Dobell, the largest single fund manager invested in the business, increased his holding from 32.25 million shares to 33.79 million or 10.2% worth £85.49 million at a share price of 253p.
Shares in African Minerals are down 44.76% over the last 12 months, as operating losses have widened and a series of brokers have cut their recommendations against the company.
Speaking in October, Dobell expressed frustration with its underperformance but added that he maintained his faith in the business.
That faith was rewarded this week when it arranged a $92 million (£57.15 million) line of credit after poor weather delayed ore shipments. The delay had caused the company to warn that annual production would come in at the bottom end of previous estimates.
Over five years Dobell has returned 13.8% versus the average UK All Companies manager return of 2.4%.