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Placer gold mining in alaska

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Seminar presentation given at the Camborne School of Mines (University of Exeter Cornwall Campus) 18th February 2015.

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Placer gold mining in alaska

  1. 1. Dylan McFarlane d.e.mcfarlane@exeter.ac.uk 1
  2. 2. Background – ASM & Placers Prospecting Exploration & Development Mining Reclamation & Marketing
  3. 3. 200 Pans = 1 cubic metre 1 cubic metre = 2 tonnes 1 gram Au = $50 US 10 flyspecks = 1 milligram (dust) 1 A colour = 1 – 2 milligrams (ball point pen) There are no B or C colours, and no nuggets > 1 cent < $1
  4. 4. 150 episodes over 5 seasons 5-10 minutes education - 30 minutes drama Yukon miners better
  5. 5. History Politics Economics Geography
  6. 6. Golden History: Beauty, Power,Value Peruvian Chacras -“gold farms” Las Medulas in Northern Spain, mined 25 a.d.
  7. 7. Serra Pelada, Brazil 1980s 7 Stereotypes of ASM (Artisanal & Small- scale Mining)
  8. 8. 8
  9. 9. Artisanal & Small-Scale Mining Bigger industry than you may think: • 20,000,000 directly employed 0 5 10 15 20 25 30 ASM Share (%) of Global Mineral Production (ICMM 2012) 3TG “Conflict minerals” 2005 Artisanal Gold Production (Tonnes) Columbia 21.6 Mexico 7.4 Ghana 6.9 Brazil 6.1 Tanzania 5.0 Bolivia 3.5 Papua New Guinea 3.2 Rural development, alternative livelihoods & ‘green gold’
  10. 10. Labour-intensive Informal Rudimentary tools & knowledge Poverty-driven
  11. 11. Green, FairTrade Gold Artisanal certified ethical standard (ARM) Social & Environmental standards $ Premium Small mining is beautiful – MarcelloVeiga, UBC Professor
  12. 12. Placer Economics Commodity Quantity Price ($ US) Value ($ US Million)Note Alluvial Gold 6,300,000 ounces 1,250per ounce $ 7,875 7% of 90 Moz Hard Rock Total (mod from USGS, WGC etc) Titanium 2,400,000 tonnes 900per tonne $ 2,160 High grade TiO2/FeTiO3 feed (mod from Credit Suisse) Zircon 1,200,000 tonnes 1,100per tonne $ 1,320 Diamonds 13,200,000 carats 300per carat $ 3,960 12% of 110 Mct gem (mod. From Bain) Tin 100,000 tonnes 25,000per tonne $ 2,500 40% of 250kt est. (mod from ITRI) $ 17,815 Also: REEs, critical metals (tungsten,coltan)
  13. 13. Significant Market & Good Prices 333 137 111 26 17 0 50 100 150 200 250 300 350 Iron Gold Copper Silver Potash Nickel Phosphate Zinc PGMs Diamonds Others Value of Global Metal Production 2011 ($ US Billion) Source: ICMM 2012
  14. 14. Rafal Swiecki (http://www.minelinks.com/) 15 19th Century Gold Rushes
  15. 15. Rafal Swiecki (http://www.minelinks.com/) 16 20th/21st Century Gold Rushes
  16. 16. Fairbanks, 8 Moz Nome, 6 Moz 14 mining regions 67 mining districts Over 25 Moz historic
  17. 17. 2014 est. 230 mines 140 operate 70,000 oz
  18. 18. Gold is whereYOU find it Prospect Explore & Develop Mining Reclaim
  19. 19. Portable sluice box Pan the Creek HistoricWorkings? Prospect Explore & Develop Mining Reclaim
  20. 20. Prospect Explore & Develop Mining Reclaim
  21. 21. Hand-stacked cobbles –YES! High-grade potential Historic cut-off grade for hand working - ground sluicing 1 opcy Prospect Explore & Develop Mining Reclaim
  22. 22. Paystreak Areas Flood Gold False Bedrock & Paleochannels Prospect Explore & Develop Mining Reclaim
  23. 23. Prospect Explore & Develop Mining Reclaim
  24. 24. Prospect Explore & Develop Mining Reclaim
