Geo log i cal Quar terly, 2017, 61 (4): 877–886 DOI: http://dx.doi.org/10.7306/gq.1377
222
Rn and
220Rn con cen tra tions in soil gas of the Izera Mas sif (Sudetes, Po land) as a func tion of sam pling depth
Dariusz MALCZEWSKI1, * and Jerzy ŻABA1
1 Uni ver sity of Silesia, Fac ulty of Earth Sci ences, Będzińska 60, 41-200 Sosnowiec, Po land
Malczewski, D., Żaba, J., 2017. 222Rn and 220Rn con cen tra tions in soil gas of the Izera Mas sif (Sudetes, Po land) as a func tion of sam pling depth. Geo log i cal Quar terly, 61 (4): 877–886, doi: 10.7306/gq.1377
This re search pres ents soil gas 222Rn and 220Rn con cen tra tions mea sured at 17 lo ca tions in the Izera Mas sif of south west Po land. The av er age 222Rn con cen tra tions at sam pling depths of 10, 40 and 80 cm were 8, 78 and 224 kBq m–3, re spec tively.
The av er age 220Rn con cen tra tions for the same depths (10, 40 and 80 cm) were 6, 10 and 13 kBq m–3, re spec tively. Pro files of the con cen tra tions ver sus depth can be fit ted by ex po nen tial, lin ear and poly no mial func tions for soils de vel oped on fault zones, above ura nium min eral de pos its, and above faulted ura nium de pos its, re spec tively. Soils de vel oped on bed rock with - out fault zones or ura nium min er ali sa tion ex hibit con cen tra tions that fol low a power func tion with an ex po nent of p <1.
Key words: ra don and thoron, fault zones, ura nium min er ali sa tion, Izera Mas sif.
INTRODUCTION
The Izera Mas sif is lo cated in the Sudetic Block (south west - ern Po land; Fig. 1) and is part of the Izera-Karkonosze Mas sif.
The cen tral part of the Izera-Karkonosze Mas sif con sists of the Variscan-aged Karkonosze gran ite pluton (Karkonosze Mas sif;
Fig. 1) while sur round ing ar eas are com posed of older meta - mor phic rocks. The Izera Mas sif forms the north ern en ve lope of the Karkonosze gran ite pluton. The mas sif re cords ex ten sive lat eral ev i dence of both ther mal and metasomatic con tact meta mor phism. The Intra-Sudetic Fault Zone runs along the north ern bor der of the Izera Mas sif. To the west, the Izera Mas - sif bor ders the neigh bour ing Lusatian Mas sif.
The ra don iso topes 222Rn (re ferred to as “ra don”, T1/2 = 3.82 d) and 220Rn (re ferred to as “thoron”, T1/2 = 55.6 s) be long to the
238U and 232Th de cay se ries and oc cur as in ert, ra dio ac tive gases. The mech a nism by which 222Rn and 220Rn dif fuses from min er als, soil and other regolith is not fully un der stood (Neznal et al., 1996; Ishimori et al., 2013; Malczewski and Dziurowicz, 2015). At mo spheric 222Rn con cen tra tions nor mally range from 4 to 19 Bq m–3, whereas soil 222Rn con cen tra tions vary be tween
~4 and 40 kBq m–3 (Eisenbud and Gesell, 1997).
Malczewski and Żaba (2007) pre sented a com pre hen sive sur vey of ra don and thoron con cen tra tions in soil gas of the Izera-Karkonosze Mas sif. The pres ent con tri bu tion re ports and in ter prets the re la tion ship be tween Rn iso tope con cen tra tions and sam pling depths within soils de vel oped in as so ci a tion with
fault zones and ura nium min er ali sa tion. This pa per also com - pares 222Rn con cen tra tions mea sured at 80 cm depth with re - sults ob tained by pre vi ous stud ies of the Izera Mas sif (e.g., Wołkowicz, 2007).
