OK. Here it is. The tune is When The Roll Is Called Up Yonder. According to the notes it was written as a fund-raising song during a miners' lock-out at Tonypandy in 1911. (The parts of the chorus in parentheses are sung as a response to the main line).

Mick

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WHEN THE COAL COMES FROM THE RHONDDA

Oh you men of Tonypandy who dig the veins of coal,
  With me little pick and shovel I'll be there.
For the boss may own the colliery but he'll never own your soul.
  With me little pick and shovel I'll be there.

Chorus:
  When the coal (Oh when the coal) comes from The Rhondda,
  When the coal (Oh when the coal) comes from The Rhondda,
  With me shovel and me pick and me little lamp and wick,
  When the coal comes from The Rhondda I'll be there.

For the owners are demanding a million tons a week,
But the owners think the miner's life is very, very cheap.

For the owners see the profits rising pound after pound,
But the miners hear the timbers crack a mile below the ground.

For the owner rides in carriages and breathes pure air alone,
But the miner walks and gasps for breath, his lungs are full of stone.

For the owners pay the wages but the miners dig the seam.
It's the miners make the profit but the owners take the cream.

Source: Calennig CD "You Can Take A White Horse Anywhere"