lateritic bauxite deposits our largest source of aluminum | geology for investors

lateritic bauxite deposits our largest source of aluminum | geology for investors

Laterite is formed when heavy tropical rainfall results in intense weathering of rock and soil.After many millions of years what is left is called a laterite, which can be either iron-rich, or in extreme cases, aluminium-rich

Most of the worlds aluminium is mined from lateritic bauxite deposits. The largest producer is Australias Weipa Mine in northern Queensland, while other countries with large reserves include Guinea, Vietnam, and Jamaica.

Formed in a similar manner to iron laterites, bauxite is created by weathering of suitable rocks in a tropical climate. Typically deposits are large and at the surface. Mining usually involves simple strip-mining, without the need for open pit development.

Laterite is formed when heavy tropical rainfall results in intense weathering of rock and soil. The chemistry of weathering silica-rich rocks sees the relatively mobile elements such as calcium, sodium, potassium and magnesium being washed away, while the immobile metals including aluminium, iron, titanium, and zirconium remain.

Most lateritic bauxites were formed in a period from the mid-Cretaceous to the late-Tertiary, that is, 100 million to 2 million years ago.During this time, laterite formation was not continuous. Instead, they formed during relatively short periods of intense weathering separated by long periods of less intense weathering.

Many lateritic bauxites are pisolitic (Figure 1). The word pisolitic comes from the Greek meaning pea-sized rock particles. When cut or broken open their inside surfaces reveal concentric bands of different mineral compositions.

The basic mineralogy of lateritic bauxites is similar throughout the world. The most sought after bauxite mineral is the aluminium hydroxide mineral gibbsite, Al(OH)3.Although it has a lower aluminium content than some other minerals, gibbsite-rich bauxite is cheaper to mine and process.Other aluminium minerals which may be present in bauxite include diaspore, boehmite (AlO(OH))andvarious types of alumina (or Al2O3).

A typical profile is really a misnomer as there are so many variations. The example shown in Figure 2 is a lateritic bauxite profile exposed in the western coastal cliffs of Cape York Peninsula, in northern Australia. Elements of this typical profile are seen in most lateritic bauxite profiles in other parts of the world.

The profile consists of a relatively thin soil layer overlying a horizon consisting of cemented pisolitic bauxite. The main mineral within this cemented layer is boehmite or monohydrate as the miners call it. Although one of the most aluminium-rich minerals in lateritic bauxite, the layer containing this mineral is normally stripped off and discarded during mining. This is because the layer is typically cemented and would therefore require crushing. In addition, the caustic soda solution that is used to extract aluminium from bauxite needs to be much hotter for boehmite than for gibbsite, so processing costs would be correspondingly higher.

Underlying the cemented bauxite is a layer of loose pisolitic bauxite 1-2m thick. The main mineral in the pisolitic bauxite is the aluminium-rich mineral gibbsite or trihydrate as it is commonly referred to. Pisolitic bauxite ore is an ideal ore for various reasons. It is located close to the surface so very little cover is needed to be removed to expose it. The bauxite is loose and easily mined with front-end loaders. Beneficiation of the ore before it is shipped out of port involves simple screening and washing. Selective mining ensures that only the highest grades are mined.

Below the pisolitic bauxite horizon is a nodular ironstone layer. At this level, the bauxite becomes increasingly iron and kaolin-rich. Kaolinite, which contains a great deal of silica, is also much lower in aluminium content than bauxite. Kaolinite tends to dissolve relatively easily in the caustic soda solution during aluminium extraction so uses up this valuable chemical. For this reason, mining has to be done very carefully as the ironstone layer is approached because kaolinite in the ore significantly reduces its value.

Beneath the ironstone layer the profile becomes increasingly less nodular and more mottled in appearance. The mottled zone has reddish coloured patches containing hematite and goethite, within a pale coloured kaolin-rich mass. At greater depths below this zone the white mineral kaolinite dominates, hence the name pallid zone given to the lowest part of the weathering profile.

handbook of gold exploration and evaluation | sciencedirect

handbook of gold exploration and evaluation | sciencedirect

Designed for geologists and engineers engaged specifically in the search for gold deposits of all types and as a reference for academics in higher schools of learning, Handbook of gold exploration and evaluation provides principles and detailed explanations that underpin the correct interpretation of day-to-day experience in the field. Problems are addressed with regard to the analysis, interpretation and understanding of the general framework within which both primary and secondary gold resources are explored, developed and exploited. Handbook of gold exploration and evaluation covers a comprehensive range of topics including the nature and history of gold, geology of gold ore deposits, gold deposition in the weathering environment, sedimentation and detrital gold, gold exploration, lateritic and placer gold sampling, mine planning and practise for shallow deposits, metallurgical processes and design, and evaluation, risk and feasibility.

