Hi,
In Colorado Rail Annual #11 page 176, (paraphrased) the last NG train out of Ouray in 1953 contained 3 box car loads of of ore concentrates from the Camp Bird Mine.
The line was pulled up Ouray to Ridgway and the remainder was standard gauged. Camp bird trucked to Ridgway and the shipped by rail.
The Dixie-Lynn mine shopped lead and zinc to Montrose by rail until about 1970
There was also ferric-oxide shipments to eastern US until about 1970 (225 car loads per year).
So these cars could have been used for different ores. Maybe the Lead had to be shipped in special cars to keep lead posioning the shugar beet shipments.
FWIW.
Doug vV