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Mineral. Deposita 31,514 522 (1996)
MINERALIUM DEPOSITA �9 Springer-Verlag 1996
The authigenic zeolites of the Aritayn Volcaniclastic Formation, north-east Jordan
K. Ibrahim*, A. Hall
Department of Geology, Royal Holloway University of London, Egham, Surrey, TW20 0EX, UK
Received: 12 December 1994/Accepted: 10 April 1996
Abstract. In the Ar i t ayn Volcaniclas t ic F o r m a t i o n , the fo rmat ion of zeolites is associa ted with the t r ans fo rmat ion of s ideromelane into pa lagoni te by react ion with percolat - ing water in an open hydro log ica l system. Three vert ical zones are described, charac ter i sed by fresh s ideromelane at the top (zone 1), pa lagoni te -smect i te in the middle (zone 2), and zeolites at the b o t t o m (zone 3). With in zone 3, a phillipsite-chabazite sub-zone overlies a faujasite - phillipsite sub-zone. The paragenetic sequence (fresh sideromelane pa lagoni te --, smecti tes (saponi te --, montmor i l lon i t e ) --, faujasite --, phil l ipsi te --, chabazi te ~ nat ro l i te ~ calcite) resembles those descr ibed in the l i terature, except for the early fo rmat ion of smectites in the Jo rdan i an occurrences. Faujas i te is more a b u n d a n t in these zeolit ic tufts than at any o ther local i ty in the world that has yet been described, and the tufts are cons idered to have excellent potent ia l for beneficiation.
Geological setting
The Cenozoic continental basalts of northeast Jordan are part of a major volcanic province which outcrops continuously from Syria across Jordan into Saudi Arabia, covering approximately 45 000 km 2. The province trends from NW to SE and is truncated on the western side by the Gulf of Aqaba Dead Sea fault system. In Jordan, about 11 415 km 2 of plateau lavas are exposed, and were mapped as the Harrat Ash-Shaam Basaltic Super-Group (HASB) (lbrahim 1993). The HASB is predominantly made up of alkali basalt to basanite, with an age range from 13 Ma to less than 0.5 Ma established by K-Ar dating (Barberi et al. 1979: Moftat 1988). De- tailed petrological studies suggest derivation from an upper mantle source by variable but always low degrees of partial melting+ with limited secondary differentiation (Barberi et al. 1979; Khalil 1991). The HASB is subdivided into three basaltic groups of Neogene age and one of Quaternary age, separated by the Quaternary Rimah Pyroclastic Group. The Rimah Group comprises a variety of scoriaceous deposits and bedded tufts, the latter being designated as the Aritayn Volcaniclastic Formation.
Zeoli tes are c o m m o n authigenic minera ls in sed imenta ry rocks of volcanic origin, but it was not until 1987 that the first zeoli te (phillipsite) depos i t was discovered in Jo rdan (Dwair i 1987). This phil l ipsi te was found in the volcanic tuff of the Jaba l Ar i t ayn volcano in nor theas t Jordan , where it occurs as a cement ing mater ia l between tuff granules. Recent deta i led geological mapp ing on the scale of 1 : 50 000 has led to the discovery of add i t iona l locali t- ies, and indicates tha t the zeol i t iza t ion is of regional extent ( Ibrah im 1993). This s tudy describes deposi ts conta in ing diagenet ic faujasite, phill ipsite, and chabazi te occurr ing at seven locali t ies in the Ar i tayn Volcaniclas t ic F o r m a t i o n (Fig. 1).
Correspondence to: A. Hall * Present address: Geology Directorate, Natural Resources Author- ity, P.O. Box 7, Amman, Jordan
Methods of study
Both vertical and horizontal sampling were performed at the follow- ing localities of the Aritayn Volcaniclastic Formation: Tell Rimah, Jabal Aritayn (north), Jabal Aritayn (south), Jabal Ashqaf, Jabal Hannoun+ Tell Muftyyah, and Jabal Tarboush. These localities are indicated in Fig. 1.
The mineral content of all samples was determined by X-ray powder diffraction using a Philips PW 1700 automatic powder difiYactometer with CoK~ radiation. For some of the samples the zeolites were first enriched using the procedure of de'Gennaro and Franco (1979). The patterns were obtained by step-scanning from 3 50' 20 in steps of 0.015 with a counting time of 1 s per step. Oriented mounts of the <2 txm grain size fraction were also pre- pared for the identification of clay minerals.
