Upgrades become available depending on the total number of real-life days in which your mineral vein is mined.
Upon reaching rank 3, the boulder face will appear worn away, granting a second mining point, Mineral Vein #2.
Upon reaching rank 5, a second boulder will appear to the left, granting a third mining point, Mineral Vein #3.
Upon reaching rank 7, the left boulder's face wears away to reveal crystals, granting a fourth mining point, Mineral Vein #4.
Instructing Yeestog to "repair the tools" will occasionally grant free mining attempts.
Every mining attempt yields items in the following order:
1-3 items, randomly chosen from the Metals+Either lists or the Precious metals+Either lists. This choice is invisible to the player, and is specific to the particular vein mined.
Choosing to mine multiple times will perform that specific action until it becomes unavailable. As a consequence, an initial "mine multiple times" that digs up metals will cause the next set of actions to dig up precious metals, and vice versa.