Ok interesting point you bring up Theo. But when i searched for it, and i did this previous to making the stage, or at least adding stuff to it, i found the answer very difficult to answer. And furthemore diffucult to locate a specific time. It's possible when i read all of these and if you do you'll see why:
http://en.wikipedia.org/wiki/Mining#Prehistoric_mininghttp://en.wikipedia.org/wiki/Railwayshttp://en.wikipedia.org/wiki/History_of_rail_transporthttp://en.wikipedia.org/wiki/MinecartThough it was more likely around 1500's or so. It's altogether possible even prior to that. The reason is due to railways. Which Minecarts did run on. Though it was noted that the Spainish used them alot in 1556, it can be traced all the way to 1350 where the first known railway was invented in Minster of Freiburg in Breisgau in Germany, dating from around 1350. Also it notes that around teh Dark Ages(''m guessing going into the Chivalry Age, Medival times), that they mined for gold,ore,copper, and varous other things deposits. So To think that between 1350 and 1556 that the minecarts, railsystem were developed seems reasonalbe. Though it does mention that these were very commonly used in 17 th Century Europe.
So more or less anywhere from roughly 14th to 17th century they had some hand in on mining in Europe. I researched further and Romans and Greeks along with Egyptains used simiar things for mining in or around 6 BC(doesnt mention mine carts though). Well theirs alot of Imformation about it. It does seem to be roughtly around that era. So it is possible to see them. I wouldn't doubt it. Although clearly you'd see more mine shafts/mine carts, and better developed ones towards the later end of 17th Century in Europe,pre dating any steam enginry.
Now that i think of it i watched a program on history channel i believe where they find holes/mine shafts in Michigan were tehy is mining shafting for copper(where the wolf and Moose population dropped cause they'd fall to their deaths). They had railways and mine carts, though the entrances where down and slanted, and i remeber them saying something about after Dark Ages. So yeah it's highly possible.
All signs in Michigan is that not only did they think Spainish Mined their before America was discovered but it may be actually that the Spainish are the first ones to Discover America prior to any of the Spainish explorer like Cortez, more likely before Vespucci,all signs point to it. Kinda of interesting what you learn. But yeah it sounds reasonably legit from what i read online and heard on tv. Can't say it's too far fetched seeing that in medieval times they searched for silver,copper,iron ore, howd they transport all that. I doubt by hand or horses. Btw sry for the long paragraph.