An ef fect of ig ne ous in tru sion on the struc ture, tex ture and microtexture of coal from the Soœnica coal mine, Up per Silesian Coal Ba sin, Po land
£ukasz SMÊDOWSKI1, *, Stanis³aw DUBER2 and Aniela MATUSZEWSKA2
1 In sti tute for Chem i cal Pro cess ing of Coal, Zamkowa 1, 41803 Zabrze, Po land
2 Silesian Uni ver sity, Fac ulty of Earth Sci ence, Bêdziñska 60, 41200 Sosnowiec, Po land
Smêdowski, £., Duber, S., Matuszewska, A., 2015. An ef fect of ig ne ous in tru sion on the struc ture, tex ture and microtexture of coal from the Soœnica coal mine, Up per Silesian Coal Ba sin, Po land. Geo log i cal Quar terly, 59 (3): 507–516, doi:
10.7306/gq.1226
Two coal sam ples from the Soœnica coal mine, Po land, were ana lysed in this study. One sam ple was the nat u ral char col - lected at the con tact of mag matic in tru sion, and an other sam ple was the raw coal that was pyrolised in a lab o ra tory fur nace.
Tem per a ture of py rol y sis was sim i lar to that cal cu lated for the in tru sion. The ob tained char was ana lysed to com pare its fea - tures with those char ac ter iz ing a nat u ral char sam ple. Op ti cal mi cros copy, trans mis sion elec tron mi cros copy and Raman spec tros copy stud ies show that the char from un al tered coal is char ac ter ized by the least de vel oped struc ture, tex ture and microtexture com pared to the nat u ral char. Hence, it can be con cluded that geo log i cal pres sure gen er ated by both the in tru - sion and the over bur den, strongly af fects the pro cess of mo lec u lar or der ing that took place dur ing the heat ing of coal. The tex tural, struc tural or microtextural pa ram e ters of coal can not be used as a geo-ther mom e ter, be cause they are strongly de - pend ent not only on the tem per a ture but also on other fac tors.
Key words: coal struc ture, trans mis sion elec tron mi cros copy, Raman spec tros copy, ig ne ous in tru sion.
INTRODUCTION
Heat and pres sure gen er ated by ig ne ous magma in trud ing within coal seams can strongly in flu ence its physicochemical and struc tural prop er ties (Tay lor et al., 1998). The de gree of rock trans for ma tion de pends on the tem per a ture of in truded magma, the du ra tion of mag matic-de rived heat, and the dis - tance be tween in truded magma and rock (Kwieciñska and Petersen, 2004; Rimmer et al., 2009; Yao and Liu, 2012). As a re sult of in tru sion im pact on coal seam, a nat u ral coke can be formed at the coal-in tru sion con tact (Kwieciñska and Petersen, 2004). The ef fects of mag matic in tru sion on the coal are ob - served in many coal fields. The larg est de pos its of ther mally al - tered coals are found in In dia, USA and China (Stew art et al., 2005; Singh et al., 2008; Yao et al., 2011). The ef fect of in tru - sion on coal al ways in cludes an in crease in coal mo lec u lar or - der ing de gree that is man i fested by an in crease in mean op ti cal reflectance and ani so tropy (Chandra, 1965; Stew art et al., 2005; Singh et al., 2007; Yao et al., 2011). The de vel op ment of pore and frac ture sys tems and a de crease in vol a tile con tent are also usu ally ob served (Coo per et al., 2007; Mastalerz et al., 2009), as well as dis tinct changes in coal chem is try and min eral mat ter trans for ma tions. The de vel op ment of vol a tile re lease
was also re ported (Golab et al., 2007; Pang et al., 2007; Walker et al., 2007; Schimmelmann et al., 2009; Jiang et al., 2011;
Valentim et al., 2011). More over, nat u ral coke is char ac ter ized by a well-or ga nized op ti cal tex ture and struc ture mea sured by var i ous tech niques. Clear dependences be tween the tem per a - ture of in tru sion body and a set of pa ram e ters mea sured via op - ti cal mi cros copy, e.g. max i mum and min i mum reflectance, bireflectance and Killby’s trans forms were re ported (Komorek et al., 2010). Sim i lar in ves ti ga tions of nat u ral coke or der ing were per formed with use of Raman spec tros copy and scan ning elec tron mi cros copy and SEM. All of the re sults con firm that the heat sup ported from the mag matic body causes an in crease in the de gree of mo lec u lar ar range ment of heated coal (Sarana and Kar, 2011; Singh et al., 2013; Wu et al., 2014). Un for tu - nately, these re sults do not an swer the ques tion about how other fac tors in flu