Hycroft Oxidation Pilot Plant Overview

Transcription

1 Hycroft Oxidation Pilot Plant Overview Hazen Research: AAO Pilot Plant Tour Friday, February 21, 2014 Bill Pennstrom Pennstrom Consulting Art Ibrado M3 Engineering Dennis Gertenbach Hazen Research

2 INVESTIGATIVE TESTWORK Previous Test Work Direct Cyanidation Test Work Direct cyanidation leach results of bulk samples taken from all zones on the deposit were conducted early in the test program in 2010 Poor gold recovery results were obtained Concentrate was ground to a P80 of 325 mesh for this testing Recoveries from Brimstone and Vortex, the two largest components of the deposit, were in the mid-20% range for gold and 80% range for silver, while other smaller components of the deposit yielded recoveries ranging from 45 to 50% for gold and 55 to 83% for silver Roaster Test Work Test work showed that roasting would work when tested on Brimstone ore Results indicated that average recoveries of 89% Au and 74% Ag are achievable from the concentrates by varying the leach and roast conditions slightly for the majority of the concentrate produced 2

3 INVESTIGATIVE TESTWORK Previous Oxidation Testing Autoclave or POX Test Work Test work showed that POX will work to oxidize the sulfide concentrate Gold liberation was good with gold recoveries achieving mid-90s Silver recoveries went down due to jarosite formation at low ph Oxidized concentrates that were treated using a lime boil were able to achieve silver recoveries in the 80s while maintaining gold recoveries in the mid-90s Bio Oxidation Test Work Test work showed that bio oxidation works for Hycroft rougher and cleaner concentrates Rougher concentrate oxidation times were predicted to be 4.5 days to obtain 83% sulfide oxidation 3

4 INVESTIGATIVE TESTWORK BIOX: Sulfide Oxidation versus Gold Recovery BIOX test work results showing percent sulfide oxidation versus gold recovery 4 The most important lessons learned from the BIOX testing were: Hycroft concentrate does not require a high level of oxidation to achieve economic metal recovery Operating and capital cost intensive systems (autoclave, roasters) are not required Other simpler oxidation process options needed to be investigated

5 INVESTIGATIVE TESTWORK Silver Leach % Gold Leach % Chlorine Oxidation Testing Chlorine Oxidation Test Work Gold Leach vs Sulfide Oxidation Sulfide Oxidation (%) Test work showed that chlorine oxidation would work on Hycroft rougher and cleaner concentrates, but at high chlorine consumptions Silver recovery dropped with increasing sulfide oxidation percentages Chlorine Oxidation Test Work Silver Leach vs Sulfide Oxidation Sulfide Oxidation (%)

6 INVESTIGATIVE TESTWORK Silver Leach % Gold Leach % Pressure Alkaline Testing Pressure Alkaline Oxidation Test Work Au Leach vs Sulfide Oxidation Sulfide Oxidation (%) Pressure Alkaline Oxidation Test Work Ag Leach vs Sulfide Oxidation Scoping tests were conducted using pressure oxidation at 100 C and 40 psi oxygen overpressure 1 As shown in these graphs, alkaline POX will effectively oxidize the sulfides, allowing for effective gold and silver leaching The results of these tests were positive and this method remains as an option for the concentrate treatment at Hycroft. However, the bottom limit for temperature and oxygen required for sulfide oxidation to occur was not obtained as test work at yet lower temperatures and ambient pressure would later prove Sulfide Oxidation (%) 1. As compared with previous POX test work completed using industry standard temperatures (250 C plus) and oxygen overpressures of 100 psi

7 BENCH SCALE TESTING Ambient Alkaline Oxidation ( AAO ) The sulfide mineral in Hycroft ore is predominantly pyrite and marcasite, with the gold associated on the rim of the sulfide crystal, not intimately associated within the sulfide crystal Hycroft concentrate is amenable to simple oxidation and leaching practices Ambient pressure oxidation is a process that has been used successfully for a number of years in the precious metals industry The Albion process is a common form of ambient pressure oxidation, however, other less familiar versions of the process have been, or are currently in operation globally The AAO process is simply described as: Air or oxygen is sparged into agitated tanks, and sufficient retention time, typically 4 to 24 hr, is provided to allow adequate oxidation and/or passivation of cyanide-consuming minerals AAO can be applied as a simple, low capital and operating cost step before cyanide leaching to oxidize and/or passivate the surfaces of some of the more reactive, reagent-consuming sulfides AAO, as it is intended to be applied in the concentrate oxidation process for Hycroft, involves using oxygen enriched air and heat generated from the oxidation process to oxidize the concentrate in an ambient pressure environment using trona to provide the alkaline environment and to neutralize the acid that is created during the oxidation process 7

