Surat Lal died with seven colleagues in an explosion at a small quarry in India, but like thousands of other casualties at mines in the developing world, his death wasn’t counted as a mining fatality.

Around 90% of the world’s miners, according to the World Bank, work in small-scale operations or illegally by trespassing on land controlled by others, including bigger mining companies. Those miners—who dig up materials used in cars and smartphones, among other products—are frequently operating in emerging economies like India,...