Musk is working on the $100B loan with the bank to fund the effort. The bank is skeptical about using the diamonds he recovers as collateral. The financial manager at the bank is concerned that the value of the diamonds recovered might actually be diminished as a result of his recovering them. In this case, the revenue from sale of the diamonds might not cover the loan payoff amount.
Just follow the DeBeers approach and monopolize the production sources and then only sell them in small quantities so the value remains high. Keep that revenue coming in forever.