Coarse-Gold Ore
Address material in which coarse particulate gold can cause strong variation between small aliquots.
Specialized Gold Testing Method
Metallic-Screen Fire Assay
Gold Determination for Coarse & Heterogeneous Gold-Bearing Material
Metallic-screen, or screen, Fire Assay is a specialised approach for gold-bearing material in which coarse gold can make a small analytical portion unrepresentative.
It uses a larger prepared sample and accounts separately for coarse and fine fractions before a combined gold result is calculated.
Bilex confirms method availability, required sample mass and preparation from the applicable procedure rather than applying a generic industry value.
Bilex Sample Handling
Why Metallic Screening Is Used
Conventional Fire Assay commonly analyses a relatively small aliquot of a prepared sample. Where gold occurs as coarse particles, different small aliquots can contain very different amounts of gold and may not describe the material consistently.
Metallic-screen Fire Assay addresses this heterogeneity by analysing a substantially larger prepared sample. The material is screened at an appropriate particle size, the coarse and fine fractions are accounted for separately, and their results and weights are combined.
The technical term ‘nugget effect’ describes variation caused by coarse particulate gold in a sample. It does not mean that a parcel of intact natural nuggets should automatically be processed by metallic-screen Fire Assay.
Applications
Where Metallic-Screen Fire Assay Is Used
Heterogeneous Ore
Use a larger prepared sample where gold distribution is not sufficiently uniform for routine aliquots.
Nugget-Effect Investigation
Account separately for coarse and fine fractions when the material shows significant particulate heterogeneity.
Suitable Concentrates
Apply only where the concentrate form and validated procedure support metallic screening.
Suitable material
Materials and Sample Forms
- Coarse-gold ore
- Heterogeneous gold-bearing ore
- Prepared material showing a significant nugget effect
- Suitable gold concentrates where confirmed
Before testing
Sample Requirements
- A larger representative prepared sample is normally required than for a conventional Fire Assay aliquot.
- Industry procedures often use approximately one kilogram, but that is not a Bilex requirement unless confirmed from the applicable Bilex procedure.
- The screening size, fraction treatment and analytical masses are procedure-specific and should not be inferred from another laboratory's method code.
- The result still depends on how the prepared sample relates to the original material or lot.
Process
From Testing Question to Report
Obtain the Sample
Obtain a larger representative prepared sample connected to the defined material.
Screen the Material
Separate coarse and fine fractions at the particle size stated by the confirmed procedure.
Account for Fractions
Record the weights and keep the coarse and fine fractions separately identified.
Apply Fire Assay
Analyse the fractions according to the validated Fire Assay procedure.
Calculate the Combined Result
Use the fraction results and weights to determine the combined gold result for the tested sample.
What it contributes
Strengths
- Addresses coarse-gold heterogeneity more directly than a small routine aliquot
- Uses a larger prepared sample
- Accounts separately for coarse and fine fractions
- Provides a combined result tied to the screened sample
Scope
Limitations to Understand
- Destructive to the analytical material
- Requires substantial, controlled sample preparation
- Specialised for coarse or heterogeneous material
- Not normally required for homogeneous finished bullion
- Not automatically suitable for intact natural nugget parcels
Method selection
How This Method Relates to Other Tests
Screen Fire Assay vs Conventional Fire Assay
Both use Fire Assay determination, but metallic screening begins with a larger prepared sample and separates coarse and fine fractions to address particulate gold distribution.
A conventional aliquot may be suitable for more homogeneous prepared material. Method selection should follow evidence about the material, not a blanket preference for a larger sample.
Metallic-Screen vs PhotonAssay
Both may be considered for suitable coarse-gold geological material. Metallic-screen Fire Assay is destructive and separately accounts for screened fractions.
PhotonAssay makes a non-destructive bulk measurement through a suitable prepared sample within a validated application and range. They are not interchangeable by name alone.
Questions
Frequently Asked Questions
What is metallic-screen Fire Assay?
It is a specialised Fire Assay approach that uses a larger prepared sample, separates coarse and fine fractions and combines their contributions to address coarse-gold heterogeneity.
What is the nugget effect?
It is the sampling variation caused when coarse particulate gold is distributed unevenly through material. It is not the same as a parcel of intact natural nuggets.
Why is a larger sample used?
A larger prepared sample improves the opportunity to account for coarse gold particles that may be missed or overrepresented in a small aliquot.
Is screen Fire Assay suitable for bullion?
It is primarily designed for coarse and heterogeneous gold-bearing material and is not normally required for homogeneous finished bullion.
What sample mass does Bilex require?
The required mass depends on the confirmed Bilex procedure and material. Bilex should state it for the specific enquiry rather than relying on a generic industry value.
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Discuss the sample
Discuss Metallic-Screen Fire Assay
Tell us the material, available sample quantity and the information the result needs to establish.
The final method and sample requirements are confirmed after the material and testing objective have been reviewed.