Sedimentary Iron Deposits Research Articles

U-Pb Ages and Hf Isotopes of Detrital Zircon Grains from the Mesoproterozoic Chuanlinggou Formation in North China Craton: Implications for the Geochronology of Sedimentary Iron Deposits and Crustal Evolution

The Chuanlinggou Formation is the lower formation of the Changchengian System, and hosts sedimentary iron deposits (marine oolitic ironstones) of the North China Craton (NCC). To determine the age of the iron deposits, and provide insight into the crustal growth of the craton, laser ablation multiple collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS)U-Pb and in situ Hf isotope analysis were performed on detrital zircon grains. Samples were taken from the roof sand-shale of the sedimentary iron deposits at Jiangjiazhai and Pangjiapbu. Overall, 186 detrital zircon grain U-Pb ages yield three major age populations, with weighted average ages of 2450 Ma, 1848 Ma, and 1765 Ma, respectively. Four younger ages from magmatic zircon grains were obtained, ranging from 1694 to 1657 Ma. Combined with observations from published studies, the results define the lower limit for the age of the Chuanlinggou Formation, and constrain the age of the sedimentary iron deposits (marine oolitic ironstone) close to 1650 Ma. The peak ages of 1848 Ma and 2450 Ma define the major collisional events of the NCC. The age of 1765 Ma can be linked to the age range of the widespread mafic dyke swarms that represent the rifting of the NCC within the Columbia supercontinent. Detrital zircon grains from the Chuanlinggou Formation form two obvious groups, with different εHf (t) values ranging from −1 to −8 and from +1 to +8, which correspond to the U-Pb age ranges of 1.7–1.9 Ga and 2.3–2.6 Ga, respectively. They have a similar two-stage Hf model age peak at 2.65–2.85 Ga, suggesting that the source rocks for each of these events were derived from the recycling of ancient crust. The source rocks of the older group of zircon grains might be derived from juvenile crust with a short reworking period. The critical crust–mantle differentiation event might happen during the period of 2.65–2.85 Ga, marking the most significant stage of the crustal growth in the NCC.

A preliminary study on ore-forming environments of Xianglushan-type iron deposit and the weathering mineralization of Emeishan basalt in Guizhou Province, China

Xianglushan-type iron deposits are one of the new types of iron deposits found in the Weining Area of Western Guizhou. The iron-bearing rock system is a paleo-weathered crustal sedimentary (or accumulating) stratum between the top of the Middle-Late Permian Emeishan basalt formation and the Late Permian Xuanwei formation. Iron ore is hosted in the Lower-Middle part of the rock system. In terms of the genesis of mineral deposit, this type of deposit should be a basalt paleo-weathering crustal redeposit type, very different from marine sedimentary iron deposits or continental weathering crust iron deposits. Based on field work and the analytical results of XRD Powder Diffraction, Electron Probe, Scanner Electron Microscope, etc., the geological setting of the ore-forming processes and the deposit features are illustrated in this paper. The ore-forming environment of the deposit and the Emeishan basalt weathering mineralization are also discussed in order to enhance the knowledge of the universality and diversity of mineralization of the Emeishan Large Igneous Province (ELIP), which may be a considerable reference to further research for ELIP metallogenic theories, and geological research for iron deposits in the paleo-weathering crust areas of the Emeishan basalt, Southwestern, China.

Ordovician volcano–sedimentary iron deposits of the Eastern Tianshan area, Northwest China: the Tianhu example

ABSTRACTThe stratabound Tianhu iron deposit, with a reserve of 104 Mt at 42% Fe, is located in the eastern part of the Central Tianshan zone in the southern part of the Central Asian Orogenic Belt. The deposit hosts schist, quartzite, marble, amphibolite, and granitic gneiss belonging to the Tianhu Group. Laser ablation inductively coupled plasma mass spectrometry was used to perform zircon U–Pb geochronology, bulk-rock geochemistry, and in situ zircon Hf isotope analyses of the metavolcanic host rocks for constraining the timing and genesis of the Tianhu iron deposit. According to the newly determined age constraints of 452 ± 3 and 477 ± 4 Ma, the iron deposit was concluded to be Ordovician in age. Geochemistry and zircon Lu–Hf isotope analyses suggested that the host rocks of the deposit represent metamorphosed arc-type volcanic rocks generated by the partial melting of a lower crustal source. Combined with geological and ore petrographic characteristics, the Tianhu iron deposit is interpreted to be of volcano–sedimentary origin with enrichment during subsequent metamorphism. The early Palaeozoic marks a critical iron mineralization epoch in the Eastern Tianshan area. The results also support the model of the Central Tianshan area as a volcanic-arc during the early Palaeozoic, associated with the subduction of the Northern Tianshan Ocean.