Polished and normal thin sections were prepared for optical and electron microscopy. Scanning electron microscope (SEM) study was performed using a Hitachi S-2400. Electron microprobe analysis was carried out also with a Hitachi S-2400 equipped with a Link microanalyser system AN 10000 operated in the energy dispersive mode at 15 kV with a defocused beam and counting time of 60 s. The reliability of the zeolite analyses was confirmed by obtaining frame- work cations (Si + A1) very close to half of the oxygen atoms, with low balance errors (E +7%) as suggested by Passaglia (1970t. Data from the microprobe were obtained by averaging several point
Fig. 1. Simplified geological map of northeast Jordan showing the sample localities
analyses from one sample. Chemical analyses of the volcanic tuff were done by inductively coupled plasma (ICP) using a Philips PV8050 emission spectrometer,
Lithological variation
The Aritayn Volcaniclastic Formation is present in com- posite cinder cones and stratovolcanic centres. The volcanoes are almost symmetrical, with steeply dipping pyroclastic deposits interbedded with lava flows, but the pyroclastic rocks are the most important volumetrically, making up more than 85% of the succession. The forma- tion consists of stratified, sorted, poorly cemented air-fall tuff and agglomerate, rarely intercalated with short lava flows from a central vent. Lithologically, the pyroclastic rocks of the Aritayn Formation are made up of fine- grained ash, angular and spherical lapilli, and volcanic bombs of different sizes and shapes, cemented either by carbonate or by zeolites plus carbonate, or in a few cases welded together. Uncemented volcanic ash and lapilli are also present, forming tephra laminae. The pyroclastic se- quence exhibits laminations, grading, welding, and diverse clast types and morphologies. A variety of bombs and blocks are found including large scoriaceous fragments, less well vesiculated lava having spindle and cowpat shapes, sometimes bombs with a breadcrust surface, and dense lava blocks. Accessory lithic clasts include both country rock and mantle-derived xenoliths. Local vari- ations in grain size, packing, and welding of the pyroclasts are visible in the field, and are responsible for variations in the porosity and permeability of the rock.
Detailed field investigation of the Aritayn Volcaniclas- tic Formation indicates the presence of a vertical dia- genetic zonation (Fig. 2) somewhat similar to that de- scribed at Koko Crater, Hawaii by Hay and Iijima (1968a, b). The zonation is defined by the degree of altera- tion of sideromelane (basaltic glass) to palagonite. At outcrop, the zones can be recognised by their distinctive weathering colours. The surface zone (zone 1) contains
515
Fig, 2. Correlation between the diagenetic zones in the Aritayn Votcaniclastic Formation
a relatively flesh sideromelane; an intermediate zone con- tains reddish-brown palagonite which is almost free of zeolites (zone 2); and the lowest zone (zone 3) is palagonitic and rich in zeolites.
In detail, zone 1 consists mainly of massive and thick layers of welded agglomerates and welded lapilli tuff that alternate with tephra laminae, all of which contain nearly fresh sideromelane and are locally cemented by carbonate. Zone 1 is distinguished by a black to light grey colour and is variable in thickness from 10 m to 40 m. Zone 2 is t0 m to 20 m thick, and comprises palagonitised tuff composed of poorly sorted lapilli and sometimes scoria blocks, and is characterised by dark brown to reddish brown colours. Zone 3 is the zeolitic zone, where the pyroclasts are cemented by a white coating of zeolites and/or calcite. It is a distinctive yellowish to light brown colour. The degree of zeolitization is not uniform. The highly zeolitized areas contain soft and friable highly altered lapilli clasts cemented by a thick coating of zeolites and calcite. Some zeolite-bearing lenses and/or bands occur within zone 2, following the joint system. The exposed thickness of the zeolitic zone is between 6 m and 40 m. The contacts be- tween the zones are sharp and roughly follow the topogra- phy but cut across the stratification. The detailed min- eralogy of the zones and their further classification into sub-zones will be discussed later.
