Geologi dan Karakteristik Mineralisasi Bijih Skarn di Daerah Sulit Air, Kabupaten Solok, Provinsi Sumatera Barat

AFRILITA, Dr.rer.nat.Ir. Arifudin Idrus, S.T., M.T., IPU.;Dr.rer.nat. Ir. I Wayan Warmada, IPM.

2021 | Tesis | MAGISTER TEKNIK GEOLOGI

Endapan skarn merupakan salah satu dari beberapa endapan hidrotermal yang menghasilkan endapan bijih yang bernilai ekonomis. Mineralisasi skarn pada daerah Sulit Air sudah diketahui sejak lama, namun belum ada penelitian rinci yang membahas tentang karakteristik alterasi dan mineralisasi di daerah ini. Penelitian ini membahas tentang geologi, karakteristik mineralogi dan geokimia skarn tembaga di daerah Sulit Air. Metodologi dalam penelitian ini adalah pemetaan geologi permukaan dan analisis laboratorium terhadap sampel yang diambil. Analisis laboratorium yang dilakukan yaitu analisis petrografi, mikroskopi bijih, fire assay-AAS (Atomic Absorption Spectrometry), ICP-AES (Inductively Coupled Plasma Atomic Emission Spectrometry), dan ICP-MS (Inductively Coupled Plasma - Mass Spectrometry). Zona alterasi skarn tembaga terbagi kedalam empat zonasi yaitu zona piroksen-K-feldspar-klorit-epidot, zona garnet-piroksen, zona piroksen-kuarsa, dan zona garnet-wollastonit-piroksen. Unsur CaO, Sr, SrO, Sn, W, U, MnO, Fe2O3, K2O pada alterasi endoskarn mengalami penambahan yang signifikan, sedangakan unsur Zr, V, Cr2O3, Cr, BaO, Na2O dan Ba mengalami pengurangan konsentrasi. Pada alterasi eksoskarn unsur SiO2, Fe2O3, TiO2, MnO, Na2O, Tb, Ho, Eu, Nb, Hf, Th, Sn, W mengalami penambahan konsentrasi sedangkan K2O, SrO, MgO, CaO, La, Rb, Ce, Zr, Cr, Ba, dan Sr mengalami pengurangan konsentrasi. Alterasi dan mineralisasi skarn terbentuk disepanjang kontak antara Satuan marmer Tuhur dengan Satuan Granodiorit Sulit Air berumur Jura. Penyebaran alterasi dan mineralisasi dikontrol oleh sesar mendatar kiri berarah utara-selatan (N-S) dan barat laut-tenggara (NW-SE). Mineralisasi skarn di daerah Sulit Air berasosiasi dengan tembaga, perak dan emas. Mineral pembawa tembaga berupa bornit, kalkopirit, kalkosit, kovelit, azurit, malakit, dan krisokola yang terdapat pada zona alterasi garnet-wollastonit-piroksen dan garnet-piroksen. Mineralisasi hadir dalam bentuk urat dan terdisseminasi pada batuan. Berdasarkan hasil analisis fire assay-AAS pada 6 sampel terpilih, kandungan tembaga berkorelasi positif dengan unsur Au, Ag, Pb, As, Bi dan tidak berkorelasi terhadap unsur Zn dan Mn.

Skarn deposit is one of several hydrothermal deposits that produce ore deposits of economic value. Skarn mineralization in the Sulit Air area has been known for a long time, but there has been no detailed study that discusses the characteristics of alteration and mineralization in this area. This study discusses the geology, mineralogy and geochemical characteristics of copper skarn in the Sulit Air area. The methodology in this research is the mapping of surface geology and laboratory analysis of the samples taken. Laboratory analyzes includes petrographic analysis, ore microscopy, fire assay-AAS (Atomic Absorption Spectrometry), ICP-AES (Inductively Coupled Plasma Atomic Emission Spectrometry), and ICP-MS (Inductively Coupled Plasma - Mass Spectrometry). The copper skarn alteration zone is divided into four zones, namely the pyroxene-K-feldspar-chlorite-epidote zone, the garnet-pyroxene zone, the pyroxene-quartz zone, and the garnet-wollastonite-pyroxene zone. The elements CaO, Sr, SrO, Sn, W, U, MnO, Fe2O3, K2O in the endoskarn alteration increased significantly, and the elements Zr, V, Cr2O3, Cr, BaO, Na2O and Ba decreased in concentration. In the exoskarn alteration of the elements SiO2, Fe2O3, TiO2, MnO, Na2O, Tb, Ho, Eu, Nb, Hf, Th, Sn, W there is an increase in concentration and K2O, SrO, MgO, CaO, La, Rb, Ce, Zr, Cr , Ba, and Sr decreased in concentration. Skarn alteration and mineralization formed along the contact between the Tuhur Marble Unit and the Jurassic Sulit Air Granodiorite Unit. The distribution of alteration and mineralization is controlled by a left slip fault trending north-south (N-S) and northwest-southeast (NW-SE). Skarn mineralization in Sulit Air areas is associated with copper, silver and gold. Minerals containing copper are bornite, chalcopyrite, chalcocite, covelite, azurite, malachite, and chrysocole are found in the garnet-wollastonite-pyroxene and garnet-pyroxene alteration zones. Mineralization is present in the form of veins and is disseminated in the rock. Based on the results of the fire assay-AAS analysis on 6 selected samples, the copper content was positively correlated with the elements Au, Ag, Pb, As, Bi and not correlated with the elements Zn and Mn.

Kata Kunci : Skarn, Alterasi, Mineralisasi/Skarn, Alteration, Mineralization