8 BENCH SCALE TESTING Silver Leach % Gold Leach % Ambient Alkaline Oxidation ( AAO ) Alkaline Ambient Pressure Test Work Au Leach vs Sulfide Oxidation Sulfide Oxidation (%) Alkaline Ambient Pressure Test Work Ag Leach vs Sulfide Oxidation Test work was initially conducted on Alkaline Oxidation at Ambient pressure (AAO) using caustic (NaOH) as the ph modifier. The test showed that oxidation of the sulfides was effective and gold and silver liberation for cyanidation was achieved Sulfide Oxidation (%)

9 BENCH SCALE TESTING Ambient Alkaline Oxidation ( AAO ) A review of possible ph modifying reagents for effectiveness and cost was conducted which included lime, sodium carbonate, sodium bicarbonate, potassium carbonate, sodium silicate, limestone and sodium sesquicarbonte (Trona). Table 1 - Results from Selected Tests Using Different ph Modifiers Oxidation Target Conditions Reagent Consumption Results Reagent P80 PSA, Oxidant Consumption Sulfide Gold Silver Test ID # μm Gas Time, h Reagent (dry basis), lb/st Oxidation, % Extraction, % Extraction, % O % NaOH O % limestone slurry O2 24 K 2 CO 3 2, O2 24 Na 2 SiO 3 1, O2 9.5 Na 2 CO O Na 2 CO 3 NaHCO 3 2H 2 O Trona

10 BENCH SCALE TESTING Ambient Alkaline Oxidation ( AAO ) Trona was found to be the most cost effective reagent for oxidizing the Hycroft concentrates Trona has the added benefit of being readily available and within relatively close proximity to Hycroft The largest known trona source in the world is situated in Green River, Wyoming, with readily accessible transportation lines to Hycroft The next phase of test work involved looking at different Trona addition rates 10

11 BENCH SCALE TESTING Ambient Alkaline Oxidation ( AAO ) with Trona The relationship between gold /silver recovery and sulfide oxidation with Trona as the ph modifier is shown in the following graphs Silver recovery at Hycroft is an important factor in the economic evaluation An economic evaluation on the degree of oxidation and gold and silver recovery versus the operating costs can be performed Initial calculations show an oxidation range between 55% and 70% will give the most economic return 11

12 BENCH SCALE TESTING Ambient Alkaline Oxidation ( AAO ) with Trona Gold extraction can be tied to Trona consumption as is depicted from the test data displayed in the following graph. 12

13 BENCH SCALE TESTING Ambient Alkaline Oxidation ( AAO ) with Trona The first parameter reviewed was the oxidation time required at varying Trona addition rates Trona addition effects the rate and degree of oxidation 13

14 BENCH SCALE TESTING Ambient Alkaline Oxidation ( AAO ) with Trona The following graph shows the effect of reaction temperature on sulfide oxidation rate. Higher reaction temperatures accelerate the oxidation reaction Additional operating parameters that have been reviewed include: reaction temperature concentrate particle size oxygen concentration, and percent solids of the concentrate slurry feeding AAO 14

15 BENCH SCALE TESTING Ambient Alkaline Oxidation ( AAO ) with Trona Particle size of the rougher concentrate and percent solids of the slurry both have an obvious impact on the sulfide oxidation reaction rate Finer grinds and lower percent solids both improve reaction kinetics 15

16 BENCH SCALE TESTING Ambient Alkaline Oxidation ( AAO ) with Trona Two distinct reaction components are affected by the percent solids: 1) the lower percent solids improves reaction kinetics by diluting the reaction products; and 2) the amount of oxygen available in the slurry for the oxidation of the sulfide is higher the lower the percent solids. 16

17 BENCH SCALE TESTING Ambient Alkaline Oxidation ( AAO ) with Trona The effect of oxygen concentration on the slurry pyrite oxidation rates is illustrated in the following graph If all other parameters are kept constant, the higher the oxygen concentration the faster the sulfide oxidation rate Although the degree of oxidation is directly proportional to the amount of oxygen consumed, higher oxygen concentrations accelerate the reaction rate 17

