I don't know of any valuable minerals in Lehigh County. But if there are, I'm sure it's minimal.
AFAIK, natural gold is scarce in PA . Some has been found in southern Lancaster County and some in York County streams. The old Cornwall Iron mine in Lebanon county was said to have produced gold over the years, and some say the workers were paid with it. That's open to question though. In any event, the mine is private and filled with water .
Not sure if the spoils banks could be checked or not. Again, they're on private property.
There's the Pequea Silver Mine tourist attraction in Lancaster County, I suppose enough silver was found years ago to make it profitable to mine it. But it's not been active for many years.
PA has state game lands or public hunting lands. These are generally off limits to searching for and removing any historic or geologic specimens. If caught, fines could be considerable and equipment confiscated.