The exploitation of glass sand in Slavonia and Moslavina has a long tradition. The open-pit »Vrtlinska« is-accordirtg to its dimensions and production capacity the biggest one in this regions. Exploitation reserves within this open pit amount about) 1 000 000 t glass sand of a very good quality, and the production capacity is 200 000 t yearly according to real needs during design and opening the pit, i. e. before the war. This article discusses geological and geomechanical characteristics of the deposit, as well as the exploitation process, which is considerably matching natural characteristics of the deposit. A more detailed description is given of the planned exploitation phase I above groundwater level which is carried out according to discontinuous system. For the exploitation of the depth part under groundwater level in the phase II, the necessity of further examination of hydrogeological characteristics of the deposit is presented, in order to acquire necessary information on groundwater regime and drainage conditions. Such knowledge will influence the choice of the most appropriate solutions in the exploitation of the depth part of the deposit.Eksploatacija kremenog pijeska u Slavoniji i Moslavini ima dugu tradiciju. Površinski kop »Vrtlinska« prema veličini i kapacitetu proizvodnje najveći je u ovim područjima. Eksploata-cijske rezerve u granicama ovog površinskog kopa iznose približno 1 1 000 000 tona kremenog pijeska vrlo dobre kvalitete, a kapacitet proizvodnje planiran je 200 000 t/god. prema realnim potrebama u vrijeme izrade projekta i otvaranja kopa, tj. prije rata. U članku su prikazane geološke i geomehaničke značajke ležišta, te tehnološki proces eksploatacije, koji je u velikom dijelu usklađen s njegovim prirodnim karakteristikama. Detaljnije je obrađena projektirana eksploatacija I. faze iznad razine podzemne vode, koja se izvodi prema diskontinu-alnom sustavu. Za eksploataciju dubinskog dijela ispod razine podzemne vode u II. fazi navedena je potreba detaljnijeg istraživanja hidrogeoloških karakteristika ležišta, u cilju stjecanja nužnih podataka o režimu podzemne vode i uvjetima odvodnjavanja. Takva saznanja utjecat će na izbor najpovoljnijih tehnoloških rješenja i eksploatacije dubinskog dijela ležišta

Borislav Perić

Slavko Vujec

English

HRČAK - Portal of Croatian Scientific and Professional Journals

EXPLOITATION OF GLASS SAND ON THE OPEN PIT NVRTLINSKA~ (MOSLAVINA, CROATIA) Rudarsko-geoloSko-naftni zbornik Slavko VUJEC and Borislav P E R I ~  Faculty of  MimRIng, Geology and Petroleum Engineering of Zagreb University, Rerottieva 6, Zagreb, Croatia Key-words: Glass sand,.Open pit planning, Working and final KljuEne rijeB: Kremeni pijesak, Projektiranje povdinskih ko- slopes, Waste dump, Vrtlinska pova, Radne i zavrSne kosine, JaloviSte, Vrtlinska UDC 622.362.37:666.122.2(697.13) StruEni Elanak Vol. 6 The exploitation of glass sand in Slavonia and Moslavina Mongtraditise.Akeqx+pituV&k~keeer~ its dimensions and production capacity the biggest one in this regions. Exploitation reserves w~thin this open pit amount about 11 000 000 t glass sand of a very good quality, and the production capacity is 200 000 t yearly according to real needs during design and opening the pit, i. e. before the war. This ar- ticle discusses geological and geomechanical characteristics of the deposit, as well as the exploitation process, which is consi- derably matching natural characteristics of the deposit. A mo- re detailed description is given of the planned exploitation phase I above groundwater level which is camed out accor- ding to discontinuous system. For the exploitation of the dep- th part under groundwater level in the phase 11, the necessity of further examination of hydrogeological characteristics of the deposit is presented, in order to acquire necessary informa- tion on groundwater regime and drainage conditions. Such knowledge will influence the choice of the most appropriate solutions in the exploitation of the depth part of the deposit. Introduction str. 95-99 The open pit >)Vrtlinskac< is the biggest produ- cer of glass sand in our country (Fig. 1). The ex- ploitation of glass sand on this open pit has been carried out since 1988 with the planned capacity of about 200 000 t