METHODS MANUALVOLUME 1

GOLD ANALYSISIN

ALKALINE CYANIDE SOLUTIONS

Society of Mineral Analysts

COPIES OF THIS MANUALMAY BE OBTAINED BY WRITING TO:

Mr. Patrick BraunManaging Secretary

Society of Mineral AnalystsP.O. Box 50085

Sparks, Nevada 89435

Compiled under the review of theSOCIETY OF MINERAL ANALYSTS METHODS COMMITTEE

A SOCIETY OF MINERAL ANALYSTS PUBLICATION

GOLD ANALYSIS IN ALKALINE CYANIDE SOLUTIONST.J. GILBERT - Topic Survey Editor

TABLE OF CONTENTS

1.0.0 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

2.0.0 Applicable Documents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62.0.1 General: Analytical References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62.0.2 General: Health & Environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

2.1.0 Spectroscopy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72.2.0 Extraction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82.3.0 Inorganic Concentration (Fire Assay) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

3.0.0 Method Summaries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93.1.0 Direct Spectroscopy (Method Group 1) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

3.1.1 Atomic Absorption (AAS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93.1.2 Atomic Emission (AES) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93.1.3 Atomic Fluorescence - (AFS X-Ray) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

3.2.0 Organic Concentration Methods for Spectroscopy (Method Group 2) . . . . . . . . . . 103.3.0 Inorganic Concentration (Fire Assay) Methods (Method Group 3) . . . . . . . . . . . . . 11

3.3.1 Copper Sulfate Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113.3.2 Chiddey Method (Composite) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123.3.3 Lead Acid Method (Composite) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123.3.4 Direct Assay Method (Newmont Method) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

4.0.0 Significance and Use . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

5.0.0 Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135.1.0 Terms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135.2.0 Abbreviations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

6.0.0 Interference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146.1.0 Interferences in Atomic Absorption Analyses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

6.1.1 Physical interferences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146.1.2 Chemical interferences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146.1.3 Ionization interferences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 156.1.4 Spectral interference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 156.1.5 Background interference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

6.2.0 Survey: AAS Common Problem Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 166.3.0 Organic Concentration Methods (Extraction) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 176.4.0 Inorganic Concentration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

7.0.0 Apparatus (General) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

8.0.0 Hazards And Precautions (General) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 198.1.0 Cyanide Hazard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

9.0.0 Sampling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

10.0.0 Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2110.1.0 Spectroscopy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

10.1.1 Atomic Absorption. Flame Composite Method . . . . . . . . . . . . . . . . . . . . . . . . 2110.1.2 Procedure. Spectroscopy. Atomic Absorption. Furnace Gold in Solution: AAS,

Graphite Furnace Atomization (Freeport Method) . . . . . . . . . . . . . . . . . . . . . . 2310.1.3 Emission Spectrometry - DCP (Homestake Method): Gold and Silver . . . . . . . 2610.1.4 Emission Spectrometry - ICP (Vegas Method): Determination of Noble Metals by

Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES) . . . . . . 2710.1.5 Atomic Fluorescence: Jumbo Mining Co. X-ray Fluorescence Spectrometry . . 33

10.2.0 Solvent Extraction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3710.2.1 MIBK Extraction From Acidified Solution (Newmont Method) . . . . . . . . . . . . 3710.2.2 DIBK/Aliquat 336 Extraction From Direct Solution (Freeport Method) . . . . . . 3910.2.3 Butyl Sulfide Extraction (North American Laboratories) . . . . . . . . . . . . . . . . . . 43

10.3.0 Reference Fire Assay Procedure (Freeport/Newmont Composite) . . . . . . . . . . . 4410.3.1 Procedure, Inorganic Concentration, Copper Sulfate (Pinson Method):

Determination of Gold and Silver in Gold Plant Solutions by Fire Assay . . . . . . 4810.3.2 Procedures. Inorganic Concentration. Copper Sulfate (Freeport Method): Gold

Determination in Liquid by Fire Assay . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5010.3.3 Procedures. Inorganic Concentration. Copper Sulfate (Golden Sunlight Method)5210.3.4 Procedures. Inorganic Concentration: Chiddey . . . . . . . . . . . . . . . . . . . . . . . . . 5310.3.5 Procedures. Inorganic Concentration: Lead - Acid . . . . . . . . . . . . . . . . . . . . . . 5410.3.6 Procedures. Inorganic Concentration. Direct Assay: Fusion of High-grade

Solutions for Gravimetric Assay . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56

11.0.0 General Calculations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57

12.0.0 Precision and Bias . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58

13.0.0 Waste Disposal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59

14.0.0 Contributing Organizations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60

15.0.0 Disclaimer of Liability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62

Page 5

1.0.0 Scope

This document is a collection based on a survey of analytical methodsin current or past usewithin the mining industry for the determination of gold in alkaline cyanide solutions. It maybe used as an indicator of mining practice for discussion purposes, but should not be viewedas a collection of standardized methods. All method comparisons are of an approximatenature.

2.0.0 Applicable Documents

Internal company documents listed as references are available from the listed companies on alimited basis at cost. Such references which are not available upon a postage-paid requesthave been deleted.

2.0.1 General: Analytical References

CC 1979 Annual Book of ASTM Standards, Part 12, "Chemical Analysis of Metals andMetal Bearing Ores," American Society for Testing and Materials.

CC C.H. Bucknam and D.M. Hausen, "Classification of Carlin Ores, Simple DiagnosticTests," (memorandum) April 22, 1986. Newmont Gold.

C Frederick M. Garfield, Quality Assurance Principles for Analytical Laboratories,Association of Official Analytical Chemists, 1984.

C Handbook For Analytical Quality Control in Water and Waste Water Laboratories,USEPA, EPA-600/4-79-019, March 1979.

C Methods For Chemical Analysis of Water and Wastes, USEPA, EPA 600/4-79-020,Revised Edition, March 1983.

C Methods For Determination of Inorganic Substances In Water and Fluvial Sediments,U.S. Geological Survey, Open File Report No.85-495 by Marvin J. Fishman and LindaC. Friedman, Editors (1985).

C Test Methods For Evaluating Solid Wastes, USEPA, SW-846, Third Edition,November, 1986.

C USEPA Contract Laboratory Program, Statement of Work for Inorganic Analysis,Multi-Media, Multi-concentration, SOW No. 787, July, 1987.

Page 6

2.0.2 General: Health & Environment

C C.H. Bucknam and S.W. Nabbs, "Procedures to Ensure Compliance with State ofConnecticut EPA. Regulations," (memorandum) Newmont Gold.

C Kraybill, Daniel D., Illinois Small Quantity Generators' Manual, Hazardous WasteResearch and Information Center. Illinois Dept. of Energy and Natural ResourcesState Water Survey Division, HWRIC TN87-002, January 1987.

C OSHA Safety and Health Standards, General Industry, (29 CFR 1910), OccupationalSafety and Health Administration, OSHA 2206, Revised January, 1976.

C Ralo, J. "Kids Leukemi~ from Parents Exposure" July 18, 1987 Science News.

C Randell C. Baselt, Ph.D. Biological Monitoring Methods for Industrial ChemicalsBiomedical Publications, 1980.

C Tacket, Sandford L., "Lead in the Environment: Effects of Human Exposure, "July1987 American Laboratory pg. 32-41.

C U.S. Dept of Health, Education & Welfare, Occupational Exposure to InorganicLead, Revised criteria, 1978.

C U.S. Environmental Protection Agency, "Understanding the Small Quantity GeneratorHazardous Waste Rules: A Handbook for Small Business, EPA1530-SW-86-019,September 1986.

2.1.0 Spectroscopy

C V. Bennett, "Metallurgical Analysis by Plasma Emission Spectroscopy", pg. 27-44,Proceedings of the First Annual Conference of the Society of Mineral Analysts, Feb.1987

C C.H. Buckman, "Gold Check Assays by Graphite Furnace AAS," Newmont Gold(memorandum) August 19, 1986.

C G.D. Christian and M.S. Epstein, Atomic Absorption Spectroscopy, ACS AudioCourse 1980.

C Scientific Apparatus Makers Association, Safety Procedures for Atomic AbsorptionSpectrophotometers, SAMA A 12-1970.

Page 7

C Thermo Jarrell-Ash Corporation, IL Video 22 AAIAE Spectrophotometer Operator'sManual @ 1985.

C Thermo Jarrell-Ash Corporation, Atomic Absorption Methods Manual for FlameOperation @ 1986.

C Thermo Jarrell-Ash Corporation, Inductively Coupled Plasma Methods @ 1984.

C Perkin-Elmer Manuals: "Model 2380 Atomic Absorption Spectrophotometer,""Model 5000 Atomic Absorption Spectrophotometer," "Analytical Methods forAtomic Absorption Spectrophotometry," "Flame Autosampler for the Model 5000".

C R.K. Winge, V.A. Fassel, V. J. Peterson, and M.A. Floyd: Inductively Coupled PlasmaAtomic Emission Spectroscopy: An Atlas of Spectral Information.

2.2.0 Extraction

C T. Gilbert, K. Smith, J. Anderson "An Examination of Some Techniques Performed atFreeport Gold," pg. 11-23. Proceedings of the First Annual Conference of the Societyof Mineral Analysts, Feb. 1987.

C T. Groenwald "Determination of Gold (I) in Cyanide Solutions by Solvent Extractionand Atomic Absorption Spectrometry," pg. 863-866 Anal. Chem. May 1968.

C A. Parks and R. Mtirry Smith, "A Rapid Method for the Determination of Gold andPalladium in Soils and Rocks," pg. 57-59, Atomic Absorption Newsletter,March-April 1979.

C P.D. SewardlT.J. Gilbert, "DIBK Extraction," Freeport Interoffice Letter (Elko), July20, 1984.

2.3.0 Inorganic Concentration (Fire Assay)

C C.H. Bucknam, "Analytical Procedure for Total Cold by Fire Assay - AAS," NewmontGold (Memorandum).

C Beamish, F.E. and J.C. Van ~)on, Analysis of Noble Metals: Overview and SelectedMethods, Academic Press, New York, 1977.

C E.E. Bugbee, A Textbook of Fire Assaying, (1940 edition) Colorado School of MinesPress, Golden, Colorado, 1984.

Page 8

C N.H. Furman, (Ed.) Standard Methods of Chemical Analysis; VI Edition:D.VanNostrand Co., Inc., Princeton; pg. 870.

C Joseph Haffty, L.B. Riley, and W.D. Gross, A Manual on Fire Assaying andDetermination of the Noble Metals in Geological Materials, Geological SurveyBulletin 1445, U.S. Government Printing Office, Washington D.C. (1977).

C South African Institute of Mining, Assay and Analytical Practice in the South AfricanMining Industry, Monograph Scores M6.

3.0.0 Method Summaries

3.1.0 Direct Spectroscopy (Method Group 1)

3.1.1 Atomic Absorption (AAS)

Direct atomic absorption is the most common means for determining gold in alkalinecyanide solutions. This choice is dictated by its relatively low cost for single elementdeterminations, short analysis time and reasonable accuracy.

With the exception of Battle Mountain Gold and the Bureau of Mines, labs in the methodsurvey use background correction (continuum source, Smith-Hieftje, or Zeeman) for alldeterminations. Double beam optics are preferred, but several labs are comfortable withsingle beam instrument quality. Graphite furnace atomization is only used for sampleswhich require lower detection limits. Organic concentration (see Method Group 2) orinorganic concentration (Method Group 3) is sometimes used to enhance sensitivity oraccuracy for flame atomic absorption.

The methods for atomic absorption consist of general operating parameters, a list ofvarious blank/standard matrix solutions and a composite of operating suggestions fromparticipating labs. Refer to Section 6.1.1 for a summary of interference types, appropriateaction, and a comparative table of instrumental background correction methods.

3.1.2 Atomic Emission (AES)

Emission equipment is relatively expensive to operate, but it is particularly cost-effectivefor multi-element analysis. A radio frequency generator (ICP) or a direct current (DCP)generates a plasma to stimulate atomic emission for analysis. Chromium (Cr), iron (Fe),

Page 9

manganese (Mn) and vanadium (V) are listed as potential emission interference elements. The ICP method programs the interference patterns out. The DCP method dilutessamples until interference is insignificant. As in the atomic absorption method, exactoperation instructions are left to the manufacturers' operating manual.

3.1.3 Atomic Fluorescence - (AFS X-Ray)

X-Ray fluorescence does not currently have accurate direct sensitivity equivalent to AASor AES, but field or benchtop instruments, which will continue to function undertreatment hostile to AAS or AES equipment, have been attractive for some mineoperations. A sealed radioisotope capsule or an X-ray tube is used as a source of highenergy x-rays to excite inner shell electrons. An x-ray sensitive detector (scintillator,gas-proportional counter, solid state detector, etc.) is used to count the characteristicfluorescent x-rays which are emitted by the excited gold. Spectra are simple, but somecorrections for spectral overlap (mercury, thallium, etc.) or background effects must bemade. This is done with dispersing crystals in high resolution sophisticated instruments orRoss filters in benchtop models. Sample preparation is not normally required, but themethod described in 10.l.3 uses preconcentration to obtain measurement precision anddetection limits equivalent to flame AAS methods,

Note: A Ross filter consists of two filters that transmit interfering x-rays equally whileone limits analytical line transmission. The transmission difference is used to calculate"true" analyte fluorescence.

