There is always more to say, of course, but I covered the source of Mansa Musa's wealth in this earlier post, and pointed out that it is likely exaggerated – the money he is so famous for spending on his pilgrimage was very probably put together over quite a few years.

The same post touches on the reasons for his lack of prominence in the Malian historical record. You might find it worth reviewing while you're waiting for fresh responses to your question:

With Mansu Musa being supposedly the richest person in history, what sort of extravagant and opulent things did Musa I of Mali have/could afford?