On the map and in the legend is a Mine icon. In both Locations of Chult and Random Encounter table, i cannot find a reason for this icon. The rest are covered in those or the Expedition Begins pages. halp
As near as I can tell from looking at it both in Roll20 and the book, other than Wyrmheart these are places to add your own mine adventure if you want. If it helps, the River Tath is home to the Aldana Lobsterfolk, so a custom mine built around that could be cool over there. And up by the Fort, you could go with something a bit more Flaming Fist or trade related.