Geochemistry of Schists of Northwest Obudu Plateau, Southeastern Nigeria

Abstract

Precambrian, highly foliated, fine -medium grained schists, which comprise migmatitic schist (MS), quartz mica schist (QMS), biotite mica schist (BMS) and hornblende biotite schist (HBS) constitute important lithological unit in Northwest Obudu Plateau. The schists are associated with gneisses, amphibolites and metaquartzites, and variously intruded by granites, pegmatites and quartzo-feldspathic veins. Sedimentary rocks, which are mostly Cretaceous sandstones, flank the western margin of the study area. Modal analysis shows that all the schists are enriched in quartz, plagioclase (An 32 ), biotite and garnet, except the HBS which is relatively depleted in quartz but highly enriched in biotite (25 vol. %) and hornblende (55 vol. %). Sillimanite and epidote occur in accessory amounts. The co-existence of quartz-plagioclase (An 32 )-garnet-biotite-muscovite-sillimanite in the MS assemblage indicates that the Schists are derivatives of metamorphism of pelitic and mafic rocks, which had attained the uppermost amphibolite facies grade. Geochemically, the schists are enriched in Si0 2 , which ranges from 60.11 wt % in the HBS, rising to 62.94 wt % in the BMS and 66.58 wt % in the QMS, with average of 64.56 wt %. The high SiO 2 content points to a probable effect of an intruding granitic magma on the Pan -African schists. The Al 2 O 3 , Fe 2 O 3 , MgO, CaO and alkalies are relatively moderate to high. The samples are quartz normative, have high molecular value of Al 2 O 3 > {CaO + Na 2 O + K 2 O}. Plots in chemical discrimination diagrams confirm the peraluminous characteristics of the schist and suggest pelitic rock protolith except for the HBS.

Preliminary review of the geology of the hornblende biotite gneisses of Obudu Plateau Southeastern Nigeria

“…(Ekwueme, 2003);4, 5, 6, 7.Data from NE Obudu (Ephraim, 2009); 8, 9. Data from NW Obudu (Obioha 2011); 10, 11.Data from NE Obudu (Obiora, 2012); 12,13. Data from SW Obudu (Ukaegbu, 2003)…”

“…Several workers have studied the geochemistry of the hornblende biotite gneiss. Table 2 is a compilation of major element and Niggli values from five authors (Ekwueme, 2003, Ukaegbu, 2003, Ephraim, 2009, Obioha 2011, Obiora, 2012 and a review of the trends in the data follows. The hornblende-biotite gneisses have high SiO₂ content (68.77 to 72.63 wt%).…”

“…This sheet has been studied in sections; NE, NW, SE, SW by various workers (e.g Orajaka, 1964;Ekwueme, 1994;Ukaegbu, 2003;Ukwang et. al., 2003;Ephraim, 2009;Obioha and Ekwueme, 2011) and these workers have grouped and described the migmatite gneisses in the area as garnet -sillimanite gneiss, garnet -hornblende gneiss, or plainly as migmatite gneiss. This study is an attempt to take a holistic look at the Obudu sheet and present a preliminary account of the petrology and geochemistry of the hornblende-biotite gneiss in the area.…”

Ba-Pb mineralization in Ugwuajirija Ishiagu area, lower Benue trough, Southeastern Nigeria: Geochemical evidence

“…The resolution was 0.001ppm for the trace and rare earth elements (REE), and 100% for the major elements. The analytical techniques were based on the methods after Skoog and West (!978), Ekwueme (1993bEkwueme ( , 1994, Ofulume (2009) and Obioha, (2014)…”

Petrology and Geochemistry of Basement Complex Rocks in Okom-Ita Area, Oban Massif, Southeastern Nigeria

“…The high SiO 2 content of mica schist in the study area is typical of pellitic to semi-pellitic schists [2] [3] [25]. Also the excess of Na 2 O over K 2 O may be attributed to possible metasomatic reaction in which Na 2 O was preferably enriched and K 2 O depleted [3] [26] [27]. The higher CaO (3.45%) in the phyllite at Old Netim could be due to the contamination of the rock by secondary calcite [3].…”