ence the struc tural trans for ma tion of coals that were heat-al tered in the coal bed. Tak ing ac count that tec tonic forces may cause tex tural trans for ma tion of vitrinite, which is man i fested by in creased mean reflectance and change in op ti - cal char ac ter (Komorek et al., 1998), it may be ex pected that the force gen er ated by in trud ing magma on the sur round ing coal may cause a sim i lar ef fect. On the other hand, it is well-known that an in crease in coal struc ture or der ing can be re - sulted by its car bon iza tion. Such a pro cess is ac com plished in lab o ra tory or in dus trial fur naces where a por tion of coal is heated in an in ert at mo sphere. As a re sult, coke or char is pro - duced and its struc ture, tex ture and microtexture are a fin ger - print of physicochemical char ac ter is tics of par ent coal and the fi nal tem per a ture of the pro cess. In gen eral, dis tinct from the con di tions of nat u ral coke for ma tion, coal car bon ized in a fur -
* Corresponding author, e-mail: lsmedowski@ichpw.pl Received: August 31, 2014; accepted: March 6, 2015; first published online: March, 30, 2015
nace is not in flu enced by strong me chan i cal forces. Hence, con clu sions drawn on the ba sis of com par i son of coke or char struc ture, per formed as a re sult of heat in flu ence on coal in geo - log i cal con di tions and in the fur nace, should par tially ex plain if geo log i cal pres sure gen er ated by an ig ne ous in tru sion af fects the nat u ral coke mo lec u lar or der ing. It has been found that geo - log i cal pres sure af fects the nat u ral coke R0 val ues (Chandra, 1965), but the re sults of de tailed in ves ti ga tions con cern ing the im pact of pres sure gen er ated in a seam on the de gree of coal or der ing de fined at dif fer ent lev els of its or ga ni za tion have not been de scribed. The aim of this work is to eval u ate the ef fect of geo log i cal pres sure and tem per a ture on the op ti cal tex ture, microtexture and struc ture of coal in coal sam ples from the Soœnica mine.
GEOLOGICAL SETTING
The Up per Silesian Coal Ba sin (USCB) is one of the ma jor coal bas ins in Eu rope, sit u ated in south ern Po land and the north ern Czech Re pub lic. It cov ers an area of ca. 7,500 km2 (Jureczka and Kotas, 1995; Kêdzior, 2009). The USCB rep re -
sents a kind of mo las ses fill ing the fore land of the Moravian and Silesian parts of the Variscan fold ing zone. The base ment of Car bon if er ous coal-bear ing rocks con sists of Pre cam brian, Cam brian, De vo nian and Car bon if er ous se quences (Jureczka and Kotas, 1995; Probierz et al., 2012). These rocks be long to four lithostratigraphic se ries (Figs. 1 and 2):
– Paralic Se ries (Up per Mis sis sip pian-Lower Penn syl va - nian; Namurian A) – char ac ter ized by the pres ence of clastic and phytogenic sed i ments with ho ri zons con tain - ing ma rine- and brakish-wa ter fau nas, thin coal seams, and ter res trial-ma rine sed i ments;
– Up per Silesian Sand stone Se ries (Lower Penn syl va - nian, Namurian B and C) – char ac ter ized by the oc cur - rence of thick coal seams that are rich in intertinite;
– Mudstone Se ries (Lower and Mid dle Penn syl va nian;
Westphalian A and B) – char ac ter ized by the oc cur rence of thin vitrinite-rich coal seams;
– Kraków Sand stone Se ries (Mid dle Penn syl va nian;
West phalian B, C and D) – char ac ter ized by the pres - ence of po rous and per me able sand stones and vitrinite- rich seams.
The west ern part of USCB is folded and cut by nu mer ous faults (Probierz et al., 2012), while the east ern part is char ac ter -
508 £ukasz Smêdowski, Stanis³aw Duber and Aniela Matuszewska
Fig. 1. A geo log i cal sketch of the Up per Silesian Coal Ba sin (mod i fied af ter Probierz et al., 2012) show ing the lo ca tion of the Soœnica coal mine
1 – Micha³kowice sad dle, 2 – Orlova fold, 3 – Jejkowice trough, 4 – Chwa³owice trough, 5 – K³odnica fault, 6 – ¯ory-Piasek-Jawiszowice-Wysoka fault zone, 7 – Gorzyce-Bzie Zameckie-Czechowice-Kêty fault zone
ized by fea tures typ i cal for plat form zones (Jureczka and Kotas, 1995). Three zones of struc tural de vel op ment can be dis tin - guished within the coal-bear ing se quence:
– fold tec tonic zone;
– fault-block tec tonic zone;
– fold-thrust tec tonic zone (Kotas, 1972).
