In communities that had active, but hidden, homosexual communities, the phrase took on a second meaning in double entendre, referring to the humiliating prospect of having to bend over, grab one's ankles, and recieve painful anal intercourse from someone who is overly aggressive and abusive.
She got the goldmine (She got the goldmine)
I got the shaft (I got the shaft)
They split it right down the middle
And then they give her the better half
Well, it all sounds sorta funny
But it hurts too much to laugh
She got the goldmine, I got the shaft