Barite - Density. Andrew Scogings Principal Consultant CSA Global, Perth, Australia

Transcription

1 Barite - Density Andrew Scogings Principal Consultant CSA Global, Perth, Australia Houston, 8 May 2018

2 Presentation outline What is density? Why is density important? How does mineralogy relate to density? How do we measure density? Le Chatelier vs Gas Pycnometer test results Quality Control Conclusions and recommendations Le Chatelier Gas Pycnometer

3 Acknowledgements Excalibar Minerals LLC CSA Global Pty Ltd IMFORMED Intertek Group plc KlipStone Pty Ltd

4 What is density?

5 What is density? Density vs SG Term Units Definition Density t/m 3 Mass per unit volume Specific Gravity Relative density: the ratio of the density of the material to the density of water at 4 o C

6 Why is density important? Incorrect density measurements WILL have consequences!

7 Mineralogy & Density

8 Density stoichiometric method Relationship between mineralogy and density Assays, or mineral contents, are expressed as weight % However, density is expressed in terms of volume Example: a quartz-copper rock has a grade of 50% copper Copper density = 8.9 g/ml; Quartz = 2.7 g/ml Mass weighted density = ( )/2 = 5.8 g/ml However copper is only 23% of the sample volume Volume based density = 4.14 g/ml Relationship between grade and density is curved Source: Lipton and Horton (2014)

9 Density stoichiometric method Example of lab-prepared Barite + Quartz (silicate) blends Seven lab blends of barite and quartz powders Ranging from 25% to 95% barite by mass Density measured using argon gas pycnometer Density calculated based on mass Density calculated based on volume BaSO 4 % (mass) SiO 2 (Mass) 100% 0% 95% 5% 90% 10% 85% 15% 80% 20% 75% 25% 50% 50% 25% 75% 0% 100%

10 Density stoichiometric method Example of lab-prepared Barite + Quartz (silicate) blends BaSO 4 SiO 2 Barite (calc) Silicate (calc) Density (calc) Density (calc) Pycnometer (% by mass) (% by mass) (% by volume) (% by volume) (g/ml by mass) (g/ml by volume) (g/ml lab blend)

11 Density stoichiometric method Density calculated by volume or mass, compared with pycnometer

12 Density stoichiometric method Conclusions Density is based on volume Thus relationship between grade and density is curved Curved line verified by pycnometer measurements The curved lines means that a quartz barite rock will have a higher volume of quartz than expected from SiO 2 content Calculated Quartz volumes Barite about 15% quartz by volume / 10% SiO 2 by mass Barite about 25% quartz by volume / 15% SiO 2 by mass Barite about 35% quartz by volume / 25% SiO 2 by mass

13 How do we measure density?

14 How do we determine density? Mass per unit volume = density We need to measure mass and volume Measuring mass is the easy bit However, the sample could be a: Competent solid (e.g. fresh drill core, rock sample) Porous solid (e.g. weathered rock) Powder (e.g. milled barite) Therefore volume is typically the difficult bit to measure Wax method Calliper method Whole core tray method

15 How do we determine density? There is a bewildering array of methods for measuring the volume of samples (as core, rocks, stockpiles, powders, etc) Weight in water vs weight in air (Archimedes principle) Calliper physical measurement Geophysical down hole Core tray weathered core Liquid displacement Le Chatelier Gas displacement - pycnometer

16 How do we determine density? Competent solid rock or drill core Immersion method (Archimedes) Volume determined by mass in air vs mass in water

17 How do we determine density? Stockpile loose density (10% moisture) using a cubic metre box Clay stockpile Steel box 1m 3

18 How do we determine density? Le Chatelier flask equipment for barite powder Heater & thermostat Water tank Weight Flask Source: Excalibar Minerals LLC

19 How do we determine density? Le Chatelier flask equipment might look like this. Balance Mill Oven Crusher Flasks Flasks Source: Andrew Scogings

20 How do we determine density? Gas pycnometers are an option for barite powder (API 13/I)

21 API Specification 13A

22 API Specification 13A API Specification 13A Sections 7 & 20

23 Le Chatelier vs Pycnometer Barite density test methods API 13I pycnometers (outdated?) The API specifies the Le Chatelier flask as the default method This utilises liquid displacement (kerosene or mineral spirits) API Recommended Practice 13I/ISO describes Air Pycnometer and Stereopycnometer methods, but: In case of dispute, the results from the Le Chatelier flask method prevail. Beckman Model 930 Air Comparison This study compares the results between Le Chatelier and gas pycnometer methods Excalibar Minerals LLC supplied 30 milled barite samples of three products PlusWate, NewWate and NewBar Densities clustered in three groups between ~3.9 to ~4.3 g/ml Excalibar in-house results compared with commercial laboratory results Quantachrome Stereopycnometer SPY2

