Mineralogical justification for potentiality of producing marketable hematite products


 
 
Hematite quartzites are a product of weathering of magnetite quartzites, which make up the ferruginous horizons of deposits of the Precambrian banded-iron formation. They occur all over the planet. The largest deposits are found in the iron-producing areas and basins of Central Kazakhstan, the Kursk magnetic anomaly, the Karelian-Kola region, Western Australia, Southeastern India, Brazil, the United States, and Canada. The geological and mineralogical issues of hematite quartzites as raw materials for producing concentrate and sinter ore have been studied most deeply and comprehensively for the deposits of the Kryvyi Rih basin and Central Kazakhstan. However, when developing an effective scheme for producing high-quality metallurgical raw materials, the mineralogical features of hematite ores have been taken into account insufficiently. The aim of the authors of the present work was to study the localization, structure of deposits and mineral composition of hematite quartzites as raw materials for sinter ore and concentrate production. Data from geological observations and mineralogical studies were used as source material. Proven geological, mineralogical, petrochemical methods were used. In accordance with the obtained results, the hematite quartzites are composed of ore-forming (quartz, hematite) and secondary (relict and newly formed) minerals. The total content of the hematite and quartz exceeds 90 mass %. The peculiarity of Ushkatyn III deposit ores is the high content of manganese oxides. The depth of distribution of the weathering crust composed of hematite quartzites varies from 200 to 1000 m. The hematite quartzites’ bodies are characterized by a zonal structure. Their central parts are represented by martite-micaceous hematite, micaceous hematite- martite quartzites; intermediate ones by martite quartzites; peripheral parts – by dispersed hematite-martite, kaolinite-martite-dispersed hematite quartzites. The horizons differ in the quantitative ratio of these varieties. The quantitative ratio of mineral varieties of hematite quartzites, morphology of individuals and aggregates of ore-forming and secondary minerals, their chemical composition and physical properties must be taken into account when developing the optimal technology for the production of high-quality hematite concentrate. 
 
 



Introduction
Hematite (martite) quartzites are the product of weathering of magnetite quartzites, which are currently mined in many regions of the world as a raw material for producing iron ore (magnetite) concentrate. Industrial deposits of hematite quartzites occur in the iron ore strata of most deposits of the Precambrian banded-iron formation. Their distribution is mainly controlled by two factors: 1) the effective action of hypergenic factors on primary magnetite quartzites; 2) the intensity of erosion of iron ore strata weathering crust under formation. The most significant reserves and resources of hematite raw materials were identified at the Karazhal deposit (Central Kazakhstan), Lebedinsky, Mikhailovsky and other deposits of the Kursk magnetic anomaly, Olenegorsk deposit of the Kola iron ore district, Kryvyi Rih basin (Ukraine), Hamersley deposits (Western Australia), the Quadrilátero Ferrífero (Brazil), the Upper Lakes (USA), etc. In the CIS countries, the problem of the use of hematite quartzites has been studied most deeply and comprehensively for the Kryvyi Rih basin deposits (Demchenko, 2018;Evtekhov, 2016;Prilepa, 2019;Tsypin, 2015).
Currently, the problem of the use of hematite raw materials at the mining and beneficiation enterprises of Kryvbas is being studied in connection with the increase in the level of integrated use of the mineral mass extracted from the subsoil. The priority directions involve the operation of deposits of hematite (oxidized) quartzites in order to produce sinter ore and concentrate . In the course of mining operations, hematite quartzites are extracted as overburden and accumulated at specially organized stockpiles (Southern Mining and Beneficiation Plant (YUGZK), Ar-selorMittal Kryvyi Rih (AMKR) Mining and Beneficiation Complex, or are stocked at waste dumps (Inhulets, Central, Nothern GZKs).
The depth of the weathering crust of different Kryvbas deposits varies from less than 50 m in areas of crust distribution to more than 2,500 m in areas of linear weathering crust along discontinuous faults (Dodatko, 1973;Yurk, 1960). .
