The shear zone-related gold mineralization at the Turmalina deposit, Quadrilátero Ferrífero, Brazil: structural evolution and the two stages of mineralization
“…The TNF8 attractive iron ore target is a complexly folded zone in the southwest of the area as shown in Figure 11(c). This has an amplitude of over 25,000 nT which is structurally comparable to several iron ore and gold deposits in West Africa and NE Brazil (Santos et al 2017;Fabricio-Silva et al 2019;El-Shazly et al 2019;Leite et al 2019;Santos et al 2021). At the TNF12 anomaly, the far southeast of the TNF11 prospect, IFs outcrops were found to be continuous up to 50 m along the strike.…”
Section: Mapping and Surface Samplingmentioning
confidence: 64%
“…The magnetic and radiometric character of the various rock units could be used for a subsequent full lithological interpretation if linked with ground geological investigation. The aeromagnetic–radiometric processing and interpretation method was successfully applied to illustrate iron and gold deposits in the whole world such as in Brazil (Fabricio-Silva et al 2019; Leite et al 2019), Australia (Holden et al 2012), South America (Combes et al 2022) and West Africa (El-Shazly et al 2019). Figure 13 Toko-Nlokeng country lithologies: (a) Amphibolite gneiss, (b) Felsic gneiss/ high strain felsic gneiss, (c) Mafic gneiss, (d) Gneissic Iron Formation; (e) Hornblendites; (f) mesoscopic scale the regional foliations (Sn) of the host rocks in the study area affected by P 3 folds.…”
Regional geophysical data are important for detecting the presence of mineral deposits under cover. This study used geophysical data coupled with field geology of the Toko-Nlokeng area, Cameroon, to locate and map structures and lithologies as part of an exploration campaign for mineral deposits. The airborne geophysical survey in the Toko-Nlokeng area located in the Nyong complex revealed a predominantly EW striking highly folded series result of polyphase deformation of iron formations and host rocks divided into domains based on magnetic and radiometric character. The geophysical data indicate that major faults and shear zones strike NE-SW, with N-S striking units on the western margin and mainly E-W striking units in the rest of the area. These data suggest a major N-S thrust fault similar to the Borborema Province (NE Brazil) terrane marked by accretionary processes during the assembly of Western Gondwana. Several significant NE-SW striking shear zones are present. The data revealed many moderate to highly magnetic bodies that are interpreted as magnetite-bearing iron formation, mafic-ultramafic intrusions and flows, skarns, carbonatites and kimberlites. The magnetic and radiometric trends reveal the internal regional rock fabric and strike, and iron ore targets with magnetic anomaly up to 27,000 nT related to iron formations and other significant targets for gold, potassium (alteration) and uranium. The Toko-Nlokeng iron deposit is comprised of magnetite-bearing quartzite beds and is concordant with the surrounding host rocks and stands as one of a broad group of magnetite-dominated iron formations that occur throughout West and Central Africa. A new geological map was produced from mapped lithologies and microstructure characteristics of the iron formations, interpretations of the aeromagnetic data and structural features. The study results have important implications for regional exploration programs.
“…The TNF8 attractive iron ore target is a complexly folded zone in the southwest of the area as shown in Figure 11(c). This has an amplitude of over 25,000 nT which is structurally comparable to several iron ore and gold deposits in West Africa and NE Brazil (Santos et al 2017;Fabricio-Silva et al 2019;El-Shazly et al 2019;Leite et al 2019;Santos et al 2021). At the TNF12 anomaly, the far southeast of the TNF11 prospect, IFs outcrops were found to be continuous up to 50 m along the strike.…”
Section: Mapping and Surface Samplingmentioning
confidence: 64%
“…The magnetic and radiometric character of the various rock units could be used for a subsequent full lithological interpretation if linked with ground geological investigation. The aeromagnetic–radiometric processing and interpretation method was successfully applied to illustrate iron and gold deposits in the whole world such as in Brazil (Fabricio-Silva et al 2019; Leite et al 2019), Australia (Holden et al 2012), South America (Combes et al 2022) and West Africa (El-Shazly et al 2019). Figure 13 Toko-Nlokeng country lithologies: (a) Amphibolite gneiss, (b) Felsic gneiss/ high strain felsic gneiss, (c) Mafic gneiss, (d) Gneissic Iron Formation; (e) Hornblendites; (f) mesoscopic scale the regional foliations (Sn) of the host rocks in the study area affected by P 3 folds.…”
Regional geophysical data are important for detecting the presence of mineral deposits under cover. This study used geophysical data coupled with field geology of the Toko-Nlokeng area, Cameroon, to locate and map structures and lithologies as part of an exploration campaign for mineral deposits. The airborne geophysical survey in the Toko-Nlokeng area located in the Nyong complex revealed a predominantly EW striking highly folded series result of polyphase deformation of iron formations and host rocks divided into domains based on magnetic and radiometric character. The geophysical data indicate that major faults and shear zones strike NE-SW, with N-S striking units on the western margin and mainly E-W striking units in the rest of the area. These data suggest a major N-S thrust fault similar to the Borborema Province (NE Brazil) terrane marked by accretionary processes during the assembly of Western Gondwana. Several significant NE-SW striking shear zones are present. The data revealed many moderate to highly magnetic bodies that are interpreted as magnetite-bearing iron formation, mafic-ultramafic intrusions and flows, skarns, carbonatites and kimberlites. The magnetic and radiometric trends reveal the internal regional rock fabric and strike, and iron ore targets with magnetic anomaly up to 27,000 nT related to iron formations and other significant targets for gold, potassium (alteration) and uranium. The Toko-Nlokeng iron deposit is comprised of magnetite-bearing quartzite beds and is concordant with the surrounding host rocks and stands as one of a broad group of magnetite-dominated iron formations that occur throughout West and Central Africa. A new geological map was produced from mapped lithologies and microstructure characteristics of the iron formations, interpretations of the aeromagnetic data and structural features. The study results have important implications for regional exploration programs.
