I meant deeper than crust.

> What if we mined deeper?

Below the crust is the mantle, which is ~2,900km thick. Like the crust, is also mostly solid rocks and minerals, but punctuated by malleable areas of semi-solid magma. Composition primarily silicon, magnesium, and oxygen.

Below the mantle is the outer core, a liquid layer mostly made up of iron and nickel. The outer core is ~2,200km thick. It is primarily responsible for generating the magnetic field of earth.

Below the outer core is the solid inner core, with diameter of about 2,400km. It is solid and primarily made up of iron and nickel.

We never reached the mantle, I think, there might be plenty of good stuff there. After all crust is primarily composed of Oxygen, silicon and aluminum which sounds equally boring.