RMZ – Materials and Geoenvironment, Vol. 57, No. 1, pp. 75–96, 2010 75

Geological evaluation of brown coal reserves at the Hrastnik mine – RTH, Rudnik -Hrastnik

Geološka evalvacija zalog rjavega premoga na območju jame Hrastnik - RTH, Rudnik Trbovlje-Hrastnik

Željko Vukelič1, *, Bojan Klenovšek2, Ladislav Placer1, Vladimir Malenković3, Evgen Dervarič1

1University of Ljubljana, Faculty of Natural Sciences and Engineering, Aškerčeva 12, SI-1000 Ljubljana, 2RTH, Rudnik Trbovlje – Hrastnik, d. o. o., Trg revolucije 12, SI-1420 Trbovlje, Slovenia HTZ, I.P., d. o. o., Partizanska 78, 3320 Velenje, Slovenia *Corresponding author. E-mail: [email protected]

Received: June 3, 2009 Accepted: December 14, 2009

Abstract: As provided by the Act on the gradual closing down of the coal- mine Trbovlje-Hrastnik and on the development restructuring of the region, until the end of 2009 Rudnik Trbovlje-Hrastnik (RTH) will continue to supply coal to the thermal power plant Termoelektrarna Trbovlje (TET) in the planned annual volume of 0.6 million tonne. RTH continues to hold significant coal reserves of national impor- tance to Slovenia, which might we worth exploiting at some point in the future. The management of the coalmine has made every effort to ensure continued coalmining at RTH after 2009 at the existing mines Ojstro and Trbovlje (Field III and Field ), at the already closed down mine Hrastnik. This paper provides an overview of the results of the study “The Legitimacy of the Extraction of Remain- ing Coal Deposits at the Mines Ojstro and Trbovlje After 2009” – Stages 2 and 3, with the emphasis on the evaluation of coal deposits at the mine Hrastnik. The study was undertaken by the Faculty of Natural Sciences and Engineering, Ljubljana, in collaboration with the Economics Institute at the Faculty of Law, Ljubljana, and RTH associates.

Original scientific paper 76 Vukelič, Ž., Klenovšek, B., Placer, L., Malenković, V., Dervarič, E.

Izvleček: Rudnik Trbovlje-Hrastnik (RTH) bo skladno z zakonom o postop- nem zapiranju in razvojnem prestrukturiranju regije do vključno leta 2009 dobavljal premog Termoelektrarni Trbovlje (TET) v predvi- deni količini 0,6 mio. ton na leto. RTH še vedno razpolaga z znat- nimi in za Slovenijo pomembnimi zalogami premoga, ki jih bo treba v prihodnje smiselno izkoristiti. Vodstvo rudnika si prizadeva, da bi eksploatacijo premoga v RTH nadaljevali tudi po letu 2009, in sicer iz že obstoječih jam Ojstro in Trbovlje (III. polje in Plesko polje) ter iz že zaprte jame Hrastnik. V tem prispevku so predstav- ljeni rezultati študije: »Upravičenost odkopavanja preostalih zalog premoga v jamah Ojstro in Trbovlje po letu 2009« – 2. in 3. faza, s poudarkom na evalvaciji zalog premoga v jami Hrastnik. Študijo je izdelala Naravoslovnotehniška fakulteta v Ljubljani v sodelovanju z Ekonomskim inštitutom pri Pravni fakulteti v Ljubljani in s sode- lavci naročnika RTH.

Key words: brown coal, coal reserves, geological evaluation, research drilling Ključne besede: rjavi premog, rezerve premoga, geološka evalvacija, raziskovalno vrtanje

Introduction from the period of intensive geologi- cal explorations between the years The geological evaluation of the re- 1982 and 1991. In accordance with maining deposits of brown coal at the Act Regulating Gradual Closure Hrastnik focused on reviewing the of the Trbovlje-Hrastnik Mine (RTH) updated brief on the categorisation, and Development Restructuring of the classification and calculation of the Region (2000), the closing of under- resources and deposits of brown coal ground mining facilities began even in the RTH mining area as at 31st De- before some hypotheses on geological cember 2002 (Mitrevski & Bravec, structure and coal reserves had been 2003). It includes the evaluation of verified. Considering the reassessment the level of observance of geological of the structural and geological model exploration of the coal deposit using used in the updated brief on coal re- drill holes and the level of observ- serves as at 31st December 2002, the ance of results of structural and geo- geological evaluation will give a gen- logical analyses of the Hrastnik coal eral assessment of the relevance of deposit creation and development further plans for additional geological

RMZ-M&G 2010, 57 Geological evaluation of brown coal reserves at the Hrastnik mine – RTH 77 exploration and indicate the most op- mapping of the surface area over the timal direction and level of further ex- mines Hrastnik and Dol in 1987 in the ploration, which might result in later brief “A Geological Structure Survey preparation of an exploration plan for in the Dol-Hrastnik Area, Part II”. In the new categorisation, classification the three-year period (1985–1987), and calculation of the resources and geologists surveyed roughly 3,200 deposits of brown coal in the Hrastnik metres of roadways, access tunnels area and an assessment of a repeated and longwalls, and drilled eleven beginning of brown coal exploitation structural exploration drill holes in the in this traditionally mining area. total length of approximately 1,500 m (Uhan, 1987). The geological data ob- Geological exploration of the coal tained in the course of the above men- deposit in the Hrastnik area tioned surveying and mapping of mine Apart from the associates employed by facilities and exploration drill holes the coalmine’s geological department yielded more detailed information on to monitor the preliminary works and the structure of the “south wing” of surveys carried out at the coalmine on the central part of the Hrastnik mine an ongoing basis, vital research over at and under Horizon VII. Building the past fifty years was undertaken by on the results of all previous surveys Kuščer (1967) with his core work Za- and having reviewed and processed gorje Tertiary, Gregorač (1975) who the entire documentation held by the focused on the hydrogeology of the coalmine, Placer preformed the most mine Hrastnik, Kuščer & Mitrevski comprehensive structural geological (1979) who researched the geology of analysis until that time, and explained the boundary area between the mines the tectonic development of the coal Hrastnik and Dol, Uhan (1991) with deposit. When it comes to the evalua- his work on the geochemical proper- tion of remaining coal reserves in the ties of coal in the central part of the Hrastnik area, certain structural geo- deposit, and Placer who carried out logical questions remain unanswered; a structural-geological analysis be- this primarily refers to the continua- tween 1982 and 1991. In the above tion of the coal seam under the hypo- mentioned period Placer completed an thetical Hrastnik thrust fault. The oth- extensive detailed geological mapping er set of debatable questions concern of the surface area between Moravče the geological structure of the Eastern and Laško, and surveyed and mapped Underground Deposit where the con- the mine facilities and the cores of ex- tinuation of the southern coal seam ploration drill holes. Placer published downwards has been established by the major findings of the survey and exploratory drill holes at Brnica.

