Petrochemical studies were conducted on granitoids in Sibolga and surrounding areas in North Sumatra, Indonesia. The granitoids presented the characteristics of A‐ and I‐type ilmenite series. The syenogranites from Sarudik, the syenogranite, quartz syenite, and quartz alkali feldspar syenite from Sibuluhan Sihaporas, and the monzogranites from Sibolga Julu are A‐type granitoids that have high SiO2, CaO, Al2O3, Na2O + K2O, and Rb content, a high FeO/MgO ratio, and low Ba, Sr, and Zr content. The alkali feldspar syenite from Sarudik, the quartz alkali feldspar syenite from Tukka, and the quartz syenite from Adian Koting show I‐type characteristics. I‐type granitoids have lower SiO2, Na2O + K2O, Rb, Yb, and total REE (ΣREE) content and low FeO/MgO ratio. However, quartz syenite from the Sibolga Julu, which exhibits I‐type characteristics, has high ΣREE content but a low FeO/MgO ratio. The granitoids consisted mainly of K‐feldspar megacrysts, quartz, plagioclase, and biotite with hornblende in some cases. Accessory minerals were zircon, apatite, allanite, and titanite. Cordierite and corundum occurred as xenocrysts and inclusions in K‐feldspar in syenogranite (Sarudik) and quartz syenite (Adian Koting). SiO2 and ΣREE content and the Rb/Sr ratio are positively correlated to each other. The REE are enriched in quartz alkali feldspar syenites from Sibolga Julu and Sarudik, quartz syenite from Tarutung, and quartz alkali feldspar syenite, syenogranite, and quartz syenite from Sibuluhan Sihaporas. These highly‐differentiated granitoids were formed within the plate settings. In contrast, the ΣREE content of hornblende‐bearing granitoids that were formed in volcanic arc settings is low. The coexistence of cordierite and corundum with biotite and hornblende indicates that the metaluminous magma was contaminated by metasedimentary basement rocks.

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Transfer massa terkait perubahan komposisi geokimia batuan induk akibat alterasi hidrotermal, metasomatisme, maupun pelapukan menjadi topik untuk mempelajari proses geologi terkait. Perubahan massa tersebut dapat dijelaskan dan divisualisasikan melalui metode Isocon. Mineralisasi tembaga teridentifikasi pada salah satu bagian dari Granitoid Sulit Air di Kecamatan X Koto Diatas, Kabupaten Solok. Tulisan ini bertujuan untuk menjelaskan transfer massa akibat mineralisasi Cu pada Granitoid Sulit Air dengan diagram Isocon. XRF dan ICP-MS di Laboratorium Pusat Survey Geologi, Kementerian ESDM (2015) digunakan sebagai perangkat pengukuran kadar oksida utama, unsur jejak, dan unsur tanah jarang. Berdasarkan korelasi antara kandidatnya, Al2O3 dianggap sebagai oksida immobile. K2O, Rb, Sr, dan Ba terkayakan sedangkan oksida utama lain maupun unsur jejak diketahui terkurangkan akibat mineralisasi Cu.UTJ terdeteksi immobile akibat mineralisasi Cu dengan karakter yang relatif sama antara batuan segar dan teralterasi. Meski demikian, sebagian Ce teroksidasi akibat proses mineralisasi sehingga menurunkan anomali positif Ce. Penurunan nilai anomali negatif Eu pada sampel teralterasi dapat mengakibatkan plagioklas semakin terkurangkan. Karakter tipe-I Granitoid Sulit Air diperjelas melalui nilai perbandingan A/CNK, perbandingan N2O terhadap K2O, perbandingan Rb/Sr, dan perbandingan Rb/Ba. Afinitas granitoid busur kepulauan menunjukkan bahwa pembentukan Granitoid Sulit Air terkait dengan vulkanisme di bagian barat Sumatra.

Indonesia needs a proven technology for REE extraction to build a national REE industry. Monazite that has been recovered from placer deposits at Bangka-Belitung areas is the most potential REE source. In the future, ion adsorption type will be another potential source of REE deposits. This paper describes the sequential REE extraction of the weathered crusts of granitoids from Sibolga using sequential extraction ICP-MS analysis is applied to determine bulk samples mineralogical compositions and REE content. The total REE (∑REE) content of weathered crusts of granitoids from Sibuluhan Sihaporas A ranges from 265 to 479 ppm, while the amount of ∑REE leached by sequential extraction range from 151 to 263 ppm, and the percentage of adsorbed ∑REE ranges from 55 to 74%. In comparison, Sibuluhan Sihaporas B ranges from 302 to 634 ppm, 82 to 198 ppm, and 28 to 44%, respectively. ∑REE content of weathered granitoids crusts from Sarudik ranges from 135 to 219 ppm, while that SREE leached by sequential extraction range from 21 to 82 ppm, and percentage of adsorbed ∑REE range from 11 to 50 %, while that Sibolga Julu ranges from 191 to 304 ppm, 111 to 138 ppm, and 27 to 44%.