3.2.0 Organic Concentration Methods for Spectroscopy (Method Group 2)

Extraction is a technique used to eliminate background interference or enhance absorbancefor atomic absorption spectrophotometry. Gold is preferentially absorbed by an organicsolvent which has been agitated with the sample solution. This organic phase is separatedfor AAS analysis. Absorbance is enhanced by using less extractant than sample, andinterference is reduced when interfering elements are not extracted with the gold.

The first method uses MIBK as the organic extractant. MIBK affinity for the gold ionsand complexes found in alkaline solution is limited, so the method requires that alkalinesolutions be acidified in a hood prior to the addition of MIBK for extraction andseparation.

The second method uses a solution of DIBK and trialkyl ammonium chloride (Aliquat336) to extract solutions over pH ranges of 1-l2.5. The method differs from 3.2.1 byadding salt solution to the sample to optimize extraction. Higher concentration ratios than

Page 10

those in the MIBK extraction method are possible if quality standard solutions can beobtained. The extreme stability of gold in this extractant gives extracted samples a longershelf life if this is required.

The third method uses a solution of xylene with dibutyl sulfide as the extractant. It is notin current mining use. Solutions require acidification before extraction and should behandled in a hood. The strong odor which is associated with dibutyl sulfide requiresventilation.

3.3.0 Inorganic Concentration (Fire Assay) Methods (Method Group 3)

Fire assay methods are more labor intensive but are preferred for checking primaryreference solutions or solutions which might contain uncorrected interference factors. These methods are considered to be relatively immune to chemical, elemental or physicalinterference factors which, in instrumental methods, can cause unrecognized falsedeterminations. Reference standard solutions are not required, but control samples arerecommended.

A general fire assay method (10.3.0) has been included for reference. The fire assaypractice outlined will produce accurate determinations for "fire assay as normal". Itassumes that fusions will be with a fluid pouring, slightly acid fusion and cupellation willinvolve 25 or more grams of lead.

Assay comparisons between analytical labs are recommended to detect errors in technique. Although the reference method and reference sources give a good basis in fire assaying,safe and accurate results depend on an experienced assayer.

Note: Unless otherwise stated all chemicals are reagent grade.

3.3.1 Copper Sulfate Methods

The Copper Sulfate Method uses a solution of copper sulfate and sulfuric acid toprecipitate gold and silver from solution. This precipitate is filtered, dried and eitherscorified or fired to produce a lead button for cupellation.

The Pinson assist the filtration Method uses potassium ferrocyanide and sodium sulfite toformation of the gold precipitate and flocculent to aid of the precipitate.

The Freeport Method does not use fldcculent or potassium ferrocyanide. They believeferrocyanide increases the amount of copper in the precipitate without an improvement in

Page 11

gold values for their type of sample solutions. They do use sodium sulfite to assistprecipitate formation.

The Golden Sunlight Method combines copper sulfate, sodium hydroxide and sodiumcyanide to make a precipitation solution. Potassium ferrocyanide is used to assist goldprecipitation, and sodium sulfite is not used in the precipitation process. Flocculent is notused with filtration.

3.3.2 Chiddey Method (Composite)

Chiddey is a term applied to a zinc precipitation method used to collect gold from solutionfor fLre assay cupellation. Three variations of this method were submitted which wereessentially identical. This is a composite of all three methods.

3.3.3 Lead Acid Method (Composite)

Gold ions from an HCl-adidified sample solution replace lead atoms granulated lead. Thegold-loaded granulated lead is dried for cupellation by standard fire assay techniques. Three essentially identical methods were submitted. Battle Mountain Gold's method is theprimary model for this composite.

3.3.4 Direct Assay Method (Newmont Method)

The direct assay method is only used on high-grade solutions. A small aliquot of solutionis dried in a crucible filled with standard flux and fire assayed by "normal" techniques. Theprocedure included here was submitted by Newmont Gold Company. No other labs arecurrently using direct assay.

4.0.0 Significance and Use

In the primary metallurgical process used by the mineral processing industry on goldbearing ores, gold is extracted with alkaline cyanide solutions. Metallurgical accounting,process control, and ore evaluation procedures for this type of mineral processing plantdepend on accurate, precise, and prompt measurements of gold concentration in alkalinecyanide solutions.

It is assumed that all who use these methods will be trained analysts capable of performingcommon laboratory procedures skillfully and safely. A technician is assumed to have basicskills in fire assay methods and applicable instruments. It is expected that work will be

Page 12

performed in a properly equipped laboratory. Since these are not necessarily standardizedmethods, it is assumed that all who use these methods will test their accuracy and safetybefore placing them in regular use.

5.0.0 Definitions

5.1.0 Terms

C Atomic Absorption Spectroscopy: The analysis of the frequency-specific lightabsorbance characteristics of atomic elements to determine elemental concentration.

C Atomic Emission Spectroscopy: The analysis of the characteristic light frequenciesemitted by atomic elements in a plasma to determine elemental concentration.

C Atomic Fluorescence: The analysis of characteristic light frequencies emitted byelemental atoms which have absorbed light at those frequencies from another lightsource to determine elemental concentration.

C Atomization: The process of converting a proportional amount of analyte element intoan atomic state within a sample cell for absorbance analysis.

C Baseline: The concentration area where non-analyte or random fluctuations obscureanalytical valves. Can also refer to the magnitude of these fluctuations.

C Detection Limit: A lab estimate which in this document is equivalent to the lowestconcentration which can be separated from the baseline during average productionconditions.

C Extraction: The selective chemical removal of an element from a sample solution into asolvent solution for spectrographic analysis.

C Fire Assay: A group of analytical techniques which use high temperature selectivereduction of precious metals and lead from a molten solution (fusion). Precious metalsare separated qualitatively by selective oxidation (cupellation) for gravimetric orinstrumental analysis.

C Precision: A lab estimate of typical standard deviation in samples with analyteconcentrations at the top of a method's analyte concentration range (definition limitedto this document).

5.2.0 Abbreviations

Page 13

C AAS Atomic Absorption SpectroscopyC AFS Atomic Fluorescence SpectroscopyC DIBK Dusobutyl KetoneC FAAS Flame Atomization Atomic Absorption SpectroscopyC GFAAS Graphite Furnace Atomization Atomic Absorption SpectroscopyC g gramsC lb/st pounds per short tonC MIBK Methyl Iso-butyl KetoneC m3 cubic metersC ug/ml micrograms per milliliterC mg/l milligrams per literC oz/T ounces troy per short tonC ppm parts per million (weight by weight)

6.0.0 Interference

6.1.0 Interferences in Atomic Absorption Analyses

There are five types of interferences encountered in atomic absorption determinations: physical, chemical, ionization, spectral and background interferences.

6.1.1 Physical interferences: When there is a difference between samples and standards in thephysical characteristics of the solutions (such as viscosity or density) it is possible for thereto be a difference in aspiration rates or droplet size that causes a difference in response.Physical interferences can cause a determination to be either too high or too low. Correction techniques are:

a) Matrix matching either by adding substances to the standards to match the physicalcharacteristics of the samples or preparing the samples in such a way as to remove theinterfering substance.

b) Method or standard additions.

c) Method of internal standardization (with a dual channel A.A. spectrophotometer).

Physical interferences always affect the slope of the calibration curve.

6.1.2 Chemical interferences: The presence of certain chemical compounds in a sample matrixcan suppress or enhance sensitivity causing a difference in response between samples andstandards. This is often caused by the formation of refractory compounds in the flame.Correction techniques are:

Page 14

a) Matrix matching.

b) Matrix modification with a releasing agent such ad EDTA or lanthanum.

c) Method of standard additions.

d) Use of a hotter flame (Nitrous oxide/acetylene).

Typical examples of chemical interferences include the formation of refractory phosphateswhen determining calcium or magnesium. The calcium phosphates do not melt in theflame, and the amount of free calcium available in the atomic state is reduced.

6.1.3 Ionization interferences: In some cases a flame can be hot enough to ionize the analyteelement. When this occurs some of the atoms will be found in an ionized state and willnot absorb light, giving a reduced response. Typically ionization interferences occur in thefirst column of the periodic table (Li, Na, K, etc.) in air/acetylene flames and the first twocolumns (Mg, Ca, Ba, etc.) in nitrous oxide/acetylene flames. Samples often will showless ionization suppression than standards. This is due to the free electrons and other ionswhich can be expected in chemically complex samples. Also ionization suppression occursto a greater extent at low concentrations than in higher concentrations. As a result,ionization interferences will cause a difference in response between standards and samplesand non-linear calibration curves at low concentrations. Correction techniques are limitedto the use of ionization buffers. This usually consists of making all samples and standardsin up in 0.1% cesium or 0.2% potassium. Since the method of standard additions isrestricted only to chemical and physical interferences, no attempt should be made tocorrect for ionization interferences using the method of standard additions.

6.1.4 Spectral interference: When there is more than one absorbing line for more than oneelement in the spectral bandpass of the atomic absorption instrument, it becomes possiblefor the readings to be a function of the concentration of two elements independently ratherthan of a single analyte element. In this case it is impossible to tell if the reading is due tothe presence of the analyte atom or some interference. Fortunately these interferences areextremely rare in atomic absorption. When encountered they can usually be eliminated by:

a) Narrow the spectral bandpass of the instrument.

b) If using a multi-element hollow cathode lamp, switching to a single element lamp.

c) Using an alternate line.

Again, when following the instrument manufacturer1 5 instructions for setup andoperation of the spectrophotometer, these interferences are almost never encountered.

Page 15

6.1.5 Background interference: One of the most co~on interferences 15 background interferencedue either to the presence of salts in the flame which can scatter the light or molecularspecies which can absorb the light. In either case, the apparent concentration of analytewill be too high. Background interference is also called non-specific absorption. Ingraphite furnace determinations, background interferences become more significantbecause they are enhanced. A quick test for background interference is to run the samplewith the background correction off and then again with it on. If the answers arecomparable, there is no interference.

Most instruments have some type of automatic background correction available. It ispossible for a background interference to give a signal even when no analyte is present. Therefore, do not attempt to correct for background interference using the method ofstandard additions. Correction techniques are:

a) Deuterium or tungsten continuum correctors. These are applicable to both flame andfurnace. They may give over or under correction under certain conditions of“structured” background. For example, in the determination of arsenic by graphitefurnace, sodium chloride will cause light scatter that can be corrected easily by thedeuterium arc. However, if aluminum is present, a structured molecular absorbancethat cannot be accurately corrected using a continuum corrector will interfere with anaccurate determination.

b) Zeeman Atomic Absorption. The Zeeman technique will correct for all kinds ofbackground interferences, both structured and unstructured. Most instruments offerZeeman background correction in a furnace-only configuration.

Ed. Note: Hitachi offers Zeeman correction in flame mode. User references are notavailable, and Hitachi marketing appears limited in the U.S.A. at this date.

• Smith-Hieftje (pronounced “Heef'-ya”) Atomic Absorption. This technique isapplicable to both structured and unstructured background, and works on both flameand furnace determinations.

6.2.0 Survey: AAS Common Problem Summary

C Iron has been reported in Australia as an interfering element for gold analysis byatomic absorption. The labs in this survey indicated that iron is not a problem. However, experience with problem iron concentrations may be limited.

C High salt concentrations (over 2%) affect nebulizer aspiration. This causes erroneousdeterminations if standards are not matrix matched.

Page 16

C Background interference is a particular problem for process tailings/liquors. Tailssolutions containing 0.1 ppm gold can have uncorrected values over 1 ppm.

CC Non-routine problems (not listed above) are usually solved by applyingOrganic/inorganic concentration methods (6.3 or 6.4).

C Atomic Emission can require programmed elimination of interfering spectral emissionlines or background elmination techniques. A method-specific discussion in method10.1.2.2 can also be of use for non-ICP methods.

C Atomic Fluorescence (X-Ray) can suffer from heavy metal interferences (mercurythallium, etc.). Instrumental correction using matrix matched standards, Ross filters,dispersing crystals or instrument-specific methods are available and should beevaluated for each application.

6.3.0 Organic Concentration Methods (Extraction)

Properly performed extractions eliminate most interferences to allow low detection limits. The increased sample handling does increase error risks. Extraction may be conbined withfire assay concentration if interference is suspected below the detection limits of direct fireassay checks.

6.4.0 Inorganic Concentration

The potential for interference is considered to be lower for inorganic (Fire Assay) methodscompared to spectroscopic methods. The primary risk lies in chemical interference orhandling loss within the initial chemical precipitation or collection from the samplesolution. Losses can also occur in fusion, cupellation and parting. The labs in the surveyreport that these problems are not significant within the precision limits of the variousmethods.