18 ECONOMIC REVIEW Oxidation Reaction FeS 2 + 4Na 2 CO H 2 O O 2 (g) = FeO*OH + 2Na 2 SO 4 + 4NaHCO 3 Oxygen supplied by water and O 2 gas 18

19 ECONOMIC REVIEW Oxygen Gas Requirement Stoichiometric 1.87 kg O 2 per kg S Utilization 85% Consumption 2.2 kg O 2 per kg S 19

20 ECONOMIC REVIEW Unit Cost of Oxygen Low pressure lower power cost Comparable to Barrick Roaster supply Estimate based on Barrick Roaster cost, with adjustments to over-the-fence, cost is about $25/t O 2 (including power cost) Air Products Estimate is $22.64/t O 2 (including power cost) Cost reduction potential if construction of O 2 plant can utilize construction capability during construction of the mill (e.g., use of cranes, etc.) 20

21 ECONOMIC REVIEW Oxygen Cost Assumptions Oxygen Supply Options Barrick Roaster Barrick POX Estimated Hycroft Air Products Sale of Equipment (SOE) Air Liquide Sale of Gas (SOG) Air Products Sale of Gas (SOG) Short tons/day 1, ,469 Metric tons/day ,240 O 2 Pressure Power Cost/month 650, ,000 1,271,453 Power unit cost, $/kwh Capital Cost $? $ 0 $ 0 Owner Contribution to Construction Cost $? $? $ 0 Operating Fee or BFC, monthly $ 80,000 $ 500,000 $ 250,000 Power Draw, MW tons/mo 29,937 16,329 67,200 $/ton O2 op fee $ 2.67 $ $ 3.72 kwh/mo 9,285,714 7,142,857 20,843,491 kwh/t $/t power Total $/mt $ $ $ 22.64

22 ECONOMIC REVIEW Oxygen Gas Requirement 80:20 O 2 :Air Ratio Purity 95% O 2 80:20 Ratio = 80.2% O 2 by Volume = 82.2% O 2 by Weight Projected O 2 Consumption: At 60% oxidation = 2,090 tonnes/day At 70% oxidation = 2,549 tonnes/day 22

23 ECONOMIC REVIEW AAO Preliminary Operating Cost 60% Oxidation 200 kg trona/mt conc 10% Sulfide Sulfur 13.8% Mass Pull Labor Staff $/hr $/day $/ton Operator 4 $33.75 $1,620 Helper 4 $29.70 $1,426 Mechanic 2 $29.70 $713 Mechanic Helper 2 $29.70 $713 Total Labor $4, Power kwh/day $/kwh $/day Conveyor 4,600 $0.061 $281 Agitators 35,000 $2,135 Blowers 705 $43 Pumps 2,837 $173 Thickener 150 $9 Total Power 43,292 $2, Reagents t/day $/t $/day Oxygen 2,090 $25.00 $52, Trona 3,255 $ $358, kg/t ore $/kg $/day Flocculant 0.04 $3.90 $2, Total Reagents $413, Maintenance equip. cost % factor $/day Parts $20,000, % $2, t $/t $/day Supplies & Services $117,935 $0.020 $2, Regrind Cost 16, $1.100 $17, Total Oxidation $443,

24 ECONOMIC REVIEW AAO Preliminary Capital Estimate Hycroft Project, Benchmarking and Scoping Capital Study M3-PN Concentrate Oxidation Concentrate Oxidation and Leach Item Description Approximate Cost ($M) Notes Rail Unloading System For Trona Rotary Car Dump, 6.00 Similar project Auxiliary Trona Storage Storage Near Rail Unloading System for Dead Storage 2.00 Allowance Rail Spur/Siding To park approximately 80 rail cars 0.00 Not included Pipeline / Flush System for Trona 2 Miles 4.00 Trona Dry Storage Non Mechanized storage area near Rail Spur 1.00 Allowance Trona Storage Tanks 2-100' Diameter Agitated Tanks 3.00 Estimated at $1.5 Million per tank General Site Work Site Work, Infrastructure, etc Allowance Steam System 5 Million BTU 2.00 Allowance Oxidation Tanks 12, 60' x 62' Oxidation Tanks, Project With Similar Sized Tanks, Approximately $3.3M per tank Oxygen Plant Considered an "over the fence" contract, therefore, no capital costs 0.00 Pre-Leach Thickener 1, 180' Diameter Thickeners 3.50 Similar project, approximately $3.5M per Thickener Subtotal Indirect Costs@ 60% Includes EPCM, Owner's Costs, Contingency and Misc. Indirects Total Concentrate Leach Item Description Approximate Cost ($M) Notes Leach Tanks 10, 54'x56' Leach Tanks Project With Similar Sized Tanks, Approximately $2.7M per tank CCD Thickeners 4, 180' Diameter Thickeners Similar project, approximately $3.5M per Thickener Cyanide Destruct Tanks 2 tanks 2.00 Project With Similar Sized Tanks, Approximately $1.0M per tank Upgrades to Merrill Crowe Plant Not Included 0.00 Subtotal Indirect Costs@ 60% Includes EPCM, Owner's Costs, Contingency and Misc. Indirects Total 68.80

