Why Grade Matters
Every mining project lives or dies on grade. Higher grade means more metal per tonne of rock mined, lower processing costs per unit of metal produced, and a wider margin between revenue and cost. A high-grade discovery can be economic at smaller scale. A low-grade deposit needs scale, infrastructure, and low operating costs just to survive.
Grade also varies by deposit type. Underground gold operations need higher grades than open cut mines because underground mining costs more per tonne. Massive nickel sulphide deposits carry different thresholds to disseminated nickel. A grade that is impressive in one context can be marginal in another. The tables below account for these distinctions.
Precious Metals
| Commodity | Symbol | Low Grade | Medium Grade | High Grade |
|---|---|---|---|---|
| Gold (Open Cut) | Au | < 2g/t | 2g/t - 4g/t | > 4g/t |
| Gold Underground | Au | < 3g/t | 3g/t - 5g/t | > 5g/t |
| Gold (Porphyry) | AuEq | < 0.5g/t | 0.5g/t - 1g/t | > 1g/t |
| Silver | Ag | < 100g/t | 100g/t - 200g/t | > 200g/t |
| Palladium | Pd | < 2g/t | 2g/t - 5g/t | > 5g/t |
| Platinum | Pt | < 3g/t | 3g/t - 6g/t | > 6g/t |
Gold grade is reported in grams per tonne (g/t). The relevant threshold depends on the mining method — underground operations require higher grades to cover the additional cost of mining underground. Porphyry gold systems are large, low-grade deposits that compensate with scale. Working with a multi-metal gold intersection? Use the Metal Equivalent Calculator to convert all metals into a single AuEq grade for direct comparison.
Base Metals
| Commodity | Symbol | Low Grade | Medium Grade | High Grade |
|---|---|---|---|---|
| Copper | Cu | < 1% | 1% - 2% | > 2% |
| Copper (Porphyry) | CuEq | < 0.4% | 0.4% - 0.7% | > 0.7% |
| Nickel (Massive) | Ni | < 1% | 1 - 2% | > 2% |
| Nickel (Disseminated) | Ni | < 0.5% | 0.5 - 0.7% | > 0.7% |
| Cobalt | Co | < 0.2% | 0.2 - 0.5% | > 0.5% |
| Zinc | Zn | < 5% | 5% - 10% | > 10% |
| Lead | Pb | < 5% | 5% - 10% | > 10% |
| Iron Ore | Fe | < 50% | 50% - 60% | > 60% |
| Manganese | Mn | < 30% | 30% - 44% | > 44% |
| Molybdenum | Mo | < 0.1% | 0.1% - 0.3% | > 0.3% |
| Tin | Sn | < 0.5% | 0.5% - 1% | > 1% |
| Tungsten | WO3 | < 0.1% | 0.1% - 0.5% | > 0.5% |
| Antimony | Sb | < 1% | 1% - 5% | > 5% |
Base metals are reported as a percentage of the rock mass. Note the distinction between massive and disseminated nickel — massive nickel sulphide deposits are rarer and higher value, with different grade thresholds to disseminated systems. Tungsten is reported as tungsten trioxide (WO3%); high-grade skarn and vein systems regularly exceed 0.5% WO3, with exceptional hits above 1%. Antimony is reported as in-situ ore grade (Sb%) — high-grade vein systems commonly return grades above 5% Sb, with exceptional intersections exceeding 10%. Manganese above 44% Mn is considered high grade and is sought after for both ferroalloy production and battery manufacturing. Reporting a multi-metal intersection? Use the Metal Equivalent Calculator to convert it into a single equivalent grade.
Energy Minerals
| Commodity | Symbol | Low Grade | Medium Grade | High Grade |
|---|---|---|---|---|
| Lithium (Hard Rock) | Li2O | < 1% | 1% - 1.5% | > 1.5% |
| Lithium (Brine) | Li | < 500mg/L | 500mg/L - 1,000mg/L | > 1,000mg/L |
| Graphite | TGC | < 5% | 5% - 10% | > 10% |
| Phosphate | P2O5 | < 17% | 17% - 26% | > 26% |
| Uranium | U3O8 | < 0.5% | 0.5% - 1% | > 1% |
| Niobium | Nb2O5 | < 0.5% | 0.5% - 1% | > 1% |
| Vanadium | V2O5 | < 0.6% | 0.6% - 1% | > 1% |
Lithium grade is reported differently depending on the deposit type. Hard rock lithium (spodumene pegmatites) is reported as Li2O percentage. Brine lithium is reported as lithium concentration in milligrams per litre (mg/L). Phosphate grade is expressed as P2O5 percentage; deposits below 17% P2O5 typically require significant beneficiation to be commercially viable, while grades above 26% P2O5 can often be processed directly. Viewing a lithium drill announcement with visual core descriptions? Use the Visual Logs Estimator to convert visual spodumene observations into an estimated Li2O grade before assays are returned.