RMZ-M&G 2010, 57 78 Vukelič, Ž., Klenovšek, B., Placer, L., Malenković, V., Dervarič, E.

Geological structure of the Hrastnik clinations in individual cross-sections, coal deposit is characterised by the lower part The Zasavje coal-rich tertiary layers containing more clay, and the upper, (the so-called “Trbovlje layers) sedi- cleaner part containing more vitrinite mented on the Triassic dolomite or substance. In the medium part, there pseudozilian slate substrata are com- appear centimetre- and decimetre-thick posed of lower clastic, predominantly inserts of volcanic ash, clay and, most clay, footwall layers, coal and upper, often, lime sandstone. With the in- hanging wall marl layers. creasing depth, there occurs an increas- ing number of decimetre-thick layers The sedimentation of the lower seg- of lime sandstone or so-called carbon- ment of the coal-rich layers begins with ate inserts, which have, at the point clastic sediments in paleo-morphologic +70 and the descending angle 45–70o depressions. Due to filling of the paleo- southwards, achieved the total thick- relief, the thickness of these predomi- ness even exceeding width across 15 m nantly clay layers is highly variable, of the long wall at the field A between amounting up to 80 m. The upper parts the ordinates 4550 and 4800 (Figure 1). of footwall clay are rich in organic component, and the black clay (the The lower part of coal layer was sedi- so-called “black footwall”) gradually mented in the reduction environment passes into clay coal. and is mineralised with sulphides. The upper semiterrestic and limnic part is The coal layer in the sedimented thick- predominantly mineralised with car- ness of 20–25 m, which can be thinner bonates, and the edge areas of paleo or thicker due to tectonic repetitions peat bogs passing to the hanging wall in the form of scales and different in- marl, it is mineralized with sulphides

Figure 1. Carbonate layers (hatched) at point +70, Field A, mine Hrastnik

RMZ-M&G 2010, 57 Geological evaluation of brown coal reserves at the Hrastnik mine – RTH 79

(Uhan, 1991). Depending on the type Discordantly on top of the Oligocene of mineralisation of final sedimentation marine clay, the sedimentation of Laško sequence of the coal layer, its position layers composed of lithotamnic lime- in the former sedimentation bed could stone, marl and sandstone begins in the be presumed. Unfortunately, such ex- area of the Hrastnik coal deposit with- plorations have not yet been performed out sandy layers. The thickness for the Hrastnik coal deposit; however, of these sediments can measure 100 m some data is available on the ratio of or more. On top of the Laško layers, mineralization types in the upper part there are discordantly sedimented Sar- of the coal layer in Trbovlje (Neža) matian layers of various thicknesses: and in the profile approximately 800 conglomerate, sandstone, siltstone and m to the east, in the Ojstro mine at the clay completing the sedimentation of point +135, while some larger distance the Zasavje tertiary bed. from the edge of the former sedimenta- tion bed is presumed for the profile at The coal deposit is shows consider- Lopata (ordinates around 2950). able tectonic deformation. The western part of the coal deposit is characteris- The upper border of the coal layer tic for relatively simple structure of the with the hanging wall marl is more coal layer of the “southern part”, but distinctive than the lower one. Where the eastern part passing into the thrust the hanging wall marl contains abun- structure of the Eastern Underground dant organic component beside coal, Deposit is more complicated in struc- such layers were named “black hang- ture. ing wall”. In the upward direction, this brackish thin-layer marl gradually turns In the western part of the coal deposit, to brown and grey until it borders the an important factor for the estimation Oligocene layers. Similarly to the foot- of reserves is the structure of the in- wall clay, the hanging wall marl also clined, southwards leaning coal layer achieves thicknesses of approximately anticline. Its northern wing, including 80 m. In the marine environment, the its core, is formed of inclined thrust Oligocene marine clay (“sivica” in scales that are often parallel to the axis Slovene) gradually sedimented above plane of the fault. Tectonic deforma- the hanging wall marl. It is character- tions of such type are very rare in the istic for being massive, non-layered, southern wing of the anticline. They are marl-like and swellable. The average presumed to be located only near the thickness of this clay sedimentation is alleged Hrastnik thrust fault indicated 30 m to 50 m, or even more in some by geological data from the drill hole locations. Hj-2/75 and Hj-6/85 as well as the data

RMZ-M&G 2010, 57 80 Vukelič, Ž., Klenovšek, B., Placer, L., Malenković, V., Dervarič, E. obtained in the course geological map- can, in vertical N-S cross sections, ex- ping of the western part of the drift at ceed 40 m and thus strongly affect the Horizon VII. The coal in the southern continuity of the thickness of the coal wing of the above mentioned anticline layer under Horizon VII and VIII (Fig- was explored, in the years 1985–87, by ure 2). ten drill holes, three of which drilled To the east of this location, the coal through the tectonically deformed coal deposit structure is significantly more layer. The system of youngest tectonic complicated, making the assessment of deformations of the Hrastnik region, reserves a significantly more demand- the Dinaric oriented (NW-SE) and ing task. cross-Dinaric oriented (NE-SW) faults is predominant in this area. Dinaric In relation with the passing of the faults usually occur in intervals of 100 Hrastnik structure into the Dol struc- m to 150 m, occasionally less, and can ture, tectonic deformations of the coal be followed in the layout from the foot- layer on the Blato anticline and the Dol wall to Laško and/or Sarmatian layers. syncline play an important role. In gen- Apparent strike slips along these faults eral, a steeper and tectonically thinner