Causes and consequences of mid-Proterozoic anoxia

Evidence for low pO2 and a ferruginous ocean characterize the mid-Proterozoic (1.8–0.8 Ga). Considerations of redox sources and sinks imply that generation of O2 via organic carbon (Corg) burial must be low to maintain a low pO2 atmosphere for geologically long intervals, yet low oxygen should result in increased Corg preservation. Marine export production must therefore be low to limit Corg burial and O2 generation. Formation of ferrous phosphate can buffer deepwater phosphate (Pi) to levels an order of magnitude or more below those in the modern ocean, limiting export production. Low deepwater Pi is consistent with the hiatus in sedimentary phosphorite deposits during the mid-Proterozoic, and low pO2 limits formation of sedimentary iron deposits (BIF). We propose that low pO2 was maintained by P limitation resulting from ferrous phosphate buffering. The near-absence of BIF and phosphorite deposition is direct and indirect consequences of the low pO2, respectively.

A Geochronological Study of the Xuanlong Type Sedimentary Iron Deposits in North China Craton: Evidence From U‐Pb Ages of Detrital Zircons From the Chuanlinggou Formation

A Geochronological Study of the Xuanlong Type Sedimentary Iron Deposits in North China Craton: Evidence From U‐Pb Ages of Detrital Zircons From the Chuanlinggou Formation

Kajian Endapan Pasir Besi di Daerah Pantai Selatan Kabupaten Ende, Flores, Provinsi Nusa Tenggara Timur

Iron as One of primary raw material in steel and construction industry, it's presence and potencies in Indonesia have an important role. Genetically, known 3 formation of iron deposits (1) Primary, (2) Lateritic, (3) Secondary/reworking process.Based on the survey conducted in Ende in 2005, the typical of iron deposits in this area is classified into sedimentary iron deposits (due to leaching, transporting, accumulating and depositing in somewhere). The accumulation of magnetite grains suggested is due to by leaching, washing in the long term and occurs intensively, so that produce high magnetite concentration in certain area. The interesting area is spread in four sectors; Rapo Rindu, Bheramari, Ruku Ramba and Ondorea sectors.The result of physical laboratory analysis (in concentrate) show the magnetite degree (MD) is vary from 10% to 50%, whereas from chemical analysis known the highest grade reach 37.10% and lowest grade is around 4.4%. However, the everage grade, in general are from 10 to 25 %.The potential of the deposits is obtained from combination between field work laboratory analysis and for those areas mentioned above the total hypothetics resources is 57.134.358,4 ton (concntrate). It seem the deposits of this area is not economic in mining view because very small (under 100 millions tonnes).

28th DeBeers Alex. Du Toit Memorial Lecture, 2004. On Cryogenian (Neoproterozoic) ice-sheet dynamics and the limitations of the glacial sedimentary record

28th DeBeers Alex. Du Toit Memorial Lecture, 2004. On Cryogenian (Neoproterozoic) ice-sheet dynamics and the limitations of the glacial sedimentary record

Unique Geochemistry of Sedimentary Iron Deposit Formed by Biologically Induced Mineralization

Abstract: Major, trace, and rare earth element contents were determined for sedimentary iron ores from the Gunma iron deposit. The deposit was precipitated from a spring water on the hillside of the active Kusatsu‐Shirane Volcano. The ores are mainly composed of goethite and jarosite with various proportions of silicified andesitic detritus. Microbial fossils are often preserved well in goethite‐rich ores. Goethite was likely precipitated by both inorganic and biogenic (biologically induced mineralization; BIM) processes, whereas jarosite was precipitated inorganically from the spring water. Si, Ti, Al, Mn, Mg, Ca, Na, Co, Rb, Y, Zr, Nb, Hf, Ta, U, and middle‐heavy REEs (Sm‐Lu) in the ores are dominantly derived from a detrital component (silicified andesitic rocks). On the other hand, Zn and V are likely to have been inorganically coprecipitated with goethite. Preferential uptake of P, Sc, Cu, Mo, Ba, Th, and light REEs occurs in the BIM ores. Unique enrichment of these elements is a promising indicator of biomineralization for ancient sedimentary iron deposits.

The major early Proterozoic sedimentary iron and manganese deposits and their tectonic setting

The recognition of Wilson cycle plate subduction in the early Proterozoic and the proposed amalgamation of a Proterozoic supercontinent from 2000 to 1800 Ma offers new insight into the tectonic setting of the large sedimentary basins of this age, which host the vast bulk of the world9s resources of iron and manganese in the very large Superior-type banded iron-formations. A reconstruction of the early Proterozoic microplates before amalgamation of Piper9s Proterozoic supercontinent shows that most of the major basins with Superior-type iron-manganese-formations have formed in a trailing margin tectonic setting. This tectonic setting is consistent with the favored geologic model in which the large iron and manganese deposits form on shallow continental margin shelves. The laterally continuous banding of these deposits also supports a stable tectonic setting.