Designed for geologists and engineers engaged specifically in the search for gold deposits of all types and as a reference for academics in higher schools of learning, Handbook of gold exploration and evaluation provides principles and detailed explanations that underpin the correct interpretation of day-to-day experience in the field. Problems are addressed with regard to the analysis, interpretation and understanding of the general framework within which both primary and secondary gold resources are explored, developed and exploited. Handbook of gold exploration and evaluation covers a comprehensive range of topics including the nature and history of gold, geology of gold ore deposits, gold deposition in the weathering environment, sedimentation and detrital gold, gold exploration, lateritic and placer gold sampling, mine planning and practise for shallow deposits, metallurgical processes and design, and evaluation, risk and feasibility.

the behavior of gold in the lateritic alterosphere | springerlink

the behavior of gold in the lateritic alterosphere | springerlink

Man has been searching for Au at the surface of the earth for more than 6ooo years, and has used it as a symbolic, social and economic reference. Since the beginning of this century, many studies have dealt with the geology of primary Au deposits of hydrothermal origin, and with secondary Au deposits which result from sedimentary, mainly alluvial processes. During the last decade, research has focused on the weathering of Au protores which generates the so-called lateritic Au in tropical climatic zones.

assessment of the geotechnical properties of lateritic soils in minna, north central nigeria for road design and construction

assessment of the geotechnical properties of lateritic soils in minna, north central nigeria for road design and construction

Laterite is a highly weathered material, rich in secondary oxides of iron, aluminum, or both. Geotechnical investigation is one of the effective means of detecting and solving pre, syn and post constructional problems. The geotechnical properties of lateritic soils and their suitability for road construction have been evaluated for selected sites in Minna, North-central Nigeria. All analyses were carried out in accordance with the British Standard Institution. The liquid limit ranged from 22.5% to 49.6% with an average value of 34.9%, plastic limits varied from 13.8% to 28% with a mean value of 21.38% while plastic index is of the order of 8.7% to 21.6% with an average value of 13.5%. The maximum dry density ranged from 1.78 g/cm3 to 2.33 g/cm3 with a mean value of 1.858 g/cm3 while the optimum moisture content varied from 6.30% to 14.3% with an average value of 9.74%. The evaluation reveals that the lateritic soils have higher plastic limits, Maximum Dry Densities (MDD) and California Bearing Ratios (CBR) while their liquid limits, plasticity indices and Optimum Moisture Contents (OMC) are lower. The lateritic soils were classified as A-3, A-2-4 and A-2-6 and are adjudged suitable for sub-grade, good fill and sub-base and base materials. This geotechnical information obtained will serve as base-line information for future road foundation design and construction in the study area.

The understanding of soil behavior in solving engineering and environmental issues as swelling soil especially expansive lateritic soils that can cause significant damage to road construction and other engineering application is the sole aim of geotechnical engineering (Abubakar, 2006; Oke and Amadi, 2008).One of the major causes of road accident is bad road which is usually caused by wrong application of constructional materials especially laterite as base and sub-base material by construction companies (Oke et al., 2009a; Nwankwoala et al., 2014). For a material to be used as either a base course or sub-base course depends on its strength in transmitting the axle-load to the sub-soil and or sub-grade (the mechanical interlock). The characteristics and durability of any constructional material is a function of its efficiency in response to the load applied on it (Oke et al., 2009b; Nwankwoala and Amadi, 2013). The mineralogical composition of the lateritic soil has an influence on the geotechnical parameters such as specific gravity, shear strength, swelling potential, Atterberg limits, bearing capacity and petrograpic properties (Amadi et al., 2012). The rate at which newly constructed roads in Minna and environs developed cracks and later damage is worrisome. Hence this study will ensure that the right lateritic soils with the right criteria are used as a base or sub-base material for road construction in Minna and environs, North-Central Nigeria, thereby ensuring their durability.

