Geological Prospection of Placer Chromium Deposits in the Waropen Regency—Indonesia (New Guinea) Using the Method of Indicator Minerals.

Indicator minerals (IM) have been used in the research of gemstone and base metals for over 100 years. IMs are a main source of information about the occurrence of deposits, hydrothermal and weathering changes, as well as bedrock source and type. Since 2013, base metal mineral exploration has taken place on New Guinea Island (the Indonesian part). The analysis of chromian spinels as IM in beach and river sediments led to the discovery of rich chromian-bearing deposits in the Botawa River sediments. The dominant detrital minerals include chromian spinels, olivine, pyroxenes and serpentine. The source of chromian spinels, olivine and pyroxenes are most likely peridotites from the Earth's mantle zone of the ophiolite series, generated under supra-subduction conditions. The terrigenous deposits contain metamorphic minerals, such as staurolites, andalusites, epidotes, amphiboles and fragments of micas, quartz and chlorite schists. Using ICP-MS analysis of the beach sands, the concentration of Cr₂O₃ was determined to be at the level of 1.17%, while in the heavy minerals concentrate from the Botawa River sediment, the content of Cr₂O₃ amounts to 24.83%. The authors conclude that the west parts of the Van Rees Mountains are the probable parent rocks for chromium-bearing sediments. [ABSTRACT FROM AUTHOR]