Banded Iron Ore Research Articles

Fractal properties of multi-order folding as a tool for exploration of low-grade banded iron ores in the Krivoy Rog basin (Ukraine)

Fractal properties of multi-order folding as a tool for exploration of low-grade banded iron ores in the Krivoy Rog basin (Ukraine)

Depositional environment and metamorphism of early Proterozoic iron formation in the Lüliangshan region, Shanxi Province, China

The early Proterozoic iron formation of the Lüliangshan region is 18 km long and has undergone different degrees of metamorphism at different localities. Within this belt, the Yuanjiacun deposit is characterized by low grade metamorphism, diverse iron sedimentation facies, a well-exposed stratigraphic section and simple structure. It is an ideal case for studying the depositional environment and the metamorphic processes of Precambrian banded iron ores. Formed in a shallow water basin of a geosyncline, the Yuanjiacun iron formation some 1200 m thick comprises three sedimentation-ore formation cycles, each of which begins with coarse- to medium-grained clastic rocks (quartz sandstone or arkose), passes through fine-grained siltstone and argillitic rocks, and grades into pure colloidal chemical deposits represented by thin-bedded ferruginous quartzites. In each cycle from the bottom upwards, in general, there successively occur pyrite, siderite, iron silicates (including Fe-rich chlorite, minnesotaite and stilpnomelane), magnetite and haematite. These iron mineral facies are products of sedimentation and diagenesis to very low grade metamorphism stages. The spatial distribution of iron facies in stratigraphic sequence shows an increasing oxygen fugacity of the depositional environment during the course of each cycle. The main factors controlling the types of iron sedimentation facies and the valence state of iron are considered to be the proportion of sandy-argillitic component to colloidal chemical materials during deposition and the relative amount of organic matter in them. The abundance of organic matter results in the creation of a reducing environment and the formation of principally ferrous facies, whereas the lack of organic matter leads to the development of oxidizing conditions and the formation of ferric facies. Under a transitional oxidation-reduction medium, mixed ferrous-ferric facies dominate. The fracture-related regional metamorphism yielded progressive metamorphic zonation in the Lüliangshan region: the chlorite zone and the biotite zone of greenschist facies, and the almandite zone, staurolite zone and kyanite zone of the amphibolite facies. These metamorphic zones cross-cut banded iron ores and produce corresponding changes in the iron formation.

Stratigraphy, type and formation conditions of the late precambrian banded iron ores in south China

Based on research on the “Xinyu-type” Sinian iron deposits in Jiangxi Province and metamorphosed iron deposits in Jiangkou and Qidong of Hunan, Sanjiang and Yingyangguan of Guangxi, Longchuan of Guangdong and some other areas in Fujian, the authors have come to the following conclusions: 1. The metamorphosed late Precambrian iron ores widespread in south China may be roughly assigned to two ore belts, namely the Yiyang-Xinyu (Jiangxi)-Jiangkou(Hunan)-Sanjiang (Guangxi) ore belt or simply the north ore belt, and the Songzheng(Fujian)-Shicheng (Jiangxi)-Bailing (Longchuan of Guangdong)-Yingyangguan (Guangxi) ore belt or the south ore belt. Tectonically, the former lies along the southern margin of the “Jangnan Old Land”, while the latter along the northwestern border of the “Cathaysian Old Land”. 2. Iron deposits of this type occur exclusively in the same interglacial horizon of the Sinian Glaciation in south China. Above and below the ore bed there lie the glacial till-bearing volcanic-sedimentary layers. 3. Based on sedimentary features, the iron formations can be divided into four types: silica-iron-basalt formation, silica-iron-clastic rock formation, silica-iron-tuff formation and silica-iron-carbonate rock formation, which progressively grade into each other. 4. Iron ores were formed at the late stage of late Proterozoic rifting in neritic environments, with their distribution governed by the rift valleys on the margins of the “Jiangnan Old Land” and “Cathaysian Old Land”. Consequently, intense mafic volcanism as well as weathering and denudation of palaeocontinent during rifting provided material sources for the formation of iron deposits. Meanwhile, warm and humid stationary neritic environment during the south China great glacial period constitutes favorable palaeoclimatologic and palaeogeographic conditions for the deposition of iron ores. 5. The iron formations have undergone regional metamorphism of greenschist-amphibolite facies. To sum up, the late Precambrian banded iron ores should be of metamorphosed volcano-sedimentary type.

The Fe [sbnd]Mn ore deposits of Urucum, Brazil: An oxygen isotope study

The Fe Mn ore deposits of Urucum are located close to the Brasilian-Bolivian border. They appear to be considerably younger (Late Proterozoic) than most other banded iron ore formations. The Mn ores occur in three or four well-defined beds. Oxygen isotope determinations have been carried out in Fe-poor and Fe-rich layers and on a few Mn ores. Due to the extremely small grain size, a conventional mineral separation was impossible. However, since the banded iron ores consist of two components only (SiO 2 and Fe 2O 3), a determination of the Fe content allows a calculation of the oxygen isotope composition of the pure end-members. The so calculated δ 18O-values vary between +21.3 and +26.4‰ for quartz and between +0.8 and +6.5‰ for hematite. Isotope equilibrium may have been reached in some but not all samples. Calculated temperatures vary between 250° and 280°C, depending upon which calibration curve is used. Such temperatures are higher than indicated by maximum burial depths. The δ 19O-values appear to reflect diagenetic and burial metamorphic conditions rather than primary conditions.

Precambrian banded iron ores; discussion

Precambrian banded iron ores; discussion

Contribution to studies of origin of Precambrian banded iron ores

The geochemical environment favorable for the formation of Precambrian banded iron ores is reconstructed and illustrated with results of experiments with the leaching of iron oxide and silica at different temperatures, at different pH ranges, and in the presence of certain elements in solution.It is suggested that the intermittent banding of silica and hematite in Precambrian banded ores is caused principally by the selective weathering of Precambrian soil. Due to the seasonal changes of temperature, amount of precipitation, and the alternately higher and lower pH range of the leaching solution, the Precambrian soil yielded alternately solutions carrying to the basin of deposition almost exclusively silica during the warm season and chiefly iron oxide during the cool period of the year.

Study on some amphibole bearing banded iron ores from Manchuria

Study on some amphibole bearing banded iron ores from Manchuria

Study on some amphibole banded iron ores from Manchuria

Study on some amphibole banded iron ores from Manchuria

The origin of the pre-Cambrian banded iron ores

Pre-Cambrian banded iron ores are products of predominantly chemical weathering of the gradually cooling crust and deposition under unique environmental conditions, not since duplicated in geological time. The banded structure of the ores is thought to originate in the cyclic precipitation of iron and silica in shallow lake basins in which the water underwent periodic changes of pH related to the alternating wet and dry seasons of a monsoon-like climate.

Garnet in banded iron ores, from Manchuria

Garnet in banded iron ores, from Manchuria

Mineral compositions of banded iron ore of low grade metamorphism from Manchuria

Mineral compositions of banded iron ore of low grade metamorphism from Manchuria

Characters on Banded Iron Ore Deposits

Characters on Banded Iron Ore Deposits

Amphibole of grünerite-cummingtonite series in banded iron ore from Manchuria

Amphibole of grünerite-cummingtonite series in banded iron ore from Manchuria

Study on blue-green hornblende bearing banded iron ore

Study on blue-green hornblende bearing banded iron ore