If you read the second paragraph of the letter dated 27/9/16 it...

If you read the second paragraph of the letter dated 27/9/16 it says :
"Under the terms of this re-negotiated Tranche 2 purchase, CZL will pay Retec A$580,000 and US$800,000 both in cash,
[instead of A$750,000 in cash and A$1,700,000 in CZL shares]"
This is for 80% ownership of Plomosas zinc mine or the purchase of an additional 39% of MLAZ shares

Now if you go to letter dated 30/10/18 it says :
"The key terms of the acquisition of the additional 39% interest in MLAZ are,
Payment of A$750,000 in cash to Retec
Issue of a$1,700,000 of CZL shares to Retec".

So it appears nothing was paid back in 2016 and they have now gone back to the original payment of "$750,000 and $1,700,000 in shares which they will pay next month for the additional 39% or 90% ownership of Plomosas . .

I find this all very weird and impossible to work out so the only conclusion I can come up with is that the Directors are buying up shares so they must know what they are doing.