24 Le Chatelier method API 13A sections 7 & 20 Le Chatelier method a slow process > 4 hours Take approximately 100 g of barite that has been oven dried for at least two hours and cooled to room temperature in a desiccator. Fill a clean Le Chatelier flask to approximately 22 mm (0.8 in) below the zero mark with kerosene. Allow the flask and contents to equilibrate for a minimum of 1 h. Read the volume to the nearest 0,05 ml without removing the flask from the constant-temperature bath. If the kerosene level is outside the 0,2 ml to +1,2 ml volume range after equilibrating, use the 10 ml pipette to add or remove kerosene in order to bring it within this range. Allow the flask to equilibrate for at least 1 h and record the initial volume. Remove the Le Chatelier flask from the bath, wipe dry and remove the stopper. Weigh 80 g ± 0,05 g of dried barite into the weighing dish and carefully transfer it to the Le Chatelier flask. Take care to avoid splashing the kerosene or plugging the flask with barite at the bulb. This is a slow process, requiring repeated transfers of small amounts of barite Gently roll the flask along a smooth surface at no more than 45 from vertical, or twirl the upright flask at the neck vigorously between the palms of both hands, to remove entrained air from the barite sample. Repeat this procedure until no more bubbles can be seen rising from the barite. Return the flask to the bath and let stand for at least 0.5 h. Remove the flask from the bath and repeat to remove any remaining air from the barite sample. Immerse the flask in the bath again for at least 1 h. Record the final volume and record the volume as V2.

25 Barite volume (ml) Le Chatelier flask accuracy How accurate is the flask? mass volume density g ml g/ml mass volume density g ml g/ml Barite density (g/ml) ~0.5 ml: 0.1 g/ml)

26 How do we determine density? Gas displacement pycnometry Inert gases, such as helium or nitrogen, are used as the displacement medium The sample is sealed in the instrument compartment of known volume Inert gas is admitted, then expanded into another precision internal volume The pressures observed upon filling the sample chamber and then discharging it into a second empty chamber allow computation of the sample solid phase volume. Only the solid phase of the sample displaces the gas Dividing this volume into the sample weight gives the gas displacement density Source: Micromeritics ACCUPYC II brochure

27 Excalibar Nitrogen (g/ml) N Pycnometer vs Le Chatelier Positive bias to Nitrogen pycnometer Excalibar Le Chatelier (g/ml) ID Excalibar Le Chatelier Excalibar Nitrogen

28 N Pycnometer vs Le Chatelier Conclusions Nitrogen pycnometer average is 0.5% higher than Le Chatelier Nitrogen pycnometer up to 1.2% higher than Le Chatelier Gas penetrates deeper into pore spaces, cracks or cavities than kerosene giving a lower volume ID Le Chatelier Nitrogen Accupyc Diff % Diff % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % Global Average %

29 Intertek Argon (g/ml) Ar Pycnometer vs Le Chatelier Positive bias to Argon* pycnometer Excalibar Le Chatelier (g/ml) * Note Argon samples were not dried ID Excalibar Le Chatelier Intertek Argon

30 Ar Pycnometer vs Le Chatelier Conclusions Argon* pycnometer global average 1.5% higher than Le Chatelier Ranges from -0.3% to 2.5% difference The Argon samples were tested as received ID Le Chatelier Intertek Argon Diff % Diff % % % % % % % % % % Average % % % % % % % % % % % Average % % % % % % % % % % % Average % Global Average % * Note Argon samples were not dried

31 Intertek Argon (g/ml) Argon vs Nitrogen pycnometer Positive bias to Argon pycnometer* Excalibar Nitrogen (g/ml) ID Excalibar Nitrogen Intertek Argon * Note Argon samples were not dried

32 Argon vs Nitrogen pycnometer Conclusions Argon* pycnometer averages 1 % higher than Nitrogen pycnometer Ranges from -0.6 % to 2.1 % The Argon samples were tested as received ID Excalibar Nitrogen Intertek Argon Diff % Diff % % % % % % % % % % Average % % % % % % % % % % % Average % % % % % % % % % % % Average % Global Average % * Note Argon samples were not dried

