Salam Alaikum,
If a mining company is early stage, that is, it is still exploring or building the infrastructure to start mining, it would have expenses but no revenue. In this stage it is typical that these companies raise funds through issuing of additional stock and these funds are used to run the company until it start selling the minerals. The cash they raise does have have some interest, but it is very small compared to what they spend on operations based on stock sales. Are these companies halal. Jazakallah.