COMPARATIVE TABLE1

COMMERCIAL INSTRUMENTAL BACKGROUND CORRECTION(LINE SOURCE ATOMIC ABSORPTION SPECTROSCOPY)

TECHNIQUE ADVANTAGES DISADVANTAGES NOTES

Page 17

Continuum Source(D2 or equivalent)

C Measures broadband orcontinuum backgroundabsorption

C Ready availabilityC High sample rate correction

available (200-240measurements/second)2 onsome instruments my reducecorrection delay problems ingraphite furnace applications

C Incorrect results in thepresence of Structuredbackground

C No correction for spectralinterferences

C Difficult to match beamsexactly because differentgeometries & optical pathsbetween hollow cathode andcontinuum Lamp exist

C Potential driftC CostC Most systems only correct up

to 0.5 absorbance units

1. Table data from an article byJoseph Sneedon "BackgroundTechniques in AtomicAbsorption Spectrometry"Spectroscopy Vol. 2, No. 5, pg.42, Table III). The tableincludes minor additions promptedby SMA member comments.

2. 50-60 backgroundmeasurements per second is thenormal range of sampling rates forvarious correction techniques. inflame and many furnaceapplications, high rates do notimprove correction quality.3. The EPA has made apreliminary recommendation thatSmith-Hieftje and Zeemancorrection techniques be pref er redover Continuum (D2)correction techniques for graphitefurnace atomic absorptionspectrometry analysis.

4. When extreme correction isrequired, the signal-to-noise ratio ofan instrument is of primaryimportance. For example, considera sample requiring 2 absorbanceunits of correction. The backgroundmatrix, in this case, absorbs 99% ofthe incident light and the analyteabsorbancemust be measured in the remaining1% of light. Although correction byZeeman and S-H methods would beaccurate, the remaining signal isdominated by the signal-to-noiseratio of a particular analyte on eachmake and model instrument.

Smith-Hieftje3 C Accurate correction forstructural background

C Spectral interferences may beovercome for many cases

C Matches of two light sources isnot required

C Visible and ultraviolet regionsare corrected

C No double-valued analyticalgrowth curves exist

C No light is lost due topolarizers

C Up to 3 absorbance units ofcorrection4

C Reduced Sensitivity (approx.40% for Au, less for otherelements)

C Special hollow cathode Lampsare required to prevent gasCleanup necessitated byrunning lamps at high current(even for a short pulse)

C CostC Not every hollow cathode

Lamp will produce a usableself-reversal effect, particularlyfor refractory elements likemolybdenum & titanium

Zeeman3 C Unaffected by structuredbackground

C Spectral interferences may beovercome if lines are 0.02 nmapart

C Matching of two light sourcesis not required, which preventsproblems of alignment,geometry, or differential drift

C Up to 3 absorbance units ofcorrection4

C Limited availability for flameatomization applications in theUnited States

C Direct overlap of Lines cannotbe corrected

C Analytical growth curves mybe dcuole-valued (two widelydifferent concentrations givethe same absorbance)

C Sensitivity Is reduced for someelements (10-20%)

C Polarizers contribute to lightloss

C Restriction of space due to themagnet

C Accuracy depends onbackground absorbance beingunaffected by magnetic fieldstrength and polarization ofsource

C Cost

7.0.0 Apparatus (General)

C Safety Equipment: Chemical-resistant lab aprons and gloves; safety glasses and chemicalmask; emergency cyanide-poisoning first aid station; emergency eye-ash and shower;self-contained breathing apparatus and rescue contingency plan.

C Reagents: Unless otherwise noted, all chemicals are reagent grade. Refer to reagent listsof individual methods.

Page 18

C Water: Deionized water or distilled water.

C Glasswarepipets: Class A, sized as needed beakers: sized as needed, borosilicate, calibratedvolumetric flasks: Class A, sized as needed glass stir rods auto-diluters assortedreagent dispensers

C Plastic Wareeyedroppers, disposable teaspoon, disposable (measure zinc powder, lead shot, etc.)

C Instrumentation

Atomic absorption spectrophotometer equipped with background correction (graphitefurnace or flame atomization), Autosampler (optional), Atomic EmissionSpectrophotometer (ICP or DCP), Precision balance (accurate to .001 mg), Standardbalance (accurate to .001 g)

C General EquipmentFire Assay Furnace equipped to fuse samples at 1950° F and cupel at 1650° F HotPlate (set at less than 100° C), Annealing and parting trays, Cupel tongs, forks, etc.,Porcelain Crucibles, MgO cupels, Crucibles (30g or 40g as preferred)

8.0.0 Hazards And Precautions (General)

8.1.0 Cyanide Hazard

C The necessity, for both safety and sample preservation, of keeping the pH of cyanidesolutions well into the alkaline range (10.5 to 14) by adding sodium hydroxide or calciumhydroxide

C The release of cyanide gas, a highly lethal poison, from any admixture of cyanide and acid(or, to a lesser extent, non-alkalinized water) -- cyanide to be mixed only under fumehoods

C The release of toxic cyanogen chloride from any admixture of cyanide and chlorine,hypochlorite, or aqua regia

C The necessity of following strict hygiene practices when handling cyanide

C An up-to-date cyanide safety program that includes a rescue contingency plan.

C Poisoning by fumes from solvents (MIBK, Aliquat 336), acids (nitric, hydrochloric, aqua

Page 19

regia, sulfuric), and lead (during cupellation, fluxing, fusion)

C Poisoning by ingestion or inhalation of lead (lead oxide dust in flux, lead acetate crystals)or of other chemicals

C Tissue destruction from acids (above) and alkalies (sodium and calcium hydroxide)

C Burns from furnaces, ovens, hot plates, tools, and from flame, torch, or electric-arcinstruments

C Cuts from glassware

C Explosions (e.g., acetylene for atomic absorption instruments)

C Hazards related to improper housekeeping and hygiene

C Offsite hazards due to improper protective clothing or personal hygiene. (e.g. organicsolvents, particularly chlorinated hydrocarbons, which are carried home on an employee'sclothing or body are associated with a higher incidence of childhood leukemia within anemployee's family).

9.0.0 Sampling

C Samples should be taken in clean containers. Small gold residues or gold-precipitatingchemical residues can be a significant problem

C Filter press samples should not be taken until flow has been established. Dilution orcontamination by press residues can be significant

C Samples should be preserved by adding an excess of cyanide and sufficient sodiumhydroxide to maintain a pH 10 or above as soon as possible after collection. This willinsure the stability of the gold in solution and prevent accidental toxic gas formative.CAUTION: All procedures which require sample acidification should be performed in anadequately ventilated hood

10.0.0 Procedures

10.1.0 Spectroscopy

10.1.1 Atomic Absorption. Flame Composite Method

Reagents:

Page 20

C Primary Standard, 1000 ppm Au (Available from several vendors). Quality should bechecked by Fire Assay Methods.

C Standards, Secondary: Prepared as needed to bracket samples with blank matrixsolution. (see matrix table)

Example: (Battle Mountain Cold)

a) Prepare 1.0 lb./ton cyanide blank (0.5 g NaCN/l000 ml H20).

b) Prepare 100 ppm Au Standard: pipette 10 ml of the stock 1000 ppm Au standard intoa 100 ml volumetric flask. Bring to volume with H20.

c) Prepare 0.015, 0.029, 0.058, and 0.116 oz/ton Au standards:

C Cut 0.5 ml of 100 ppm, bring to 100 ml with CN-Blank. Makes 0.015 oz/ton

C Cut 1.0 ml of 100 ppm, bring to 100 ml with CN-Blank. Makes 0.029 oz/ton

C Cut 2.0 ml of 100 ppm, bring to 100 ml with CN-Blank. Makes 0.058 oz/ton

C Cut 4.0 ml of 100 ppm, bring to 100 ml with CN-Blank. Makes 0.116 oz/ton

d) Standard and Blank Matrix: (table)Lab Blank Notes

Page 21

Asamera 2 Ib/st NaCN 1. These labs alter matrix as required whenmatrix interference become, apparent. Example:Dissolved salts greater than 2% require a similarviscosity matrix.2. These labs do direct spectroscopic analysis onAqua regia digested dore beads. This requires a10% Aqua regia standard and blank matrix.3. These labs use organic Concentration(extraction) to enhance detection limits. Theorganic extractant or the applicable method iswed for a blank and standards are extracted bythe same method from appropriate aqueousstandards.4. Triton X-l00 (alkylaryl pelyelher alcohol)acts as a conditioner /cleanser for the burnerchamber. The matrix absorbance is identical todeionized water when diluted to 0.075 g/l indeionized water.

Battle Mtn. Gold 0.5 g/l NaCN

Bureau of Mines 0.25% NaCN, 0.1% NaOH

Dee Gold 5 Ib/st NaCN, pH adjusted to 10.5 to 11 with NaOH

Freeport 1,3,4 0.075 g/l Triton X-l00 (3 g/l NaCN, 0.1 g/l NaOH)

FRM 1 Distilled water

FMC 1.5 g/l NaCN pH adjusted

Golden Sunlight 2.6 g/l NaCN, adjusted above pH 10 with NaOH

Goldfields NaCN concentration and pH of Mill in last 24 hrs.

Newmont 2,3 0.3% NaCN, pH adjusted above 10.5

Procedures:

Set up the A.A. as required by the instrument manufacturer.AA Parameters: Wavelength: 242.8 nm

Burner: Straight (no angle)Flame: Lean, blue @ maximum absorbanceIntegration: 1.0 Second (increase if jumpy)Slit: .7 nm

Allow 10 minute AAS warmup if needed.

Zero instrument with matrix-blank. Use two-or-more point calibration curve, andbracket the sample with a higher and lower standard.

Operating Suggestions

a) Use background correction unless verified as unnecessary (see section 6.1.1comparison table for background correction options).

b) Should be able to read samples to three significant places (.XXX oz.t/s.t., XXXoz.t./s.t., X. XXppm. XX.Xppm.).

c) If results are excessively noisy, may want to increase integration time.

d) Advise the use of a corrosion resistant nebulizer (Pt-Rh).

e) Salt concentrations above 2% cause significant changes in aspiration rates. Standards for these types of samples should be matrix matched.

f) Do not allow standards to stand open except during standardization. Evaporation

Page 22

or contamination may change the concentration of the standard.

g) Check standards and blank often.

h) Do not aspirate directly from stock gold standard solutions. A portion of standardmay be poured fresh for each standardization into a disposable test tube or a small,sealable working standard container may be used. Replace the solution or blankfrom the stock if contamination is suspected.

i) Large production batches of samples should include control and duplicate samplesof known concentration as an aid to maintaining quality control on precision andaccuracy.

j) Check all primary commercial gold standards by fire assay analysis. They are notalways as accurate as vendors claim. CanMet or NBS standards are preferred foroptimum accuracy.

d) Solutions from unfamiliar sources should be checked by fire assay to eliminate thepossibility of unexpected interference. See section 6.1.1 for a discussion ofpossible problems and corrective action.

10.1.2 Procedure. Spectroscopy. Atomic Absorption. Furnace Gold in Solution: AAS,Graphite Furnace Atomization (Freeport Method)

Principle

Liquor samples containing 0.02-3.0 mg/L Au are analyzed by furnace AAS. Thesamples are diluted with ammonium citrate-lanthanum nitrate buffer to decreasechemical and background interferences (see Note 2). If interferences are minimal(within the capability of the instrumental background correction), the buffering may beeliminated for direct readings. This will result in lower detection limits when standardshave a matrix similar to the samples.

Reagents

C Ammonium citrate - (CH4)2HC6H507

C Lanthanum nitrate - La(N03)3 -6H20

C Ammonium citrate - Lanthanum nitrate buffer solution, 10 g/l Ammonium citrateand 5g/l Lanthanium nitrate - Using a large powder funnel, weigh 20 g ofammonium citrate and 10 g of lanthanum nitrate directly into a 2 liter volumetric

Page 23

flask. Bring volume to the mark with distilled water. Add a magnetic stir bar tothe flask and place flask on a mag mixer. Allow to stir overnight. Filter as neededjust prior to use.

C Gold wire - Au - 99.99+ % pure

C Sodium hydroxide solution - Na0H, 1 N - Dissolve 40 g of NaOH in distilledwater, cool, and dilute to 1 liter with distilled water.

C Sodium hydroxide solution - NaOH, 0.1 N - Dissolve 4 g of NaOH in distilledwater and dilute to 1 liter with distilled water.

C l0g/l Sodium cyanide solution - Dissolve 10 g of NaCN in 500 ml of 0.1 N NaOHand dilute to 1 liter with distilled water. This solution should be made fresh asneeded and in conservative quantities. Excess amounts should be properly treatedand disposed of and NOT STORED.

C 1 g/l Sodium cyanide/sodium hydroxide solution - NaOH, 0.1 N; Dilute 100 ml ofthe 10 g/l NaCN solution above to 1 liter with 0.1 N NaOH. This solution shouldbe made fresh as needed and in conservative quantities. Excess amounts should beproperly treated and disposed of and NOT STORED.

WARNING: Keep cyanide solutions separate from all acids.

Note 1: Matrix problems can be complex for furnace atomization. Seesection 6.1.1

Note 2: The La buffer method works for Au in typical solutions but must betested on a case-by-case basis for alternate elements. VarianAssociates (Palo Alto, Calif.) uses palladium in a universal matrixmodifier method but none of the survey labs have tried the method.

