The coal-pit we are looking for can be found in Great Chaparral, at the foot of the mountain, close to a vehicular route.
After reaching the entrance we demolish it with a series of firearms or, which is faster, with a rocket launcher or grenade launcher. Each way is good.
In the coal-pit at the bifurcation you will see a corpse. Having interact with it, you will obtain a prize for completing the whole mission - that is 2 specific Noir filters.
They can be used in two ways. Firstly, choosing Isaac in contacts and calling him by mobile phone we automatically activate a new graphical view (another phone is the second filter and the third means returning to the basic one - mechanism works cyclically), while during taking photos, these filters will be available in effects adjusting options.