Shigar valley gemstones, their chemical composition and origin, Skardu, Gilgit-Baltistan, Pakistan

Abstract

A variety of gemstones is being mined in the Shigar valley, Skardu, Pakistan. These include beryl (goshenite and aquamarine), tourmaline (schorl), garnet (almandine–spessartine), apatite, topaz, fluorite, zoisite, clinozoisite, and axinite, mostly occurring in complex or zoned pegmatites and metamorphic rocks. These have been analyzed using electron probe micro-analyzer and X-ray diffractometer. The mineral chemistry of each gemstone is similar to its respective typical gemstone variety with homogenous chemical composition. Field and chemical characteristics suggest that beryl, tourmaline, garnet, apatite, topaz, and fluorite are occurring in zoned pegmatites which are largely formed by magmatic hydrothermal fluids in the cavities and vugs within the intermediate zone. However, zoisite, clinozoisite, and axinite may have a metamorphic and/or metasomatic origin.

Full text

ORIGINAL PAPER
Shigar valley gemstones, their chemical composition
and origin, Skardu, Gilgit-Baltistan, Pakistan
Muhammad Hassan Agheem & Mohammad Tahir Shah &
Tahseenullah Khan & Mamoru Murata &
Muhammad Arif & Humaira Dars
Received: 6 April 2013 /Accepted: 19 July 2013 /Published online: 20 August 2013
#
Saudi Society for Geosciences 2013
Abstract A variety of gemstones is being mined in the Shigar
valley, Skardu, Pakistan. These include beryl (goshenite and
aquamarine), tourmaline (schorl), garnet (almandine–spessar-
tine), apatite, topaz, fluorite, zoisite, clinozoisite, and axinite,
mostly occurring in complex or zoned pegmatites and meta-
morph ic ro cks. These have been analyzed using electron
probe micro-analyzer and X-ray diffractometer. The mineral
chemistry of each gemstone is similar to its respective typical
gemstone variety with homogenous chemical composition.
Field and chemical characteristics suggest that beryl, tourma-
line, garnet, apatite, topaz, and fluorite are occurring in zoned
pegmatites which are largely formed by magmatic hydrother-
mal fluids in the cavities and vugs within the intermediate
zone. However, zoisite, clinozoisite, and axinite may have a
metamorphic and/or metasomatic origin.
Keywords Shigar valley
.
Skardu
.
Gemstones
.
Zoned
pegmatites
Introduction
Shigar valley , located north of Skardu, is one of the most famo us
valleys of the Gilgit-Baltistan region of Pakistan as it is the
gateway for most of the expeditions to the K-2, the second
highest peak of the world. In recent years, this valley received
much attention due to gemstone occurrences. Pegmatites, which
are the hosts of gemstones, occur in Karakoram, Hindu Kush,
and the Himalayan Mountains. Pegmatite related gemstones
have also been reported from other localities of Pakistan such
as Shengus, Stak Nala, Garam Chasma by Kazmi et al. (1985)
and Laurs et al. (1998). In addition, the re are many pegmatites
worldwide, which are famous among the mineral and gemstone
coll ectors for the occ urrence of various gemstones (e.g. ,
Rosenberg 1972; Shearer et al. 1984; London 1986;Vianna
et al. 2002b; Peretyazhko a et al. 2004). Shigar valley is unique
in this regard as many gemstones occur in pegmatites and the
metamorphic rocks (Fig. 1). Hassa n (2007) and Agheem et al.
(2011) have studied the Shigar valley pegmatites in detail.
According to them, the pegmatites of the area, on the basis of
mineralogy, internal structure, and texture, are complex and
zoned. Unzoned and simple pegmatites are also not uncommon
and are barren of the gemstones. The complex pegmatites show
both s ymmetrical and asymmetrical zoning. Each zone is litho-
logically, texturally, and compositionally distinct from other
zone(s). The outermost zone is fine-grained, an intermediate
coarse-grained, and central blocky zones. Gemstones occur in
the central parts of the intermediate zone and/or at the core-
margin zone. Gemstones are generally found in cavities usually
rounded or ovoid in shape. The cavities are found tightly packed
with gemstones, usually surrounded by a light pink or white
clayey material.
As a common observation during geological fieldwork, it
was noticed that the size of the gemstone crystals was directly
proportional to the size of the cavity as described elsewhere
(e.g., London 1986, 1992). Various types of gemstones have
also been reported in different localities, including the Shigar
M. H. Agheem (*)
:
H. Dars
Centre for Pure and Applied Geology, University of Sindh,
Jamshoro, Sindh, Pakistan
e-mail: mhagheem@yahoo.com
M. T. Shah
National Centre of Excellence in Geology, University of Peshawar,
Peshawar, Pakistan
T. Khan
Department of Earth and Environmental Sciences, Bahria University,
Islamabad, Pakistan
M. Murata
Department of Geosciences, Faculty of Science, Naruto University
of Education, Naruto T okushima 772-8502, Japan
M. Arif
Department of Geology, University of Peshawar, Peshawar, Pakistan
Arab J Geosci (2014) 7:3801–3814
DOI 10.1007/s12517-013-1045-8

