What Is an Oxidized Gold Mine? Full Equipment List Included

Let’s be blunt: “Oxidized gold ore” is one of the most dangerously simplistic terms in mining. A rookie hears “oxidized” and thinks “easy gold, cheap to process.” A veteran hears “oxidized” and asks, “How much clay? And more importantly, what kind of clay?”

The answer to that second question dictates everything. Your entire oxidized gold ore processing flowsheet, your capital cost, and whether you make money hinges on it. This guide will walk you through the process, focusing on selecting the right gold processing equipment by first understanding your ore.

First, What Is Oxidized Gold Ore and Why Is It Different?

An oxidized gold ore is a type of ore where the original sulfide minerals have been broken down by weathering (exposure to air and water). This is good news and bad news.

• The Good: The gold is often “free-milling,” meaning it’s not locked inside sulfide minerals like pyrite. This makes it easily accessible to cyanide solutions. The chemistry of gold cyanidation is simple and has been used for over a century.
• The Bad: The weathering process creates a lot of fine particles and, critically, clays. This turns the project into a materials handling nightmare. An oxidized gold mine is a mud-moving operation that happens to have gold in it.

The hard part isn’t dissolving the gold; it’s physically moving sticky, variable material through a plant without it grinding to a halt. Your equipment choice is a strategy to defeat the mud.

Before Processing, What Key Ore Characteristics Must You Know?

Before you buy a single piece of gold processing equipment, you need a detailed metallurgical report. This is non-negotiable. It must tell you:

1. Gold Grade (g/t): This determines the economic viability. Is there enough gold to justify the cost of extraction?
2. Clay Content & Type: This is the most important physical property. How much clay is there? Is it a manageable kaolinite, or a swelling clay like montmorillonite that turns to impassable slime when wet? The clay type will determine your entire processing path.
3. Particle Size & Liberation: How fine is the gold? Do you need to grind the ore to expose it, or is it coarse enough to be liberated by simple crushing?

These three factors will point you down one of two strategic paths.

The Two Paths: The Fork in the Road for Every Oxidized Ore Project

Your entire plant design will follow one of two strategies, dictated by your ore.

• Path 1: The Heap Leach Route (“The Finesse Game”)
  • Best For: Low-grade ores (< 1.5 g/t) with good rock structure and manageable clay content.
  • Philosophy: Low cost, high volume. Preserve the ore’s natural permeability at all costs. Do not create extra fines.
• Path 2: The Mill-Leach (CIL/CIP) Route (“The Brute Force Solution”)
  • Best For: Higher-grade ores (> 1.5 g/t), ores with very high or swelling clay content, or ores with very fine gold that needs grinding.
  • Philosophy: High cost, high recovery. Obliterate the ore’s natural structure and turn it into a uniform slurry (pulp) that you can completely control.

Crushing Stage: Which Crusher Handles Oxidized Gold Ore?

The goal of crushing depends entirely on which path you take.

For the Heap Leach Path:

Your goal is to create a crushed product with minimal fines. The key equipment includes:

• Vibrating Grizzly Feeder & Scalping Screen: This is your first and most important tool. It removes the naturally fine, clay-rich material before the crusher. Why waste money crushing dirt that is already small?
• Jaw Crusher (Primary): A standard, robust primary crusher for initial size reduction.
• Cone Crusher (Secondary/Tertiary): Used for finer crushing. You run it carefully to crack the rock, not pulverize it. This means avoiding aggressive choke-feeding to minimize the creation of new fines.

For the CIL/CIP Path:

Your goal is simply size reduction for the mill. Fines are not a concern.

• Jaw Crusher & Cone Crusher: A standard, robust two or three-stage crushing circuit is perfectly fine here. The mission is simply to get the rock small enough for the grinding mill to handle efficiently, reducing wear and tear on your mill liners and media.

Grinding Stage: Does Oxidized Ore Need Special Ball Mills?

This is a trick question. The “grinding” stage is fundamentally different for each path.

For the Heap Leach Path: Agglomeration, Not Grinding

You do not grind the ore. Instead, you agglomerate it to improve permeability. Key equipment includes:

• Agglomeration Drum: This is the heart of a successful heap leach operation for clay-rich ores. It’s a large rotating drum where crushed ore is gently tumbled with a binder (like cement and/or lime) and a small amount of cyanide solution. This process rolls the fine clay particles onto larger rock fragments, creating durable, porous pellets.
• Belt Conveyors & Stacker: A system of conveyors is used to gently transport the agglomerated ore and stack it on the leach pad without breaking the pellets.

For the CIL/CIP Path: Turning Rock into Slurry

Here, grinding is essential for liberation.

• SAG Mill / Ball Mills: This is your primary weapon. A Semi-Autogenous (SAG) mill is often preferred for sticky, clay-rich ores. A Ball Mill then takes over to grind the material down to a target size (e.g., 80% passing 75 microns).
• Hydrocyclone or Spiral Classifier: This unit works in a closed circuit with the ball mill. It separates the ground slurry, sending correctly sized particles to the leach circuit and returning oversized particles to the mill for more grinding. This ensures an optimal particle size for gold liberation.

Leaching Stage: Choosing Heap Leach, CIL, or CIP Equipment?

This is the core of your Gold Processing Plant where the gold is dissolved.

For the Heap Leach Path:

The “equipment” is a large-scale civil engineering project.