Figure 2. A structural geological prognosis of the coal seam in the south- ern part of the mine Hrastnik at Horizon VII

Table 1. Off-balance coal reserves at the mine Hrastnik according to the calculations provided in the updated brief on coal reserves as at 31st December 2002

Coal reserve categories A B C1 C2 Southern part 134 000 4 346 000 10 269 000 - Corner field 229 000 244 000 72 000 - Eastern Corner Field 77 000 455 000 2 378 000 6 272 000 Total Hrastnik 440 000 5 045 000 12 719 000 6 272 000 24 476 000

RMZ-M&G 2010, 57 Geological evaluation of brown coal reserves at the Hrastnik mine – RTH 81 coal layer is expected in this part of the No 53/79), the Hrastnik mine has been coal deposit. classified in the third group and second sub-group. Individual categories of re- Geology-related problems in coal ex- serves were calculated pursuant to the ploitation can be expected particularly prism-method on the basis of parallel in relation with tectonics-related thin- geological profiles north-south in the ning and discontinuities of the coal lay- scale 1:2000. For the Hrastnik mine, the er and increasingly thicker sedimented volume mass of 1.45 t/m3 of coal was carbonate barren inserts in the coal observed and 25-percent exploitation layer. loss was taken over. When calculating the coal reserves in the Hrastnik mine Updated brief on coal reserves as at between the ordinates 4050 and 5350, 31st December 2002 the occurrence of carbonate inserts in Update of the brief on the categorisa- the coal layer, increasing with depth, tion, classification and calculation of was considered. The calculated coal re- the resources and deposits of brown serves have therefore been reduced by coal in the RTH mining area as at 31st 25 percent in this part of the mine. Ac- December 2002 is based on the Brief cording to the indication in the brief as on the coal reserves in the RTH min- at 31st December 1997, the parameters ing area as at 31st December 1997. of average quality of the reserves are Changes in the assessment of reserves the following: 20.71 percent of moist, contained in the above mentioned up- 21.17 percent of ash, 2.38 percent of date are related to the closure process total sulphur and the calorific value of based on the Act Regulating Gradual 14.78 MJ/kg of coal. In the coal sam- Closure of the Trbovlje-Hrastnik Mine ples obtained from structure drill holes and Development Restructuring of the during the last period of more exten- Region (Official Gazette of the Repub- sive exploration drilling in the Hrastnik lic of Slovenia, No. 61/2000). Within mining area, a slightly lower calorific the framework of the 2002 update, all value was assessed as well as ash con- current coal reserves in the Hrastnik tents higher by a few percent. mine according to the 1997 brief were assessed as off-balance reserves in cat- In the period from 31st December 1997 egories A, B, C1 and C2 (Table 1). to the update of the brief on the catego- risation, classification and calculation of Based on the Rules on classifying the the deposits as at 31st December 2002, reserves of hard mineral substance in 120 drill holes in total length of 3,421 classes and types and on the records m were drilled in the Hrastnik mine be- thereof (Official Gazette of the SFRY, tween the points +45 and 0; however,

RMZ-M&G 2010, 57 82 Vukelič, Ž., Klenovšek, B., Placer, L., Malenković, V., Dervarič, E.

Figure 3. The main mine roadways at the coalmine Hrastnik and a se- quence of geological cross-sections N-S used in the updated brief on re- maining deposits (2002) for the purpose of determining actual reserves, and the share of deposits at the Southern End, Corner Field and Eastern Corner Field of the mine Hrastnik

Figure 4. Coal deposits as at 31st December 2002 in the Southern End, Corner Field and Eastern Corner Field of the mine Hrastnik the purpose of this drilling was predom- to design exploitation levels. In the pe- inantly to determine the boundary be- riod between the years 1997 and 2002, tween coal and the adjacent rock mass there was no structural and geological

RMZ-M&G 2010, 57 Geological evaluation of brown coal reserves at the Hrastnik mine – RTH 83 drilling, the results of which could influ- the Eastern Corner Field to the ordinate ence the calculation of reserves. 5700 have been determined on the basis of only a few drill holes and a strongly

The A+B+C1 coal reserves in the Hrast- simplified structural geological model. nik mine (off-balance), the amount of From the ordinate 4900 towards east, which has not significantly changed the reliability of the estimation of coal since the end of the year 1997, rep- reserves is considerably lower. Explo- resent precisely one third of the en- ration drilling in this area could un- tire (both balance and off-balance) doubtedly improve the categorisation, A+B+C1 coal reserves for RTH, the but due to current structural geological Trbovlje-Hrastnik mine (53,893,000 simplifications in the updated brief on t). In addition, further sources of the reserves as at 31st December 2002, a

C2 category (6,272,000 t) have been re- reduction in quantity of currently re- corded in the Eastern Corner Field in corded coal deposits and resources is the mine Hrastnik (Figure 3). not excluded.

The calculation of coal reserves in the Structural view on the extension of Hrastnik area between the ordinates the coal seam in the Hrastnik mine 3700 and 5350 is based predominantly beneath the exploitation level upon on the data obtained from exploration the closure of the mine mine drilling and mapping of mine The opinion on the extension of the roadways between the years 1985 and coal seam in the Hrastnik mine be- 1998 and from surface drilling holes in neath the exploitation level upon the the Brnica area. The reliability level of adoption of the act regulating a grad- this largest part of reserves in the Hrast- ual beginning of closure of the mines nik mine is high. Exploration drilling Trbovlje and Hrastnik in the year 2000, for the purpose of recategorisation of was elaborated on the basis of the Pre- C1 reserves to B reserves poses any liminary analysis of the structure of risks here, but no significant changes in Ojstro and Hrastnik (Placer, 1988). quantity are to be expected. More risk Additionally, it includes the data on lies in exploration drilling for the pur- the structure of the Laško syncline and pose of determining the continuation the reconstruction of the coal deposit of the coal layer beneath the alleged in Upper Oligocene (Placer, 1994) Hrastnik thrust fault where the cal re- and two published articles, one on the serves have not yet been recorded. The structure of the Hrastnik coal deposit exploration risk is also increasing to- (Kuščer & Mitrevski, 1979) and one wards east where the coal reserves of on the regional structure of the Posavje

