Our heroes leave the spiders alone and return to the rubble room (Area 22). (OOC: I forgot to answer Dame S's question: No, she did not see any prey-bundles trapped in the web, Hobbet or other-sized. Good question! Also I should mention, that the spiderwebs were thick and sturdy, not dusty and tattered.)
Hobbets are natural burrowers, and it doesn't take long to figure out a likely explanation for the rubble: a cave-in! Two of the three unexplored tunnels are narrow and appear to have been carved by a miner's pick. The third tunnel (the one in the middle) appears to have caved in, at some time in the past, revealing an open area on the other side. There are a couple of rotten support timbers half-buried in the stone rubble, supporting the miner/cave-in theory. Shining their lanterns through the breach, the Hobbets see the unmistakeable gleam of silver nuggets on the other side, mixed in with the scree! It would appear the miners of yore discovered a cache of silver, but perhaps they abandoned it due to the cave-in.
It should be possible to travel west or south, into either of the narrow tunnels, hugging the walls to avoid disturbing the rubble. To go southwest into the silver-strewn chamber, would require scrambling over the rubble left behind in the cave-in. (Difficult terrain; half movement rate.)