First of all you need to lose this ideology that mechanical has more scope and mining has less scope. Every field has top notch research going in it and provides dynamic and challenging work opportunities.
I also had the same dilemma and I chose Mining at IIT Kharagpur over other departments for to following reasons:-
No particular brand is better than the other as it all depends on your own preference and inclinations. One needs to stop thinking that mechanical is the most demanded branch. In my opinion, every branch is important and has the scope to attract people who are passionate about it. Hence it is illogical to say that one branch is superior to another.
I suggest you go for a branch not because it has scope but because you are genuinely interested in that branch and are ready to pursue a career in it. For instance, my brother chose mechanical engineering not because he thought it had a higher scope than mining, but because my father himself is a mechanical engineer and he wanted to continue the legacy.
Rather than following the sheep mentality and choosing a certain branch, you can refer to the following options