Answer: He was more interested in mining and exaggerated the potential mineral wealth of the area.
"In 1715, Cadillac and his son Joseph prospected in the Illinois Country (Upper Louisiana), where they claimed to have discovered a copper mine, although there is no copper ore in that area. They established a farm and founded the settlement of St. Philippe on the east side of the Mississippi River. Cadillac directed the first mining of lead in present-day Missouri at what is now called Mine La Motte on the west side of the river. The French brought in slaves to work at the mine; they were the first people of African descent in the future state of Missouri. The production of lead was important for ammunition in the colonies. The Southeast Missouri Lead District is still a major source of that metal.
After many arguments, Crozat withdrew any authority Cadillac had in the company. The following year, he ordered Cadillac removed from colonial office."