I would like to ask our informed geologists here, how the...

I would like to ask our informed geologists here, how the accumulation of mineable amounts of minerals occurred???
   Given that about 4.8 billion years ago the “earth” was a molten ball of silicate, rock and assorted minerals formed from the remnants of the newly formed and ignited Sun, and also from the outer regions of the Galaxy. And compressed together under the massive forces of gravity.
This mass then began to slowly cool over one and a half billion years and started to form a solid crust.
   Then about one billion years later we smashed into another recently formed planet about the size of Mars. The impact releasing trillions of tons of debris into near space and sending the earth spinning at 6 hours per revolution! Again earth became a molten bubbling swirling mass of rock, iron and other minerals and covered with volcanoes, for a further half billion years.
After which time the outer layer of the earth once again started to cool and the trillions of tons of rocks circling the earth collected together under gravitational force to form the moon circling the earth at only about 100,000Km.
A further billion years later, and the earth cooled further, slowed down to about 15 hour per day. and the moon slowly moved to where it is now.
During these billions of years of formation, the planet was bombarded with meteorites carrying water and assorted minerals from the outer Galaxy.
Also, and this is where it gets interesting; the now solidified outer crust of the planet started to form platelets which were pushed across the planet’s surface by still molten internal forces. First forming a total land mass and then breaking into pieces again.
During the last one billion years the planet then endured a total ice age lasting for millions of years and totally freezing the oceans. Not to mention that we later lost all our Dinosaurs!

Now my question is: If the planet was a churning mass of molten rock and minerals for billions of years, how is it that these minerals (Cobalt?) and all the others managed to coaless into the large deposits that we know today and rise to levels just below the earths surface where we can mine them??? (Iron ore I guess is possibly an exception since the earth's core is made of it.)
Surely reason would dictate that all these minerals would have remained as a total diluted mixture of rock/silicate evenly spread across the earth’s surface.