Petrology and Geochemistry of Rocks of Ishiagu and Environs Southeastern Nigeria Using Ed-Xrf Method

Abstract

Geochemistry of rocks of Ishiagu area was carried out using Energy Dispersive X-Ray fluorescence (ED-XRF) method. Twelve samples were analyzed and their geochemical properties determined using Excel-Software. Geological mapping reveals that basalts, dolerites and diorites emplaced in shale and mudrock country hosts are the main lithological units occurring in the area. They have silica content of 40.4–49.2wt.%, indicating they are basic-ultrabasic in character. The dolerite and diorite contain average plagioclase (An70-17.4vol.%), hematite 26.29vol.%, showing enrichment in ferromagnesian minerals and depletion in quartz. The Na2O and K2O averaged 1.22wt.% and 1.46wt.% respectively, indicating depletion in alkali, thus corroborating their basic–ultrabasic property. The TiO2 value is 3.6wt. %, indicating oceanic magma derivation. The industrial metals Pb, Cu, Ni and Zn were relatively similar with average values of 37.13, 23.96, 23.69, and 20.08ppm respectively, showing common protolith. The diorite and dolerite are enriched in trace elements Zr, Sr, with average concentration of 172.49, 109.73ppm, and relatively depleted in As and Au with values of 0.04 and 0.03ppm respectively. Petrogenetic analyses using ternary diagram TiO2–K2O–P2O5 for discriminating magma type, the dolerites and diorites all plot in continental basaltic field. In the AFM, and P2O5 versus Zr plots all the dolerites and diorites fall in the tholeiitic field, corroborating that they originated from tholeiitic basaltic magma, probably derived from lower crust/upper mantle. In the Na2O/Al2O3 versus K2O/Al2O3 diagram the dolerites and diorites all plot in the igneous field, the shale plot in metasedimentary field, while the ironstone fall on the boundary between igneous and metasedimentary fields indicating hybrid provenance.