Trading halts typically are 48 hrs. But this is not a trading halt, it's a suspension. And it's not voluntary, it has been imposed by the ASX under listing rule 17.3:
https://www.asx.com.au/documents/rules/Chapter17.pdf
That's the rule whereby e.g. mining companies get temporarily suspended for not producing their quarterly cash flows by the required date. But that doesn't apply here. I note that the ASX notice specifically says the suspension is in relation to a pending "announcement in relation to the Woodlark project".
So there has been some sudden development in relation to Woodlark. So sudden, that the ASX had to move without getting a formal written request from GPR? But I thought the company could request a trading halt over the phone anyway, so I don't think that explanation works. So did the ASX gets its info from a third party? Or from the news - has there been a coup in PNG??
Interestingly, the ASX has not suspended Kula Gold. Which makes no sense at all.
Executive summary: I have no idea.