Two troughs (Jejkowice and Chwa³owice) and two over - thrusts (Micha³kowice sad dle and Orlova fold) oc cur within the fold tec tonic zone. The fault-block tec tonic zone cov ers most of the USCB area. Hor i zon tal coal beds are in ter rupted by ma jor fault zones of par al lel strike and sig nif i cant throw to wards the south (K³odnica, ¯ory–Piasek–Jawiszowice–Wysoka and Go - rzy ce–Bzie Zameckie–Czechowice–Kêty fault zones). Fold- thrust tec tonic el e ments abut ting the ba sin to the north and north-east include several anticlinal structures.
Nu mer ous ig ne ous in tru sions within the Car bon if er ous rocks were found in the south west ern part of the Up per Sile sian Coal Ba sin (USCB). Their oc cur rence has been re ported in both the Rybnik Coal Area (Kuhl, 1963; Borowski and Pi³at, 1968; Chodyniecka and Stankiewicz, 1972, 1978; Gabzdyl, 1964) and in the Gliwice and Knurów re gion (Kuhl, 1954;
DuŸniak et al., 1976; Kapuœciñski, 1990). In tru sive bod ies of var i ous ages that oc cur within the USCB rocks rep re sent dif fer - ent petrographic types such as ba salt, diabase, melaphyre and vol ca nic brec cia (Chodyniecka and Hanak, 2000). Strong trans for ma tion of these rocks in di cates that hy dro ther mal phe - nom ena were as so ci ated with these in tru sions. Some of the in - tru sive bod ies were found within the Up per Silesian coal seams. The in tru sions were in ter preted as dykes and branch -
ing sills that were squeezed into the ceil ing parts of the seams (Gabzdyl et al., 1992). The in tru sive rocks are rep re sented by carbonatized bas alts, melaphyres, diabases, andesites and microdiorites which are fre quently undistinguishable mac ro - scop i cally from the clastic fine-grained rocks. The pres ent chem i cal com po si tion of volcanites is a re sult of magma con - tam i na tion. The sec ond ary min er als are as fol lows: do lo mite, cal cite, chlorites, zeolites, uralite, bi o tite, seri cite and kaolinite.
At the di rect con tact with the in tru sion, coal changed into coke or nat u ral semicoke, my lon ite and con tact anthracites. The cur - rent amount of ev i dence on vol ca nic phe nom ena in the west ern part of the Up per Silesian Coal Ba sin shows that they are re - gional in char ac ter.
The Soœnica coal mine (cur rently the Soœnica-Makoszowy coal mine) is lo cated in the north west ern part of USCB in Gliwice (Fig. 1). The old est coal-bear ing rocks rec og nized in these re gion be long to the Petrkovice Beds. These are over lain by the Hrusov and Jakovlec beds. Thin coal seams oc cur ring within these beds are ex ploited by Soœnica coal mine. The Paralic Se ries is di rectly over lain by strongly coal-bear ing rocks rep re sent ing the Up per Silesian Sand stone Se ries. Coal seams ex ploited from these beds are thick (<12.5 m) and sur rounded by coarse-grained sand stones and con glom er ates. These rocks are over lain by the Ruda, Za³ê¿e and Orzesze beds. The Kraków Sand stone Se ries is ab sent in this part of USCB. The Soœnica re gion is lo cated be tween two large tec tonic struc tures:
Main Sad dle and Orlova Overthrust. Be cause of that, coal seams in this re gion are folded and cut by nu mer ous faults.
More over, some in tru sion bod ies were found within the coal-bear ing rocks in this re gion.
Fig. 2. Sim pli fied lithostratigraphic di vi sion of the Car bon if er ous in the Up per Silesian Coal Ba sin (mod i fied af ter Jureczka and Kotas, 1995)
INTRUSION CHARACTERISTICS
The in tru sion body that was de tected within the coal seam in the Soœnica coal mine can be de fined as a dyke orig i nated from ba saltic-doler it ic-trachytic magma (Chodyniecka and Hanak, 2000). This ver ti cal dyke, 8 ´ 12 m in size, branches off into two veins, each 2 m across, 0.6–0.8 m thick sills branch ing off the dyke are found in the coal seams nos. 503, 501 and 416.