The Pre‐Sinian Basement and Mineralization on the Western Margin of the Yangtze Paraplatform

Abstract The pre‐Sinian basement on the southwestern margin of the Yangtze paraplatform consists of three metamorphic rock series of different ages. Being products of different tectonic events and environments, they differ markedly in original rock sequences, metamorphism, tectonic style and characteristics of granitoids and mineral deposits. The Late Archean Kangdian craton mainly comprises the Kangding and Julin Groups with a metamorphic age of nearly 2500 Ma. They are supracrustal rocks dominated by mafic volcanics enclosed in trondhjemitic rocks. The craton is believed to represent a granite‐greenstone terrane of Late Archaean age. There occur mineral deposits such as graphite and kyanite deposits of metamorphic origin, muscovite deposits in pegmatites and gold quartz veins in gneissic granites, banded hornblende‐magnetite mineralization and copper and zinc mineralizations related to felsic volcanics. Large V‐Ti‐bearing magnetite deposits were also formed in the mafic‐ ultramafic stratiform intrusions emplaced on the margins of the craton during the Middle Proterozoic. Copper and nickel deposits are found in several ultramafic intrusions. Extending in a north‐south direction, the Proterozoic mobile belt consists mainly of the Early Proterozoic Hekou Group and Middle Proterozoic Huili and Kunyang Groups, and they are thought to be accumulations in a Proterozoic rift trough or aulacogen. During the Early Proterozoic, the rift trough was characterized by intense volcanism and presence of iron ore deposits of volcano‐magmatic type, iron‐copper deposits of exhalative‐sedimentary type. The Mid‐Late Proterozoic of the rift trough mainly witnessed the formation of sedimentary stratiform copper deposits and submarine sedimentary iron deposits. In the wake of the emplacement of the Jinningian and Chengjiangian granites in the Late Proterozoic, skarn‐type tin and tin‐iron ore deposits were formed.

A Study of Metamorphosed Sedimentary Iron Deposits Using Remote Sensing Information in Shanxi Province

A Study of Metamorphosed Sedimentary Iron Deposits Using Remote Sensing Information in Shanxi Province

The Precambrian magnetite deposits of New York and New Jersey

Magnetite, magnetite with associated hematite, and magnetite skarns form grossly conformable tabular deposits that have the forms of deformed sedimentary deposits. The host rocks, however, include gneisses of diverse composition and amphibolite. The iron oxides now present are late minerals that have replaced their host rocks. If the iron is primarily of sedimentary origin, the original rocks must have had compositions significantly different from those of known sedimentary iron deposits, even with allowance for significant later modification by hypogene solutions. 'An origin by direct contributions and emplacement by magmatic emanations has most support.'

Hot brines and recent iron deposits in deeps of the Red Sea

Sedimentary iron and heavy-metal deposits of undetermined size have been found in the middle of the Red Sea some 2000 meters below the surface of the sea (Fig. 1). This discovery has been made from the Research Vessel Atlantis II, which is still at sea engaged in a series of oceanographic investigations which ultimately will end in November 1965, after the ship has circumnavigated the globe. The discovery is significant because the environment and the processes controlling deposition of heavy metals are observable and appear to be still active.

GEOLOGICAL BASES FOR THE EXPLORATION AND PROSPECTING OF ORE DEPOSITS, (PART II, SECTIONS III AND IV)

The Russian system of classification of ore reserves is defined; it includes five categories of reserves. Methods of estimating and designating the four main groups of ore deposits for the purpose of estimating reserves are described. Examples used include sedimentary marine iron, manganese, and bauxite deposits; residual limonitic iron ore, alluvial bauxite, magnetite skarn, copper-bearing sandstones, stratified copper-nickel sulfides, vein disseminated copper in secondary quartzite, lensing pyrite, hydrothermal ore vein, chromite, scheelite skarn, lateritic nickel ores, and placers. --M. Russell.

CONTRIBUTION TO THE STUDY OF SEDIMENTARY MANGANESE DEPOSITS

The iron content of rocks is 50 times that of manganese; yet sea water, as is the case for sedimentary manganese oxide deposits, contains iron and manganese in the ratio of 2:1 respectively. Apparently, manganese enrichment occurs in marine environment; under oxidizing conditions, iron precipitates at a relatively low potential (Eh), manganese remaining in solution. It is noted that sedimentary iron deposits contain comparatively little manganese. Manganese precipitation is accompanied by comparatively little iron; this is in agreement with the observed iron content of manganese oxide deposits. Domains of iron and manganese precipitation as carbonates (weakly oxidizing, weakly reducing environments) and sulfides (reducing environments) indicate: the carbonates are similar and can precipitate simultaneously; the sulfide of manganese is not known to occur, and, in agreement with observation, the manganese carbonate precipitates again with the sulfide of iron. D. D. Fisher