33 Intertek Argon dry (g/ml) Argon (dry) vs Argon original pycnometer Slight positive bias towards Argon original Intertek Argon original (g/ml) Note that original Argon samples were not dried ID Argon pycnometer Argon pycnometer (dry)

34 Argon (dry) vs Argon pycnometer Conclusions Density is 1% lower on average after 2 hours drying Differences between -3.8% and +1% Drying seems to make a difference Ar pycnometer Ar pycnometer ID (original) (dry) Diff % Diff % % % % % % % % % % Average %

35 Intertek Argon dry (g/ml) Argon (dry) vs Nitrogen pycnometer No bias to Argon (dry) pycnometer ID Nitrogen pycnometer Argon pycnometer Excalibar Nitrogen (g/ml) Note that Argon samples were dried 2 hours

36 Argon (dry) vs Nitrogen pycnometer Conclusions Average density for Nitrogen (4.15 g/ml) almost identical to Argon dry (4.14 g/ml) Between -2.2% and +1% difference Drying appears to be important However, the customer uses barite as received moisture Preferable to test barite product as received rather than after drying? ID Nitrogen pycnometer Argon pycnometer Diff % Diff % % % % % % % % % % Average %

37 Intertek Helium (g/ml) Helium pycnometer vs Le Chatelier No obvious bias ID Excalibar Le Chatelier Excalibar Nitrogen Intertek Helium Conclusions Only three data points Helium pycnometer is very close to Le Chatelier Excalibar Le Chatelier (g/ml) Note that Argon samples were dried 2 hours

38 Quality Control

39 Quality Control Where do we want our analytical results to be? good accuracy good precision poor accuracy good precision high bias Source: Scogings and Coombes (2014)

40 Quality Control What is QA / QC? QA is planned actions to provide confidence in the data collection process QC is the use of statistical tools to ensure that the analytical systems are in control QC samples are necessary to monitor contamination, precision, accuracy and bias QC samples include standards, duplicates and external checks (umpire) Standards are samples of known or accepted value that are submitted to assess the accuracy of a laboratory Duplicates are samples collected, prepared and assayed in an identical manner to an original sample, to provide a measure of the total error of sampling External laboratory checks generally rely on pairs of pulverised exploration samples (also known as umpire samples) to define inter-laboratory precision and bias. Source: Scogings and Coombes (2014)

41 Quality Control Types of QC charts used in geological exploration Source: Scogings and Coombes (2014)

42 Quality Control Calibration mass and volume

43 Quality Control ORIGINAL (Le Chatelier) Original (Nitrogen) ORIGINAL (Argon) DUPLICATE (Argon) DUPLICATE (Argon dry) UMPIRE (Helium) SAMPLE NUMBERS Density Density Density Density Density Density BaSO4 Standard 4.43 Quartz-1 Standard 2.64

44 Quality Assurance & Control Conclusions density QA / QC Equipment should be regularly calibrated (QA) QC samples (each approximately 5% of originals): Standards Duplicates External checks (umpire) Alternative test methods o e.g. if testing by Le Chatelier, use gas pycnometer as a check o For incoming crudes, test using Le Chatelier for a milled sample and also run some using whole rock by the Archimedes method

45 Conclusions

46 Barite density Conclusions density methods Le Chatelier Robust method However, very time consuming ~ 4 hours Cannot be automated or digitised labour intensive Relatively inexpensive equipment (~$1K) Gas pycnometer Biased to higher densities (~ 1 % difference) Quick and easy to use ~ 5 minutes No chemicals to be disposed Can be automated and free up the operator Smaller footprint than Le Chatelier Relatively expensive equipment (~20K)

47 Barite density General comments and questions If it is assumed that kerosene does not penetrate the barite in the same way as a gas atom does, could a systematic correction factor be applied to pycnometer data? Perhaps the API Le Chatelier method is more appropriate? (even if more tedious to perform than pycnometry) Could the Le Chatelier method be improved by using two separate funnels* to add liquid, or dry barite powder? Assuming that drilling muds are mainly water, perhaps water should be used for Le Chatelier tests? Gas pycnometers are already accepted for refractory materials density (ASTM C604). Why not for barite? * e.g. Helsel et al., 2016

