Enriched BIF hypogene in natural process is a commercially important iron ore deposit. This kind of iron formation can have from medium to high grade. Thus, to understand the relevant knowledge is important for both the mining industry and academics. Recently, many research conducted to analyze the alteration and upgrade process and can be used for finding new concealed iron ore or extending existing iron ore. This report focuses on finding information, literature reviews and an extended abstract of BIF hypogene iron ore. It includes four sections, specifically, history, mineral system analysis, other aspects and metallurgy of BIF hypogene.
Keywords: BIF (Banded Iron Formation), Hypogene, Iron ore
The BIF was formed almost always of Precambrian age (mainly from Archean to Early Proterozoic). According to the difference in the era of the formation of the deposit and the ore,it can be sorted in "Algoma-type mainly formed in Archean Eon and Superior-type mainly formed in Proterozoic Eon"(Li, Huo & Yong-sheng 2007)
1.2 Typical sizes and Locations worldwide
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BIF is the main source of industrial iron ore in the world and it is the most important one of iron ore deposits, accounting for more than 60% of the total world iron reserves and 70% of the high-grade iron ore reserves.
Table 1 The Summary of Major BIF Reserves and Grade Worldwide (Based on Shen& Wang 1995,Yao Pei-hui 1993)
2 Mineral System Analysis
Banded iron formation (BIF) hypogene iron ore is an important commercial source of iron deposit that occurs deep below the surface of the earth. According to Prof Steffen Hagemann's presentation "Controversies in Iron Models", hypogene deposits commonly formed by "ascending and ancient meteoric fluids". (Steffen Hagemann 2013) Unlike the supergene process, the hypogene process tends to "form deposits of primary minerals rather than secondary minerals." (Rakovan & John 2003)
Regarding the origins of BIF, these layers were formed under the ocean. The dissolved iron in the ocean is oxidized by the oxygen which is released by algaes. They combined with each other becoming insoluble. This insoluble iron oxides precipitated out forming a thin layer. This process circulates in a long period of formation, iron oxide layers from different time with different chemical composition and combine together. The silica-rich layers are alternate with the iron-rich layers forming the deposition of BIF in sedimentary rock. According to "BIF-hosted iron ore research and exploration- a synthesis and proposal for future work" the source of hypogene fluids is from "Associate hypogene iron mineralisation with regional geological events" such as magmatism and metamorphism. (Paul,Â Thomas, &Steffen 2013)
Concerning the chemical and/or physical processes, the primary chemical process is the chemical sedimentation of the minerals in the marine environment. This process forms the mineral resources after volcanic and geological activity which are the source of the energy. "Sedimentary rocks like sandstones also occur in the group due to weathering and transportation of rocks which occurred during the period." (Rio Tinto Iron Ore, no date)
In the natural, circulating ground waters or other natural process accomplished the hypogene. "Non-iron minerals in the BIF were largely replaced by hydrous iron oxides (notably goethite) and partly dissolved out". (Rio Tinto Iron Ore, no date) Feasible climate conditions and geological structures such as faults and folds will precipitate this process.
Furthermore, in BIF hypogene ore "Oblique reactivation of these early extensional normal faults prior may have been instrumental to tap into the underlying dolomites and create fluid pathways. These pathways are essential for silica-undersaturated, hypogene hydrothermal fluids ascend upwards into the BIF, causing large-scale silica removal and subsequent iron enrichment that formed the giant iron ore bodies."(Hagemann, Hodkiewicz & etc., 2012) Water is the most important transport agent,
Figure 1 Summary Diagram of Mineral System (Based on Geoscience Australia)
Part 3 Aspects
3.1Controls deposit location
Structure is an important control on the location of BIF deposition. it is complex to Clarify the structural history of mineralized areas. Take the structural controls of bedded iron ore in the Hamersley Province for example, "the Province underwent three orogenic events, and three regional extension events followed the main episodes of compression.Steeply E to ENE dipping normal faults immediately predated deposition of the Beasley Quartzite of the lower Wyloo Group after the Ophthalmian Orogeny". (H.J.Dalstra (2005)."Structural controls of bedded iron ore in the Hamersley Province, Western Australia - an example from the Paraburdoo Ranges")
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Steeply NE and SW-S dipping normal faults predated deposition of the McGrath formation of the middle Wyloo Group, following the Panhandle Orogeny. During the Capricorn Orogeny, the resulting interpreted rift reactivated and tilted. Late NE trending normal faults are confined to the eastern half of the Province. High-grade hematite deposits occur in rocks that range from intensely folded to rocks with less, or only little deformation, suggesting that folding had at best limited influence on ore genesis.