X-ray diffraction study indicated that phillipsite is the most abundant zeolite, and it occurs in all the analysed
516
Table 1. Zeolite contents (mean and range) of zeolitized tufts from N E Jordan
Locality Tell Rimah (N) Jabal Aritayn (S) Jabal Hannoun
Chabazite sub-zone Phillipsite (%) 22 (8 33) 35 (27 49) 27 (12 35) Chabazite (%) 24 (16 32) 25 (6 33) 20 (0 45) Faujasite (%) 0 0 0 Total zeolites (%) 46 (28 59) 57 (47-69) 47 (31-57) Number of samples analysed [13] [9] [6]
Faujasite sub-zone Phillipsite (%) 25 (16 -34) 30 (29 32) 20 (11 22) Chabazite (%) 16 (13 26) 0 0 Faujasite (%1 11 (11-11) 5 (9 26) 18 (0 30) Total zeolites (%) 52 (40 63) 45 (39 58) 38 (22 51) Number of samples analysed [4] [8] [10]
samples in zone 3. In a few cases, it is the only zeolite present, but usually it is accompanied by either faujasite or chabazite. Zone 3 can be further subdivided into a phil- lipsite chabazite sub-zone occuring at the top and a faujasite phillipsite sub-zone at the bottom. The con- tact between the sub-zones is gradational (within less than three metres) at Tell Rimah, but sharp at Jabal Aritayn and Jabal Hannoun. This pattern of zoning of zeolites has not been described previously, although Hay (1978) de- scribed somewhat similar zoning in Koko Crater, Hawaii, where analcime occupies the position of faujasite. In one locality (Jabal Tarboush) natrolite was also found, occur- ring with phillipsite and chabazite.
In the pyroclastic rocks of the Aritayn Volcaniclastic Formation as a whole, zeolites are extremely abundant (Table 1), locally making up more than half the rock. The most unusual feature of this formation is the relative abundance of faujasite, which occurs at very few other localities worldwide, and then only as a very minor phase. Its normal occurrence elsewhere is as a cavity-filling min- eral in basalt, and it has been found in palagonitised tuffat only two localities, one in Hawaii (lijima and Harada 1969) and the other in California (Wise 1982). It is not abundant at either of these localities. The richest occur- rence of faujasite in Jordan is at Jabal Hannoun, where in one series of beds about 6 metres thick the average faujasite content of the rock is 29%.
Description of the host materials
Petrography of the tufts
The fresh tuff ranges from massive, poorly cemented vitric lapilli tuff to coarse vitric ash tuff. Clasts are generally sub-angular, and mostly less than 5 mm in grain size with poor packing. However, in a few instances the clasts are welded. In addition to fresh and palagonitized sidero- melane clasts, the tuffcontains smaller amounts of crystals and lithic clasts. The crystals are mainly olivine, with smaller amounts of ortho- and clinopyroxene, and minor spinel. The lithic clasts consist of the following lithologies:-
1. Vesicular, brown to dark brown, microcrystalline ol- ivine-phyric basalt, and sometimes pyroxene-olivine- phyric basalt. 2. Sedimentary inclusions, including sandstone, limestone, quartzite, argillite, chert and phosphorite. 3. Ultramafic xenoliths, including spinel-peridotite, spinel- pyroxenite and garnet-pyroxenite.
Diagenesis involved palagonitisation of sideromelane and the formation of authigenic minerals, including zeolites, smectites and calcite. The amount of the authigenic minerals is generally proportional to the amount of palagonite in the tuff, as has been observed in previous studies (Hay and |ijima 1968a, b). In zone 3, the percentage of zeolites present in the tuff is variable. Zeolites occur chiefly in the form of a cement holding together the clasts and also lining or filling vesicles. In some examples, zeolites were also found replacing glass shards where relicts of shards are still preserved.
Chemical analyses of tufts from the different diagenetic zones are given in Table 2, and plotted in Fig. 3a, b to show the difference between their fresh and altered com- positions. Both Table 2 and Fig. 3 reveal a marked de- crease in the amount of SiO2 and Na20 from zone 1 to zone 3, accompanied by an increase in LOI (loss on ignition), i.e. H 2 0 and CO2. The rest of the elements show a relatively smaller variation between the original and the altered tuff. An important feature is the strong depletion of Na20 in the phillipsite-chabazite sub-zone, and its relative enrichment in the lower faujasite-phillipsite sub- zone.
Sideromelane
The fresh sideromelane forms a greenish to light brown, hypohyaline, texturally uniform glass with fresh olivine phenocrysts. Curved perlitic cracks are marked by dark brown to black staining. Some microlites and crystallites of pyroxene and plagioclase are present. Vesicles are mostly rounded, and are of varying sizes. They are some- times encrusted by a rim of calcite.
