I'm not an expert on the matter. So happy for someone more knowledgable on the matter to comment more definitely.
That said, my understanding is that a substantial increase in the PoG would likely result in an adjustment in the carrying value of the mine's asset.
Here is what they said in the FY15AR:
That said, I'm not certain what MML accounting policies are in terms of when you need to recognize write down or write up in an assets carrying value.
I suspect the gold price (or reserves) would need to be substantially different from the existing assumptions to warrant a reassessment (ie PoG finish below $1100 or above $1300).
That said, asset write ups and write downs might look good to the accountants and traders, but I think most serious long term investors are looking at shares like businesses and are going to heavily discount the "promise" of future returns when compared to how much cash is being put in the bank today...
So in my opinion the most important thing the increase in PoG will bring to MML is not an increased book value rather an increased rate at which it produces FCF and paying a dividend.
