Trying to do a numerical comparison between buyback and Rentails...

Trying to do a numerical comparison between buyback and Rentails based on 2017 DFS numbers. It's very back-of-the-envelope, so I appreciate you all poking holes and correcting mistakes.

Here it goes:
(1) Assume the company has A$10mn to do a buyback. How much of annual tin production does that buy you? A$10mn gets you a bit more than 33mn shares @ 30c or about 3.67% of outstanding shares. Annual (MLX share of) tin production is, say, 5500 tons. So, A$10mn buys you 3.67% of 5500 = 202t of annual tin production at Renison.

(2) According to 2017 DFS, A$200mn will buy you (MLX share of) 2700t of tin and 1100t of copper. Given current prices let's call that 3052t of tin equivalent. So proportionally, A$10mn buys you 10/200 of 3052t = 153t.

Clearly, the share buyback price matters a lot. If the share price was 40c we would get about the same amount of tin for our hypothetical A$10mn. Similarly, if the Rentails cost turned out to be 300mn instead, then corresponding "break-even" share buyback price would be 60c.

In conclusion, at 30c a buyback is clearly the far better option for shareholders, especially since it stands to reason that capex costs to get Rentails on the road should have increased quite a bit in this inflationary environment.