Mine Rock Geochemistry and Pit Lake Model

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A presentation on the Mine Rock Geochemistry and Pit Lake Model associated with the Rosemont Copper Project developed by the Tetra Tech. This presentation was given to the Forest Service and their contractors during technical transfer meetings in November 2008.

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Mine Rock Geochemistry and Pit Lake Model

  1. 1. Mine Rock Geochemistry and Pit Lake ModelFor the Rosemont Copper ProjectBy Mark Williamson, PhD
  2. 2. Presentation Topics §  Approach to characterization of mine rock (for pit walls as well as waste disposal facilities) and summary results §  Tailings characterization §  The conceptual pit lake hydrochemical model §  Overview of components of pit lake model §  The Dynamic Systems Model (DSM)
  3. 3. Mine Rock Characterization Test Protocol Purpose Acid-Base Accounting (ABA) Evaluate relative proportions of potentially acid generation and acid- consumption capacity. Humidity Cell Testing (HCT) Accelerated weathering test for samples showing potential or unclear capacity to generate acidity. Synthetic Precipitation Leaching Arizona-required laboratory leaching Procedure (SPLP) test on powdered material using weak acid solution. Meteoric Water Mobility Procedure Laboratory leaching test on coarse/ (MWMP) run-of-mine rock using plain water
  4. 4. Summary of Mine Rock Tests Anticipated Percent of Whole Rock Type ABA SPLP MWMP Tonnage Waste Rock Arkose 620,630,000 49% 57 23 8 8 Limestone 119,448,000 9% 11 2 1 1 Conglomerate Abrigo 102,460,000 8% 5 1 5 0 Overburden 91,620,000 7% 7 4 3 2 Horquilla 77,091,000 6% 19 3 8 3 Andesite 73,671,000 6% 35 12 4 5 Martin 39,084,000 3% 8 2 4 0 Bolsa 34,661,000 3% 13 1 6 0 Earp 27,680,000 2% 13 5 6 0 Epitaph 26,914,000 2% 14 1 5 0 Escabrosa 24,776,000 2% 9 3 4 0 Colina 22,200,000 2% 8 3 4 0 Qmp 14,555,000 1% 9 4 2 1 Totals 1,274,790,000 100% 208 64 60 20
  5. 5. Acid-Base Accounting Rosemont Acid Base Accounting 200 Tailings 180 Qmp NNP = -20 NP/AP = 1, Overburden NNP = 0 160 Martin Acid Generating Potential (kg/T) 140 NNP = +20 Limestone Leach Material 120 Horquilla NP/AP = 3 Escabrosa 100 Earp Colina 80 Bolsa Arkose 60 Inert Material per ADEQ Andesite 40 policy Abrigo Precambrian 20 Epitaph 0 0 100 200 300 400 500 600 700 800 900 1000 Neutralization Potential (kg/T)
  6. 6. Humidity Cell Testing (Andesite) Andesite (AR2010-03) 1.67% Sulfide-S, NNP = -25.2 kg/t 100 9.0 Calcium 8.0 Sulfate 75 Acidity Leaching Rate (mg/kg/wk) 7.0 Alkalinity pH 50 Iron 6.0 pH 25 5.0 0 4.0 0 10 20 30 40 Week
  7. 7. Mean Extractable Concentration (mg/kg) Su 0.0001 0.001 0.01 0.1 1 10 lfa te 100 S - C al ci um Po ta ss iu m C hl or id e So di M um SPLP vs MWMP ag ne si umN Fl O uo 2 rid + e N O 3 as N Se le ni um C opConstituent pe r Ba ri u m Al um Rosemont Geochemistry in Augusta Rosemont Geochemistry um Ar se M ni c an ga ne se Zi nc M SPLP er c MWMP ur y
  8. 8. Presentation Topics §  Approach to characterization of mine rock and summary results § Tailings characterization §  The conceptual pit lake hydrochemical model §  Overview of components of pit lake model §  The Dynamic Systems Model (DSM)
  9. 9. Tailings Characterization Current Testing Whole Sample Date ABA NAG SPLP MWMT Kinetic Status Rock May 2006 Completed X X X X February 2007 Completed X X X X June 2007 Completed X X X X X July 2008 In Progress X X X X X