RMZ-M&G 2010, 57 84 Vukelič, Ž., Klenovšek, B., Placer, L., Malenković, V., Dervarič, E.

folds (Placer, 1999). The last situation y = (+3500 and +5700), presumably in the mine prior to its closure has been extending to 5900 as evident form the derived from the Update of the coal projection in Figure 1, and x = (–700 deposits and resources in the Hrast- and +200). nik mine as at 31st December 2003 (Mitrevski & Bravec, 2003). Structure of the Hrastnik coal deposit The structure of the Hrastnik coal The Laško syncline deposit is evident from the existing From the geological point of view, the transverse profiles on the coordinate Zasavje coal mines are situated in the y (abscissa). However, there are two Laško syncline, the upper part of which concepts regarding the conditions in has been named the Laško tertiary de- the depth and in the eastern part where pression with a productive coal seam. there is little or no mining activity. In the tectonic sense, the syncline is The first one was set by Kuščer and divided in three large structure blocks Mitrevski (1979) and the other one by separated by the Jug and Hrastnik in- Placer (1988). The substantial differ- clined strike slip fault. The Jug fault ence between them lies in three struc- lies in the direction SW-NE and runs tural questions. The first one is related along the western edge of the coal de- to the existence of the Hrastnik thrust posit in Trbovlje and across the town. fault introduced by Placer. According The Hrastnik fault lies in the direction to Placer, the thrust is supposed to have NW-SE and runs through Hrastnik. cut off the coal seam, while according The following mines are situated in in- to Kuščer and Mitrevski, the coal seam dividual structure blocks: Strahovlje, extends in the depth direction. The sec- Loke, Kisovec, Zagorje-Kotredež and ond question refers to the difference Orle in the western block, Trbovlje and in understanding the extension of the Ojstro in the central block between the internal thrust panes towards east, and Jug and Hrastnik fault, and Hrastnik, the third one is related to the interpre- Dol, Krištandol, Brezno, Huda jama tation of the connection between the and Mihael in the eastern block. Hrastnik and Dol structure, i.e. the re- lation between the Blato anticline and Local coordinate system the Hrastnik and Dol structure. The Zasavje coal mines use the local coordinate system with the reference The significance of different aspects lies point at the height point 425.5 above in the fact that according to the concept the living quarter of Vode in Trbovlje. by Kuščer & Mitrevski, the coal depos- The productive area of the Hrastnik its and resources are larger than the de- coal mine lies between the coordinates posits according to the concept by Plac-

RMZ-M&G 2010, 57 Geological evaluation of brown coal reserves at the Hrastnik mine – RTH 85 er. The latter model is presented here. coal seam is formed by the Hrastnik In the calculation of updated reserves thrust, running in the direction W-E. of 31st December 2003 (Mitrevski in In the central part, the main coal seam Bravec), the authors took into account is longitudinally cut by the internal the existence of the Hrastnik thrust, thrust panel dividing the seam, which while the conditions relating to the sec- is uniform in the west, in two parts, the ond and third point of differences in so-called “northern” seam and “south- concepts were as described by Kuščer ern” seam. In the economic sense, the & Mitrevski. The conditions in the bor- “southern” seam is more significant. der area between the Hrastnik and Dol The internal thrust panel is sloped in structure are therefore strongly simpli- the slip (non-flexive and unbent) an- fied and idealised, and probably even ticline, with the crest descending ap- incorrect. The above applies to the area proximately by 25 % in the eastern di- of profiles from y = (+5500 to +5700). rection, forming at the same time the upper and the eastern boundary of the The brown coal seam in the area of “southern” seam and, simultaneously, the Hrastnik coal mine lies in the the lower boundary of the “northern” north-eastern wing of the Hrastnik seam. Kuščer & Mitrevski described fault which has cut through the origi- the sloped thrust panel as a “barren an- nally uniform seam, separating it in the ticline”. The “northern” seam is gradu- Ojstro and Hrastnik part. The economi- ally reduced in the upward direction cally most important part of the Hrast- along one of the thrusts to the south of nik coal seam, the so-called main seam, the Trbovlje fault. with its medium-steep descent towards south and limited in the north by thrust The structure of the Hrastnik coalmine faults in the direction W-E lying south and the coal seam above Horizon VIII at to the Trbovlje normal fault in the same the point +50 m is well known. At this direction, representing the southern point, coal is almost entirely excavated border of the Blato anticline, the core and the remaining part is well explored. of which contains pseudozilian layers, Under this height point, the coal seam and to its easternmost point, there lies was drilled from the standing points a preserved, anticlinally sloped and at Horizons VII and VIII and from the heavily deformed coal seam, approxi- surface. The level of exploration varies mately 10 m thick and declining in the depending of the density of drills. It is eastern direction. To the north of the higher in the west and lower in the east. Blato anticline, there lies the heavily compressed and deformed Dol syn- The presumed volume of the “south- cline. The southern border of the main ern” seam is shown in Figure 1, in the