Apparatus

C Volumetric flasks, 10, 100, 1000, and 2000 mlC Pipets, 5, 6 and 10 mlC Eppendorf pipet, 100 umlC Atomic Absorption Spectrophotometer, Perkin-Elmer Model No. 5000 with

HGA-500 graphite furnace and AS-40 automatic sampler.C Gold (Au) hollow cathode lamp (HCL)

Standards

Page 24

Au stock solution, 1,000 mg/L, (1000 ppm) (prepared when quality commercialstandards are not available) - Dissolve 1 g (+ .0001 g) of pure gold wire or sponge in aminimum volume of aqua regia. Evaporate to approximately 2 ml. Dissolve theresidue with 100 ml of concentrated hydrochloric acid. Heat gently to facilitatedissolution. Cool and transfer to a one liter volumetric flask, add 150 ml ofconcentrated hydrochloric acid and dilute to the mark with distilled water.

Prepare the following Au-cyanide stock solutions:

C Solution I.0.100 g/l (100 mg/L) Au - Into a 100 ml volumetric flask, pipet 30 ml of 1N NaOH and 10 ml of 10 g/l NaCN solution. Mix thoroughly, then pipet10 ml of the g/l Au stock solution into the flask and dilute to the mark withdistilled water.

C Solution II.0.05 g/l (50 mg/l) Au - Into a 100 ml volumetric flask, pipet 15 ml of 1 NNaOH and 10 ml of 10 g/l NaCN solution. Mix thoroughly, then pipet 5ml of the 1 g/l Au stock solution into the flask and dilute to the mark withdistilled water.

C Solution III.0.01 g/l (10 mg/l) Au - Into a 100 ml volumetric flask, pipet 10 ml of the0.100 g/l Au (Soln. I) stock solution. Bring to volume with NaOH (.1 N) -NaCN (1 g/l) solution.

C Solution. IV.0.001 g/l (1 mg/l) Au - Into a 100 ml volumetric flask, pipet 10 ml of the0.01 g/l Au (Soln. III) stock solution. Bring to volume with NaOH (.1 N)- NaCN (1 g/L) solution.

From these stocks prepare the following liquor standards given as actualconcentrations:

Au Concentration (mg/L)*: 0.02 0.05 0.1 0.5 1.0 3.0Volume used of stock

solution (ml): 2(a) 5(a) 10(a) 5(b) 10(b) 6(c)

(a) Use a 1.0 mg/l Au stock solution (Soln. IV)(b) Use a 10.0 mg/l Au stock solution (Soln. III)(c) Use a 50.0 mg/l Au stock solution (Soln. II)

* Note: mg/l = ppm

Pipet the respective volume of each Au-cyanide stock solution into 100 ml volumetricflasks. Bring to volume with NaOH (.1 N)-NaCN (1 g/l) solution. Along with thesample preparations, dilute 100 ml of each standard to 10 ml with ammoniumcitrate-lanthanum nitrate buffer. The standards are now ready for analysis by furnace

Page 25

AA.

High Background Procedure

Pipet 100 uml of sample into a 10 ml volumetric flask. Bring to volume withammonium citrate-lanthanum nitrate buffer solution. Mix well. Use the graphitefurnace atomic absorption table to set the parameters for Au in liquors and run againsta set of correspondingly-prepared standards.

Minimal Background Procedure (within background correction capabilities)

When a comparison of determinations with and without buffering place the undiluted(no buffering) determinations within the accuracy limits of the buffer method, directdeterminations are preferred. Sensitivity can improve by a factor of 100.

Use the graphite furnace atomic absorption table to set the parameters for Au inliquors and run against a set of corresponding standards which have not been dilutedwith buffer solutions.

10.1.3 Emission Spectrometry - DCP (Homestake Method): Gold and Silver

Method

C Single element DCP mode.

Range

C 1000 ppm to 0.008 ppm for Au.C 1000 ppm to 0.004 ppm for Ag.

Precautions

Analyses affected by matrices which provide false gold signals. For high matrixinterferences, make dilutions until signal is unaffected by matrix.

Reagents

C Gold &Silver Standards in 0.025% NaCN and 0.1% NaOH (100.0, 10.0, 1.0, 0.1,and 0.01 ppm)

Procedure

Page 26

C 50 ml Mill Solution Samples are centrifuged at a centrifuge setting of 35 for 20minutes. Analyses are performed on the upper half of the tube.

C Calibrations are effected by running the following standards: 0, 0.01, 0.1, 1.0 ppm. DCP alignment is attained with 10 ppm Au and Ag standards.

C For enriched refinery samples, run calibration samples 0, 1, 10,100 ppm. Runsamples. Make appropriate dilutions of samples so that analysis will fall between0.1 and 2.0 ppm. Calibrate with 0, 0.01, 0.1, 1.0, 2.0 ppm standards. Run dilutedsamples.

Calculations

C Adjusted ppm = Reading (ppm) x Dilution Factor

Some labs (not including Homestake) have encountered problems with Ironinterferences. If instrumental background correction does not solve the problem,extract the sample with an organic solvent and back extract iron with HCl (see 10.2.2).

For the 100 ppm preparation, add solution containing NaCN (2.5%) NaOH (10%) tillsolution turns pink to phenolphthalein indicator. Bring up to volume with solutioncontaining 0.025% CN and 0.1% NaOH.

Manganese represents a potential interfering element at 242.8 nm, but has not beenencountered in problem concentrations.

10.1.4 Emission Spectrometry - ICP (Vegas Method): Determination of Noble Metals byInductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES)

Scope and Application

The Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES) techniqueis applicable for the determination of over 70 elements of the periodic table. Thepresent discussion is limited to the precious metal elements namely, rhodium,palladium, iridium, platinum, gold and silver. The technique is applicable for samplesdissolved in acidic solutions. A detailed description of the method is given in thereferences (2.0 General References Analytical: EPA 60014-79-020, Mar. 1983;USEPA SW-846, Nov. 1986: USEPA SOW No. 787, July 1987; U.S.G.S. Open FileReport 85-495, pub. 1985).

Table I gives the list of elements with their wavelengths, typical instrument detectionlimits (IDL), and possible interfering elements (2.1 Spectroscopy reference: R.K.

Page 27

Winge and others, 1985). The interferences from other elements become verysignificant when their concentrations exceed 1000 mg/l. It is desirable to determinethe IDLs and interference correction factors for each instrumental system and eachnew sample matrix prior to sample analysis.

Description of Method

The ICP-AES method is based on the measurement of atomic emission in theUltraviolet-Visible (160-800 nm) spectral region by the optical spectroscopictechnique. A sample in the form of a solution is fed to a nebulizer and the resultingaerosol enters the central channel of the plasma torch. A radio frequency (typically27.12 or 40.0 MHz) Inductively Coupled Argon Plasma (ICAP) is made up of veryhot (6000-100000 K) and highly ionized argon atoms. The donut-shaped flame-likeICAP has a cooler central channel where the sample aerosol enters. The sampleaerosol is desolvated, dissociated, atomized, ionized and excited in the plasma. Theradiation emitted by the excited sample atoms and ions is focused on to the entranceslit of the spectrometer. The atomic emission is dispersed by a grating spectrometerinto individual spectral lines. The intensity of the spectral lines is measured by aphotomultiplier tube (PMT). The entire system is controlled by a computer whichconverts the measured radiation into elemental concentration.

There are two types of ICP-AES instrument, simultaneous and sequential. In asimultaneous ICP-AES system, several spectral lines are measured simultaneously(hence the name) by a photo-multiplier tube (PMT) for each element wavelength. Thissystem offers the advantage of high speed and less consumption of sample. However,interferences and the high cost of individual PMT systems are the major disadvantages.

With the sequential ICP-AES system, a computer-controlled diffraction grating pointsthe correct wavelength of light towards one PMT. The advantage of this method isthat when one wavelength is interfered by another element spectra, other wavelengthsmay be selected simply by telling the monochromator to turn to other positions. Sequential ICP-AES has the advantage of lower cost over the simultaneous. Whenyou need to analyze the sample for many elements the sequential system will consumemore samples as well as time.

An alternative to the above systems uses two monochromators and two detectorSystems. This allows for double the speed, and a wider range of spectral emission.Two examples of this type of ICP-AES are the Thermo Jerrell-Ash Plasma-200,Plasma-300, and the Perkin-Elmer Plasma II.

Instrumentation

The ICP-AES instrumentation system consists of 1) a radio frequency generator with

Page 28

plasma torch assembly, 2) a sample introduction system consisting of a peristalticpump, nebulizer, aerosol expansion chamber and a drain system, 3)computer-controlled atomic emission spectrometer with background correction, and4) a supply of argon gas (welding grade or better) which should give 20 Llmin. @ 60psig.

Operating Conditions

Since various makes and models of ICP-AES differ in their operation, it is difficult toprovide a common operating procedure. It is important that the analyst follow theprocedure given by the manufacturer of a particular instrument. Various operatingparameters such as R.F. power, sample flow rate, argon flow rate, observation heightin the plasma, integration time, standard concentrations, background correction, are tobe set according to the manufacturer's instructions and experimental requirements.Instrument detection limits, linear dynamic range, sensitivity, precision and spectralinterference correction factors are to be investigated and established for each spectralline on that specific instrument prior to the actual sample analyzation.

Reagents And Standards

C Deionized - distilled water.

A supply of deionized - distilled water of ASTM Type II purity is essential forpreparation of all blanks, standards and sample dilution. The purity of the watermust be checked with a conductivity meter and also by actual analysis.

C Concentrated acids.

A supply of reagent grade (or better) acids including Hydrochloric, Nitric, andSulfuric acids.

C Standard solutions for calibration

Primary standards: 1000 mgIL solutions of silver, palladium, rhodium, iridium,platinum and gold may be purchased commercially (from Spex, J.T. Baker,Inorganic Ventures etc.) or may be made by dissolving pure metals in appropriateacids. Use nitric acid to dissolve silver and aqua regia to dissolve other elements. Store in tightly capped glass or plastic bottles in a cool dark place. Check theconcentration of these primary standards by comparing with known independentstandards or a fire assay.

Secondary working standards are prepared from these primary standards bydiluting 1.0 ml of 100 mg/l standards to 100.0 ml with 1% nitric acid. Mixed

Page 29

standards of several elements (except silver) may be prepared. All secondarystandards should be prepared fresh at the time of analysis.

Calibration blank solution contains the same acid as the standards and at the sameconcentration. Generally a 1 to 2% solution of nitric or hydrochloric acid willwork as well.

C Quality control standards:

A) Initial Calibration Verification (ICV). ICV should be made from a differentsource than that of a primary standard. The ICV will identify any errorsthat were made while preparing secondary standards.

B) Initial Calibration Blank (ICB) and Continuing Calibration Blank (CCB). Acalibration blank may be used as ICB and CCB. The concentration of thisstandard should always read below the instrument dection limit (IDL).

C) Continuing Calibration Verification (CCV). To ensure calibration accuracyduring the analysis, a CCV should be analysed before and after the analysisof up to ten samples. The before and after concentrations of the CCVshould not differ by more than 10%. The CCV'is prepared in such a waythat the analyte concentrations are at one half of the maximumconcentration of that analyte in the standard.

D) Laboratory Control Sample (LCS). A ICS containing the elements ofinterest whose concentrations has been previously determined should bedigested and analysed with each batch of twenty or less samples. The LCSanalysis will ensure the accuracy of digestion and analysis procedures.

E) Instrument Detection Limit Standard (IDLS). A solution containing theanalyte element at a concentration equal to twice its detection limit shouldbe analyzed prior to the sample analysis. This will ensure the accuracy ofthe calibration at the low end of the calibration curve.

A detailed quality assurancelquality control program described in references (2.0General References, analytical: Garfield, 1984 or EPA-60014-79-019, March1983) should be followed for the preparation and use of the quality controlstandards. Hence a separate detailed discussion on QAIQC program is not givenhere.

An analyst may use any acceptable range for the various quality control standards. However, plus or minus ten percent is the normally acceptable range.

Page 30

Safety

The toxicity or the carcinogenicity of the reagents used in this method has not beenwell defined. Each chemical reagent should be treated as a potential health hazard. Exposure to these chemicals should be kept at a lowest possible level. Extra careshould be taken while handling cyanide solutions since they generate the deadly HCNgas even with mild acids. Good laboratory practice must be followed. Safety devicessuch as gloves, safety glasses and face mask should be used while handling thesechemicals. Prepare all solutions in a fume hood with proper air flow. A reference fileof materials handling data sheets should be available to all personnel involved in achemical analysis. Additional references on laboratory safety are given at the end (2.0General References, Health & Environment: OSHA 2206, Jan.1976; or 1979) for theinformation of the analysts.

Operating Procedure

Start the instrument according to the manufacturer's instructions. Allow sufficient time(about 15-30 minutes) for the system to become thermally stable. Make sure that theargon, colling water supply, exhaust system and other safety locks are satisfied beforeturning on the plasma. Most instruments will not allow the plasma to be ignited unlessthese requirements are met.

Turn on the computer and call in the proper operating program. Profile theinstrument's spectral lines in correct places using mercury alignment lamp. Calibratethe instrument according to the instructions using a mixed calibration standard solutionand check the calibration using an initial calibration verification standard describedearlier. Aspirate calibration blank solution between samples to avoid contamination. Begin analyzing samples after first analyzing CCV and CCB. After analyzing tensamples (or less), analyze CCV and CCB for the calibration check.