The Skeliuvatka (Southern GZK) and Valyavkinske (AMKR GZK) hematite quartzite deposits belonging to the Southern iron ore region of the Kryvbas are recognized to be the priority for the development. The explored reserves of hematite raw materials here exceed 2 billion tons. The deposits were considered to be the raw material base for oxidized ores GZK (GZKOR).
The authors studied the bodies of hematite quartzites of the Valyavkinske deposit in detail, the explored reserves of which make up about 25 mass % of its productive stratum. The depth of distribution of the weathering crust of magnetite quartzites varies from 200-250 m in the southern part to 700-800 m in the northern part of the deposit. A significant part of the hematite raw material (about 400 million tons) was extracted from the subsoil and is stored in two stockpiles. Reserves in the subsoil are about 500 million tons. The average iron content in hematite quartzites is about 37 mass %.
Since the 1960s attempts have been made to use hematite raw materials on a commercial scale. Concentration plants were designed and built on the basis of magnetic technology for beneficiating low grade hematite ores: roasting-magnetic plant for beneficiating hematite quartzites of Central GZK, Kryvyi Rih GZKOR, section №10 of the beneficiation plant #2 of AMKR GZK. The obtained results showed that it is impossible to obtain hematite concentrate with an iron content of more than 60-61 mass % in industrial conditions by the method of wet magnetic separation. The suggested repreparation of the rough concentrate by the method of reverse flotation contributed to the increase of the iron content in the final concentrate to 64-65 mass %. Thus, flotation recovery does not allow a high quality concentrate to be obtained (67-69 mass %).
The technology of wet gravitational beneficiation with the use of conical and spiral separators has proved to be the most effective. In the Kryvbas, it is implemented in three industrial plants with a capacity of up to 1 million tons of raw materials per year, it allows hematite concentrate to be obtainined with iron content of not less than 65 mass %. Semi-industrial tests were also conducted for the ores of the Karazhal, Ushkatyn III deposits.
The results of laboratory and industrial tests of the authors of the present work showed the fact that it is possible to produce the end-product with various iron content from hematite quartzite deposits of Karazhal iron ore region, Southeast India, Kursk magnetic anomaly, Kryvyi Rih basin and similar deposits from other regions depending on the selected technologies for ore preparation and beneficiation: low-grade sinter ore (total iron content 55-57 mass %), ordinary sinter ore (58-60%), high-quality sinter ore (60-62%), sinter concentrate (62-64%), ordinary concentrate (64-66 %), high-quality concentrate (67-69%).
The goal of the authors of this work was to study the localization, structure of deposits and mineral composition of hematite quartzites as raw materials for the production of sinter and concentrate using the example of the Valyavkynske deposit in the Kryvbas and the Ushkatyn III deposit in Central Kazakhstan.

Source material and research methods
The results of geological observations and mineralogical studies of hematite quartzites of these deposits were used as source material. Proven geological and mineralogical methods were used.

Research results
The Valyavkinske deposit of ferruginous quartzites is located in the southwestern part of the Kryvyi Rih structure (Fig. 1). The rocks of the Skeliuvatka, Saksagan and Hdantsivka suites of the Kryvyi Rih Paleoproterozoic series occur in its structure. The Novokryvorizka and Hleyuvatka suites within the deposit boundaries have not been opened up (Belevtsev, 1962;Svital'skyi, 1932;Shcherbak, 1988).
Geology of hematite raw material deposits. Geologically, the deposits of hematite raw materials of the Kryvbas and Central Kazakhstan are similar, represented by layers, lenses of hematite quartzites, which alternate with layers of low-ore, ore-free rocks. They differ in age -Paleoproterozoic deposits of the Kryvbas, Paleozoic -Central Kazakhstan and mineral composition: the deposits of Central Kazakhstan are characterized by manganese-iron ore specialization. The genesis of both iron ore basins is volcanic-sedimentary.
As the main object, the authors have chosen the more deeply and comprehensively studied deposits of the Saksagan suite of the Kryvbas.
The Saksagan suite is represented by six schistose and six ferruginous horizons. The thickness of the weathering crust of the first, second and third ferruginous and first, second, third, fourth schistose horizons does not exceed 50-70 m. The main deposits of hematite ores belong to the fourth, fifth, sixth ferruginous horizons.
