C. Drebenstedt and R. Singhal (eds.), Mine Planning and Equipment Selection, 491 DOI: 10.1007/978-3-319-02678-7_47, © Springer International Publishing Switzerland 2014

Geotechnical Considerations for Mining Method Selection of a Potential Underground Iron Ore Mine in Mideastern, Turkey

Levend Tutluoglu, Celal Karpuz, Hasan Ozturk, Dogukan Guner, and A. Gunes Yardimci

Middle East Technical University, Ankara, Turkey

Abstract. Geotechnical analysis plays an important role in determining mining method selection. This study presents the geotechnical design analysis of a potential U/G iron ore Mentes Mine at Yahyali province of Kayseri district in Turkey. Iron ore body is initially planned to be mined by using long hole mining method. Detailed geotechnical site investigation and laboratory work are carried out to assess the applicability of the selected mining method. Diamond-drilled borehole cores are logged and geotechnical characterization of rock mass units is conducted by assigning RMR89 and Q classification values to the basic rock units. Extensive laboratory test work is carried out to find the geotechnical material properties of the ore and the wall rocks. Based on the results of rock mass classification efforts, empirical stope dimensioning work and detailed numerical (finite element) modeling for the stability analyses of pillar-stope layouts and overall mine are conducted. Finally, it is concluded that planned long hole stope dimensions appear to be unsafe and drift and fill mining method appears to be more suitable for this project.

Keywords: Mining methods, rock characterization, long hole, drift and fill mining, empirical stope dimensioning, numerical modeling, stability analysis.

1 Introduction

Throughout the history, iron has always been one of the most commonly used metal products in a variety of industries due to its unique features like high strength, electrical and heat conductivity and being the major component of steel, which is a high strength structural material, with a reasonable price. Considering its wide range of use in developing countries in different sectors like construction and industrial production, it can be considered to be a vital metal in Turkey. Kayseri- Adana region hosts the second important high grade iron ore deposits [1] of Turkey.

In this study, Mentes iron ore deposit in Yahyali district of Kayseri city is investigated. Location of the mine can be seen in fig. 1. Close to the study area,

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four operations of two surface and two underground mines in Karaçat and Karamadazi are actively working. Iron ore body is initially planned to be mined by using long hole mining method. A detailed geotechnical site investigation and laboratory work are carried out to assess the applicability of the selected mining method. For this purpose, field studies are combined with laboratory experiments in order to carry out empirical and numerical analyses.

2 Geological Conditions

Dominantly existing geological formations are named as Zabuk, Değirmentaş and Armutludere in the site. Contact between the deposit and host rock formations is tectonically controlled. Exposition of the deposit is caused by post-mineralization faults. Alterations from siderites and iron oxides to limonite and goethite are caused by karstification and weathering developed at contact zones. This results in partly enriched iron levels forming raw material for exploitation.

As alteration products of siderites, ore minerals are dominantly composed of hematite and goethite. Together with siderites, pyrite and limonite-goethite combinations exist. Pyrite, pyrolusite and psilomelane, limonite-goethite, rutile, anatase and carbonate minerals are observed together with hematite. In addition, manganese minerals and rutile-anatase occur either as inclusions or fillings in limonite and euhedral pyrites take place in the cavities of limonite. [2]

Tiringa et. al. (2009) concluded that iron deposits at Yahyali (Kayseri) and Mansurlu (Feke-Adana) districts are closely associated with volcanic sync-sedimentary or exhalative sedimentary iron ore deposits.

During the formation of main tectonic structures, breccia zones are observed mostly in the direction of secondary faults formed mainly inside carbonate rocks. Ore minerals located in these kinds of breccia zones form the irregularly shaped ore bodies and veins. Karstic caverns are mostly filled with ore minerals.

The main fault observed on the site has an orientation of NE-SW and it has the characteristics of reverse faults. Main ore body has a strike of N70E and its dip varies between 55°-60°. Mentes district part of the ore body has relatively mild dip with around 20° inclination.

It is observed that the ore bearing rocks are a composition of siderite, hematite, goethite and limonite; hanging wall rocks are schist and recrystallized limestone and footwall rock is quartzite. In the scope of this study, rock units will be considered in terms of structural means. Thus, excluding minor rock types three main rock mass units are in consideration. These are ore body including all the ore minerals, recrystallized limestone as being the hanging wall and quartzite as being the footwall rock.

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Fig. 1 Location of the Kayseri-Yahyalı District

3 Geotechnical Studies

During the field study, geotechnical logging of six drill holes representing the site has been done and the basic rock units have been characterized in terms of rock quality. Geotechnical mapping in a neighboring open pit mine has been carried out. Karacat underground mine has been visited to investigate the stability conditions of current pillar-stope layouts. In laboratory, more than 300 tests have been carried out to determine geo-mechanical parameters and properties of rock units.

3.1 Field Investigations

Field studies consist of geotechnical logging, geotechnical mapping and sample selection for laboratory tests.

Geotechnical logging is necessary to assign basic rock units with RMR and Q rates, which are two of the most widely used empirical design methods. These rates are used for the preliminary stability investigation of underground openings.

