1. Banded Iron Formation(BIF) Pramod kumar Behera AcSIR-JRF CSIR-NGRI Hyderabad-500 007

2. Introduction Types of BIF Origin BIF 1

3. 3 Iron rich sedimentary rocks are 2 types (James 1966): (b) IRON FORMATIONS (BIF) which are typically laminated with chert non oolitic and largely of Precambrian age (a)IRONSTONES These are- noncherty oolitic poorly banded of Phanerozoic age IRONSTONES IRON FORMATION

4. 4 TYPES OF IRONSTONES: Clinton-type Minette-type They constitute mainly hematite–siderite–chamosite(Fe-rich chlorite) beds with oolitic textures. BANDED IRON FORMATIONS (BIFs): BIFs are chemical sediments, typically thin bedded or laminated, containing 15% or more iron of sedimentary origin and are variably inter-layered with quartz, chert and carbonates. Commonly associated with greenstone belts and Precambrian shield areas. In fact there is no major cratonic area that lacks iron formations as prominent members of its stratigraphic column. AGE- Their ages range between 3.8 Ga and 1.8 Ga, with an exception of a few iron formations between 0.8 to 0.6 Ga Banding --metres (macrobanding) to centimetres (mesobanding) to millimetres (microbanding).

5. 5 TYPES OF BIF: (A)Based on their iron mineralogy: BIFs are classified as oxide-, carbonate-, silicate- or sulfide-facies (James, 1954). Iron oxide species -- magnetite & hematite, The magnetite subfacies is the most abundant Iron silicates – FeSiO 3, greenalite (Fe-serpentine), minnesotaite (Fe-talc), stilpnomelane carbonate facies -- siderite, Ankerite sulfide facies – pyrite (+-pyrrhotite) (least abudant) They apparently formed in environmental conditions defined by the stability fields of their dominant iron minerals.

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8. 8 (B) Based on depositional environment and geotectonic setting, Gross(1980) 1.Algoma-type 2.Lake Superior-type 3.Raptian-type BIFs TYPES OF BIF: The above classification scheme has served well to separate deposits of distinctly different associations (and perhaps genesis), but many iron formations don’t fit neatly into this scheme. For example, the iron formations of the very extensive Orissa Bihar belt in India (older than singhbhum granite which is dated as 3.12 +_0.01 Ga). Also,Radhakrishnan et al.(1986) have argued that iron formations in the archean granulite terrains of southern India are not merely highgrade metamorphic equivalents of Algoma or superior type,but represent a distinct type, the “Tamil Nadu type” of Prasad et al.(1982).

9. 9 1. Algoma-type commonly of Archaean age. Associated with volcanic rocks Deposited in volcanic arc or rift settings The associated rocks --- shale, graywacke,volcanics They are generally of limited strike extent (up to tens of kilometres) and thickness (a few metres), but can be up to about 100 m thick. Example – Greenstone Belts of the Indian shield, karnataka

10. 10 2. Lake Superior-type laterally extensive (hundreds of kilometres of strike length and original surface extent) in units up to hundreds of metres thick These are mainly late-Archaean or Palaeoproterozoic age Deposited on stable continental platforms Depositional environment of superior type is interpreted to be shallow water continental shelves Example -- Lake superiour region, USA –Canada, Hamersley supergroup, Australia

11. 11 3. Raptian-type Least abundant type, derives its name from the type occurrence in the late Proterozoic (about 700Ma ) Rapitan Group in the Mackenzie Mountain, Canada exclusively Neoproterozoic in age glacially influenced depositional environment, mostly restricted to Phanerozoic mobile belts Example -- Rapitan Group in the Mackenzie Mountain, Canada

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13. 13 Figure 5.3 Abundance of cherty iron formations of Algoma and Superior types through geological time (after Bekker et al., 2010), and major events in the evolution of oxygen in the atmosphere

14. 14 ORIGIN OF BIF  Iron-foramtions exhibit significant differences in thickness, lateral continuity, sedimentary structures,lithologic aassociation and stratigraphic framework, indicating a spectrum of depositional environments  The critical features which must be accounted for a viable gentic model are : (a) source of the vast amounts of iron and silica, and transport of the ore forming constituents to the sites of deposition; (b) mechanisms of iron and silica precipitation and facies variation; (c) rhythmic banding and the lateral continuity of meso banding ; and (d) a virtual lack of iron-formations younger than 1.7 Ga.

