if my understanding is correct most of the earths crust has been recycled into the mantle due to subduction. there is very little of the original surface of the earth left. diamonds are formed from carbon that was trapped in the crust during the subduction of that particular piece of crust. there is also a theory that says the entire surface of the earth has a layer of gold deposit but geo dynamics has caused gold to become solid at different depths of the earths crust. it is an accepted theorem that gold will only solidify in white quartz. if gold came to earth from above the earths crust it would have had to be subducted where there was enough moisture to dissolve salts to form the acids that would eventually dissolve the gold so that it could be forced by geo thermal pressure through small fractures in quartz formations effecting the precipitation of elemental gold deposits known as load gold.