You can never go wrong paying down the mortgage (unless you're living in the US and you have negative equity). Investing/trading is gambling. You should only use money you can afford to lose, or at least won't need for a long time.

Junior resource stocks have great potential, but as you know, they can also blow up. To minimize individual stock risk, you either have to buy a large basket (my usual approach), or buy an ETF. GDXJ is a good one, but because it's American, you can't put it in a TFSA without having to pay currency conversion fees. ZJG solves the problem, and when the gold stocks start their inevitable run, it will have more juice than XGD. So when you are ready to put money in your TFSA, I think it's a pretty good bet.