If you are simply mining bitcoins and don't sell them or trade them for anything, then there are zero tax implications.
It is like digging up shiny rocks (or gold) in your back garden and storing it in a safe place inside the house. But even more nebulous, you are finding special digital patterns on the network, that may or may not be valuable to others, and storing the output on your electronic equipment.
I think you are wrong. If u r in a baseball game and happen to catch the 3,000th hit for a most valuable player and the ball is valued @ $1,000,000, Uncle Sam considers that a taxable event & charges u taxes on the fair market value of that ball.
The rocks you dig up would already be yours if they were in your back garden. However, if someone realized your house was on a gold mine, your property taxes would be reassessed on the increased value of your property (which happens to have gold that no one ever found yet)
Oh yeah, I forgot to add the conditional about what kind of fucked up country you might live in ..... I'm sure Zimbabwe govt. considers anything that happens in your house a taxable event ... hell they probably charge you for breathing in some less freedom loving countries ...