Lyric discussion by JayWalker 

Cover art for Sixteen Tons lyrics by Tennessee Ernie Ford

This song is about the coal mining indeed. and about debt bondage. Miners had to spend a certain percent of their wages in the shops owned by the company they worked for. this created an even bigger dependency on the company. These systems of debt bondage (have) existed all over the world.

"another day older and deeper in debt was a phrase oft used by the original songwriter, Mister Merle Travis.