Or even more than so... you could e.g. aim for 6 gem pits...
For the sake of simplicity, let's assume a year is 360 days...
Day 0Day 180
- Build gem pit 1: -20,000 gems
- Gem pit 1 contains 40,000 gems
Day 270
- Excavated +20,000 gems ... build gem pit 2: -20,000 gems
- Gem pit 1 contains 20,000 gems
- Gem pit 2 contains 40,000 gems
Day 330
- Excavated +20,000 gems ... build gem pit 3: -20,000 gems
- Gem pit 1 contains 10,000 gems
- Gem pit 2 contains 30,000 gems
- Gem pit 3 contains 40,000 gems
Day 360
- Excavated +20,000 gems ... build gem pit 4: -20,000 gems
- Gem pit 1 contains 3,333 gems
- Gem pit 2 contains 23,333 gems
- Gem pit 3 contains 33,333 gems
- Gem pit 4 contains 40,000 gems
Day 370
- Excavated +13,333 gems ... gem pit 1 exhausted
- Gem pit 2 contains 10,000 gems
- Gem pit 3 contains 30,000 gems
- Gem pit 4 contains 36,666 gems
Day 415
- Excavated +20,000 gems ... build gem pit 5: -20,000 gems
- Gem pit 2 contains 7,777 gems
- Gem pit 3 contains 27,777 gems
- Gem pit 4 contains 34,444 gems
- Gem pit 5 contains 40,000 gems
Day 440
- Excavated +20,000 gems ... build gem pit 6: -20,000 gems
- Gem pit 2 contains 2,777 gems
- Gem pit 3 contains 22,777 gems
- Gem pit 4 contains 29,444 gems
- Gem pit 5 contains 35,000 gems
- Gem pit 6 contains 40,000 gems
Day 454
- Excavated +13,888 gems ... gem pit 2 exhausted
- Gem pit 3 contains 20,000 gems
- Gem pit 4 contains 26,666 gems
- Gem pit 5 contains 32,222 gems
- Gem pit 6 contains 37,222 gems
Day 490
- Excavated +20,000 gems ... rebuild gem pit 1: -20,000 gems
- Gem pit 3 contains 18,472 gems
- Gem pit 4 contains 25,138 gems
- Gem pit 5 contains 30,694 gems
- Gem pit 6 contains 35,694 gems
- Gem pit 1 contains 40,000 gems
Day 620
- Excavated +20,000 gems ... rebuild gem pit 2: -20,000 gems
- Gem pit 3 contains 14,472 gems
- Gem pit 4 contains 21,138 gems
- Gem pit 5 contains 26,694 gems
- Gem pit 6 contains 31,694 gems
- Gem pit 1 contains 36,000 gems
- Gem pit 2 contains 40,000 gems
- Excavated +86,832 gems ... gem pit 3 exhausted... rebuild gem pit 3: -20,000 gems ... net balance +66,832 gems
- Gem pit 4 contains 6,666 gems
- Gem pit 5 contains 12,222 gems
- Gem pit 6 contains 17,222 gems
- Gem pit 1 contains 21,528 gems
- Gem pit 2 contains 25,528 gems
- Gem pit 3 contains 40,000 gems
After 620 days (less than 21 months) your intitial investment of -20,000 gems would have given you +66,832 gems.
A net gain of +46,832 gems!
From here on you would basically excavate 20,000 gems every month and build a new gem pit for -20,000 gems every 2 months.
A net gain of +10,000 gems per month. :)