Mineralogy of Bara Formation from Lakhra Area, Sindh, Pakistan.
Asgher Ali alias Daahar Hakro1, Adnan Khan2 Sadaf Naseem2*
Abstract
Twenty two rock samples were collected for their bulk mineralogy from Bara Formation in
Lakhra anticline near Lakhra coal field. Detailed mineralogical investigations were carried out
using optical microscope, scanning electron microscopy (SEM) and X-ray diffraction techniques.
Data reveals that quartz, feldspars, gypsum, chlorite, goethite and hematite are dominant
minerals. The occurrence of quartz, feldspars and chlorite indicates that the sediments source is
igneous and metamorphic rocks, while the presence of hematite and goethite suggests that Bara
Formation was deposited in fluvial environment.
Key Words: Bulk Mineralogy, Bara Formation, Lakhra, Quartz, XRD and SEM.
1. Centre for Pure & Applied Geology, University of Sindh, Jamshoro. Pakistan,Email:asgheralihakro@hotmail.com
phone: 03002904972
2*. (Correspondence author) Department of Geology, University of Karachi, Pakistan.Email: snaseem@uok.edu.pk
Phone: 0092-343-2289613
2, Department of Geology, University of Karachi, Pakistan. Email: adkhan@uok.edu.pk: Phone: 03003635848
1. Introduction
The Bara Formation was named at the type section at Bara Dohoro in the Laki Range
(Cheema et al. 1977). Bara Formation occurs in the core of the Lakhra anticline, near Lakhra
coal field, whereas the Laki Formation is the youngest Formation of this area and occurs on the
flanks of Lakhra anticline. Structurally, it is doubly plunging anticline, which runs North-South.
The Lakhra, Laki and Manchar Formations are extensively exposed in the study area (Hakro,
2012) the studied area (Table 1). Bara Formation is composed of sandstone, shale, siltstone and
coal beds. The coalfields of Lakhra, Ongar, Jherruck, Sonda, Indus East, Badin and Thar
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developed in the Bara Formation and hold the largest Coal resources of country in the Sindh
province (Outerbridge et al. 1991).
Age
Eocene
Late Paleocene
Formation
Laki Formation (Sonhari member and Meting Limestone)
Lakhra Formation
Lithology
Limestone, Sandstone, shale
Limestone and Shale
Middle Paleocene
Bara Formation
Sandstone, Siltstone, shale
Table1. Stratigraphy of the Lakhra area.
The exposed section of Bara Formation in Lakhra area is 20 meter thick; it is located near Lailian
Nala and is comprises of sandstone and shale with minor siltstone. Sandstones are variable in
color, poorly sorted, friable, unconsolidated to consolidated and cross bedded in nature (Fatmi
and Khan, 1995). Shale is splintery, fissile and earthy in color, while siltstone is interbedded with
shale and sandstones. Wnuk et al. (1992) interpreted these sediments as inner-shelf tidal
sandwaves grading upward into estuarine sediments followed by intertidal and coastal plain
deposits.
Q
Q
A
B
Q
Q
D
Q
Q
Q
Q
Q
Q
Q
C
Q
Q
E
Fig. 1. SEM images of Bulk-rock minerals of the Bara Formation from LakhraAreas.
A = S-8La(E) (B)Quartz , B = S-10 L(E) (B)Quartz , C = S-12La(E) A-Quartz, D = S-13La(E) D-Quartz , E = S10La(W) A-Quartz .
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2. Materials and Methods
Two exposed sections of Bara Formation from Lakhra anticline were measured for their
thickness. Twenty two rock samples were collected from the exposed part of Bara Formation.
The samples were properly labeled and packed in sealed plastic bags. In the laboratory detailed
mineralogical characteristics of Bara Formation were investigated using petrographic, scanning
electron microscopic and x-ray diffraction techniques.
A
B
C
D
E
F
Fig. 2. Microphotograph of rock samples of Lakhra areas. Quartz=
A=Ordinary light Photomicrograh of S.6La(W)Lakhra westSection, B=Polarized light photomicrograph of
S.6La(W)Lakhra west Section, C= Ordinary light Photomicrograh of S.7La(W)Lakhra westSection, D= Polarized
light photomicrograph of S.7La(W)Lakhra west Section, E= Ordinary light Photomicrograh of S.11La(W) Lakhra
east Section, F= Polarized light photomicrograph of S11La(W) Lakhra east Section.
