Karakteristik mineralogi endapan nikel laterit di daerah, Kabupaten Seram bagian barat Propinsi Maluku

RUMPUIN, Rony E, Dr. Ir. I Wayan Warmada

2010 | Tesis | S2 Teknik Geologi

Nikel laterit adalah produk residual kimia pada batuan ultrabasa. Proses ini berlangsung selama jutaan tahun dimulai ketika batuan ultrabasa tersingkap dipermukaan bumi. Pelapukan pada peridotit menyebabkan unsur-unsur dengan mobilitas rendah sampai immobile seperti Ni, Fe, dan Co mengalami pengayaan secara resindual dan sekunder. Penelitian yang dilakukan adalah karakteristik mineralogi endapan nikel laterit pada batuan peridotit, (terserpentinisasi) jumlah sampel yang dianalisis sebanyak 12 sampel titik bor yang mewakili dengan tujuan mengetahui proses laterisasi dan karakteristik dalam zona pelapukan. Kondisi morfologi, dan struktur lokal daerah penelitian, dapat mempengaruhi olah pola penyebaran endapan nikel laterit, seperti pembentukan rekahan-rekahan pada batuan dasar yang itensitasnya berbeda-beda sehingga berpengaruh pada tingkat pelapukan dan pengkayaan unsur Ni, serta unsur-unsur lain yang ada pada profil laterit. Ketidakteraturan dari distribusi pengkayaan unsur-unsur dan ketebalan laterit tergantung intensitas pengkekaran daerah tersebut. Pembagian zona lateritisasi pada daerah penelitian seperti limonit, saprolit, dan bedrock dilakukan berdasarkan hasil analisa dilapangan dan diskripsi sampel core, yang secara petrografi batuan penyusun daerah penelitian merupakan batuan lherzolite dimana mineral-mineral lempung yang hadir pada zona limonit menunjukkan kehadiran mineral hipersten dan antigorit pada kedalaman 1-5 meter. Zona saprolit menunjukkan kehadiran mineral enstatit, dan antigorit, pada kedalaman 5-20 meter. Zona bedrock menunjukkan kehadiran mineral enstatit, antigorit, forsterit, pada kedalaman 20-23 meter. Zona limonit menunjukkan kehadiran mineral hipersten, antigorit, pada kedalaman 1-7 meter. Zona saprolit tidak menunjukkan kehadiran mineral. Zona bedrock menunjukkan kehadiran mineral hipersten, antigorit, forsterit, pada kedalaman 10-20 meter. Zona limonit menunjukkan kehadiran mineral goetit, pada kedalaman 1-10 meter. Zona saprolit menunjukkan kehadiran mineral goetit, pada kedalaman 10-35 meter. Zona bedrock menunjukkan kehadiran mineral enstatit, antigorit, forsterit, pada kedalaman 35-38 meter. Zona limonit menunjukkan kehadiran mineral goetit, gibbsit, pada kedalaman 1-5 meter. Zona saprolit menunjukkan kehadiran mineral goetit, pada kedalaman 5-21 meter. Zona bedrock menunjukkan kehadiran mineral enstatit, antigorit, pada kedalaman 21-23 meter. Karakteristik mineralogi daerah penelitian berdasarkan hasil analisa petrografi menunjukkan perilaku mineral yang berbeda, tergantung pada tingkat pelapukan dan kedalaman lubang bor. Titik bor 01 sampai 09 menunjukkan peningkatan mineral olivin, ortopiroksen, klinopiroksen, serpentin, dan mineral opak. Dan mengalami perubahan pada titik bor 15 dimana mineral serpentin mengalami kelimpahan dari mineral olivin, klinopiroksen, dan mineral opak.

Nickel laterite is a residual product of chemical process in ultrabasic rocks. The process has occurred for million years when the ultrabasic rocks was exposed into surface. Weathering of peridotite caused the elements with low-to-immobile mobility such as Ni, Fe, and Co undergone enrichment in a residual and secondary manner. Purpose of this research is to find out the mineralogical characteristics of nickel laterite deposits in (serpentine) peridotite rocks. The number of samples analyzed is 12 representative drill points for finding out laterization processes and characteristics in weathering processes. Morphological conditions and local structures of location of the study can influence the distribution pattern of nickel laterite deposits, such as the formation of splits in bedrocks with different intensities, so being able to influence the rates of weathering and enrichment in Ni element and other elements contained in the laterite profile. Irregularity in distribution of elements enrichment and the width of laterite deposits depends on the intensity of area splitting. Subdivision of laterization zone in location of the study, such as limonite, saprolite, and bedrocks was done based on results of both field analyses and the description of core samples. Petrographically, the rocks forming location of the study was serpentine lherzolite rocks, where clay minerals presented. At the drill point limonite zone shows the presence of enstatite and antigorit minerals at the depths of 5-20 meters. Bedrock zone indicates the presence of enstatite, antogorit, and forsterite minerals at the depths of 20-23 meters. At the drill points limonite zone indicates the presence of hyperstene and antigorit minerals at the depths of 1-7 meters. Saprolite zone did not indicate the presence of mineral. Bedrock zone indicates the presence of hyperstene, antigorit, and forsterite minerals at the depths of 10-20 meters. At the drill point limonite zone indicates the presence of geotite mineral at the depths of 1-10 meters. Saprolite zone indicates the presence of geotite mineral at the depths of 10-38 meters. Bedrock zone indicates the presence of enstatite, antigorit, and forsterite minerals at the depths of 35-38 meters. At the drill point limonite zone shows the presence of geotite and gibbsite minerals at the depths of 1-5 meters. Saprolite zone shows the presence of geotite mineral at the depths of 5-21 meters. Finally, bedrock zone shows the presence of enstatite and antigorite minerals at the depths of 21-23 meters. Based on results of the petrological analysis, mineralogical characteristics of location of the study indicate the different behaviors of minerals, depending on the rates of weathering and the depth of drill holes. The drill points 01 to 09 indicates the increased contents of olivine, orthopyroxene, clinopy-roxene, serpentine, and opaque minerals and undergone change in the drill points 15 where serpentine minerals undergone the overwhelming number of olivine, clinopyroxene, and opaque minerals

Kata Kunci : Karakteristik mineralogi nikel laterit di daerah Piru,Seram Barat Propinsi Maluku