  10. 10. Tailings Characterization § Net acid consuming material § High pH/generally low TDS humidity cell effluent •  Recent sample relatively high TDS § Low trace metals in SPLP, MWMT and HCT
  11. 11. Presentation Topics §  Approach to characterization of mine rock and summary results §  The conceptual pit lake hydrochemical model §  Overview of components of pit lake model §  The Dynamic Systems Model (DSM)
  12. 12. Conceptual Pit Lake Hydrochemical Model Direct Precipitation Q = 22”/yr x Area C = Weighted means (NADP) Wall Runoff Q = 22”/yr x Area C = weighted means (SPLP) Evaporation Q = 75”/yr x Area Rosemont Pit Lake Groundwater Inflow Q = groundwater flow model (gpm) C = mean from bedrock wells
  13. 13. Conceptual Pit Lake Model § Sum of flows and concentration n § Monthly time steps ∑Q C i =1 i i § Geochemical equilibration § Probabilistic simulation
  14. 14. Presentation Topics §  Approach to characterization of mine rock and summary results §  The conceptual pit lake hydrochemical model §  Overview of components of pit lake model §  The Dynamic Systems Model (DSM)
  15. 15. Hydrologic Components §  Groundwater Inflow §  Direct Precipitation §  Wall Runoff §  Evaporation
  16. 16. Groundwater Inflow §  Principal hydrologic component §  Important considerations: •  Terminal vs. flow-through •  Rates of infilling §  Groundwater model currently under development
  17. 17. Direct Precipitation Comparison of Rosemont and Santa Rita Monthly Precipitation 6 Santa Rita (1950-2006) Rosemont (2007-2008) 5 Precipitation (inches) 4 3 2 1 0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Month
  18. 18. Pit Wall Runoff
  19. 19. Evaporation 18 Measured Pan Evaporation: Total = 107 inches. 16 Calculated Lake Evaporation: Total = 75.1 inches. 14 Evaporation (inches) 12 10 8 6 4 2 0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Month
  20. 20. Geochemical Components §  Groundwater Flow §  Direct Precipitation §  Pit Wall Runoff
  21. 21. Groundwater Inflow Chemistry§  Typically the largest potential contributor of chemical mass§  Requires characterization of local groundwater
  22. 22. Precipitation Chemistry National Atmospheric Deposition Program (NADP)
  23. 23. Pit Wall Runoff § Derived from mine rock characterization •  Representative Sampling •  Chemical loading parameters •  Outcrop areas
  24. 24. Representative Sampling § How many is enough? § Sample until no improvement 60 50 40 NNP 30 20 10 NNP - Mean NNP - Std. Dev. 0 0 5 10 15 20 25 30 35 40 Number of Samples
  25. 25. Chemical Loading Parameters § SPLP data used as source concentration for pit wall outcrops § SPLP, long-term HCT water composition and MWMP produce consistent results § Due to general lack of sulfide mineralization, water composition more closely tied to equilibrium than kinetic concerns
  26. 26. Areas of Exposed Rock Types
  27. 27. Dynamic Systems Model (DSM) § GoldSim § Graphical User Interface § One time data and formula entry § Probabilistic ability •  Range of possibilities as a result of parameter uncertainty •  Probability of occurrence
  28. 28. Rosemont Pit Lake DSM
  29. 29. Hydrology Module
  30. 30. Summary and Status § Mine rock is, on total mass basis, acid-consuming § Representative samples of principal lithologies outcropping pit complete § Geochemical characterization of pit wall lithologies complete § DSM largely complete, dependant upon completion of hydrologic evaluation § No useful DSM runs to date
  31. 31. QuestionsMark Williamson, PhDmark.williamson@tetratech.com970.223.9600

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