Re: exploring Mercury
Not unless we find a very cheap way of propelling mass out of planet orbits. Your mining operation would need to propel all the mining equipment and humans/robots to Mercury, land it there, set up the mine, and start mining ore.
Next step, is whether you want to propel the ore into orbit back to earth for refining, or refine it there. It would be better to refine it there, otherwise you are wasting energy propelling unwanted dregs into space. However then you need refining infrastructure on planet, which is an even more complex undertaking.
Basically, by the time you send your basics to Mercury, set up your mining/refining operation, then ship the mined good back to earth, the cost of the elements would be astronomical.
You would have to find some really rare element (by earth standards), like a room temperature semiconductor, that would make the whole thing worthwhile.
If it is not some crazy unobtanium you have found, but some precious metal like gold/platinum, the moment you discover the massive haul, and start your operation to ship it to earth, you will find the price drops on the markets due to the new supply, so you may not end up making a lot of money on your venture.
It is more likely we will start mining asteroids before we start mining operations on other planets. Asteroids have a far lower gravity well, making them relatively easy to ship the mined ore to a central point for processing.
And as a final point, I just realised that anyone who controls the technology to put random lumps of metal in earths orbit and have it land somewhere on the surface has all the basics of a powerful weapon, something akin to https://en.wikipedia.org/wiki/Kinetic_bombardment .
Then there is the worry of non deliberate bombardment (i.e. a lump goes astray accidentally and hits the earth in an uncontrolled fashion), can you imagine the legal liability for the mining company that would result from such an accident? If the shipping costs don't bankrupt you, the liability and insurance costs probably will.
So IMO there are a lot of hurdles to pass (and not just technological, but social) before we can reliably have off planet mining operations (icon cos of what happens when a random lump of metal impacts the earth surface)