What Is Placer Gold?
Quick answer
Placer gold is loose gold that weathering has freed from its source rock and water has carried into sand and gravel, mostly in streams. It is the flakes, specks and nuggets that panners find, and it can be recovered with water and gravity alone.
If you have ever seen a flake of gold in a pan, you have seen placer gold. It is the kind of gold hobby panners go after, and the kind that started the great gold rushes. This guide explains what placer gold is, how it forms, the different kinds of placer deposits, where the gold settles, what it looks like and how people recover it.
What is placer gold?
Placer gold is gold that has been worn out of the rock it formed in and dropped somewhere in loose sediment, usually the sand and gravel of a stream. The word "placer" covers any valuable mineral collected this way, but gold is the one most people mean.
The U.S. Geological Survey explains in its booklet on gold that placer deposits are gold that erosion has taken out of lode deposits and gathered together somewhere else. In other words, every placer started out as part of a vein in solid rock.
How do you pronounce placer?
It rhymes with "passer". Washington's Department of Natural Resources spells it out as "plasser" in its recreational panning sheet. The California Geological Survey says the word probably came from early Spanish miners in the Americas, who used it for gold in stream sand and gravel. Its first meaning was something like a sand bank, or a place in a stream where gold had dropped.
What is the difference between placer gold and lode gold?
Lode gold is still in the rock where it formed. Placer gold has left it. The Utah Geological Survey describes lode gold as gold laid down inside rock by gold-bearing fluids, and placer gold as what is left when that rock wears away and the free gold collects in stream beds. Geologists sometimes call lode deposits primary and placers secondary for the same reason.
The difference matters in practice. Washington's state geologists point out that lode gold takes blasting, milling or chemical treatment to get out, while placer gold can be recovered with simple gravity tools. It even matters in law. The Bureau of Land Management treats them as different kinds of mining claims: lode claims cover veins with clear boundaries, and placer claims cover the other deposits, such as gold in gravel.
How does placer gold form?
Slowly, over a very long time. The California Geological Survey tells the story using the gold James Marshall found at Sutter's Mill in 1848, and it shows the steps clearly:
- Gold forms in veins. Miles underground, gold-bearing fluids left gold in quartz veins. California's Mother Lode belt formed about 140 to 150 million years ago.
- The rock wears away. Over a very long time the land rose and eroded, bringing the veins to the surface. Weathering and erosion broke the gold free.
- Water carries the gold. Streams and rivers picked up the loose gold and carried it downstream.
- The gold collects. Because gold is so heavy, it dropped out wherever the water slowed and gathered in good spots along the streams. Those gatherings are placer deposits.
Placers can also be buried and uncovered again. The same survey describes how, between about 33 and 4 million years ago, volcanic eruptions buried California's old gold-bearing river channels under lava and ash. Later rivers cut down through it all and made new placers, including the one Marshall found on the South Fork of the American River. The survey also says most of that gold probably came from the Mother Lode belt, a strip about half a mile to a mile wide and some 120 miles long that the river crosses a few miles upstream of the mill. These ages are for California's Sierra Nevada only, so other gold country has its own timeline.
Why does gold last long enough to form placers?
Because it is heavy and it does not break down. Gold does not rust or tarnish, so it survives a long trip down a river when other minerals wear away or dissolve. California's state geologists name that mix of weight and resistance to corrosion as what makes gold such a good fit for placer deposits.
What are the different kinds of placer deposits?
Stream placers are by far the most common, but official sources describe several others.
Stream placers
Gold in the sand and gravel of a creek or river bed. This is where nearly all recreational panning happens.
Bench placers
As rivers cut deeper, they can leave old gravel stranded above the present valley floor. The U.S. Forest Service calls these bench placers. They often sit in banks and hillsides, and many land managers do not allow digging there, so check the rules first.
Beach placers
The USGS notes that some ocean beach sands have produced gold. Washington's placer map even lists a few Pacific beaches, though the state is careful to say that being on the map does not mean an area is open to panning.
Residual placers
Gold that never traveled far. As the rock around a vein breaks down where it stands into a soft, rotten layer, the gold is left behind close to its source.
Desert placers
In dry country, gold collects along washes that only run after storms. With little water to work with, prospectors there use dry methods such as dry washers.
Buried channels
Old river channels covered by later rock, like the ones under California's volcanic layers described above. The USGS calls these fossil placers.
Where does placer gold settle in a stream?
On or near bedrock, and wherever the current slows. During floods the whole streambed moves, and gold sinks down through it until it reaches bedrock or a hard clay layer. Fine gold also gathers in hollows and on gravel bars where the water slackens. A band of gravel rich enough in gold to be worth working is called a pay streak. Our guide on where to find gold in a river shows how to read a creek for these spots.
Gold also keeps company with black sand. Many heavy minerals are dark, and Washington's state geologists note that they settle into the same cracks and hollows as gold. That is why a dark streak in your pan is a good sign you are keeping the heavy material. Our page What Is Black Sand? explains what it is made of.
What does placer gold look like?
Its shape tells you how far it has traveled. The Forest Service and BLM explain that rough, chunky gold is close to where it came from, flat and smooth gold has come a long way, and the finest flour gold has been hammered so thin it can float. Most placer gold is flakes and specks, not nuggets. Our guide What Do Gold Flakes Look Like? covers color, shape and size in detail.
How pure is placer gold?
Never completely pure. Natural gold always carries some silver and other metals. The USGS measures this as fineness, the parts of gold in every thousand, so a piece that is 885 parts gold is called 885 fine. In one older USGS study of more than 1,500 samples of Alaska placer gold, fineness ran from a little under 565 to more than 970.
How is placer gold recovered?
With water and gravity. Because gold is so much heavier than sand and gravel, the USGS lists the gold pan, the rocker and the sluice box as the tools that do the job. You shake or wash the gravel, the gold sinks, and the light material washes away. Our sluice box guide explains the step up from a pan.
Whichever tool you use, you finish with a small pile of black sand to sort through. A black sand magnet lifts out the magnetite, the magnetic part of it, and in a normal pan it pulls up all the black sand we see. A magnet does not pull gold, but a tiny flake can ride along stuck to a grain of magnetite, so check what you lift. Then a quick final pan leaves the gold.
Where is placer gold found in the United States?
Today most placer mining in the country happens in Alaska and the western states, according to the USGS, though the East has placer gold too. North Carolina's Reed Gold Mine, the site of the first documented gold find in the country, started as creek mining for placer gold. Underground mining only followed in 1825, once people learned the gold also ran in veins.
