Here is a halfway decent story about mining in South Kivu:
I say only halfway decent because this article does exactly what they want to pretend they (unlike "the international community") are not doing — demonizing the FDLR.
I'd say it's probably a pretty good bet that many of the mines in the Kivus are under the thumb of the FDLR (former Rwandan soldiers who came to the Congo after wreaking genocide in 1994). If they're not directly controlling and/or taxing the mines, they are deeply embedded in the entire market structure because most of the mined materials leave the Congo via Rwanda bound for your grocery store shelves or cellphones.
However, where it isn't the FDLR, you could substitute FARDC (the official Congolese army), the Mayi Mayi, the CNDP or God knows who else and the situation for the local guy trying to dig cassiterite out of the ground is/would be exactly the same — someone with a gun is going to force him to pay some bogus "tax" that minimizes his earnings from back-breaking work.
The other thing about this article — all the stuff about "Hutus" and "Tutsis" you should just ignore. It is irrelevant and has little or nothing to do with the situation here, now. That's somebody else's fight.