This not working.
mate-terminal /home/andy/Downloads/
This not working.
mate-terminal /home/andy/Downloads/
Please see - https://askubuntu.com/questions/75222/how-can-i-start-gnome-terminal-at-a-particular-directory
So in your case that would be
mate-terminal --working-directory="/home/andy/Downloads/"
which opens a new instance at the desired directory.
Thanks for your help.