Tab
le 2
. C
hem
ical
ana
lyse
s of
tuf
ts f
rom
dif
fere
nt d
iage
neti
c zo
nes
of t
he
Ari
tay
n V
olca
nicl
asti
c F
orm
atio
n
Fres
h tu
ff Pa
lago
nitic
tuf
f Ph
illip
site
-Cha
bazi
te t
uff
Fauj
asite
Phi
llips
ite t
uff
J58
J64
J68C
J7
7 J8
4 J3
8 J4
1 J4
2 J7
4 J7
6 J9
J1
3 J1
7 J2
7 J3
0 J3
3 J3
7 J4
9 J5
1 J5
5
SiO
2
42.2
0 41
.73
43.0
7 43
.52
42.3
9 A
lzO
3 12
.64
11
.82
12
.82
13.4
0 14
.04
Fe2
0 3
13
.37
13
.70
15
.20
12.2
4 1
2.3
5
Mg
O
CaO
N
a20
K
20
T
iO 2
P
2O
s M
nO
L
OI
To
tal
9.40
10
.77
9.17
10
.91
9.79
9.
35
7.68
8.
69
9.32
9.
72
3.13
4.
04
4.03
2.
50
2.88
1.
49
2.07
1.
54
1.34
1.
30
2.34
2.
57
2.91
2.
58
2.59
0.
62
0.73
0.
74
0.42
0.
48
0.18
0.
18
0.20
0.
15
0.17
3.
39
2.37
1.
55
3.53
2.
62
98.1
1 97
.66
99.9
2 9
9.9
1
98.3
3
37.0
9 37
.72
38.6
5 40
.66
41.0
2 9.
56
9.71
9.
93
12
.53
1
3.0
8
13.0
3 1
3.2
2
12
.81
11
.54
11.8
0 14
.69
13
.66
12
.66
10.8
2 9.
16
7.68
7.
53
8.35
9.
96
9.28
1.
38
1.17
1.
17
1.89
1.
74
1.29
1.
19
1.46
1.
02
0.90
2.
06
2.24
2.
19
2.23
2.
39
0.76
0.
78
0.76
0.
42
0.42
0.
18
0.19
0.
18
0.16
0.
15
10.7
5 10
.60
10.6
1 7
.55
10
.00
98.4
7 9
8.0
1
98.7
7 98
.78
99.9
4
39.4
0 34
.98
34
.81
33
.76
35.3
0 12
.73
10
.77
11
.24
11
.57
1
1.7
5
11.4
5 9.
48
9.63
9.
84
10
.34
7.
44
7.10
7.
30
9.92
10
.68
6.52
12
.67
9.36
9.
48
8.25
0.
26
0.46
0.
42
1.24
1.
50
1.84
1.
05
1.65
1.
98
1.78
2.
56
2.10
2.
13
2.11
2.
16
0.42
0.
47
0.39
0.
38
0.35
0.
16
0.13
0.
13
0.13
0.
13
16.0
0 1
9.9
2
20.4
3 1
8.1
9
17.9
9
98.7
8 99
.13
97.4
9 98
.60
100.
23
35.6
0 35
.59
35.6
4 34
.09
36.5
5 1
1.1
3
11
.32
1
1.1
6
10.4
3 10
.81
10
.59
11
.00
12.2
0 11
.72
12.1
4 9.
73
9.42
7.
40
6.88
6.
63
6.44
6.
46
9.08
8.
67
7.74
2.
43
2.62
2.
42
3.42
1.
97
1.60
1.
56
1.29
0.
85
1.16
2.
19
2.30
2.
10
2.05
2.
08
0.32
0.
33
0.55
0.
58
0.51
0.
13
0.14
0.
17
0.16
0.
17
18.2
2 18
.72
15
.96
19
.52
18.7
3
98.3
8 99
.46
97.9
7 98
.37
98.4
9
~ ~
~'~
--
~
F,'
~
'<
~ ~
m'~
~ m
~.='
~ o
- ~
-~
-.
~"
~.
' O
"~
.~
~,.
~
~"<
~
'O
~-"
O..
"---
_ ~
__
O
o0
o~
~ ~
'~.~
=~
=
=re
~
< ~
e0
"~
="~
~
'~.:
s-~
;~
o
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2.
--
~.
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~-
.~c~
~.~
':~
-~:~
~
. ~-
: O
,-~
t.,,
~,"
~
~,~
..--
~
"~-'
.~
= ~
-",-
, f~
~-
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0
- i-~
~
kJ
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,, ..~
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�9
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~-
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~" ~
o-~
~~
N
~.~
o
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-.,
~@
3:=
<
=~
='e
" e~
.
>~
_=
.=
~..=
:" =~
~.
.N
~,~
9"
o-
o
K2
0 W
t%
0
~
~
tO
O
O
o O
O
09
4 ~
.
