Boy are you right about the difference in work envrironement.  I would have to check on the elevation over at Thacker Pass, but I'm going to venture a WAG off the cuff of less than 6,000 feet elevation, maybe 7,000, vs over 13,000 feet of elevation at Cauchari-Olaroz.  Since Covid-19 often attacks the lungs via ACE-2 receptors in the lungs you can bet that you don't want to have the slightest underlying pulomonary compromise up at 13,000 feet in an oxygen poor work environment.  I know, Coeruleus, your own knowledge base makes you extremely cognizant of all the particulars of this specific work environment mismatch.

Working at over 13,000 feet requires that individual to be in tip top physical condition and having a virus or just having the possibility of a exposure to a virus that causes such devastation to the lungs is incompatable to a viable safe working environment. 

 Thanks, Coeruleus, for all of your insights!