Scifi novel from the 80s or 90s with a trash mine
Set far into the future. Humanity has spread to other planets and have been there for hundreds of years. One of our characters is from one of these far flung civilizations and is the heiress of a trash mining fortune (they've been wasteful enough on the planet for long enough that they're mining through their own trash piles for plastics and metals since that's more economical than chasing played out mines).
Someone finds an alien artifact that does *something*. A quest is kicked off with a ragtag band of misfits.
I read it in the late 90s or early aughts.