RMZ-M&G 2010, 57 86 Vukelič, Ž., Klenovšek, B., Placer, L., Malenković, V., Dervarič, E. seam projection to the vertical plane in fore there is no data on the existence the direction west - east, at the scale of a coal seam in the outermost part in of 1 : 5,000. The surface (only in the the Hrastnik structure. The thickness of western half of the projection) and the the “southern” seam amounts from 25 m extension of old excavations are de- to 40 m. The “width” of the seam on rived from the update of the brief on the vertical axis in the projected plane reserves (Mitrevski & Bravec, 2003). is not correct, it is actually longer by The same goes for the drill holes’ drill- the ratio depending on the inclination ing points. For the purpose of orienta- of the seam. The value of the ratio to tion, the level of Horizon 8 is drawn. be multiplied with the measured width The unexploited part of the “southern” in the profile is indicated on the pro- seam can be relatively well traced from file line for the individual profiles and the transverse profile y = +4200 to the amounts from 1.05 to 1.25. The west- profile y = +5400, i.e. at the length of ern part of the profile reflects the actual 1200 m and further to the profile y = situation, but in the eastern direction +5650 where it has been established at and in the depth direction, the accuracy the easternmost point by the drill hole level gradually falls lower. This par- Br. 10. This means that in the most ticularly applies to the location of drill favourable structural and lithological points with the coal seam and to the lo- conditions, its length would amount to cation of the internal thrust panel and 1,460 m. In the profile y = +4200, the the Hrastnik thrust. coal seam extends approximately from the point +90 m to approximately +60 According to interpretation as present- m, and in the profile y = +5400 from ed here, the “southern” seam is gradu- approximately +60 m to approximately ally reduced in the eastward direction. –220 m in the profile 5700 from ap- However, as it is evident from the fol- proximately –110 m to approximately lowing text, the conditions as predicted –290 m. Unlike the profiles y = +4100 by Mitrevski & Bravec (2003) should in y = +4450, the location of the Hrast- also be taken into consideration. nik thrust in the profile y = +5700 has been determined according to interpo- The unexploited part of the “northern” lation between the drill holes Br. 13 and seam can be traced in the mine from Br. 10, and therefore very inaccurate. A the profile y = +5000 to the profile lower level of accuracy of the thrust’s y = +5500 where it has been drilled location also applies for the profilesy = through by a drill hole from Horizon +4950 and y = +5390. In the profiley = VIII. Further, towards east, it has only +5950, the drilling at the hole D 1 was been extrapolated. In Figure 1, the halted in the hanging wall marl, there- “northern” seam is not shown, as it is

RMZ-M&G 2010, 57 Geological evaluation of brown coal reserves at the Hrastnik mine – RTH 87 impossible to show its actual volume the coal thrust on the Laško layers, due to unclarified tectonics. The thick- thus the Hrastnik thrust. The internal ness of the seam amounts to 10 m to thrust panel separating the “northern” 15 m, only occasionally it reaches 20 and the “southern” seam was deter- m. The coal seam in the Blato anticline mined according to the study of mine is not included in this presentation. profiles, while its role was established The longitudinal projection in Figure according to the structural analysis of 1 has been complemented by the ori- the deformation dynamics (Kuščer & entation profile on the coordinate y = Mitrevski, 1979; Placer, 1988). +5400 in Figure 2 at the scale 1 : 5,000 taken from the preliminary analysis of The characteristics of the coal seam in the structure of Ojstro and Hrastnik the “northern” and “southern” seam (Placer, 1988). It shows the structural differ from one another. Above all, the relation between the “northern” and “northern” seam is thinner and tec- “southern” seam and the location of the tonically much more affected than the internal thrust panel and the Hrastnik “southern” one. Coal in the “northern” thrust. seam has been thrust and then hori- zontally shifted along vertical faults, The extension of the unexploited part resulting in formation of scales and of the coal seam has been determined thinner layer; both contacts, foot wall by mapping of the Horizon VII and and hanging wall, are mostly abnormal VIII of the Hrastnik mine and by drill- and tectonised. The “southern” seam is ing from the mine and the surface. De- considerably less damaged. It contains spite numerous data, the existence of normally developed footwall and hang- all faults and thrusts limiting the coal ing wall contact. The barren inserts are seam has been determined with more or less damaged than in the “northern” less probability, as despite everything, seam. a different interpretation is always pos- sible. The least data is available on the The discussion on conditions in the location of the Hrastnik thrust fault in eastern part of the Hrastnik struc- the depth. All data sets except one are ture and/or on the structure model by obtained from the surface drill holes Kuščer & Mitrevski on one side, and ((Br.12, Br. 2, Br. 12, Br. 13). The only Placer on the other, is of great signifi- data set obtained from the mine is from cance due to its relation with eventual the drill hole Hj 19 at Horizon VII in planning of exploration works. The in- the profile 4350 drilling the coal and ternal thrust panel occurs in the central the Hrastnik thrust fault; However, part of the coal deposit; in the western this data is of high quality as it proves part, the coal seam is merely flexurally

RMZ-M&G 2010, 57 88 Vukelič, Ž., Klenovšek, B., Placer, L., Malenković, V., Dervarič, E. bent, and in the eastward direction, the ditions in this part of the coal deposit flexure increases and is discontinued in are represented on the simplified dia- the profile y = +5100. Further towards gram of the profile y = + 5700 from the east, the size of the discontinuation the updated brief. According to Placer in the known part of the mine is increas- (1988), however, conditions are more ing. The difference between both con- complicated. Considering the struc- cepts lies in the prediction by Kuščer ture of Brezno, Krištandol and Dol, the & Mitrevski for the eastward shift to Blato anticline and the Dol syncline lie gradually reduce again. Therefore, the in a strongly compressed thrust zone of “northern” and the “southern” seam are pseudozilian and coal-rich layers. The reunited into one seam in the profiles connection between the main seam in from y = (+5500 to +5700) (Mitrevski Hrastnik and the Dol seam is therefore & Bravec, 2003). Placer allows a pos- severely deformed by currently verti- sibility that the eastward shift is not cal thrusts and strike slip faults in the reducing, so the seams would remain direction W-E. separated. However, there is no proof to substantiate it. The original coal deposit For a complex estimation of the per- The southern wing of the Blato anti- spective of the coal deposits in Hrast- cline is supposed, according to Kuščer nik, an important role is played by & Mitrevski, to represent a normal sub- the ratio between the location of the strate of the main seam, i.e. the “north- original coal deposit in the time of ern” seam. At its southern side, only the coal silt sedimentation in the Upper internal thrust panel is supposed to be Oligocene and the current location of situated, and the stronger thrust panel the Laško syncline lying in the direc- should be located in the north. A simi- tion west-east, while the direction of lar thrust panel should be running into the original coal deposit was WSW- the footwall of the Dol seam. Further ENE. Strahovlje, Loke and Kisovec towards east, the conditions should be therefore lie in the southern wing of simplified even more, and the coal from the syncline, Kotredež and Orle in the the Dol syncline should pass towards southern and partially central part of south, into the Blato anticline and in its the syncline, Trbovlje in the central southern wing, into the main coal seam part of the syncline, and Ojstro, Hrast- of the Hrastnik coal deposit. In this nik, Dol, Brezno, Huda Jama and Mi- sense, the profiles from y = +5500 to y hael in the northern wing of the syn- = +5700 in the upgrade of the brief on cline. Accordingly, the current coal coal reserves by Mitrevski & Bravec mines are located in various parts of (2003) have also been elaborated. Con- the original Upper-Oligocene coal de-

