Published by StLToday, written by Valerie Schremp Hahn, Wednesday 20th June, 2012.   It’s a history lesson, a treasure hunt, a nature encounter and Christmas morning all rolled into one. And to “coinshooters” like Brent Halwachs of Caseyville, nothing beats the bleeps and bloops of a metal detector. Because those sounds signal something: Possibility. “It…