Acid Rock Drainage
ARD is the femme fatale of geochemistry, imho. It's so so bad for the environment but so so beautiful and interesting... The point of this post is the pictures.
The mineralogy of ARD is complex and consists mostly of iron oxyhydroxides (goethite - brown/red in the images & iron(III) hydroxide known as yellow boy is likely the yellow), oxyhydroxy-sulphates, sulphates (jarosites - more brown/red), Cu-carbonates. The hints of blue in the images shown are chrysocolla.