The route of the dyke was in ves ti gated over a dis tance of about 300 m from coal seam 507 to coal seam 416. The in tru sion ex - posed in the Soœnica coal mine can be com pared with vol ca nic phe nom ena found in the Pol ish part of the Lower Silesian Coal Ba sin, with re spect to its size and in flu ence on coal. The in tru - sive rock is char ac ter ized by a low sil ica con tent while the con - tri bu tions of cal cium and mag ne sium are rel a tively high. Mi cro - scopic ex am i na tion shows the pres ence of a num ber of spe cific min er als such as: bi o tite, quartz, cal cite, he ma tite, py rite, illite, kaolinite, do lo mite and zeolites. The min eral com po si tion pre - sented above con firms that the ini tial ig ne ous rock was strongly meta mor phosed. It was found that the con tact tem per a ture at the time of the in tru sion pen e tra tion into the coal seam was in the range of 700–800°C (Matuszewska and Cebulak, 2006).
Us ing Ar-K dat ing, it was also es ti mated that the in tru sive body was formed dur ing Late Perm ian and Tri as sic times (Matu - szewska and Cebulak, 2006).
STUDIED OBJECTS
Sam ples stud ied in this work were col lected from coal seam 416 in the Soœnica coal mine in Gliwice (Fig. 1). Each sam ple, 2 kg in weight, was col lected from the coal seam bot tom. Sam - ple 1 was col lected at the dis tance of 1.5 m from the in tru sion, and it was not un der the in flu ence of magma heat (Fig. 3A).
Sam ple 2 was taken at the con tact of in tru sion, and it was strongly changed un der high tem per a ture pro vided from the in - tru sion as well as un der over bur den pres sure. It can be as - sumed that it was a nat u ral char char ac ter ized by thick-walled and po rous tex ture (Fig. 3B). The un al tered sam ple of coal was pyrolised in a lab o ra tory fur nace to a tem per a ture of 800°C, in an ar gon at mo sphere. Ob tained char (Fig. 3C), marked as sam ple 3, was ana lysed to com pare its fea tures with those char ac ter iz ing a char sam ple that was formed in nat u ral con di - tions. Ba sic char ac ter iza tions of the stud ied sam ples are pre - sented in Ta ble 1.
METHODS
OPTICAL MICROSCOPY
Mi cro scopic char ac ter is tics of the tex ture of sam pled rocks were de ter mined with a re flected light op ti cal mi cro scope Axioskop MPM-200 (Opton-Zeiss, Ger many) us ing mono chro - matic plane po lar ized light of l = 546 nm. Coal grains of
£3.0 mm di am e ter were em bed ded in ep oxy resin and pol ished ac cord ing to the pro ce dure rec om mended by the In ter na tional Com mit tee for Coal and Or ganic Pe trol ogy (1963). The ap par - ent max i mum (Rmax) and min i mum (Rmin) reflectance val ues were au to mat i cally mea sured on ran domly ori ented coal grains, in im mer sion oil, at the mag ni fi ca tion 500´. For ac cu rate de ter - mi na tion of the reflectance in di cat ing sur face (RIS), the mod i -
fied Killby’s method was used. Val ues of ap par ent max i mum and min i mum reflectances were mea sured and pro cessed ac - cord ing to the Kilby’s method (Kilby, 1988) and its mod i fi ca tions (Duber et al., 2000).
TRANSMISSION ELECTRON MICROSCOPY
Sam ples to be ana lysed by means of trans mis sion elec tron mi cros copy (TEM) were pre pared us ing the fol low ing pro ce - dure. Firstly, they were ground with eth a nol in a mor tar. The spec i mens were then put into an ul tra sonic bath to dis perse ag - gre gates. The re sult ing sus pen sion was placed on a cop per grid cov ered with a car bon film. Af ter evap o rat ing the al co hol, the spec i mens were placed into the mi cro scope col umn for anal y sis. The TEM ob ser va tions were per formed us ing a Philips EM400T with mag ni fi ca tion 23,000´ and ac cel er a tion volt age 100 kV. The 002 dark field tech nique of ob ser va tion (002DF) was se lected for the study. Mo lec u lar-ori ented do - mains form ing microtexture were ob served on the TEM im ages as white fields marked in Fig ure 4 by white rect an gles. Each white field was reg is tered by two im ages col lected for two or - thogo nal ap er ture po si tions. Over 3,000 ob jects rep re sent ing mo lec u lar-ori ented do mains were ana lysed for each sam ple.
Ob tained TEM im ages were dig i tally pro cessed and the av er - age area of MOD sur faces, SMOD, were de ter mined ac cord ing to a tech nique de vel oped by Smêdowski (Smêdowski and Krzesiñska, 2013).