Figure 2: A Cross-section 1820E through the Paraburdoo 4 East deposit, looking west (modified after Taylor et al. 2001). B Reconstructed cross section 1820E through the 4 East deposit during the syn-Wyloo Group deposition and prior to the F4 Capricorn orogeny; modified after Dalstra, 2005).
Figure 3 includes two cross-section graphs of the iron ore deposit used as an example cross-section of BIF-related iron ore deposit. According to Prof Steffen Hagemann's article"Recent Advances in BIF-related Iron Ore Models and Exploration Strategies",A reconstructed long section through the Paraburdoo Ranges syn-Upper Wyloo group deposition indicates that the proto-hematite ore bodies had already formed at that time and that some were actively eroding, farming hematite conglomerates (Dalstra 2005). The ore bodies at 4 West, 4 East and 64 East which were formed in grabens or half-grains are also shown in the long-section. The ore bodies were at least several hundred of meters below the surface, so it was well preserved since the ore bodies were shielded from erosion. Oblique reactivation of earlier
3.3 Ore,alteration Mineralogy
Figure 3 Summary of deformation and events for the Madoonga and Beebyn Fe ore deposits in the Weld Range greenstone belt
To study BIF deformation and alteration, a hydrothermal alterationand the structural alternation model were established stated by professor Steffen Hagemann's in his presentation with the name Genesis of superimposed hypogene and supergene Fe orebodies in BIF at the Madoonga deposit. If the input of terrigenous sediments is not enough, BIF will form in a deep seafloor circumstance when volcanism stops for some minutes which makes the AI contents in BIF low. Between two primary episodes in the process of BIF deposition, sediment with fine grain, reworking and volcanism of volcanic material happen. After that, in ca.2745, Ma will go into the rock sequence. This leads to thick sills of basalt, dolerite, and gabbro among BIF.
Because of the East-west shortening in the regional event of D1, South BIF and North BIF in the Madoonga deposit was folded isoclinal. At the same time, the zones in the reverse sides formed along marins in the South and North BIS because they are paralleled to the bands in those units. The major channel of hydrothermalfluids near the margins sheared of the South and North BIF leaded to the hypogene mineral alteration zones such as ferroan talc and ferroan chlorite0 in the mafic igneous countryrocks nearby. In rare cases, Beebyn deposit presents shear zones or these narrow magnetite-rich mylonite. On the contrary, magnetite-rich ore zones at Beebyn are produced in the 2-stages processes which involve the silica-rich bands replacement by minerals of hypogene carbonate in BIF, which are followed by the concentration and dissolution of magnetite-rich bands residual. Suppose that there are no clear differences in the stratigraphic sequences along BIF in any of the deposit (that is each deposit is merely a BIF-mafic rock sequence principally with no carbonate-rich countryrocks ), it is unclear why only Beebyn Deposit records magnetite ore formation 's 2-stage process , but others do not. Perhaps, the following is possible. Carbonate-magnetite alteration assemblages have ever existed in Madoonga. However, now, they are metamorphosed to talc-magnetite assemblages. In the regional D2 event, North-south shortening gives rise to the folding of isoclinal F1 folds and the tectono-stratigraphy tilting and magnetite-talc veins which are shortened by shear zonehosted, into the steep attitude in the current time. Faulthosted specular hematite, which is also called quartz veins, is developed paralleled to bands with ENE-trending, however, in the areas of dilational jog, vein networks and hydrothermal breccias are formed to the major zones with enechelon and ENE-trending fault. Microplaty hematite in the inner side and jasperlite hypogene alteration zones in the outer side along with veins, which are specular hematite-ric, replace magnetite-talc veins commonly though D1 magnetite- alc vein is seldom cut by quartz veins -subparallel D2 specular hematite. In the deposit of Beebyn, there is very similar spatial and timing relationships, though the veins which are specular hematite-rich, are more commonly hosted by parasitic F2 fold hinges. In the regional D3 event, East west shortening gave rise to the F2 folds folding and hypogene magnetite- zones which are hematite-rich ore form N-trending F3 folds in the deposit of Madoonga. With ENE-trending lithological contacts, for example, with the southern margin of South BIF, shearing take place. Quartz veins, which are shear zone-hosted locally cut magnetite cut magnetite-talc veins. In the regional D4 event, which gave rise to NNW- to NNE-trending brittle faults and joints, which cut hematite-rich ore and hypogene magnetite zones. In the process where BIF respond to the circulation of oxidised fluids, hematite alteration -Supergene goethite zones are developed along with the zones which are subvertical fault and into wall rock which surround them by a of faults and fractures network. Along this deformed contact, intense goethite- hematite alteration in BIF is promoted by the shear zone Reactivation which is located along margin in the south in the South BIF. Erosion and exposure and in the least-altered BIF in the recent time , hypogene ore, , mafic igneous countryrocks zones gave rise to these materials' transportation up to 200 m from the source and deposition in palaeo-topographic depressions, which flanks the primary rides in the Madoonga W14 prospect. The distances of short transport gave rise to fragmental heterolithic sorted sediment which was later cemented by supergene goethite affected by circulation of supergene fluid from the sediment of detrital matter.
