Suspicious Snow Artifacts/Treasure:
Like the title implies, what if as an extra bonus element of resource gathering in frozen caves, copy over the suspicious sand mechanic over to snow blocks.
With these snow blocks, a brush is needed to uncover treasures, leaning more into the “lost items vibe.” Either your classic minerals and treasures, or the odder items you might find while fishing, etc.
Frozen in Ice Artifacts:
A more drastic addition would be Ice-Encased [Encasing Ice ?] treasures.
Similar to the snow above, but you can see the item frozen in the center, meaning bones, artefacts, and maps could be more fun in this scenario.
Breaking it with a Silk Touch Pickaxe, drops both the Encasing Ice as well as the item within. (Also it “pops-upward” from the ice, like uncovered suspicious sand items, to work with ideas below.)
This means it could make an excellent display case as well, maybe created by dropping an item in water surrounded by 4-6(?) brittle ice blocks.
It could even spawn naturally in the center of a sheet of brittle ice, creating an “Indiana Jones-type” scenario where you need to dig it up before the ice breaks under you.
…Alternates rules for Stuck-in-Ice Artifacts:
…If you don’t want it to be ‘silk-touch-locked’, it could just be a trigger block, causing all brittle ice to shatter around it. This could work with trope-y “treasure in a wall of ice:” freeing a bunch of ice zombies at the same time as the treasure.
Or you need to break the directly adjacent ice (then the treasure one) or both the treasure is lost and the ice shatters below you…