Hi Ron,
The fact that the Quincy mining company refused all efforts to buy the equipment wasn't because they held out hopes of resuming mining. Anyone would see that steam locomotives would be of no value for a re-opened mine. What was really going on was the Quincy Mining Company, located in Boston, was using the Mineral Depletion Allowance to reduce their taxes on other enterprises and by leaving the physical plant intact, they could claim that they had merely temporarily suspended mining. After 30 years the IRS finally figured out what was going on and disallowed their Mineral Depletion Allowance claim. The scrapping began immediately after that. Frankly, I was amazed that they allowed the four locos and the hoist house to be preserved.
The new boiler for the #4 was supposedly built by Alco around 1938. I would imagine that it was ordered before the #4 was torn down for overhaul and that when they did start to work on it, realized that it was hopeless and scrapped it. I would guess that after wearing out the #3 during the war years, they decided to try adapting the #4 boiler to the #3 frame but shut down before getting very far with the project.
If you took any photos in the roundhouse, it would be nice if you could post a few.
Michael Allen