Answers

2016-03-14T00:46:41+08:00
Because those places dig in deep inside the ground which is really the places of metallic deposits
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2016-03-15T09:37:24+08:00
 metallic deposits are abundant in places where trenches and volcanoes are found because these openings allow metallic deposits from within the earth to go out as movements of material like volcanic  eruption will force this deposit out
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