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APPLICATION NOTE

Gold by Aqua Regia (large sample size)

SUMMARY

This application note summarizes the digestion of gold by aqua regia in various certified reference materials using ColdBlock Digestion Technology.
Instrument:

ColdBlock CBL, chiller, ICP-MS

Published:

May 2024

Digestion Time:15 Minutes
Acid Used:Aqua Regia
Average ColdBlock Recovery vs. CRM:

  • 101% Gold

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METHODOLOGY

  1. Chiller temperature was set to -5°C
  2. 30g of each sample were weighed and placed into ColdBlock™Digestion vessels (15g for high sulphide samples)
  3. 120 mL of Aqua Regia (AR) or reverse Aqua Regia (rAR) was added (reverse Aqua Regia was used for high sulphide samples)
  4. Samples were digested at 100% power for 15 minutes
  5. Samples were cooled and bulked to 200 mL using 15% HCl v/v

DISCUSSION

  • For samples with a Sulphide content >10%, it is recommended to drop the sample size to 15g and invert the ratios of Aqua Regia (3:1 – HNO3:HCl), add HNO3 slowly and allow the samples to react before adding HCl (reaction can be vigorous and deep brown/red fumes will be generated (see table 1 for summary of sample types and methods used)

Results

Table 1 – Summary of sample types

CRM ID

TYPE

Sample Weight

Method

OREAS 991

Copper-Gold Concentrate

15

rAR

OREAS 990

Copper-Gold Concentrate

15

rAR

OREAS 602

High Sulphidation Epithermal Ag-Cu-Au Ore

30

AR

OREAS 251

Gold Oxide Ore

30

AR

OREAS 504b

Porphyry Copper-Gold-Molybdenum

30

AR

OREAS 992

Copper Sulphide

15

rAR

OREAS 604

High Sulphidation Epithermal Ag-Cu-Au Ore

30

AR

OREAS 605

High Sulphidation Epithermal Ag-Cu-Au Ore

30

AR

OREAS 501C

Porphyry Copper-Cold Molybdenum

30

AR

OREAS 520

Iron Oxide Copper-Gold Ore

30

AR

OREAS 221

Gold Ore (Andy Well Gold Mine, Western Australia)

30

AR

OREAS 601

High Sulphidation Epithermal Ag-Cu-Au Ore

30

AR

OREAS 905

Copper-Gold Oxide Ore

30

AR

OREAS 620

VHMS Zn-Pb-Cu-Ag-Au Ore

30

AR

OREAS 991 – Copper-Gold Concentrate

Method:

15g

Slowly add 90mL HNO3 (5mL at a time) once sample has finished reacting, add 30mL HCl and digest at 100% for 15 minutes. Let cool, and bulk to 200mL with 15% v/v HCl

Element

Certified Fire Assay (ppm)

95% Confidence Limits

Sample A

Sample B

Sample C

Average (ppm)

Stdev

% RSD

% Recovery

Low

High

Au

47.04

46.70

47.37

44.27

45.73

46.8

45.60

1.04

2.3%

97%

OREAS 990 – Copper-Gold Concentrate

Method:

15g

Slowly add 90mL HNO3 (5mL at a time) once sample has finished reacting, add 30mL HCl and digest at 100% for 15 minutes. Let cool, and bulk to 200mL with 15% v/v HCl

Element

Certified Fire Assay (ppm)

95% Confidence Limits

Sample A

Sample B

Sample C

Average (ppm)

Stdev

% RSD

% Recovery

Low

High

Au

76.11

75.65

76.57

79.07

82.49

81.47

81.01

0.59

1.2%

108%

OREAS 602 – High Sulphidation Epithermal Ag-Cu-Au Ore

Method:

30g

Slowly add 90mL HCl, and 30mL HNO3 and digest at 100% for 15 minutes.

Let cool, and bulk to 200mL with 15% v/v HCl

Element

Certified Fire Assay (ppm)

95% Confidence Limits

Sample A

Sample B

Sample C

Average (ppm)

Stdev

% RSD

% Recovery

Low

High

Au

1.95

1.93

1.98

1.92

1.97

1.96

1.95

1.43

1.8%

106%

OREAS 251 – Gold Oxide Ore

Method:

30g

Slowly add 90mL HCl, and 30mL HNO3 and digest at 100% for 15 minutes.

Let cool, and bulk to 200mL with 15% v/v HCl

Element

Certified Fire Assay (ppm)

95% Confidence Limits

Sample A

Sample B

Sample C

Average (ppm)

Stdev

% RSD

% Recovery

Low

High

Au

0.504

0.498

0.510

0.522

0.542

0.504

0.523

0.02

1.1%

100%

OREAS 504b – Porphyry Copper-Gold-Molybdenum

Method:

30g

Slowly add 90mL HCl, and 30mL HNO3 and digest at 100% for 15 minutes.

