"......Now when was the Chili line rebuilt south of Antonito to reach the Perlite plant? "
The rail has always been in south of Antonito. The Grande stored stock cars down there. There is a pic in a book captioned "112 car stock train arriving in Antonito". The pic is actually on the stub end remnent of the Chili Line and the crew is shoving empty stock cars into the track. The train is sitting on the San Antonio River bridge, which today sits in the middle of the perlite and scoria rock loading facilities.
When ever I go down there I think "wow, this used to be the mainline of the Santa Fe Branch..."