The way it was explained to me (in very basic terms) is that this may be the A4 vein at depth. If you think of it like a tree the thin veins they are mining are the upper branches and these are the thicker branches. Now if they can just hit the trunk!!

Now that they have hit at depth they should be able to drill daughter holes from the bottom (again explained to me in simple terms...drill holes around like the spokes of a wheel) and define the surrounding area much quicker.