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STUDI PETROGRAFI DAN GEOKIMIA TERHADAP DISTRIBUSI UNSUR TANAH JARANG PADA LAPUKAN GRANIT DI PULAU BANGKA

PETROGRAPHIC AND GEOCHEMICAL STUDY ON RARE EARTH ELEMENTS DISTRIBUTION IN WEATHERED GRANITE OF BANGKA ISLAND

Master Theses from JBPTITBPP / 2018-07-13 15:14:07
Oleh : FILDZIA IRSINA HANINI (12013079), S1 - Geological Engineering-FITB
Dibuat : 2018-07-12, dengan 11 file

Keyword : Pulau Bangka, unsur tanah jarang, pelapukan granit, distribusi unsur, mineralogi, horizon B

Studi petrografi dan geokimia pada batuan dan lapukan granit di Pulau Bangka, dilakukan untuk memperkirakan faktor-faktor yang berperan pada pelapukan terhadap distribusi unsur tanah jarang. Penelitian difokuskan pada granit tipe S bagian dari Granit Klabat, terletak di Kabupaten Bangka Induk, Pulau Bangka Utara. Penelitian dilakukan pada 9 sampel batuan dan 18 sampel lapukan. Sampel dianalisis secara petrografi dan geokimia, berupa XRF, XRD, dan ICP-MS yang didukung data sekunder serta referensi. Batuan granit di daerah penelitian disominasi oleh alkali felspar, kuarsa, biotit, plagioklas, muskovit, opak, dan mineral pembawa unsur tanah jarang, berupa apatit, monazit, dan zirkon. Proses pelapukan batuan menghasilkan mineral sekunder dominan berupa kaolinit, gibsit, dan kuarsa residual. Profil lapukan granit daerah penelitian terbagi menjadi horizon O, A, B, C, dan batuan asal. Unsur tanah jarang dapat mengalami mobilisasi, menyebabkan migrasi maupun akumulasi di horizon B akibat terikat oleh mineral lempung. Akumulasi unsur tanah jarang pada horizon B di daerah penelitian dipengaruhi oleh fraksinasi light rare earth elements (LREE)/heavy rare earth elements (HREE), akibat afinitasnya terhadap kaolinit dan gibsit. Horizon B mengalami akumulasi LREE lebih tinggi dibanding HREE, karena HREE lebih mudah terlarutkan saat pelapukan terjadi. Profil lapukan di daerah Kangurung, Sambunggiri 1, Sambunggiri 2, dan Pemali, memiliki pola distribusi unsur tanah jarang yang relatif terakumulasi di horizon B. Namun, profil lapukan di daerah Belinyu 1 dan Air Nyatoh tidak mengalami akumulasi. Faktor topografi, drainase, tingkat pelapukan serta mineralogi, menjadi faktor yang mempengaruhi distribusi unsur tanah jarang pada lapukan.

Deskripsi Alternatif :

Petrographic and geochemical studies on rocks and weathered granite of Bangka Island are carried out to predict the primary factors which influence the weathering process and distribution of rare earth elements. Research focused on S-type granitoids of Klabat Granite, which is located in Bangka Induk Regency, North Bangka. The research is conducted on 9 samples of rock and 18 samples of weathered Klabat Granite. The analysis consists of petrography, XRF, XRD, and ICP-MS, supported by secondary data and references. The granite in the research area consists of alkali felspar, quartz, biotite, plagioclase, muscovite, opaque, and REE-bearing minerals such as apatite, monazite, and zircon. Weathering processe result in dominant secondary minerals such as kaoline, gibbsite, quartz residuals. Weathered granite consists of O, A, B, C horizon, and parent rocks. Rare earth elements can mobilized and commonly distributed or accumulated in B horizons by adsorption of clay minerals. The accumulation of rare earths in B horizons is influenced by the fractionation of LREE/HREE by their affinities with kaoline and gibbsite. In B horizons, LREE are highly accumulated than HREE, because HREE are preferred to leaching. Rare earth elements in weathered profile of Kangurung, Sambunggiri 1, Sambunggiri 2, and Pemali, are accumulated in B horizons. However, rare earth elements in weathered profile of Belinyu 1 and Air Nyatoh are not accumulated. Factors such as topography, drainage, weathering index and mineralogy are important factors that affecting the distribution of rare earth elements in weathered profile.


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