LEAD-ZINC SUPPLIER PRACTICE · SAMPLING & QUANTITY
Lead-Zinc Sampling: Moisture, WMT and DMT
An assay is useful only when you know which cargo it represents, how it was sampled and which moisture and weight bases apply.
For suppliers offering lead, zinc or mixed lead-zinc concentrates to RTV. Sampling plans, test methods, settlement weight and retesting procedures are agreed against the actual cargo and contract.
- Match results to the same lot
- Retain moisture and assay bases
- Dry-tonne conversion is not settlement approval
DEFINE WHAT IS BEING CHECKED
Results need a common lot
Define the cargo first
State the country, storage point, stockpile or package identifiers and quantity offered. The same mine or warehouse can contain several lots; it does not establish that one report covers all available stock.
Check its condition when sampled
Record the sampling date, quantity, packaging and cover at that time. Explain any replenishment, blending, relocation, rain exposure or repacking since the report. Changes require a review of whether the original results still apply.
Link assays and weighing records
Connect the report, sample ID, weighing records and physical cargo markings. Distinguish net weight, tare and estimates. Apparent volume in a photo is not verified tonnage.
- Define the lotLocation · identifiers · quantity
- Agree samplingCoverage · method · operator
- Seal and dispatchSample ID · seal · custody
- Link the resultsMoisture · assay · weight
SAMPLING AND PREPARATION
Establish what the sample represents
A handful selected from an attractive part of a stockpile may describe that spot; it cannot alone establish the composition of the entire lot. ISO 12743’s public abstract favours moving-stream sampling and recognises systematic errors with stationary lots. Suitable personnel should follow an applicable method and agreed plan, rather than imposing one fixed number of sampling points on every stockpile.Reference: ISO 12743:2021 public abstract ↗
Coverage
Which stockpiles, packages or loading/discharge stages are covered? Which areas are inaccessible, and how will those limits be recorded?
Execution and witnessing
Who arranges and performs sampling, who attends, which plan applies and who confirms the record?
Preparation and testing
How do sample division, preparation, dispatch and intended tests connect? The testing party should confirm suitable methods; one preparation treatment is not suitable for every element.
Sample custody
How are sample IDs, seals, handover parties and receipt dates traced? Where and how long are retest samples retained, and by whom?
How moisture, assay and retest sample purposes connect
| Purpose | Question addressed | Records to retain |
|---|---|---|
| Moisture test sample | Determines moisture or mass loss under the agreed drying method | Handle, seal and transfer as specified in the plan. Record timing and condition between sampling and receipt; a sample that has lost or gained moisture may no longer represent the original state. |
| Chemical analysis sample | Determines Pb, Zn and agreed impurities or associated elements | Retain the sample ID, lot link and reported dry/wet basis. Preparation and methods require confirmation by the testing party; moisture alone does not establish metal content. |
| Sealed retest sample | Supports an agreed review or dispute procedure | Record seals, purpose, quantity, custodian, storage conditions and handovers under the plan. A retained sample does not automatically have arbitration status; retesting rules must be agreed. |
These are different sample purposes, not an instruction to take three unrelated bags from different locations. Where applicable, an agreed plan can link tests through a common representative sample. For material susceptible to oxidation or decomposition, the testing party should confirm how moisture and chemical-analysis sampling and treatment relate.
CLARIFY THE WEIGHT BASIS
How 100 wet tonnes can become 92 dry tonnes
WMT means wet metric tonnes; DMT means dry metric tonnes. State whether the quantity is wet cargo net weight after deducting packaging, vehicle and other tare, or an equivalent dry quantity. ‘Tonnes’ without that basis is incomplete.
Hypothetical example: one lot has a net wet weight of 100 WMT, with moisture equal to 8% of wet material mass. This illustrates a quantity relationship only: it is not inventory, an acceptable moisture limit, an assay result or RTV’s settlement formula.