Part 4 Metallurgy
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Iron (Fe) is one of the most important, useful, abundant and cheap metal in our life. The iron alloy is widely used in all aspects of industry and agriculture as the most important and basic structural material. To a certain extent, the capacity of iron and steel can stand for a country's level of industrialization. It is known that iron Is widely distributed in nature. According to an Australian Atlas of mineral resources, mines and processing centre's report "iron constitutes about 5% of the Earth's crust. It is the fourth most abundant element after oxygen, silicon and aluminium, and after aluminium, the most abundant and widely distributed metal." (Australian Mines Atlas, no date)
The price of Iron is fluctuant. It depends on many reasons, such as the world economic condition, stocks and so on. The graph below shows the price of steel from 09/Feb/2013 to 09/Mar/2013. From this graph, it can be seen that the price of steel is declining now, it may be because of the economic crisis which is happening around the world.
Figure 4 Historical Price Graph For steel (London Metal Exchange,2013)
Iron is easy to oxidize thus in the nature it is rare to find pure iron. Iron exists in the state of the compounds mostly. It is after the invention of smelting furnaces and blast furnaces that iron became widespread used.In most iron ores the compounds contain oxides and sulphides. The iron oxide minerals include Goethite (FeO (OH)), Hematite (Fe2O3), Magnetite (Fe3O4) and Limonite which is "a mixture of hydrated iron oxides." (Australian Mines Atlas, no date)
The iron sulphide contains different chemical formulas and crystalline structures. Specifically, there are toilet (Fes), Greigite (Fe3S4), Marcasite and Pyrite (both are FeS2 , but in different structures). The other elements in iron ore include phosphorus (normally less than 0.1%), silica (around 3%-7%) and aluminium (no more than 3%). (Iron Ore, no date) Besides, there are also some chlorides such as FeCl2, FeCl3.
The process of extraction is based on the reduction of the iron oxides with carbon. The process of the extraction includes "concentration of ore, calcination or roasting of ore and reduction of ore." (City Collegiate, no date) In the concentration process, the ore is crushed and broken into small pieces. Besides, crushed ore will be washed with water to remove impurities. In calcination process, the ore is heated with access of air. The purpose of this process is to remove "moisture, moisture,Â CO2, impurities of sulphur, arsenic. FerrousÂ oxide is also oxidized to ferric oxide." (City Collegiate, no date) The process of reduction which is also called smelting is carried out in a blast furnace.
Figure 5 Blast furnace (Tutorvista, No date)
In the blast furnace Iron oxide will be deoxidated into iron by the carbon, carbon will be oxidated into Carbon Dioxide.
Reactions in blast furnace
Fe2O3Â + 3CÂ Â 2Fe + 3CO
Fe3O4Â + 4COÂ Â 3Fe + 4CO2Â
CO2Â + CÂ Â 2CO
The Overall reaction:
Fe2O3Â + 3COÂ Â 2Fe + 3CO2
Limestone is heated to decompose to CaO and CO2.
CaO + SiO2Â Â CaSiO3
CaO + Al2O3Â Â Ca(AlO2)2
CaO will react with the impurities. The chemical formulas are
CaO + SiO2Â Â CaSiO3
CaO + Al2O3Â Â Ca(AlO2)2
In this process impurities will change into slag which is a useful byproduct.
This report is guided by Professor Steffen Hagemann. His support is very appreciated. We also thank to our classmates who helped us in different ways. Because of the limit of knowledge and language, this work has many shortages and mistakes. It needs further work to be improved.