"In non-aboriginal Canadian society old people are not considered important"

Pity and nothing to be proud of.

"what makes old aboriginals very important to mine development?"

Because in traditional societies the elderly are holders of wisdom and are used as advisors of how a community should behave. My guess is that Webequie and Marten Falls communities still listen to their elders.

We Europeans (I am one, as most Canadians) used to do same centuries past but we became too smart to listen to the elderly. I suppose partly because our world is moving now faster then the elderly can keep up. At least that is the perception.