There is nothing in the Act that says the chaior’s resignation has to be endorsed a general meeting.
Given that the committee chooses the chair by a simple majority (of the committee) and the committee can sack the chair, again by a simple majority vote, and you can’t force someone to stay if they want to go, I would have thought that a letter of resignation would be enough.
If the chair resigns from the committee as well as from the chair, the committee can elect a new member.
The committee can also sack a member if they have missed 25 per cent of meetings in a year.
Put all that together and you can see that the control of the committee is entirely in the hands of committee members. The idea that you might need a general meeting to deal with the resignation of the chair is a complete furphy.