• Heap Leach Pad System: A massive, engineered area with an impermeable liner to contain the cyanide solution.
• Drip Irrigation System: A network of pipes and drippers that slowly and evenly applies the dilute cyanide solution over the entire surface of the heap.
• Pregnant & Barren Solution Ponds: Large ponds to collect the gold-rich “pregnant” solution coming off the heap and to store the “barren” solution after the gold has been removed, ready to be reused.

For the CIL/CIP Path:

This is where the CIL process takes place in a series of controlled tanks.

• High Efficiency Concentrator (Thickener): This is a multi-million-dollar decision. A thickener removes excess water to reach the optimal leach density (~50% solids). Clayey ores settle very poorly, requiring a much larger, more expensive thickener and significant amounts of chemical flocculant.
• Leaching Agitation Tanks: A train of large, agitated tanks where slurry, cyanide, and activated carbon are mixed.
• Carbon Screens & Pumps: Inter-tank screens prevent the coarse activated carbon from leaving each tank. Carbon pumps or airlifters move the carbon counter-current to the slurry flow. These are weak points, as fine clays can easily blind the screens.

Gold Recovery: What Equipment Extracts Gold from Carbon?

Once the gold is loaded onto the activated carbon, the recovery process, often called the elution circuit, is similar for both paths.

• Acid Wash Column: The loaded carbon is first washed with acid to remove inorganic contaminants.
• Desorption & Electrowinning System: This is the final step. The carbon is moved into a stripping vessel where a hot caustic-cyanide solution strips the gold back off the carbon. This now-rich solution is pumped to electrowinning cells, where an electric current causes the pure gold to plate out onto cathodes.
• Smelting Furnace: The recovered gold sludge is then melted in a high-temperature furnace and poured into doré bars, which are a semi-pure alloy of gold and silver.

How Do You Configure a Full Oxidized Gold Plant?

The answer always starts with your ore report. That report will tell you which path to take.

Feature	Path 1: Heap Leach Flowsheet	Path 2: CIL/CIP Flowsheet
Ore Type	Low-grade, good permeability, manageable clay	High-grade, high/swelling clay, fine gold
Crushing	Jaw Crusher + Cone Crusher (focused on minimizing fines)	Jaw Crusher + Cone Crusher (standard operation)
“Grinding”	Agglomeration Drum & Stacking System	SAG Mill / Ball Mill & Cyclone Circuit
Pre-Leach	(None)	High-Capacity Thickener
Leaching	Heap Leach Pad & Drip/Pond System	Leaching Agitation Tanks with carbon circuit
Gold Recovery	Desorption & Electrowinning + Smelting	Desorption & Electrowinning + Smelting
Result	Lower capital cost, lower recovery (60-80%)	Higher capital cost, higher recovery (90-97%)

Trying to force a high-clay ore down the heap leach path to save money is a recipe for disaster. You won’t build a mine; you’ll build a very large, very expensive mud pie.

Frequently Asked Questions

1. What is the biggest challenge in oxidized gold ore processing?
The biggest challenge is not the gold chemistry; it’s managing the physical properties of the ore, specifically the content and type of clay. High clay content can cause major material handling problems, blind screens in CIL circuits, and completely block solution flow in heap leaching, making it the single most important factor in choosing the correct processing route and equipment.

2. Should I choose Heap Leaching or a CIL process for my oxidized gold ore?
The choice depends entirely on your ore’s characteristics found in a metallurgical test report. Heap Leaching is a low-cost option for low-grade ores with good permeability and low-to-moderate clay content. A Gold CIL Plant is a more expensive but robust solution for high-grade ores, ores with high or swelling clay content, or ores that require fine grinding to liberate the gold.

3. What is an agglomeration drum and why is it important for heap leaching?
An agglomeration drum is a rotating drum that mixes crushed ore with a binder (like cement or lime) and a small amount of cyanide solution. It rolls the fine particles onto larger ones, creating durable, porous pellets. This is critical for heap leaching because it prevents fine clay particles from turning to mud and blocking the flow of the cyanide solution through the heap, ensuring good permeability and gold recovery.

4. Can gravity separation be used for oxidized gold ores?
Yes, and it is often highly recommended. If the ore contains even a small amount of coarse, free gold, using gravity separation equipment like a Centrifugal Concentrator before the leaching circuit can recover a significant portion of the gold very early and at a very low cost. This reduces the load on the CIL or heap leach process and improves overall plant efficiency.

5. What are the main factors affecting the cost of an oxidized gold processing plant?
The main cost drivers are: 1) Throughput (tons per day), which dictates the size of all equipment. 2) Ore Characteristics, as high clay content requires larger, more expensive thickeners and higher reagent consumption. 3) The Chosen Process, with heap leaching having lower initial capital cost (Capex) and CIL plants having higher Capex but often better recovery rates.

About ZONEDING

At ZONEDING, we are more than just an equipment manufacturer; we are process solution experts. Since 2004, we have provided robust gold processing equipment for projects worldwide. More importantly, we help our clients choose the right equipment. Our services include complete metallurgical testing, process design, and engineering for your entire oxidized gold ore processing plant. We understand the challenges of clay and will help you choose the correct path for a profitable operation.

Contact our engineers today to discuss your ore report and begin designing a plant that is built for your specific needs.