Slavery could have been adopted to minining.
In Colorado? Isn't that above the 36° 30' parallel? (Missouri Compromise)
Also there is the issue of white miners absolutely not tolerating that.
The dirty little secret of slavery in the United States is that most of the opposition to it came not from people being concerned about the welfare of the slave, they were mostly concerned about the slave taking jobs away from them.
Slaves picking cotton was a job white people didn't want, so they more or less tolerated it, but the one thing that would have caused an instant confrontation and bloodshed was slaves attempting to do jobs whites wanted.
The parts of the country that were heavily anti-slavery back in the 1850s are the same parts of the country that are heavily Unionized (as in labor unions) today. They saw slaves as "scabs", and they would absolutely not tolerate any slave taking money out of their own pockets.
So no, you would have had an explosion of rage if anyone had attempted to use slaves to do that kind of work. I bet the US government would have stepped in and put a stop to it.