Fig. 1 Location map of the
Shigar valley, Gilgit-Baltistan,
Pakistan
Fig. 2 Map showing gemstone occurrences in the Shigar valley
3802 Arab J Geosci (2014) 7:3801–3814

Table 1 EPMA analyses of various gemstones found at different localities of Shigar Valley
Beryl
Goshenite Aquamarine
Locality Yuno Kashmol Nyit
Sample 4A 16B 16C 50
Grain Core Rim Core Rim Core Rim
SiO
2
65.13 65.35 65.02 63.91 63.55 63.64 65.33
TiO
2
0.00 0.00 0.00 0.00 0.00 0.15 0.07
Al
2
O
3
17.98 18.24 18.00 17.31 17.28 17.63 19.91
FeO
t
0.14 0.28 0.20 0.69 0.77 3.92 0.50
MnO 0.120.000.000.040.010.130.06
MgO 0.000.010.040.000.000.010.11
CaO 0.000.010.010.000.002.340.48
Na
2
O 0.120.090.120.000.380.000.16
K
2
O 0.020.010.000.040.040.140.42
Cr
2
O
3
0.00 0.04 0.03 0.01 0.00 0.02 0.00
Total 83.51 84.08 83.45 82.00 82.03 87.98 87.04
Structural formulas calculated on the basis of 36 oxygens
Si 12.03 12.00 12.02 12.04 11.98 11.51 11.69
Ti 0.00 0.00 0.00 0.00 0.00 0.02 0.01
Al 3.91 3.95 3.92 3.84 3.84 3.76 4.20
Fe
2
0.02 0.04 0.03 0.10 0.11 0.53 0.07
Mn 0.00 0.00 0.01 0.01 0.00 0.02 0.01
Mg 0.02 0.00 0.00 0.00 0.00 0.00 0.03
Ca 0.00 0.00 0.00 0.00 0.00 0.45 0.09
Na 0.04 0.03 0.04 0.00 0.14 0.00 0.06
K 0.000.000.000.010.010.030.10
Cr 0.00 0.01 0.00 0.00 0.00 0.00 0.00
Tourmaline (Schorl)
Locality Kashmol Dassu
Sample 15M 20A 20D 20F
Grain Core Rim Core Rim Core Rim Core Rim
SiO
2
33.51 34.75 35.06 34.52 33.16 33.47 34.25 33.55
TiO
2
0.26 0.29 0.22 0.08 0.07 0.01 0.08 0.27
Al
2
O
3
32.80 33.11 33.79 34.30 34.92 34.64 34.50 34.87
FeO
t
13.52 14.66 14.37 13.05 14.02 13.78 15.03 15.02
MnO 1.05 1.00 0.58 0.67 0.54 0.71 0.80 0.68
MgO 0.13 0.00 0.21 0.00 0.00 0.00 0.01 0.06
CaO 0.66 0.17 0.04 0.04 0.16 0.05 0.06 0.11
Na
2
O 2.16 1.86 1.88 1.31 0.97 1.27 1.24 1.39
K
2
O 0.05 0.10 0.02 0.01 0.03 0.03 0.02 0.02
Cr
2
O
3
0.00 0.00 0.03 0.03 0.00 0.00 0.00 0.00
NiO 0.01 0.05 0.07 0.04 0.11 0.04 0.02 0.02
Total 84.15 85.99 86.27 84.05 83.98 84.00 86.01 85.99
Arab J Geosci (2014) 7:3801–3814 3803