GEOLOGICAL SETTING
The Izera Mas sif con sists mainly of gneiss es, gran ite -gneiss - es, gran ites, granodiorites, leucogneisses, leuco gra nites and mica schists. Hornfelses, leptinites, grei sens, skarns, erlans, am - phi bo lites, quartzites and quartz veins are rare but pres ent. The Izera gran ites were emplaced by Early Pa leo zoic (Cam brian to Or do vi cian) magmatism. The gran ites, grano diorites and gneiss - es from the east ern part of the Izera Mas sif have been dated us - ing sev eral dif fer ent meth ods and span a gen eral age range of 550–460 Ma (Borkowska et al., 1980; Jarmołowicz-Szulc, 1984;
Korytowski et al., 1993; Kröner et al., 2001).
The Izera gneiss es are thought to be a polygenic group.
Most were formed by de for ma tion of the Izera gran ite (Oberc - -Dziedzic et al., 2005). The orthogneisses are mainly flaser gneiss es and flaser-augen gneiss es. Their de for ma tion oc - curred over mul ti ple ep i sodes from the Early Pa leo zoic to the Penn syl va nian. A sub set of gneiss es in clud ing lam i nated gneiss es or lam i nated augen gneiss es prob a bly re flects meta - mor phism of Neoproterozoic supracrustal se ries (Żaba, 1984).
The protoliths were Neoproterozoic pelites such as clay rocks and mudstones. Mica-schists (supracrustal se ries) en velop the in tru sive Izera gran ites (Oberc-Dziedzic et al., 2005) and form four par al lel belts (Fig. 1). Mica-schists were meta mor phosed at greenstone or am phi bo lite fa cies (Żaba, 1985; Cook and Dudek, 1994). Mica-schists from the Szklarska Poręba belt and from part of the Stara Kamienica belt have been meta mor - phosed to cor di er ite-an da lu site-bi o tite hornfelses.
* Corresponding author, e-mail: dariusz.malczewski@us.edu.pl Received: April 27, 2017; accepted: July 18, 2017; first published online: September 11, 2017
The Izera Mas sif for ma tions ex pe ri enced sev eral ep i sodes of de for ma tion (¯aba and Teper, 1989; Mierzejewski and Oberc -Dziedzic, 1990; Mazur and Kryza, 1996). The Izera Mas sif is cut by nu mer ous faults run ning E–W, NW–SE, N–S and NE–SW (Fig. 1). The old est E–W-trending faults fre quently formed in as so ci a tion with the schist belts and gen er ally run par al lel to them. Multiphase fault-re lated ac tiv ity and as so ci ated metasomatic pro cesses (Smulikowski, 1972; Koz³owski, 1974;
¯aba, 1984) re sulted in the for ma tion of leucogneisses, leuco - granites and leptinites (Fig. 1). Metasomatic pro cesses have pro duced sev eral dif fer ent va ri et ies of greisen (Fig. 1), which com monly ex hibit ore-bear ing min er ali sa tion. Polymetallic min - er ali sa tion also oc curs within the Stara Kamienica schist belt (Cook and Dudek, 1994; Mochnacka et al., 2015). Ura nium and tho rium min er ali sa tion oc curs through out the Izera Mas sif (Mochnacka and Banaœ, 2000).
MATERIALS AND METHODS
Mea sure ments of soil 222Rn and 220Rn con cen tra tions were per formed us ing a RAD7 por ta ble ra don anal y sis sys tem (Fig.
2). The de tec tor op er ates with a sen si tiv ity of 4 Bq m–3 and an up per lin ear de tec tion limit of 800 kBq m–3. The up per range can be in creased us ing a pe riph eral de vice. Af - ter in sert ing the stain less steel probe at the spec i fied sam pling depth (10, 40 and 80 cm), the sam pling out let was con nected to the in let of the RAD7 via a dry ing tube.
The soil gas mea sure ments were car ried out in sniff mode. In this mode, the built-in pump runs con tin u ously and 222Rn and
220Rn con cen tra tions are cal cu lated from the data in elec tronic win dows A and B, re spec tively. The cy cle time was 15 min and three cy cles were per formed for all mea sure ments. An av er age of these three cy cles pro vided re sults re ported for a given depth. Be fore each mea sure ment, the RAD7 was pur ged for at least 10 min, or lon ger if the pre vi ous anal y sis de tected high ra - don and thoron con cen tra tions. Fig ure 3 shows sam pling lo ca - tions de scribed in Ta ble 1.
