Deep drilling has lots of technical challenges but companies are doing it in 'hard rock to depths of several thousand meters. Cypress Development Corp in Red Lake has drilled 2500+ meter holes in rocks that are similar to what we have.

It’s not the hardness of the rock that is the challenge. Core drill bits (open at the end to allow the core to slide up the core tube) are designed for specific rock conditions. The matrix that contains the diamonds in the drill bits have different hardness so that the matrix will strip off at the appropriate rate and expose fresh diamonds.

Solid drill bits (non coring) are similarly designed for the rock type/hardness and application they are used in.

While the hardness of the rock will impact the life of the bit (how many meters you get out of it) the big differences are due to differences in rock hardness (going in and out of layers of rock of different hardness and operator issues. Just like at home if you push your tools to hard, jam them in, try to force them, get to much friction, etc you have problems. The same applies in diamond drilling. If you push your bits they wear out faster, if you lose water pressure they burn out, if the rock hardness changes suddenly you can over torque and burn a bit, if you hit open fault/shear/cavity etc you can 'drop' your drill string and the bits takes the brunt and of course it just gets tougher and tougher to make things work as depths get longer.

So if you don't have the right equipment with very experienced people that know what they are doing and you attempt to do what is at the limits of current technology you can and likely will run into problems. On the other hand Cypress is an example of a relatively close neighbour that is doing it.

... Been There