If the CCV standard does not read within 10% of its original analysis value, check forthe following problems. In any case, recalibrate the instrument, and recheck with ICV,CCB, and CCV prior to the actual sample analysis.

Trouble-Shooting:C Change in the environmental temperature: It is important to have the ICP-AES

system located in a room with constant temperature. Large fluctuations in thesurrounding area temperature affect the optical alignment of the instrumentresulting in a calibration drift.

C Change in the sample uptake rate: A clogging of the nebulizer after running asample containing high dissolved solids or suspended particles, will result in lessand less sample injected in the plasma. Correct the problem by washing the

Page 31

neublizer tip, and filtering and/or diluting the sample.

C Argon pressure drop: Check the argon flow rates and pressure tank. Near the endof the tank, if the pressure is dropping, the argon tank.

C R.F. Power fluctuation: If you notice a significant change in the R.F. Powerduring the analysis, notify your instrument service department of the problem.

C If the CCB standard reads more than the IDL, check for any contamination.Prepare a fresh CCB and check again.

The procedure described here uses standards and samples made in acidic solutions. However, in the mining industries, cyanide solutions are commonly used to leach noblemetals. A direct analysis of the solutions containing cyanides can be done if allstandards and blanks are made up of similar matrix and pH. A sample introductionsystem including nebulizer, expansion chamber, drain introduction system includingnebulizer, expansion chamber, drain line and drain container should be free from acidsand be rinsed with deionized water followed by 0.1% NaOH solution. All standards,blank and solutions should be prepared with 0.1% NaOH solution.

Interferences

A) Spectral Interferences are caused by 1) overlap of a spectral line from otherelements present in the sample, 2) unresolved overlap of molecular band spectra or3) background contribution from continuous or recombination phenomena.

The spectral overlap can be compensated by first determining interferencecorrection factors (ICF) and using computer correction of the raw data to obtainthe correct concentration. The ICFs are to be determined for each element presentin the matrix. A 1000 mg/l solution of a pure interfering element is analyzed and aconcentration read out for each analyte wavelength is recorded. The correction ismade by using the amount of interfering element concentration and the ICFs. If allthe operating conditions such as plasma power, argon flow, sample intake rate,observation height, etc. are same as they were at the time ICFs were determined,than a fairly good interference correction can be done. It is desirable to measurethe ICFs every three months or whenever the operating conditions are changed. Table I. indicates possible interfering elements. This information is only forguidance; one should determine if any other elements are interfering or not.

In a sequential ICP-AES, one can select an alternative spectral line or change inoperating conditions to avoid or minimize spectral interferences.

The problem of background contribution can be corrected by a background

Page 32

correction adjacent to the analyte spectral line.

B) Physical interferences are caused by sample transport and nebulization processes.A change in the viscosity and surface tension can cause significant change in theinstrument response when analyzing solutions containing high dissolved solids orhigh concentration of acids. The problem can be reduced by diluting the solutionand using a peristaltic pump, or by using a method of standard additions. A saltbuild-up on the nebulizer tip can also create problems. This can be corrected byusing a tip washer and diluting the sample. The use of mass flow controllers tocontrol the argon gas flow rates can also improve the instrument performance.

Table 1 Spectral Lines of Noble Metals For Use in ICP-AESElement Wavelength Relative Sensitivity Detection Limit Interfering Elements

Ag 320.068 380 0.007 Fe, Mn, V

Ag 338.289 230 0.013 Cr, Ti

Au 242.795 170 0.017 Fe, Mn

Au 267.595 96 0.031 Cr, Fe, Mg, Mn, V

Ir 224.268 110 0.027 Cr, Cu, Fe, Ni

Pd 340.458 68 0.044 Fe, Ti, V

Pd 363.470 55 0.054 Ar, Fe, Ni, Ti

Pt 214.423 100 0.030 Al, Fe

Pt 203.646 54 0.055 Al, Cu, Fe

Rh 249.077 52 0.057 Cr, Fe, Mn

Rh 343.489 50 0.060 V

10.1.5 Atomic Fluorescence: Jumbo Mining Co. X-ray Fluorescence Spectrometry

Principle

Gold-bearing cyanide solution is passed thru a filter made of activated carbon. Thecarbon filter is then analyzed directly by the x-ray fluorescence (XRF)spectrometer. This approach offers several advantages over direct analysis of thesolution: the gold is concentrated by several orders of magnitude, the background dueto scattering of the excitation x-rays is greatly reduced because of the low mass of thesample, and because the sample is thin, matrix effects are virtually eliminated.

Standards

C 1000 ppm Au standard, available from many vendors (Jumbo/ASOMA Method)

C This solution is diluted to simulate actual samples. The final volume of the

Page 33

solution should be at 300-500 ml.

C 20, 50, and 100 microgram/sq. cm. Au thin film standards. Available from:Micro-Matter, Seattle, WA

Reagents

C Activated carbon cloth filter, 1.25 inch diameter, available fromASOMA Instruments, Inc.12212-H Technology Blvd.Austin, TX 78727(512) 258-6608

Special Equipment

C A filter holder for the carbon disks and a pump for recirculating the solution thruthe filter. A compact, hand operated device is available from ASOMAInstruments. This is a 500 ml syringe with fittings to hold the activated carbonfilters.

C Instead of forcing the solution thru the filter, the filter may simply be placed in a jarof the solution and agitated for a few hours. This method is used when conductingbottle cyanidation tests.

Model 8620 )CRF analyzer (or equivalent) available from ASOMA Instrument

Note: Many or all of the following instrument set up procedures may be automated bythe on-board micro processors of the particular equipment being used.

Procedure

Configure the instrument for measurement of the Au L series x-rays and any otherx-rays that might interfere due to spectral overlap. The Au L-beta x-ray is generallyused for analysis since the carbon filters contain some zinc which interferes with theAu L-alpha x-ray. If necessary, use absorption edge filters to improve rejection ofinterfering x-rays (Reference: ASOMA Instruments, Inc. Model 8620 OperatingManual).

Instrument Calibration

C Run suitable blanks, such as fresh carbon filters to determine the instrument'sbackground corrections.

Page 34

C Run the MicroMatter standards to determine instrument sensitivity (S) in terms ofcounts per second (Au x-rays) per microgram Au per sq. cm. (Reference: ASOMAInstruments, Inc. Model 8620 Operating Manual).

Recovery Testing

C The instrument itself is now calibrated. The following operations determine therecovery efficiency of carbon filters. The operations involved are the same as foranalyzing unknown samples.

C Prepare standard solutions in the range of 0.5 to 2.0 ppm.

C Develop separate calibrations for samples that are agitated in the solution andthose that are filtered.

Agitated Samples

C Place a known volume (300 to 500 ml) of a standard solution in a bottle. Encloseone carbon cloth filter in a mesh envelope and secure with a rubber band. Themesh will prevent the surface of the filter from fouling when this analysis is done aspart of a bottle cyanidation test. Place the filter into the bottle and put the bottleon the agitator or roller. Recovery is usually complete after 6 to 8 hours, but toallow more complete extraction of gold from ore samples, the agitation is usuallyallowed to continue for 12 hours or more.

C After the allotted time, remove the filter, rinse off any ore that might be on thesurface, dry the filter by pressing it between layers of paper towel, and present thesample to the XRF analyzer. Convert the gold x-ray intensity to micrograms ofgold on the filter as follows:

ug Au = net count rate * area of filter (sq. cm) S (defined as CPS per cmg/sq. cm)

C The concentration of gold in the solution is given byppm Au = ug Au on filter

volume of solution (ml)

C This value may be compared to the known concentration of the solution to find therecovery efficiency. With 8 hours agitation, the recovery is usually 95% or higher.

Filtered Samples

C Take a known volume (approximately 400 ml) and pass it thru the filter 20 timesor more. If the large syringe is used, prepare a stack of two filters and place them

Page 35

in the holder on the syringe. Pour the sample into a large container (e.g. 1000 mlplastic beaker), insert the syringe tip into the beaker and operate the plunger 10times, drawing the whole sample into the syringe and forcing it out each time.Remove the filters and dry them by pressing between layers of paper toweling.

C Present the sample to the XRF analyzer and obtain the net count rate for the goldx-rays. Convert the intensity to micrograms of gold as follows:

ug Au = net count rate * active area of filter S

C This value may be divided by the known amount of gold in the solution (mg Au =ppm* volume in ml) to determine the recovery efficiency. The efficiency will varywith technique, but should be at least 75%.

C Actual samples should be filtered in the same manner as the calibration samples.For routine analysis, the calculations are:

ug Au on filter = net count rate * area of filter instrument sensitivity * recovery efficiency

ppm Au = ug Au on filter sample volume (ml)

C For future analyses, the instrument sensitivity, the filter area and the recovery maybe combined to obtain one overall calibration factor that will yield the total amountof gold in the solution. The reported concentration will be the weight of the golddivided by the sample volume. Actual samples should be filtered in the samemanner as the calibration samples. Recovery efficiency should be checkedroutinely, especially when changing lots of the carbon filter material.

C If an ore sample was prepared, the concentration of extractable gold is given byppm Au = ug Au on filter

wt. of ore (grams)

C For future analyses, the instrument sensitivity, the filter area and the recovery maybe combined to obtain one overall calibration factor that will yield the total amountof gold in the solution. Recovery efficiency should be checked routine, especiallywhen changing lots of the carbon filter material.

Precision For XRF Analysis of Au in Solution

C The measurement precision will depend greatly on instrument type and the analysistime used. For the Asoma Instruments Model 8620, the measurement precision is+1- 10 micrograms Au (1 sigma) for a 200 second analysis. This refers to the total

Page 36

amount of gold in the filtered solution. If a 500 ml volume was filtered, theprecision in ppm is

ppm = 10 ug = 0.020 ppm500 ml

C The precision varies as a function of the square root of the count time. Forexample, a 50 second analysis would be four times quicker and have measurementprecision two times higher than the 200 second measurement.

10.2.0 Solvent Extraction

10.2.1 MIBK Extraction From Acidified Solution (Newmont Method)

Introduction

C Gold-bearing solutions are acidified with aqua regia prior to extraction into methylisobutyl ketone (MIBK) containing chelating agent (1% Aliquat 336). Thispreparation procedure assures dissolution of the gold contained in the solution andprovides a universal matrix for presentation to the AAS for measurement.1 Alkaline cyanide solutions prepared using this procedure may be grouped withacid-fixed chlorination solutions, bottle test wash solutions, as well as dissolveddore beads, for instrumental analysis from 16 x 125 mm test tubes using the flameautosampler.

Reagents

C Extractant: 1% Aliquat 336 (Trialki methyl ammonium chloride) in MIBK

C 1:1 Nitric acid: dilute concentrated nitric by 50%.

C Concentrated hydrochloric acid

Apparatus

C Pipets (Class A) sized as neededC Culture tubes sized as neededC Shaker tableC Centrifuge

Procedures

Page 37

C Acidification

Ten milliliter aliquots of each solution to be assayed, a solution of known valueand a deionized water blank are transferred by pipet into clean test tubes in anumbered rack. the rack is placed into a sonic water bath at eighty degreescentigrade. A half milliliter portion of 1:1 nitric acid and a three quarter milliliterportion of concentrated hydrochloric acid are added to each of the tubes. Afterheating for ten minutes, the rack is removed from the bath and the solutions arecoiled to room temperature.

C Extraction

Five milliliter portions of standards, in the range of one-tenth to five parts permillion gold in ten percent aqua regia matrix, are transferred by pipet into cleantest tubes in the rack and diluted with a five milliliter portion of deionized water. A five milliliter portion of MIBKcontaining one percent Aliquat 336 is dispensedinto each test tube. They are capped, shaken for two minutes, centrifuged for fiveminutes, and transferred from the centrifuge, in the order of measurement on theAAS, to the flame autosampler carousel.

Note1: Some labs would prefer to filter any undissolved gold solids prior toacidification. This is to insure that assay values reflect only dissolved gold whenmetullurgical balances are calculated.

C Measurement

The AAS instrument is optimized for gold with a lean flame in MIBK which iscontinuously burned during setup and measurement. Measurements are recorded inabsorbance with deuterium arc background correction. Assays are calculated basedon a linear regression of the known standard values, the concentration factor(2.00), and the conversion factor from parts per million to troy ounces per ton(0.02917).

Samples which require higher sensitivity (below 0.0005 Au oz./ton) may beassayed by graphite furnace MS and samples above the high standard (above 0.075Au oz./ton) may be assayed on another calibration or diluted. Extracts are stablefor at least one week.

10.2.2 DIBK/Aliquat 336 Extraction From Direct Solution (Freeport Method)

Principle

Page 38

C This procedure uses solvent extraction followed by atomic absorption (flameatomization) to determine gold liquor values below .300 ppm. Gold is extractedfrom alkaline solutions by 1% trialkl methyl ammonium chloride (aliquat 336) andextracted from acid solution by diisobutyl ketone (DIBK).