RESULTS AND DISCUSSION
Ta bles 2 through 5 re port pa ram e ters de rived from fit ting
222Rn and 220Rn data to sam pling depths. All of the fit ting pa ram - e ters are valid for sam pling depths in the range of 10 to 80 cm.
878 Dariusz Malczewski and Jerzy ¯aba
Fig. 1. Geo log i cal map of the Izera Mas sif area, show ing mea sure ment lo ca tions 1–17 – lo ca tions of in situ mea sure ments
Fig. 2. The 16, 46 and 100 cm gas probes and RAD7 de tec tor
222Rn and 220Rn con cen tra tions in soil gas of the Izera Mas sif (Sudetes, Po land)... 879
Fig. 3. Pho tos of ra don and thoron sam pling lo ca tions
A – lo ca tion 1 (Radoniów), B – lo ca tion 2 (Proszówka), C – lo ca tion 3 (Proszówka – Gryf Cas tle), D – lo ca tion 4 (Mroczkowice), E – lo ca tion 5 (Pobiedna), F – lo ca tion 6 (Pobiedna), G – lo ca tion 7 (Gierczyn), H – lo ca tion 8 (Kotlina), I – lo ca tion 9 (Opaleniec Mt.), J – lo ca tion 10 (Świeradów Zdrój – SE area), K – lo ca tion 11 (Izerski Stóg Mt.), L – lo ca tions 12 and 13 (Wojcie - szyce), M – lo ca tion 14 (Rozdroże Izerskie), N – lo ca tion 15 (Szklarska Poręba Dolna – Mniszy Las), O – lo ca tion 16 (Szklarska Poręba Dolna – Zbójeckie Skały), P – lo ca tion 17 (Szklarska Poręba Średnia)
CONCENTRATIONS OF 222Rn AND 220Rn IN SOILS DEVELOPED WITHIN FAULT ZONES
Sam pling points lo cated within fault zones (lo ca tions 9–11) showed ex po nen tial de pend ence of 222Rn on sam pling depth (Fig. 4). The same pat tern was also ob served for 220Rn at lo ca -
tions 9 and 11 (Fig. 4). Con cen tra tion vs. depth pro files can be de scribed by the ex po nen tial func tion:
C222/220(Bq m–3) = A exp (b × d) [1]
where: d is the depth (cm).
Ta ble 2 lists cal cu lated val ues for A, b and the 222Rn and
220Rn con cen tra tions at a depth of 80 cm. Con cen tra tions of
220Rn at lo ca tion 10 do not ad here to Eq. [1] be cause the sam - ple lo ca tion oc curred on a steep slope. For slope sam ple lo ca - tions, 220Rn con cen tra tion showed a pro nounced in verse re la - tion ship with depth whereby the con cen tra tion sig nif i cantly de - creased with in creas ing depth (Malczewski and Żaba, 2007).
As shown in Ta ble 2, lo ca tion 9 (Opaleniec Mt.) gave the high - est b term val ues for both 222Rn and 220Rn (0.123 and 0.135, re spec tively). The high est 222Rn con cen tra tion (282 kBq m–3) was re corded at lo ca tion 11, whereas the high est 220Rn con - cen tra tion (29 kBq m–3) was re corded at lo ca tion 9 (Ta ble 2).
En hanced ra don flux has been in ter preted as an in di ca tor of ac tive fault zones since the 1970s. King (1978) re ported an ex - po nen tial trend of ra don con cen tra tion vs. depth on the San Andreas Fault.