RAMAN SPECTROSCOPY
The Raman anal y ses were car ried out us ing a Jobin Yvon T64000 spec trom e ter con tain ing an Ar la ser of wave length 514.5 nm. The la ser power at the sam ple sur face was con - trolled at 0.5 mW, and the la ser spot di am e ter reach ing the sam ple – at ca. 1 mm. Thus, the Raman microprobe ac tu ally pro vided av er aged in for ma tion for a large num ber of ran domly dis trib uted microcrystallites. The spec tra were re corded in the range of 800–2,000 cm–1, cov er ing first-or der bands, e.g. the D-band and G-band (Fig. 5). Each Raman spec trum was de - com posed into four curves re lated to dif fer ent struc tures that form car bon ma te ri als, and the char ac ter is tic struc tural pa ram e - ters were cal cu lated (Sadezky et al., 2005).
RESULTS
Dif fer ent pa ram e ters de scrib ing the de gree of mo lec u lar or - der ing of coal and char were dis cussed to ana lyse the in flu ence of geo log i cal fac tors on their struc ture, microtexture and tex - ture. The val ues of el e men tal com po si tion of sam ples are pre - sented in Ta ble 1. Un al tered coal (sam ple 1) is char ac ter ized by the el e men tal com po si tion typ i cal for bi tu mi nous coals from the Soœnica coal mine. It is char ac ter ized by the rel a tively low car - bon con tent which in di cates that this sam ple can be in dus tri ally clas si fied as a steam coal – the car bon con tent in cok ing coals mined in Po land is typ i cally >86% (Smêdowski and Krzesiñska, 2013). Both mois ture and ash con tents are rel a tively low. Nat u - ral char sam ple (sam ple 2) is char ac ter ized by high car bon con - tent; how ever, it is lower than the con tri bu tion of this el e ment in sam ple 3. It means that the ef fect of devolatilisation and chem i - cal trans for ma tion of stud ied sam ples was stron ger for the con -
510 £ukasz Smêdowski, Stanis³aw Duber and Aniela Matuszewska
Fig. 3. Mi cro pho to graphs of: A – sam ple 1 – un al tered coal, B – sam ple 2 – nat u ral char, C – sam ple 3 – char per formed in a lab o ra tory
T a b l e 1 Ul ti mate and prox i mate anal y sis
Sam ple Cdaf
[%]
Hdaf [%]
Sdaf [%]
Ndaf [%]
Odaf [%]
Mad [%]
Aad [%]
1 – un al tered coal 83.50 4.65 0.32 1.39 10.14 2.12 1.50
2 – nat u ral char 93.22 1.04 0.57 0.71 4.46 1.20 5.50
3 – ar ti fi cially pro duced char 97.28 0.86 0.34 1.50 0.02 5.67 4.36
C – car bon, H – hy dro gen, S – sul phur, N – ni tro gen, O – ox y gen, M – mois ture, A – ash, daf – dry and ash free ba sis,
ad – as-de ter mined ba sis
di tions pre vail ing in the lab o ra tory fur nace than for those in the coal bed af fected by the in tru sion.
Fig ure 6 shows Kilby’s cross-plots drawn for all three sam - ples. For the nat u ral char (Fig. 6A) it can be seen that Rmax and Rmin sets of data are al most sep a ra ble, whereby only two tex - tural classes have been dis tin guished. It means that this sam ple is very ho mo ge neous in terms of op ti cal ani so tropy so it can be con cluded that its op ti cal tex ture is rel a tively well-or ga nized.
More over, val ues of reflectances vary over a wide range from 1–12% and the max i mum dif fer ence be tween Rmax and Rmin
mea sured in the same point, bireflectance, is also high, at al - most 8%. For the un al tered coal, it can be seen that the Kilby’s plot (Fig. 6B) clearly dif fers from the for mer one. Sets of Rmax
and Rmin strongly over lap each other and it is im pos si ble to dis - tin guish a bor der be tween these two classes with out dig i tal data pro cess ing. As a re sult of these anal y sis, up to five tex tural classes have been found within the sam ple. Max i mum bire - flectance de tected on the Kilby graph is <0.4%, and it in di cates that the mo lec u lar units form ing coal tex ture are very small and not ar ranged in larger ob jects. Op ti cal tex ture of the char sam - ple that was ob tained by the py rol y sis of un al tered coal does not cor re spond with the chem i cal changes that took place dur ing the car bon iza tion. Al though sam ple 3 is strongly devolatilized, which is man i fested by the very high car bon con tent, the de gree of mo lec u lar or der ing de scribed by reflectance is not very high.
