By talking to Prospector Percy and asking him if there's any other things you can unlock, he will reveal that for 100 golden nuggets and a level 72 Mining level (not boostable) you can use the upper section of the Motherlode Mine. For 200 golden nuggets you can get the larger sack upgrade, increasing the capacity of the sack at the end of the cleaning machine from 81 to 162.
These items can only be bought with golden nuggets.
|Item||Stock||Price (in )||Exp boost||Boost per nugget|
|Soft clay pack||1000||10|
|Bag full of gems||100||40|
If you choose to sell back Prospector items to the shop you will be refunded 80% of the golden nuggets.
380 nuggets are required to purchase all of the non-consumable items from the shop (180 for the prospector kit, 100 each for the coal bag and gem bag). Obtaining this many nuggets would require mining 13870 Pay-dirt on average.
From the 'Boost per nugget' section, you can see that some pieces are more efficient than others. Therefore in order to get the most out of your nuggets, it is highly recommended you save up, and obtain each piece in the following order: 1st - jacket, 2nd - legs, 3rd - helmet, 4th - boots.