Mineralogy, geochemistry and petrogenesis of the V-Ti-bearing and chromiferous magnetite deposits hosted by Neoarchaean Channagiri Mafic-Ultramafic Complex, Western Dharwar Craton, India: Implications for emplacement in differentiated pulses

Abstract

The Channagiri Mafic-Ultramafic Complex occupies lowermost section of the Neoarchaean Shimoga supracrustal group in the Western Dharwar Craton. It is a segmented body occupying the interdomal troughs of granitoids. The magnetite deposits occur in the northeastern portion; typically occupying the interface zone between gabbro and anorthositic. Mineralogically, the deposits are simple with abundant magnetite and ilmenite. Hogbomite is a consistent minor mineral. Magnetites are typically vanadiferous (0.7–1.25% V2O5). Ilmenite consistently analyses more MgO and MnO than coexisting magnetite. Chlorite, almost the only silicate present; lies in the range of ripidolite, corundophilite and sheridanite. The chromiferous suit occupying eastern side of Hanumalapur block (HPB) contains Fe-Cr-oxide analysing 37.8–11.9% Cr2O3 and 40.5–80% FeOt. In these too, chlorite, typically chromiferous (0.6–1.2% Cr2O3), is the most dominant silicate mineral. Geochemistry of V-Ti-magnetite is dominated by Fe, Ti and V with Al, Si, Mg and Mn contributing most of the remaining. Cr, Ni, Zn, Co, Cu, Ga and Sc dominate trace element geochemistry. The Cr-magnetite is high in Cr2O3 and PGE. Two separate cycles of mafic magmatism are distinguished in the CMUC. The first phase of first cycle, viz., melagabbro-gabbro, emplaced in the southeastern portion, is devoid of magnetite deposits. The second phase, an evolved ferrogabbroic magma emplaced in differentiated pulses, occupying northeastern portion of the complex, consists of melagabbro→gabbro-anorthosite→V-Ti magnetite→ferrogabbro sequence. Increase in oxygen fugacity facilitated deposition of V-Ti magnetite from ferrogabbroic magma pulse emplaced in late stages. The second cycle of chromiferous PGE mineralized suite comprises fine-grained ultramafite→alternation of pyroxinite-picrite→Crmagnetite sequence formed from fractionation of ferropicritic magma. HPB also includes >65m thick sill-like dioritic phase at the base of the ferriferous suit and a sinuous band of coarse-grained ultramafite enclosed within the chromiferous suit; both unrelated to the two mafic magmatic cycles.

Mafic-ultramafic rocks and alkaline-carbonatitic magmatism and associated hydrothermal mineralization: A special issue (Part-I) dedicated to Piero Comin-Chiaramonti

“…On the other hand, late-stage fluids derived from alkaline felsic complexes can parallel those in ultramafic complexes as suggested in the paper by Singh et al [4], who studied bastnäsite-(Ce) from the Kanigiri alkaline felsic complex of Andhra Pradesh, South India. Hydrous fluids from less alkaline mafic-ultramafic complexes seem different and are more specific for tellurium and PGE concentration as suggested by the papers of Dora et al [5], who studied the mineralisation of Gondpipri, Central India, and the paper by Devaraju et al [6], which describes the Channagiri complex, India. Even small volcanic or subvolcanic outcrops may have undergone the intense action of magmatic fluids as observed in the small melilitolitic sub-volcanics in Central Italy described by Stoppa and Schiazza [7], or the regional swarm of ultramafic dykes described by Comin-Chiaramoti et al [8] from Planalto da Serra, Brazil, which show several generations of latestage minerals.…”

The REE-Zr-U-Th Minerals of the Maronia Monzodiorite, N. Greece: Implications on the Saturation and Segregation Mechanisms of Critical Metals in Intermediate–Mafic Compositions

“…A possible interaction of the Maronia monzodiorite with a less-evolved melt is indicated by the presence of late magmatic vanadiferous magnetite (0.7-2 wt.% V 2 O 3 , Table 2) that engulfs yttrian zirconolite and is in contact with Mn-ilmenite (Figure 11b). The formation of V-magnetite and Mn-ilmenite has been attributed to interactions with oxidized Fe-rich gabbroic magmas [108][109][110][111]. This demonstrates that the crystallization of zirconolite took place under the influence of an oxidized mafic melt.…”

Multi‐episodic formation of baddeleyite and zircon in polymetamorphic anorthosite and rutile‐bearing ilmenitite from the Chiapas Massif Complex, Mexico

“…The formation of högbomite has been associated with a wide spectrum of geological environments including hydrothermal, magmatic and UHT metamorphic rocks (Devaraju et al, 1981;Konzett et al, 2005;Liati & Seidel, 1994;Nishimiya et al, 2009;Perumala & Merkle, 2014;Petersen et al, 1989;Rakotonandrasana et al, 2010;Razakamanana et al, 2000;Visser et al, 1992). Högbomite has been reported from other Ti-Fe deposits around the world (Beura et al, 2009;Devaraju et al, 1981Devaraju et al, , 2014Jayaraj et al, 1995;Konzett et al, 2005;Mohanty et al, 1995). However, the conditions and processes of its formation in this particular setting are still unclear.…”