Weighted-average-grade (WAG) Stockpiles

• Weighted-average-grade (WAG) Stockpiles
• • Analyte Balancing
  • • WAG Stockpiles with no Analyte Balancing
    • WAG Stockpiles with Analyte Balancing
  • Analyte Quality Relevance on WAG Stockpiles
  • Impact of Relevance on WAG Calculation

Weighted-average-grade (WAG) stockpiles are an inventory management system where the grade (that is, the quality) of the stockpile is determined by calculating the weighted average of the grades of the individual batches of materials added. This strategy provides an accurate representation of the stockpile's overall quality, while being more efficient than storing data about each batch. In MineMarket, WAG stockpiles can be configured to consider the grade of only stacked material, or the grade of both stacked and reclaimed material.

Analyte Balancing

Analyte balancing refers to the process of accurately tracking and balancing the concentrations of chemical elements or compounds (analytes) in the stockpile. This process ensures that the calculated weighted average grade accurately reflects the true grade of the material, taking into account the varying analyte levels in different batches both stacked onto and reclaimed from the stockpile.

WAG Stockpiles with no Analyte Balancing

WAG stockpiles consider stacked and reclaimed quantity. If analyte balancing is not enabled, only stacked analyte quality is considered.

Example: A mine has the following stockpiles:

• MS-1—Mine Source stockpile 1 has Cu=25%, H2O=10% and has ABC Mining as a 100% contributor.
• MS-2—Mine Source stockpile 1 has Cu=20%, H2O=5% and has Diversified Mining as a 100% contributor.
• WAG—Run of Mine (ROM) stockpile starts with 0 tonnes of material.
• PROD—Production stockpile starts with 0 tonnes of material.

The following transactions take place:

1. 5000 tonnes is stacked onto WAG from MS-1.
2. 5000 tonnes is stacked onto WAG from MS-2.
3. 7500 tonnes is reclaimed from WAG and stacked onto PROD.

The following table displays the transaction history of the WAG (unbalanced) stockpile.

Sequence	Mass	Balance	Cu %	Cu (t)	H2O%	ABC Mining	Diversified Mining
1	5,000.00	5,000.00	25.00	1,125.00	10.00	5,000.00 (100.00%)
2	5,000.00	10,000.00	22.43	2,075.00	7.50	5,000.00 (50.00%)	5,000.00 (50.00%)
3	7,500.00	2,500.00	22.43	518.75	7.50	1,250.00 (50.00%)	1,250.00 (50.00%)

WAG Stockpiles with Analyte Balancing

WAG stockpiles consider stacked and reclaimed quantity. If analyte balancing is enabled, both stacked and reclaimed analyte quality is considered.

Important: Analyte balancing should only be used if accurate sample data is available for both stacking and reclaiming transactions.

Example: A mine has the following stockpiles:

• MS-1—Mine Source stockpile 1 has Cu=25%, H2O=10% and has ABC Mining as a 100% contributor.
• MS-2—Mine Source stockpile 1 has Cu=20%, H2O=5% and has Diversified Mining as a 100% contributor.
• WAG—Run of Mine (ROM) stockpile starts with 0 tonnes of material.
• PROD—Production stockpile starts with 0 tonnes of material.

The following transactions take place, and the material in each transaction is sampled:

1. 5000 tonnes is stacked onto WAG from MS-1. Sampling returns values of Cu=23% and H2O=9.5%.
2. 5000 tonnes is stacked onto WAG from MS-2. Sampling returns values of Cu=18% and H2O=6%.
3. 7500 tonnes is reclaimed from WAG and stacked onto PROD. Sampling returns values of Cu=20.6% and H2O=7.5%.

The following table displays the transaction history of the WAG (balanced) stockpile.

Sequence	Mass	Balance	Cu %	Cu (t)	H2O%	ABC Mining	Diversified Mining
1	5,000.00	5,000.00	23.00	1,040.75	9.50	5,000.00 (100.00%)
2	5,000.00	10,000.00	20.45	1,886.75	7.75	5,000.00 (50.00%)	5,000.00 (50.00%)
3	7,500.00	2,500.00	20.01	457.62	8.50	1,250.00 (50.00%)	1,250.00 (50.00%)

Analyte Quality Relevance on WAG Stockpiles

Analyte quality relevance is expressed as a percentage and refers to the proportion of a WAG stockpile's mass for which analyte sample values are known.

Relevance = Sum of transaction masses with known analyte sample values / Stockpile Mass

The relevance of analyte sample values displays in a tooltip over the analyte sample value on the Activity tab of the WAG Stockpile screen. The tooltip displays two values:

1. The relevance of the sampled analyte value to the total mass of the WAG stockpile, and the sample result type. For example, a relevance of Rapid (50%) indicates that the analyte value entered via a Rapid sampling template is relevant to 50% of the stockpile mass.
2. The percentage of the mass that has been sampled.

Impact of Relevance on WAG Calculation

A standard calculation of the weighted-average grade is:

Weighted Average = Sum ( Analyte Value * Mass ) / Sum (Mass)

However, the calculation of the mass of analytes in WAG stockpiles includes the relevance of the analyte sample values. The formula used is:

Weighted Average = Sum ( Analyte Value * Mass * Relevance ) / Sum ( Mass * Relevance )

Note: Billboards use the standard calculation of the weighted-average grade.

Example of relevance calculation: A stockpile has 100 t of coal. The stockpile has not been surveyed; therefore, the Ash value is unknown.

1. A loading (stacking) transaction is made of 100 t of coal, which has been sampled at 10% Ash with 100% relevance. After the transaction, the stockpile has 200 t coal at 10% Ash with 50% relevance. The 10% Ash value is relevant to 50% of the total mass on the stockpile.
2. A second loading transaction is made of 50 t of coal, which has been sampled at 10% Ash with 100% relevance. After the transaction, the stockpile has 250 t coal at 10% Ash with 60% relevance. The 10% Ash value is relevant to 60% of the total mass on the stockpile.