(Na
20
+K
20
) W
t%
Ix9
CO
.~
O'1
O~,
! i
i !
| i
G
�9
E
I~0
:/"
518
Table 3. Chemical analyses of fresh sideromelane, palagonite and saponite from the Aritayn Volcaniclastic Formation
Fresh sideromelane Palagonite Saponite J54 J58 J77 J90 J91 J19 J29 J36 J50 J59 J19 J29 J66 J67
SiO2 45.04 45.27 46.36 44.92 44.28 36.64 26.34 33.65 38.87 23.96 42.40 42.98 47.19 44.79 TiO2 3.32 3.44 4.32 3.69 3.12 6.67 13.56 7.77 5.65 10.48 n.d n.d 0.02 0.08 A1203 15.31 16.20 15.83 16.25 16.34 7.81 4.39 9.80 9.78 5.63 11.27 9.20 11.86 15.19 Fe203 12.18 11.80 9.07 11.29 12.62 25.90 32.20 24.75 25.35 39.32 1.53 1.75 0.60 1.27 MnO 0.27 0.25 0.49 0.28 0.16 n.d n.d 0.39 0.20 1.11 n.d n.d n.d n.d MgO 9.02 4.08 4.41 4.74 5.15 4.36 4.56 8.33 1.33 2.28 25.43 24.17 21.90 23.86 CaO 6.35 10.78 11.10 1 1 . 2 1 10.24 4.05 3.81 1.87 5.82 3.79 1.21 1.13 1.32 1.10 Na20 4.61 3.29 3.60 3.74 2.77 0.33 0.48 0.44 0.58 0.64 0.07 0.13 0.23 0.12 K20 1.72 2.16 2.30 2.07 2.00 0.50 0.50 0.48 0.16 0.42 0.18 0.26 0.22 0.12 P205 0.35 0.51 0.18 0.64 0.86 n.d n.d n.d n.d 0.04 n.d n.d n.d n.d
Total 98.16 97.77 97.67 98.83 97.54 86.26 85.83 87.48 87.74 87.66 82.08 79.62 83.34 86.53
enriched in Fe and Ti compared with the fresh sidero- melane. Also, in contrast to the fresh sideromelane, the chemical composition of palagonite is rather variable, depending on the degree of palagonitization. As has been noticed by many authors, the Fe and Ti contents of the palagonite are proportional to the degree of the palagonit- ization of the sideromelane (Hay and Iijima 1968a, b; Fumes 1980).
The authigenic minerals
Faujasite
Faujasite occurs in colourless, equant, isotropic, isolated or aggregated crystals that are 50 to 100 ~tm in size. It sometimes grew directly on the vesicle walls and was sometimes preceded by smectite. In many instances it forms a continuous isotropic rim enclosing palagonite clasts and preceding the crystallisation of phillipsite. This was previously interpreted by Dwairi (1987) as an amorphous aluminosilicate gel. Scanning electron micro- scopy shows that the mineral occurs in the form of octa- hedral crystals, sometimes with spinel twinning (Fig. 4a).
The average compositions of faujasite, phillipsite and chabazite in a selection of specimens are given in Table 4. Faujasite is lower in potassium than the other zeolites and has a higher water content. Its Na/Ca ratios fall within the range for the other zeolites (Fig. 5), Additional details on the occurrence of faujasite are given elsewhere (Ibrahim and Hall 1995).
Phillipsite
Phillipsite occurs mainly as colourless, radiating crystal aggregates forming a thin rim on pyroclasts. It is also present as isolated, euhedral, stout prisms. Rosettes of radiating crystals and spherulites are typical (Fig. 4b). The pseudo-orthorhombic symmetry is evident from the two- sided dome which terminates crystals. Crystals are com- monly less than 50 ~tm long and only rarely as long as 300 [.tin.
Phillipsite shows a wider compositional range than the other two zeolites, and differs in composition between the two diagenetic sub-zones (Fig. 5). In the phillipsite- chabazite sub-zone it has a high Ca/Na ratio, but in the faujasite-phillipsite sub-zone it has a low Ca/Na ratio. In both sub-zones it is the most potassium-rich of the zeolites. There is a similar two-fold grouping of the phil- lipsite compositions with regard to the ratio of framework cations (Fig. 6). The Ca-rich phillipsites of the phillipsite- chabazite sub-zone have lower Si/A1 ratios than any of the other zeolites.
