Friday Fractal X

When you peer into a fractal, you're seeing the edge of chaos. If you sift through enough Julia or Mandelbrot sets, you might catch a hint of fractal fever. When you find that point, where order is filtered out of randomness, and glimpse a familiar pattern, you might feel tempted to shout "Eureka!" That triumphant feeling is, of course, much older than the computers that generate fractals. We've been seeking precious patterns for centuries. Compare this fractal image, taken from a section of a Julia set colored with fractal Brownian motion...

...with a much older sorting method:

Panning for gold. As sediments are shaken in a gold pan, they begin to separate. Denser minerals, such as flakes of gold and grains of magnetic iron sand, sink in the center of the pan, while lighter minerals are washed to the edge.

Since we're in the midst of a series about development in Colorado, the Friday Fractal seemed like the perfect time to talk about gold, which I mentioned only briefly yesterday. Read on to learn how to pan your own gold--in your own backyard. But first, we need to understand the importance of gold in Colorado history. To do this, we need to turn back the clock not just 150, but millions of years. Over these vast periods of time, amounts of sand and clay have collected as compressed layers.
The deeper the layers, the more the heat and pressure they face. Add in a few sliding continental plates, pushing things here and there, and things are bound to act up. As one plate slides beneath another, into the fiery depths, those serene layers begin to buckle and bend, leaving new cracks and crevices behind. The molten lava is pushed up into these cracks, which branch and stretch towards the surface.

As the lava cools, no longer so close to the oven, various minerals begin to crystallize. Eventually, lava turns to rock, but not just any rock. Some of the veins have crystallized into precious minerals, including gold. The gold sometimes forms in thick nuggets, but more often as small inclusions in between other minerals. These veins are buried within the bulging rock, which have been pushed miles into the sky. Over time, gravity and weather take their toll on the new mountains. Water collects, as creeks cutting through canyons, and glaciers gutting the tall, frozen peaks. The mountains begin to wear down; crystal veins and sedimentary bedrock alike begin to crumble into boulders, cobbles, sand and clay. When the minerals separate, the flakes of gold are loosened and washed downstream with other sediments.

So, the first settlers in Colorado were enchanted by the mountain views. But the same processes that made the spectacular beauty also hid their shiny, golden secrets. When homesteaders looked for the right places to build their cabins, they eyed the fertile creek sides. It was only a matter of time before they realized what they had. All it took was Lewis Ralston, glimpsing that flash of gold in the water, back in 1850, for history to be born. The real gold rush in Colorado wouldn't begin for another 10 years, when prospectors tracked down the headwaters of Clear Creek and began to mine in earnest. Before they brought pick-axes, however, they brought pans.

Panning for gold is known under the more technical term, "placer mining." Placer was originally a Spanish word meaning "sand bank." While placer mining refers to any type of mining process that doesn't involve tunneling, the most common method is panning. Since gold is denser than the surrounding sediment, mostly lighter, silica or carbon based minerals, it tends to sink while other minerals are washed away. This is the basis not only for panning, but for large scale placer mines, where water and sediment are run through ditches and sluice boxes, filtering out the gold. The first ditches in Colorado were dug for this purpose, only later to be used for irrigation by ranchers and farmers.

Placer mining has become a bit more sophisticated over the years. Even before the turn of the 20th century, there were concerns about the impact of placer mining on the environment. If sluice boxes empty directly back into the river or creek, they tend to drop large amounts of silt, sand and sludge along with the excess water. In order to keep the water clear, placer miners now use settling ponds to clean the water before returning it to the source.

You can try a bit of placer mining on your own, without worries about environmental impact or traveling to your nearest mountain range. Many sand banks, including those dug up, washed, bagged, and labeled as "play sand" often include trace amounts of gold.* This inexpensive (around $2-3 a bag) sand is readily available at your local hardware store, and can be recycled into a number of uses around the house and garden--that is, if you don't have a child nearby with a sandbox running low. (We use our extra sand to fill in gaps between flagstone steps, to put traction on icy walkways in a pinch, or for sand art.) The other necessary supplies can probably be found lying around the house. While I can't promise that DIY gold panning is going to make any sort of profit, it is rather fun, especially on a hot day.