All collected samples (n=22) were prepared for XRD analysis, while four samples were
selected for SEM and petrographic studies respectively (Fig. 1, 2). Random powder samples
from sections of Lakhra area were scanned on XRD from 2, 2θ, to 65, 2θ to detect the presence
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of non-clay minerals and were identified by the characteristics d-spacing of common minerals
(Schultz, 1964; Klug and Alexander, 1954; Weaver, 1959).
3. Results and Discussion
Petrographic study reveals the occurrence of quartz and feldspars (Alkali and Plagioclase) in
studied rock samples (Table 2 Fig. 2).
Quartz and feldspars are the major components with
minor amounts of silt and clay matrix (Fig, 2). These samples contain sub-mature sandstones,
which is friable to slightly compact. Reddish-brown patches indicate the presence of ferruginous
cement suggesting sandstones were deposited under fluvial environment.
S.No
6La (W)
Grain
Size
Medium
Grain
Shape
Subangular
Grain
Sorting
Moderately
7 La(W)
Fine
Subangular
Well
11La(W)
Coarse
AngularSubangular
Moderately
Matrix
Cement
Mineral Content
Grain
Supported
Grain
Supported
Grain
Supported
Siliceous &
clayey
Ferruginous
& clayey
Ferruginous
(low) &
clayey
Quartz & Plagioclase.
alkali feldspar
Quartz & alkali feldspar
Plagioclase, alkali
Feldspar, Quartz
Table 2. Results of petrographic study of selected Samples from Lakhra Sections.
Scanning Electron Microscopy showed the presence of quartz and broken fragments of the
Kaolinite (Table 3, Fig. 1). Mineralogical study using XRD technique indicates that rock is
mainly comprised of quartz, hematite, gypsum and potash feldspar (Fig. 3, 4).
Sample
S-8La(E)
S-10La(E)
S-12La(E)
Mineral which has been found in SEM
Sample
Mineral which has been found in SEM
Quartz
S-13La(E)
Quartz, Fragments of Kaolinite
Quartz,
S-10La(W)
Quartz, Fragments of Kaolinite
Quartz, Fragments of Kaolinite
Table 3. Interpretation of SEM results of selected samples from Lakhra Sections.
Quartz (Low) showed strong peaks on X-ray diffractograms which suggested that quartz (low) is
well crystalline. Higher quantity of quartz (low) in the rock samples may be due to near-shore
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light brown S-12 La(E)
700
Quartz
600
Lin (Cps)
d=3.29304
500
400
d=1.45244
d=1.53691
d=1.48556
d=1.59460
d=1.69581
d=1.66238
d=1.84562
d=1.80745
d=1.97165
d=2.12565
d=2.28125
d=2.23375
d=2.19643
d=3.67613
100
d=2.70394
d=4.20961
200
d=2.51100
d=2.44269
Quartz
Hematite
300
0
5
10
20
30
40
50
60
2-Theta - Scale
light brown S-12 La(E) - File: asgher05a.RAW - Type: 2Th/Th locked - Start: 5.000 ° - End: 65.000 ° - Step: 0.500 ° - Step time: 4. s - Temp.: 25 °C (R
Operations: Y Scale Add 15 | Strip kAlpha2 0.500 | Background 0.000,1.000 | Import
01-0649 (D) - Quartz - SiO2 - Y: 49.15 % - d x by: 1. - WL: 1.5406 - Hexagonal - a 4.903 - b 4.90300 - c 5.393 - alpha 90.000 - beta 90.000 - gamma
89-0599 (C) - Hematite, syn - Fe2O3 - Y: 12.64 % - d x by: 1. - WL: 1.5406 - Rhombohedral - I/Ic PDF 3.1 - S-Q 7.7 % -
Fig. 3. Diffractograms of sample S-12 La (E) of Lakhra East Area.
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camel coloer S-10 La(W)
Quartz
800
d=3.36667
700
600
Quartz
d=1.80804
Hematit
e
d=2.42764
0
5
10
20
30
40
50
60
2-Theta - Scale
camel coloer S-10 La(W) - File: asgher11.RAW - Type: 2Th/Th locked - Start: 5.000 ° - End: 65.000 ° - Step: 0.500 ° - Step time: 4. s - Temp.: 25 °C (
Operations: Y Scale Add 42 | Background 0.174,1.000 | Import
01-0649 (D) - Quartz - SiO2 - Y: 77.89 % - d x by: 1. - WL: 1.5406 - Hexagonal - a 4.903 - b 4.90300 - c 5.393 - alpha 90.000 - beta 90.000 - gamma
89-0599 (C) - Hematite, syn - Fe2O3 - Y: 21.72 % - d x by: 1. - WL: 1.5406 - Rhombohedral - I/Ic PDF 3.1 - S-Q 8.3 % -
Fig. 4. Diffractograms of sample S-10 La (W) of Lakhra West Area.
