Geology And Genesis Of The Gouap BIF-hosted Iron Deposit,Ntem Complex,South Cameroon

The Ntem Complex represents the northwestern edge of the Archean Congo craton in southern Cameroon where numerous banded iron formation?BIF?-hosted iron deposits have been discovered.The Gouap iron deposit is a recent discovered iron deposit and is located on the western border?Nyong Group?of the Ntem Complex.In this study,geological mapping,detailed drillcore logging and petrographical studies reveal that the Gouap iron deposit comprises of two lithostratigraphic units,namely the BIF and the Country rocks,which are well interlayered in sharp or gradational contacts.The BIF unit consists of amphibole BIF and amphibole-pyrite BIF,whereas the Country rocks unit is made up of gneisses?garnet,amphibole-magnetite and amphibole-garnet-pyrite gneiss?,schists?amphibole-magnetite and garnet-magnetite micaschist?,quartzites and dolerite sills.The mineral assemblages of both rocks indicate that they have been metamorphosed under amphibole facies conditions.Two main iron ore types are identified in the Gouap deposit:the soft iron type in the western and northern parts and the hard iron type confined to the southern sector of the deposit.Three main deformation events?D₁,D₂ and D₃?have led to the development of foliation,folding and faulting in the Gouap deposit.The iron ore is mostly concentrated on the F₂ fold hinge zones and fractures.Three major processes have led to the formation of the Gouap deposit:?i?the chemical precipitation of chert and iron-oxide followed by sedimentation and diagenesis that formed chert-magnetite BIF;?ii?the amphibolite facies metamorphism and deformation that formed quartz-magnetite BIF;and?iii?the Gouap BIF have been upgraded to medium-grade iron ore by supergene enrichment processes.The Gouap BIF are characterized by dominant Fe₂O₃+SiO₂ contents and variable contents of CaO,MgO and SO₃,consistent with the presence of amphibole,chlorite,epidote and pyrite.The Gouap BIF also display high contents of trace and rare earth elements?REE?,suggesting the influence of detrital materials and hydrothermal alteration.The Post Archean Australian Shale?PAAS?-normalized REE-Y profiles of the Gouap BIF display positive La,Eu anomalies,weak negative Ce anomalies,indicating a mixture of low-temperature hydrothermal fluids and relatively oxic conditions probably under relative shallow seawater.Additionally,the isotopes data of BIF(³⁰Si_NBS28 values of quartz,?³⁴S_V-CDT values of pyrite,and?¹⁸O_V-SMOW values of quartz and magnetite)confirm that they might have precipitated from low-temperature hydrothermal fluids with detrital input distant from the volcanic activity.According to their geochemical and isotopic characteristics,we propose that the Gouap BIF belong to the Superior type.In situ U-Pb zircon dating of BIF was conducted to assess the BIF depositional age based on strong evidence of zircon in thin section.The Gouap BIF were probably deposited at ca.2422±50 Ma in a region where sediments extended from continental shelf to deep-water environments along craton margins like the CauêFormation of the Minas Supergroup,Brazil.The studied BIF have experienced regional hydrothermal activity and metamorphism at ca.2089±8.3 Ma during the Eburnean-Transamazonian orogeny.These findings suggest a physical continuity between the protocratonic masses of both the S?o Francisco and the Congo continents in the Rhyacian Period.The metasedimentary wallrocks associated with the Gouap BIF derived from slightly immature shale to Fe-shales of felsic and mafic in composition.The Gouap metasediments were formed after 2611±19 Ma and have experienced metamorphism at ca.2093±6 Ma.The depositional timing and environment of the Gouap BIF and its associated rocks correspond to the Neoarchean-Paleoproterozoic orogeny established within the Nyong Group.