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The growing demand for critical raw materials (rare earth elements—REE, Nb, Ta, and others) enforces a need to look for their alternative sources. Distortions of the mineral supply chain caused by COVID-19 have necessitated a re-evaluation of what exists as mining waste from previous exploitation. Consequently, this study aims to provide an inventory of raw materials on the Indonesian Tin Islands (Bangka and Belitung). Geological and mineralogical examinations on Bangka have permitted an economic appraisal of tailings from the processing of cassiterite-bearing sands and confirmed the presence of REE-bearing minerals, chiefly monazite and xenotime, zircon, ilmenite, rutile, niobium-tantalum phases. In general, the mineral content of the tailings varies depending on the sampling site and the type of processing used during ore-production. ICP-MS (inductively coupled plasma–mass spectrometers) analyses revealed anomalous concentrations of LREE (light rare earth elements): La > 5%, Ce > 5%, Pr > 1%, Nd > 1%, Sm > 1% and HREE+Y (heavy rare earth elements and yttrium) up to 2.51 wt%. High values have been found for the “most critical” metals of the HREE group: Dy (up to 0.34 wt%), Tb (up to 0.08 wt%), Eu (up to 61.8 ppm), Nd (>1.0 wt%), and Y (up to 1.20 wt%). In addition, the following contents have been defined: Ga (to 0.03 wt%); Hf (to 0.64 wt%); Ta (to 0.08 wt%); Nb (to 0.23 wt%); W (to 0.14 wt%); Zr (>5.0 wt%); and Sc (to 0.01 wt%). Such high concentrations suggest the tailing dumps to be a potential new source of “critical raw materials”.

1 Pol ish Geo log i cal In sti tute -Na tional Re search In sti tute, Rakowiecka 4, 00-975 Warszawa, Po land Zglinicki, K., Szama³ek, K., 2020. The Cy clops Moun tains Mas sif (New Guinea, In do ne sia) as the prov e nance area for metal-bear ing shelf sed i ments from the Car o lin ian Sea. Geo log i cal Quar terly, 64 (2): 480-491, doi: 10.7306/gq.1512 As so ci ate Ed i tor: Stanis³aw Wo³kowiczIn 2009, on the ini tia tive of PT Halmahera Perkasa the "Jayapura" ex plo ra tion pro ject was car ried out in In do ne sia. As part of this pro ject, ex plo ra tion of the sea bot tom in the north ern coast of New Guinea was car ried out over a dis tance of ~45 km. The suc tion dredge col lected 59 sam ples of loose sed i ments from the shelf bot tom sur face of the Car o lin ian Sea (to a depth of 60 m be low the sea-floor). The ex tracted sam ples are usu ally poorly and mod er ately sorted sands (5 sam ples), medium-grained sands (21 sam ples), and fine-grained sands (33 sam ples). The sand com po si tion shows, among oth ers, a wide spec trum of heavy min er als of ul tra-mafic (Cr-gar net, chro mium spinel, Mg-ol iv ine) and meta mor phic (epidote, clinochlore, am phi bole, ti tan ite) or i gin. The con tent of heavy min er als in the sed i ments is up to 54.77 wt.%. It was found that the source of heavy frac tion in the east ern and west ern parts of the coast is the rock of the ophiolite se ries build ing the Cyclops Moun tains Mas sif. The min eral com po si tion of sed i ments from the cen tral coastal zone cor re sponds to the types of rocks build ing the meta mor phic core of the Cy clops Moun tains (am phi bo lite, gneiss es, an de site). Three min eral-geo chem ical subprovinces were de ter mined on the ba sis of anal y ses of heavy min eral de com po si tion and chem i cal anal y ses of sed iments. Shelf sed i ment from the east ern part of the coast is char ac ter ized by an in creased con tent of stra te gic met als (Ni up to 3560, W up to 3130 and Co up to 142 ppm). In the cen tral zone, the V con tent in creases up to 244 ppm and the Ag con tent up to 5 ppm. In the shelf sed i ments there is a strong de ple tion in the REE.

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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.