Let cool, and bulk to 200mL with 15% v/v HCl

Element

Certified Fire Assay (ppm)

95% Confidence Limits

Sample A

Sample B

Sample C

Average (ppm)

Stdev

% RSD

% Recovery

Low

High

Au

1.61

1.59

1.62

1.59

1.56

1.55

1.57

0.02

1.1%

97%

OREAS 992 – Copper Sulphide

Method:

15g

Slowly add 90mL HNO3 (5mL at a time) once sample has finished reacting, add 30mL HCl and digest at 100% for 15 minutes. Let cool, and bulk to 200mL with 15% v/v HCl

Element

Indicative Fire Assay (ppm)

95% Confidence Limits

Sample A

Sample B

Sample C

Average (ppm)

Stdev

% RSD

% Recovery

Low

High

Au

7.92

N/A

N/A

7.91

7.46

7.79

7.72

0.19

2.5%

97%

OREAS 992 – Copper Sulphide

Method:

15g

Slowly add 90mL HNO3 (5mL at a time) once sample has finished reacting, add 30mL HCl and digest at 100% for 15 minutes. Let cool, and bulk to 200mL with 15% v/v HCl

Element

Indicative Fire Assay (ppm)

95% Confidence Limits

Sample A

Sample B

Sample C

Average (ppm)

Stdev

% RSD

% Recovery

Low

High

Au

7.92

N/A

N/A

7.91

7.46

7.79

7.72

0.19

2.5%

97%

OREAS 604 – High Sulphidation Epithermal Ag-Cu-Au Ore

Method:

30g

Slowly add 90mL HNO3 (5mL at a time) once sample has finished reacting, add 30mL HCl and digest at 100% for 15 minutes. Let cool, and bulk to 200mL with 15% v/v HCl

Element

Certified Fire Assay (ppm)

95% Confidence Limits

Sample A

Sample B

Sample C

Average (ppm)

Stdev

% RSD

% Recovery

Low

High

Au

1.43

1.41

1.45

1.41

1.48

1.47

1.45

0.03

2.1%

102%

OREAS 605 – High Sulphidation Epithermal Ag-Cu-Au Ore

Method:

15g

Slowly add 90mL HNO3 (5mL at a time) once sample has finished reacting, add 30mL HCl and digest at 100% for 15 minutes. Let cool, and bulk to 200mL with 15% v/v HCl

Element

Certified Fire Assay (ppm)

95% Confidence Limits

Sample A

Sample B

Sample C

Average (ppm)

Stdev

% RSD

% Recovery

Low

High

Au

1.67

1.63

1.70

1.65

1.69

1.68

1.67

0.02

1.0%

100%

OREAS 501c – Porphyry Copper-Cold Molybdenum

Method:

30g

Slowly add 90mL HNO3 (5mL at a time) once sample has finished reacting, add 30mL HCl and digest at 100% for 15 minutes. Let cool, and bulk to 200mL with 15% v/v HCl

Element

Certified Fire Assay (ppm)

95% Confidence Limits

Sample A

Sample B

Sample C

Average (ppm)

Stdev

% RSD

% Recovery

Low

High

Au

0.221

0.219

0.224

0.22

0.233

0.22

0.224

0.01

2.7%

102%

OREAS 520 – Iron Oxide Copper-Gold Ore

Method:

30g

Slowly add 90mL HNO3 (5mL at a time) once sample has finished reacting, add 30mL HCl and digest at 100% for 15 minutes. Let cool, and bulk to 200mL with 15% v/v HCl

Element

Certified Fire Assay (ppm)

95% Confidence Limits

Sample A

Sample B

Sample C

Average (ppm)

Stdev

% RSD

% Recovery

Low

High

Au

0.176

0.174

0.178

0.167

0.166

0.166

0.166

0.0003

0.2%

94%

OREAS 221 – Gold Ore (Andy Well Gold Mine, Western Australia)

Method:

30g

Slowly add 90mL HNO3 (5mL at a time) once sample has finished reacting, add 30mL HCl and digest at 100% for 15 minutes. Let cool, and bulk to 200mL with 15% v/v HCl

Element

Certified Fire Assay (ppm)

95% Confidence Limits

Sample A

Sample B

Sample C

Average (ppm)

Stdev

% RSD

% Recovery

Low

High

Au

1.06

1.05

1.07

1.04

1.05

1.07

1.05

0.01

1.2%

99%

OREAS 601 – High Sulphidation Epithermal Ag-Cu-Au Ore

Method:

30g

Slowly add 90mL HNO3 (5mL at a time) once sample has finished reacting, add 30mL HCl and digest at 100% for 15 minutes. Let cool, and bulk to 200mL with 15% v/v HCl

Element

Certified Fire Assay (ppm)

95% Confidence Limits

Sample A

Sample B

Sample C

Average (ppm)

Stdev

% RSD

% Recovery

Low

High

Au

0.780

0.769

0.791

0.793

0.787

0.813

0.798

0.01

1.4%

102%

OREAS 905 – Copper-Gold Oxide Ore

Method:

30g

Slowly add 90mL HNO3 (5mL at a time) once sample has finished reacting, add 30mL HCl and digest at 100% for 15 minutes. Let cool, and bulk to 200mL with 15% v/v HCl

Element

Certified Fire Assay (ppm)

95% Confidence Limits

Sample A

Sample B

Sample C

Average (ppm)

Stdev

% RSD

% Recovery

Low

High

Au

0.391

0.388

0.394

0.407

0.393

0.4

0.40

0.01

1.4%

102%

OREAS 620 – VHMS Zn-Pb-Cu-Ag-Au Ore

Method:

30g

Slowly add 90mL HNO3 (5mL at a time) once sample has finished reacting, add 30mL HCl and digest at 100% for 15 minutes. Let cool, and bulk to 200mL with 15% v/v HCl

Element

Certified Fire Assay (ppm)

95% Confidence Limits

Sample A

Sample B

Sample C

Average (ppm)

Stdev

% RSD

% Recovery

Low

High

Au

0.685

0.676

0.693

0.687

0.7

0.693

0.693

0.01

0.8%

101%

Click here to download the Application Note in PDF format.

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