yearly, established according to real economic of the broader area of that time. B J x m s e a f t h e w - c e * Q ~ p * *  tivity only a half of the planed production has be- en achieved up to now. However, technological solutions are conceptualized in such a way that al- so bigger quantities than the plane ones can easily be produced, depending on the development and needs of the major consumer, )>The Glass Indus- try Lipika. The open it >)Vrtlinska(i is situated near Caz- ma, within t E e mining claim of Slavonia, where glass sand has been produced for a long time at the area of Pakrac and Slavonska Poiega. Accor- ding to its dimensions and the shape, the deposit )>Vrtlinskai< belongs to big deposits of glass sand, whose total worcable reserves amount about 11 million tons. Glass sand is of very good quality. According to the medium content of 93.19% SiOl and satisfactory granulometric composition with slight content of harmful constituents, they can be classified as glass sands of the best quality in Cro- atia, widely applied in glass industry, metallurgy, industry of ceramics, production of abrasives and for other purposes. Zagreb, 1994. Eksploatacija kremenog pijeska u Slavoniji i Moslavini ima dugutmticGjii. ~ v S 5 i s E T k o p ~ V X i E E a ~ ~ a  X i ~ i n i i k a -  pacitetu proizvodnje najveti je u ovim podruEjima. Eksploata- cijske rezerve u granicama ovog povrSinskog kopa iznose pri- bliino 1 l 000 000 tona kremenog pijeska vrlo dobre kvalitete, a kapacitet proizvodnje planiran je 200 000 t/god. prema real- nim potrebama u vrijeme izrade projekta i otvaranja kopa, tj. prije rata. U Elanku su prikazane geoloSke i geomehanitke znaEajke leiiita, te tehnoloSki proces eksploatacije, koji je u velikom dijelu uskladen s njegovim prirodnim karakteristika- ma. Detaljnije je obradena projektirana eksploatacija I. faze iznad razine podzemne vode, koja se izvodi prema diskontinu- alnom sustavu. Za eksploataciju dubinskog dijela ispod razine podzemne vode u 11. fazi navedena je potreba detaljnijeg istra- iivanja hidrogeoloSkih karakteristika leiigta, u cilju stjecanja nuinih podataka o reiimu podzemne vode i uvjetima odvod- njavanja. Takva saznanja utjecat Ce na izbor najpovoljnijih tehnoloSkih rjeSenja i eksploatacije dubinskog dijela IeiiSta. Fig. 1. View of the open pit at opening 1988. Geological and hydrogeological characteristics of the deposit Stratigraphically, glass sands of this deposit are of the Pontian age and according to their genesis they are residua developed on the crust of weathe- red granite rocks of the nord-western marginal area of the MoslavaCka gora ( Krkal o, 1985). The development of the Pontian sediments begins in weathered zone of granite, which gradually tran- sforms into mica sands and the development of predominantly white middle-coarsed sands fol- lows further in superpositions. Sands generated 96 Rudarsko-geoloSko-naftni zbornik, Vol. 6, Zagreb, 1994 BROOK o w i ! 14Gt 120+ '"t LEGENDA: 0 10 50m 1m 7 E  2m 51+== 1m 3f' . *. ,....'. Fig. 2. Characterictis profile of the deposit ~Vrtlinskacc (after Krkalo,  1985, and Vu j ec et al., 1987) 1 loess, 2 sandy and silty clays, 3 glass sand, 4 weathered granite zone, 5 granite, 6 pit topography above groundwater level, 7 final pit topography, 8 investigations boreholes. by granite weathering, are accumulated into tecto- nically predisposed depression of granite paleore- lief. By exploratory drilling and by the open pit de- velopment, the relation of spreding of sand, over- lying and underlying strata was established. The deposit has a rather regular shape. Sand sedimen- ts are almost horizontal and the bed thickness va- ries depending on the paleorelief composition and different impact of errosion on the area surfa- ce. It is characterized by extremene thickness, which amounts maximum 70 m, and in average for the entire deposit 39 m. Overlying strata compose a graudal transforma- tion of clayey sands into yellow-brown sandy cla- ys, or are directly developed bedded light-gray clayey marls on white pure sands. Marls are follo- wed by the transition from blue-gray kaolin-mon- tmorillonitic clays to brown sandy and silty clays. On the places where sand is close to the area sur- face, the Pontian overlying strata are not