I'm not an expert in takeovers however I believe that it is not compulsory, so for example had SQM approached with another marginally higher offer that the AZS board still considered totally inadequate the Board could just reject the offer with no disclosure.
This seems to me to be an offer that is more worthy of consideration by the AZS Board, hence the trading halt. It would not surprise me if there have been negotiations going on behind the scenes between AZS and SQM management to get to this point.
GLTA & DYOR
AZS Price at posting:
$2.44 Sentiment: Hold Disclosure: Held