ArcelorMittal's South African share price sank by more than 40% on Tuesday after the steelmaker said it expected interim headline earnings to tumble into a loss in the face of the surge in rolling blackouts. ArcelorMittal is not a huge company in JSE terms, but South Africa's economy can hardly industrialise without its product.

ArcelorMittal is sub-Saharan Africa's largest steelmaker, and it is in a power-intensive industry. So, when the lights go out, it illuminates South Africa's path to deindustrialisation.

The company issued a trading system on Tuesday for its financial performance in the first six months of 2023 that underlined the toll of the power crisis on heavy industry.

It said it expected headline earnings per share to topple into the red, from a R2.71 headline profit per share for the comparative period to a headline loss per share within a range of between R0.38 and R0.46 per share, largely because of the surge in rolling blackouts.

This knocked its share price almost 43% lower.

"The softness of the market amidst the unprecedented severity of the electricity load shedding in the last six months was very much underestimated, which in turn affected the response time with which production could be adjusted in a responsible and well-considered manner," the company said.

"Building and maintaining any semblance of operating rhythm, which is an absolute necessity in running a continuous, integrated steelmaking process in a cost-aware manner, proved especially problematic."