DMT = WMT × (1 − moisture % ÷ 100)
100 × (1 − 8 ÷ 100) = 92 DMT
At 10% moisture, the same 100 WMT would equal 90 DMT: a difference of 2 dry tonnes. The parties need to agree which weighing and moisture results apply, rather than selecting whichever result benefits one side.
TRACK CHANGES AFTER SAMPLING
The cargo’s condition can change
| Change on site | Where the risk lies | What to check next |
|---|---|---|
| Rain exposure after testing | Earlier moisture may not represent the shipping condition | Explain rainfall, covering and handling. Check whether moisture and quantity need to be reconfirmed for the affected lot. |
| A new truckload added to the stockpile | The lot boundary and represented material have changed | Record added quantity, source and extent of mixing. Establish whether it remains the original lot before discussing report applicability or retesting. |
| Quoting wet tonnes with a dry-basis assay | Quantity and assay bases may not align | List WMT/DMT, moisture and assay basis separately, then discuss agreed pricing terms without omitting those distinctions. |
| A report with no sampling record | The sample-to-cargo link is difficult to trace | Provide available dates, site identifiers, sampling and seal records. Do not reconstruct witnessing or sample retention that never occurred. |
KEEP THE EVIDENCE CONNECTED
Records for testing, weighing and retesting
- Lot and condition
- Location, stockpile/package markings, available quantity and units; any replenishment, mixing, rain exposure or relocation.
- Sampling and custody
- Date, operator, plan or method reference, coverage and limitations, attendees, sample IDs and seal numbers.
- Testing and weight
- Report issuer and date, separate Pb/Zn values, dry/wet basis, moisture, weighing date and net/tare evidence.
- Disagreement procedure
- Applicable results, retained-sample custodian and period, retest laboratory and process, costs and objection deadlines, as agreed in the contract.
The parties may discuss an agreed scope for SGS, CCIC or another suitable independent party. Chemical testing alone, witnessing sampling, and also verifying quantity are different assignments. Define the scope before reviewing the deliverables. Naming an organisation does not imply a standing partnership or endorsement.Reference: SGS mineral and metal quality/quantity inspection ↗
Sampling and quantity fields
LEAD-ZINC LOT: SAMPLING AND QUANTITY INFORMATION Material and available Pb/Zn results: Location, stockpile/package and lot ID: Sampling date, operator and witnessed scope: Sampling plan, coverage and limitations: Sample IDs, seal numbers and custody records: Moisture result, method and report ID: Assay report and dry/wet basis: Weighing date, WMT/DMT and net/tare evidence: Any replenishment, mixing, rain or relocation after sampling: Retained-sample location, custodian and agreed retest matters: Missing or unconfirmed information: This is an information checklist, not an assay report, sampling certificate or settlement confirmation.
FURTHER CHECKS
Questions before offering cargo
Is the same number of sampling points and sample weight required for every lot?
This guide sets neither. Stockpiles, packaging, particle size, quantity, accessibility and testing purposes differ. Select and record the plan against applicable methods and actual conditions.
Can I first submit results from a sample taken by the supplier?
Yes. State who took the sample, how and when, and what it represents. A submitted sample is not automatically equivalent to independent witnessed sampling of the full lot. Any retest is discussed against the actual cargo.
Can moisture results directly replace the report’s dry- or wet-basis grade?
Do not rewrite the report yourself. Retain its original basis and ask the issuer to clarify the method. Any conversion requires the same lot, a consistent applicable basis and an agreed method, with original values and calculations retained.
Does RTV always settle on dry tonnes or use one testing organisation?
This guide explains how records connect. Settlement weight, testing organisation, governing results, sampling, retesting and costs are agreed per lot and contract. It makes no uniform payment or testing commitment.
OFFER CARGO TO RTV
Start with the lot; then agree checks and delivery
Share available assays, site photos, location and quantity. Mark unknown items. Submission does not confirm a purchase, import eligibility or settlement.
Technical terms refer to the public sources linked above, checked 2026-10-24. Testing follows applicable methods and the agreed plan; transaction responsibilities follow the parties’ contract. References imply no endorsement of RTV by testing organisations or rule publishers.