Structural formulas calculated on the basis of 24.5 oxygens
Si 5.68 5.75 5.80 5.77 5.58 5.63 5.65 5.54
Ti 0.03 0.04 0.03 0.01 0.01 0.00 0.01 0.03
Al 6.54 6.46 6.59 6.76 6.92 6.86 6.70 6.79
Fe
2
1.72 1.83 1.99 1.64 1.77 1.74 1.86 1.87
Mn 0.15 0.14 0.08 0.10 0.08 0.10 0.11 0.10
Mg 0.03 0.00 0.05 0.00 0.00 0.00 0.00 0.02
Ca 0.12 0.03 0.01 0.01 0.03 0.01 0.01 0.02
Na 0.71 0.60 0.60 0.43 0.32 0.41 0.40 0.45
K 0.01 0.02 0.00 0.00 0.01 0.01 0.00 0.00
Cr 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Ni 0.00 0.01 0.01 0.01 0.01 0.01 0.00 0.00
Garnet
Analysis Yuno Dassu
Sample 5 20H
Grain Core Rim Core Rim
SiO
2
37.77 37.61 36.28 35.83
TiO
2
0.00 0.00 0.00 0.05
Al
2
O
3
23.72 23.42 24.95 20.73
FeO
t
21.55 21.37 21.32 20.42
MnO 16.80 16.76 16.94 23.05
MgO 0.130.310.12 0.00
CaO 0.000.270.28 0.23
Na
2
O 0.020.170.00 0.02
K
2
O 0.030.000.00 0.00
Cr
2
O
3
0.00 0.00 0.00 0.03
NiO 0.000.000.00 0.00
Total 100.02 99.91 99.89 100.36
Structural formulas calculated on the basis of 24 oxygens
Si 6.27 6.23 6.01 5.90
Ti 0.00 0.00 0.00 0.01
Al 4.64 4.57 4.87 4.02
Fe
2
2.69 2.66 2.66 2.81
Mn 2.36 2.35 2.38 3.21
Mg 0.03 0.08 0.03 0.00
Ca 0.00 0.05 0.05 0.04
Na 0.01 0.05 0.00 0.01
K 0.000.000.00 0.00
Cr 0.00 0.00 0.00 0.00
Ni 0.00 0.00 0.00 0.00
Almandine 52.86 52.54 51.97 43.68
Andradite 0.00 0.00 0.00 0.00
Grossular 0.00 0.97 0.97 0.60
Pyrope 0.63 0.57 0.58 0.00
Spessartine 46.38 46.36 46.48 55.51
Uvarovite 0.000.000.00 0.09
Table 1 (continued)
3804 Arab J Geosci (2014) 7:3801–3814