Neznal et al. (1996) re ported the high est val ues of 222Rn con cen tra tions among the sam pling points, reach ing 100–120 kBq m–3. These val ues oc curred in soils at a depth of 80 cm at lo ca tions in the test area (Chaby area, Prague, the
880 Dariusz Malczewski and Jerzy Żaba
T a b l e 1 Lo ca tion of in situ mea sure ments
No. Lo ca tion Rocks Tec ton ics
1. Radoniów – closed ura nium mine
Fine-grained augen gneiss es with gran ite-gneiss es, leucogneisses, leucogranites, leptinites, mica-schists
and am phi bo lites
2. Proszówka Augen gneiss es NE–SW-trending fault nearby
3. Proszówka – Gryf Cas tle Con tact be tween Ce no zoic bas alts and
augen gneiss es Vol ca nic fea tures in the area fol low a NE–SW-trending fault zone 4. Mroczkowice near Mirsk –
Wyrwak Hill Grei sens WNW–ESE-trending fault zone run ning par al lel
along the north ern bor der of the Mirsk schist belt 5. Pobiedna – closed ura nium mine Augen gneiss es with symp toms
greisenization
Fault zones trending N–S and NE–SW, cre at ing a dis tinct tec tonic loop in the area 6. Pobiedna – old ura nium
pros pect ing drift Augen gneiss es and gran ite-gneiss es Re gion cut by a NE–SW-trending fault zone 7. Gierczyn – Blizbor Hill Mica-schists (ore-bear ing min er al isa tion)
8. Kotlina Leptinites The leptinites fol low an old E–W-trending fault
zone, run ning along the south ern bor der of the Stara Kamienica schist belt
9. Świeradów Zdrój (Czerniawa) –
Opaleniec Mt. Leucogranites
Units near two fault zones: an older E–W-trending fault zone along the south ern bor der of the Stara
Kamienica schist belt and a slightly youn ger N–S-trending fault zone
10. Świeradów Zdrój – SE area Lam i nated augen gneiss es Gneiss es oc cur at the in ter sec tion of a WNW–ESE-trending fault and a slightly youn ger
NE–SW fault zone 11. Izerski Stóg Mt. Fine-grained flaser-augen gneiss es Area cut by a dis tinct N–S fault zone 12. Wojcieszyce – closed
ura nium mine Augen gneiss es and gran ite-gneiss es Con tact zone of the Variscan Karkonosze gran ites 13. Wojcieszyce – closed
ura nium mine Augen gneiss es Con tact zone of the Variscan Karkonosze gran ites 14. Rozdroże Izerskie – closed
quarry Quartz vein The fault zone runs NE–SW; zone cut by nu mer -
ous youn ger, trans verse, NW–SE trending faults 15. Szklarska Poręba Dolna –
Mniszy Las Hornfelses Con tact zone of the Variscan Karkonosze gran ites
16. Szklarska Poręba Dolna –
Zbójeckie Skały Hornfelses Con tact zone of the Variscan Karkonosze gran ites
17. Szklarska Poręba Średnia Hornfelses Con tact zone of the Variscan Karkonosze gran ites
T a b l e 2 Fit ted pa ram e ters for the ex po nen tial func tion given
by Eq. [1] (see text)
Lo ca tion
222Rn
A b C80 (kBq m–3)
9 10 0.123 186.0 ±5.2
10 149 0.087 157.0 ±4.6
11 182 0.092 282.0 ±7.1
Lo ca tion 220Rn
9 0.581 0.135 29.2 ±4.2
11 653 0.043 20.4 ±2.8
Un cer tain ties es ti mated for pa ram e ters are ≤10%; C80 re fers to the av er age ac tiv ity con cen tra tions of 222Rn and 220Rn at 80 cm depth
Czech Re pub lic) where there are tec tonic zones with trans - verse faults. Barnet and Pacherová (2015) re corded av er age val ues of 222Rn con cen tra tions that ranged from 12 to 22 kBq m–3 and 18 to 60 kBq m–3 in sites lo cated in con tact zones (granitoids or migmatites with sand stones, and tra chytes with Cre ta ceous sed i ments; Klatovy, Kytlice, Veseli nad Lužnici and Chrudim ar eas, the Czech Re pub lic) at depths of 50 and 80 cm, re spec tively. Al-Tamimi and Abumurad (2001) re ported the soil ra don con cen tra tions that ranged from 25 to 60 kBq m–3 at 50 cm depth along faults in Wadi um Ghudram and Wadi Es-sir For ma tion (N Jor dan).
