If you are getting some jewelry out and exported at the Port, then the factory is getting input even if nothing shows in the input queue.
While estimating the quantity of gold (or other mineral) in a particular load takes a bit of experience, none-the-less players need to remember that there is nothing in the game that limits the number of mines which may be built to work a particular ore load to one
Remembering that the mine building "foot-print" blocks use of the ore there, it is possible to build several mines to exploit one ore location.
Further, if there are mixed minerals at that location, building several mines all set to the "all metals" option may be the best way to speed exploitation.
But then you have to remember that the lode eventually will be exausted. Since then, it has been discovered that "Lode Exaustion" is not tracked in the ground -- rather it is tracked by the Mine building(s). Therefore, when a mine building stops producing - bulldoze it and build another to continue production.