  25. 25. Geophysics? Unlikely… Ground Magnetometer – variable success, lots of false positives. Metal detecting is a hobby. Seismic – successful in simple, homogenous conditions (Valdez Creek 460,000 ounces placer gold) but can be expensive, complex Ground Penetrating Radar – Same, but less success LIDAR – Useful in characterizing geomorphology and locating features (channels, terraces, historic workings) but too expensive. Satellite imagery good enough. Drilling must be done anyway, so most operators don’t bother with the distraction, complexity, risk, and high costs.Cheap methods needed. Prospect Explore & Develop Mining Reclaim
  26. 26. Geochemistry & Geomorphology Again – not much use yet… Geochemistry Defining gold signatures, lode mineralization types, spatial and temporal evolution  Identify hard-rock lode sources Geomorphology & Grain Morphology Morphology: Particle Size & Shape = Distance Magadan success  Arc GIS today? Flume tank modelling to understand deposition Improve knowledge of geological controls, better models WhiteChannel Gravels inYukon Prospect Explore & Develop Mining Reclaim
  27. 27. Panning with a Batea Then, drilling & bulk sampling
  28. 28. Portable Highbanker Up to 1 m3 samples 1.5” Pump Prospect Explore & Develop Mining Reclaim
  29. 29. Prospect Explore & Develop Mining Reclaim
  30. 30. Pan Color Count Color Category Abbreviati on Mass (mg) Description Micro- flyspeck Mf 0.03 (30 = 1 mg) Cannot see 30cm away, must squint close-up; fine dust; flat and flaky Flyspeck F 0.1 (10 = 1mg) Specks visible 30cm away; flat or flaky A Colour A 1-2 ~1mm diameter, ball-point pen sized B Colour B 2-5 Up to ~2mm, elongate or spherical in 3 dimensions C Colour C 5-25 Up to 3mm, smaller than pea grain, clunk sound Nugget Nug +25, weigh individually Heft in hand 31 Estimating Particle Mass Using Size Classification Blue is Best Prospect Explore & Develop Mining Reclaim
  31. 31. Grades and Resources • Measured in volume not tonnage • Square ft. of bedrock • LOW GRADE: • 0.3 g/m3……………0.01 oz/yd (equivalent to 0.1 – 0.2 gpt ore) • $10 per yard • Fineness (850? 950? 700?) • Cut-off pan: 2 mg • 20 flyspecks, or: • 1 – 2 ‘A’ colours, or: • 1 ‘B’ colour, or: • 60 micro-flyspecks • 500 – 500,000 ounces • 10,000 – 100,000 oz • Depth? • How much overburden-muck? • 0 – 200 feet, 1000 ft.??? • Frozen or thawed? • Multiple paystreaks? • Old workings? • Clay? Boulders? • Fine grained or nugget, flat or round grains? Prospect Explore & Develop Mining Reclaim
  32. 32. Camm 1988 Prospect Explore & Develop Mining Reclaim
  33. 33. Placer Deposit Classification Traditional classification based on environmental process nearest lode source: • Eluvial & Coluvial • Fluvial, Bench &Terrace • Buried Channels • Alluvial Fan, Floodplains • Beach Strandline & Marine • Rare: Desert, Glacial, Coastal Aeolian Russian Classification: Gradient-Geomorphological & Aggradational-Degradational (energy systems)  + 25 depositional categories 34Prospect Explore & Develop Mining Reclaim
  34. 34. Eluvial • Weathering/Leaching in-situ on hill slopes and outcrops • Rain, wind, percolating waters, heat, chemical and biological degradation • Upgrading through removal of soluble minerals or sheet flow Colluvial • Located at base of hill slopes • Downslope movement of weathered rock, wind, rain, freeze-frost action • Poorly sorted and erratic grade and size distribution • Rarely economic • Mkuvia placers in SouthernTanzania? Prospect Explore & Develop Mining Reclaim