Chabazite
Chabazite occurs in transparent rhombohedral crystals showing simple penetration twinning (Fig. 4c). Crystals vary in size from several microns up to 200 ~tm. Chabazite crystals are commonly zoned. The Si/A1 ratio in unzoned crystals varies from 2.53 to 2.90 in different samples, and in zoned crystals the range is from 1.94 to 2.93. Chabazites have lower Na/Ca and Na/K ratios than faujasite and phillipsite, and have a higher K/Ca ratio than faujasite (Table 4).
Smectite
Smectite is restricted to zone 2 and zone 3, where it is present in small amounts. Optical and scanning electron microscopy show that the smectite occurs as a colourless rim fringing palagonite granules, or encrusting vesicle walls as an aggregate of tiny flakes (Fig. 4d). The maximum thickness of the fringe is 401am, but it is sometimes absent. X-ray diffraction of the <2 ~m frac- tion indicates that the (001)yeflection of the oriented air-dried specimens is 14 15/~, which expands to 17/~ with glycolation. Microprobe analysis shows the presence of two compositions of the smectite: a montmorillonite, which occurs only in zone 2; and another variety rich in Mg, classified as saponite (Table 3), which is found in zone 2 and zone 3.
519
Fig. 4a-d. SEM photographs of zeolitic tufts showing: a octahedral crystals of faujasite with spinel twinning (from Jabal Hannoun); b rosettes of phillipsite which have grown inside a vesicle (from Jabal Hannoun); e rhombohedral crystals of chabazite with simple penetration twinning, overgrown on phillipsite (from Tell Rimah); d saponite encrusting a vesicle wall (from Jabal Hannoun)
Ca~iw
Calcite occurs in most of the analysed samples, in all of the diagenetic zones. It was the latest of the authigenic min- erals to crystallize, occurring in the form of rim and blocky cement, and filling central parts of vesicles and the intergranular space.
Paragenesis of the authigenic minerals
The paragenetic sequence of the authigenic minerals in the Aritayn Volcaniclastic Formation, based on petrographic and scanning electron microscopy, aided by electron microprobe analysis and micro-chemical mapping is as follows:- fresh sideromelane --. palagonite ~ smectites (saponite ~ montmorillonite) ~ faujasite ~ phillipsite -~
chabazite ~ natrolite ~ calcite. This is a depositional se- quence, not involving replacement, and the authigenic minerals were deposited in the same sequence in all the samples that were examined. Where one or more of the minerals is absent, the remaining minerals retain the same sequence. This sequence of authigenic minerals, although resembling that described by Hay and Iijima (1968a, b), shows a slight difference in that smectites precede zeolites in the Jordanian examples but follow zeolites in the exam- ples from Hawaii.
Origin of the zeolites
Hay and Iijima (1968a, b) have shown that the trans- formation of sideromelane into palagonite by reaction with percolating meteoric water can provide material for
~..,h
'Fab
le 4
. C
hem
ical
ana
lyse
s of
fau
jasi
te,
chab
azit
e an
d ph
illi
psit
e fr
om t
he A
rita
yn V
olca
nicl
asti
c F
orm
atio
n
Fauj
asite
C
haba
zite
Ph
ittip
site
48
(5)
53(1
1)
54(1
1)
55(5
) 36
I (6
) 19
A (
6)
19B
(3)
9
(ll)
29
(18)
29
R (
6)
48(5
) 9(
6)
35(6
) 53
(7)
19(4
) 36
(7)
29(9
t
SiO
z 48
.30
48.t
0 46
.58
49.1
2 47
.60
52.3
1 53
.36
54.9
0 46
.90
55.2
7 53
.65
48.0
1 54
.28
54.6
8 49
.38
52.2
8 47
.15
TiO
2 0.
04
0.05
n,
d.
0.05
n.
d,
n.d.
n.
d.
0.04
n.
d.
n.d
0.02
0.
05
0.01
0.
13
n.d,
n.
d,
n.d.
A
1203
16
.51
16.1
1 17
.27
16.2
3 17
.62
17.5
6 17
.06
16.8
8 20
.61
16.0
2 18
.12
22,4
5 18
.50
17.2
3 22
.79
20.7
8 22
.74
Fez
O3
0.18
0.
12
0.t0
0.
16
n.d.
n.
d.
0.20
0,
08
0.15
n.
d.
0.16
0.
13
0.04
0.
12
0.23
n,
d.
n.d.
C
aO
6.29
4.
54
3,48
5.
47
4.03
5.
06
4.80
4.
71
6.34
2.
35
n.d.
9,
04
1.22
1.
32
7.70
13
0 6,
11
MgO
0.
39
0.36
0.
39
0.58
1.
