Comparator neutron activation analysis of the solid volumetric rock samples for gold content
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2022-06-30 |
| Journal | International Journal of Biology and Chemistry |
| Authors | I.Yu. Silachyov, V.A. Glagolev |
| Citations | 6 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis analysis details the application of Comparator Instrumental Neutron Activation Analysis (INAA) combined with an internal standard method for non-destructive, bulk gold determination in solid rock samples.
- Core Value Proposition: The method uses large, solid volumetric samples (15-20 g) cut directly from drill cores, eliminating the need for grinding, chemical digestion, or separation, thereby mitigating the ânugget effectâ and sample contamination.
- Internal Standardization: Iron (Fe) is used as the internal comparator, with its mass fraction determined independently via Energy Dispersive X-ray Fluorescence (XRF) using the RLP-21T spectrometer.
- High Sensitivity: The approach achieved extremely low Limits of Detection (LODs) for gold, reaching less than 0.001 ”g g-1 (ppb level) in homogeneous ultramafic rocks (serpentinites).
- Correction Minimization: The internal standard approach successfully minimized corrections for neutron self-shielding (Geff) and gamma-ray self-absorption (F), keeping them below 1% and 5%, respectively, and proving them largely constant across various rock types.
- Applicability: The technique is deemed reliable and expedite for analyzing sufficiently homogeneous magmatic and metamorphic rocks (e.g., picrites, diabase-picrites).
- Methodological Limitation: The reliability hinges on the accurate determination of the internal standard (Fe). For highly heterogeneous sedimentary rocks (like black shales), the shallow penetration depth of Fe characteristic X-rays (<0.2 mm) during XRF leads to high variability, necessitating multiple measurements or alternative internal standards.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Sample Mass Range | 15 - 20 | g | Solid volumetric pucks |
| Sample Diameter | 28.5 - 29.0 | mm | Drill core slices |
| Sample Thickness | 9.5 - 10.0 | mm | Drill core slices |
| Thermal Neutron Flux Density | 8.9 x 1013 | cm-2 s-1 | WWR-K Reactor (Irradiation) |
| Fast Neutron Flux Density | 6.0 x 1012 | cm-2 s-1 | WWR-K Reactor (Irradiation) |
| Irradiation Time | 1 | min | Per package |
| Decay Time (Minimum) | 9 - 10 | days | Required for 24Na decay |
| Au Analytical Gamma Line Energy | 411.80 | keV | 198Au radionuclide |
| Gold LOD (Serpentinite) | < 0.001 | ”g g-1 | Lowest achieved value |
| Neutron Self-Shielding Correction (Geff) | < 1 | % | Deviation from unity for common rocks |
| Gamma-Ray Self-Absorption Correction (F) | < 5 | % | Deviation from unity for common rocks |
| Fe Characteristic X-ray Penetration Depth (Black Shales) | ~0.15 | mm | Fe K-alpha line (6.4 keV) |
| XRF Spectrometer Used | RLP-21T | N/A | Energy Dispersive XRF (Kazakhstan) |
| Gamma Detector Used | GX5019 | N/A | Extended-range HPGe (50% relative efficiency) |
Key Methodologies
Section titled âKey Methodologiesâ- Sample Preparation: Drill cores (28.5-29.0 mm diameter) were sliced using a diamond saw to create planar cylindrical pucks (9.5-10.0 mm thickness). No further physical or chemical pretreatment was applied.
- Internal Standard Measurement (XRF): The mass fraction of the internal standard, Iron (Fe), was determined non-destructively on the flat surfaces of the puck samples using the RLP-21T XRF spectrometer. For heterogeneous samples (black shales), Fe content was measured multiple times (eight total: four per side, rotated 90°).
- INAA Irradiation Setup: Samples were sealed in polyethylene, wrapped in aluminum foil, and stacked upright in the irradiation container, oriented parallel to the radial neutron flux gradient.
- Neutron Activation: Samples were irradiated for 1 minute in the WWR-K light-water research reactor at a thermal neutron flux density of 8.9 x 1013 cm-2 s-1.
- Gamma Spectrometry: After a minimum 9-day decay period (allowing 24Na to decay), samples were counted using an HPGe detector (GX5019) for approximately 40 minutes to measure the 411.80 keV gamma line of 198Au.
- Data Processing: Gold content was calculated using the comparator INAA equation, incorporating the XRF-derived Fe content as the internal standard to automatically compensate for neutron flux gradients and minor self-shielding/self-absorption effects.
Commercial Applications
Section titled âCommercial ApplicationsâThe developed methodology offers significant advantages for industries requiring high-accuracy, bulk analysis of precious metals, particularly in geological and metallurgical contexts:
- Geochemical Exploration: Provides a highly sensitive (<1 ppb LOD) and reliable method for determining gold content in large, representative rock samples, crucial for identifying new ore occurrences in early-stage surveys.
- Mining and Ore Reserve Estimation: The use of large (15-20 g) solid samples directly addresses the challenge of gold heterogeneity (ânugget effectâ) in drill cores, leading to more accurate bulk grade estimation than methods relying on small, powdered subsamples.
- Metallurgical Feedstock Analysis: Expedite, non-destructive analysis of Au content in homogeneous magmatic and metamorphic rocks (e.g., picrites, serpentinites) used as mineral resources, ensuring rapid quality control without complex sample preparation.
- Certified Reference Material (CRM) Verification: Suitable for verifying and certifying gold content in CRMs derived from homogeneous flotation concentrates or metallurgical products, ensuring high accuracy and minimizing sample waste compared to traditional fire assay methods.
- Non-Destructive Sample Preservation: Ideal for analyzing unique or valuable geological specimens where physical alteration (grinding, dissolution) must be avoided.
View Original Abstract
The application of comparator instrumental neutron activation analysis (INAA) combined with the internal standard method was considered to analyze solid volumetric samples of different rocks, 15-20 g of the mass, for Au content. Fe was used as the internal comparator with its mass fraction determined by X-ray fluorescence method (XRF) with the help of a laboratory energy dispersive XRF spectrometer RLP-21T, Kazakhstan. The puck-like samples about 29 mm across diameter and about 10 mm of the thickness were sliced up from rock drill-cores with a diamond saw. No other pretreatment was applied. Sample dimensions were fitted in compliance with that of the XRF spectrometer dishes to substitute them during analysis, i.e. they were the highest possible allowed by the spectrometer. Relative corrections for neutron self-shielding and for gamma-ray self-absorption by the samples of the same dimensions corresponding by their macrocomponent composition to the different types of common rocks turned out rather small, simply accounted using the internal standard, and almost irrespective of the rock types. By the example of serpentinite, picrite and diabase-picrite samples (Western Ulytau Belt, Central Kazakhstan) the whole approach was found as rather expedite and reliable being applied to determine Au content of sufficiently homogeneous magmatic and metamorphic rocks. More efforts resulting in Fe multiple measurements due to its heterogeneous distribution are necessary to analyze industrially significant Au contents in sedimentary rocks like black shales (Bakyrchik, Eastern Kazakhstan).