Conversation so far:
Was types of exploration happened before da Gama?
From the earlier part of the 15th century, Portuguese expeditions organized by Prince Henry the Navigator had been reaching down the African coastline, principally in search of west African riches.
Were any riches found?
They had greatly extended Portuguese maritime knowledge, but had little profit to show for the effort.
After Henry's death in 1460.
What happened after Henry's death?
the Portuguese Crown showed little interest in continuing this effort and, in 1469, sold off the neglected African enterprise to a private Lisbon merchant.
What was the result of neglection of the African enterprise?
Within a few years, Gomes' captains expanded Portuguese knowledge across the Gulf of Guinea, doing business in gold dust, Melegueta pepper, ivory and sub-Saharan slaves.

Question: What was the most profitable trade?
Self-contained rewrite: What was the most profitable trade across the Gulf of Guinea?