Somewhere in West Africa, while conducting reconnaissance on a remote site where a major gold rush took place in 2014, I found a sample that was unexpected in the context of the gold deposits in the sub-region.
At this site, while most of the artisanal miners focused on saprolite, some miners followed the mineralisation down to the bedrock, which consisted of very hard quartzite on the edge of a granitic intrusion. Artisanal mines in fresh rock are relatively rare given the challenges of digging at these depths; only very high grades could justify such work.

On the ground, a small fragment of rock catches my eye because of its richness in sulphides other than pyrite found elsewhere in the rest of the dumps. Surely a remnant of ore fell from a tricycle that shuttles between the mine and the washing site by the river. Instead of pyrite, I was surprised to recognise galena and, most notably, what I suspect to be greenockite, a cadmium sulfide. Presence of Cd was confirmed a few hours later by XRF analysis and later its hexagonal crystals observed under the SEM.
Several peri-batholitic quartz veins with sphalerite-pyrite-galena-chalcopyrite have been described in West Africa, notably by Bassot in eastern Senegal. They are also mineralised with gold but are generally less economically interesting than the more classic shear zones found in the same terrain.

Here, the presence of cadmium and lead adds a new problem for the health of artisanal miners and the environment of the sites being exploited.