Don,
Check out Iron County, the area around Viburnam MO at an old mine called Brushy Creek Mine. Also, check out Magmont Mine near Boss, MO.Also, up along the Chariton River in Macon and Adair counties, I have heard that one can pan for Gold and Diamonds (Rarely found) in the Glacial deposits.
Also, you can have a good trip by going to Alexandria. MO (North of Hannibal) to search for Geodes. There is a rock shop on the Highway at the intersection of the East West Highway that goes into town. The owner has the Geode mines (open pits).
The rock shop itself is very interesting. The owner is an elderly lady and her son. The house is hand made from rock of all kinds and is very interesting itself.
You can also try the area around Elephant Rocks State park (Not in Park. It is illegal to collect there). There is a Granite mine or two in the area. Also, in the area around Johnson's Shut-in’s is interesting Geologically.
If you want to travel for a long weekend, you can go to Arkansas to the area around Mt. Ida for Quartz crystals, and Murfreesboro for Real Diamonds. At Murfreesboro, the state of Arkansas has the Crater of Diamonds State Park where you can pay $6.00 (I think) and search all day for Diamonds. You can keep any that you find. They have a website at www.craterofdiamonds.com
Hope this helps.
Phil