Rare Earths
| Commodity | Symbol | Low Grade | Medium Grade | High Grade |
|---|---|---|---|---|
| TREO - Hard Rock (LREO) | TREO | < 2% | 2% - 5% | > 5% |
| TREO - Clay / Ionic Absorption (HREO) | TREO | < 0.1% (< 1,000ppm) | 0.1% - 0.2% (1,000ppm - 2,000ppm) | > 0.2% (> 2,000ppm) |
Rare earth grades are expressed as Total Rare Earth Oxide (TREO), which combines all rare earth elements into a single percentage. The distinction between LREO (light rare earth elements) and HREO (heavy rare earth elements) is important — HREO deposits trade at a significant premium because heavy rare earths are less common and carry higher value applications. A low TREO grade in an HREO system can be more valuable than a high TREO grade in an LREO system.
Frequently Asked Questions
What does grade mean in mining?
Grade refers to the concentration of a target mineral or metal in the host rock. It is usually expressed as a percentage for base metals and energy minerals, or as grams per tonne (g/t) for precious metals. Higher grade means more metal per tonne of rock mined.
What is considered high grade gold?
For open cut gold mining, high grade is generally above 4 g/t. For underground gold mining, high grade is above 5 g/t. Porphyry gold systems operate at much lower grades — above 1 g/t AuEq is considered high grade for that deposit type given the large scale of the ore body.
What is considered high grade tungsten?
Tungsten grade is reported as tungsten trioxide (WO3%). A grade above 0.5% WO3 is considered high grade. Medium grade sits between 0.1% and 0.5% WO3. High-grade skarn and vein systems can return grades well above 0.5% WO3, with some exceptional intersections exceeding 1%.
What is antimony used for and what is high grade?
Antimony is a critical mineral used in flame retardants, lead-acid batteries, and next-generation battery technologies. It is also a key material in defence applications. High-grade antimony in-situ ore is above 5% Sb. Vein-hosted systems commonly exceed this, with some intersections returning grades above 10% Sb.
What is high grade manganese?
Manganese above 44% Mn is considered high grade and is the standard for battery-grade and premium ferroalloy applications. Medium grade sits between 30% and 44% Mn. Manganese above 44% Mn can often be shipped as lump ore without significant processing.
Why do nickel grades have two thresholds?
Nickel deposits come in two main types: massive sulphide and disseminated sulphide. Massive nickel sulphide is rarer, richer, and easier to process. Disseminated nickel is more common but lower grade. The two types have different economic thresholds, so separate grade benchmarks apply.
Why is lithium grade reported differently for hard rock vs brine?
Hard rock lithium (found in spodumene pegmatites) is a solid mineral and graded as Li2O percentage by mass. Brine lithium is dissolved in underground water and measured as concentration in milligrams per litre. The two are physically different materials with different processing routes — direct comparison requires conversion.
What is a cut-off grade?
Cut-off grade is the minimum grade at which mineralisation is economic to mine. Material above cut-off is classified as ore. Material below cut-off is classified as waste. Cut-off grades vary by commodity, mining method, and prevailing metal prices. Use the Residual Grade Calculator to check whether a drill intersection remains above cut-off after the high-grade core is removed.
How do I calculate metal equivalent grades?
Use the Metal Equivalent Calculator to convert multi-metal intersections into a single AuEq, CuEq, or other equivalent grade. It also outputs gram x metre values for direct comparison between intersections.
How do I estimate the size of a mineral resource from drill data?
Use the Resource Estimator. Enter the grade and dimensions from available drill data and the calculator returns an estimated tonnage and contained metal — enough to do a back-of-envelope Tier 1 to Tier 4 assessment before a formal JORC resource is announced.