KARAKTERISTIK ALTERASI DAN MINERALISASI BIJIH BESI SKARN DI NAGARI LOLO, KECAMATAN PANTAI CERMIN, KABUPATEN SOLOK, SUMATERA BARAT

PANDU DEYA ANANKE, Dr.rer.nat. Ir. Arifudin Idrus, S.T., M.T., IPU. ; Ir. Anastasia Dewi Titisari, M.T., Ph.D., IPU.

2023 | Tesis | MAGISTER TEKNIK GEOLOGI

Nagari Lolo secara administratif berada di Kecamatan Pantai Cermin, Kabupaten Solok, Provinsi Sumatera Barat. Secara fisiografis daerah penelitian termasuk ke dalam provinsi metalogeni Sunda Arc yang merupakan bagian dari busur magmatik Sunda-Banda. Pada daerah penelitian terdapat potensi bijih besi yang telah diketahui sejak lama namun belum diteliti secara rinci. Penelitian ini bertujuan untuk mengetahui kontrol geologi terhadap proses mineralisasi serta karakteristik endapan melalui kegiatan pemetaan geologi lapangan, analisis petrografi batuan penyusun lokasi penelitian, analisisis mikroskopi bijih dan mikro-XRF sampel batuan termineralisasi, analisis XRD batuan teralterasi, serta karakteristik geokimia mineral bijih dengan analisis XRF, ICP-AES dan ICP-MS. Mineralisasi pada daerah penelitian ditemukan pada hostrock berupa batugamping berumur Jura yang diintrusi oleh granodiorit berumur Kapur. Mineralisasi ditemukan mengikuti kemenerusan struktur sesar mendatar kanan Lolo sebagai struktur pre-mineralisasi. Alterasi hidrotermal yang terdapat pada daerah penelitian merupakan alterasi skarn yang diindikasikan oleh kehadiran mineral kalk-silikat seperti garnet, klinopiroksen dan wollastonit pada batugamping serta klorit dan epidot pada batuan intrusi. Berdasarkan analisis kesetimbangan massa proses alterasi mengakibatkan terjadinya pengurangan massa pada granodiorit sebesar 3,356%, sedangkan pada batugamping terjadi penambahan massa sebesar 0,159%. Unsur besi (Fe) ditemukan terdapat pada mineral oksida seperti magnetit, hematit, goetit, dan limonit yang berasosiasi dengan sulfida seperti pirit, kalkopirit, dan kovelit dalam jumlah kecil. Dari hasil analisis XRF diperoleh kadar besi (Fe) sekitar 94,02-95,88%, sedangkan kandungan Cu sebesar 936,7-1180 ppm.

Nagari Lolo is administratively located in Pantai Cermin District, Solok Regency, West Sumatra Province. Physiographically the study area is included in the metallogenic province of Sunda Arc which is part of the Sunda-Banda magmatic arc. In the research area there is potential for iron ore which has been known for a long time, yet has never been studied in detail. The purpose of this study is to determine geological control on the mineralization process and deposit characteristics through field geological mapping, petrographic analysis of the rocks making up the study area, ore microscopy and micro-XRF analysis of mineralized rocks, XRD analysis of altered rocks, and geochemical characteristics of ore minerals through XRF, ICP-AES and ICP-MS analysis. Mineralization in the study area was found in the hostrock of Jurassic Limestone that intruded by Cretaceous Lolo granodiorite. The mineralization was found constrained along the lineament of the Lolo dextral strike-slip fault as a pre-mineralization structure. The hydrothermal alteration found in the study area is skarn alteration which is characterized by the presence of calc-silicate minerals such as garnet-clinopyroxene-wollastonite in limestone and chlorite-epidote in intrusion rock. Based on mass balance analysis the alteration process results in decreasing in granodiorite's mass by 3.356%, on the other hand, the limestone wallrocks gain a mass of 0.159%. Iron was found in oxide minerals such as magnetite, hematite, goethite, and limonite associated with sulfides such as pyrite, chalcopyrite, and covellite in a small amount. Based on XRF analysis, the iron (Fe) content was about 94.02-95.88%, while the Cu content was 936.7-1180 ppm.

Kata Kunci : Nagari Lolo, besi, skarn, alterasi, mineralisasi.