While logging suitable samples for laboratory testing are collected from drill holes.

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3.2 Laboratory Studies

In METU (Middle East Technical University) rock mechanics laboratory, uniaxial compressive strength tests, triaxial compression tests, deformation tests, dry unit weight tests, indirect tensile strength (Brazilian) tests and direct shear tests are carried out on the samples obtained from drill hole cores according to ISRM suggested methods. Summary of laboratory test results are presented in tab. 1.

Table 1 Laboratory Test Results

Rock Unit Recrystallized

Limestone Ore* Quartzite

Unconfined compressive strength-UCS (MPa) 61.9 17.9 24.4

Young modulus-E (GPa) 12.99 6.91 7.99

Poisson ratio-ν (MPa) 0.11 0.17 0.38

Cohesion-c (MPa) 2.83 1.59 1.56

Internal friction angle-φ (o) 49.7 38.1 37.6

Tensile strength-σt (MPa) 9.30 2.44 3.72

Density (g/cm3) 2.68 2.60 2.63

* siderite, hematite, goethite, limonite.

3.3 Rock Mass Characterization

Three basic rock mass units are identified based on their structural similarities. However, these three classes are divided into subclasses by considering their Table 2 RMR and Q values

Rock Unit

RMR89

Quality Description

Q

Quality Description

Recrystallized Limestone (Immediate Roof)

(Hanging wall)

50

Fair Rock

2.68

Medium

Ore 46 Fair Rock 1.54 Medium

Quartzite (Immediate Floor) (Foot Wall)

48

Fair Rock

2.65

Medium

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distance to the orebody. 10m above and below of the orebody are named as immediate roof and floor. The final RMR, Q scores and quality descriptions be seen in tab. 2.

4 Possible Mining Methods

There are many factors taken into consideration in the selection of the underground mining method.Among them rock mechanics is one the key factor.In the site Mine management decided to apply long hole U/G mining method.The research results presented in the paper investigated the suitability of the planned method.

The ore body at the interested site has an average extends of 600 meters by 250 meters and 100 meters. The block model of the orebody is given in fig. 2.

Fig. 2 The block model of the orebody.

4.1 Long Hole Mining Method

Long hole stoping is a bulk mining method; it has a low operating cost and typically applied to large ore bodies in strong wall rock. In this method, two sill drifts are excavated from top and bottom of a given production level. Height between these drifts is typically 20 to 30 m. Long holes are drilled parallel from the bottom sill drift and blasted in row. After mucking out the stope with remote controlled LHD's from the bottom sill drift, the stope is backfilled from the upper sill drift with LHD's.

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4.2 Drift and Fill Mining Method

This method is preferred in ore bodies exceeding 6 m in width with a moderate to poor ore body competency. Parallel drifts with vertical walls are driven with a heading driven along the foot wall to provide access to the drifts. Mining starts with driving a drift cut at about 5.0 m slice height. The mined out area is then backfilled which then provides support for the next production drift. This process continues until the end of the cut and the same procedure to extract the slice above is repeated.

5 Stability Analysis

For stability analyses of the excavations and pillars of the two methods, empirical and numerical modeling methods are employed.

5.1 Long Hole Mining Empirical Studies

First of all empirical analyses are carried out for long hole stoping method. Maximum stope dimensions are the main focus of these empirical analyses. For a specified stope width and height combination, level stope length is to be determined.

The studies of Potvin (1988), Potvin and Milne (1992), Nickson (1992), Mathews et al. (1981)[3,4,5,6] used the parameters affecting the open stope design to come up with “Graphical Design Method” with the help of data gathered from approximately 350 Canadian underground mines. The stability graph can be seen in fig. 3.

Design procedure depends on calculating; N (Mathews’ stability number) parameter which represents the ability of the rock mass to stand up under a given stress condition, and the shape factor S (also named hydraulic radius) which accounts for the dimensions of the stope.

Stability number “N” is determined from the equation (1)

(1) Q’: modified NGI rock mass rating, A: Rock Stress factor, B: Rock defect orientation factor, C: Orientation of design surface factor. Q’ is calculated by taking joint water reduction parameter (Jw) and the stress

reduction factor (SRF) both equal to one in the Barton’s Q rock mass classification system.

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Fig. 3 Mathew's Stability Graph

In these analyses, the maximum unsupported stable spans for different scenarios (different stope lengths) are attempted to be estimated. Typical input parameters used in the scenarios are given in tab. 3.

The maximum unsupported stope span for stopes with stope length 20 meter (from roof to floor 25 meter) and stope width 5 meter is attempted to be determined for long hole stoping method with extraction sequence and filling. According to the analyses’ results, the maximum unsupported stope span was found to be 7 meters for 5 m wide and 25 m high stopes assuming 45o critical joint dip. When it was assumed that there were no joint sets the maximum unsupported stope span was found to be 20 meters for 5 m wide and 25 m high stopes.

Considering a single joint set existence with a dip of 45°, applicability of long hole method becomes impossible as this method being a bulk mining method and requiring big stope dimensions.

Therefore, after empirical analyses of long hole stope dimensioning, it is found that drift and fill method is better suited for this deposit.