Discussion

C The standard 10:1 extraction is accurate to + .005 ppm with a detection limit of.001 ppm. A 50:1 extraction has been tested as accurate to + .001 ppm with a.0003 ppm detection limit. Concentration ratios up to 500:1 are possible, butaccuracy is limited by the need for a quality standard.

C Extractions maintain accuracy limits from acid to base solutions for the 10:1 ratio,but this has not been verified for other ratios. Liquors of pH less than 1 or gre~terthan 12.5 have not been tested.

C MIBK may be substituted for DIBK. MIBK is more volatile and water soluble,therefore environmental risks are slightly higher. DIBK-and MIBK-extractedstandards are not interchangeable. MIBK-based extractant may have a lowermaximum concentration ratio than DIBK due to its higher solubility.

C The accuracy limits of this method were originally tested on a Perkin-Elmer model5000 atomic absorption spectrometer with continuum (D2) background correction. They have also been verified on a Thermo Jarrell-Ash Video 22 atomic absorptionspectrometer in both continuum and Smith-Hiefje background correction modes. The detection limits are slightly poorer on Perkin-Elmer model 2380 withcontinuum correction (.003) due to a poorer signal to noise ratio. In general,accuracy, detection limits and absorbance values may alter with the model ofspectrometer.

Caution

C Salt concentrations less than 10 g/l as NaCl affect gold extraction. All samples andstandards should be adjusted above this level.

C Age can affect the quality of a DIBK/Aliquat 336 extractant solution. Theextractant solution should be made every two weeks or less.

C Gold extracted from acid solution is not always stable. Do not allow anacid-extracted sample to stand more than twenty-four hours. A gold precipitatedoes form at the interface between the extractant and aqueous liquors if DIBK orMIBK alone (no Aliquat 336) is the extractant.

Page 39

C Standards and extracted samples should not be left unsealed. Extractions fromalkaline solution are stable, but all extractions are subject to contamination andevaporative concentration. Although sealed alkaline extractions may be accuratefor several weeks, AA determination within five days is recommended.

C Dispose of all wastes in the tailings pond or as approved by the environmentaldepartment.

C Iron interference is a concern at some labs. Although iron will extract, alkalinesolutions of up to 1% Fe as potassium ferrocyanide have been tested onbackground-corrected atomic absorption instruments without showing any effect. (Fe appears to reach its saturation point in this extractant from gold solutions witha 1% Fe conc.). If modern quality instrumental correction is not available, HClback extraction (step 6, note C) may be employed for high Fe concentrations.

Reagents / Equipment

C Diisobutyl ketone (2, 6-dimethyl-4-heptanone)C Trialkl methyl ammonium chloride (aliquat 336, available from Aldrich chemical)C Sodium CyanideC Sodium HydroxideC Sodium ChlorideC AcetoneC 500 ppm primary Au standard with + 1 ppm certified valueC 100 ml volumetric flasks (as needed)C 50 ml volumetric cylinderC 2 jet pipet dispenser (5 ml + .003 ml)

Prepared Reagents

C Extractant (1% Aliquat 336 in DIBK):Weigh 20.Og Aliquat 336 into a 100 ml beaker. Dilute this with a smallquantity of DIBK and pour into a two liter volumetric flask. Rinse the beakerwith DIBK into the flask and bring to volume with DIBK.

C Matrix (.5 g/l NaCN, .1 M NaOH, 15 g/l NaCl):Dissolve 12.5g NaCN, 100 g NaOH, 375 g NaCl in 25 1 of deionized water.

C Stock gold standard (5.00 + .01 ppm) Calculate the weight of primary standard needed to make one liter of 5 ppm

gold standard based on its certified concentration (liquors are weighed forstock standards to improve accuracy).

Page 40

given: the primary standard is certified 495 ppm

g primary = (intended stock conc.) * (intended stock volume)(certified primary conc.)

g primary = 5 ppm * 1000 ml = 10.1 g 495 ppm

Weight accuracy beyond + .005 g doesn't improve standard quality unless abetter primary standard is available.

Use a transfer pipet to weigh the primary standard into a tared 1000 mlvolumetric flask.

Bring to volume with matrix solution and mix contents. This solution shouldbe sealed and protected from light over its six month lifetime.

C Working Gold Standards (ppm Au): Prepare fresh each day in pre-equilibratedflasks (flasks which have held identical solutions for the previous 24 hrs).

.100 + .0005 @ 200C: pipet (class A)5 ml of 5 ppm stock into a 250 ml volumetric cylinder.Bring the flask to volume with matrix solution

.300 + .001 @ 200C: pipet (class A)15 ml of 5 ppm stock into a 250 ml volumetric cylinder.Bring the flask to volume with matrix solution.

C Saturated salt solution: Dissolve 358 g of sodium chloride in one liter of hotdeionized water. Allow the solution to cool and pour the saturated solution into ajet pipet dispenser.

C Atomic Absorption Gold Standards

Extract the working standards by the same procedures and ratio used on samplessubmitted for analysis.

Accuracy will vary with the extraction ratio. Normal multiple 10:1 extractionshould match within .005 standardized ppm. The .100 ppm extraction will have anabsorbance of approximately .06 (D2) or .02 (Smith Hieftje) and the .300 ppmextraction will be within .005 absorbance units of three times the .100 standardabsorbance. If these conditions are not met, re-extract the standards.

Procedure (10:1 Extraction Ratio)

Page 41

1) Prepare the 100 ml volumetric flasks for extraction by dispensing 5 ml of saturatedsalt solution into each flask with the jet pipet. This prevents poor extraction andpoor separation.

Note: a) Check gold absorption and solvent interactions before substitutingplasticware.b) Alternate glassware may be substituted, but at least 50% open spacemust remain in the container at step 4 for extractions of consistent quality.

2) Measure 50 ml of sample with a volumetric cylinder into each flask for eachsample.

3) Squirt 5 ml of extractant solution into each flask using calibrated jet pipet ordispenser of equivalent accuracy (+ .003 ml).

4) Hand shake eight (or more if comfortable) extractions vigorously for 45 seconds.

Note: a) Shaking should be vigorous enough to create a foamy appearance.b) If a machine shake is used, 2-5 minutes is required, depending on thepattern and vigor of agitation.

5) Add water to each flask to raise extractant into the glass neck.

6) Allow to separate for at least 45 minutes.

Note: A) If the extractant is not given this time to clarify, the entrapped water canlower gold values during aspiration by as much as 6%.

B) If iron interference is a concern, Fe may be back extracted with two washesof 10% HCl. Increasing iron concentration is marked by a darker yellowextractant. A green (iron) precipitate will form from extractions of 1% ormore iron in alkaline solution. Interference is not a problem on equipmentwith quality background correction at 242.8 nanometers.

C) Settling time may be decreased to two minutes if the extraction isperformed in 100 ml centrifuge tubes and the tubes are centrifuged for twominutes.

7) Replace the burner assembly used for standard liquor determinations with theDIBK assembly. When separate assemblies are not used, standard liquordeterminations will be affected. If the DIBK assembly is not cleaned ultrasonicallyat least once per week, determination quality can deteriorate.

8) Set the fuel/air ratio as lean as possible. Maximize absorbance with one of thestandard extractions.

Page 42

9) Use raw extractant as a blank. .100 ppm and .300 ppm working extractions serveas standards.

Note: A) Samples with more than .300 ppm gold values must be extracted using lesssample. Gold values may be calculated as follows:

Calculated ppm = standardized value ppm * actual sample volumenormal sample volume

B) Burner slit deposits occur just before absorbance problems. Stop and cleanthe head ultrasonically when this appears.

C) On P-E 5000 w/D2 correction .100 ppm, abs. approximately .06 w/D2;w/Smith-Heifje correction on TJA Video 22, abs approximately .02.

Cleanup

10) Dump 100 ml flask contents into environmental department approved sinks(must drain into the tailings pond). Four or more flasks may be done at onetime.

11) Rinse with acetone until clear to remove DIBK.

12) Rinse flasks with HCl to clean off any scale.

13) Rinse flasks followed by three D.I. washes for the final cleaning.

14) Rinse with acetone to speed drying and then set the flasks on the drying rack.

10.2.3 Butyl Sulfide Extraction (North American Laboratories)

Reagents

C Conc. HClC Dibutyl sulfide extractant:

3,750 ml reagent-grade xylene with 100 g dibutyl sulfide

Procedure

Measure 50 ml of sample & acidify w/HCl. Add 5.0 ml of butyl sulfide-xylenemixture, cap, and shake in an Eberbach or similar machine for 3 minutes. Allow the

Page 43

phases to separate, and compare the gold absorbance from the organic solution againststandards extracted from HCl solution in a similar manner.

Atomic absorption conditions are those recommended by the manufacturer of theparticular instrument to be used. The wavelength is 242.8 nm, and backgroundcorrection is required.

1) If the sample contains organic material, it must be filtered prior to acidification.Organic material (i.e. carbon) may compete for gold during extraction.

2) Perform all steps in a ventilated hood. Butyl sulfide has a strong odor.

10.3.0 Reference Fire Assay Procedure (Freeport/Newmont Composite)

Introduction

Fire assay practice varies a great deal. This basic outline of one pattern is included tocomplete references to “fire assay as normal” in the collected methods. Depending onthe method, begin with fusion or cupellation. It is recommended that anyone learningthese methods obtain training and advice from an experienced fire assayer. While thismethod represents acceptable practice, it should not be regarded as universal practice.

Reagents

C Flux: Flux formulas are detailed in each individual method as needed. A respiratorshould be worn while handling soda ash, silica, borax and litharge (see leadcontrol).

C Inquarts: silver wire, foil or Herman inquarts as required.

C Parting solution (1:4, Gravimetric Finish): measure four liters water for each literof nitric acid.

C Parting solution (1:1, Instrument Finish): measure 1 liter nitric acid for each literwater.

C Aqua regia (Instrument Finish) measure 3 ml hydrochloric acid for each 1 ml nitricacid. Make fresh daily.

C Extractant (MIBK or DIBK w/5% Aliquat 336, Instrument Finish): weigh 50gAliquat 336 into a 250 ml beaker. Dilute this with a small quantity of MIBK orDIBK. Pour into a one liter volumetric flask. Rinse the beaker into the flask with

Page 44

the same organic solvent several times. Fill the flask to 1000 ml mark with thesame organic.

Equipment

C Furnace equipped to fuse at 1950EF and cupel at 1650EFC pour moldsC pouring tongsC heat-protective glovesC face shield (should stop U.V. and I.R. to avoid eye damage)C 30g cruciblesC cupels (MgO preferred for gold)C cupel forkC parting trays (stainless steel preferred)C parting china cups (sized to fit trays, hold about 10 ml)C hotplate

Lead Control

Lead is a toxic metal. TLV exposure level is .15 mg/m3. The general population haslevels of 10-12 mg per deciliter1. Freeport-McMoRan Gold withdraws techniciansfrom fire assay at levels as low as 20 mg/deciliter, but acceptable blood leadconcentrations vary between labs.

Note 1: Levels are higher in urban areas

1) Ventilation is recommended in any Fire Assay or flux exposure area.

2) A respirator should be worn while in any area with airborn lead concentrationsabove .15 mg/m3.

3) Wear disposable plastic gloves when handling lead in any form.

4) Wear lab coats or other protecting clothing which can be removed upon leavingthe exposure area (don't wear lead home).

5) Maintain a clean work area.

Procedure

Fusion:

1) Prepare liquor sample as the chosen method indicates. Flux charges and treatment

Page 45

are included in individual methods. Exact silver inquart values must be known ifsilver is also being assayed. Control assays of known grade are recommended. (Example: @ Freeport, #16 Fusion is always a blank or standard. #17 is always arefire of #20 from the previous fusion set).

2) Load charged crucibles in the furnace at 19500F. A standard order should be usedto maintain sample identity. Fuse for 45 minutes.

3) Pour fusion in standard order.

4) Allow the slag to cool 5-10 minutes. The lead "button' at the bottom of the moldcontains gold, silver and other precious metals. It should weigh about 25 g.

5) Break the slag and shape the lead button into a cube with a hammer. This shattersloose remaining slag.

Cupellation:

1) Set furnace at 16500F (raise as required for MgO cupels) Note: If assaying forsilver also, controls of known silver should be used to monitor silver volatilizationlosses.

2) Use a cupel fork and gloves to load the appropriate quantity of cupels (MgOcupels will give better and more consistent gold recovery. However silver assaytemperature control is more difficult with these cupels) Draft damper (if soequipped) should be closed.

3) Preheat for 10 minutes

4) Load lead buttons in a consistent order. They should melt, then develop an openglowing surface. Raise the furnace temperature if cupels fail to open. (removingoxygen by burning objects in the furnace by the cupels will also help)

Note: Higher temperatures increase silver volatilization losses. Cupellation is theprocess of 2 Pb+O2 ÷ 2PbO with the PbO draining into the cupel.

5) Once cupels are glowing ("driving"), the draft damper should be opened.

6) When glowing stops, leaving a round bead of silver and gold, remove the cupelsusing gloves and a cupel fork.

Inorganic Concentration Finish (Parting) Of Dore' Bead:

Page 46

1) Pound the "dore'" beads flat and, using a consistent order, place them in china cupsarranged on a metal parting tray. Weigh dore prior to parting if a silver assay isalso being performed.