The fourth ferruginous horizon is characterized by a thickness of 260 to 540 m, 392 m on average. Up to a depth of 200 to 400 m it is composed of hematite quartzites, below it -of magnetite quartzites, which are currently mined as raw materials for producing magnetite concentrate. The horizon is characterized by the heterogeneity of the mineral composition, structural and textural features of the ores, corresponding to the features of the authigenic mineralogical zonation of ferruginous horizons (Evtekhov, 1971;Lazarenko, 1977;Strakhov, 1962). The central zones of the horizon are represented by micaceous hematite-magnetite, the intermediate ones -by magnetite, peripheral zones -by cummingtonite-magnetite and magnetite-cummingtonite quartzites. In this direction, the texture of ores naturally changes, from thinbedded to medium-bedded and wide-bedded. The average value of the total iron content (Fe tot.) is about 37 mass %, the iron content in the magnetite (Fe magn. ) makes up about 32 mass %.
There was a change in the mineral composition of ores in the weathering crust due to iron oxidation. The section of the horizon here in the same direction is as follows: micaceous hematite-martite → martite → dispersed hematite-martite → kaolinite-martitedispersed hematite quartzites. In the upper parts of the weathering crust there is an intense goethitization of ferruginous quartzites to a depth of 30 m. The textural features of the ores are preserved. The average value of the total iron content due to its poor mobility in the weathering crust is almost unchanged, it makes up 37.2 mass %, the iron content in the magnetite varies from less than 1 mass % (in the upper part of the weathering crust) to 15 mass % (in the lower part).
The fifth schistose horizon is composed of alternating layers of barren quartzites and graphite-containing schists of muscovite-chlorite-cummingtonitequartz-biotite composition. The thickness of the horizon varies from 20 to 50 m.
The sixth schistose horizon is also composed of hypergenically altered ferruginous rocks -lowore dispersed hematite-martite, martite, and ore-free quartzites, which are often intensely marshalitized. Silicate, quartz-silicate interlayers of initial rocks have been converted into kaolinite-dispersed hematite-quartz ones. The thickness of the horizon varies from 10 to 50 m.
The sixth ferruginous horizon completes the section of the Saksagan suite of the deposit. Its section is similar to the section of the fourth ferruginous horizon. At a depth of up to 700 m, the original magnetite-containing ferruginous quartzites are replaced by hematite varieties. Its constituent rocks are also intensely hypergenically altered. The texture of ores is medium-bedded, more rarely thin-bedded and widebedded. The average content of Fe tot. is 36.7 mass %, that of Fe magn. is 0.8% in hematite quartzites of the horizon. The thickness of the horizon within the boundaries of the deposit is from 200 to 500 m.
The mineral composition of hematite quartzites of the fourth, fifth and sixth ferruginous horizons of the Valyavkinske deposit is relatively simple due to the hypergenic replacement of polymineral associations of primary metamorphogenic magnetite quartzites by their hypergenic hematite varieties: -magnetite has been replaced by hematite (martite); -iron-free carbonates (calcite, dolomite, etc.) have been completely dissolved; -iron-containing carbonates (siderite, sideroplesite, pistomessite, etc.) have partially been dissolved (calcium, magnesium components), the iron component has been replaced by dispersed hematite or dispersed goethite; -iron sulfides (pyrite, pyrrhotine, etc.) have been replaced by dispersed hematite or dispersed goethite; sulfur in the form of sulfur dioxide passed into solution; -alumina-free silicates (cummingtonite, ferrous talc (minnesotaite), celadonite, etc.) have been replaced by an aggregate of fine-crystalline quartz (chalcedony, opal) and dispersed hematite (dispersed goethite); the calcium and magnesium ions, which are a part of them, passed into solution; -alumina-containing silicates have been replaced by fine crystalline aggregate of quartz, dispersed hematite (dispersed goethite) and kaolinite (Lazarenko, 1977;Martynenko, 1971;Yurk, 1960).
