This is a set of four hand drawn ALIEN 3 storyboards by Martin Ashbury. The pages bear numbers 20, 21, 22 and 24.
They depict scenes that were part of the last chapter of the film, when Ripley (Sigourney Weaver) and Dillon (Charles S. Dutton) try to trap the Alien in one of the furnace moulds of Weyland Yutani work correctional facility FURY 161.
The scene where Dillon's forehead is blown to bits by the Alien wasn't filmed as planned on these storyboards, but I guess it was a last minute change as a completed head casting can be seen in the pages of a japanese SFX exhibition catalog published in the mid-nineties (image 08).
Though they don't appear in any of the ALIEN Quadrilogy DVD or BR, these storyboards were heavily featured in issue 179 of STARLOG magazine, in an article about Martin Ashbury and his work on ALIEN 3 (image 09). Martin Ashbury can be seen interviewed aside similar storyboards pinned on a wall next to him in one of the DVD bonuses (image 07).
The pages are in excellent production used condition.