How to Test Gold Ore Before You Buy a Plant

How to test gold ore before you buy a plant is a question every serious mine developer asks. You don't want to spend millions on equipment that doesn't match the ore. A proper testwork programme answers that question in eight ordered steps. Xinhai runs this programme in a CNAS-accredited laboratory, and the company reports CIL/CIP recovery can reach 99% on suitable ores. The steps below show what to sample, what each test measures, and what the result decides in your flowsheet.

You'll need to understand the ore before you can size a mill, choose a leaching method, or set a recovery target. This guide walks you through the sequence that Xinhai's metallurgists use, from the first sample to the final pilot run.

Why test gold ore before buying a plant

Metallurgical testwork refers to the laboratory and pilot-scale experiments that measure how an ore responds to crushing, grinding, and recovery methods. It's the foundation of every sound plant design. If you're new to this, read gold ore milling for the basics. A well-planned testwork programme prevents three common mistakes: buying a plant that is too large, choosing a recovery method that doesn't suit the ore, and missing payable metals. The test sequence below is ordered from cheap and fast to expensive and slow, so you get maximum information per dollar spent.

Step 1: Sampling and compositing

Sampling is the process of collecting representative portions of ore from the deposit. Compositing is the blending of multiple small samples into one larger representative sample. The ordered steps are: (1) collect drill core or channel samples from different depths and locations; (2) split the samples into size fractions if you plan to test different grind targets; (3) composite samples according to geological domains or ore types; (4) send a representative portion to the lab. The JORC Code sets out minimum standards for sampling and public reporting; the full code is available at JORC Code. Poor sampling is the single largest source of error in gold ore testing, so don't cut corners here.

Step 2: Fire assay

Fire assay is a type of quantitative analysis that fuses a small sample with lead flux to separate gold and silver. The process follows these ordered steps: weigh the sample, mix with flux, fuse in a furnace, cupel the lead button, and weigh the resulting gold bead. Fire assay gives you the head grade of the ore, which is the most basic economic question. The USGS Mineral Commodity Summaries (USGS Mineral Commodity Summaries) provides background on gold measurement and reporting practices. The lab will specify the exact sample mass needed for fire assay; a few grams are usually enough, but you should confirm with the lab.

Step 3: Mineralogy

Mineralogy refers to the identification of the minerals that host the gold and the gangue minerals that consume reagents. It answers two questions: is the gold free-milling or locked in sulfides, and what minerals will interfere with cyanidation. Ordered steps include: prepare polished thin sections, examine them under an optical microscope, and run X-ray diffraction if needed. If the gold is locked in arsenopyrite or pyrite, you'll need a different flowsheet. This step also tells you whether gravity recovery will work well. The result decides the overall processing route, so don't skip it.

Step 4: Gravity recoverable gold (GRG)

GRG is the fraction of gold that can be recovered by gravity methods such as centrifugal concentrators or shaking tables. The test simulates a gravity circuit in the lab. If a large fraction of the gold reports to the gravity concentrate, you can add a gravity stage before leaching. This test is part of the standard suite at Xinhai's laboratory. You can learn more about how milling affects recovery in how gold milling works. The result helps decide whether to include a gravity circuit and what size it should be.

Step 5: Bottle-roll cyanidation

Bottle-roll cyanidation is a batch leaching test that simulates CIL/CIP conditions in the lab. It's the key test for deciding between heap leaching and tank leaching. Xinhai reports CIL/CIP recovery can reach 99% on suitable ores, but the test result tells you what your ore can actually achieve. The test involves placing a known mass of ground ore in a bottle with cyanide solution, rolling it for a set period, and measuring gold dissolution. The result helps determine whether a CIL plant is suitable. For more on CIL and CIP, read CIL and CIP. For leaching chemistry, see gold leaching.

Step 6: Flotation

Flotation is a concentration method that uses air bubbles to collect hydrophobic gold-bearing minerals. The test determines whether flotation can recover gold from sulfide ores. It's necessary when the gold is not free-milling and not directly amenable to cyanidation. The lab will run a series of flotation tests with different reagent schemes. The result decides whether to include a flotation circuit and what reagents to use. If you need a flotation plant, see gold flotation plant.

Step 7: Bond work index

Bond work index is a measure of the energy required to grind an ore from a large feed size to a product size. It's used to size the grinding mills. The test is performed in a laboratory mill and gives a number in kilowatt-hours per tonne. The result decides the mill power draw and the grinding circuit configuration. Xinhai performs Bond work index tests as part of its metallurgical testwork programme. For more on milling, see ball milling gold processing. Don't skip this test if you're designing a new grinding circuit.

Step 8: Pilot testing

Pilot testing is the continuous operation of a small-scale version of the full flowsheet. It validates the laboratory results and provides engineering data for scale-up. Xinhai operates an industrial pilot base alongside its CNAS-accredited laboratory. The pilot plant runs the chosen flowsheet for a period of time, producing enough gold to confirm recovery and reagent consumption. Pilot testing is more expensive and slower than the previous steps, but it's the last check before you commit to a full-scale plant. For a complete design and construction package, see gold processing plant design.

What the lab needs from you

You don't need to be a metallurgist to provide useful information. The lab will need: a representative sample mass of a few kilograms for each composite, the sample location and depth, the geological description of the ore, and your proposed plant capacity if you have one. Send your samples in sealed bags to avoid contamination. If you're unsure, Xinhai can help you design a sampling plan. For a tailored testwork proposal, contact the team via the contact page.

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