I found a temporary fix that seems to work in my game, although it's a bit of a pain and it seems that for it to work consistently, I have to go through this process every time I send something to the geo council.
Step 1: Make sure you have the item(s) on hand and ready to send once you're done with this stuff. Ideally, have it be a Monday or Tuesday in game, so the stuff will get delivered during the work week. Mail seems more consistent on those days.
Step 2: Put an item in your family inventory. You can take it out again afterward. For whatever reason, this seems to help clear whatever is going on.
Step 3: Turn on testing cheats.
Step 4: Shift-click on the mailbox, and select reset.
Step 5: Exit the game completely.
Step 6: Clear your cache files.
Step 6: Go into Origin and repair the install of your game.
Step 7: Go into your game and place an item in and out of the family inventory again.
Step 8: Turn on testing cheats, and reset the mailbox again.
Step 9: Send your items to geo council in one shot. Do not ask for postcards or do anything else with the mailbox. (If bills are due, that doesn't seem to affect it, so don't worry about that.)
Step 10: Do not travel to Granite Falls or take any vacation until after the next mail delivery. It might be best to not leave the home lot at all until the mail comes. The times I got my mail, my sim had not left the lot other than to go to work. Mail usually comes sometime after 10 AM and before late afternoon the following day.
I did not have any luck having it work again after a couple of days, so I went through the whole process again. Also, any stuff I had sent previously was just lost. I don't recommend testing your rare metals or gems on this. I did get elements from everything sent in that first attempt, though!
Good luck, and I hope this helps some of you get your elements until the bug is fixed!
Edited to Add:
FYI, when I deleted and bought a new mailbox instead of resetting it in testing cheats, it didn't work for me. A bit more good news, I asked for postcards the following day, and sent off another sample to the geo council, and both came back like they should have. I don't know if that was just luck, or if it will continue to work, but I wouldn't risk sending anything you're not willing to lose on a follow-up attempt.
Edited By: MrsFlynn - Mar.31.2015