Double labor structure at Potosí--resembles mines of New Spain except more slaves in New Spain (10-15% of total force)
Mitayos (~13,000 yearly from 1575) did the dirty work underground, yet preferred to work in Potosi as a means of paying tribute
Many yanaconas, after 1580, mingas, were attracted to mines and refineries by opportunities for specialized laborers--half of total workforce.
Blacks, slaves or free, also worked only above ground, but only in small numbers.