You'll need:

• Sand (from anywhere, even a bag of play sand)
• A pie plate or any wide dish with sloping sides
• Washtub (generally the wider the better, in this case)
• Tweezers or eyedropper
• Magnifying glass
• Magnet
• Ball bearings or BB pellets (optional)
• Strainer or sieve (to sort out thick clumps, if using sand from a creek)
• Shovel (again, if the sand comes from a creek)
• Small jar or bottle (for instance, perfume sample vials, washed and dried. Craft stores usually carry small corked glass bottles in the jewelry section, which are perfect.)

Typical gold pans have more of a rounded bottom to catch debris, but the pie plate works. The pans also usually have "riffles", bumps or grooves to help separate the minerals--the ball bearings can achieve the same purpose. Beyond that, material is a matter of preference. Plastic is lighter, but you can't cook your dinner in it.

How to placer mine at home:

• Pick a spot outside--this can get messy.
• Fill the plate with sand, and dip it into the tub to flood with water. Some sand will spill out; that's OK... in fact, it's the whole idea.
• Gently swirl it over the tub, allowing the sand and water mix to spill over the edge as you go. The heavier pieces will sink to the bottom. Keep it tilted and partially submerged to wash the lighter stuff away.
• Adding ball bearings might help to break up clumps, but don't be afraid to use your fingers to sift and separate. (That's one reason I prefer the sanitized sand, especially when letting kids help.)
• Swirling it is important--just tipping the water and sand out of the pan will cause the mixture to clump. Be patient, and use a gentle motion, allowing the sand to splash into the tub, but not across the yard.
• Keep dipping the pan back into the water as needed to keep the mixture very wet. Dip the pan into the water softly, trying not to slosh it around. Before you remove it from the water, give the pan a little shake. This helps any gold fall back to the bottom, ready for more swirling. If you have a hose handy, you might refresh the water once or twice... that's one area where a running stream helps.
• Eventually, you'll notice that most of the lighter material will start to wash away, separating from the darker sand. That's the stuff you want--don't let the black sand wash out of the pan.
• When only the darkest sands remain in your pan, you're ready to look for gold. In bright light, look for a yellowish color against the black sediment. (The flashier stuff is usually iron pyrite, which I think is a cool mineral, all in its own right. Gold is softer, and has a duller appearance. To be certain, rub a flake against a tile, and check the color of the streak. Gold always streaks yellow, while pyrite leaves a black streak.) If you use a plastic or aluminum pan, you can use a magnet to pull the black sand away from any gold flakes, which can be picked up with tweezers or an eyedropper. The black sand is magnetite, a form of iron, and can be fun all on its own. (Does anyone remember those old toys with black sand inside? You could take a little wand with a magnet inside, and drag the sand over pictures of faces to make mustaches and beards.... ah, the days before video games.)
• Store any flakes you find in the vial, dry or with clean water for a nice effect.

Note: (*) These same techniques work at popular panning sites on creeks and rivers, as well (although you might add a shovel and a hat) if there are any in your area. You might be surprised--Gold has been found all over the world and in all 50 states. If you would still like to try at-home placer mining with a higher rate of success, it is possible. Some sites online sell bags of sand pre-loaded with gold dust, but they can cost quite a bit more than the playground stuff. I haven't compared to know if there's that much of a difference. If there's anyone out there who isn't quite as cheap as I, and wants to experiment, please let me know.

Image credits: Picture of crystallized gold via the Web Mineral Gallery. The photo of women panning for gold via the Western History Photo Collection at the Denver Public Library. All other photos taken by the author. All fractals made by the author using ChaosPro.