Lower 222Rn and 220Rn soil gas con cen tra tions than those pre sented here were re ported by Al-Hamidawi et al. (2012) in the vi cin ity of Al-Kufa city (Iraq), which is cut by fault zones lo - cated in sand stones. They ob served av er age 222Rn con cen tra - tions of 3630, 4411 and 4717 Bq m–3, and the 220Rn con cen tra - tions of 13, 65, and 84 Bq m–3 at sam pling depths of 50, 100 and 150 cm, re spec tively. Sim i lar low val ues in the range of 29 to 7059 Bq m–3 at 50 cm depth were re ported for soil ra don mea - sure ments around fault lines in the west ern part of the north Ana to lian fault zone (Tur key) by Yakut et al. (2017).
CONCENTRATIONS OF 222Rn AND 220Rn IN SOILS DEVELOPED ABOVE URANIUM DEPOSITS
WITHOUT FAULT ZONES
Lo ca tions 1 and 12 rep re sent known ura nium de pos its and ex hib ited lin ear re la tion ships be tween 222Rn con cen tra tions and soil depth (Fig. 5). Lo ca tion 1 also showed lin ear 220Rn vs. depth re la tions (Fig. 5). This in di cates that tho rium fol lows a dis tri bu tion sim i lar to that of ura nium at lo ca tion 1. The 222Rn con cen tra tion vs. depth re la tion at lo ca tions 1 and 12, and 220Rn con cen tra tions vs. depth at lo ca tion 1 can be fit ted by the lin ear ex pres sion:
C222/220(Bq m–3) =A + (b × d) [2]
Ta ble 3 lists cal cu lated val ues for A and b along with 222Rn and 220Rn con cen tra tions at 80 cm depth. As with lo ca tion 10, lo ca tion 12 also oc curred along a slope and ex hib ited in verse
220Rn con cen tra tion vs. depth re la tions. Sim i lar 220Rn con cen - tra tion val ues at depths of 10, 40 and 80 cm from lo ca tion 12 likely re flect in ter ac tions be tween in verse and lin ear in flu ences on 220Rn con cen tra tions (Fig. 5).
222Rn and 220Rn con cen tra tions in soil gas of the Izera Mas sif (Sudetes, Po land)... 881
Fig. 4. 222Rn (red cir cles) and 220Rn (blue cir cles) con cen tra tion vs. sam pling depth at mea sure ment
points lo cated within fault zones Solid lines rep re sent ex po nen tial fit Eq. [1];
R2 – co ef fi cient of de ter mi na tion
CONCENTRATIONS OF 222Rn AND 220Rn IN SOILS DEVELOPED ABOVE FAULT ZONES
WITH URANIUM MINERALISATION
Lo ca tions 5 and 6 (600 m apart) were lo cated in Pobiedna amid both fault zones and ura nium de pos its. At these sites,
222Rn con cen tra tion vs. depth mea sure ments can be fit ted by a sec ond or der poly no mial func tion (Fig. 6):
C222 (Bq m –3) = A + (b1 × d) + (b2 × d2) [3]
Ta ble 4 lists cal cu lated val ues for A, b1, b2 and the 222Rn con cen tra tions at 80 cm depth. As shown in Ta ble 4, lo ca tion 6 pro vided the high est 222Rn con cen tra tion (~2.2 MBq m–3) ob - served in the Izera Mas sif. The high est soil gas 222Rn con cen - tra tion was also re corded in Pobiedna (~7 MBq m–3) dur ing ura - nium ore pros pect ing ac tiv i ties from 1945–1954 (Solecki, 1997). The ob served de vi a tion from lin ear ity (Fig. 6) prob a bly re sults from en hanced gas flow along fault zones in the area (Malczewski and ¯aba, 2007). Lo ca tion 5 ex hib ited a sim i lar poly no mial depth de pend ence of 220Rn (Fig. 6 and Ta ble 4). Be - cause the RAD7 counts be came non-lin ear at 80 cm depth, the ex act 220Rn con cen tra tion at lo ca tion 6 could not be de ter - mined.
