Given TSV hasn't got the cash to buy an asset of any decent...

Given TSV hasn't got the cash to buy an asset of any decent magnitude, I would reckon that there is some sort of recapitalization plan involved with any potential purchase (most likely involving Alcoa). This might explain both the share price rise and the need for the company to impose a trading halt while all aspects of the deal are hammered out.
Then again, this is all speculation. But you'd think Origin has decided to sell at least something to TSV and whoever's backing them (i.e. missing out on the asset sale is hardly news worthy.)