MSHA is hiring Inspectors pretty regularly these days. Many of the original guys are retiring. They hold "Job Fairs" across the country and you can check them out for an event near you at MSHA.GOV.  I went to one in Golden, CO. last December. Close, but no cigar.
The "in house" QC's I know are UT II or III certified.

There are welding jobs in mining but almost everyone wants someone who has other mechanical experience such as heavy equipment, crushers, milling etc to go along with that. If you have NDT certs you could apply for one of the few positions in that field. The NDT jobs are highly sought after and pay well. As far as CWI work I just contract it when the need arises because I hardly ever need it. Look at infomine.com for mining jobs all over the globe.