Since I don't Know which Bloch you are talking about I will answer both. (You fight Bloch twice)

In Forbidden Depths after you kill all of the enemies on side of the track Bloch will start shooting at you shoot at him until he goes inside the middle structure he is on then the bottom of the stucture will open and and a cut scene will indicate the giant fan on the ceiling that has stopped spinning. Cycle through your weapons and you should have a rocket launcher. Aim up and guide the rocket up at the red vents behind the fan. Repeat untill all three are destroyed. Do this quickly as the heat will slowly diminish your health.

On the last level if you still have some sniper ammo avoid his rockets and shoot him once he will move to a new platform. After a while he will go to the top level and destroy the middle structure. You are still not done yet so recharge your Q jet and use it to jump on to the fallen middle structure go up as far as you can turn around 180 degrees. There is a vent that your Q claw can cling to. Use it to get on the other side and go down the tunnel in front of you. Once you reach the end Bloch will be hovering on the far side of the room. Don't move left or right because Bloch blows up the floor except the floor in front of you. Walk forward a bit to get a rocket launcher. Take it out and shoot Bloch.
Congratulations, you just won the game!

q jet

When you first come up the elevator pull out your sniper and shoot bloch once in the head. This will skip the entire first round use your Q jet to get to the upper level and then run up the stairs and dodge two rockets then snipe at him and run do this several times until he goes up to the top level and disappears. Than go down to the bottom level and use your q jet to jump on the walkway that bloch blew up. turn towards where he went in the blue tube and you will see a spot to latch onto using your q claw, zip up there. when you walk into the tube you will see a cut scene of bloch floating infront of the window. when you drop down you will have 10 seconds. There is MAL 22 ammo directly infront of you pick it up and shoot bloch. another cut scene and your done. Congrats! You've beaten the game.

with a gun