I have. That was what got me reading about American-style black chattel slavery being practiced by First Nations. I looked around a bit for way to verify the upper estimate of numbers of FN-owned black chattel slaves. But any numbers seem to come from very limited, and as I remember, suspect, sources. I did a pretty cursory search, though, just internet, no census records, or scholarly articles. 

Another thing about that article on FN slavery you sent me; it says nothing about the horrendous impact of post-Columbian American pandemics, brought from Europe, which wiped out what has been widely estimated at around 90% of the FN populations in North America.

The pandemics meant that any form of FN slavery observed by white settlers/explorers would very likely have been strongly shaped by population shortages. I suspect we understand little about how the People lived before the pandemics, and those white observers certainly didn't see it.

Hey. I'm signing off. WLW