Grammar mavens - a question

"Coal-mine subsidence means the collapse of an underground coal mine resulting in damage to a surface structure."

I made "coal mine" (the noun) two words because that's the way the United Mine Workers do it. I hyphenated "coal-mine" (the adjective) using the compound modifier rule in the AP Stylebook. Am I right or wrong?

It's certainly the way I would have done it - so we're either both right, or ....

I think we're right. I have some engineers editing my copy (heaven help me).

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