develo- ped, so loess detritus lies directly on the sand. On the broader area under exploitation three basic fault types were found, which give the main characteristic of morphostructural set with parqu- etlike block composition of the field. Fig. 2 illus- trates the characteristic geological profile of the deposit >>Vrtlinskacc, and Fig. 3 view 1990. Differently as other deposits of glass sand in Croatia, the deposit >>Vrtlinskaic is with its larger part under groundwater level. Deposit is generally drained westwardly, with the overflow elevation 116 m. On the deposit area only one water flow is formed, the brook Ciglenica. In the larger part of the deposit groundwater is subartesian which is the result of slightly permeable overlying strata, practically impermeable underlying strata and tectonically created barrier in western edge. Hydrogeological characteristics of the deposit are not satisfying for sand exploitation. The estab- Fig. 3. View of the open pit 1990. lished groundwater level is rather high, it reaches the elevation + 124 m, thus the larger part of the sand is located under groundwater level. Natural gravitational drainage of the deposit may be achi- eved only by mining over the elevation + 120 m. Geomechanical conditions of exploitation In order to protect the stability of working and final pit slopes, the extensive examination of geo- mechanical properties of the overburden strata and sand as well as of the material on the waste dump were carried out during the period of mine design (Vujec et al., 1987). Stability of the final overburden slope was es- tablished under the angle of 25", and for working slopes a diagram according to particular clay sorts was created depending on the bench heights and stable slope angles. Sand has a stable final slope angle 35" indepen- dently of bench height, and the angle of working slope 32" to 35" depending on water saturation. Vujec, S. and Perid, B.: Glass Sand " Foundation of the waste dump must be prepa- red by cleaning and cascade shaping, and by the creation of drainage trenches in the watered part. Bearing capacity of the foundation was controlled and the stability of the waste dump slopes angle was established to be 25". Waste dump is bulit in two horizons, the down one bearing 10 m heigh and the upper one 15 m. In order to keep necessary stability, it is advi- ced to conduct efficient drainage of the entire open pit area, to control regularly the dip of the working slopes and to organize periodic inspecti- ons and evaluations during its development. Technological process of exploitation Location, shape, size, settling depth and other characteristics of the deposit have influenced the open pit exploitation with a favourable stripping ratio. The results of deposit exploration, especial- ly geological, hydrogeological and geomechanical characteristics pointed to rather complex conditi- ons of the open pit exploitation and the need for possibly most favourable compatibility between technological process and natural properties of the deposit. The deposit has an irregular trapezoidal shape, its maximum east-western length being around 550 m and the width in eastern part around 400 m decreasing westwardly to about 110 m. The plan area of deposit within proved reserves amount 45 230 m2. The ground over the deposit is hilly and it raises from its central part from the elevati- on 128 m nordwardly to the elevation 150 m, and south-eastwardly to the elevation 160 m. Hanging side of the deposit behaves similarly to the gro- und morphology and it generally settles gently from east to west under the angle to 5". The thic- kness of overburden is the slightest in the central part of the deposit, where it amounts only 3 to 3.8 m. Towards the marginal area, the overburden thickness increase 15 to 30 m. The average thic- kness of overlying sediments amounts 12.6 m. By the analysis of natural properties of the de- posit, technological conditions and general con- ceptions of open cut mining, the entire exploitati- on technology was designed and operated in two basic phases: PHASE I:  Deposit mining above groundwa- ter level, i. e. above the elevation 120 m, in operation PHASE 11: Deposit mining under groundwa- ter level, i. e. under elevation 120 m, collection of