25 SUMMARY AND CONCLUSIONS Bench Scale Testing: Summary and Conclusions Hycroft concentrate is easily oxidized and can be processed by simple oxidation techniques Oxidation testing of rougher concentrate resulted in a sulfide oxidation percentage of 60% and recoveries of 85% gold and 82% silver oxidation time of 24 hours, a reaction temperature of 75 C, slurry percent solids of 15% w/w, and a grind size of 15 microns Positive results from bench scale testing and preliminary economic review of the oxidation circuit warrant a pilot plant study Bench scale test results set pilot plant baseline target parameters AAO is a very flexible process Oxidation rates are driven by capital and operating costs The pilot plant will investigate various adjustments to the inputs to assess optimal operating parameters as compared to their associated capital and operating cost 25

26 PILOT PLANT TESTING Ambient Alkaline Oxidation ( AAO ) Pilot Plant Based on the knowledge obtained from the bench scale testing, the following baseline parameters for the pilot plant were developed: Trona addition 300 kg/t Reaction temperature 75 C Conc. particle size P80 25um Oxygen concentration 100% O 2 Slurry percent solids 25% w/w Reaction time 36 hours 26

27 Mill General Arrangement Oxygen Plant DEVELOPMENT AAO Circuit Grinding and Flotation Crushing 27

28 DEVELOPMENT Mill Flowsheet 28

29 DEVELOPMENT Oxidation Circuit Flowsheet 29

30 PATH FORWARD Next Steps Refine optimal operating parameters based on pilot plant runs Refine capital and operating cost assumptions using pilot plant results Complete prefeasibility study for oxidation circuit by end of Q Assuming positive outcome of prefeasibility study, revise the mill feasibility study incorporating the oxidation circuit and changes to the mill flowsheet by the end of Q

31 QUESTIONS Flotation Cell QUESTIONS AAO Feed AAO Discharge

32 Hycroft Operations Update 32

33 HYCROFT UPDATE 8-Aug 13-Aug 18-Aug 23-Aug 28-Aug 2-Sep 7-Sep 12-Sep 17-Sep 22-Sep 27-Sep 2-Oct 7-Oct 12-Oct 17-Oct 22-Oct 27-Oct 1-Nov 6-Nov 11-Nov 16-Nov 21-Nov 26-Nov 1-Dec 6-Dec 11-Dec 16-Dec 21-Dec 26-Dec 31-Dec 5-Jan 10-Jan 15-Jan 20-Jan 25-Jan 30-Jan 4-Feb 9-Feb Opt Au Hycroft Mine Update Pad Recovery and Well Plan Status: 300 gpm each, 60 ft. above liner Au and Ag solution grade increases Tracer study deferred for exiting wells Plan Forward: New 16 injection wells on Lewis AFE for new injection wells initiated Daily monitoring of pad returns Lewis Injection Well Map Exiting Injection wells Proposed new Injection wells Lewis Return Solution 33 Date LRTN-1 LRTN-2 LRTN-3 Wells On

34 Reserve/Resource Update 34

35 HYCROFT UPDATE Rolling 6 Month Reconciliation Released Ore Control Material Type Tonnage AuFA Grade AuCN Grade AuCN/AuF A Ratio AgFA Grade AuFA oz AuCN oz AgFA oz Leach Ore 27,277, , ,296 6,575,839 Reserve Model Material Type Tonnage AuFA Grade AuCN Grade AuCN/AuF A Ratio AgFA Grade AuFA oz AuCN oz AgFA oz Leach Ore 25,647, , ,529 6,031,460 Positive Variances 106% of Leach Tons 103% of AgFA Grade 102% of AuFA Ounces 109% of AgFA Ounces Negative Variances 97% of AuFA Grade 90% of AuCN Grade 96% of AuCN Ounces 35