2) Fill each china cup with 1:4 parting solution. Over strength acid at this step willleave gold in a finely divided ("floured") state and cause poor assays.

3) Place parting tray on the hotplate. As the tray slowly warms, the acid will attackthe silver in the beads with increasing vigor. When all effervescence stops, partingis complete (gold is not significantly attacked by the nitric).

4) Remove tray from the hotplate.

5) Decant the parting solution. A few drops of concentrated nitric may be used toensure thorough parting at this point.

6) Decant again and rinse china cups with a 2% ammonia solution followed bydistilled water. Incomplete rinsing will leave a dark stain in the China cup afterrinsing and cause incorrect assays.

7) Return the tray to the hotplate for thorough drying.

8) Place the tray of china cups in a 19500F furnace for 1 minute to anneal the goldbeads.

9) Cool to room temperature and weigh gold beads on a Micro balance to .001 mg.

10) Calculation: mg weight * 29.166 = Au ozt/st ml sample

Silver oz/t is calculated using the difference between dore weight (less inquart'ssilver weight) and parted weight.

Instrument Finish (Newmont Gold):

1) The bead is transferred with small tweezers from cupel to 16x126-mm (16-mlcapacity) glass culture tube.

2) .5 ml of 1/1 nitric acid is dispensed into the tube and heated for 10 min at 90EC3) .8 ml of fresh concentrated hydrochloric acid is added and heated at 90EC for 30

min.

4) 8.7 ml of deionized water is added.

Page 47

5) Depending upon the desired concentration factor, MIBK containing 5% Aliquat336 is carefully dispensed into the culture tube -- for most l00-ml chiddeys, 5.0 mlof MIBK is adequate (factor 20.0).

6) The extraction is tightly capped and agitated for 2 mm.

7) The extraction is centrifuged for 5 mm., then transported to instrument room foratomic absorption spectroscopy.

10.3.1 Procedure, Inorganic Concentration, Copper Sulfate (Pinson Method): Determinationof Gold and Silver in Gold Plant Solutions by Fire Assay

Scope

This method determines the gold and silver content in gold plant and heap leachsolutions by fire assay.

Equipment

C 500 ml conical beakersC 100 mm funnelsC 20.5 cm fast filter paperC assay furnaceC 30 gram cruciblesC cupelsC annealing cupsC bead balance

Standard Flux (blended in batches, used in 120 g charges.See standard flux survey for more information)

C PbO - 100 lbC Soda Ash - 100 lbC Silica - 4,4 lbC Borax - 10.6 lb

Reagents

1) Potassium ferrocyanide - dissolve 50 grams/liter of distilled water.

2) 10% copper sulfate - dissolve 100 grams copper sulfate/liter distilled water.

Page 48

3) 20% sodium sulfite - dissolve 20 grams/100 mls of distilled water. MAKE FRESHDAILY.

4) 10% sulfuric acid - add 100 mls of sulfuric acid to 500 mls of distilled water. Cool, make to one liter with distilled water.

5) Silver nitrate - dissolve 4.335 grams of silver nitrate in one liter of chloride-freedistilled water. Store in an amber bottle (labeled as made-not a standardizednormal solution).

6) Flocculent solution - disperse 2.0 grams of flocculent (Superfloc 16 or equivalent)in 10 mls of methanol, add to 900 mls of hot distilled water until dissolved.

Note: Flocculent type works with typical solutions. A lab changing this methodshould test available commercial flocculents on their solutions to eliminate anypossibility of introducing bias.

Procedure

1) Measure a 5 assay ton (over .01 ozt/st Au expected) or 10 assay ton sample (150or 300 mls) into a 500 ml conical beaker.

2) Add 1.0 ml of silver nitrate solution for inquart.

3) Add 1.0 ml of potassium ferrocyanide solution, stir briefly with a glass rod.

4) Add 40 ml of 10% copper sulfate solution, stir briefly with a glass rod.

5) Add 15 ml of 20% sodium sulfite, stir briefly with a glass rod.

6) Add 15 ml of 10% sulfuric acid, stir briefly with a glass rod.

7) Add several drops of flocculent solution and stir vigorously with a glass rod for afew seconds.

8) Allow precipitate to settle.

9) Filter precipitate through fast filter paper (VWR grade 615 or equivalent), washwith deionized water once.

10) Sprinkle small amount of assay flux on precipitate, transfer wet filterpaper/precipitate to a 30 gram crucible containing 1/3 of a normal flux charge.

Page 49

11) Cover with remaining flux, do not stir. Total charge 120 g of flux. Add 1/4 tsp(3/4 gram) flour to obtain 25 g lead.

12) Fire assay as normal (see 10.3.0 and references).

10.3.2 Procedures. Inorganic Concentration. Copper Sulfate (Freeport Method): GoldDetermination in Liquid by Fire Assay

Reagents

C NaCN SolidC Copper sulfate solution (15% hydrated salt by weight in deionized H20)C Sodium sulfite solution (10% anhydrous salt by weight in deionized H20)C Sulfuric acid (20% by volume diluted in deionized H20)C Borax glassC Lead (granular test lead) - scorification method onlyC Soda ashC LithargeC Flour or wood charcoal (flour preferred)

Note: Reagents mixed as a percent may vary plus or minus a percent without aproblem (as opposed to normal solutions which must be exact).

Procedure

1) Take 50 to 500 ml solution according to the probable amounts of gold and silverfor barren solution and tails.

2) Add 25 ml copper sulfate solution and stir.

3) Add 25 ml sodium sulfite solution and stir.

4) Add 25 ml dilute sulfuric acid and stir.

5) If sufficient cyanide is present, a fairly heavy white precipitate of cuprous cyanidewill form; otherwise, add 0.5 gram sodium cyanide dissolved in 50 ml and stir. Anexcess of cyanide is important to insure an accurate assay. The clear layer of thismixture should be blue. If not, add another 25 ml copper sulfate solution.

6) Filter through an 18 cm No. 40 Whatman filter paper. No washing is necessary. Fold filter paper (containing residue) in a 3-1/2 inch scorifier or in a fire assay

Page 50

crucible. Dry and char until all carbon is destroyed. Charring should not produce aflame since it will carry off gold. With improper precipitation, gold may be presentin the form of AuCl. This will volatilize with charring.

7) If you are using a scorifier, add 35 grams granular lead and 5 grams of borax.

8) Add 3 inquarts for tail solutions, 40 mg Ag for pregnant solutions, or add silveraccording to probable gold bead weight (Ag added = 3x expected wt of Au).Scorify at 1950EF.

9) If you are using DFC or A.P. Green fire clay crucible, add:C 35 8 lithargeC 30 g Soda ashC 10 g boraxC 1 g wood charcoal or 3/4 tsp. (about 2.5g) of flourC 3 pieces of herman inquart for barren and tailC 40 mg silver for pregnant solution

10) Fuse, cupel, and part in the usual manner. (See 10.3.0)

11) ppm Au = bead wt (mg) * 1000 ml sample

Note: Charge size and reagent balance can require some adjustment with differentbrands of fire clay crucibles.

Note: Charcoal has a tendency to “spark" during the fusion reaction. Flour gives amore controlled reduction.

Note: A concern was expressed about the inexact silver content of gold-free hermaninquarts. Parting practice (1:4 nitric slowly warmed from cold to near boilingduring parting) allows silver values between 2.5 and 4 times the expected goldcontent in dore beads without affecting gold assay quality. Of course, silvercontent must be exact if a silver assay is also being done by this method.

10.3.3 Procedures. Inorganic Concentration. Copper Sulfate (Golden Sunlight Method)

Equipment / Reagents

C AgNO3 solution - 4.71g AgNO3/liter distilled H20.

C Potassium ferrocyanide - saturated solution 55 ml-300m1 H20.

Page 51

C Precipitating solution - To a saturated solution of copper sulfate (75m1-400m1),slowly add a saturated solution of NaOH (5Om1-400m1) stirring constantly until alight precipitate is formed. Then carefully add a little more caustic solution untilthe color changes to a darker blue (still maintaining a heavy precipitate). To thismixture, slowly add a saturated solution of sodium cyanide (125-15Om1-400m1)stirring constantly until the blue formed with the NaOH solution is just dissolvedand a yellow tea color is formed.

C Standard Flux: (70 grams), 46 g litharge, 12 g soda ash, 1 g borax glass.

Procedure

1) Measure 10 AT of sample solution into 450 ml beaker.Note: For low grade solutions, measure 20 AT in a 1000 ml beaker and add 1.5

times the additions in steps #3, #4, and #5.

2) Add 2 ml of AgN03 solution.

3) Add 4 drops ferrocyanide solution and stir.

4) Add 15 ml. of precipitating solution and stir well.

5) Add, carefully, 20m1 of concentrated sulphuric acid and stir well.

6) Allow precipitate to settle for 10 minutes and then filter through S & S 595 15 cmfilter paper (or equivalent fast quantitative filter paper).

7) Wash three times with hot distilled water.

8) Transfer filter paper containing precipitate into 40 ml perforated bottom crucibles. Place crucibles in drying tray on a hot plate. Do not heat to burning temperatures.

9) Transfer dried paper with precipitate to a 20 g crucible.

10) Flux with a 70g charge of already-mixed flux plus 10 g silica - Do not stir. About 1.5 g flour may be blended into the surface. With the carbon containedin the filter paper, a minimum of 15 g of lead should form.

11) Fire assay according to accepted practice (see 10.3.0 and references). Slagshould be neutral or slightly acid (adjust flux if not).

10.3.4 Procedures. Inorganic Concentration: Chiddey

Page 52

Reagents

C Lead Acetate Soution - 200 grams Lead Acetate/liter distilled or deionized H20.

C Zinc Dust

C Concentrated HCl

Procedure

A spectroscopic finish is helpful when it is necessary to gain maximum measurementsensitivity on extremely low-grade solutions. Samples expected to measure above .010oz/ton (e.g., mill pregnant solutions) are adequately concentrated by the gravimetricfinish.

1) Assay by spectroscopic scan to determine appropriate sample volume and labeledlabware:Sample (Newmont Format example) Aliquot l-L BeakerUnder .010 oz/ton 300 ml BarrenUnder .010 oz/ton for AAS Finish 100 ml Barren.010 - .050 oz/ton 100 ml PregOver .050 oz/ton 100 ml High GradeLimited Sample Available 100 ml (by grade)Instrument Calibration Standard 100 ml (by grade)

2) Pipet sample aliquot and transfer into l-L beaker. Use l00-ml pipet for all samples.

Caution Note: Beaker must first be rinsed with concentrated HCl acid if it containszinc from previous Chiddeys. Low-grade and high-grade glassware must beclearly marked and used for appropriate samples.

3) Place on hotplate and warm (approximately 40EC) solution then add 60 ml of leadacetate solution. Heat to just below the boiling point (steaming). Solid leadacetate may be dissolved directly in the sample instead of preparing a lead acetatesolution for additions.

4) Add zinc dust until all lead is precipitated (approx. 5 gr). Complete precipitationcan be checked by adding a few drops of concentrated HCl. If a white precipitate(PbCl2) forms, the lead is not completely precipitated.

5) Add concentrated HCl in excess to dissolve excess zinc (80 ml). Lower heat. (Note: some labs add HCl before adding zinc dust) step 4).

Page 53

Caution Note: If undissolved zinc is retained and HCl is not added in excess ofzinc dissolution, low gold values will occur. Boiling temperatures will break upthe lead sponge. This may result in low gold values due to lost lead particles.

6) When all action ceases, warm 5-15 minutes below boiling temperature (40-60EC).

7) Decant and wash lead sponge 3-4 times with deionized or distilled H2O. Press thewater from the lead sponge by hand (fingers) until dry. CAUTION: Any "lost" leadrepresents a potential gold loss.

8) Wrap the dried lead sponge in 15g of lead foil. Put 2 herman Inquarts in withsponge. A hole should be punched in the lead foil so that any retained moisturemay escape as steam.

9) Cupel and continue as in a standard fire assay (10.3.0, start with cupellation).

Note: A concern was expressed for the exact silver content of herman inquarts. Herman inquarts are convenient. Parting practice (1:4 nitric warmed tonear boiling during parting) allows silver between 2.5 and 4 times the goldcontent in the dore' without errors in gold analysis. Of course, silveraddition must be known precisely if a silver determination is also beingdone.

Note: (Historical) The chiddey method is named for Alfred Chiddey, whodescribed the original version of this method (Bugbee, 1940, pg. 241).

10.3.5 Procedures. Inorganic Concentration: Lead - Acid

Reagents

C Granulated lead: + 10 mesh - (screened test lead may be used)C Concentrated HClC Lead Foil (7.5 cm x 7.5 cm)C Ag for inquartation (AgNO3, solid inquart, etc.)

Procedure

1) Measure an appropriate aliquat of sample (typically 300 ml or 150 ml) of cyanidesolution into a 600 ml beaker.

2) Add 1 ml AgN03 solution (6g/l) and mix well.

Page 54

3) Heat to just below boiling point. Add about 1/2 tsp (9 to 16 g) granulated lead.

4) Add 10 ml concentrated HC1 (CAUTION), cover with watch glass, and boilstrongly for 10 to 15 minutes.

