Nigerian rare-metal pegmatites and their lithological framework

Abstract

Most of Africa's rare-metal potential is linkcd to Proterozoic pegmatite fields exccpt for the Jurassic tin-bearing ring complees of the Jos Plateau Nigeria. In order to establish the position of the Nigerian tin province in terms of economic rare-metal mineralization, occurrences of mineralized pegmatitic phases of the Nigerian basement complex. including the so-called 'Older Tin-Ficlds'. have been investigated. RbiSr geochronology confirms the end Pan-African ages for the pegmatites in the range 580-530 Ma. Although emplaced within the same time span. the mineralogy. geochemistry. and mineralization of these pegmatites differ according to the lithology of their host-rock. Pegmatite occurrences from southwest Nigeria. which are emplaced into Proterozoic metasedimentary-metavolcanic sequences, are enriched in tantalum relative to niobium. These geochemical characteristics are also displayed by the composition of eluvial heavy-mineral concentrates as well as by the trace-element distribution in cassiterites.Although Pan-African granites with an age range of 70(l-S20 Ma are dispersed throughout Nigeria, associated rare-metal mineralized pegmatites are known almost exclusively along a southwest-northeast striking belt about 400 km long, which interwets the Jos Plateau tin-fields. A direct genetic link between the rare-mctal hearing pegmatites and proximal granite occurrences was never obscrved. I t is suggested that reactivation of old tectonic lineaments during the Pan-African orogcny provided excess heat and fluid to concentrate rare-metal pegmatites by partial melting with selective leaching lrom the country rocks, i.e. their lithological framework.

Tectonic environments and rare metal mineralization in pegmatites of Komu Area, Southwestern Nigeria

“…The Rb-Sr isochron age of 185-183 Ma on biotite from pegmatites of Egbe was earlier thought to indicate a possible link between the pegmatites and Mesozoic granite (Matheis and Caen-Vachettee, 1983). This could not be supported by further chemical and field data which established a genetic link between the pegmatites and Pan-African granites (Matheis, 1987;Kuster, 1990).…”

Petrography and Petrochemical Characteristics of Rare Metal Pegmatites around Oro, Southwestern Nigeria

“…The overall trends invariably indicate the relative enrichment of Ta in the soil samples. Ta concentration values in the pegmatite samples of the area of study fall below Egbe pegmatite (Matheis, 1987) as well as Ijero pegmatite (Okunlola and Jimba, 2006) and much below the highly productive Tanco, Homestead and Withrope Ta-pegmatites (Cerny, 1989;Beus, 1966). (after Gordiyenko, 1971 and Beus, 1966).…”

“…12) for the Oro pegmatites. This plot also reveals a high degree of albitization and it indicates a significant difference between the mineralized and unmineralized pegmatite samples (Matheis and Emofurieta, 1990;Okunlola and King, 2003;Okunlola and Somorin, 2005;Jacobson and Webb, 1946), however these values are still low compared to those of the economically viable bodies like Tanco Canada (Moller and Morteani, 1987), but there are indications that the pegmatites of Oro area compare favorably with those of other mineralized pegmatite areas like Egbe and Igbeti areas southwestern Nigeria (Matheis and Emofurieta, 1987;Okunlola and Oyedokun, 2009). This is also indicative of the degree of fractionation.…”

Mineralization of pegmatites in parts of the Oban Massif, Southeastern Nigeria: A preliminary analysis

“…These pegmatites have an average silica content of 71.02wt% which is comparable to the rare metal pegmatites of Southwest and North-central Nigeria (Table 2) (Matheis, 1987;Elueze, 1982). Total iron concentrations are low with the contents of 1.02wt% at Akwa Ibami I and 2.39wt% in Iwuru II.…”