“Railgun” should read “Linear Motor”, the broader category that includes railgun.
http://en.wikipedia.org/wiki/Linear_motor
Common lunar minerals
Calcium (Ca)
Aluminium (Al)
Iron (Fe),
Magnesium (Mg)
Silicon (Si)
Titanium (Ti)
Oxygen (O)
The value of these is that they are common industrial raw materials and they are NOT at the bottom of the earth’s gravity well. They may be used to fabricate space vehicles & habitat without having to pay the HUGE cost for the freight elevator ride up out of Earth’s enormous (relative to the Moon’s) gravity well.
You are seriously suggesting an economic advantage in going all the way to the moon to extract elements that on earth are literally as common as dirt?
You're ignoring the little problem that these not very expensive materials aren't just lying around in useful metallic form on the lunar surface. They're chemically bound in rocks similar to basalts here on earth. To actually use any of this stuff a complete industrial base (and I use the word "base" in the sense that the Chinese have a vibrant industrial base) would have to be moved from the earth to the moon. How many thousands of tons of machinery go to make up a mining operation, an ore processing plant, a power plant large enough to run an industrial complex and a metal fabricating plant, all of which have to operate and be built in a vacuum which means the workers have to have all of their food, air, and water shipped up to the moon along with additional vacuum habitat to house them. Not to mention that the normal building materials of the industrial infrastructure (ie concrete) won't work - no water, and no way to make concrete.) EVERYTHING would have to be prefabricated on earth and shipped at great expense to the moon. Sorry FRiend. The idea just isn't economically feasible.
Suppose you got the costs down to 1% of the Apollo return costs (which is extremely unlikely due to the cost of building a complete industrial economy on the moon). Think $4.5 million an ounce delivered to the earth multiplied by .01 and try and determine just what raw material is worth $45,000 an ounce. It sure wouldn't be anything you listed.