Instead of its economic impact, tin mining activities cause environmental problems. The tin occurrence which is related to tin-bearing alteration on S-type Muncung Granite and its mining history in Singkep Island describes in this study. This work assessed the heavy metals concentration in six tin tailings and two soils from Singkep using inductively coupled plasma-mass spectrometry in correlation to environmental hazard. Both primary and placer mining methods applied in tin excavations on the studied area. Concentration tendency of heavy metals in the six studied tailings samples is generally Cr>Pb>As>Ba≈V. The identical heavy metals trend represented by the three samples from Bukit Tumang might reflect a similar primary tailings character. On the other hand, anthropogenic activities and different surrounding rocks caused the dissimilarity of heavy metals pattern on placer wastes. Higher environmental problems are detected on the primary wastes than the placer one, especially arsenic and chrome. Severe arsenic pollution degree is also indicated in the soil sample just outside the mining location at Betong Village. Conservation and amelioration programs are useful in improving the environmental condition on studied locations.

No abstract

The presence of mineral alteration or secondary processes to rocks on submarine volcano of Abang Komba was caused by an introduction of hydrothermal solutions. Those are indicated by the presence of a resembly of minerals alteration seen in their petrographic analyses. They are characterized by replacement partially surrounding of plagioclase phenocrysts, partially replacing plagioclase by sericite, carbonate and clay minerals. The replacement of pyroxene partly by chlorite, and the presence of albitisation (secondary albite) contained in fine rectangular plagioclase sized. Other fitures occasionally observed by the presence of partial oxidation of ore minerals and the presence of quartz, and epidote as an alteration from plagioclase and pyroxene. Keywords : alteration, resembly of minerals alteration, oxidation, submarine vulcano of Abang Komba. Gejala alterasi atau proses-proses sekunder yang terjadi pada batuan di gunung bawah laut Abang Komba adalah disebabkan oleh introduksi larutan hidrotermal. Semua ini ditunjukkan dengan kehadiran kumpulan mineral ubahan yang terlihat dalam sayatan batuan. Kumpulan mineral ini dicirikan dengan adanya penggantian sebagian yang mengelilingi fenokris plagioklas, penggantian sebagian plagioklas oleh serisit, karbonat dan mineral lempung. Penggantian sebagian piroksen oleh klorit, dan adanya gejala albitisasi (albit sekunder) yang terdapat pada plagioklas berbentuk balokan yang berukuran halus. Gejala lainnya yang kadang-kadang teramati adanya oksidasi sebagian dari mineral bijih dan hadirnya kuarsa, serta epidot sebagai hasil ubahan plagioklas dan piroksen. Kata kunci : alterasi, kumpulan mineral ubahan, oksidasi, gunung bawahlaut Abang Komba.

Previous investigations of granitoids in Sumatra were focused on age dating with minimum geochemistry composition analysis. The purpose of this study is to define the geochemistry classification of the intrusions in central Sumatra and to explain the rocks' correlation to Southeast Asia tectonic activities. A polarizing microscope was used for petrography description while XRF and ICP-MS were applied for geochemistry measurements. According to the geochemistry, almost all of the intrusions are the I-type volcanic arc granitoids. The oldest studied rock is the Late Permian Ombilin Granite that should have been formed before West Sumatra and West Burma move away from the Cathaysia. Sulit Air Granite and Tanjung Gadang Granite intrusion were triggered by the subduction of Meso-Tethys beneath West Sumatra while Lassi Pluton and Lolo Pluton due to Indo-Australia and West Sumatra convergency. The Triassic Sijunjung Granite depicts A-type granite natures to suggest an extension in the West Sumatra plate.

Sumberdaya bauksit yang ada di Tayan, Kalimantan Barat belum dimanfaatkan secara optimal dan perlu dilakukan peningkatan nilai tambah bauksit melalui proses pencucian dan pengolahan, sehingga perlu dilakukan pengkajian peningkatan mutu bijih bauksit. Percontoh bijih bauksit yang diambil dari daerah Tayan memiliki kadar SiO2 total 11,55%, Al2O3 43,64%, Fe2O3 9,63%. Proses peningkatan mutu (upgrading) bijih bauksit bertujuan untuk menaikkan kadar bauksit agar memenuhi persyaratan alumina di atas 51% Al2O3, maksimum 3% SiO2 dan maksimum 7 % Fe2O3 untuk bahan baku alumina. Tahapan proses scrubbing meliputi pemercontohan, scrubbing, pengayakan, pengeringan, penimbangan, penggerusan, pemisah magnetik dan analisis kimia. Parameter mutu yang digunakan untuk menilai keberhasilan adalah persen kumulatif ukuran butiran +2 mm (+10 mesh), perolehan Al2O3, kadar SiO2 total, Al2O3, dan Fe2O3. Uji coba proses pencucian-magnetik separator ini telah memberikan hasil yang baik ditinjau dari peningkatan kadar Al2O3 dan perolehan Al2O3. Kadar Al2O3 hasil uji coba berkisar antara 57,29-59,78% dengan perolehan berkisar 69,67-85,58%. Bauksit tercuci-magnetik separator yang dihasilkan telah meningkatkan mutu bijih bauksit sebagai bahan baku pembuatan alumina melalui proses Bayer.