Goodwin et al. (2008) mea sured soil gas 222Rn con cen tra - tions that ranged from 0.1 to 207 kBq m–3 with a mean of 25 kBq m–3 at a depth of 60 cm. These val ues were ob tained from 72 sam pling points in Nova Sco tia (Can ada). Nova Sco tia is char - ac ter ized by ar eas of el e vated back ground lev els and oc cur - rences of ura nium. The same au thors re ported soil gas ra don
con cen tra tions of 500 to 1500 kBq m–3 that were as so ci ated with the well-known Milet Brook ura nium de posit. These val ues are sim i lar to those pre sented here at lo ca tions 1 (Radoniów) and 6 (Pobiedna).
CONCENTRATIONS OF 222Rn AND 220Rn IN TYPICAL SOILS
In typ i cal soils (with out fault zones and/or ura nium min er al - isa tion) both the 222Rn and 220Rn con cen tra tions vs. depth fol low a power func tion:
882 Dariusz Malczewski and Jerzy ¯aba
Fig. 5. 222Rn (red cir cles) and 220Rn (blue cir cles) con cen tra tions vs. sam pling depth at mea sure ment points lo cated above ura nium de pos its
Solid lines rep re sent lin ear re gres sions – Eq. [2]; R – cor re la tion co ef fi cient
T a b l e 3
Fit ted pa ram e ters for the lin ear ex pres sion given by Eq. [2] (see text)
Lo ca tion
222Rn
A b C80 (kBq m–3)
1 11981 5126 420.0 ±10.6
12 –10552 1827 131.0 ±4.2
Lo ca tion 220Rn
1 998 166 13.7 ±3.2
Un cer tain ties es ti mated for the pa ram e ters are £10%.
C80 re fers to the av er age ac tiv ity con cen tra tions of 222Rn and 220Rn at 80 cm depth
C222/220(Bq m–3) = A × dp [4]
with the ex po nent p <1 (Ta ble 5). Fig ure 7 shows depth con - cen tra tions of 222Rn and 220Rn in soils de vel oped on grei sens (lo ca tion 4) and hornfelses (lo ca tion 15). As seen in Ta ble 5, the cal cu lated p value for 222Rn at lo ca tion 4 is no tice ably higher than that cal cu lated for 220Rn. Lo ca tion 15, how ever, gave com - pa ra ble p val ues (within un cer tain ties).
Wang et al. (2016) re ported av er age 222Rn and 220Rn con - cen tra tions of 130 and 188 kBq m–3, re spec tively, at a depth of 80 cm in soils de vel oped on weath ered gran ite (S China).
These val ues ex ceeded those ob tained in our work at lo ca - tions 4 and 15. For se lected sites in the in ves ti gated area, the au thors showed an al most ex act log a rith mic in crease of 222Rn con cen tra tions with sam pling depths from 20 to 160 cm at in -
ter vals of 20 cm. No rule was ob served for the 220Rn con cen - tra tions (Wang et al., 2016). Almayahi et al. (2013) ob tained ra don and thoron con cen tra tions at a depth of 50 cm in North - ern Pen in su lar Ma lay sia that ranged from 134 Bq m–3 to 143 kBq m–3, and 55 to 423 Bq m–3, re spec tively. The mea - sure ments were taken in soils mostly de vel oped on gra nitic rocks, and the cal cu lated av er age ra don con cen tra tion was 29 kBq m–3 (Almayahi et al., 2013). Elzain (2017) has re cently re ported 222Rn con cen tra tions rang ing from 4.2 to 15.2 kBq m–3 with an av er age of 9.1 kBq m–3 in soils formed mainly on ba saltic rocks in the east ern part of Su dan. In the pa per, the
222Rn con cen tra tions in creased with sam pling depth from 10 to 50 cm at in ter vals of 5 cm (Elzain, 2017).