Apatite
Locality Yuno Kashmol
Sample 3 M 3C 9A 9B
Grain Core Rim Core Core Rim Core Rim
SiO
2
0.34 0.21 0.18 0.55 0.29 0.37 0.25
TiO
2
0.01 0.26 0.00 0.05 0.00 0.04 0.02
Al
2
O
3
0.03 0.00 0.01 0.05 0.00 0.02 0.00
FeO
t
0.04 0.03 0.04 0.28 0.28 0.16 0.10
MnO 0.75 0.20 1.07 7.36 6.84 0.42 2.04
MgO 0.00 0.00 0.00 0.00 0.01 0.00 0.00
CaO 56.77 58.33 57.83 49.64 50.18 57.13 57.83
Na
2
O 0.26 0.08 0.07 0.13 0.06 0.05 0.03
K
2
O 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Cr
2
O
3
0.00 0.00 0.00 0.00 0.05 0.02 0.01
NiO 0.05 0.00 0.03 0.03 0.04 0.07 0.08
P
2
O
5
41.76 39.90 40.76 41.91 42.26 41.73 39.65
Total 100.01 99.01 99.99 100.00 100.01 100.01 100.01
Structural formula calculated on the basis of 26 oxygens
Si 0.06 0.04 0.03 0.10 0.05 0.06 0.04
Ti 0.00 0.03 0.00 0.01 0.00 0.01 0.00
Al 0.01 0.00 0.00 0.01 0.00 0.00 0.00
Fe
2
0.01 0.00 0.01 0.04 0.04 0.02 0.01
Mn 0.11 0.03 0.16 1.08 1.00 0.06 0.30
Mg 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Ca 10.48 10.98 10.77 9.23 9.32 10.54 10.86
Na 0.09 0.03 0.02 0.04 0.02 0.02 0.01
K 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Cr 0.00 0.00 0.00 0.00 0.01 0.00 0.00
Ni 0.01 0.00 0.00 0.00 0.01 0.01 0.01
P 6.09 5.93 6.00 6.16 6.20 6.08 5.88
Topaz
Locality Yuno Kashmol Goyungo
Sample 6 19 M 29
Grain Core Rim Core Rim Core Rim
SiO
2
32.37 32.13 32.25 31.82 31.87 31.75
TiO
2
0.00 0.00 0.00 0.00 0.00 0.00
Al
2
O
3
55.12 55.45 57.16 55.12 56.73 56.65
FeO
t
0.00 0.02 0.00 0.00 0.00 0.00
MnO 0.00 0.00 0.00 0.00 0.00 0.00
MgO 0.06 0.03 0.07 0.00 0.00 0.01
CaO 0.00 0.00 0.11 0.00 0.00 0.00
Na
2
O 0.02 0.00 0.03 0.00 0.00 0.00
K
2
O 0.05 0.01 0.13 0.06 0.01 0.02
Table 1 (continued)
Arab J Geosci (2014) 7:3801–3814 3805

Cr
2
O
3
0.00 0.00 0.00 0.00 0.00 0.00
NiO 0.00 0.00 0.00 0.00 0.00 0.00
F 18.77 19.46 20.15 19.28 20.17 20.25
O≡ F 7.90 8.19 8.48 8.12 8.49 8.53
Total 95.52 95.83 98.23 95.12 97.10 96.96
Structural formulas calculated on the basis of 24 oxygens
Si 4.79 4.75 4.67 4.74 4.66 4.65
Ti 0.00 0.00 0.00 0.00 0.00 0.00
Al 9.60 9.65 9.74 9.67 9.77 9.78
Fe
2
0.00 0.00 0.00 0.00 0.00 0.00
Mn 0.00 0.00 0.00 0.00 0.00 0.00
Mg 0.01 0.01 0.02 0.00 0.00 0.00
Ca 0.00 0.00 0.02 0.00 0.00 0.00
Na 0.01 0.00 0.01 0.00 0.00 0.00
K 0.01 0.00 0.02 0.01 0.00 0.00
Cr 0.00 0.00 0.00 0.00 0.00 0.00
Ni 0.00 0.00 0.00 0.00 0.00 0.00
F 7.39 7.66 7.76 7.65 7.86 7.91
Fluorite
Locality Yuno Kashmol Goyungo
Sample 1CM 1DM 18AM 21C 26M
Grain Core Rim Core Rim Core Rim Core Rim Core Rim
SiO
2
0.28 0.14 0.21 0.13 0.20 0.26 0.34 0.18 0.30 0.17
TiO
2
0.11 0.00 0.11 0.09 0.07 0.10 0.00 0.17 0.09 0.10
Al
2
O
3
0.00 0.00 0.00 0.00 0.00 0.07 0.00 0.04 0.10 0.00
FeO 0.00 0.02 0.00 0.00 0.00 0.00 0.00 0.00 0.01 0.00
MnO 0.03 0.06 0.02 0.01 0.04 0.01 0.00 0.04 0.00 0.00
MgO 0.00 0.00 0.01 0.00 0.00 0.00 0.00 0.00 0.00 0.02
CaO 52.12 51.42 51.91 50.29 51.71 52.61 51.29 51.71 51.75 52.42
Na
2
O 0.01 0.00 0.00 0.04 0.02 0.02 0.00 0.00 0.00 0.02
K
2
O 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Cr
2
O
3
0.04 0.01 0.02 0.06 0.00 0.00 0.00 0.00 0.04 0.03
NiO 0.00 0.05 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
F 48.41 48.25 48.62 47.38 48.63 47.91 48.35 48.84 48.69 48.24
Total 101.00 99.95 100.90 98.00 100.67 100.98 99.98 100.98 100.98 101.00
Zoisite
Locality Alchuri
Sample 11AM 11BM
Grain Core Rim Core Rim
SiO
2
39.89 39.67 39.88 39.65
TiO
2
0.06 0.04 0.00 0.03
Al
2
O
3
31.17 30.09 32.64 32.54
FeO
t
1.89 2.23 2.40 2.16
Table 1 (continued)
3806 Arab J Geosci (2014) 7:3801–3814