Due to incomplete substitution, relic magnetite has been preserved in hematite ores in an amount of from less than 1 to 15 mass %. The average content of Fe magn. as a part of hematite raw materials of all three studied ferruginous horizons is 4.2 mass %.
The quantitative ratio of mineral varieties of hematite quartzites in the ore bodies of the three ferroginous horizons, which has been determined from detailed geological exploration data, operational exploration data and topomineralogical studies conducted by the authors, of the faces of the Valyavkynskyi open-pit, is given in Table. 1. Fig. 2 shows schematic sections of the fourth, fifth and sixth ferruginous horizons. As can be seen, they are represented by the same mineral varieties of hematite quartzites, but differ in quantitative ratio. The fifth ferruginous horizon is characterized by the maximum prevalence of micaceous hematitecontaining varieties, and the fourth and sixth ones are characterized by prevalence of martite varieties.
The ore mined in the open-pit and accumulated in stockpiles contains mineral varieties of low-grade hematite ores of the three studied ferruginous horizons in the amount determined not only by the natural ratio of hematite raw materials in the subsoil, but also by the dynamics of stripping conducted in different directions of open-pit development. Petrographic study of the material of hematite quartzite stockpiles showed that the following quantitative ratio of the main mineral varieties of low-grade hematite ores (volume %) can be expected in the primary hematite quartzite raw material of the beneficiation plant of the Valyavkynske deposit: martite-micaceous hematite quartzites; micaceous hematite-martite quartzites -19.3; martite quartzites -36.9; dispersed hematite-martite quartzites -23.9; martite-dispersed hematite quartzites -8.1. The average content of diluting non-metallic impurities (sсhists of different composition, silicate quartzites) in the ore material is 4.8% by volume.
Mineralogy of ores. Martite-micaceous hematite quartzites are the product of weathering of the original magnetite-micaceous hematite quartzites (Fig.  3a). They form layered, less often lenticular bodies which are up to 50 m thick, spatially tend to the central zones of the studied ferruginous horizons. The ores are strong, relatively easily cleave along lamination. The structure is microcryptocrystalline and fine-crystalline. The texture is micro-bedded, rarely thin-bedded and medium-bedded. The quantitative ratio of ore-forming and secondary minerals is given in Table 2.
Martite quartzites are the product of weathering of the original magnetite quartzites (Fig. 3b). They form embedded bodies with a thickness of up to 70 m in the sections of the fifth and sixth ferruginous horizons and up to 150-200 m of the fourth ferruginous horizon. In the primary magnetite quartzites micaceous hematite or silicates (cummingtonite, chlorite, biotite) occurred in an amount of up to 5 mass %. In this regard, martite quartzites contains both weatheringresistant micaceous hematite and dispersed hematite, which is the product of hypergenic changes of silicates. The ore is strong, cleaves poorly along lamination. The structure is microcryptocrystalline and fine-crystalline. The texture is bedded, due to the alternation of ore (quartz-martite) and nonore (quartz, micaceous hematite-quartz, dispersed hematite-quartz) interlayers. The medium-bedded texture predominates, thin-and wide-bedded texture is less common. Manifestations of coarse-and giantbedded texture are rare.
Dispersed hematite-martite quartzites were formed as a result of hypergenic changes of the initial silicate-magnetite quartzites. They form layered bodies with a thickness of up to 30 m in the section of the fifth ferruginous horizon, up to 50 m in the section of the sixth ferruginous horizon and up to 80 m in the section of the fourth ferruginous horizon. They spatially tend to the peripheral zones of the horizons. The ores have reduced strength, cleave well along lamination due to the layer-bylayer presence of dispersed hematite. The structure is microcryptocrystalline and fine-crystalline. The texture is wide-bedded, less often medium-and coarsely bedded. Manifestations of thin-and giantbedded texture are rare.
Martite-dispersed hematite quartzites are the product of weathering of the original magnetite silicate quartzites. In the layers that prior to weathering contained up to 30% or more by volume of chlorite, biotite and other alumina-containing silicates, kaolinite is present in an amount of more than 5% by volume. Martite-dispersed hematite quartzites form layered bodies, which are up to 10 m thick in the section of the fifth ferruginous horizon, up to 15 m in the section of the sixth ferruginous horizon and up to 20 m in the section of the fourth ferruginous horizon. They compose the extreme peripheral zones of the horizons. The ores have medium strength, cleave well along lamination. The structure is microcryptocrystalline and fine-crystalline. The texture is wide-bedded, less often coarse-and medium-bedded.