RMZ-M&G 2010, 57 Geological evaluation of brown coal reserves at the Hrastnik mine – RTH 89 posit, some in its central part, some at Without the Hrastnik thrust, one can- the outermost edge and some in the in- not explain the structure of the south- termediate area. It is logical to expect ern edge of the Hrastnik structure and the thickest seam in the central part, the depth extension of the coal seam. and the thinnest one at the borders, al- In the eastward direction, it is related though the original paleogeographic to the proven southward oriented Ko- shape of the swamp might have been jzica thrust near Šmarjeta. Along the different. The above described model Hrastnik thrust, the northern wing of is ideal, but fits reasonably well the the Laško syncline overlapped, in the conditions in the nature. In the central southward direction, its southern wing, part of the syncline and the original with the largest shift along the Hrast- coal deposit, where Trbovlje is situat- nik thrust fault, causing extensive nar- ed, the coal seam and the footwall clay rowing of the syncline in this area. It layer are the thickest. The coal seam is can thus be presumed that the cut-off gradually becoming thinner and poorer part of the coal seam along the Hrast- in western and eastern direction. The nik thrust is covered with the mine thinnest and economically least im- structure and shifted in the depth di- portant part is situated in Strahovlje in rection towards the north. The size if the west and in Mihael near Laško in the shift can only be roughly estimated the east, partially reaching across the from two aspects: in the first aspect, Savinja river. The main coal seam in we add the reduced thickness of the Hrastnik, i.e. the “southern” seam, is syncline in Hrastnik against its width situated between the central and bor- in Laško and the size of the shift along der region of the original coal deposit, the thrust in the Kojzica profile. The so it can be expected to become thin- sum amounts to approximately 1000– ner and poorer in the depth and eastern 1500 m. The shift may not be that direction. Due to the inclined position extensive, considering the compensa- of the original coal deposit against the tions due to bending. Another aspect is Laško syncline, the erosion has re- an assumption that the covered part of moved a large part of it, possibly even the coal deposit is situated in the pro- a half of it. longation of the Ojstro seam. In such case, the shift would be less extensive. The Hrastnik thrust fault is an impor- However, it is a theoretical question. tant structural element of the Hrastnik The explorations in this sense should structure. It has been proven in the be abandoned, as the missing part was western part of the coal deposit, and situated near the edge of the original in the eastward direction, its existence coal deposit, therefore resulting in a is not at questionable as its position. presumably thinner and poorer seam.

RMZ-M&G 2010, 57 90 Vukelič, Ž., Klenovšek, B., Placer, L., Malenković, V., Dervarič, E.

Field exploration and its costs the exploration of the “northern” seam Given the characteristics of the Hrast- should be attempted only in the case of nik rock strata and coal seam, and its thickness proving economically vi- assuming that the investment is eco- able. The thickness of the “northern” nomically viable, it would be advis- seam is 10–15 m and only occasionally able for initial exploration to focus on reaches 20 m. Given what we know, the “southern” seam over the Hrastnik any surveys of the coal deposit under thrust, which is only –40 m deep, while the Hrastnik thrust would be pointless

Table 2: Estimated cost of three structural exploration drill holes DRILLING WORKS DRILL HOLE V-1 / HOLE DEPTH: 650 m Amount No. Type of works Unit Quantity Price (EUR) (EUR) 1. Construction of the access road M 50 50.00 2 500.00 2. Construction of the platform for the drilling set m2 250 10.00 2 500.00 Transportation of the drilling set and equipment, 3. lump-sum 3 000.00 assembly and dismantling Drilling for the first column without core 4. M 12 150.00 1 800.00 sampling and column installation 5. Core drilling M 638 230.00 146 740.00 6. Core containers (archive) pcs 130 60.00 7 800.00 8. Transport of the core to the laboratory lump-sum 2 000.00 TOTAL 166 340.00

GEOLOGICAL AND LABORATORY ANALYSES DRILL HOLE V-1 Type of works Quantity Price (EUR) Amount (EUR) 1. Geological works 13 000.00 Geological mapping of the core Sample collection Elaboration of the drill hole profile Elaboration of the transverse geological cross-section 2. Laboratory analyses 8 000.00 3. Elaboration of report 3 000.00 TOTAL 24 000.00

DRILL HOLE V-1 Price (EUR) Drilling works 166 340.00 Geological and laboratory analyses 24 000.00 TOTAL 190 340.00

RMZ-M&G 2010, 57 Geological evaluation of brown coal reserves at the Hrastnik mine – RTH 91 at this point, primarily on account of its drill holes from the surface with an av- extreme depth and costs involved. erage depth of 650 m. Upon acquisition of positive results, one drill hole will On the basis of comprehensive refer- be equipped as a piezometer. Estimated ence points of the geological evalua- costs for the drill hole construction are tion of coal reserves, we propose a con- shown in Table 2 for each individual struction of three structural exploration drill hole.

DRILLING WORKS DRILL HOLE V-2 / HOLE DEPTH: 650 m - PIEZOMETER Amount No. Type of works Unit Quantity Price (EUR) (EUR) 1. Construction of the access road M 50 50.00 2 500.00 2. Construction of the platform for the drilling set m2 250 10.00 2 500.00 Transportation of the drilling set and equipment, 3. lump-sum 3 000.00 assembly and dismantling Drilling for the first column without core 4. M 12 150.00 1 800.00 sampling and column installation 5. Delivery and installation of the piezometer pipe M 650 100.00 65 000.00 6. Core drilling M 638 230.00 146 740.00 7. Core containers (archive) pcs 130 60.00 7 800.00 8. Transport of the core to the laboratory lump-sum 2 000.00 TOTAL 231 340.00

GEOLOGICAL AND LABORATORY ANALYSES DRILL HOLE V-2 Type of works Quantity Price (EUR) Amount (EUR) 1. Geological works 13 000.00 Geological mapping of the core Sample collection Elaboration of the drill hole profile Elaboration of the transverse geological cross-section 2. Laboratory analyses 8 000.00 3. Elaboration of report 3 000.00 Total 24 000.00

DRILL HOLE V-2 Price (EUR) Drilling works 166 340.00 Geological and laboratory analyses 24 000.00 TOTAL 255 340.00

RMZ-M&G 2010, 57 92 Vukelič, Ž., Klenovšek, B., Placer, L., Malenković, V., Dervarič, E.