On the other hand, het er o ge ne ity of this sam ple is quite low and only three tex tural classes have been de ter mined as a re sult of Kilby’s plot anal y sis (Fig. 6C). The max i mum bireflectance
512 £ukasz Smêdowski, Stanis³aw Duber and Aniela Matuszewska
Fig. 4. TEM im ages of sam ple microtexture:
A – sam ple 1, B – sam ple 2, C – sam ple 3 White ob jects in rect an gles rep re sent
mo lec u lar-ori ented do mains (MOD)
Fig. 5. Raman spec tra of the sam ples
found on this plot was about 2% and it is al most 6% points less than for the nat u ral char sam ple.
All data pre sented on the cross-plots were dig i tally pro - cessed, and weighted mean val ues of Killby’s pa ram e ters, e.g.
max i mum reflectance (RMAX), min i mum reflectance (RMIN), bire - flectance (Rbi), equiv a lent RIS ra dius (Rev), and RIS elon ga tion (Ram) have been de ter mined (Ta ble 2). Val ues of RMAX, RMIN, and Rbi clearly in di cate that op ti cal struc ture of sam ple 2 dif fers from that de tected for sam ple 3. The RMAX is higher while RMIN is lower for the nat u ral char, whereby the bireflectance of this sam ple is al most 6% points higher than for the char ob tained by the car bon iza tion of coal in the fur nace. Sim i lar con clu sions can be drawn from the val ues of other Kilby’s pa ram e ters; e.g. Ram val ues de fine RIS elon ga tions and con firm that sam ple 2 shows the most anisotropic struc ture. Based on the cal cu lated RMAX
and RMIN val ues, av er aged RIS shapes have been drawn for each sam ple (Fig. 7). The pre sented curves con firm all con clu - sions dis cussed above.
Mo lec u lar struc ture and microtexture of the sam ples were also ana lysed by means of Raman spec tros copy (RS) as well as trans mis sion elec tron mi cros copy (TEM). These two meth - ods are much more sen si tive than op ti cal mi cros copy so they were used to iden tify and de pict the de tails of the dif fer ences be tween mo lec u lar or der ing of coal and char sam ples. The 002DF TEM im ages of the char sam ples are pre sented in Fig -
ure 4B, C, while an im age of un al tered coal is shown in Fig ure 4A. It can be seen that the microtexture is clearly dis tin guish - able in the im ages of chars. White dots rep re sent ing ba sic struc tural units (BSU) are clus tered form ing mo lec u lar-ori ented do mains (MOD) whose av er age ar eas seem to be sim i lar for both chars. Such clus ters are not ob served in the im ages of coal. To de scribe microtexture in de tails, val ues of mo lec u - lar-ori ented do mains av er age area (SMOD) were cal cu lated with use of a method de vel oped by Smêdowski (Smêdowski and Krzesiñska, 2013). These val ues in di cate that the microtexture of nat u ral char is slightly better or ga nized than that ob served for char marked as sam ple 3. The value of SMOD de ter mined for sam ple 3 is sim i lar to that cal cu lated for coke pro duced in a Jenkner’s re tort from coal col lected from the Krupiñski coal mine, which is char ac ter ized by sim i lar fea tures as that stud ied in this work (Smêdowski and Krzesiñska, 2013). The av er age area of MOD cal cu lated for sam ple 2 is higher by <1.7 nm2 than that de ter mined for sam ple 3.
Fig ure 5 pres ents Raman spec tra of stud ied sam ples. It can be seen that the spec trum of un al tered coal is very dif fer ent from the other two. The ba sic line of this shift is strongly in clined, which re sults from the high flu o res cence as an ef fect of un or - dered aliphatic car bon at oms pres ent in the whole struc ture.
The val ues of geo met ri cal pa ram e ters cal cu lated for a par tic u - lar Raman band are pre sented in Ta ble 3. In the whole spec -
Fig. 6. Killby’s cross-plots drawn for:
A – sam ple 1, B – sam ple 2, C – sam ple 3
trum, con tri bu tion of two bands rep re sent ing poorly or dered car bon forms, e.g. D1 and D2 bands, which cor re spond to a high de gree of struc tural dis or der, is the high est for the un al tered coal. The same con clu sions can be drawn based on the D and G band FWHM val ues. Both the G-band and D-band for sam ple 1 are very broad. It in di cates that there are a lot of dif fer ent de - fects within the pack ets of car bon lay ers. Sum ma riz ing, this spec trum is char ac ter ized by a shape that is typ i cal for raw coals. Com par ing the Raman spec tra de tected for stud ied chars, it can be seen that they clearly dif fer from each other. Al - though both main bands of sam ple 2 are lo cated in a sim i lar po - si tion as ad e quate curves on the spec trum of sam ple 3, e.g.