The study area is Sauka-Kahuta industrial layout, behind the Minna building material market. It lies within longitude 062811E to 063213E of the Greenwich Meridian and between latitude 093522N to 093036N of the Equator (Figure 1). The study area has an undulating topography drained by river chanchaga and its tributaries. The area is within the Guinea Savannah with an annual rainfall of about 1100 mm in the northern part and 1600 mm in the southern part. The rainy season spans between the month of April- October and an optimum temperature of 41C in dry season and minimum of 22C during the rainy season (Sheriff, 2012).The study area is assessed through Talba farm road, Mandella road, other minor untarred road.

The sub-soil conditions was investigated by excavating five trial pits from existing ground level to a maximum of 4.5 m according to British standard code of practice for site investigation (1981), depending on topography and overburden. Disturbed samples soil samples were collected from the trial pits and analyzed at civil engineering laboratory, Federal University of Technology, Minna, Nigeria for relevant geotechnical analysis.

The laboratory analysis was performed according British standard methods of test for soil for civil engineering purposes (BS 1377: Part 1-9, 1990). The laboratory test carried out to determine the suitability of the lateritic soils for use as base and sub-base material using the AASHTO standard method in relation to the generation specification for roads and bridges.

Sieve analysis was performed in order to determine the soil particle size distribution. Representative sample of approximately 500 g was used for the test after washing and oven-dried. The sample was washed using the BS 200 sieve and the fraction retained on the sieve was air dried and used for the sieve analysis. The sieving was done by mechanical method using an automatic shakers and a set of sieves.

This test determines the clay content in terms of liquid limit, plastic limit, plasticity index and shrinkage potential in order to estimate plasticity, strength and settlement characteristics of the soil sample. For the determination of liguid limit, the soil sample passing through 425 m sieve, weighing 200 g was mixed with water to form a thick homogeneous paste. The paste was collected inside the Casangrades apparatus cup with a grove created and the number of blows to close it was recorded. Similarly, for plastic limit determination, the soil sample weighing 200 g was taken from the material passing the 425 m test sieve and then mixed with water till it became homogenous and plastic to be shaped to ball. The ball of soil was rolled on a glass plate until the thread cracks at approximately 3 mm diameter. The 3 mm diameter sample was placed in the oven at 105C to determine the plastic limit.

Moisture content is defined as the ratio of the weight of the water in a soil specimen to the dry weight of the specimen. The moisture content of lateritic soil can be influenced by the mineralogy and formation environment.

The densification of soil with mechanical equipment thereby rearranging the soil particles which makes them more closely packed resulting in an increase of the ratio horizontal effective size to the vertical effective stress. The degree of compaction is measured in term of its dry weight and it increasing the bearing capacity of road foundation, stability slopes, controls undesirable volume changes and curb undesirable settlement of structures. The mould is filled and compacted with soil in five layer via 25 blows of a 4.5 rammer.

The California bearing ratio (CBR) test is a penetration test carried out to evaluate the mechanical strength of a sub-base or base course material. It measures the shearing resistance, controlled density and moisture content. Both the soaked and unsoaked method of CBR was conducted to characterize the lateritic soil for use as a base or sub-base material. A portion of air-dried soil sample was mixed with about 5% of its weight of water. This was put in CBR mould in 3 layers with each layer compacted with 55 blows using 2.5 kg hammer at drop of 450 mm (standard proctor test). The compacted soil and the mould was weighed and placed under CBR machine and a seating load of approximately 4.5 kg was applied. Load was recorded at penetration of 0.625, 1.9, 2.25, 6.25, 7.5, 10 and 12.5 mm.

In this test, horizontal load was applied as soon as vertical load has been imposed and shearing continued at the rate of 0.25 mm/min until the shear force goes beyond its maximum value and becomes constant or decreases, representing failure condition. Normal stresses of 188.0 kPa, 324.3 kPa, 460.5 kPa and 596.8 kPa were employed in all the direct shear tests. The results of the direct shear tests for the lateritic soils are presented in the form of stress-strain curves and plots of shear stress versus normal stress. From these, the shear strength parameters (angle of cohesion (c) and angle of internal friction ()) were obtained.