DRILLING WORKS DRILL HOLE V-3 / HOLE DEPTH: 650 m Amount No. Type of works Unit Quantity Price (EUR) (EUR) 1. Construction of the access road M 50 50.00 2 500.00 2. Construction of the platform for the drilling set m2 250 10.00 2 500.00 Transportation of the drilling set and equipment, 3. lump-sum 3 000.00 assembly and dismantling Drilling for the first column without core 4. M 12 150.00 1 800.00 sampling and column installation 5. Core drilling M 638 230.00 146 740.00 6. Core containers (archive) pcs 130 60.00 7 800.00 8. Transport of the core to the laboratory lump-sum 2 000.00 TOTAL 166 340.00

GEOLOGICAL AND LABORATORY ANALYSES DRILL HOLE V-3 Type of works Quantity Price (EUR) Amount (EUR) 1. Geological works 13 000.00 Geological mapping of the core Sample collection Elaboration of the drill hole profile Elaboration of the transverse geological cross-section 2. Laboratory analyses 8 000.00 3. Elaboration of report 3 000.00 TOTAL 24 000.00

DRILL HOLE V-3 Price (EUR) Drilling works 166 340.00 Geological and laboratory analyses 24 000.00 TOTAL 190 340.00

TOTAL COSTS FOR THE CONSTRUCTION OF DRILL HOLES Price (EUR) V-1, V-2 and V-3

DRILL HOLE V-1 190 340.00

DRILL HOLE V-2 255 340.00

DRILL HOLE V-3 190 340.00

TOTAL 636 020.00

RMZ-M&G 2010, 57 Geological evaluation of brown coal reserves at the Hrastnik mine – RTH 93

During the execution of exploration an estimate and identify the necessary drill holes, a decision on the relevance scope of activities that would enable of the execution of all three drill holes the remaining reserves to be determined and on the manner of execution of the with a higher degree of precision and piezometer would be made, consider- subsequently recategorised as actual re- ing the individual data collected from serves, and to verify the exploitable coal the drill hole V-1. The depths of the reserves which, once confirmed, would drill holes have been estimated, but provide a basis of determining the eco- should not exceed the depth of 650 m. nomic viability of further mining at the coalmine Hrastnik.

Conclusion Summary

The off-balance A + B + C1 coal re- serves in the Hrastnik mine, the amount Geological Evaluation of Brown Coal of which has not significantly changed Reserves at Hrastnik Pit - RTH, Rud- since the end of the year 1997, represent nik Trbovlje – Hrastnik precisely one third of the entire (both balance and off-balance) A+B+C1 coal The geological evaluation of the remain- reserves for RTH, the Trbovlje-Hrastnik ing deposits of brown coal at Hrastnik mine (53,893,000 t). In addition, further focused on reviewing the updated brief sources of the C2 category (6,272,000 on the categorisation, classification and t) have been recorded in the Eastern calculation of the resources and depos- Corner Field in the mine Hrastnik. The its of brown coal in the RTH mining elaborated geological evaluation and area as at 31 December 2002 (Mitrevski the necessary scope of research surface and Bravec, 2003). drilling represent a good basis for coal reserve recategorisation. The results of Apart from the associates employed by exploration drilling will enable the final the coalmine’s geological department to confirmation of exploitation reserves of monitor the preliminary works and sur- brown coal in the Hrastnik mine. veys carried out at the coalmine on an on- going basis, vital research over the past The purpose of the study “The justifi- fifty years was undertaken by Kuščer ability of the exploitation of the remain- (1967) with his core work Zagorje Ter- ing coal reserves at the mines Ojstro and tiary, Gregorač (1975) who focused on Trbovlje after the year 2009” – Phases II the hydrogeology of the mine Hrast- and III, and the evaluation of coal depos- nik, Kuščer and Mitrevski (1979) who its at the mine Hrastnik was to produce researched the geology of the bound-

RMZ-M&G 2010, 57 94 Vukelič, Ž., Klenovšek, B., Placer, L., Malenković, V., Dervarič, E. ary area between the mines Hrastnik and area, certain structural geological ques- Dol, Uhan (1991) with his work on the tions remain unanswered; this primarily geochemical properties of coal in the refers to the continuation of the coal seam central part of the deposit, and Placer under the hypothetical Hrastnik thrust who carried out a structural-geological fault. The other set of debatable questions analysis between 1982 and 1991. In the concern the geological structure of the abovementioned period Placer complet- Eastern Underground Deposit where the ed a geological survey and mapping of continuation of the southern coal seam the surface area between Moravče and downwards has been established by ex- Laško, and surveyed and mapped the ploratory drill holes at Brnica. mine roadways and the cores of explora- tion drill holes. Placer published the ma- Given the characteristics of the Hrastnik jor findings of the survey and mapping of rock strata and coal seam, and assum- the surface area over the mines Hrastnik ing that the investment is economically and Dol in 1987 in the brief “A Geologi- viable, it would be advisable for initial cal Structure Survey in the Dol-Hrastnik exploration to focus on the “southern” Area, Part II”. In the three-year period seam over the Hrastnik thrust, which is 1985–1987 geologists surveyed rough- only 25–40 m deep, while the explora- ly 3,200 m of roadways, access tunnels tion of the “northern” seam should be and longwalls, and drilled eleven struc- attempted only in the case of its thick- tural exploration drill holes in the total ness proving economically viable. The length of approximately 1,500 m (Uhan, thickness of the “northern” seam is 10 1987). The geological data obtained in m to 15 m and only occasionally reaches the course of the abovementioned sur- 20 m. Given what we know, any surveys veying and mapping of mine roadways of the coal deposit under the Hrastnik and exploration drill holes yielded more thrust would be pointless at this point, detailed information on the structure of primarily on account of its extreme the “south wing” of the central part of the depth and costs involved. coalmine Hrastnik at and under Horizon VII. Building on the results of all previ- The western end of the “southern” seam ous surveys and having reviewed and has been comparatively well surveyed. processed the entire documentation held However, more detailed surveys of the by the coalmine, Placer preformed the eastern end should be carried out; this most comprehensive structural geologi- applies in particular to the layout of the cal analysis until that time, and explained Hrastnik thrust. the tectonic development of the coal de- posit. When it comes to the evaluation of The question of a direct connection be- remaining coal reserves in the Hrastnik tween the “southern” and “northern”

