| The East Metal logenic Province of Cameroon of the Pan-African orogeny is characterized by a complex history of metamorphism,polyphase deformation,widespread crustal anataxis and magmatism,and gold-forming events.In particular,controversy exists regarding the temporal evolution of the metamorphic and magmatic events within the Lom Belt,as well as on the mineralization style in the province.Whole-rock geochemical,Lu-Hf isotopic,and U-Pb zircon data were obtained to constrain the tectonic evolution of eastern Cameroon,while ore minerals,fluid inclusions,and O-H-C-S stable isotopes were examined to constrain the mineral assemblages,nature(s)and source(s)of ore-forming fluids and metals.The Bétaré-Oya and Woumbou-Colomine-Kette gold districts,underlain by metamorphic and magmatic rocks,respectively,were chosen for this study.The U-Pb zircon,Lu-Hf isotope,and whole-rock geochemical results revealed that granitic rocks are relatively reduced to oxidized and were emplaced during two magmatic events at ca.650-635 Ma and ca.630-610 Ma.They were generated by partial melting(T=～720-850℃)of Paleoproterozoic supracrustal rocks,with a zircon HfTDM model age range of ca.1.8-2.4 Ga.Metamorphic zircons from the Lom Belt schists gave ages between ca.655 and 585 Ma,while detrital ages were measured at ca.1035 Ma and ca.784 Ma,with εHf(t)values of14.6 and-19.3 and+3.0 and+8.6,respectively.Zircon U-Pb ages together with structural,geochemical,and isotopic data indicate three deformational phases in the two districts at ca.655-635 Ma(D1),630-615 Ma(D2),and 600-580 Ma(D3).The D3,the more transpressional event,was associated with gold mineralization.Ore mineralogical and quartz microstructure studies of the Betare Oya and Woumbou-Colomine-Kette districts revealed two stages of gold mineralization.Stage 1 led to pyrite,chalcopyrite,sphalerite,pyrrhotite,bismuthinite,tellurobismuthite,galenobismuthite,hematite,petzite,hessite,wolframite,electrum,and native gold deposition with quartz,sericite,muscovite,chlorite,calcite,and ankerite as gangue minerals.Stage 2 included the precipitation of pyrite,hematite,tellurobismuthite,galena,greenockite,and native gold.Two fluid inclusion assemblages(FIAs)were observed.The FIA 1 is aqueous-carbonic(±N2±CH4),with As-and CO32-bearing trapped or daughter minerals,which is related to stage 1 of the gold mineralization and composed of low salinity(～7.0 wt.%NaCl equiv.)H2O-CO2-NaCl(type 1),CO2-rich(type 2),and H2O-rich(type 3,observed in the Woumbou-Colomine-Kette quartz veins only)fluid inclusions.The FIA.2 consists of aqueous(type 4)fluid inclusions with a salinity of 0.2 to 11.7 wt.%NaCl equiv.and trapping temperatures between 160 and 245℃.Theδ18Oquartz(+10.9 to+16.0‰),δDfluid(-50.6 to-21.8‰),and δ13Cfluid(-5.8 to-4.1 ‰)suggest a metamorphic source for the ore-forming fluids,although some contribution from the mantle and/or magmatic source(s)cannot be ruled out.Theδ34S(+5.3 to+8.2‰)for gold-bearing sulfides suggests a supracrustal source for the sulfur that transported gold and was involved in the precipitation of ore minerals.The CO2-rich and CO2-poor fluid inclusions of gold-bearing quartz veins provide evidence of episodic phase separation,with unmixing at P～2 kbar,T～300-310 ℃,and at a paleodepth of～6-9 km.These data revealed that the Bétaré Oya and Woumbou-Colomine-Kette gold occurrences spatially controlled by the Sanaga Shear Zone are best classified as mesozonal orogenic gold deposits.The East Metallogenic Province of Cameroon is an important part of the emerging greenfields exploration region for Pan-African orogenic gold,with the more significant targets defined by jogs and lithological contacts along NE-and Estriking shear zones. |