  35. 35. Fluvial, Bench &Terrace: Stream Placers Classic, most common, and most important River, stream, creek, gulch and relicts (bench or terrace) Lighter particles winnowed away while heavy minerals concentrate on bedrock, or • inside bends and areas of lower velocity-pressure -gradient • Crevices, boulders and other natural traps Slatey, vertical bedrock good; rough & irregular good. Usually formed within few kilometers of source rock • Grain morphology and inclusions to relate placer to lode (R. Chapman, Mortenson, etc.) With distance, particle sizes reduce and sorting improves, UNLESS it is re-worked, glaciated, or disturbed 36Prospect Explore & Develop Mining Reclaim
  36. 36. Prospect Explore & Develop Mining Reclaim
  37. 37. Prospect Explore & Develop Mining Reclaim Typical Profile
  38. 38. Waterfalls…Rarely Gold Rush ‘Glory Hole’ Fail Prospect Explore & Develop Mining Reclaim
  39. 39. Deep, Buried Channels • Can be High Grade!!! • Valdez Creek, Alaska 1981 • Most productive in N.America • 100,000 oz Au/year • 9 year mine life • 10 oz/yd3 • 15 ft. pay sections • Formed by Alaska Range uplift causing southward stream migration • Seismic survey and drilling discovered channel at 165 ft. 40Prospect Explore & Develop Mining Reclaim
  40. 40. Alluvial Fan •Aggradational placer - depositing high-grade pay into thick section of low-grade pay (100 ft. +) •Patchwork of lenses and highly erratic local concentrations  Bulk •Little Squaw, Alaska Canyon, Bench and Alluvial Fan • 200,000 oz Au @ 0.02 oz/yd3 • 200 ft. thick but 100 ft. till overburden 41Prospect Explore & Develop Mining Reclaim
  41. 41. Beach Strandline & Marine • Sorting action of waves, tides, currents and winds concentrating heavies along lines • Offshore deposits scoured by glaciers, sorted by tides, concentrated in storms and re-worked by fluvial processes • NomeCoastal Plain, Alaska AnglogoldAshanti • Discovered 1899, hand-miners 1-5 oz/day from beach • 5-6 M oz historical production • Current resource: .5 - 2.5 M oz @ 0.002 oz/yd3 42Prospect Explore & Develop Mining Reclaim
  42. 42. 43 Marine Offshore - Nome Prospect Explore & Develop Mining Reclaim
  43. 43. Other PlacerTypes • Desert – wind principal transport & concentration agent although flash flooding can locally enrich • Most scams occur in the desert (stay away fromArizona!) • Glacial – rare economic concentrations • Unsorted, unstratified, high-clay • Moraines, tills and shorelines • Yukon, but nothing significant in Alaska • CoastalAeolian – sand dune systems • Richards Bay (ilmenite, rutile, zircon) 44Prospect Explore & Develop Mining Reclaim
  44. 44. Prospect Explore & Develop Mining Reclaim
  45. 45. TOP: 20 g gold nugget within 1 tonne gravel  sample #1 = 0 g/t  sample #2 = 40 g/t UNREPRESENTATIVE BOTTOM: 20g gold dust within 1 tonne gravel  both sub-samples = 20 g/t Prospect Explore & Develop Mining Reclaim
  46. 46. Heterogeneity and Nugget Effect 47 Proportion of Ore Mineral versus Homogeneity E= Evaporite; C= Coal; Fe= Bedded Iron Ore; P=Phosphate; B=Bauxite; PbZn=Stratiform lead-zinc; Ni=Stratiform Ni; SSn=Stratiform tin; PC=Porphyry Copper; VSn=Tin veins; V=Gold, Silver veins; U=Uranium; D=Diamonds; AD=alluvial diamonds (After Haddon King et al 1980) High LowHigh Low ProportionofOreMineral Homogeneity E C Fe B P Ni SS n VS n VD AD PC U Source: King, McMahon & Bujtor CRA (Australia) 1980 Nuggety Creeks Fans, Terraces Flood- plains, Offshore Prospect Explore & Develop Mining Reclaim
