Placer Gold: The Ultimate Guide to Formation, Types & Mining

Placer gold mining is a business of efficiently moving huge volumes of dirt to liberate a tiny fraction of value. Success depends on understanding the geology, using the right placer gold equipment, and focusing on your cost per ton.

This is not a guide about finding a few flakes of gold. This is a guide to understanding the business of moving massive volumes of worthless dirt to liberate the tiny fraction of value within. This guide covers everything from placer gold exploration to designing an efficient gold washing plant.

What is placer gold, and why is it easier to mine than lode gold?

Placer gold is native gold that has been eroded from a lode deposit and concentrated in a new location by gravity and water. It is easier to mine because it is in loose sand and gravel, requiring no blasting or crushing.

Mining lode gold from a Hard Rock Gold Processing Plant means drilling, blasting, and using massive crushers and Ball Mills. The gold is locked inside solid rock. Placer gold processing is much simpler. The gold is already free, mixed in with loose material. Your job is not to break rocks; it is to separate the heavy gold from the light sand. This means lower capital costs and a much simpler process.

How does gold actually form in rivers, valleys, and beaches?

The formation of a placer deposit is a lesson in patience and physics. It is a process that takes millions of years, and a river acts like a giant, lazy sluice box.

Gold is freed from lode deposits by weathering. Rain and rivers transport it downstream. Because gold is extremely dense, it drops out of the current wherever the water slows down, concentrating in “pay streaks.”

This is the single most important fact in all of placer mining: gold is incredibly dense (19.3 g/cm³), while common rock like quartz is light (2.7 g/cm³). As a river tumbles everything downstream, it sorts materials by weight. The light sand and gravel keep moving, but the heavy gold sinks.

Where Does Gold Settle?

• On the inside bend of a river, where the current is slowest.
• Behind large boulders or natural rock outcroppings.
• Where a fast-moving tributary enters a slower, larger river.
• Most importantly, wherever the river hits bedrock. Gold will sink until it can sink no further, getting trapped in cracks and crevices. This layer of gravel sitting directly on bedrock is the pay streak.

How Can You Judge an Area’s Placer Gold Potential?

Finding gold isn’t about luck; it’s about reading the landscape and understanding where gold is likely to be trapped.

Look for places where water slows down:

• Inside Bends: The water on the inside of a river curve moves slower, dropping heavy materials.
• Behind Obstacles: Large boulders, rock outcrops, or even fallen trees create low-energy zones behind them where gold can settle.
• Confluence Points: Where a fast-moving stream enters a larger, slower river, the sudden drop in velocity causes gold to deposit.
• Bedrock: Gold will sink through gravel until it hits an impassable layer, like solid bedrock or a dense clay layer. Cracks, crevices, and depressions in the bedrock are natural gold traps.

A key indicator is the presence of “black sand.” This is a concentration of other heavy minerals like magnetite and hematite. Since they are also dense (though not as dense as gold), they accumulate in the same places. If you find lines of black sand, you are in the right type of environment for placer gold exploration.

What Are the Main Types of Placer Gold Deposits?

Not all placer deposits are the same. From a miner’s perspective, each type presents a different business opportunity and a unique set of challenges.

Deposit Type	Description	Miner’s Perspective & Challenge
Alluvial (Stream) Placers	Gold found in the gravel of existing or ancient rivers.	Bread and butter of the industry. The main challenge is the “overburden”—the worthless gravel you must move to reach the pay streak on the bedrock. Your profit depends on moving this overburden cheaply.
Bench Placers	Ancient riverbeds left as terraces high up on a valley side after the river cut a new, deeper channel.	High potential, but high cost. The gold is often far from a water source. The main challenge is logistics: you must either pump massive amounts of water up to the deposit or haul tons of gravel down to the water.
Eluvial Placers	Gold that has weathered from a lode but only moved a short distance downhill, not yet in a river.	A prospecting clue, not a production target. The gold is often angular and close to its source. The challenge is that it’s usually dispersed over a wide area, making it difficult to mine economically.
Beach Placers	Fine gold concentrated by wave action on a beach, often in lines of black sand.	A specialized game. The deposit is constantly moving with tides and storms. It requires equipment specifically designed for fine gold recovery, and operations must be mobile.

What Basic Tools Do You Need for Small-Scale Exploration?

Before you invest in a full plant, you must test the ground. This initial gold panning and prospecting phase is essential for verifying the value of a deposit.

• Gold Pan: The most fundamental tool. Used to separate a few handfuls of material to see if any gold is present.
• Sluice Box: A long channel with riffles on the bottom. It allows you to process much more material than a pan. You shovel gravel into the top, and water washes the lighter material away while the riffles trap the heavy gold.
• Shovel and Buckets: For digging and moving material to your sluice box.

These tools are for prospecting, not production. Their purpose is to collect samples and determine the average grade of the pay dirt.

What Core Equipment is in a Small to Medium Placer Gold Plant?

Once you have proven a deposit, it is time to scale up. A commercial placer gold processing plant is designed for one thing: volume. The typical process flow uses gravity separation at every stage.

