Earthlight

From back cover Del Rey paperback September 1991:

THE TIE THAT BINDS The human race had been born on a unique world... a world loaded with mineral wealth, unmatched elsewhere in the solar system. This accident of fate gave a flying start to man's technology -- but it made man dependent on his home world. What were the independent republics on Mars and Venus to do? United in a Federation, they were still dependent on Earth for such essentials as mercury, lead, uranium -- and modern technology could not survive without them. There had to be a better way...