When you enter a cave that repuires four hoppers, the cave won't close over if there are people in there. So try to get as many people in as you can! I have estimated that for every 100 silver you will get 20 gold. This may be helpful?
Also, when you are retrieving bamboo and wheat, make sure you have the required tool with you. These materials will disappear FAST and you may not even get any! So make sure you go prepared.
Gemstones are more likely to appear in caves in the rocks that fall from the wall. Simply ask people where they are, I'm sure they'll tell you! Don't be afraid to ask!
When gathering materials, speed is key. If you collect them in the mini game really fast, you can get up to 7 of them! So think Speedy Gonzales!
Did this help? Idk XP