The Diadem | Buried Chests Map.
So it seems that popping buried chests in the diadem gives you points towards your next track message and when I found out about it while Solo gathering in Diadem, I decided to map out their location so that when you go Diadem-ing again you can have a shot for a second or third spawn for your party by having 1 party member go and look for them quickly.
Now keep in mind this map is NOT 100% but its around 80-70% complete and these marks is where I found them consistently.
http://i.imgur.com/7p6d3UY.jpg
Feel free to add or edit it for more spawn points as well, and keep in mind that sometimes you will not get any buried chest in a run I dont know why would that happen but I couldnt find ANY on a HM party last night.
Hope it helps.
Edit: Getting 10 chests = getting the "Immediate Vicinity" Message.