The result of the laboratory analyses are summarized in Table 1 while the revised AASHTO system of soil classification is contained in Table 2. The description of the lateritic soils is shown in Table 3 and Figure 3 while the physical properties of soil samples are presented in Table 4. Federal Ministry of Works and Housing general specification for roads and bridges is shown in Table 5. According to Federal Ministry of Works and Housing (1997) specification, the lateritic soil samples are suitable for subgrade, subbase, and base materials as the percentage by weight finer than No. 200 BS test sieve is less than 35% except locations 8 and 10 (Table 1). The liquid limits value, ranged from 15.8% to 49.6%, the plastic limits varied from 12.0% and 28.0% while the plastic index is of the order of 3.8 to 19.4 (Table 1). Federal Ministry of Works and Housing (1997) for road works recommend liquid limits of 50% maximum for subbase and base materials. All the studies soil samples fall within this specification, thus making them suitable for subgrade, subbase and base materials. The plot of plasticity index versus liquid limit is shown in Figure 4. The unsoaked California bearing ratio value for the lateritic soil sample range from 0.0% to 83.8%. Federal Ministry of Works and Housing recommendation for soils for use as: subgrade, subbase and base materials are: 10%, 30% and 80% respectively for unsoaked soil. This implies that locations [2, 8, 9] with values less than 10% are excellent subgrade materials, locations [1, 2, 3, 8, 9, 10] having values less than 30% are good materials for subbase.

All the locations except location 5 have their unsoaked CBR value less than 80% which is the maximum value recommended for soils to be used as base materials (Federal Ministry of Works and Housing, 1997). By interpretation the lateritic soils from other locations except location 5 are suitable materials for subgrade, subbase and base materials. Location 5 failed the geotechnical characteristics for use as subgrade, subbase or base material. The maximum dry density for the soil samples varied between 1.81 mg/m3 and 2.35 mg/m3 while that of optimum moisture content ranged between 7.81% and 14.4%. According to OFlaherty (1988) the range of values that may be anticipated when using the standard proctor test methods are: for clay, maximum dry density (MDD) may fall before 1.44 mg/m3 and 1.685 mg/m3 and optimum moisture content (OMC) may fall between 20-30%. For silty clay MDD is usually between 1.6 mg/m3 and 1.845 mg/m3 and OMC ranged between 15-25%. For sandy clay, MDD usually ranged between 1.76 mg/m3 and 2.165 mg/m3 and OMC between 8 and 15%. Thus, looking at the results of the soil samples, it could be noticed that they are sandyclay. The cohesion (c) of the quick undrainedtriaxial compression test (Figure 5) ranged from 130 KN/m2 to 165 KN/m2 and the angle of internal friction () was found to be 8 and this implies low plasticity, high permeability, shear strength and bearing capacity.

The moisture content from the compaction test in ranged from 6.30% to 14.4% with an average value of 10.39 (Table 1 and Table 3) indicating that the soil is generally poorly graded and sandyclay with plastic fines (material passing sieve No. 200) and this finding is in agreement with other determined geotechnical parameters. Federal Ministry of Works and Housing (1972) for road works recommend liquid limits of 50% maximum for subbase and base materials. All the studies soil samples fall within this specification, thus making them suitable for subbase and base materials.

The geotechnical properties of Minna, North-central Nigeria has been carried out in compliance with BS 1377 (1997) and head of (1990) methods of soil testing for Civil engineers. The result showed that the studied soil samples are classified as sandyclay, incompressible, easily compactable with good drainage. The soil samples tested from the study area indicate a general cohesive nature with low moisture content, high granular material which is suitable for road construction except location 5. These valuable data obtained from the geotechnical analysis can be useful for civil engineers in the design and construction of roads in Minna and environs for maximum durability and efficiency. It is recommended that engineering confirmatory test be carried out before embarking on any construction such as road. Location 5 which failed lateritic soil should be stabilized with either cement, sand; crushed stone (gravels) of and 3/4 inch size in order to meet the sub-base or base course requirement.

classification of mineral deposits | geology for investors

classification of mineral deposits | geology for investors

Geologists, are known to have more opinions than economists, so it should come as no surprise that the classification of mineral deposits, is an on-going hot topic. The details will be debated until the sun cools, but the broad-brush classification of mineral deposits is generally understood.

