Waco Gem and Mineral Club, Waco, Tx

12.5 Field Trip to a Gold Mine

 

12.5: Field trip to a gold mine

We have approximately 30 major gold mines operating in a big-scale sort of way in our country, with most of today‘s U.S. gold coming from the states of Alaska and Nevada. But gold deposits have been found coast-to-coast, and there are a lot of smaller operations scattered across the country. Because it‘s so valuable, great efforts are made to recover even small amounts. Every time the price of gold spikes, new mines seem to sprout.

Check with your state geological survey or division of mines for any operating gold mines in your state and try to arrange a field trip to one if the mine owners will allow such a visit. You might need to go outside your own state and venture further into your general region, thus making for a longer two- or three-day field trip.

There are two major types of gold deposits, each requiring different mining techniques to retrieve the gold within: 1) lode or vein deposits in which gold is found where it precipitated along cracks and veins in the bedrock, and 2) placer deposits where gold has weathered out of its original lode or vein deposit and is often found mixed with sand and gravel laid down by stream channels and rivers.

In a lode deposit, mining involves blasting ore and crushing huge amounts of it to recover small amounts of gold. The crushed ore is heated or "smelted" to melt and release the gold, which is usually poured into bar shapes. In placer deposits, huge quantities of sand and gravel must be sorted and screened with the help of running water to retrieve gold nuggets. Gold is very heavy, with a density of 16 to 18 as compared to a density of about 2.5 of "waste rock" (the sand and gravel). This difference in density means that miners can use gravity to help separate gold from gravel by devices that agitate the rocks and collect the gold. Such devices include hand-held gold pans, rockers, and sluice boxes.

Gold is also recovered using various chemical procedures, such as amalgamation (where mercury, or quicksilver, bonds with gold from ore) or the cyanide process (where potassium cyanide is used to dissolve and recover gold from low-grade ore).

Note: Kids can use this activity toward satisfying requirements toward earning their Field Trip badge simultaneously (Activity 8.3).