Why would women miners prefer to work naked and with a belt around their waist and a chain between their legs?

Hrm, I would suggest checking who the source is that says they prefer that. A belt around their waist and a "chain between their legs"? That sounds more like a chastity belt than a mining tool.

My guess is that hen children and women were forced to work in the mine, it was because they had nowhere else to go, no other way to get money. And the bosses knew this, and manipulated the women for their own personal...uses.

I mean, it's hot down there...but not THAT hot.

The only thing I can think of is that having no clothes on would prevent the clothes from getting stuck in the mining equiptment (like the lifts and the buggys), which would get them stuck in the mine, injured. Without clothes, the clothes cannot get stuck, and they cannot get hurt...that way. But I see no practical reason for the belt and chain.

They wouldn't.

Good question. Why would they???