15. SOURCE The sources of FeO, SiO2,and O2 in banded iron-formation are still debated For the precipitation of FeO as Fe 2 0 3, free oxygen was required in the Archcean ocean water They are not introduce as solid particles because terrigenous sediments would inevitably have contained more aluminum relative to iron. Iron and silica were introduce as dissolved constituents. If during the early history of the earth, ananoxic atmosphere and reducing environment prevailed from 4.0Ga (Kasting, 1993),a gradual concentration of FeO would have taken place in the ambient ocean reservoir ) for precipitation as Fe203 only when O2 became available 3 major sources are ; (a) chemical weathering of continents under anoxic atmospheric conditions (b) contintntal sediments in the ocean and (c) submarine hydrothermal emanations. Manikyamba et al.(1993) showed that the trace element compositon of BIF of the archean sandur greenstone belt (india) requires the mixing of minor volcaniclastic and terrigenous components with a dominantly MOR_TYPE hydrothermal source

16. 16 Mechanisms of BIF Deposition Deposited in a marine environment at a shallow shelf below the photic zone & wavebase. Photosynthesis- Chemoautotrophy- Iron(II) was biogenically oxidised without free oxygen in the photic zone, for instance by Fe-oxidising photosyntheticanoxygenic bacteria. radiogenic dissociation of H20 The oxygen may be produced in the ocean by : UV light

17. 17 Figure 5.5 Possible mechanisms of precipitation of Fe and SiO2 from seawater to form oxide-facies BIF (Morris, 1993). Fe2þ in upwelling water is oxidised to Fe3þ either through reaction with O2 produced by photosynthesis in the photic zone, directly by anoxygenic photosynthesis, or by photochemical processes. Fe3þ is weakly soluble and once formed is precipitated as hydroxide. In this model, SiO2 is precipitated largely as a result of evaporation on the shallow platform

18. 18 Precambrian iron formations from the Cauvery Suture Zone : sub-marine hydrothermal origin

19. 19 ArchcanBandedIron-Formation from the BababudanSchistBelt, India The relationship between REE andCo+ Ni + Cu has been found useful hydrothermal and hydrogenous deposits. All cherry banded iron-formation samples and two shaly bandediron-formation samples fall within the fieldo fhydrothermal deposits (field afterKleinandBeukes, 1989). The rest of the shaly bandediron-formation samples fall outside this field but much below the field of hydrogenous metalliferous deep-sea sediments(Manikyamba et.al.1993)

20. 20 References: Manikyamba, C.,andNaqvi, S.M.,1995, Geochemistry of Fe-Mnformations of Archaean Sandurs chist belt,India—mixing of clastic and chemical processes at a shallow shelf : Precambrian Research, v.72,p.69-95 Manikyamba, C.,Balaram, V.andNaqvi, S.M.,1993, Geochemical signatures of polygenetic origin of a bandedironformation (bandediron-formation) oftheArchaean Sandur greenstone belt(schist belt)Karnataka nucleus, India:Precambrian Research, v.61,p. 137-164 Yellappa, T., et al., Precambrian iron formations from the Cauvery Suture Zone, Southern India: Implications for submarine hydrothermal origin in Neoar..., Ore Geol. Rev. (2015) BOOKS: John Ridley :ore deposit geology Kurla.c. Mishra : Understanding Mineral Deposits

21. 21 THANK YOU THE END