Quite simply, if geologists can classify mineral deposits based on rock types, geologic settings and formation conditions, then they can start to make useful predictions of where other similar deposits might be. For example:

Most mineral deposits are formed by more than one process, so attaching a single label to them is difficult. Hence, there is a tendency to talk about Stillwater Complex type or Carlin-type gold deposits, which rather defeats the purpose of finding a general from the specific.

There are two main approaches to mineral deposit classification. The descriptive models are a more objective label, which describes the rocks and tectonic setting of the deposit. These have now evolved to what is known as a genetic model, which includes theories on deposit formation as well as the physical properties of the mineral deposit.

More sophisticated are occurrence probability models, which predict the probability of a deposit type occurring within a particular location, based on known rock types and structural geology.While any discussion of classification will no doubt result in an over-simplification of what is a very complex subject, there are some general and useful concepts that can be shared.

The Earths crust primarily composed of lighter minerals formed of lighter elements. As we travel deeper within the earth heavier elements and minerals dominate. One method of classifying rocks is by this association, which considers both the composition and conditions of formation. The table below outlines these main rock types: Ultramafic, mafic and felsic rocks.

Although rocks may form at a variety of temperatures and depths within the Earth, they may also be exposed at the surface by erosion, tectonic processes or volcanic eruption. This brings us to our next classification.

Also called extrusive rocks, volcanic rocks are those that formed through volcanic eruption. Eruptions on the sea floor, where the crust is thinner are generally mafic, while volcanic rocks associated with thick continental crust are more likely to be felsic.

Intrusive rocks are those formed from the cooling of magma bodies that have never erupted to the surface, but have instead been exposed through erosion or uplift. These rocks generally have a more crystalline appearance since they have the opportunity to cool more slowly than volcanic rocks and the crystalline minerals can more fully form.

Sedimentary rocks are formed from the erosion of older instrusive, volcanic rocks or even other sedmentary rocks. They may also be formed through biologic processes, such as coral reef formation. Mineral deposits may form in sedimentary rocks through the erosion of ore-bearing rocks or through the mobilization of ore-bearing fluids through sedimentary rock.

Laterites Laterites are red colored iron-rich soils that have been leached through tropical weathering processes. They can host important mineral deposits including Iron, Nickel, Bauxite (Aluminum) and REEs.

These are rocks that have been altered by heat and pressure so much so that they become another rock type. Often geologists can recognize the original rock that has been metamorphosed and will refer to the rock as a meta-sedimentary rock or meta-volcanic. Though sometimes it is not possible to confidently determine the original rock type.

Metamorphic rocks may often be labelled as high grade or low grade metamorphic. These grades are are a reference to the temperature and pressure to which the rock was exposed based on its texture and mineralogy and does not have any specific economic meaning. However,metamorphic processes may help concentrate economic minerals.

While there many, many more ways to classify rocks and mineral deposits, understanding the basics of rock classification and mineral associations can go a long way in helping one understand the processes involved and the descriptions of economic deposits published by geologists.

leaders in mining software & advisory

leaders in mining software & advisory

RPMGlobal integrates planning and scheduling, with maintenance and execution, together with simulation and costings, on RPMGlobals Enterprise Planning Framework, the mining industrys only digital platform that enables insight and control across these core processes.

Our Advisory team advise the global mining industry on their most critical issues, challenges and opportunities, from exploration to mine closure. Their deep domain expertise, combined with their culture of innovation, and global footprint, ensures our mining customers continue to lead.

multiple-point statistical simulation of the ore boundaries for a lateritic bauxite deposit | springerlink

multiple-point statistical simulation of the ore boundaries for a lateritic bauxite deposit | springerlink

Resource estimation of mineral deposits requires spatial modelling of orebody boundaries based on a set of exploration borehole data. Given lateritic bauxite deposits, the spacing between the boreholes is often determined based on the grade continuity. As a result, the selected drill spacing might not capture the underlying (true)lateral variability apparent in the orebody boundaries. The purpose of this study is to investigate and address the limitations imposed by such problems in lateritic metal deposits through multiple-point statistics (MPS) framework. Rather than relying on a semivariogram model, we obtain the required structural information from the footwall topographies exposed after previous mining operations. The investigation utilising the MPS was carried out using the Direct Sampling (DS) MPS algorithm. Two historical mine areas along with their mined-out surfaces and ground penetrating radar surveys were incorporated as a bivariate training image to perform the MPS simulations. In addition, geostatistical simulations using the Turning Bands method were also performed to make the comparison against the MPS results. The performances were assessed using several statistical indicators including higher-order spatial cumulants. The results have shown that the DS can satisfactorily simulate the orebody boundaries by using prior information from the previously mined-out areas.

