Simply means "inter-racial sex". Can be used as "mud-larking" (hyphenated) or "mudlarking". It is non-derogatory and non-condemnatory. It applies equally to either female or male pursuits. Often it is used when referring to "exploratory" experiences.
"Well, I think she was just in for the mudlark"...

or

"Guess who's been mudlarking just of late?"
by Marc Hugo July 11, 2008
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The practice of larking in muddy areas (e.g. river banks, beaches) in search of long-forgotten relics.
"Have you ever gone mudlarking to the Thames?"
"Yes, I have, it's absolutely littered with clay pipe stems!!"
by Богдан April 4, 2020
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