Hard Rock Gold Plant Guide: Choose the Right Process Flowsheet

A gold deposit represents a potential source of great value. But the path from raw rock to pure gold is a technical minefield. Choosing the wrong multi-million dollar processing plant is the fastest way to financial ruin. The most critical mistake is assuming a “standard” gold processing plant exists; it does not.

The correct gold processing flowsheet is determined entirely by an ore’s specific mineralogical characteristics. The choice between Gold gravity concentration, Gold flotation, or the CIL/CIP process depends on factors like gold particle size, its association with other minerals, and its response to leaching, as determined by comprehensive metallurgical testing.

Why Must Mineral Processing Tests Be Completed Before Planning an Investment?

Planning a hard rock gold processing plant without detailed metallurgical data is not a calculated risk; it is a guaranteed failure.

A mineral processing test is a small upfront investment that acts as the blueprint for an entire project. It diagnoses an ore’s unique properties to determine the most effective and profitable extraction method. Without this data, any approach amounts to guesswork, which can lead to catastrophic losses in the gold recovery rate and a failed investment.

This testing is analogous to a medical diagnosis before surgery. It will provide all the necessary information:

• Liberation Size: How fine must the rock be ground to free the gold? This determines the size of the crushing and grinding circuit.
• Gold Character: Is the gold coarse and free (“free milling gold“) or fine and locked in sulfides (“refractory ore“)?
• Recovery Methods: What percentage of gold can be recovered by gravity? By flotation? By cyanide leaching?
• Reagent Consumption: How much cyanide, lime, and other chemicals will the plant consume per ton? This is a major operating cost.
• Deleterious Elements: Are there “preg-robbing” carbon or copper minerals that will interfere with the process?

Building a plant without this information is like navigating a ship in a storm without a compass.

Solution 1: Why Should Gravity Concentration Be Prioritized for Ores with Coarse, Free-Milling Gold?

When an ore is generous enough to contain coarse, visible gold, the simplest path is often the most profitable.

For ores containing a significant amount of coarse, free milling gold, gold gravity concentration is the preferred method. It is a low-cost, chemical-free process that recovers gold based on its high density. This method can capture a large portion of the value early in the process, providing rapid cash flow and reducing the load on subsequent, more complex recovery stages.

The gravity circuit typically uses equipment like centrifugal concentrators and shaking tables. The key advantage is its efficiency and low operating cost. The operation is not just producing gold; it is producing low-cost gold. By recovering 40%, 50%, or even 60% of the gold before it ever sees a chemical, the size and cost of the rest of the plant are dramatically reduced. This is the ideal scenario for many vein-type gold deposits.

Solution 2: When Gold Is Tightly Associated with Sulfide Minerals, How Does Flotation Achieve Separation?

When the gold is invisible, locked inside other minerals like pyrite, chemistry comes into play.

When gold is finely disseminated within sulfide ores (like pyrite, arsenopyrite, chalcopyrite), gold flotation is the most effective separation technology. This process uses specific reagents in flotation machines to make the gold-bearing sulfide particles float to the surface, where they are collected as a concentrate. This separates the small volume of valuable minerals from the large volume of waste rock.

The goal of flotation is not to produce pure gold, but to produce a high-grade concentrate. For example, an ore with 5 grams per ton of gold can be turned into a concentrate with 50 grams per ton. This concentrate then becomes the feed for another process, such as cyanidation or smelting. Flotation is a powerful tool for upgrading low-grade, complex ores and is a cornerstone of processing in many of the world’s largest gold mines.

Solution 3: Which Difficult Gold Ores Does the CIL/CIP Cyanidation Process Primarily Solve?

This is the workhorse of the modern gold industry, designed to recover fine, liberated gold that gravity and flotation might miss.

The CIL/CIP process (Carbon-In-Leach / Carbon-In-Pulp) is the solution for recovering fine, disseminated gold that is not locked in sulfides. The process uses a weak cyanide solution to dissolve the gold into the slurry, and then uses activated carbon to adsorb the dissolved gold. It is highly effective for large-volume, low-grade oxide ores and gravity/flotation tailings.

In a CIL/CIP circuit, the ground ore slurry flows through a series of large, agitated tanks. Cyanide is added in the first tanks to dissolve the gold (leaching), and activated carbon is added to the tanks to collect it (adsorption). The loaded carbon is then removed, and the gold is stripped off in a separate process before being smelted into doré bars. This technology is what makes it possible to economically process many of the world’s large-scale gold deposits.

Why Are Combined Process Flowsheets like “Gravity + Cyanidation” More Common?

Most gold ores are not simple; they are a mix of different characteristics. Therefore, the most efficient plant is often a hybrid.

A combined process flowsheet is often the most profitable solution because it uses the most cost-effective method for each type of gold present in the ore. For example, a “Gravity + CIL” circuit uses low-cost gravity to recover coarse gold first, which reduces the gold load on the more expensive CIL circuit, making the overall plant smaller, cheaper, and more efficient.

This can be viewed as an optimization strategy. It is inefficient to use expensive cyanide to dissolve a piece of gold that can be easily and cheaply captured with a centrifugal concentrator. Removing the “easy gold” first improves the efficiency of the entire downstream process. The most common and successful combinations are Gravity + CIL (for free-milling ores) and Gravity + Flotation + CIL (for complex sulfide ores).

How Do Different Process Options Critically Differ in Cost, Opex, and Gold Recovery?

The choice of flowsheet has a direct and massive impact on a project’s financial model.

Gravity concentration has the lowest investment cost (CAPEX) and operating cost (OPEX). The CIL/CIP process has higher OPEX due to reagent consumption (cyanide, carbon). Gold flotation is intermediate. The ultimate gold recovery rate depends on choosing the correct process for the ore, with combined flowsheets often yielding the highest overall recovery.

Here is a general comparison to guide plant design:

Process Option	Investment Cost (CAPEX)	Operating Cost (OPEX)	Typical Gold Recovery
Gravity Only	Low	Very Low	Variable (depends on GRG)
Flotation Only	Medium	Medium	85-95% (into concentrate)
CIL / CIP Only	High	High	90-97% (for suitable ores)
Gravity + CIL	High	Medium-High	92-98% (often highest)
Refractory (Oxidation)	Very High	Very High	85-95% (for difficult ores)

What Core Stages and Equipment Does a Complete Hard Rock Gold Processing Plant Contain?

From a bird’s-eye view, all gold plants share a similar logical structure, regardless of the specific recovery method used.

A complete hard rock gold processing plant typically consists of four core stages: 1) A Crushing stage with jaw and cone crushers; 2) A Grinding stage using ball mills to create a fine slurry; 3) The Gold Beneficiation stage (Gravity, Flotation, or CIL); and 4) Tailings Management and Water Recirculation.

Each stage is a system of machines working together. The crushed ore is ground into a fine pulp, which then enters the specific recovery circuit designed for the ore. The barren rock, or tailings, is dewatered, and the water is recycled back into the plant to minimize environmental impact and reduce costs. As an EPC service provider, ZONEDING specializes in designing and supplying these complete, integrated solutions.

Conclusion

Choosing the right gold processing flowsheet is the most important decision in any mining venture. It’s a decision that must be driven by science, not by speculation. By investing in thorough metallurgical testing and partnering with experienced engineers, a hard rock gold processing plant can be designed that is perfectly matched to the ore, maximizing the recovery rate and ensuring the long-term profitability of the project.