45
1.25
1.
49
1.91
0.
05
2,17
n.
d.
0.08
n,
d.
0.03
0.
12
n.d.
n.
d.
Nae
O
2.59
2.
63
3.96
2.
78
3.33
0.
71
0.50
0,
28
3.36
1,
28
5.15
0.
34
5.49
4.
62
1.01
6.
91
2.14
K
20
0.
54
2.93
2.
72
0.78
0.
45
4.32
3.
40
3.12
3.
46
3.46
4.
49
5.62
6.
15
6.32
6.
53
5.83
7.
08
SrO
n.
d.
n.d.
0
52
n.
d.
0,31
n.
d.
n.d,
n.
d.
0.04
n.
d,
n.d,
n.
d.
n,d.
n.
d.
0.28
0.
50
n.d.
Tot
al
74.8
4 74
.83
75,0
5 75
.16
74.7
9 81
,21
80.8
1 81
.07
80.9
1 80
.54
84.2
9 85
,73
85,6
9 84
.46
87.9
8 87
.54
85.2
2
Ato
mic
pro
port
ions
on
the
basi
s of
384
oxy
gens
for
fau
jasi
te,
24 o
xyge
ns f
or c
haba
zite
and
32
oxyg
ens
for
phil
lips
ite
Si
136.
15
137.
11
133,
50
137.
57
133.
89
8.58
8.
70
8.79
7.
88
8.96
11
.42
10.2
7 11
.44
11.6
5 10
.33
10.9
0 10
.22
A1
54.8
5 54
.12
58.3
3 53
.57
58.4
1 3.
40
3.28
3.
18
4.09
3.
06
4.55
5.
66
4.59
4.
33
5.55
5.
12
5.81
C
a 19
.00
13.8
7 10
.69
16.4
1 12
.15
0.89
0.
84
0.81
1.
14
0.41
0.
62
2,07
0,
28
0.30
1.
73
0.29
1.
42
Mg
1.64
1.
53
1.67
2.
42
6.08
0.
30
0,36
0.
45
0.01
0.
52
0.00
0.
03
0.00
0.
01
0.04
0.
00
0.00
N
a 14
.16
14.5
4 22
.00
15.1
0 18
.16
0.23
0.
16
0.09
1.
09
0.40
2.
12
0,14
2.
24
1.91
0.
41
2.80
0.
90
K
1.94
10
.66
9.94
2.
79
1.62
0.
91
0.71
0.
64
0.75
0.
72
1.21
1.
54
1,66
1.
72
t.74
1.
55
1.96
F
e 0.
38
0.26
0.
22
0.34
0.
00
0.00
0,
03
0.01
0.
02
0.00
0.
03
0.02
0.
01
0.02
0.
00
0.00
0.
00
Ti
0.09
0.
11
0.00
0.
11
0.00
0.
00
0.00
0.
00
0.00
0.
00
0.00
0.
01
0.00
0.
02
0.04
0.
00
0.00
S
r 0.
00
0.00
0.
86
0.00
0.
51
0.00
0.
00
0.00
0.
00
0.00
0.
00
0.00
0.
00
0.00
0.
03
0.00
0.
00
0 38
4 38
4 38
4 38
4 38
4 24
24
24
24
24
32
32
32
32
32
32
32
E%
--
4.0
9 --
3.0
3 0.
44
-- 2
.93
2.26
-
3,40
1.
07
-- 1
.69
- 1.
03
2.72
0.
08
- 3.
22
3.43
2.
33
- 1.
86
1.27
2.
06
Si/A
I 2.
48
2.53
2,
29
2.57
2.
29
2.52
2,
65
2.76
1.
93
2.93
2.
51
1.81
2,
49
2,69
1.
86
2.13
1.
76
Na/
K
7.29
1.
36
2.21
5.
42
11.2
4 0.
25
0.23
0.
14
1.45
0.
56
1.75
0,
09
1.35
1.
11
0.24
1.
81
0.46
N
a/C
a 0.
75
1.05
2.
06
0.92
1.
50
0.26
0.
19
0.11
0.
96
0.98
3.
42
0.07
8.
00
6.37
0.
24
9.66
0.
63
K/C
a 0.
10
0.77
0,
93
0.17
0.
13
1.02
0.
85
0.79
0.
66
1.76
1.
95
0.74
5.
93
5.73
1.
01
5.34
1.
