Petrogenesis of the peralkaline Dutsen Wai and Ropp complexes in the Nigerian younger granites: implications for crucial metal enrichments

Abstract

Supplementary document for the paper: Petrogenesis of the peralkaline Dutsen Wai and Ropp complexes in the Nigerian Younger Granites: Implications for crucial metal enrichments. Amuda et al., 2020. Local geology and sampling Dutsen Wai plutonsThe complex consists of alkaline epizonal plutons, discordantly intruded into migmatite and granite gneiss basement. It comprises of two main phases; volcanic and plutonic rock units peculiar to the NYG province. Most of the intrusive plutons (over 90%) are made up of biotite granites, granite porphyry and albite riebeckite-arfvedsonite-aegerine granites.Structurally, the entire massifs trend nearly north-south (Supp Figure 1a). Remnants of volcanic breccias that strike almost east-west (050º ESE) border the extreme south of the complex (Supp Figure 1b).The most prominent structure is the series of NW-SE to nearly NS trending joint systems (Fig. 2a).Two peralkaline plutons (about 10 -15% by volume) are poorly exposed and covers an area of approximately 1.9km 2 , flanks the northeast and eastern margin of the main biotite granite (about 75% by volume) of the complex (Fig. 2a). A low-lying sheet like pink coloured medium to coarse-grained granite intrusion ('reddened' granite) straddled between the two peralkaline plutons (Supp Figure 1c). The roof zones of the granite outcrops appear compositionally homogenous. 15 samples (Dt's, DyL and Db's) were collected in a network at about 45 by 45m 2 systematic random grid pattern.

Petrogenesis and tectonic implication of the alkaline ferroan granites from Ropp complex, north‐central Nigeria: Clues from zircon chemistry, U–Pb dating, and Lu–Hf isotope

“…As is typical of southern ring complexes in the Nigerian alkaline anorogenic province, the Ropp complex consists of abundant biotite granites (Figure 1c), which, together with the minor albite arfvedsonite granites occasionally host rare metal Nb–Sn mineralization (Amuda et al, 2020; Buchannan et al, 1971). In particular, the biotite granite in central part of the Ropp complex (in Bukka Bakwai village) host the largest primary columbite with economic values up to 1 lb per ton, while in terms of tin production, the Ropp biotite granites are the second largest, after the Jos‐Bukuru biotite granites (Buchannan et al, 1971; Jacobson et al, 1958).…”

“…These features are requisite attributes that can provide crucial information on the petrogenesis and tectonic implications of anorogenic alkaline magmatism, a hotly debated topic in the geologic literature. Indeed, recent studies have shown that the Nigerian ferroan granites were generated as a result of fractional crystallization of highly differentiated basaltic (OIB) magmas from the enriched lithospheric mantle with variable contributions from the lower crust (Ahmed et al, 2021; Amuda et al, 2020; Girei et al, 2019; Kamaunji et al, 2020). However, other workers (Girei et al, 2020; Vincent et al, 2021) opined that the Nigerian A‐type granites, particularly the highly oxidized and less radiogenic Mo– and Pb–Zn mineralized biotite granites from Mada and Ningi‐Burra complexes, were derived from the lower crust with upper mantle involvement.…”

“…(c) Geological map of the Ropp alkaline ring complex (extracted from Kinnaird et al, 1985). (1) Rahaman et al (1984), (2) Van Breemen et al (1975), (3) Van Breemen and Bowden (1973), (4) Dickina et al (1991), (5) Girei et al (2019), (6) Kamaunji et al (unpublished data), (7) Kamaunji et al (2020) (8) Ahmed et al (2021), (9) Van Breemen and Bowden (1973), (10) Vincent et al (2021), (11) Amuda et al (2020), (12) Girei et al (2020). Ages of Air and Damagaran in Niger Republic are based on Rb–Sr dating obtained from Bowden et al (1976).…”

“…In particular, the biotite granite in central part of the Ropp complex (in Bukka Bakwai village) host the largest primary columbite with economic values up to 1 lb per ton, while in terms of tin production, the Ropp biotite granites are the second largest, after the Jos‐Bukuru biotite granites (Buchannan et al, 1971; Jacobson et al, 1958). Previous studies in Ropp complex focused mainly on geologic mapping and field description of the mineralization (Buchannan et al, 1971; Jacobson et al, 1956), including petrogenesis and melt enrichment (Amuda et al, 2020). However, isotopic and geochemical studies on their origin and evolution require further detailed investigation.…”

“…Whether the N–S age migration is driven by reactivated shear zones along ENE–WSW trends (Ahmed et al, 2021; Black et al, 1985; Girei et al, 2019, 2020; Vincent et al, 2022), or is associated with a mantle plume hotspot (Bowden et al, 1976; Kamaunji et al, 2020) require further investigation. In addition, high precision U–Pb zircon dates are needed to further confirm the general trend of decreasing ages from north to south (Amuda et al, 2020).…”