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d=1.45100
d=1.50473
d=1.48485
d=1.56149
d=1.54519
d=1.60287
d=1.69673
d=1.65775
d=1.84029
d=1.97127
d=2.28154
d=2.22982
d=2.17654
d=2.12212
d=2.67283
d=2.83782
d=3.03163
d=3.64482
d=4.79213
d=5.71223
d=7.07561
d=8.29110
d=13.50735
100
d=10.80268
200
d=2.52670
300
Hematit
e
400
d=4.22676
Lin (Counts)
500
type of deposition (Ronov, 1965; Baig, 1982; Hakro, 2012). Alpha quartz is present in all
samples of studied rock which may has been contributed by the weathering pre-existing igneous
complexes (Baig and Ahmed, 2007). Kaolinite occurs less abundant in ancient sediments as
compared to younger sediments and it must be changed to some other clay minerals. Clays
strongly reflect their source material and show only slight modification in their depositional
environment (Grim and Johns, 1954; Weaver, 1958). Kaolinite is generally formed by the
weathering and alteration of potassium feldspar, which is an essential ingredient of granite.
Kaolinite probably was supplied to the detritus of the studied sediments from the Nagarparkar
Igneous and Metamorphic Complex. Presence of Kaolin mines in the surroundings of the
Nagarparkar area also supports the statement.
Hematite is found as cementing material in studied samples. Ferric hydroxide colloids present in
many streams, and transported in rivers and the near-shore ocean as a dilute suspension or
adsorbed on the surfaces of clay minerals, may be the source of iron minerals in soils.
Sample Number
1La(E)
2La(E)
Mineral Composition
Quartz (low)
Quartz (low)
Sample Number
7La(E)
8La(E)
3La(E)
4La(E)
6La(E)
Sample Number
2La(W)
3La(W)
4La(W)
5La(W)
6La(W)
Quartz (low)
Quartz (low), Hematite
Quartz (low), Gypsum
Mineral Composition
Quartz low, Hematite
Quartz (low), Gypsum
Quartz (low)
Quartz low,
Quartz low
10La(E)
12La(E)
13La(E)
Sample Number
7La(W)
8La(W)
9La(W)
10La(W)
11La(W)
Mineral Composition
Quartz low, K-feldspar
Quartz(low) Hematite &
K-feldspar(1p)
Quartz (low),K-feldspar
Quartz (low), Hematite
Quartz (low,) feldspar
Mineral Composition
Quartz (low)
Quartz (low)
Quartz (low)
Quartz low, Hematite
Quartz low
Table 4. Minerals identified by XRD of Samples Bara Formation from Lakhra.
Gypsum is found in only two samples (Table 4) and suggests the occurrence of high salinity in
pockets, during the deposition of studied rocks. Potash feldspar is an essential mineral of granite
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which is also common in gneisses, therefore it may be assumed that potash feldspar in the
samples of Lakhra sections was supplied from the granites/ gneisses exposed in the Nagarparkar
Igneous and Metamorphic complex.
4. Conclusion
Mineralogically Bara Formation comprises of quartz (Low), potash feldspar, gypsum and
hematite. The occurrence of quartz and potash feldspar indicates granite as source of these
sediments, while the presence of hematite suggests the oxic environment of deposition. It is
concluded that the detritus of these minerals was supplied from the Indian shield rocks which is
exposed in the southeast of the studied area.
5. Acknowledgements
The authors are grateful to the Scietific officcer, Mr. Kamalludin Shaikh, PCSIR laboratory
Karachi and Mr.Yousuf of General Centralized Laboratory (GCL), University of Karachi, for the
permission of using the XRD Lab facilities and his fruitful suggestions are also acknowledged.
The author is indebted to offer his sincere thanks to Prof. Dr. Mohammed Atique Ahmed Baig,
for the guidance, encouragement patience for reading and correcting the first draft of this paper
and his valuable suggestions. Author is also thankful to the Prof. Dr. Sarfraz H. Solangi,
Director, Centre for Pure and Applied Geololgy, University of Sindh, Jamshoro, for his moral
support.
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