17:15 〜 19:15
[HRE12-P06] Mineralogical and geochemical characteristics in the Wariki Granitoid, West Papua, Indonesia
キーワード：Manokwari, Papua, allanite , granitoid, REE-bearing minerals
The Wariki Granitoid in Manokwari Regency, West Papua Province, Indonesia, is considered a source of REE-bearing minerals in placer deposits. The geology of the study area is composed of metamorphic rocks of the Kemum Formation, which were intruded by the Wariki Granitoid, consisting of Devonian–Carboniferous S-type granite and Permian–Triassic I-type granite. We describe the mineralogical, textural, and geochemical characteristics granitic rocks from the Wariki Granitoid.
Based on field observations, the Wariki Granitoid is located along the WNW–ESE trending Sorong Fault. The Wariki Granitoid consists of the biotite-muscovite granite, tourmaline granite, and granodiorite. The biotite-muscovite granite is characterized by the presence of microcline, plagioclase, biotite, orthoclase, quartz, allanite, apatite, zircon, and muscovite, where plagioclase and biotite are partly replaced by sericite and chlorite, respectively. It sometimes exhibits a myrmekite texture. The tourmaline granite is characterized by a pegmatitic texture, consisting of tourmaline, muscovite, K-feldspar, and quartz. This rock is relatively more altered compared to the biotite-muscovite granite and the granodiorite. The granodiorite consists predominantly of plagioclase, biotite, muscovite, orthoclase, and quartz. REE-bearing minerals, such as allanite and monazite, are identified in the biotite-muscovite granite of the Wariki Granitoid. Allanite in the muscovite-biotite granite is subhedral prismatic form with oscillatory zoning and metamictization in part, containing inclusions of apatite and zircon. Elemental maps obtained by EPMA of the allanite from the biotite-muscovite granite show oscillatory zoning associated to the variations of LREE contents (La, Nd, and Th).
Magnetic susceptibility of the biotite-muscovite granite, tourmaline granite, and granodiorite ranges from 0.274 × 10-3 to 0.765 × 10-3 SI, 0.002 × 10-3 to 0.399 × 10-3 SI, and 0.094 × 10-3 to 0.471 × 10-3 SI, respectively, suggesting an ilmenite-series. Bulk chemical compositions of the Wariki Granitoid samples indicate peraluminous characteristics. Their plots on the Rb versus Nb + Y discriminant diagram suggest that the Wariki Granitoid formed within a volcanic arc setting. Chondrite-normalized REE patterns of the granitoid exhibit enrichment in LREE over HREE, as well as negative Eu anomalies. Total LREE contents of the biotite-muscovite, the tourmaline granite, and granodiorite have averages of 115 ppm, 67.6 ppm, and 243 ppm, respectively.
Based on field observations, the Wariki Granitoid is located along the WNW–ESE trending Sorong Fault. The Wariki Granitoid consists of the biotite-muscovite granite, tourmaline granite, and granodiorite. The biotite-muscovite granite is characterized by the presence of microcline, plagioclase, biotite, orthoclase, quartz, allanite, apatite, zircon, and muscovite, where plagioclase and biotite are partly replaced by sericite and chlorite, respectively. It sometimes exhibits a myrmekite texture. The tourmaline granite is characterized by a pegmatitic texture, consisting of tourmaline, muscovite, K-feldspar, and quartz. This rock is relatively more altered compared to the biotite-muscovite granite and the granodiorite. The granodiorite consists predominantly of plagioclase, biotite, muscovite, orthoclase, and quartz. REE-bearing minerals, such as allanite and monazite, are identified in the biotite-muscovite granite of the Wariki Granitoid. Allanite in the muscovite-biotite granite is subhedral prismatic form with oscillatory zoning and metamictization in part, containing inclusions of apatite and zircon. Elemental maps obtained by EPMA of the allanite from the biotite-muscovite granite show oscillatory zoning associated to the variations of LREE contents (La, Nd, and Th).
Magnetic susceptibility of the biotite-muscovite granite, tourmaline granite, and granodiorite ranges from 0.274 × 10-3 to 0.765 × 10-3 SI, 0.002 × 10-3 to 0.399 × 10-3 SI, and 0.094 × 10-3 to 0.471 × 10-3 SI, respectively, suggesting an ilmenite-series. Bulk chemical compositions of the Wariki Granitoid samples indicate peraluminous characteristics. Their plots on the Rb versus Nb + Y discriminant diagram suggest that the Wariki Granitoid formed within a volcanic arc setting. Chondrite-normalized REE patterns of the granitoid exhibit enrichment in LREE over HREE, as well as negative Eu anomalies. Total LREE contents of the biotite-muscovite, the tourmaline granite, and granodiorite have averages of 115 ppm, 67.6 ppm, and 243 ppm, respectively.