G-band po si tion is 1605 cm–1 and D-band po si tion is 1350–1355 cm–1, but they are dis tinctly nar rower and have much lower FWHMs.
INTERPRETATION AND DISCUSSION
Anal y sis of the re sults shows that the struc ture, tex ture and microtexture of coal af fected by the in tru sive body were better de vel oped than of char pro duced in lab o ra tory scale. As might
be ex pected, the pa ram e ters de fin ing the mo lec u lar or der of un - al tered coal are the worst from among all sam ples stud ied. It is im por tant that such a poor ani so tropy of sam ple 3 is not strange con sid er ing that the pyrolised coal was char ac ter ized by a rel a - tively low rank. Thus, the ani so tropy of nat u ral char is rel a tively high, sug gest ing that there were other fac tors that af fected coal trans for ma tion that took place in the coal bed. Pre sented re sults con firm the con clu sions drawn by Chandra (1965) who showed that the op ti cal ani so tropy of heat that af fected coals may also be ad di tion ally de te ri o rated due to geo log i cal pres sure.
Chandra (1965) has shown that, for some Amer i can heat-af - fected coals, the val ues of Ro, max and Ro, min are sim i lar to those cal cu lated for chars pro duced as a re sult of car bon iza tion of un - al tered coals. Whereas, for some other sam ples, the dif fer - ences be tween op ti cal bireflectances de tected for nat u ral and ar ti fi cially pro duced chars, are very high. It is an ev i dence for the oc cur rence of an ad di tional fac tor that in flu ences coal tex ture or der ing. Other au thors (Coo per et al., 2007; Golab et al., 2007;
Singh et al., 2007, 2008; Mastalerz et al., 2009; Rimmer et al., 2009; Schimmelmann et al., 2009; Valentim et al., 2011) also re ported that the op ti cal reflectances of nat u ral chars are af - fected by mag matic in tru sions, but they did not study the in flu - ence of par tic u lar fac tors, e.g. tem per a ture or pres sure, on tex - tural or der ing of coals. Schimmelmann et al. (2009) found that the larger the in tru sive body, the higher reflectance of char af - fected by it. It can be as sumed that such an in crease of reflectance may be par tially caused by the in crease of pres sure gen er ated by larger in tru sion.
Tak ing into ac count that the Soœnica re gion is strongly af - fected by tec tonic ac tiv ity and the stud ied sam ples were col - lected from a depth of about 200 m, it can be as sumed that the op ti cal char ac ter is tics of nat u ral char are an ef fect of tem per a - ture and pres sure ex erted by the over bur den and in tru sion body. This pres sure could be high enough to cause the mo lec u - lar units to be ar ranged in one plane, form ing larger ob jects.
Hence, it can be sus pected that the strong re or ga ni za tion of coal op ti cal tex ture, due to heat ing in geo log i cal con di tions, is caused by the com bi na tion of two factors, e.g. temperature and geological pressure.
514 £ukasz Smêdowski, Stanis³aw Duber and Aniela Matuszewska
T a b l e 3 Val ues of pa ram e ters char ac ter iz ing Raman bands
Sam ple
G-band D-band D1+D2 band Band ra tios
Cen tre [cm–1]
Area [%]
FWHM [cm–1]
Cen tre [cm–1]
Area [%]
FWHM [cm–1]
Area
[%] ID/IG AD/AG SMOD
[nm2]
1 1594 23.25 72.4 1365 56.53 195.9 20.23 0.76 2.43 1.53
2 1605 19.35 50.9 1350 63.92 109.9 16.73 1.15 3.30 6.56
3 1605 14.98 70.7 1355 68.41 185.7 19.96 1.25 4.57 4.87
T a b l e 2 Val ues of op ti cal pa ram e ters
Sam ple RMAX RMIN Rbi = RMAX–RMIN Rev Ram Num ber of tex tural
classes
1 0.92 0.81 0.11 0.85 0.080 5
2 8.65 5.59 3.06 6.33 0.220 2
3 7.57 6.72 0.85 7.21 0.065 3
RMAX – max i mal av er age reflectance, RMIN – min i mal av er age reflectance, Rbi – bireflectance, Rev – equiv a lent RIS ra - dius, Ram – RIS elon ga tion
Fig. 7. Reflectance In di cat ing Sur faces (RIS) of the sam ples
Based on the TEM re sults, it can be con cluded that the ef - fect of geo log i cal con di tions on char microtexture is not very strong. The av er age area of MOD cal cu lated for sam ple 2 is higher only by <1.7 nm2 than that de ter mined for sam ple 3. This is prob a bly caused by ini tial coal char ac ter is tics. It is known that the de vel op ment of char microtexture is con trolled by two fac - tors as so ci ated with the cak ing abil ity, i.e. coal rank and coal flu - id ity. The Soœnica coal is a rel a tively low-rank and low-flu id ity coal, and there fore the con di tions that oc curred dur ing the heat - ing of it do not pre fer a BSU or der ing.
