I agree Phred6 and the average hours I show per week is close to what you show. I show 9.6 hrs worked per mining person a day which is 48 hours a week :)
I like your process an it does make sense :) so in december if they rean 201.6 hrs at 150 per hour that could mean they ran 30240 yrds for December and you do the math on that for ounces :)
I was trying to figure the MSHA hours to the rates PCFG posted.But it obviously didnt work right.I forgot to divide it by the number of employees to get the actual hours of plant time.Sorry