Gold Panning

Gold is about nineteen times as dense as water and roughly seven times as dense as the quartz sand it sits among. That single number is the whole method: agitate a pan of gravel under water and everything sorts itself by density, with the gold working relentlessly downward through the lighter material until it lies against the bottom. Then wash the light material away over the lip, a little at a time, and whatever refuses to leave is what you came for. No reagent, no heat, no machinery — the separation is done by gravity and patience. The same principle scales up to the sluice box, the rocker and the industrial jig, and it is the oldest mineral processing technique there is.

初学者

1 hour

说明

Prove density does the sorting

Use lead shot or steel nuts as a stand-in for gold — you are testing the physics, not prospecting.

Mix a few dense pieces into a pan of sand and gravel.
Submerge and shake the pan side to side.
Stop and dig down to find where the dense pieces went.

They are at the bottom, every time, however you started. Shaking briefly liquefies the mixture so particles can move past one another, and in that moment density decides who goes down. This is why the shaking matters more than the washing.

此步骤所需材料：

Gold Pan1 个

Classifier Sieve1 个

Classify before you pan

Remove what you already know is worthless.

Screen the material to remove everything above about 6 mm.
Check the oversize pieces briefly and discard them.
Pan only the fines.

Large stones take up pan volume, trap fine material underneath and make the shaking less effective. Classifying is not tidiness — a classified pan holds several times more of the material that might actually contain gold.

此步骤所需材料：

60-Mesh Sieve1 个

Shake, then wash — in that order, repeatedly

The cycle is always settle first, remove second.

Submerge, shake side to side to settle the heavies.
Tilt and let the top layer wash over the lip.
Level the pan, submerge, and shake AGAIN before removing more.

The commonest beginner's error is continuous washing without re-settling. Every time you tilt and pour you disturb the layering, so the heavies must be driven back down before the next wash — otherwise you pour your gold over the edge with the sand.

Deal with the black sand

What remains at the end is not gold — it is mostly magnetite and other heavy minerals.

Reduce to a spoonful of dark concentrate.
Draw a magnet across it, in a bag, to lift the magnetite out.
Examine what is left in good light.

Gold stays bright in shadow and does not glitter or flash as you move it; pyrite — fool's gold — flashes and goes dull from other angles, and mica floats away as flakes. Gold is also malleable, so a genuine grain flattens under a pin instead of shattering.

此步骤所需材料：

Bar Magnet Set1 套

Convex Lens1 个

History and context

Panning is prehistoric and essentially unchanged. The golden fleece of Greek legend is usually explained as a sheepskin pegged in a stream to catch fine gold — the wool's fibres trapping particles exactly as the riffles in a sluice do — and the technique is documented in the Caucasus.

Where the gold is follows from the same density argument. Flowing water carries light sediment further than heavy, so gold drops out wherever the current slows: on the inside of bends, behind boulders, in bedrock cracks, at the downstream end of gravel bars. A prospector reads a stream for places where the water gives up, and that is the actual skill.

The gold rushes were brief and the panning phase briefest. California in 1849, Victoria in 1851, the Klondike in 1897 — in each case individual panning gave way within a few years to sluicing, then hydraulic mining that blasted whole hillsides into rivers, then corporate dredging and hard-rock mining. Very few of the individuals who arrived first got rich; the people who consistently made money sold them shovels.

The environmental legacy is severe and still present. Hydraulic mining in California moved so much sediment that it buried farmland and choked rivers, and it was eventually enjoined by the courts in 1884 — an early and important environmental judgment. Worse, mercury was used to amalgamate fine gold in both California and Latin America, and that mercury is still in the sediment, still methylating into fish, more than a century later. Artisanal gold mining remains today the largest single source of mercury pollution worldwide.