Prospecting for Gold
Post-World War II mining efforts were directed mainly toward locating base-metal ores rather than panning for placer deposits. A placer deposit is a concentration of mineral that has accumulated along with the sediment in a stream. Because of the length of time needed for gold to corrode and its relatively heavy weight in comparison to the sediment in the stream, gold tends to accumulate in placer deposits close to the rocks from which it came. 【題組】 1. Placer gold is to be found (A) in the rocks (B) in the stream (C) in the mine
(D) on the ground.
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