A review of granite melt source, and associated gold fertility potential in Batouri, Betare Oya, Meiganga, and Ngazi-Tina gold districts in the eastern goldfield of Cameroon: Insight from zircon chemistry

Abstract

Zircon mineral can resist post-crystallization alteration and store information relating to chemical elements since crystallization time which makes it a potential tool with variable applications in geoscience. These applications include melt and fluid sources tracer through Hf-isotopes in zircon, the evaluation of redox state of magma using Eu and Ce, as well as the degree of fractional crystallization which can give valuable information relating to ore type, mineralization, and the source rock. This review uses magmatic zircon data (trace and rare earth elements) from published works in the eastern goldfield of Cameroon, to establish the regional trend of the melt source, redox state, and water content of the melt batches at the time of emplacement of the granitic intrusions. The eastern goldfield of Cameroon is situated within the Adamawa-Yaoundé Domain, which forms part of the larger Central African Gold Belt, characterized by granitic intrusions of Pan-African age and presumed to host the gold mineralization along this belt. Zircon trace ratios (Nb/Yb ≥ 0.01, Yb/U ≥ 0.1, U/Nb > 20, and Th/Nb > 10) classify the studied zircons within the continental field which elucidates a predominant crustal melt source with mantle input envisaged in places. The data also show characteristic low values of ¹⁷⁶Hf/¹⁷⁷Hf (ƐHf<0) which also support the dominant crustal source of the melt. Moreover, concentrations of K, Rb, Th, Y and Nb together with Sr and Nd isotopic signatures in the area are high depicting low pressure melting of older crustal rocks. With the widely reported genetic link between gold origin and granitic intrusions that resulted from the above melt, this study also evaluated the redox state and water content proxies of the melt that are believed to have a great impact on gold mineralization. Eu/Eu* values in zircon grains range from 0.02 to 1.6 while Ce/Nd ratios are from 0.28 to181.67, and illustrate features of reduced to oxidized melts. With reference to the fertile and infertile suites reported by Lu et al. (2016), the reviewed data plot within the fertile and infertile fields with a domination of fertile intrusions. Dy/Yb data plot above and below the discriminant line of Dy/Yb = 0.3 with <0.3 values revealing elevated magma water content while Dy/Yb >0.3 are critical of an anhydrous melt. The research concludes that the major melt source was from the reworking of older crustal rocks with sporadic mantle inputs. The melt batches involved in the emplacement of these intrusions fluctuated between reduced and oxidized sets with the oxidized batches together with elevated magma water content aiding the gold mineralization.