data for desing. Deposit mining above groundwater level is suc- cessfully carried out and it covers the height of open pit on which classical way of mining is ap- plied under conditions influencing the determina- tion of technological process, with the stripping ratio 0.7 m3/t (1 300000 m3 overburden to 1 850 000 glass sand). Stripping ratio is more favourable in mining of the depth part of the deposit (in IInd phase) and amounts only 0.2 m3/t. Definite boundaries of the open pit on the gro- und surface are established already in the first mi- ning phase. Geometric indicators of the open pit are established on the basis of geological and geo- mechanical characteristics of mineral ore body and accompanied rocks, and mining-technologi- cal conditions of exploitation. Exploitation tec- hnology is acquired according to the up-to-now experience in glass sand exploitation in Slavonia, especially on the open pit VraniC. Open pit division according to height has not been designed in classical way by forming ben- ches, because the mining technology is based on opening the whole burden on a single bench. By bulldozer pushing waste is removed to the loading level on the hanging-wall surface of the sand bed. The sand is also by bulldozer pushing and accumulated on the loading level at elevation 120 m (Fig. 4). Fig. 4. Bulldozer pushing of sand on the loading plateau Thereby the heights of overburden and orebody benches vary depending on the thickness of cap- ping and sand above the elevation 120 m. Thus the overburden bench height varies from 5 to 15 m and the bench height in sand alter from 1 to 20 m. The construction of working and final slopes of the open pit are illustrated on Figs. 1. 5. and 6. Fig. 5. working slope of the open pit in exploitation phase I 1 overburden, 2 sand Fig. 6. Final slope of the open pit in exploitation phase I 1 overburden, 2 sand, 3 granite 4 fault Open pit and waste dump planing The open pit development was performed in ac- cord with the designed exploration system, pro- duction capacity, location of waste dump, and the objects on the area. It is directed from western si- de, where access towards the deposit is most favo- urable satisfying in the sense of developing the works, drainage, transportation of waste and sand, and location of mine objects. Within deve- lopment works a 500 m lon acces road was built from the main traffic roa d to the deposit, the channels of the brooks Ciglenica and Vrtlinska Ja- rak were sunk and prepared and a working plate- au was created on the basic loading horizon (ele- vation + 120), necessary for further development of the open pit (Fig. 7). Rudarsko-geoloiko-naftni zbornik, Vol. 6, Zagreb, 1994 The choice of exploitation technology is based on the analysis of the most essential factors influ- encing the condition of technological process, and there are: natural characteristics of the depo- sit, quantity of the reserves of mineral raw materi- als, capacities of production and overburden, lo- cation of waste dump, existing experiences in the open pit exploitation of glass sand, characteristics of the mechanization available to the enterpreise a. o. In such a way a discontinued system of wi- nning, loading, transportation and dumping of overburden was chose, as well as a discontinued system of glass sand production by application of the following mechanization: bulldozers, loaders, dump trucks Volvo BM with capacity 9 m3, hydra- ulic excavator with bucket capacity 2.5 m3, and Fig. 7. Development of open pit ,>Vrtlinskacc 1 limit line of glass sand reserves, 2 slope of overburden, 3 slope of sand, 4 loading plateau, 5 waste dump, 6 access road, 7 brook, 8 working buildings, 9 A-A position of profile on Fig. 2. Vujec, S. and PeriC, B. : Glass Sand 99 trailer trucks for the transport of mineral raw ma- 2 exploitation in classical way with preliminary terials to customers. Winning and loading of glass decrease of groundwater level under the eleva- sand is illustrated by Figs. 4. and 8. tion of deposit cut, and - exploitation by hydraulic winning with hydra- ulic transport by pipe-line outside open pit bo- undaries. Fig. 8. Shema of winning and loading of glass sand I bulldozer, 2 loader, 3 truck, 4 overburden, 5 sand The waste dump is located on the