So using the table in the free sample of their book posted at the link you shared, we are looking at 35 to 260 gp per week per miner from a gold mine, depending on the quality of the miner. If we go with the 30 miners assumed necessary to work a mine from the Magical Medieval Society Western Europe (MMSWE) book (and I don't know who based in history that number is) we get 1,050 to 7,800 per week.
Based on the posted YouTube video I got to 6,666 per month, which is 1,538 per week, which is on the lower end of the Angry Golem Games Dwarves & Mines numbers--but it makes sense that Dwarves would be more efficient than historical humans.
For the MMSWE book est of 50,000 per year, we get 962 gp / week, Magical Europe is doing worse than estimated historical Europe.
I'm going to just go with 6,666 per month until they exhaust the mine in 2.5 years, just because my players will think that there must be something cursed about it, despite the math.
Or it's just not a very good vein.
I searched medieval gold mines on YouTube there's several videos
I know more about Roman gold mines.