1. Feeding & Scrubbing: An excavator or front-end loader dumps gold-bearing gravel into a hopper. From there, it enters a Trommel Screen. This is a large rotating drum with a spray bar inside. It tumbles and washes the gravel, breaking up any clay and ensuring all the gold is liberated.
2. Sizing (Classification): The trommel screen has different-sized holes along its length. It separates the large, worthless rocks from the smaller, gold-bearing sand and gravel.
3. Primary Concentration: The smaller material is then fed into primary recovery equipment. For most operations, this means large Sluice Boxes. For deposits with finer gold, a Jigging Separator Machine may be used for better recovery.
4. Final Concentration: The material collected from the sluices or jigs (the “concentrate”) is then processed on a Shaking Table. This machine uses a combination of vibration and water flow to separate the gold from the remaining heavy minerals, producing a very high-purity gold concentrate.

This combination of robust, high-volume equipment forms the core of a modern Gold Processing Plant.

What Other Factors Severely Impact Profitability?

You can have the richest ground in the world and still go bankrupt. Success in placer gold mining comes from avoiding two cardinal sins.

The Sin of Ignoring Volume: Your profit is NOT determined by the grams-per-ton in your best pay streak. It is determined by the average grade of all material you process, multiplied by your processing volume, minus your total operating cost. A successful operation is a dirt-moving business first and a gold business second. Focus on your cost-per-ton to move material.

The Sin of Chasing Fine Gold: Many operators become obsessed with recovering 100% of the gold, especially the microscopic “flour gold.” The reality is that 80-95% of the value is often in the larger gold particles that are easily caught. Chasing that last 5% can double your equipment cost and halve your processing volume. You will go broke “efficiently.”

Focus on a simple, robust plant that maximizes tonnage. Move the dirt, bank the profitable gold, and don’t cry over the dust.

For large-scale commercial mining, how do you design an efficient gold washing and processing line?

Large-scale mining is a dirt-moving business. Efficiency and volume are everything. The plant must be designed to process hundreds of tons per hour with minimal downtime.

A large-scale gold washing plant is built for high throughput and recovery of a wide range of gold sizes. It often includes a trommel, multiple recovery stages with jigs and sluices, and a final concentrate circuit with Centrifugal Concentrators and shaking tables.

The placer gold processing flowsheet is optimized for the specific deposit.

The High-Volume Production Line

• Heavy-Duty Feed System: A large hopper and apron feeder to handle continuous feeding from multiple large excavators or trucks.
• Primary Scrubbing & Sizing: A very large and robust trommel or scrubbing drum is used to break down any clay and ensure all gold is liberated.
• Multi-Stage Recovery: Instead of just a sluice, large plants often use Jig separators first to recover coarse nuggets. The finer material then flows to sluices. This is more efficient for deposits with a mix of gold sizes.
• Fine Gold Circuit: To capture the fine “flour gold” that sluices might miss, a portion of the tailings is often fed to Centrifugal Concentrators. These machines use high G-forces to recover microscopic gold.
• Water Management: Large plants require massive amounts of water. Efficient water recycling systems with settling ponds and thickeners are essential for environmental compliance and cost control.

Besides equipment, what other factors seriously impact gold recovery and profit?

You can have the richest ground and the best equipment in the world and still go bankrupt. Placer mining is an operational challenge. Success is in the details.

The most critical factors are the percentage of clay in the feed, water availability and management, and the efficiency of your material handling. Overlooking any of these can crush your recovery rates and profitability.

It is the things around the equipment that often determine success.

The Profit Killers

1. Clay Content: Sticky clay is the enemy. It can roll through your trommel in big, barren balls, taking gold with it to the tailings pile. A plant must have enough washing energy (high-pressure spray bars, scrubbers) to completely break down clay.
2. Water Volume: Water is the lifeblood of gravity separation. Too little water, and your sluices will clog up. Too much, and you will blast fine gold right out the end. You need the right volume at the right pressure, consistently.
3. Material Handling: Your profit is made by moving dirt. The layout of your mine, the cycle time of your excavator, and the efficiency of your feed system determine your throughput. A poorly planned site can easily halve your production.

How is the gold concentrate from the wash plant finally refined into gold bars?

After all that work, you do not have a gold bar. You have a bucket of heavy mineral concentrate with gold in it. The final step is to separate the gold from this last bit of sand.

The gold concentrate is first upgraded on a shaking table to remove the last of the black sand. The nearly pure gold is then dried and melted in a furnace with flux to remove any remaining impurities, before being poured into a mold to create a gold bar.

This is the final, satisfying step in the process.

The Final Cleanup

1. Final Concentration: The raw concentrate from the sluices is carefully run over a shaking table. This separates the material into three distinct bands: gold (heaviest), a mix of middlings, and black sand tailings (lightest).
2. Amalgamation or Direct Smelting: For fine gold, mercury was historically used to form an amalgam, though this is now heavily regulated due to environmental concerns. The modern and safer method is direct smelting.
3. Smelting: The clean gold is placed in a crucible with a flux mixture (like borax and soda ash). It is heated in a furnace to over 1,064°C (1,948°F). The gold melts, and the flux captures the last impurities, forming a glassy layer called slag on top.
4. The Pour: The molten gold is then poured into a mold, leaving the slag behind. Once it cools, you have a solid gold bar, or dore bar, ready for the refinery.

About ZONEDING

Since 2004, ZONEDING has engineered and manufactured complete solutions for the mining industry. We specialize in designing and building robust, high-efficiency Placer Gold Mining plants. We understand that profitability comes from moving volume reliably. Our factory-direct model allows us to provide custom-designed trommels, jigs, shaking tables, and complete wash plants that are built for the harsh realities of the field. We have delivered profitable solutions to miners in over 120 countries.

If you are evaluating a placer gold project, contact us. Let our engineers help you design a plant that is built for one purpose: to make you money.