Base is a bridge between databases and the OOo office suite. I don't see a way to link Base to the Google Mail database though. I'm pretty sure Google don't allow 'public' access to that!
Here's a way to do what you need though:
In Google Mail, Export all of your contatcs to Outlook CSV format. This will create a .csv file on your desktop.
Open that .csv file in Calc. Save that as a Calc spreadsheet.
Then follow the instructions in the following article to link Base to the spreadsheet, allowing you to mail merge from the spreadsheet of contacts just as if it were a database.
Mail Merge in OpenOffice Writer: Creating Mail Merge Documents From Text/CSV or Spreadsheets
If this has answered your question please go to your
first post and use the Edit button, and add [Solved] to the start of the title. You can use the green tick icon at the same time if you like.