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Activities

Panning For Gold

Introduction:

Gold is one of the few minerals in the world that occurs in the native state, i.e., occurring in nature as a single element (though in some cases other metal impurities, such as silver, occur in the native gold). Other familiar examples include native copper (used for tools and jewellery by "native" North Americans), nickel-iron in some meteorites, and native carbon, which we find as graphite (and use in pencils) and diamond, the hardest substance and well-known as a gem.

Because native gold is chemically and physically inert, it can survive the weathering processes that can break down its original host rock (where it formed in igneous or metamorphic events). weathering and transport can release the gold grains, which can then exist as individual particles in residual sand and gravel (e.g., in rivers and streams). Throughout history, humans have recovered such gold grains by panning these gravels, recovering the dense gold and discarding the lighter materials. Other recovery methods are also used today (especially in the more common mining of gold directly from its original host rocks) but panning, or sluicing, remains a viable recovery method, even in some large-scale modern mining operations.

The principle behind gold panning is that gold has a very high density, that is mass per volume. The density of pure gold is approximately 19 g/cm3, which contrasts with densities of 2.5-2.6 g/cm3, for quartz and feldspars that are the most common minerals in sands and gravels. Thus, with appropriate shaking of a gold-bearing sand, all of the gold drops to the bottom of the mass of sand. Doing this in water facilitates the sinking of the gold. The remaining trick is to remove the upper layer of gold-free sand.

In our little demonstration, we will use actual gold pans, and work with "ordinary" play sand that has been spiked with gold (actually recovered by a gold-panning hobbyist). A method of simulating this procedure without real gold is outline below.

Steps:
  1. Fill a large tub with water (e.g., a laundry tub).
  2. Place about 1 cup of gold-bearing sand in the gold pan.
  3. Gently immerse the pan with the sand in the tub, without splashing out any sand.
  4. With the pan under water, shake the pan in a small circular motion, so that all of the sand is moving. With this motion, you have mobilized the bed. That is, water os moving freely between the sand grains of gold to sink rapidly to the bottom of the pan. With correct motion, all of the gold should be at the bottom of the pan within a few seconds.
  5. Continue the swirling motion, but tilt the pan away from yourself. This moves the gold grains to the edge of the pan, or the cease (right at the edge of the bottom of the pan and the upward sloping sides of the pan).
  6. Using a vigorous motion, begin to slop out the sand on the top of the bed. The gold is so dense that it will remain on the bottom, so don't worry about losing it (as long as you are not too vigorous)! At this stage, unlike step 4. the bed should not be mobilized. The sand should be "still", and just the top layers of sand should be washing away.
  7. Continue slopping out the upper sand, even using little "waves" coming into and out of the pan when the only the far half of your pan is immersed, sweeping sand off the top.
  8. When you are nearly out of sand, you can shake the pan in a horizontal position (i.e., this time you can also pour out the sand + gold onto a dark coloured tray and pick out the gold grains with tweezers.
Panning: Substitute for gold and gold pans can be made and this can still be a fun and successful project.

Aluminum pie pans can be used instead of real gold pans. By spray painting the inside of the pan with black paint, the gold grains show up better than on the silver aluminum surface.

Other dense minerals can be used as substitutes for gold. Dense minerals such as pyrite, or "Fool's Gold" (density 5.0 g/cm3) or silver-coloured galena (density 7.5 g/cm3) can obtained from mineral dealers such as Ward's for a modest price (Ward's telephone number is 1-800-387-782, and they sell pyrite in packages of 10 samples, each about walnut size, for $17.40, and similar galena samples for $16.70. That is enough material to last a life time!). These minerals can be crushed with a hammer (in a bag (cloth is preferred) and, of course, when wearing safety goggles) and sieved through a window screen to get a uniform small grain size (similar to that of the sand) for best panning results.

"Play sand" obtained from Canadian Tire or a similar outlet is rather pure (and clean) and thus unlikely to contain any interesting heavy minerals what might be found by panning. However, naturally occurring sand (on beaches and in rivers) is likely to have some dense minerals in it (possibly even gold!), and these can be turned up by panning. You may have noticed on some lake shores lines of reddish and blackish sand. these are little deposits of garnet (red) and limonite and magnetite (black). Nature has left these small dense mineral deposits through a natural winnowing action. If you scoop up some of this dark sand, you can pan away the quartz and be left with garnet, ilmenite and magnetite. You can even test to see if the black material is the mineral magnetite, because it is magnetic and will be attracted to a hand magnet (when dry).

Other minerals besides gold are recovered in real mining operations because of their high densities, including diamond, native platinum, cassiterite (a ore of tin) and the titanium-rich minerals ilmenite and rutile. Natural sedimentary deposits of these dense minerals are called "placer deposits" (as opposed to bedrock deposits, where these minerals formed).

   

    Last Modified: 2004-12-10