I do not see good profit prospects on it...to see a value, we need to be able to imagine end users, to whom the domain would suit well.
So lets see some gold producer / gold company / gold seller / gold store in Joburg..
they can have names like
JoburgGold.Company
JoburgGold.Store
JoburgGold.Site
JoburgGold.Online
and all this also in .com. (JoburgGoldStore.com, etc...)
So there are so many alternatives, all available for reg fee. If you want to have a profit on the domain name, you need to be able to sell it higher then for reg fee - I think chances here are very slim that someone in Joburg would need the domain so urgently, but it can happen of course.
I think it is not very profitable to pair new gTLD names with GEO keywords, unless it is some very good combination (like LasVegas.City)
Also, .gold has high yearly renewal, so it will eat from profit every year when you keep the domain.