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.
Analytical purpose
What Metallic-Screen Fire Assay Can Help Determine
The method is selected from the material and the analytical question—not from a claim that one technology is best for every sample.
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 Materials
Suitability is confirmed against the sample form, expected composition and applicable analytical procedure.
- Coarse-gold ore
- Heterogeneous gold-bearing ore
- Prepared material showing a significant nugget effect
- Suitable gold concentrates where confirmed
Before testing
Sample & Preparation 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.
Main 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
Important Limitations
- 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
Compare Related Testing Methods
Different methods provide different kinds of evidence. Complementary testing may be appropriate where one result cannot answer the full question.
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.
A Result Represents the Sample Actually Tested
The analytical result describes the identified sample and stated method. Applying that result to a bar, parcel, shipment or multi-kilogram lot depends on whether the sampling procedure reasonably connects the tested sample to the defined material.
Testing does not by itself establish ownership, lawful origin, seller legitimacy, export authorisation or payment security.
Common questions
Metallic-Screen Fire Assay FAQ
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.
Gold Testing & Assaying
Related Testing Methods
Use these links to compare the evidence each method can provide before selecting an analytical approach.
Specialized Gold Testing Method
Discuss Your Sample Before Testing
Tell Bilex what material you have, what you need to establish, whether the item must remain intact and how the result will be used. The team will review method suitability and confirm the next step.
Method availability, equipment or partner-facility arrangement, sample requirements, timing and reporting scope are confirmed for the specific enquiry.