Identifikasi Karakteristik Mineralogi dan Geokimia Batuan Granitoid Kabupaten Belitung, Provinsi Bangka Belitung

DZAKY AHMAD DHANY SEMENGUK, Ir. Esti Handini, S.T., M.Eng., D.Sc., IPM., Dr.rer.nat. Ir. I Wayan Warmada, IPM.

2026 | Skripsi | TEKNIK GEOLOGI

Penelitian ini dilakukan untuk mengidentifikasi karakteristik mineralogi dan geokimia batuan granitoid di Kabupaten Belitung, Provinsi Bangka Belitung. Metode penelitian meliputi analisis mineralogi pada lima sampel primer menggunakan sayatan tipis dengan metode point counting, serta analisis geokimia (unsur mayor, jejak, dan tanah jarang) dengan metode ICP-AES dan ICP-MS. Data primer dilengkapi dengan data sekunder dari studi sebelumnya untuk memperkuat interpretasi. Hasil analisis mineralogi menunjukkan bahwa batuan granitoid di daerah penelitian didominasi oleh kuarsa (29–45%), K-feldspar (28–52%), dan plagioklas (5–12%), dan dilengkapi oleh biotit, muskovit, hornblenda, dan klorit. Berdasarkan diagram QAPF, batuan diklasifikasikan sebagai syenogranit dengan tekstur holokristalin, ekuigranular, serta ditemukannya tekstur graphic dan zoning. Analisis geokimia mengindikasikan bahwa batuan termasuk dalam seri granit berdasarkan diagram TAS. Nilai A/CNK (0,97–1,30) menunjukkan sifat peralumina hingga metalumina. Afinitas magma cenderung high-K calc-alkaline hingga shoshonit. Spider diagram dan diagram REE menunjukkan pengayaan unsur LREE serta anomali negatif Eu yang mengindikasikan fraksinasi plagioklas. Plot unsur jejak pada diagram tektonik menempatkan batuan pada lingkungan transisi antara syn-collisional dan within plate. Berdasarkan diagram source rock, sampel berasal dari batuan metasediment. Berdasarkan diagram source rock, komposisi SiO?, dan nilai A/CNK, disimpulkan bahwa granitoid Belitung termasuk dalam tipe S. Penelitian ini merekomendasikan penambahan jumlah sampel primer dan variasi titik pengambilan untuk meningkatkan akurasi dan representativitas data di wilayah studi yang luas.

This research was conducted with the goal of identifying the mineralogical and geochemical characteristics of granitoid rocks in Belitung Regency, Bangka Belitung Province. The research methods include mineralogical analysis of five primary samples using thin sections with the point counting method, and geochemical analysis (major, trace, and rare earth elements) using ICP-AES and ICP-MS methods. Primary data were supplemented with secondary data from a previous study to strengthen the interpretation. The results of mineralogical analysis shows that the granitoid rocks in the study area are dominated by quartz (29–45%), K-feldspar (28–52%), and plagioclase (5–12%), accompanied by biotite, muscovite, hornblende, and chlorite. Based on the QAPF diagram, the rocks are classified as syenogranite with holocrystalline, equigranular texture, and the presence of graphic and zoning textures. Geochemical analysis indicates that the rocks belong to the granite series based on the TAS diagram. A/CNK values (0.97–1.30) show peraluminous to metaluminous characteristics. Magma affinity tends to be high-K calc-alkaline to shoshonite. Spider diagrams and REE diagrams show enrichment of LREE and a negative Eu anomaly, indicating plagioclase fractionation. Plots of trace elements on tectonic discrimination diagrams place the rocks in a transitional environment between syn-collisional and within plate. Based on the source rock diagram, the samples are derived from metasedimentary rocks. Considering the source rock diagram, SiO? composition, and A/CNK values, it is concluded that the Belitung granitoids belong to the S-type. This study recommends increasing the number of primary samples and varying sampling points to improve the accuracy and representativeness of data in the relatively large study area.

Kata Kunci : Batuan granitoid, granit, Kabupaten Belitung, mineralogi, geokimia