In all honesty, I'd have to dig out the early issues of the Dynamite! comics run and see. I do recall that it has a certain sort of "Bat Cave" feel to it, with a set of tools and various equipment for caring for the Ranger and Tonto's weapons, plus a collection of other plot-device specific materiel. As for De Re Metallica, John Reid was, I think, sent away to college by his father and brother, in an attempt to keep him out of the Texas Rangers (to Chicago, I think; they had a story arc a few months ago where the pair have to go there to deal with a villain, and the Ranger reminisces about his time in the Big City). It's possible that he would know of it and other esoteric academic knowledge through that. It's worked in other pulp stories, for other pulp characters.

Ebony the Black Dragon

"Life is like an anole. Sometimes it's green. Sometimes it's brown. But it's always a small Caribbean lizard."