By com par ing the Raman re sults with the con clu sions drawn by other re search ers (Sheng, 2007), it can be as sumed that the nat u ral char sam ple stud ied by us is char ac ter ized by a higher de gree of struc tural or der ing than the char pro duced by the car bon iza tion of coal in lab o ra tory scale. More over, both band ra tios, i.e. ID/IG and AD/AG, are higher for sam ple 3 in di cat - ing that the con tri bu tion of dis or dered struc tures rep re sented by the D-band out weigh the con tent of more or dered ob jects rep - re sented by the G-band of Raman spec tra.
Based on the re sults ob tained with use of both Raman and TEM mea sure ments, sim i lar con clu sion to that found from op ti - cal in ves ti ga tions can be drawn. The de gree of or der ing de tected for the nat u ral char sam ple is dis tinctly higher than that de tected for char pro duced in the lab o ra tory. Un for tu nately, in lit er a ture there is no ev i dences on the in flu ence of other fac tors, e.g. pres - sure, on the di men sion of mo lec u lar-ori ented do mains or the Raman spec tra shape. How ever, tak ing into ac count that SMOD and struc tural pa ram e ters cal cu lated from Raman spec tra cor re - late with op ti cal ani so tropy (Smêdowski et al., 2011; Smêdowski, 2011; Smêdowski and Krzesiñska, 2013), it can be con cluded that the heat as so ci ated with the ig ne ous in tru sion and pres sure gen er ated by both over bur den and in trud ing magma, have a clear im pact on the de gree of or der ing of car bon lay ers and on the di men sion of mo lec u lar-ori ented do mains.
Sum ma riz ing, all the pre sented re sults in di cate that the sam ple col lected from the Soœnica coal mine seam was al tered not only by the tem per a ture of in tru sion but also by the other fac tors. Tak ing ac count the geo log i cal con di tions of the Soœnica re gion and the con clu sions drawn by Chandra (1965),
it can be pre sumed that the geo log i cal pres sure was an ad di - tional fac tor that af fected the struc ture, microtexture and tex ture of the stud ied nat u ral char.
CONCLUSIONS
The struc tural, microtextural and tex tural de gree of or der ing of two char sam ples was in ves ti gated in this study. One of them orig i nated from a coal seam af fected by a ba saltic in tru sion. The sec ond one was pro duced in the lab o ra tory scale by the car - bon iza tion of un al tered coal sam pled from a coal seam with a max i mum tem per a ture sim i lar to that es ti mated for the in tru - sion. The re sults al low draw ing the following main conclusions:
– all re sults in di cate that the un al tered coal sam ple strongly dif fers from the stud ied chars in terms of struc - ture, microtexture and tex ture;
– an ef fect of devolatilisation and chem i cal trans for ma tion of coal is stron ger in the case of coal pro cessed in the lab o ra tory fur nace than in the coal bed af fected by the in - tru sion;
– val ues of pa ram e ters de ter mined for both chars in di cate that the sam ple col lected from the coal seam is char ac - ter ized by a higher de gree of or der ing than the char pro - duced un der lab o ra tory con di tions;
– the high est dis crep ancy was de tected for the val ues of op ti cal pa ram e ters, while the low est was found for the fac tor de ter mined by means of TEM;
– val ues of struc tural, tex tural and microtextural pa ram e - ters can not be used as a “geothermometer”, be cause they are dis tinctly af fected by other fac tors, e.g. a com bi - na tion of over bur den-re lated geo log i cal pres sure, in trud - ing magma, or tec tonic ac tiv ity.
Ac knowl edge ments. The au thors thank the Re view ers – D. Zivotic and anon y mous Re viewer as well as Ed i tor-in-Chief of Geo log i cal Quar terly for their help ful com ments and sug ges - tions which im proved this manu script.
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516 £ukasz Smêdowski, Stanis³aw Duber and Aniela Matuszewska