Dagasan Y, Renard P, Straubhaar J, Erten O, Topal E (2018c) Pilot point optimization of mining boundaries for lateritic metal deposits: Finding the trade-off between dilution and ore loss. Nat Resour Res 28:153171

Dimitrakopoulos R, Mustapha H, Gloaguen E (2010) High-order statistics of spatial random fields: exploring spatial cumulants for modeling complex non-gaussian and non-linear phenomena. Math Geosci 42(1):6599

Erten O (2012) Profiling and mining control to mitigate dilution effect from SiO2 at the base of a bauxite deposit. PhD Thesis, School of Mechanical and Mining Engineering, The University of Queensland

Guardiano FB, Srivastava RM (1992) Borrowing complex geometries from training images: the extended normal equations algorithm. Stanford Center for Reservoir Forecasting Report, Stanford University, Stanford

Meerschman E, Pirot G, Mariethoz G, Straubhaar J, Van Meirvenne M, Renard P (2013) A practical guide to performing multiple-point statistical simulations with the direct sampling algorithm. Comput Geosci 52:307324

Osterholt V, Dimitrakopoulos R (2018) Simulation of orebody geology with multiple-point geostatisticsapplication at yandi channel iron ore deposit, WA, and implications for resource uncertainty. In: Advances in applied strategic mine planning, Springer, New York, pp 335352

Pasti HA, Costa JFCL, Boucher A (2012) Multiple-point geostatistics for modeling lithological domains at a Brazilian iron ore deposit using the single normal equations simulation algorithm. In: Geostatistics Oslo, Springer, New York, pp 397407

van der Grijp Y, Minnitt RCA (2015) Application of direct sampling multi-point statistic and sequential gaussian simulation algorithms for modelling uncertainty in gold deposits. J South Afr Inst Min Metall 115(1):7385

The authors would like to thank Ilnur Minniakhmetov and Ryan Goodfellow from the Department of Mining and Materials Engineering of McGill University for providing the hosc software and their kind help.

Dagasan, Y., Erten, O., Renard, P. et al. Multiple-point statistical simulation of the ore boundaries for a lateritic bauxite deposit. Stoch Environ Res Risk Assess 33, 865878 (2019). https://doi.org/10.1007/s00477-019-01660-8

mercury-free gold mining technologies: possibilities for adoption in the guianas - sciencedirect

mercury-free gold mining technologies: possibilities for adoption in the guianas - sciencedirect

The rudimentary nature of small-scale gold mining activities often generates a legacy of extensive degradation and deplorable social conditions, both during and after activities have ceased. Small-scale mining usually involves the extraction of secondary gold from placer deposits (alluvial, colluvial or elluvial), which can be liberated and treated using gravity methods. In the Guianas, the most popular form of small-scale gold mining is referred to as land dredging, a combination of hydraulicking and suction dredging. This method requires application of large volumes of water for both mining and mineral processing; in most cases, there are no containment structures for the waste tailings generated. Mercury, a dangerous pollutant, is the preferred method employed by small-scale miners for gold recovery. Gold extraction using mercury is comprised of the following four stages: (1) amalgamation, (2) separation of amalgamation, (3) removal of excess mercury, and (4) burning of the remaining amalgam to produce a gold sponge. Mercury can be released into the environment at each stage, which makes the promotion of mercury-free alternatives imperative.

Technical alternatives for small-scale gold mining, however, must be thoroughly evaluated, pre-tested, modified accordingly and successfully transferred. Moreover, technology must be inexpensive, relatively simple and easy to adapt, while allowing a rapid rate of return. WWF-Guianas is working with the regulatory agencies and other relevant stakeholders of the Guianas to reduce the environmental footprints caused by small-scale mining. The major aspects of this program are to develop the capacity and regulatory mechanisms within the local government, to promote mercury-free technology, and monitor mercury in the environment. This paper reviews the alternative technologies being investigated by the WWF-Guianas for use in the small-scale gold mining industry.

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