’s construction (c. 1934). In all probability, a second launder dumped tailings southeast of the mill foundation—an area still covered with slide debris.
49. SGS Minerals Services, Toronto (the same lab contracted to analyze USGS samples collected in 1996), performed 40-element ICP-AES total digestion and cold-vapor AAS for tailings samples collected in 2001. Tailings and other samples from the 2001 season were also analyzed using MacMillian Hall Environmental Chemistry facilities at Brown University. Here, ICP-AES analysis was performed on a JY2000 Ultrace ICP Atomic Emission Spectrometer, and XRF on a Philips PW 1480 wavelength dispersive sequential diffractometer, controlled by Phillips X40 4i software, and with data reduction by UniQuant 5 software.
50. Roehm, “Preliminary Report,” 7 (see n. 25); Moffit, “Lower Copper River,” 10–11 (see n. 30).
51. Eppinger et al., “Geochemical Data,” CD Rom data files; Rock Samples, sample field nos. 6BR002R, 6BR003R1, 6BR010R, 6BR012R, 6BR014R1 (see n. 43).
52. Percentage based on dry sample weight.
53. Eppinger et al., “Geochemical Data,” CD Rom data files; Heavy Mineral Concentrate, sample field no. 6BR002C2 (see n. 43). Significant gold (100 ppm) was found in the concentrates using an alternative sampling methodology, in which a large sample (approximately 16 pounds) was hand panned, sieved, and further concentrated to leave only heavy nonmetallic concentrates. By boosting gold values, this qualitative technique may facilitate the identification of some metal phases under microscopic techniques.
54. Some operators chose to introduce mercury into the ball mill under the rubric that it was best to extract gold as early in the cir-cuit as possible. The downside of this practice was that, unlike stamp batteries, cleaning out the ball mill was an involved process, and it also increased the danger of mercury loss by “flouring” (refer to Gardner and Johnson, “Mining and Milling,” 22 [n. 26]). According to diary entries, Baldwin recovered 1/2-ounce worth of amalgam “pellets” from under the ball mill liners in the 1941 season (“Journal,” entry 10 October 1941) and gold recovery from the ball mill is suggested also in the previous year (“Journal,” entries 15–18 October 1940) (see n. 33). That both cleanups occurred at the end of the milling season and recovered only a small amount of amalgam suggests that mercury in the ball mill came only from the reintroduction of table concentrates.
55. As an element approaches minimum detection limits, the signatures of other elements in the sample can cause instruments to read higher values.
56. Averages taken from Taggart, Handbook, 960 (see n. 8); Richards and Locke, Textbook, 65 (see n. 11); M. W. Von Bernewitz, Hand-book for Prospectors and Operators of Small Mines, 4th ed. (New York: McGraw-Hill, 1943), 395. Taggart directly states average losses in troy ounces per ton. The other estimates, which are higher, state only ounces per ton (for an explanation of troy ounces, see n. 22). In converting these numbers to ppm, I conservatively took all textbook estimates to be in troy ounces per ton.
57. Arsenic induces the formation of a black film over the mercury, preventing it from alloying with gold. Charles F. Jackson and John B. Knaebel, “Gold Mining and Milling in the United States and Canada: Current Practices and Costs,” U.S. Geological Survey Bulletin 363 (Washington, DC: GPO, 1932), 106.
58. Particle size does not rule out the possibility that the Bremner Gold Mining Company also experimented with grinding sizes.
59. State of California et al., Abandoned Mine Lands, Appendix D and E (see n. 14).

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