- Does Comminution Alone Always Liberate More Than 80% of Gold?
Does Comminution Alone Always Liberate More Than 80% of Gold?
A Technical Perspective from Start Your Own Gold Mine
Start Your Own Gold Mine (https://www.StartYourOwnGoldMine.com) is a proven, end‑to‑end consulting and training program that empowers entrepreneurs, investors, and small‑to‑mid‑size mining operators to launch and manage sustainable gold‑mining ventures worldwide. Since 2012, our multidisciplinary team of licensed geologists, mining engineers, and prospectors has guided clients through every stage of a new operation: from initial geological assessment and resource validation to securing permits, designing cost‑effective extraction plans, and implementing mercury‑free recovery systems that meet the latest environmental regulations.
Our methodology blends systematic site surveys, advanced geophysical imaging (including Matrix Gold Prospecting tools), and rigorous geotechnical analysis to locate high‑grade alluvial, eluvial, and lode deposits with the lowest exploration risk. We provide tiered service packages—Basic (initial set‑up and training) and Full‑Service (licensed sites, equipment, and ongoing mentorship)—so clients can start small and scale to larger production levels while staying compliant with local mining laws, environmental standards, and community‑engagement best practices.
The Core Question
A question we often receive from new and experienced operators alike is:
“In any mining, is more than 80% of gold always liberated by comminution?”
On the surface, this sounds like a reasonable rule of thumb. But as we teach our clients during the Basic package site assessment, this statement is false—and misunderstanding it can lead to poor equipment choices, failed recovery targets, and lost revenue.
To explain why, we first need a clear definition of the key term.
What Is Comminution?
Comminution is the process of reducing the particle size of solid ore from large, run‑of‑mine blocks down to finer particles. It is the first and most energy‑intensive step in mineral processing.
Comminution consists of two main stages:
- Crushing – Breaking large rocks (often >1 meter in diameter) down to smaller sizes (typically 5–25 mm) using jaw, gyratory, or cone crushers.
- Grinding – Further reducing the crushed material to a fine powder (often 75 microns or less) using ball mills, rod mills, or SAG mills (Semi‑Autogenous Grinding mills).
The purpose of comminution is liberation—physically separating valuable mineral grains (like gold) from the worthless surrounding rock (gangue). When done effectively, comminution produces free gold particles that can then be recovered by gravity separation, flotation, or leaching.
Think of a chocolate chip cookie: comminution is crumbling the cookie; liberation is the resulting individual chocolate chips (the “gold”) separated from the dough crumbs.
Why the 80% “Always” Claim Is Wrong
The statement “more than 80% of gold is always liberated by comminution” fails because of two critical words: “always” and “by comminution alone.”
In reality, the percentage of gold liberated solely by crushing and grinding depends entirely on the type of gold deposit. Here are the major categories where the 80% figure does not hold:
1. Refractory Gold Ores (The Most Common Counter‑Example)
Over one‑third of the world’s new gold deposits are refractory. In these ores, gold is microscopic or even submicroscopic (individual atoms) encapsulated within the crystal lattice of sulfide minerals like pyrite or arsenopyrite.
Comminution alone will NOT liberate this gold. You can grind the ore to talcum powder (10 microns or less), and the gold remains chemically trapped inside the host mineral. To liberate it, you must add processes after comminution: pressure oxidation (autoclave), bacterial oxidation, roasting, or ultra‑fine grinding followed by aggressive leaching.
For true refractory ores, comminution liberates less than 10–20% of the gold.
2. Sulfide‑Locked Gold
Even in non‑refractory ores, gold particles can be physically locked inside sulfide gangue. A typical hard‑rock sulfide operation might see comminution liberating only 30–50% of the gold, with the rest remaining in sulfide middlings that require further processing.
3. Placer and Alluvial Deposits
In rivers, beaches, or ancient paleo‑channels, the gold is already liberated as flakes or nuggets. Comminution is not even used. Liberation is achieved by simple washing and gravity separation (sluices, jigs, centrifuges). Adding a crusher or mill would be wasteful and counterproductive.
4. Coarse Free‑Milling Gold (The Exception)
In rare deposits with large, visible gold flakes or nuggets, comminution can liberate >80% of the gold. However, even here, some gold is smeared across grinding media or trapped in mill “corners.” An 80% target is achievable, but it is never guaranteed across all ore zones.
The Correct General Rule
Based on our experience across hundreds of client sites worldwide, here is the realistic breakdown for typical hard‑rock gold mines:
| Ore Type | Gold Liberation by Comminution Alone |
|---|---|
| Free‑milling oxide ore | 60–90% (80% is a design target, not a constant) |
| Sulfide ore with coarse gold | 30–70% |
| Refractory sulfide ore | <10–20% (requires oxidation before leaching) |
| Placer / alluvial | Comminution not applicable |
In fact, the goal of comminution in gold mining is not always to achieve >80% physical liberation. Often, the goal is to create enough exposed surface area for cyanide or alternative lixiviants to reach and dissolve the gold. True liberation (a free gold particle) is not strictly necessary for recovery.
Practical Implications for Your Mining Venture
At Start Your Own Gold Mine, we have seen entrepreneurs lose significant capital by assuming that “crushing and grinding alone will do the job.” Here is what we advise:
- Always conduct a mineralogical assessment before designing your comminution circuit. Knowing whether your gold is free‑milling, sulfide‑locked, or refractory determines your entire processing flow sheet.
- Do not over‑grind. Excessive comminution wastes energy (often 50–70% of a plant’s power budget) and can create slimes that interfere with gravity recovery or leaching.
- Match your recovery method to your liberation profile. Free gold can be recovered by gravity (centrifugal concentrators, shaking tables). Locked gold may require flotation. Refractory gold needs pre‑oxidation.
- For alluvial operations, skip comminution entirely. Your capital is better spent on efficient washing and gravity circuits.
Final Answer from Start Your Own Gold Mine
No. In any mining, more than 80% of gold is NOT always liberated by comminution.
- For refractory ores, comminution liberates very little gold directly.
- For placer deposits, comminution is not used at all.
- Even for free‑milling ores, the percentage varies widely (30–90%), and 80% is an achievable target, not a universal constant.
The accurate statement we teach our Full‑Service clients is this:
“The goal of comminution in gold mining is to maximize exposed gold surface area, but the percentage of gold physically liberated as free particles depends entirely on the ore type—ranging from near 0% (refractory) to over 90% (coarse free‑milling). Always verify your ore’s mineralogy before committing to a comminution and recovery circuit.”
Ready to start your own gold mine? Contact Start Your Own Gold Mine today for a site‑specific assessment. Whether you need our Basic package (training and setup) or Full‑Service package (licensed sites, equipment, and ongoing mentorship), we ensure you never rely on false assumptions—only on proven, data‑driven mineral processing.
From geological assessment to mercury‑free recovery—since 2012, we’ve been building sustainable miners, not just mines.
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