ABSTRACT
Nodules consisting of low-F apatite occur concentrated as a discreet band in graphitic Fe-Zn ore of the 160 Mt Gamsberg deposit. Their shape, geochemistry (particularly REE) and analogy to modern equivalents strongly suggests the precursors of these nodules to be francolite concretions that formed during diagenesis in organic-rich muds. The features of the nodules differ significantly from those of coarse-grained apatite in iron formations overlying the ore zone, whose signature is similar to hydrothermal apatite elsewhere. Although the origin, sedimentological environment and mineralogical association of the two occurrences is fundamentally different, the close genetic and spatial relationship of apatite with iron-rich sediments and bedded base metal sulfides is characteristic. As a result, it might hold important implications for exploration for stratiform sulfide mineralisation in Proterozoic terranes.