  47. 47. How DoYou Raise Finance? Ex: Petropavlovsk Equivalent ‘ore’ grades: 0.1 - 0.18 g/tonne Disposed assets for $25 M b/c high alluvial cash costs  $1,319/oz Prospect Explore & Develop Mining Reclaim
  48. 48. Exploration Methods - Drilling 49 Banka Auger Churn Hammer & RAB RC Double Cased Hammer Sonic Which one do you choose? • 3in. – 12in. (8in. Minimum in >60 mesh) • $5/ft - $90/ft • Penetration rate – gold loss/migration – recovery - Boart Longyear Sonic Mini-Auger Banka Prospect Explore & Develop Mining Reclaim
  49. 49. Sample Processing - MiniWashplant 50 Goldfields Prospector Prospect Explore & Develop Mining Reclaim
  50. 50. Prospect Explore & Develop Mining Reclaim
  51. 51. Laboratory De-mag concentrates, classify Clean, dry and weigh gold (milligrams) Prospect Explore & Develop Mining Reclaim
  52. 52. Prospect Explore & Develop Mining Reclaim Mobile Lab Scale in mg Special clean-up pans
  53. 53. Bulk Sampling – Pilot Production Representative samples (1 to 5,000 m3) Detailed geology, stratigraphy, mineralogy Simple model PSD Optimize Prospect Explore & Develop Mining Reclaim
  54. 54. Prospect Explore & Develop Mining Reclaim
  55. 55. Prospect Explore & Develop Mining Reclaim
  56. 56. Channel – Gulch Section Prospect Explore & Develop Mining Reclaim
  57. 57. Alluvial Fan Section Prospect Explore & Develop Mining Reclaim
  58. 58. Methods Equipment Washplants Prospect Explore & Develop Mining Reclaim
  59. 59. Underground Placer Mining – 1900s Fairbanks Thawing Frozen Gravels in Narrow, High-Grade Paystreaks Prospect Explore & Develop Mining Reclaim
  60. 60. 1. Remove forest & thaw 2. Strip black muck loess (save for final restoration) 3. Strip overburden gravel 4. Mining paydirt 5. Processing plant - discharging into settling pond(s) 6. Restored area Prospect Explore & Develop Mining Reclaim
  61. 61. Prospect Explore & Develop Mining Reclaim Hydraulicking – 1.5 Billion cubic yards in California Blue Babe – baby mammoth
  62. 62. Prospect Explore & Develop Mining Reclaim Hydraulicking John Miscovich - Legend Intelli-giant – automatic monitor
  63. 63. Baker Family – Mudminers inTofty Prospect Explore & Develop Mining Reclaim
  64. 64. Dragline Mining Prospect Explore & Develop Mining Reclaim
  65. 65. Don’tTangle the Cable on the Spool! Prospect Explore & Develop Mining Reclaim
  66. 66. Skyline-Drag System, Nome Prospect Explore & Develop Mining Reclaim
  67. 67. Bucket-Ladder Dredge Over 100 in AK Continuous, high volume Mercury, then trapezoidal jigs Prospect Explore & Develop Mining Reclaim Problems: Water Climate
  68. 68. Davidson Ditch – 90 mile pipeline (1920) Prospect Explore & Develop Mining Reclaim
  69. 69. Steam Fields – ColdWater Saved Alaska Prospect Explore & Develop Mining Reclaim
  70. 70. TheTweet Dredge +110Years Operation Prospect Explore & Develop Mining Reclaim
  71. 71. Bima Dredge, Nome 1987 – 1990 World’s largest dredge Marine deposits 118,000 ounces Built for MalaysianTin Failed due to severe conditions – Arctic Storms!!! Prospect Explore & Develop Mining Reclaim
  72. 72. Marine Mining: New Techniques &Technologies All theTime Prospect Explore & Develop Mining Reclaim
  73. 73. Pomrenke Dredge Prospect Explore & Develop Mining Reclaim
  74. 74. The Future: Jack-up Barge (from Namibia Al. D.) Prospect Explore & Develop Mining Reclaim
  75. 75. OtherTechniques Ross-box Suction Dredging Reverse spirals Hydro-clean Prospect Explore & Develop Mining Reclaim
