What is true about most higher-grade metallic ores?

Question

Most of them can be extracted using placer method.
They are usually very close to earth's surface- less than 1,000 ft underground.
Most of them have been extracted without requiring drilling.
They are usually found deep below Earth's surface- more than 1,000 ft underground.

Answer 1

They are usually found deep below Earth's surface- more than 1,000 ft underground.