48 Barite density Conclusions Mineralogy & QC Mineralogy Relationship between grade and density is curved A quartz barite rock will have a higher volume of quartz than expected from SiO 2 content This may have implications for plant wear Quality Control Test equipment should be calibrated Insert QC samples (approximately 5% of originals): Standards, duplicates, external checks (umpire) Alternative test methods

49 Recommendations

50 Barite density Recommendations Evaluate alternate liquids for Le Chatelier e.g. Escaid 110, isopropyl alcohol, ethyl alcohol (and water?) Try and improve the Le Chatelier method (e.g. adding barite via a funnel) Assess the effect of temperature on Le Chatelier does it have to be at 32 o C? Approach the API about updating the recommended pycnometers to currently available models Collaboration between producers and commercial labs to compare different methods and convince API to add gas pycnometer as an alternative to Le Chatelier in Specification 13A Use QA and QC methods to ensure accurate and precise results

51 Thank you Acknowledgments Excalibar Minerals LLC (David Henrick, Joe Gocke, Lori Garcia) CSA Global Pty Ltd Intertek Group plc IMFORMED Industrial Mineral Forums and Research KlipStone Pty Ltd Houston, May 2018

52 Bibliography Abzolov, M. Z., Quality Control of Assay Data: A Review of Procedures for Measuring and Monitoring Precision and Accuracy. Exploration and Mining Geology, Vol. 17, Canadian Institute of Mining, Metallurgy and Petroleum. Abzolov, M. Z., Use of Twinned Drillholes in Mineral Resource Estimation. Exploration and Mining Geology, Vol. 18, Canadian Institute of Mining, Metallurgy and Petroleum. CIM, Estimation of Mineral Resources and Mineral Reserves Best Practice Guidelines. Available from: Canadian Institute of Mining, Metallurgy and Petroleum. Helsel, M., Ferraris, C. and Bentz, D. (2016). Comparative study of methods to measure the density of cementicous powders. Journal of Test Evaluation, 44 (6). Lipton, I.T. and Horton, J.A. (2014). Measurement of bulk density for resource estimation - methods, guidelines and quality control. Mineral resource and ore reserve estimation : the AusIMM guide to good practice. Monograph 30. Micromeritics (2014). Accupyc II gas pycnometry system. Information brochure Quantachrome (2017). Gas Pycnometers. True density analysis of powders, foams and bulk solids. Quantachrome Corporation Rev B 0217 Scogings, A.J. (2015). Drilling grade barite. Supply, Demand & Market. Industrial Minerals Research, January pp. Scogings, A. J. (2015). Bulk Density: neglected but essential. Industrial Minerals Magazine, April 2015, Scogings, A.J. (2015). Bulk density of industrial minerals: Reporting in accordance with the 2007 SME guide. SME Mining Engineering, July 2015 Web Exclusive. Society for Mining, Metallurgy & Exploration. Scogings, A. J. and Coombes, J. (2014). Quality Control and Public Reporting in Industrial Minerals. Industrial Minerals Magazine, September 2014, Verly, G., Geostatistical Mineral Resource / Ore Reserve Estimation and Meeting JORC Requirements: Step by step from sampling to grade control. Course Notes, October 15-19, Perth WA, Australia Professional Development Seminar Series; The Australasian Institute of Mining and Metallurgy.

53 Andrew Scogings CV Andrew Scogings PhD (Geology), MAIG, MAusIMM, RPGeo (Industrial Minerals) Dr Scogings is a geologist with more than 25 years experience in industrial minerals exploration, product development and sales management. Andrew has published papers on reporting requirements of the JORC Code 2012, with specific reference to Table 1 and Clauses 18 and 19 (industrial mineral Exploration Results) and Clause 49 (industrial mineral specifications). He has published numerous articles on industrial minerals in Industrial Minerals Magazine, SEG Mining News, AIG News and AIG Journal amongst others; addressing aspects of QA/QC, bulk density methods and petrography for industrial minerals exploration. He was recently senior author of two significant reviews: Natural Graphite Report strategic outlook to 2020 and Drilling grade barite - Supply, Demand & Markets published in 2015 by Industrial Minerals Research (UK). He has coauthored several papers on lithium pegmatites including: Reporting Exploration Results and Mineral Resources for lithium mineralised pegmatites published during 2016 in the AIG Journal. Andrew is a Registered Professional Geoscientist (RP Geo. Industrial Minerals) with the Australian Institute of Geoscientists.