Easy cave. Dig the dirts, kill the red blob and the purple rat. Mine the 2 soft stone blocks near the rat and take the bronze key. Open the door and chop the sticks (don't release the boulder now), open the bronze door and take the silver key + cooper ore. Mine the coal, open the silver door, kill the purple bat and take the gold key.
Now you can release the boulder, move right if you don't want to be smashed or trapped. Kill the last purple blob and mine the soft stone, once again be carefull when the boulder fall. You have to mine that boulder before openning the treasure chest.
The wood and the cooper can be obtained without special tools but you'll need a red key to clear that mine.