Anyway, this isn't really Minesweeper at all, it's exactly like BitKong (I actually like Minesweeper type games) so I don't really feel like continuing unless there are better options to play. Might also want to change your motto. Lucrative isn't exactly typical for a casino, unless you've got great comps and giveaways. Top player already put down 0.01 BTC, so you're not doing too badly, I guess.
Why can't you allow users to explore your site without providing email address first and if user interested continue your site let them add an email address?
People like me don't want to verify email addresses to any new gambling sites you may lose so think about improving that part. I can create a one junk email id but people want to try games instantly and they may not interested finish sing up process before they like the site.