Reading Selection, Lesson 19
Gold rush prospectors (like the one shown in the drawing) found gold in rivers and streams, because rain had washed it there from surrounding hills over thousands of years.
The dense flakes of gold settled quickly in streams and were caught in nooks and crannies on the bottom. Panning worked well at first. But once all of the easy pickings were gone, prospectors began to use water jets to wash whole hillsides away. They then used long sluices to search through the washings. Sluices are wooden troughs with riffles in the bottom. The gold would get stuck in the riffles as water and mud washed down the sluice. Every now and then, the prospectors would stop the flow and remove the gold. Because this method of prospecting caused large amounts of silt to pollute rivers, it was restricted in California as early as the 1880s.
Density Makes It Possible
To prospect for gold, prospectors use a pan to dredge up silt and rocks from the bottom of a river. They pick out the big rocks and add water from the river to the pan. Then they swirl the pan of silt and water, allowing anything that does not sink quickly to the bottom of the pan to flow out of the pan (see the photograph).
Prospectors repeat this process until they are left with only “black sand,” which is very dense. If they are lucky, the black sand will contain tiny gold flecks. Then they pick out the flecks, and start again. If they are very lucky, they will find nuggets of gold (see the photograph).
Use library and Internet resources to investigate other methods of gold extraction and processing . Answer these questions: Which countries produce gold? What are the main uses of this metal?
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