I asked Chat: Back in the old days, what was the typical amount of gold per ton of the ore. I heard 1/2 to 1 ounce per ton.
Yes — ½ to 1 troy ounce of gold per ton of ore was quite realistic for many of the richer old underground gold mines, although there was a huge range.
For perspective:
- 0.5 oz/ton = about 17 grams/ton
- 1 oz/ton = about 34 grams/ton
- Some exceptionally rich veins ran several ounces per ton, and occasional pockets were extraordinarily higher.
- Lower-grade ore could be 0.1 oz/ton or less.
A very good historical example is the Idaho-Maryland Mine in California, which operated from 1866–1955. Its reported lifetime average mill-head grade was about 0.50 oz of gold per ton.
Another historical study of Virginia mines calculated grades ranging from about 0.29 to 0.58 oz/ton, with one property ranging as high as 1.55 oz/ton.
So your recollection of ½ to 1 ounce per ton is quite reasonable for high-grade historical gold ore.
And here’s the interesting part: 1 ounce per ton sounds small, but one ton of rock is an enormous amount of material. At the old official gold price of $20.67/oz, that was about $20.67 worth of gold per ton before mining and milling costs.