They are expanding their throughput from 8mtpa earlier this...

They are expanding their throughput from 8mtpa earlier this quarter to 12mtpa by the end of March next year and will be profitable and cash flow positive at that level. Their C1 costs for the Jun20 quarter will be 77c/lb and AIC will be 86c/lb so they'll be cashflow positive above that level. I expect them to declare Commercial Production as from 1Apr20 if not earlier.
The extra facility is like an insurance policy against a short term dip in the zinc price which will protect them in this scenario. The other way to protect themselves would have been by hedging the zinc price but it seems they're confident that the zinc price will rise in 2020 rather than fall so they don't want to surrender profits by hedging.
So they are essentially taking on debt as they're becoming profitable, this is a cheap option IMO compared to issuing more equity that is a permanent debt that you can't repay cheaply after the share price increases.
They might well draw down the facility when it becomes available next month or just keep it undrawn until such time, if at all, that they actually need it - it might actually be used six months down the track if they decide to go ahead with their In-situ expansion.