SEM-EDS Characterization of Metal-Bearing Particles in Kali Kabur River Sediments, Mimika, Central Papua, Indonesia: A Preeliminary Mineralogical Assessment

Abstract

The Grasberg porphyry copper-gold mining district in Central Papua, Indonesia, has historically discharged tailings into the Ajkwa river system, raising concerns about downstream heavy-metal contamination in tributaries such as Kali Kabur, Mimika Regency. Because bulk geochemical techniques (e.g., XRD, XRF, ICP-MS) characterize average sediment composition but cannot resolve which specific mineral grains host which metals, this preliminary study applied Scanning Electron Microscopy with Energy Dispersive X-ray Spectroscopy (SEM-EDS) spot analysis to two grab sediment samples from Kali Kabur (TS1, Lab No. 3647.25; TS2, Lab No. 3648.25), examined at the accredited tekMIRA laboratory (Certificate of Analysis No. 1044/LFM/10/2025) following internal method PU-3002FM. Backscattered electron imaging guided selection of eight metal-bearing particles (four per sample) for quantitative elemental analysis in weight percent. Results identified a Cu-Fe-S particle consistent with a chalcopyrite-like phase (TS1, Spectrum 1: Cu 44.78 wt%, Fe 22.58 wt%, S 32.64 wt%), a near-stoichiometric pyrite grain (TS1, Spectrum 2: S 47.19 wt%, Fe 52.81 wt%), iron oxide particles in both samples, quartz/silicate particles in both samples, and, in TS2, a Ti-Fe-Al-Si-O particle consistent with altered ilmenite/titanomagnetite intergrown with aluminosilicates, together with an Mn-bearing aluminosilicate phase. These assemblages are mineralogically consistent with the known porphyry Cu-Au mineralization and associated alteration facies of the Grasberg district. However, because no upstream or background reference samples, bulk metal concentrations, or independent mineralogical confirmation (e.g., XRD) were obtained, the data cannot, by themselves, distinguish natural geogenic inputs from mining-derived material, nor support quantitative statements about bioavailability or ecological/human health risk. The findings are reported as a preliminary, particle-level screening that complements but does not substitute for bulk geochemical and mineralogical characterization. We recommend that future work expand sample coverage with georeferenced, depth-controlled sampling and paired background sites, integrate SEM-EDS with XRD or automated mineralogy (e.g., QEMSCAN/MLA) and bulk ICP-MS/AAS analysis, and apply sequential extraction to evaluate bioavailable metal fractions before firm conclusions about environmental health risk in the Kali Kabur system can be drawn.