Hello there you will need to use plots for the chunk the quarry is in and with that chunks perm set modify to true and enter to false. And for your towns perm enter to false as well. As with modify on anyone can come in there and steal something in anything with modify on so you'll not want people to get in that chunk or really near it.
If you want people to still get in your city but not that chunk I'd suggest making a wall of plots around the quarry chunk with perm enter to false.
P.S repost from ManYouForgot