13:45 〜 14:00
[SCG48-07] Characterization of Libeli Banded Iron Formation (BIF) and surrounding rocks, Niger State, Nigeria
キーワード：Banded iron formation (BIF), Basement complex, protolith, Zircon, Libeli, Nigeria
This work involves detailed geological and geochemical investigation of the iron ores and surrounding rocks in Libeli area, Niger State, Nigeria to understand the process of formation of BIF (Banded Iron Formation). About one half of Niger state is underlain by basement complex rocks while the other by Cretaceous sedimentary rocks of the Bida Basin and part of the Sokoto (Iullemedden) Basin. The Basement rocks consist of a suite of migmatites, and schists intruded by granitoids. The study area is characterized by the occurrence of rocks of various lithologies that includes banded iron formation (BIF), quartzite, amphibolite, mica-schist, and augen gneisses. The Libeli iron ore is hosted in a parallel shear zone in a folded sequence of schist. The general trend is in the N-S direction. Present in the area were iron ore boulders resulting from rupturing of iron ore veins intruded by quartz, iron-enriched laterite, and iron ore cobbles.
Samples of banded iron ores, granites, and schist were collected in the study area. The schist shows a fault relationship with the BIF and the granite intruded the iron ores. BIF mineralogy consists of hematite, quartz, garnet, and minor amounts of magnetite and chromite as shown by both XRD result and petrological observation. The medium to coarse-grained pelitic schist, composed mainly of hornblende, plagioclase and K-feldspar and trace amount of zircon, titanite, muscovite and opaque minerals. Granite is composed of quartz, plagioclase, K- feldspar, hornblende, biotite, titanite, zircon and garnet.
The iron ores are characterized by medium grade content of (53.1 – 57.5 wt% Fe2O3) and SiO2 of 14.1 – 22.0 wt%, Al2O3 of 4.61 – 5.45 wt % and relatively higher content of MnO of 11.9 – 12.93 wt%. Trace element concentration determined using ICP-MS reveals Li ranges from 8.1 – 27.2 ppm, Sc from 9.4 – 11.3 ppm, while Sr from 41.1 – 71.12 ppm, Rb from 0.95 – 0.99 ppm, Cr from 86.4 – 128 ppm, Y from 90.2 – 142 ppm, Co from 146 – 159 ppm, V from 495 – 695 ppm, Ni from 296 – 359 ppm and Eu from 4.6 – 5.4 ppm. The REE of the BIF shows high concentration. The granite is I-type. The schist shows S-type characteristics and peraluminous protolith.
The U-Pb dating of zircon was attempted with the LA-ICP-MS utilize a New Wave Research 193UC excimer laser ablation system, coupled to an Agilent 7700 quadru-pole ICP-MS at the Graduate School of Engineering Science, Akita University.
The result show that 206Pb/238U magmatic ages of zircon from the granite is 852 ± 11 Ma.The granite zircons have inclusion of biotite, k-feldspar, quartz, albite, apatite and titanite. some detrital core rimmed by oscillatory zone is seen in the cathodoluminescence image of the zircons.
The 206Pb/238U ages of zircon from the schist is 593 ± 8 Ma which shows the metamorphic age accompanied to Pan-African Orogeny. The zircons in the schists show some inclusion of quartz, k-feldspar, FeO, apatite and biotite. The biotite inclusions in core of zircon are not found in matrix of the schist.
The iron ores have a contact metamorphism during the intrusion of the granites. According to our study, the Libeli BIF is believed to be of the Lake-superior type.
Samples of banded iron ores, granites, and schist were collected in the study area. The schist shows a fault relationship with the BIF and the granite intruded the iron ores. BIF mineralogy consists of hematite, quartz, garnet, and minor amounts of magnetite and chromite as shown by both XRD result and petrological observation. The medium to coarse-grained pelitic schist, composed mainly of hornblende, plagioclase and K-feldspar and trace amount of zircon, titanite, muscovite and opaque minerals. Granite is composed of quartz, plagioclase, K- feldspar, hornblende, biotite, titanite, zircon and garnet.
The iron ores are characterized by medium grade content of (53.1 – 57.5 wt% Fe2O3) and SiO2 of 14.1 – 22.0 wt%, Al2O3 of 4.61 – 5.45 wt % and relatively higher content of MnO of 11.9 – 12.93 wt%. Trace element concentration determined using ICP-MS reveals Li ranges from 8.1 – 27.2 ppm, Sc from 9.4 – 11.3 ppm, while Sr from 41.1 – 71.12 ppm, Rb from 0.95 – 0.99 ppm, Cr from 86.4 – 128 ppm, Y from 90.2 – 142 ppm, Co from 146 – 159 ppm, V from 495 – 695 ppm, Ni from 296 – 359 ppm and Eu from 4.6 – 5.4 ppm. The REE of the BIF shows high concentration. The granite is I-type. The schist shows S-type characteristics and peraluminous protolith.
The U-Pb dating of zircon was attempted with the LA-ICP-MS utilize a New Wave Research 193UC excimer laser ablation system, coupled to an Agilent 7700 quadru-pole ICP-MS at the Graduate School of Engineering Science, Akita University.
The result show that 206Pb/238U magmatic ages of zircon from the granite is 852 ± 11 Ma.The granite zircons have inclusion of biotite, k-feldspar, quartz, albite, apatite and titanite. some detrital core rimmed by oscillatory zone is seen in the cathodoluminescence image of the zircons.
The 206Pb/238U ages of zircon from the schist is 593 ± 8 Ma which shows the metamorphic age accompanied to Pan-African Orogeny. The zircons in the schists show some inclusion of quartz, k-feldspar, FeO, apatite and biotite. The biotite inclusions in core of zircon are not found in matrix of the schist.
The iron ores have a contact metamorphism during the intrusion of the granites. According to our study, the Libeli BIF is believed to be of the Lake-superior type.