Approximately when did people in the region south of the sahara develop a technique for melting iron ore to create tools, weapons, and other objects?

The people in the south of the sahara did not develop the technique in melting iron. the technique was brought to them through the trans-saharan trade.  it was a trade route frequented by merchants primarily from arabia and some parts of asia. trough the trading, the civilizations in the sahara over time adopted the technique for melting iron. this would be around 12th century