Special thanks to Christopher Docksilver for taking the screenshots.
What do you guys think of this? I personally think the Silver Mines he's referring to are the ores in Beckett's Quarry.
They could be unearthing the "Silver" ship material from the game's files,
Or they discovered the mysterious item Jolly has been looking for.
Don't forget to read my guide to keep tabs on them all the time.