Abstract
Syenitic and mafic rocks in Mindif Complex (Far North of Cameroon) were surveyed and characterized to classify them, understand their formation history, and assess their economic interest. Syenitic bodies (hololeucocratic microsyenites; mesocratic aplitic quartz-syenite; leucocratic porphyritic quartz-biotite syenite, and leucocratic porphyritic biotite-syenite) are silica-oversaturated to silica-saturated, alkaline, and metaluminous. Hololeucocratic microsyenites are structural oriented rocks, cooled in shallow depth from low trace and REE dry residual alkaline melts. Mesocratic aplitic quartz-syenite also crystallized in shallow depth from a much Ba-rich less dry residual melt. Leucocratic porphyritic quartz-biotite and biotite syenitic stocks represent two different rock types cooled from hydrous-rich melts in deep seated environments. The Mindif syenites probably crystallized in crustal source magmas (with important alkali feldspar accumulation) from partial melting of pre-existing igneous protoliths. Medium to coarse-grained-peraluminous granite found at the edge of pink microsyenitic dykes (in contact with granite host), is probably a crystallized product from magmatic mixture between the intrusive syenitic melt and a melt from partial fusion of the granite host rock. Mafic igneous rocks in Mindif are peridotgabbro and gabbro with different characteristics. Peridotgabbro, alkaline, holomelanocratic, medium-grained and ultrabasic, is an REE and incompatible elements depleted rock crystallized in shallow depth from a more evolved mantle source magma with plagioclase accumulation. Tholeiitic gabbro, melanocratic, and also medium-grained, was cooled in shallow depth, from a low-K and slightly LILE-enrichment magma probably originated from partial melting ultradepleted mantle source in sub-duction environment. Syenites and peridotgabbro with their high aluminum content (up to 18.5 wt%) greater than that of many parent rocks of lateritic bauxite in Cameroon, can be good parent rocks for bauxite-rich soils if found in a plateau topography and hot-humid tropical climate. The geochemical features of Mindif syenites are close to that of some syenites mined and used as raw materials in ceramic and glass industries. This similarity shows that these syenites are good for glass and ceramic manufacture.
Highlights
Syenites are hololeucocratic to leucocratic intermediate, and rarely mesocratic igneous rocks, formed from cooling of a crustal or mantle source silica-saturated to silica under-saturated magma [1] [2] [3] [4]
Mindif Complex is composed of syenites, contact-granite, gabbro, peridotgabbro and amphibolite schist with different characteristics and crystallization history
Pink syenites are dyke-like, fine to medium-grained cooled in shallow depth from much Al-rich and dry residual alkaline-silica-saturated melts during fractured tectonic-magmatic evens
Summary
Syenites are hololeucocratic to leucocratic intermediate, and rarely mesocratic igneous rocks, formed from cooling of a crustal or mantle source silica-saturated to silica under-saturated magma [1] [2] [3] [4]. Syenitic rocks are very good in mining and processing industries as they can host gemstones and ore minerals [9] [12] [13] [14] [15] [16], or can enrich soil profiles with some minable metallic elements [17]. Uncharacterized syenitic complex is found in Mindif at about 10 km SE of Maroua, Far North Region, Cameroon (Figure 1(c) adapted from [25] and [26]) Rocks in this complex are still not well characterized as limited information is available on them. We used field geology, petrographic studies and element geochemical analyses to: 1) characterize and classify rocks found in the Mindif syenitic complex; 2) understand their formation history; and 3) assess their economic potential
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