Copper Resource Reconciliation at Andean Open-Pit Mine

Case Study 1: Copper Resource Reconciliation at Andean Open-Pit Mine

Scenario A Tier-1 copper mining operation in northern Chile (Atacama Desert) is undergoing NI 43-101-compliant resource reconciliation between historical drill-hole assays (reported in % Cu) and new metallurgical testwork requiring input in g/t for process simulation. Regulatory auditors require unit consistency across all technical reports, and legacy database fields inconsistently store grades in % or g/t — introducing reconciliation errors up to ±8% in reserve estimates.

Given Data

• Ore Grade Input: 0.85 % Cu
• Input Unit: %
• Output Unit: g/t
• Element: Cu

Calculation The tool applies the standard conversion: g/t = % × 10,000 (since 1% = 10,000 g/t by mass). No molecular weight adjustment is needed for elemental copper reporting (Cu is reported as metal, not oxide or compound).

• Step 1: Confirm input is elemental Cu grade → no valence or compound correction required.
• Step 2: Apply conversion factor: 0.85 % × 10,000 = 8,500 g/t.
• Step 3: Round to specified precision (4 decimal places): 8500.0000 g/t → displayed as 8500.0000 (though trailing zeros are omitted per convention; tool outputs 8500.0000 internally for traceability).

Result and Decision The converted grade is 8500.0000 g/t Cu, matching independent manual calculation and lab QA/QC logs. This value was ingested into the mine’s block model software (Datamine), resolving a 0.7 Mt discrepancy in Measured Resource tonnage previously attributed to unit misalignment. The project team adopted the tool as mandatory for all assay ingestion workflows and updated SOPs to enforce pre-load unit validation.

Lesson Unit inconsistency is a silent source of material balance error — always convert before aggregation, not after; automated, auditable conversion (with versioned logic) prevents cascading inaccuracies in resource statements.