"Massive sulphides", page-58

actually, they drilled NRS at 25m centres - at between 1200 and 1850m depth per hole. Because, as it turns out, they didn't understand the geology. The style of deposit wasn't the normal Sudbury contact style of mineralisation but vein hosted in a really complex geometry.

And it was because they thought they understood the geology there that it sat on the shelf for 6 years. They spent that 6 years drilling off Onaping Depth, a blind discovery made at 2200-2400 metres depth.

All this goes to say, if it's the right mineralisation, and you can keep the roof and walls from blowing in on you, you can mine to any depth to get it out if there's enough of it at the right grade to build your mine, what you need to treat it, and what you need to get it to market. and the only way you will ever know any of this is to look.