  76. 76. New-ZealandType Dredge – A Model Mine 1. Strip topsoil 2. Push overburden 3. Basic equipment: 1. 40t ext x 2 2. D6 dozer or 920 FEL & 40t truck 4. 2-man operation 1. Backhoe Feed 2. Ancillary (Tails, Strip, Fuel, etc.) 5. Convey tails 6. Place overburden 7. Reclaim topsoil 8. Natural revegetation < 2 years 9. Farmland restored! Floating Washplant Fed from Land Prospect Explore & Develop Mining Reclaim
  77. 77. N.L.Wimmler (1927) – Review of Placer Mining Methods and Costs Few Good Miners Time for a Revision! Prospect Explore & Develop Mining Reclaim
  78. 78. Tools of theTrade – Basic Equipment D11 – 11 tonne push FEL versatility 40 t Excavator ‘backhoe’ Prospect Explore & Develop Mining Reclaim
  79. 79. Derocker Prospect Explore & Develop Mining Reclaim
  80. 80. Home-made trammel with hopper, punch plant, forklift/truck tires & sluice boxes Prospect Explore & Develop Mining Reclaim
  81. 81. Double-deck screen Coarse rock conveyor Even feed distribution to sluices Prospect Explore & Develop Mining Reclaim
  82. 82. Prospect Explore & Develop Mining Reclaim Sluice Box Riffles Expanded Metal – Fine Au Angle Iron – Coarse Au
  83. 83. Prospect Explore & Develop Mining Reclaim Miners Moss – 3M Nomad Carpetting
  84. 84. Ground-breaking Sluice & Riffle Design 85 RandyClarkson • Riffle Spacing • Feed Rates • Riffle Types (Angle Iron, Flat Bar, Expanded Metal) • Matting • Oscillation • Hydraulic Riffles • Punch-Plate • Triple-Run Box • Pre-Screening Prospect Explore & Develop Mining Reclaim
  85. 85. GoldWheels -Toy Prospect Explore & Develop Mining Reclaim
  86. 86. Prospect Explore & Develop Mining Reclaim
  87. 87. Jigs, Centrifuges, Bowls &Tables 88 Prospect Explore & Develop Mining Reclaim
  88. 88. Transporting Gold Prospect Explore & Develop Mining Reclaim
  89. 89. Advice 1. Maintenance, Maintenance, Maintenance! 2. Do Not Fire Assay Placer Gold 3. Washplant Design – K.I.S.S. 4. Coarse Gold ≠ Fine Gold 5. Sampling Evidence and Production History 90Prospect Explore & Develop Mining Reclaim Barry Clay with the 294oz Centennial Nugget found whilst on his dozer!!!
  90. 90. Prospect Explore & Develop Mining Reclaim
  91. 91. Concurrent Reclamation Best Practice Prospect Explore & Develop Mining Reclaim
  92. 92. 2014 Indictment at Platinum Creek Mine I blame the Aussies Prospect Explore & Develop Mining Reclaim
  93. 93. Closure & Marketing • Turbidity – Settling Ponds Required! • Keep it Safe & Stable –Wetlands & Moose Pasture • Mercury unnecessary; retort  Green Gold, Ethical Jewelry • Heritage &Tourism • Nugget prices 3x for jewelery 94 Prospect Explore & Develop Mining Reclaim
  94. 94. Resources – thank you Websites • Alaska Gold Forum http://bb.bbboy.net/alaskagoldforum • AMDS Prospecting Forum http://www.akmining.biz/forums/forum.html • ICMJ Prospecting & Mining Journal Forum http://forum.icmj.com/ • Canadian Prospector’s Forum http://gpex.ca/smf/index.php • World Placer Journal http://www.mine.mn/ • New 49’ers Forum http://www.goldgold.com/ Books • Wells, John. Placer Examination • MacDonald, Eoin. Alluvial Mining • IMM. Alluvial Mining Conference Proceedings 1990 • M.I.R.L. Reports & Alaska Placer Conference Proceedings 95 A Great Read – A Mining Legend
  95. 95. Gold in Cornwall (Simon Camm)
  96. 96. University of Leeds Placer Mineral Group (Rob Chapman): http://see-web-01.leeds.ac.uk/misc/miner/97
  97. 97. 99
  98. 98. 101 Pandora’s Inn Prospect Explore & Develop Mining Reclaim

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