How to Evaluate the Grade of Oxidized Gold Ore (Key Metrics You Can’t Ignore)

 The grade of oxidized gold ore is the single most important factor determining its economic value—yet evaluating it requires a nuanced approach, especially compared to primary gold ore. In this article, we break down the key metrics to measure oxidized gold ore grade and how to interpret them for extraction planning.

First, total gold content is the foundational metric, measured in grams per ton (g/t) or ounces per ton (oz/t). For oxidized gold ore, grade can vary widely: low-grade ore might sit at 1-3 g/t, while higher-grade deposits can reach 5-10 g/t or more. However, total gold content alone isn’t enough—you must also account for free gold vs. refractory gold.
Free gold in oxidized ore is gold that is liberated from its host minerals (e.g., visible gold grains or gold adsorbed onto oxide surfaces) and can be extracted with relatively simple methods. Refractory gold, by contrast, is gold trapped within oxide or clay minerals, or locked in residual sulfide particles that survived oxidation. Refractory gold requires more intensive processing (like bioleaching or pressure oxidation) to unlock, so its proportion in the ore directly impacts extraction costs.
Next, oxidation intensity is a critical secondary metric for grade evaluation. Oxidized ore is typically classified by the degree of sulfide destruction: mild oxidation (residual sulfides >5%), moderate oxidation (1-5% residual sulfides), and severe oxidation (<1% residual sulfides). Severe oxidation often means more liberated free gold but may also lead to clay formation, which can clog leaching systems and reduce efficiency.
Gangue composition also ties to grade evaluation. Oxidized ore is often rich in iron oxides (limonite, hematite) and clays, which can adsorb gold or leaching reagents (like cyanide), lowering overall recovery. For example, high clay content in oxidized ore can reduce heap leaching efficiency by limiting solution flow through the ore pile.

Finally, spatial distribution of gold matters. Even if an ore has a high average grade, if gold is concentrated in small, isolated zones, extraction may be less profitable. Core sampling and grade mapping are essential to identify these high-value pockets.
For a step-by-step guide to sampling and assaying oxidized gold ore to accurately measure its grade, visit: [LINK]. Proper grade evaluation is the foundation of any profitable gold extraction project.

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