I know he was shot while leading his troops after they had forded the river. I'm hoping that somebody else has come across more detail. Thanks in advance.
I've gotten on Google Books Ryan Quint's Determined to Stand. Quickly searching his name in the book, found this passage on page 100.
There seems to be little detail in how the man died, just that he did in the fight against Rickett's division.
I doubt he was mounted though. From what I can tell, most officers brigade level downward would often fight on foot, rather than mounted. There are exceptions though. They could if they had their own mount available and chose to. For example, Richard Garnett, leading the Gamecock Brigade at Pickett's Charge, chose to lead his unit on horseback, due to an injury in his leg. His other brigadiers like Armistead would go in on foot.