Many African mine owners confuse placer gold and hard rock gold processing. These two gold deposits have totally different ore properties, processing flows, equipment investment and gold recovery performance. Choosing wrong process will lead to low gold recovery and wasted capital. This article compares the complete workflow from raw ore feeding to final gold concentrate.
1. Basic Difference Between Placer Gold & Hard Rock Gold
| Item | Placer Gold (Alluvial Gold) | Hard Rock Gold (Lode Gold) |
|---|---|---|
| Gold Occurrence | Free gold particles separated from rock, mixed with sand, gravel, clay | Gold locked inside rock, combined with quartz, pyrite or other sulfide minerals |
| Grain Size | Coarse gold, fine gold, flour gold; no crystal binding | Fine disseminated gold, must liberate by crushing & grinding |
| Main Separation Principle | Gravity separation | Crushing + grinding + gravity / flotation / CIL leaching |
| Water Requirement | High water demand for washing clay and sluicing | Water for grinding and slurry transportation |
| Typical Recovery Rate | 75% ~ 92% (gravity separation) | 80% ~ 95% (comprehensive process) |
2. Full Processing Flow of Placer Gold (Raw Ore → Gold Concentrate)
- Raw Ore Feeding & Scalping: Loader feeds alluvial ore into hopper, remove big rock debris.
- Clay Washing & Screening: Trommel screen / vibrating gold wash plant breaks clay balls, wash out slime, separate gravel. Critical step for high-clay placer ore.
- Gravity Pre-concentration: Sluice box, jig machine capture coarse gold. Fine gold enters centrifugal gold concentrator.
- Concentration Cleaning: Gold rough concentrate goes to shaking table for further upgrading.
- Final Gold Concentrate: High-grade gold concentrate collected for smelting.
Core equipment for placer gold: Trommel screen, vibrating gold wash plant, centrifugal gold concentrator, sluice box, shaking table. Low investment, fast setup, suitable for mobile mine site.
3. Full Processing Flow of Hard Rock Gold (Raw Ore → Gold Concentrate)
- Primary Crushing: Jaw crusher breaks big rock into 20~50mm particle size.
- Secondary Crushing: Cone / impact crusher reduce rock to 5~10mm.
- Grinding & Liberation: Ball mill grind crushed ore into fine slurry. This step unlock gold wrapped inside rock matrix.
- Separation Stage: Gravity separation for free gold; flotation for sulfide associated gold; CIL for low-grade oxide ore.
- Concentrate Dewatering: Concentrate filter press removes water, get dry gold concentrate.
Core equipment for hard rock gold: Jaw crusher, cone crusher, ball mill, classifier, flotation cell, CIL leaching tank, filter press. Higher CAPEX, longer construction cycle, stable long-term production.
4. How to Choose the Right Process for Your Mine
- If your ore is river sand, alluvial sediment with lots of clay and gravel: Placer gold gravity wash plant is recommended.
- If ore is solid quartz rock with gold embedded inside: Hard rock crushing + grinding circuit is mandatory. Gravity only cannot unlock locked gold.
- Small-scale mine with limited budget & short mining life: Placer mobile wash plant is preferred.
- Large reserve, long-life mine: Hard rock processing line brings stable long-term gold output.
FAQ
Q1: Can I use placer gold wash plant for hard rock gold?
A: No. Without crushing and ball milling, gold remains locked inside rock. Gravity washing will get almost no gold recovery.
Q2: Which one has lower operating cost?
A: Placer gold processing normally has lower OPEX, no grinding media consumption. Hard rock mines have high ball mill liner and steel ball wear cost.
Q3: What if my mine has mixed placer and hard rock ore?
A: Build two separated processing circuits or pre-screen to split sand-gravel fraction and rock fraction, process them separately.
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