Ore Grade Was Correct. The Recovery Was Wrong. Those Are Different Problems.
Quote from chief_editor on May 30, 2026, 6:44 pmA copper ore grade specification does not guarantee metallurgical recovery. The gap between grade and recoverable content is where buyers absorb losses they didn't expect.
A concentrator plant in South America contracted to purchase 30,000 dry metric tonnes of gold-bearing copper ore from a small miner at a price based on the ore's assayed grade: 1.8% copper and 1.4 g/t gold. The assay was conducted on a representative sample by an accredited laboratory. The numbers were accurate.
When the ore was processed through the concentrator, the metallurgical recovery for copper was 72% instead of the plant's standard 85%. Gold recovery was 61% instead of the expected 79%. The concentrator produced significantly less copper-gold concentrate than the feed grade suggested it should. The shortfall in payable metal was equivalent to approximately 380 tonnes of copper content and 280 kg of gold content — a significant financial loss against the purchase price.
The buyer's instinct was to pursue a quality claim against the seller. The assay grade was not the problem. The problem was in what the ore was doing in the processing plant.
Grade Is a Chemical Measurement. Recovery Is a Process Result.
The distinction between ore grade and metallurgical recovery is fundamental in mining and processing, and is frequently not understood by commodity buyers who are new to mining-output trades.
Grade — copper content expressed as a percentage, gold content in grams per tonne — tells you what is there chemically. It does not tell you how much of it can be practically extracted using the processing methods and equipment at a specific plant. Recovery depends on the mineralogy of the ore: the specific copper minerals present (chalcopyrite recovers well, chalcocite somewhat less, cuprite poorly by flotation), the grain size and liberation characteristics, the presence of deleterious elements that interfere with flotation chemistry, and the clay and silica content that affects process water management.
Two ore parcels with identical assay grades can produce dramatically different recoveries depending on their mineralogy. An ore that assays at 1.8% copper but has a significant portion of its copper content locked in oxide minerals — while a flotation plant is designed for sulfide ores — will produce poor recovery regardless of the grade.
The contract between the concentrator and the small miner specified grade, not recovery. This is standard in ore purchase contracts where the seller is not responsible for the buyer's processing performance. The seller sold compliant ore — the grade was correct. What the ore did in the concentrator was the concentrator's problem, not the miner's.
Industry estimates from concentrators processing multiple ore sources suggest that recovery variability between ore types from different mineralogical origins is one of the largest single sources of profitability variance in concentrator operations, often exceeding the variance from grade. Concentrators that blend multiple ore sources specifically to manage recovery — combining high-recovery sulfide ores with lower-recovery sources to maintain average recovery rates — are managing this risk actively. Concentrators that purchase ore on grade alone without mineralogical characterization are accepting unknown recovery variability.
The Contract That Should Have Specified More
An ore purchase contract that includes recovery guarantees — where the seller guarantees minimum recoverable copper and gold content, with price adjustments if actual recovery falls below the guarantee — transfers some recovery risk to the seller. These contracts require the seller to have sufficient knowledge of their ore's metallurgical behavior to make meaningful guarantees, which small miners often lack.
The alternative is a contract that explicitly acknowledges recovery uncertainty, prices the ore on a recoverable-metal basis using an agreed standard recovery factor, and includes provisions for the buyer to conduct metallurgical testing on representative samples before committing to large purchases. This testing — a bench-scale flotation test conducted in a laboratory — costs a few thousand dollars and provides a recovery prediction for that specific ore type under the buyer's process conditions.
Buyers who skip metallurgical testing to close deals faster are accepting recovery risk that is entirely characterizable before purchase. The recovery loss on 30,000 DMT at the concentrator plant described above represents a financial impact many times larger than what a pre-purchase metallurgical test program would have cost.
A copper ore grade specification does not guarantee metallurgical recovery. The gap between grade and recoverable content is where buyers absorb losses they didn't expect.
A concentrator plant in South America contracted to purchase 30,000 dry metric tonnes of gold-bearing copper ore from a small miner at a price based on the ore's assayed grade: 1.8% copper and 1.4 g/t gold. The assay was conducted on a representative sample by an accredited laboratory. The numbers were accurate.
When the ore was processed through the concentrator, the metallurgical recovery for copper was 72% instead of the plant's standard 85%. Gold recovery was 61% instead of the expected 79%. The concentrator produced significantly less copper-gold concentrate than the feed grade suggested it should. The shortfall in payable metal was equivalent to approximately 380 tonnes of copper content and 280 kg of gold content — a significant financial loss against the purchase price.
The buyer's instinct was to pursue a quality claim against the seller. The assay grade was not the problem. The problem was in what the ore was doing in the processing plant.
Grade Is a Chemical Measurement. Recovery Is a Process Result.
The distinction between ore grade and metallurgical recovery is fundamental in mining and processing, and is frequently not understood by commodity buyers who are new to mining-output trades.
Grade — copper content expressed as a percentage, gold content in grams per tonne — tells you what is there chemically. It does not tell you how much of it can be practically extracted using the processing methods and equipment at a specific plant. Recovery depends on the mineralogy of the ore: the specific copper minerals present (chalcopyrite recovers well, chalcocite somewhat less, cuprite poorly by flotation), the grain size and liberation characteristics, the presence of deleterious elements that interfere with flotation chemistry, and the clay and silica content that affects process water management.
Two ore parcels with identical assay grades can produce dramatically different recoveries depending on their mineralogy. An ore that assays at 1.8% copper but has a significant portion of its copper content locked in oxide minerals — while a flotation plant is designed for sulfide ores — will produce poor recovery regardless of the grade.
The contract between the concentrator and the small miner specified grade, not recovery. This is standard in ore purchase contracts where the seller is not responsible for the buyer's processing performance. The seller sold compliant ore — the grade was correct. What the ore did in the concentrator was the concentrator's problem, not the miner's.
Industry estimates from concentrators processing multiple ore sources suggest that recovery variability between ore types from different mineralogical origins is one of the largest single sources of profitability variance in concentrator operations, often exceeding the variance from grade. Concentrators that blend multiple ore sources specifically to manage recovery — combining high-recovery sulfide ores with lower-recovery sources to maintain average recovery rates — are managing this risk actively. Concentrators that purchase ore on grade alone without mineralogical characterization are accepting unknown recovery variability.
The Contract That Should Have Specified More
An ore purchase contract that includes recovery guarantees — where the seller guarantees minimum recoverable copper and gold content, with price adjustments if actual recovery falls below the guarantee — transfers some recovery risk to the seller. These contracts require the seller to have sufficient knowledge of their ore's metallurgical behavior to make meaningful guarantees, which small miners often lack.
The alternative is a contract that explicitly acknowledges recovery uncertainty, prices the ore on a recoverable-metal basis using an agreed standard recovery factor, and includes provisions for the buyer to conduct metallurgical testing on representative samples before committing to large purchases. This testing — a bench-scale flotation test conducted in a laboratory — costs a few thousand dollars and provides a recovery prediction for that specific ore type under the buyer's process conditions.
Buyers who skip metallurgical testing to close deals faster are accepting recovery risk that is entirely characterizable before purchase. The recovery loss on 30,000 DMT at the concentrator plant described above represents a financial impact many times larger than what a pre-purchase metallurgical test program would have cost.