Who is the silversmith Robert koeppler?

Robert Koeppler was an amazing silversmith who made silver jewelry with agates he found, cut and polished himself. He lived in Quartzsite, AZ in the winter and Crane, MT in the summer. I assume he has passed because I no longer hear from him and he used to write regularly. He was a good friend and teacher to my mother, also a silversmith. He taught her to make life-like miniatures of everyday items. He also handmade the boxes he put his jewelry in and his own note paper he wrote all his letters on. He was part of the FDR art train in the 1940's.