The Iron Mountain Steamboat
Later that day, another boat, the Iroquois Chief, came upon their string of barges floating free down the river. The towline had been cut instead of broken.
There is no other information.
The boat with its 54 (although I've also read 52 and 55) passengers disappeared without a trace. Some thought it could have been a boiler explosion, but no wreckage was ever found. I did find mention of the Army Corps of Engineers publishing a report about finding the boat in a cotton field months later, but this was on a message board from someone else seeking information from a rumor.
There are a few mentions in various strange disappearance or quick fact sites like these:
morticom weird disappearances
Grand Illusions reviewed
LePicayune.com _MS Quick Facts
I even came across a small write up in a book called Haunted Places by Dennis William Hauck. According to this, witnesses have heard a woman screaming in the middle of the river near St. Joseph, Mississippi. Occasionally, they'll hear her saying, "Aidez-moi au nome de Dieu. Les hommes me blessent!" (Help me, in the name of God. The men are hurting me!")
They believe it's the voice of an Iron Mountain passenger. Most speculate that river pirates hijacked the ship and killed everyone. Still, one would think some evidence would have remained.