Diluting non-metallic impurities. Due to the suboptimality of drilling-and-blasting and mining technologies, low-ferruginous rocks are present in the material of hematite raw material stockpiles. The most common are chlorite-cummingtonite-quartz-biotite (Fig. 3c) schists and monomineral silicate quartzites of the fourth, fifth, and sixth schistose horizons. Fragments of vein quartz in monomineral form or in intergrowth with hematite quartzites are noticed less often (Fig. 3d).
The Ushkatyn III deposit is part of the Zhairem ore district (Brusnitsyn, 2018). In terms of mineral and petrographic composition of the productive stratum, it is similar to the Valyavkynske deposit of the Krivbas. The increased content of manganese oxides (from 1 to 20 mass %) is the difference between them. Ironcontaining minerals are represented by hematite of three morphological varieties: martite, micaceous hematite (specularite, dispersed hematite) (Fig. 4). A characteristic feature of individuals and aggregates of hematite is their much smaller size in comparison with the ores of the Kryvyi Rih deposits. In this regard, the same degree of grinding (0.05-0.06 mm), allows a full release of hematite from the Valyavskinske deposit, the hematite of the Ushkatyn III deposit retains intergrown pieces with non-metallic minerals -quartz, carbonates, silicates. Thus, the ore-forming minerals of hematite raw materials of the studied deposits are represented by hematite (martite, micaceous hematite, dispersed hematite), quartz. Their total content in all mineral varieties of hematite quartzites exceeds 90 mass %. Secondary minerals include relict (magnetite, metamorphogenic silicates, carbonates, sulfides, etc.) and newly formed (iron hydroxides, clay minerals, etc.) minerals. Their quantitative ratio, morphology of individuals and aggregates, chemical composition and physical properties must be taken into account when developing an optimal technology for the production of high-quality hematite concentrate.
The production of hematite sinter ores and concentrates is not associated with fundamental technological difficulties for deposits of different scales. The first results of the search for an effective technology for the enrichment of hematite raw materials were obtained during the 1960s. Technological schemes based on the use of magnetic, gravitational, flotation units were considered. To date, the optimal technology has not been determined. Reducing the explored volumes of magnetite quartzites helps to intensify its search. According to the authors of this publication, the least energy-consuming, the most technologically efficient is gravity technology.
This also applies to the ores of Central Kazakhstan, the feature of which is the presence of a wide range of minerals ; manganese and other metals. Effective involvement of the latter in the operation can be achieved by updating the ore preparation (Demchenko, 2018;Evtekhov, 2016;Prilepa, 2019;Tsypin, 2015), including utilization of the lump sorting module of mineral raw materials produced by scientific production enterprise "Gamayun". The module provides a significant reduction in energy a -martite-micaceous hematite quartzite (jaspilite) of the fifth ferruginous horizon; b -martite quartzite of the fourth ferruginous horizon; c -chlorite-cummingtonite-quartz-biotite schist of the fourth schistose horizon; d -vein quartz from martite quartzite of the sixth ferruginous horizon.
The maximum size of samples is 10 cm. consumption, mobility, efficiency of integration with existing structures. It was tested at the Atasui ore deposits of Central Kazakhstan (Karazhal, Ushkatyn III, Zhairem).

Conclusions
1. Hematite quartzites belong to the types of iron ore which commonly occur all over the planet. Depending on the technologies of ore preparation and beneficiation, it is possible to produce metallurgical raw materials with different iron content (from 55 to 69 mass %).
2. The optimal technology for hematite quartzite beneficiation for ores of most deposits has not been developed due to insufficient mineralogical justification.
4. The results of geological and mineralogical research must be taken into account when drawing up effective technological schemes for ore preparation and beneficiation of hematite quartzites in order to produce metallurgical raw materials with different iron content.