222Rn and 220Rn con cen tra tions in soil gas of the Izera Mas sif (Sudetes, Po land)... 883
Fig. 6. 222Rn (red cir cles) and 220Rn (blue cir cles) con - cen tra tions vs. sam pling depth at mea sure ment points lo cated above ura nium de pos its and fault zones
Solid lines rep re sent poly no mial re gres sions – Eq. [3];
R2 – co ef fi cient of de ter mi na tion
T a b l e 4 Fit ted pa ram e ters for the poly no mial func tion given
by Eq. [3] (see text)
Lo ca tion
222Rn
A b1 b2 C80 (kBq m–3)
5 –202647 20149 5124 2200 ±22.6
6 –17604 1676 11 187.5 ±10.6
Lo ca tion 220Rn
6 –47 –21 4.1 24.3 ±3.8
Un cer tain ties es ti mated for the pa ram e ters are £10%. C80 re fers to the av er age ac tiv ity con cen tra tions of 222Rn and 220Rn at 80 cm depth
T a b l e 5 Fit ted pa ram e ters for the power func tion given
by Eq. [4] (see text)
Lo ca tion
222Rn
A p C80 (kBq m–3)
4 2140 0.856 88.9 ±3.1
15 1798 0.640 27.4 ±1.5
Lo ca tion 220Rn
4 3689 0.353 16.1 ±2.7
15 560 0.732 13.0 ±2.1
Un cer tain ties es ti mated for the pa ram e ters are £20%. C80 re - fers to the av er age ac tiv ity con cen tra tions of 222Rn and 220Rn at 80 cm depth
Sim i lar to the fault zones, con sid er ably lower val ues of
222Rn con cen tra tions were re ported for soils de vel oped on sand stones (Hasan et al., 2011; Alharbi and Abbady, 2013).
Hasan et al. (2011) pre sented soil gas 222Rn con cen tra tions of 788, 1490, 2128 and 3273 Bq m–3 in the vi cin ity of Al-Najaf Al-Ashart city (Iraq) at depths of 5, 25, 35 and 60 cm, re spec - tively. Alharbi and Abbady (2013) re corded av er age ra don con - cen tra tions of 123, 163 and 220 Bq m–3 in the Al-Quassim area (Saudi Ara bia) at depths of 20, 40 and 60 cm, re spec tively.
AVERAGE DEPTH CONCENTRATIONS OF 222Rn AND 220Rn IN SOILS FROM THE IZERA MASSIF
Fig ures 8 and 9 com pare 222Rn con cen tra tions at 80 cm ob - tained by Malczewski and ¯aba (2007) with those re ported by Wo³kowicz (2007). As seen in Fig ure 8, Wo³kowicz (2007) re - ported av er age 222Rn val ues nearly three times lower than val - ues pre sented here. This dis crep ancy likely re flects the el e - vated ra don con cen tra tions ob served in fault zones. Wo³kowicz
884 Dariusz Malczewski and Jerzy ¯aba
Fig. 7. 222Rn (red cir cles) and 220Rn (blue cir cles) con cen tra tions vs. sam pling depth at mea sure ment points lo cated in typ i cal soils (with out ura nium de pos its or fault zones)
Solid lines rep re sent power func tion fits – Eq. [4]; R2 – co ef fi cient of de ter mi na tion
Fig. 8. Av er age 222Rn (red bars) and 220Rn (blue bars) con cen tra tions of soil gas in the Izera Mas sif at spec i fied depths
(2007) avoided fault zones whereas this re search did not. Re - sults re ported in Wo³kowicz (2007) are con sis tent with those re - ported here, which were de rived from lo ca tions with out fault zones and ura nium de pos its (Fig. 9).
CONCLUSIONS
Re sults of 222Rn and 220Rn con cen tra tions vs. depth in the Izera Mas sif have shown dif fer ent pat terns de pend ing on the bed rock li thol ogy, ura nium min er al isa tion, and oc cur rence of fault zones. In soils de vel oped above fault zones, a pro - nounced ex po nen tial re la tion ship be tween 222Rn con cen tra -
tions and depth was ob served. This re la tion ship may char ac - ter ize ac tive fault zones. Ex clud ing fault zones and ura nium de pos its, the av er age 222Rn con cen tra tions at 80 cm depth pre sented in this work re sem ble val ues re ported for Izera Mas - sif soils by pre vi ous re search.
Ac knowl edge ments. This work was sup ported by the Na - tional Sci ence Cen tre, Po land, through grant No.
2014/15/B/ST10/04095. We thank S. Wo³kowicz and A.T. Sole - cki for crit i cal com ments that im proved the fi nal ver sion of this pa per. The au thors also thank T.M. Peryt for his help and ed i to - rial guid ance.
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886 Dariusz Malczewski and Jerzy Żaba