RMZ-M&G 2010, 57 Geological evaluation of brown coal reserves at the Hrastnik mine – RTH 95 coal seams at the far eastern end of the Access for the purpose of surveying coal deposit at Hrastnik remains open, the “northern” seam from the surface is as there is always a possibility that the less favourable. shift along the internal thrust layer in that direction may be diminishing. The far eastern boundary of the Hrast- Should the opening of the “southern” nik coalmine deposit has not been de- seam be deemed economically viable, termined. Known findings about the however, that possibility should also be position of the originally identified explored. deposit relative to the Laško syncli- nal lead us to believe that the uniform Suitable drilling sites have been identi- or divided main seam is leaning at an fied both on the surface and in the mine. angle onto the thrust zone along the At Horizon 8 (+50 m) the relevant tun- northern perimeter of the Laško syn- nel reaches up to coordinate y = +5350. clinal. Since we are approaching the Access to Level 0 is provided from outermost boundary of the originally Horizon 7 (+85 m) downwards. Point 0 identified deposit in the eastern direc- is located at cross-section y = +4900. tion, the potential of this area is limited Horizon 8 is more suitable for drill- by that boundary, which translates into ing; the required access tunnel to the a gradual diminishing and thinning of far end of the “southern” seam would the coal seam. be at least 600–700 m long and pos- sibly longer with drill holes reaching The proposed surveys at the Hrastnik 200 m to 300 m deep, depending on coalmine deposit should facilitate a re- the layout of the proposed tunnel. The categorisation of reserves and resourc- “southern” seam can also be accessed es, and should focus primarily on the from the surface. The average depth of eastern end of the mine. The proposed the proposed drill holes would be about exploration involves three drill holes to 600 m i.e. between 500 m to 700 m. The the depth exceeding 650 m. The total cost/benefit analysis would indicate cost of drilling would amount to EUR which part should be explored from the 636,000. mine and which part from the surface. Total actual deposits are expected to be The most promising point at which the below the figure suggested in the reas- connection between the “southern” and sessment of resources and reserves car- “northern” seams at the eastern end of the ried out in 2003 (Mitrevski and Bravec). coal deposit should be explored would The proposed downgrading of reserves be at cross-section y = +5650 at the loca- applies to the “northern” seam and the tion of the existing drill hole Br.10. transitional area between the Hrastnik

RMZ-M&G 2010, 57 96 Vukelič, Ž., Klenovšek, B., Placer, L., Malenković, V., Dervarič, E.

and Dol mines due to the tectonic thrust Dervarič et al. (2009): Upravičenost od- and shifting tectonic plates, which kopavanja preostalih zalog premoga v thinned the original seam and broke it jamah Ojstro in Trbovlje po letu 2009 up into individual lens. Due to the lack in zaprtega dela jame Hrastnik – II. in of field data, the figures presented in the III. faza (Justifiability of exploitation reassessed resources and reserves brief of the remaining coal reserves in the mines Ojstro and Trbovlje after the are somewhat idealised. year 2009 and the closed-down section of the Hrastnik mine - Phase II and The purpose of the study “The Legiti- III). UL NTF OGTR, March 2009. macy of the Extraction of Remaining Kuščer, D. & Mitrevski, G. (1979): Ge- Coal Deposits at the Mines Ojstro and ologija mejnega območja med jamama Trbovlje After 2009” – Stages 2 and 3, Hrastnik in Dol (Geology of the border and the evaluation of coal deposits at area between the mines Hrastnik and the mine Hrastnik was to produce an es- Dol). Rudarsko-metalurški zbornik timate and identify the necessary scope 26/2–3, 167–178, Ljubljana. of activities that would enable the re- Placer, L. (1988): Preliminarna analiza maining reserves to be determined with strukture Ojstrega in Hrastnika (Pre- a higher degree of precision and sub- liminary analysis of the structure of sequently recategorised as actual re- Ojstro and Hrastnik). RTH Archive. serves, and a verification of exploitable Placer, L. et al. (1994): Stratigrafski in tektonski razvoj Laške sinclinale coal reserves which, once confirmed, (Stratigraphic and tectonic develop- would provide a basis of determining ment of the Laško synclinal). RTH Ar- the economic viability of further min- chive. ing at the coalmine Hrastnik. Placer, L. 1999 (1998): Structural mean- ing of the folds. Geologija 41, 191–221, Ljubljana. References Mitrevski, G. & Bravec, B. (2003): Ren- ovelacija elaborata o kategorizaciji in Dervarič et al. (2008): Upravičenost od- klasifikaciji izračunanih zalog in virov kopavanja preostalih zalog premoga v rjavega premoga na območju prido- jamah Ojstro in Trbovlje po letu 2009 bivalnega prostora Rudnika Trbovlje- in zaprtega dela jame Hrastnik – I. faza Hrastnik (RTH) s stanjem 31. 12. 2003 (Justifiability of exploitation of the (Update of the brief on the categorisa- remaining coal reserves in the mines tion, classification and calculation of Ojstro and Trbovlje after the year the resources and deposits of brown 2009 and the closed-down section of coal in the RTH mining area as at 31st the Hrastnik mine - Phase I). UL NTF December 2003). OGTR, September 2008. RTH Archive.

RMZ-M&G 2010, 57