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Table 3 Input parameters for Different scenarios in Graphical Design Method

Q’

UCS (MPa)

Stope height (m)

Stope width (m)

Stope length (m)

Critical Joint Dip (degree)

5.7 8.4 25 5 20,30,40,50 60 0 to 45

5.2 Long Hole Mining Numerical Analysis Studies

In order to determine the structural applicability of 2 different mining method alternatives, the finite element program Phase-2 is used with 2D plane strain assumption. Analyses are carried out for 2 different typical model sections of the ore body; NW-SE axis (along the long axis of ore body) and NE-SW axis (along the short axis of ore body). Fig. 4 represents the typical model section along NW-SE direction.

Fig. 4 NW-SE section model

NW-SE Section Stability Evaluations Before carrying out the plastic analyses, Strength factor distributions are

investigated using elastic solution modeling. When the strength factor is -1, there occurs failure by loosening due to tensile stresses. While the strength factor is between 0 and 1 there occurs failure due to compressive stresses.

After filling first and second levels with primary and secondary low quality filling material, a vertical softening zone about 20 meters above the top level cross cut roof occurs. As the production precedes to upper levels this zone extends horizontally up to 80 meters. At the end of the production, the extent of this zone reaches to 35 meters height and about 200 meters length. The results showed that even if all the openings were filled with high quality primary filling material,

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similar stability problems existed. Excavating such large scale stopes is not structurally appropriate.

NE-SW Section Stability Evaluations The solutions for this section will help us to interpret the stability of stopes and

pillars. As a result of these solutions it was observed that when the 5 meters wide and 25 meters high primary stopes were opened, the failure occurred in adjacent 5 meters length pillars (secondary stope). Moreover, about 6 meters long failure zones were observed in sidewalls of the stope.

These failures continue in the mid-level pillars. After production is ended in bottom levels and primary and secondary fillings are done, around footwall and sidewalls there occur serious softening zones. These zones extend up to 17 meters with the fault zone and the horizontal extend of this zone exceeds 90 meters.

As a result of these analyses, 5 meters wide and 25 meters high stopes seemed to be unstable due to the poor rock mass strength of ore the body resulting in failure of the column type pillars.

Therefore, it was concluded that long hole method with large-scale stopes was not the right choice.

5.3 Numerical Analyses for Drift and Fill Mining Method

The same sections used for long hole method are also used for the modeling work here. In this part, 5m width 5m height cuts are modeled.

As production continues by an application of mid quality filling and proceeding to mid-level, there occurs about 2.5 meters softening zone above the openings nearby hanging wall. Since failure zone is restricted to some small parts of the adjacent pillars (secondary stopes), no major instability problem is expected.

Around the footwall the situation is much better. At the end of the production, it is observed that there is no major global instability issue. In zones close to the hanging wall especially in the top levels, the instability issue can be solved by conventional local support systems. It is predicted that only in about 10 % of the ore body, heavy support systems will be required.

If the suggested standards of mid-quality fillings are satisfied and mixing and application procedures are done properly, there is no major instability issue predicted for the mine.

6 Conclusions

This study presents the geotechnical design analysis of a potential U/G iron ore mine in Mentes Mine at Yahyali province of Kayseri district of Turkey. Iron ore body is initially planned to be mined by using long hole mining method. Detailed geotechnical site investigation and laboratory work are carried out to assess the applicability of the selected mining method.

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As a result of empirical and numerical studies, it is concluded that the long hole mining method considered by the mining company is not suitable for the ore body. From empirical studies, it is determined that 5m width 20m height long hole stopes are only stable with 7m strike length stopes. Numerical studies of long holes proved that stress induced failure is the main failure type for this weak ore body and applicability of long hole mining method is impossible for this deposit. Therefore, drift and fill mining method is decided to be applied to this deposit.

References

[1] Yıldız, N.: Iron Report- Chamber of Mining Engineers in Turkey (2009) [2] Tiringa, et al.: Mining Geology of Karaçat Iron Deposit, Karaköy, Yahyalı, Kayseri –

Türkiye. Journal of Geological Engineering Turkey (2009) [3] Potvin, Y.: Empirical open stope design in Canada. Ph.D. thesis, Dept. Mining and

Mineral Processing, University of British Columbia (1988) [4] Potvin, Y., Milne, D.: Empirical cable bolt support design. In: Kaiser, P.K., McCreath,

D.R. (eds.) Rock Support in Mining and Underground Construction, Proc. Int. Symp. on Rock Support, Sudbury, pp. 269–275. Balkema, Rotterdam (1992)

[5] Nickson, S.D.: Cable support guidelines for underground hard rock mine operations MASc. thesis, Dept. Mining and Mineral Processing, University of British Columbia (1992)

[6] Mathews, K.E., Hoek, E., Wyllie, D.C., Stewart, S.B.V.: Prediction of stable excavations for mining at depth below 1000 metres in hard rock. CANMET Report DSS Serial No. OSQ80-00081, DSS File No. 17SQ.23440-0-9020. Dept. Energy, Mines and Resources, Ottawa (1981)