south part of the open pit in a natural valley, and divided in two levels on the elevations 145 and 160 m. Bul- ldozers on the waste dump are used for flattening and compaction of material. To eliminate pore- -water pressure and to insure stability of waste dump on the heights less than 2 m the layers of sand 5 to 10 cm thick are build in (Fig. 9). Fig. 9. View of waste dump Environmental aspects Open pit exploitation of glass sand has no sig- nificant impacts on the environment, because it differs considerably from any other more com- plex mining production according to the techno- logy of mining activities procedure within the de- signed boundary and to the possibility of causing demage. The nearest villages are about 300 m far from the open pit and they are not much exposed to impacts and changes considering eco-system, microclimatic conditions, qulity of water and air. Prevention of dust accumulation is conducted on all origins of dustiness according to the up-to- -now known and efficient methods, by using a wa- ter treatment. It is convenient that sand has suffi- cient natural moisture during the most of time in the year. In the >>Glass industry Lipik(<, like as in other countries (Bauer, 1970, Kennedy, 1992), the quality of restauration of sand quariess have been improved in last decades. According to the condi- tions of space arrangement, restoration activities are also planned in quarry Vrtlinska, which are necessary to be carried out in order to eliminate Exploitation of the depth part of open pit will follow after the exploitation of the height part fi- nished and this will be separately designed. A spe- cial distinction of the exploitation in that part of the deposit is the presence of groundwater, witho- uth any possibility of drainage by gravitation out- side the open pit boundaries. That is the reason why the beginning of exploitation under the basic elevation + 120 m must be proceeded by a detai- led exploration and analys~s of hydrogeological characteristics of the deposit and of the broader environment in order to acquire necessary infor- mation on the groundwater regime, quantity, way of inflow and drainage conditions. According to especially worked out exploration program which will serve as the basis to conduct the mining pro- ject concerning the continuation of exploration of this glass sand deposit. The exploration of such deposits under groun- dwater level can be founded on two basic techno- logical solutions: disturbahces in space, caused by mining explora- tion. Thus the angles of final slope of the height I part of the open pit (above the elevation 120) and waste dump are established according to the crite- ria of stability protection and sliding, as well as according to the conditions of recultivation activi- - - - - - - - - - ty (afforgsting) of the devasted area. The area of depth part of the open pit (lower than the elevati- on 120) i. e. under groundwater level is planed for a lake, supposed for sport and recreative purposes after exploitation perlod is over. Received: 18. I. 1994. Accepted: 9. VI. 1994 REFERENCES B auer, A.  M . (1979): A Guide to Site Development and Re- habilitation of Pits and Quarries. Ontario Deparment of Mines, 60 pp. Toronto. Kennedy,  A.  (1992): Advances in Mine Reclamation. Mi- ning Magazine June, 334-338, Edenbridge. Kr kal o ,  E.  (1985): Pronalazak i istrakivanje kvarcnog pijes- ka >>Vrtlinskacc kod Cazme s posebnim osvrtom na koru troSenja granitnog masiva sjeverozapadnog obodnog pod- ruEja MoslavaEke gore (magistarska radnja). (Discovery and explorations of the glass sand svrtlinskcc near Cams especially considering weathered crust of granite massif on the north-westem skirt area of the MoslavaEka gora [mas- ter thesis]). Rudarsko-geoloSko-naftni fakultet SveuEiliSta u Zagrebu. Vujec, S., Krkalo, E . ,  ProkopoviC, S .  (1987): Glavni rudarski projekt eks loatacije kremenog i'eska ~Vrtlin- &ax imad ruvoa po&emne vode (k, 120). N i n e  projea of the nvrtlinskacc glass sand exploitabon above groundwater level [elev. 1201). Rudarsko-geoloSko-naftni fakultet Sveu& liSta u Zagrebu, 153 pp. (Unpubl). 

EKSPLOATACIJA KREMENOG PIJESKA NA POVRŠINSKOM KOPU "VRTLINSKA" (MOSLAVINA, HRVATSKA)

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