36 HYCROFT UPDATE 2013 Reconciliation Released Ore Control Material Type Tonnage AuFA Grade AuCN Grade AuCN/AuF A Ratio AgFA Grade AuFA oz AuCN oz AgFA oz Leach Ore 46,354, , ,709 10,240,408 Reserve Model Material Type Tonnage AuFA Grade AuCN Grade AuCN/AuF A Ratio AgFA Grade AuFA oz AuCN oz AgFA oz Leach Ore 39,361, , ,480 9,250,877 Positive Variances 118% of Leach Tons 103% of AuFA Grade 102% of AuCN Grade 122% of AuFA Ounces 120% of AuCN Ounces 111% of AgFA Ounces Negative Variances 94% of AgFA Grade 99% of AuCN/AuFA Ratio 36

37 HYCROFT UPDATE Reconciliation by Material Types Released Ore Control Material Type Tons AuFA Grade AuCN Grade AuFA Oz AuCN Oz Gold Ratio Waste 13,880,344 Oxide 13,903, , , Transitional 22,797, , , Sulfide 3,833, ,034 15, Total Ore Tons 40,534, , , Total Tons 54,414,558 Reserve Model Material Type Tons AuFA Grade AuCN Grade AuFA Oz AuCN Oz Gold Ratio Waste 11,840,932 Oxide 13,954, , , Transitional 25,916, , , Sulfide 2,702, ,695 10, Total Ore Tons 42,573, , , Total Tons 54,414, Includes tons mined at Bay, Brimstone, and Gap Pits for 2013

38 HYCROFT UPDATE Reconciliation by Material Types Released Ore Control to Reserve Model Material Type Tons AuFA Grade AuCN Grade AuFA Oz AuCN Oz Gold Ratio Waste 1.17 Oxide Transitional Sulfide Total Ore Tons Total Tons 1.00 Model is good predictor of: Oxide ore tons Total ore tons Total Contained Au Ounces Includes tons mined at Bay, Brimstone, and Gap Pits for 2013 Positive numbers indicate actual outperforming model Model over/under predicts: Transitional Ore Tons AuCN grade and Ounces Sulfide Ore Tons 38

39 HYCROFT UPDATE Tons per Hour Shovel Efficiencies 8,500 Shovel Dig Rates 30 Day Moving Average 8,000 7,500 7,000 6,500 6,000 Shovel 6 Shovel 7 Linear (Shovel 6) Linear (Shovel 7) 5,500 5,000 Dig rates do not include any wait or spot times. Truck load times only. 4,500 9-Sep 23-Sep 7-Oct 21-Oct 4-Nov 18-Nov 2-Dec 16-Dec 30-Dec 13-Jan 27-Jan 39

40 HYCROFT UPDATE Shovel Efficiencies Rope Shovel Availability and Utilization 89.0% 87.0% 85.0% 83.0% 81.0% 79.0% 77.0% 75.0% Sept Oct Nov Dec Jan Mechanical Utilization 40

41 HYCROFT UPDATE Truck Efficiencies Since the end of Q3: Average payload has increased from 290 tons to 305 tons per load Goal is 320 tons per load Average operating hours has increased from 8 hours per shift to 9.7 hrs per shift Max possible with breaks and pre-shift inspection is 10.7 hrs First load has decreased by 6.6 minutes First and Last Load Times (Minutes from start and end of shift) Sep. Oct. Nov. Dec 41 First Load Last Load

42 HYCROFT UPDATE Opportunities in 2014 Increase payload Dispatch has just started using the on-board truck scales to calculate daily production instead of a set payload Efficient drilling and blasting for optimum dig rates Improved planning for large shovels Shovels should be scheduled at 2 side loading 75% of the time Increase in TPH is estimated to be 1,000 TPH Improved utilization of truck fleet Drilling of fill material in Q4 increased oxide ore for by 11.3 million tons and 106,000 ounces AuFA 42

43 HYCROFT UPDATE 2013 Flow and Ounces -v- Plan Hycroft Combined Flow-v- Targets Combined Flow Flow Target Au Produced Budget

44 HYCROFT UPDATE Leach Model Performance 44 Major variance to model is application rate (0.002 v ) Impacts Rate of recovery Since February 2014 we have returned to an application rate of on the North Pad We expect to return to the recovery rate per the model predictions