It is valid no matter where the silver price is.
December 2018-December 2020 (don't know how much each year), overall US$7m.
If the silver price is above US$16/oz the price gets adapted using a base price of US$15/oz.
So at US$17.22 silver price Troy will get US$8m starting from December 2018. That amount should be discounted with an appropriate rate for two years (average duration) to get present value. Austral is not required to make use of the options though (they would be crazy not to do so). Think of it as a silver-price based bond.
TRY Price at posting:
11.5¢ Sentiment: Buy Disclosure: Held