38
E =
bal
ance
err
or,
afte
r P
assa
glia
(19
70);
( )
=
nu
mb
er o
f po
ints
ana
lyse
d
521
Na+K Ca+Mg / k / ~ ~ Phillipsite-Chabazite ? \ / \ sub-zone
/e \ / \ ~ Faujasite-Phillipsite I X / \ sub-zone
~ W ~.'~ u Faujasite /~'~ Jo ,L X, o Phillipsite I ~ ~'= A / ~ ~ t ~ J, Ohabazite
C a / , , N a / , , , " = / , , ~g , , XK
Fig. 5. Triangular plot of the exchangeable cations in the Jordanian zeolites
Faujasite has a relatively high ratio of water molecules to cations compared with other zeolites, and Wise (1982) suggested that faujasite is most likely to form from relat- ively dilute solutions compared with other zeolites. At first sight this is difficult to reconcile with the apparently low availability of water. The northeastern region of Jordan is extremely arid, with annual precipitation of less than 150 mm and a mean annual maximum temperature be- tween 34~ and 37~ However, as a result of these conditions, the rate of weathering is extremely low, so that the inadequate supply of cations may result in a very low degree of saturation in the water present in the lower levels of the tuff sequence.
E c o n o m i c potent ia l o f the Jordan ian natural zeo l i tes
1.00-
-ff o ~ 0.75- + w, +
,,e 0.50- +
z r
1.-)o 1.5o
[]
rl
[] An [] �9
z'10 zg0 zg0 2.?0 z50 3.'10 Si/AI
Fig. 6. (Na + K)/(Na + K + Mg + Ca) ratio versus Si/A1 ratio of the Jordanian zeolites. Symbols as in Fig. 5
the formation of zeolites, and can account for vertical zoning of the altered tufts and their interstitial minerals. This explanation is applicable to zeolitization in the Aritayn Formation. The high porosity and permeability of the tuff sequence of the Aritayn Formation and the aridity of this part of Jordan imply that all mass movement of rain water is downwards, giving rise to an open hydrologi- cal system. In zone 1, where the pH and salinity of the percolating water are normal, fresh sideromelane is found. Where the pH and salinity became slightly higher as a result of the transformation of sideromelane into palagonite, crystallization of smectite took place, as in zone 2. Increased pH and salinity with depth due to solution and hydrolysis of the sideromelane produced an environment where zeolites could form, i.e. zone 3. The elements released from the fresh sideromelane by this reaction (Si, A1, Na, K, Ca and Mg) were redeposited as authigenic minerals in the paragenetic sequence described already, forming the intergranular cement.
Phillipsite and chabazite are characteristic authigenic minerals in tufts formed from igneous rocks high in alkalis and low in silica, such as the alkali basalts of nor th- eastern Jordan. The relatively high abundance of faujasite is a more unusual feature of the tufts in this region and may be related to the particular hydrological conditions prevailing there.
Zeolite-rich tufts of the Aritayn Volcaniclastic Formation are currently being worked at Tell Rimah as a cement additive, and have previously been marketed on a small scale as a soil-conditioner. Two companies are currently attempting to develop these zeolitic materials as a slow- release fertilizer and for use in water purification. Re- search in progress by the first-named author shows en- couraging signs that the zeolitic tufts can be beneficiated to increase their zeolite content and value. There is con- sidered to be particular potential for the production of a high-grade faujasite concentrate.
Natural faujasite has not hitherto been considered of potential economic interest because of its rarity, but its synthetic counterpart is a very important industrial com- modity. The value of faujasite arises from its very open crystal structure. It has the lowest framework density and largest channel diameter of any zeolite structure, leading to its use in the petroleum industry as an absorbent for large organic molecules, and it is also a more effective ion exchanger than many other zeolites.
A factor which may be advantageous for the utilization of the Jordanian zeolitic tufts is that they are relatively poorly lithified and porous, and contain zeolites of large grain size, in contrast to some clinoptilolite- and anal- cime-bearing tufts derived from more felsic protoliths. These properties are all favourable for successful beneficia- tion.
Acknowledgements. The paper reports part of a PhD study jointly founded by the British Council, the Natural Resources Authority of Jordan (NRA), and the Overseas Research Students award scheme (ORS), to whom the first author is grateful. Special thanks are due to Mr. F. Ad-Daghistani, Director General NRA, and Mr. B. Sunna', Director of Geology NRA, for their support of the study. Many thanks are due to Ms J. Riddell and Ms. F. Nelson of the Electron Microscopy Unit, Royal Holloway University of London for their help in the SEM and microprobe analysis and to Mr. N. Holloway for thin-section preparation.
References
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