“…The undulose extinction coarse-grained quar intergrown with spodumene and albite undergoes recrystallization at the edges into granoblastic quar , which is commonly observed in ρ40 elbaite pegmatite and ρ36 spodumene pegmatite (Figure 5b,h,i). These characteristics represent the synkinematic emplacement of the pegmatites, which are restricted to the shear zones [87]. The Altun region was undergoing simultaneous compression and amalgamation of three micro-continental blocks, resulting in intense compression and the formation of shear zones from the north and south at ~450 Ma (see Section 6.3).…”
Section: Formation Times Of the Tashitaban LI Granitic Pegmatitesmentioning
The Central Altun orogenic system is a result of the amalgamation of multiple micro-continental blocks and island arcs. This complex system originated from subduction–accretion–collision processes in the Proto-Tethys Ocean during the Early Paleozoic. Research has reported the discovery of several Li-Be granitic pegmatite deposits in the Central Altun Block, including the North Tugeman granitic pegmatite Li-Be deposit, Tugeman granitic pegmatite Be deposit, Tashisayi granitic pegmatite Li deposit, South Washixia granitic pegmatite Li deposit, and Tamuqie granitic pegmatite Li deposit. The Tashidaban granitic pegmatite Li deposit has been newly discovered along the northern margin of the Central Altun Block. Field and geochemical studies of the Tashidaban granitic pegmatite Li deposit indicate: (1) Spodumene pegmatites and elbaite pegmatites, as Li-bearing granitic pegmatites that form the Tashidaban granitic pegmatite Li deposit, intrude into the two-mica schist, and marble of the Muzisayi Formation of the Tashidaban Group. (2) Columbite–tantalite group minerals and zircon U-Pb dating results indicate that the mineralization age of Tashidaban Li granitic pegmatites is 450.2 ± 2.4 Ma with a superimposed magmatic event at around 418–422 Ma later. (3) Whole-rock geochemical results indicate that the Kumudaban rock sequence belongs to the S-type high-K to calc-alkaline granites and the Tashidaban Li granitic pegmatites originated from the extreme differentiation by fractional crystallization of the Kumdaban granite pluton.
“…These are recognized as classic orogenic mesozonal gold deposits where the host rocks are at greenschist facies, and the mineralized bodies show substantial structural control (Lobato et al 2001a, b). In the northwestern QF, rocks of the Pitangui greenstone belt (PGB) host gold deposits with hypozonal features, including São Sebastião (Brando Soares et al 2018) and Turmalina (Fabricio-Silva et al 2018), plus several minor occurrences of uncertain classification. São Sebastião is hosted in 2.86-Ga banded iron formations (BIFs) of the lower section of the PGB.…”
Several gold deposits display complex Bi-bearing mineralogy. Bismuth-bearing phases are generally sensitive to changes in physicochemical conditions such that the interpretation of Bi-Au associations is useful to understand these mineralizing systems. However, gaps in the physicochemical constraints given by the Bi enrichment in these systems prevent robust metallogenic models in some complex deposits. São Sebastião is a hypozonal gold deposit in the Quadrilátero Ferrífero historic mining district in Brazil, and unlike other Archean gold deposits in this area, it displays a disseminated high-temperature and high-grade sulfide overprint with Bi enrichment. The Bi-bearing mineralogy at São Sebastião is heterogeneously distributed in the BIF-hosted ore bodies. Bismuth-sulfosalts, Bi-chalcogenides, and native bismuth have crystallized in a variable set of intercalated patches, yielding different ore facies given by the fractionation of hydrothermally assisted melts. Base metalbearing Bi-sulfosalts, electrum, and acanthite result from high-temperature (~ 600 °C) immiscible melts rich in chloride ligands, while late crystallization of high-fineness native gold associated with native bismuth at 271 °C is evidence for Au scavenging by protracted low-temperature Bi-enriched metallic melts. This mechanism has favored gold remobilization from early sulfide assemblages and the development of localized upgraded ore stringers. Rapid uplift from a reduced (low fO 2 ) hypozonal environment to oxidized brittle conditions is suggested by crosscutting bismuthinite-bearing veins' fluid inclusion patterns and the absence of maldonite (Au-Bi alloy). Many hypozonal deposits like São Sebastião show similar mineralogy and have developed at the boundaries of Archean terrains, registering multiple tectonic overprints where partial melts may have had an essential role in the final ore formation.
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