It was mined a long time ago by some very antique mining techniques. With the advances in mining technology, a lot more ore can be extracted today than in yesteryear.
The mine I work at is reprocessing waste rock from as little as 30 years ago to extract the ore that couldn't have been extracted even as recent as that. With today's technology, they can also extract ore from solution by electoplates using high amperage.
So with this being an established mine already, probably a lot has been missed. This is almost a guarantee there is gold ore there because it was an operating mine at one time. The big question, which the labs will tell, is how much. My guess is it could be significant.
In some old mines, especially gold, they are actually going through tailings from 100 to 150 years ago to extract ore in significant quantities. In those days, they took what they could see for the most part, in today's mill's, they extract almost all.
How much is there will show up in the assay results from the lab. That can take from a few weeks to a couple of months depending on how busy the labs are.