5) Cool solution, and carefully decant so as not to lose any lead.

6) Wash lead twice with deionized water by decantation and dry on a hotplate.

7) When dry, transfer the lead into a piece of prefolded lead foil. Wrap carefully, andcupel. Part dore , anneal, and weigh gold bead.

Calculation

Au in solution (oz/ton) = Bead weight (mg) * 29.166/sample volume (ml)

C Notes (Battle Mountain Gold)Method has been compared to several others we have used, in particular theCopper Sulfate Collection method. With most solutions, assay results showedno significant bias. With foul solutions, the amount of HC1 added may have tobe increased and reaction times may have to be increased as well. This alsoholds for high Au concentrations, though we have not made any detailedstudies regarding this cutoff concentration.

C Note (Freeport)A minor amount of gold remained in waste solutions checked by AAS/DIBKmethods. This did not affect the determination accuracy within precisionlimits. The method is ideal as a quick check for potential interference in higher(above .3 ppm) grade solutions.

10.3.6 Procedures. Inorganic Concentration. Direct Assay: Fusion of High-grade Solutionsfor Gravimetric Assay

Scope

When a gravimetric assay is required on alkaline cyanide solutions containing highconcentrations of gold (e.g., refinery process samples), the chiddey assay is oftenrendered inappropriate by chemicals present in the solution; these solutions, however,may be fused by the following procedures and finished by gravimetric means.

Procedure

Page 55

1) 80 g standard (see topical survey on standard fluxes) fusion flux is placed into aused 40-g crucible (Caution: the glass lining in a used crucible is necessary toprevent sample from soaking into the porous ceramic.)

2) 15 ml of sample is transferred by class-A pipet into an indentation made by spatulain the center of the flux charge and covered with surrounding flux.

3) The sample is allowed to dry for 10 minutes, then microwave-dried for 2 minutes.

4) The sample is fired at 2000 degrees F for 45-60 minutes.

5) The fusion is poured and de-slagged, then cupeled.

6) The dore is weighed, and silver weighing approximately four times the dore weight is wrapped in lead foil with the dore.

7) The dore and inquarts are cupeled.

8) The bead is hammered flat and placed into a china cup to which nitric acid 1:4parting solution is added.

9) The solution is heated on a hot plate until parting ceases; the solution is decantedand replaced, and several drops of pure nitric acid are added to ensure thoroughparting.

10) The solution is decanted and the china cup is rinsed with ammonia solution,finally with distilled water.

11) The cup is thoroughly dried on the hot plate, then inserted into the furnace for1 mm to anneal the gold bead.

12) After cooling to room temperature, the gold bead is weighed on amicro-balance (See Gravimetric Assay composite procedure for details onreagents, equipment).

13) Calculation: mg weight * 1.944 = Au Troy oz/ton.

11.0.0 General Calculations

Dilutions

Page 56

1st Dilution 2nd Dilution Each Additional Dilution

Total Dilution Volume x Total Dilution Volume x Total Dilution VolumeAliquot Volume or Aliquot volume Aliquot volumeSample Weight

Dilution Factor x Diluted Sample Analysis = Original Sample Concentration

Conversions

ppm Concentration * .029167 = oz/t concentration

oz/t Concentration * 34.285 = ppm concentration

ppm = mg/l = ug/ml

for solutions with a specific gravity of 1 (same as water):1 g of solution = 1 ml of solution

12.0.0 Precision and Bias

These methods are a result of a survey of mining practice. The precision reported isbased on the rough estimates of participating labs. Interested parties should refer tocontributing labs for details. The bias (absolute accuracy) has not been quantitativelyverified. Most labs do indicate that bias is within precision limits as checked byCanadian, American, and commercial standards.

Gold Precision Gold Detection Limit

Direct Spectroscopic Methods

Page 57

Atomic absorption with flameatomization

0.xxx bracketed range ±0.002 oz/t (±0.07 ppm) 0.001 oz/t (0.03 ppm)

x.xx bracketed range ±0.01 oz/t (±0.3 ppm) 0.01 oz/t (0.1 ppm)

With Graphite Furnace Atomization(w/o buffer)

±0.00020 oz/t (±0.005ppm)

0.00003 oz/t (0.001 ppm)

Atomic Emission (DCP) Not Available 0.00003 to 0.0002 oz/t (0.001 to 0.005 ppm)

Atomic Emission (ICP) Not Available 0.0006 to 0.0000 oz/t (0.02 to 0.03 ppm)

Atomic Fluorescence (X-Ray) w/500ml preconcentration

±0.0006 oz/t (±0.02 ppm) 0.002 oz/t (0.06 ppm)

Organic ConcentrationMethods (Extraction)MIBK from acidified solution

Direct from sample

1:1 concentration ratio ±0.002 oz/t (±0.07 ppm) 0.001 oz/t (0.03 ppm)

3:1 concentration ratio ±0.001 oz/t (±0.04 ppm) 0.0005 oz/t (0.02 ppm)

4:1 concentration ratio ±0.001 oz/t (±0.04 ppm) 0.0003 oz/t (0.01 ppm)

w/100 ml Chiddy

20:1 concentration ratio ±0.0005 oz/t (±0.02 ppm) 0.0001 oz/t (0.003 ppm)

w/300 ml Chiddy

60:1 concentration ratio ±0.0002 oz/t (±0.007 ppm) 0.0001 oz/t (0.003 ppm)

DIBK/Aliquat 336 direct

10:1 concentration ±0.0001 oz/t (±0.005 ppm) 0.00003 oz/t (0.001 ppm)

50:1 concentration ±3x10-5 oz/t (±0.001 ppm) 1x10-5 oz/t (0.0004 ppm)

Dibutyl Sulfide from AcidifiedSolution

Not Available Not Available

Page 58

Inorganic ConcentrationMethods (Fire Assay)Copper Sulfate

Pinson Not Available Not Available

Freeport ±0.001 oz/t (±0.03 ppm) 0.0002 oz/t (0.005 ppm)

Golden Sunlight Not Available Not Available

Chiddy

300 ml sample ±0.0003 oz/t (±0.01 ppm) 0.0001 oz/t (0.003 ppm)

100 ml sample ±0.001 oz/t (±0.03 ppm) 0.0003 oz/t (0.01 ppm)

Lead Acid

100 ml sample ±0.002 oz/t (±0.07 ppm) 0.0003 oz/t (0.01 ppm)

Direct Assay Not Available Not Available

13.0.0 Waste Disposal

All commercial and non-mine laboratories are required to meet EPA hazardous wastedisposal regulations. Small and medium size labs (up to 2,200 lb/month hazardous wasteor about five drums of waste with the density of water) are regulated as Small QuantityGenerators (SQGs) under the Resource Conservation and Recovery Act (RCRA).1 Mining lab waste is exempt from hazardous waste designation by the Bevill Amendment toRCRA, but details should be confirmed with state and local EPA Jurisdictions. Forexample, the Nevada Department of Environmental Protection (NDEP) regulates certainmining and lab wastes and requires disposal in zero discharge tailings impoundments inconformance with the exemptions noted in Chapter 450.465 of the Nevada RevisedStatutes (NRS) and the ensuing codes and policies.

Hazardous wastes are generated in these gold analysis methods and are disposed asfollows:

Heavy Metalslead, silver, copper, selenium, etc.: Contact Jack Scott of Encycle, Inc. (An ASARCOsubsidiary) at 801-262-2459. They may accept cupels and other metal waste forrecycling. If this is not practical, locate an EPA-approved hazardous waste facility. InNevada, call NDEP Solid Waste Division and Sierra Chemical Company in Reno.

Organic SolventsMIBK, DIBK, Xylene, Acetone, etc.: Gibraltar Chemical Resources (subsidiary ofGilbraltor & Mobley Industries) in Kilgore, Texas (214) 983-2377 will recyclesolvents. If recycling is not practical, use an EPA-approved hazardous waste dump,approved incinerator, or a zero discharge tailings pond. Ensure when placing wastes

Page 59

in the tailings impoundment that it meets with federal, state and local approval.

Sodium CyanideMaintain cyanide solution pH above 10.5 prior to disposal. Destroy cyanide in awell-ventilated hood with a strong oxidizer, i.e., chlorine or peroxide solution, prior todisposal in sewer drains. Care is required due to toxic gas produced in this process. Excess alkalinity must be neutralized before offsite disposal.

Acid/Base ReagentsAlkaline or acid reagents must be neutralized before offsite disposal.

Non Specific WasteAny waste-water can potentially be classified as hazardous. Consult the code ofFederal Regulations, 40 CFR 261.

This list should not be regarded as complete and other wastes or treatments may besignificant depending on local jurisdiction.

Don't avoid the waste disposal problem by storing waste. It may be illegal and couldmove a company into a more difficult category. Choose a waste management firm withcare. Unless the waste is recycled, the original waste generator can retain permanentliability for any problems.

This waste disposal section suggests the general nature of the waste problem. Detailedassistance is available from a number of sources. The EPA has published an excellentplain English handbook to assist the small business (EPA/53O-SW-86-019, Sept. 1986). The Illinois Hazardous Waste Research and Information Center (HWRIC) published amore detailed manual which includes tips on how to choose waste management firms andtips for staying out of trouble (Kraybill, January 1987). Although, these documents aredifficult to obtain due to heavy demand, local regulatory officials may have copies. Inaddition, Ocal EPA jurisdictions will answer any general questions on compliancerequirements.

Note 1: SQG regulations became effective Sept. 22, 1986 and March 24, 1987

14.0.0 Contributing Organizations

Methods listed under a company and underlined were the primary model for acomposite or were included in entirety.

Contributing companies and the types of methods they submitted are as follows (inalphabetic order) with Chief Chemists or contacts in parenthesis):

Page 60

Asamera Minerals (Dave Potter) (509) 663-73131) Inorganic Concentration (Fire Assay) - Lead Acid2) Direct Atomic Absorption - Flame

Asarco Corp. (Steve McCann) (406) 227-71001) Commentary

ASOMA Instrument~, Inc. (John Schindler) - 512-258-66081) Inorganic preconcentration (XRF)

Battle Mountain Gold (Paul Corona) (702) 635-24651) Inorganic Concentration (Fire Assay) - Lead Acid2) Direct Atomic Absorption - Flame

Dee Gold (Lee Koch) (702) 738-64401) Direct Atomic Absorption - Flame

FMC - Paradise Peak (Luis Acre) (702) 285-00601) Inorganic Concentration (Fire Assay) - Chiddy2) Direct Atomic Absorption - Flame

Freeport McMoRan Gold (Jim Anderson) (702) 738-9221,contribution compiled by T. Gilbert

1) Inorganic Concentration (Fire Assay) - Lead Acid, Chiddy, and Copper SulfatePrecip. Methods (indicated low usage)2) Direct Atomic Absorption - Flame, Furnace (no longer used)3) Extraction - DIBK/Aliquat 336, Dibutyl Sulfide/Xylene (not in use)4) Reference Fire Assay Method5) Waste Disposal

FRM Corp. (Dave Maddox) (702) 635-50011) Direct Atomic Absorption - Flame

Golden Sunlight Mine (John Stratton) (406) 287-32571) Gravimetric (Fire Assay) - Chiddy, Copper Sulfate2) Direct Atomic Absorption - Flame

Cold Fields Mining (Bob Gerteis) (303) 277-13781) Direct Atomic Absorption - Flame

Homestake Mining (Wilson Tsu) (916) 446-10701) Direct Atomic Emission - DCP (Direct Coupled Plasma)

Page 61

Jumbo Mining Company (E.B. King)1) Atomic Fluorescence (X-Ray)

Newmont Gold (Gerry Scott) -- Contribution compiled by Jim Force (702) 738-71961) Direct Atomic Absorption - Flame2) Inorganic Concentration (Fire Assay) - Chiddy, Direct Fire3) Extraction - MIBK from Acidified Solution4) Hazards & Precautions (section 8.0)5) Fire Assay, Reference Method6) Fire Assay, Instrument Finish

Pinson Mining (Jack Simmons) (702) 623-50361) Inorganic Concentration (Fire Assay) - Copper Sulfate

Skyline Labs (Edwin V. Post) (303) 424-77181) Final proof review (tech. spelling, punctuation, etc.)

Spectroscopy (B. Jane Ellis, Associate Ed.)1) Permission to use BC correction table

Thermo Jarrell Ash Corporation (Jack Robert) (415) 327-56091) Comments on instrumental methods2) General AAS Interference (section 6.1)

U.S Bureau of Mines (Reno Office - Gene Elliot) (702) 784-53911) Direct Atomic Absorption

University of Lowell, Mass., (Joseph Sneddon) (617) 452-5000 ext. 25521) Permission and review of the comparative table for instrumental backgroundcorrection.

Vegas Analytical Laboratory (B.M. Joshi) (702) 365-12011) ICP Emission

15.0.0 Disclaimer of Liability

Neither the Editor, Society of Mineral Analysts nor the contributing organizationsassume any liability for the 'use and application of the methods, procedures or otherinformation contained in this document. The contents of this document should not beused without prior critical evaluation.

The mention of any particular brandname, trademark, commercial service, or brand

Page 62

name product herein does not imply any form of endorsement by the Society ofMineral Analysts.