Trump said the countries exempted from the tariffs were Canada and Mexico.
South Africa was not included on the list.
Kumba Iron Ore was the most affected by the tariff announcement.
The share price declined to R280.15 on Friday morning, but later recovered to close at R293.57.
Kumba is a supplier of high quality iron ore to the global steel industry. It sells most of its steel to China.
Kumba reported its results for the year to end December last month, where headline earnings increased by 12percent to R9.7billion (R113.51bn), while headline earnings per share also increased 12percent.
Another steel producer, Arcelor Mittal, was down 8.4percent on Friday. It reached its lowest level on the day and closed at R2.40 a share.
Base minerals and metals company Assore was also down by more than 5percent. The share declined to R307 a share, but recovered during the day to R308.99 and closed the day at 309.90.
Hulamin’s share price dropped 8.33percent and closed at R4.40 on the JSE on Friday.