MnO 0.00 0.00 0.02 0.11
MgO 0.02 0.00 0.09 0.00
CaO 25.28 26.93 24.56 25.42
Na
2
O 0.05 0.00 0.00 0.00
K
2
O 0.00 0.00 0.00 0.00
Cr
2
O
3
0.03 0.03 0.00 0.00
NiO 0.06 0.00 0.00 0.05
Total 98.45 98.99 99.57 99.96
Structural formulas calculated on the basis of 13 oxygens
Si 3.03 3.02 2.99 2.97
Ti 0.00 0.00 0.00 0.00
Al 2.79 2.70 2.88 2.87
Fe
2
0.11 0.13 0.14 0.12
Mn 0.00 0.00 0.00 0.01
Mg 0.00 0.00 0.01 0.00
Ca 2.06 2.20 1.97 2.04
Na 0.01 0.00 0.00 0.00
K 0.00 0.00 0.00 0.00
Cr 0.00 0.00 0.00 0.00
Ni 0.00 0.00 0.00 0.00
Clinozoisite
Locality Alchuri Hashupa
Grain 10C 13C 22
Grain Core Rim Core Rim Core Rim
SiO
2
40.36 40.72 39.48 38.98 39.11 39.21
TiO
2
0.09 0.21 0.14 0.18 0.15 0.14
Al
2
O
3
27.78 27.55 27.48 26.08 27.57 26.85
FeO 7.44 6.88 7.29 8.73 7.54 7.49
MnO 0.15 0.02 0.05 0.23 0.14 0.14
MgO 0.00 0.05 0.10 0.00 0.14 0.00
CaO 22.30 22.59 23.44 24.68 23.30 23.98
Na
2
O 0.00 0.00 0.01 0.00 0.00 0.04
K
2
O 0.00 0.00 0.00 0.00 0.00 0.00
Cr
2
O
3
0.00 0.06 0.00 0.00 0.00 0.00
NiO 0.00 0.00 0.04 0.02 0.07 0.00
Total 98.12 98.08 98.03 98.90 98.02 97.85
Structural formula calculated on the basis of 13 oxygens
Si 3.23 3.26 3.18 3.15 3.16 3.18
Ti 0.01 0.01 0.01 0.01 0.01 0.01
Al 2.62 2.59 2.61 2.48 2.62 2.56
Fe
2
0.45 0.41 0.44 0.53 0.46 0.46
Mn 0.01 0.00 0.00 0.02 0.01 0.01
Mg 0.00 0.01 0.01 0.00 0.02 0.00
Ca 1.91 1.94 2.02 2.14 2.02 2.08
Na 0.00 0.00 0.00 0.00 0.00 0.01
K 0.00 0.00 0.00 0.00 0.00 0.00
Table 1 (continued)
Arab J Geosci (2014) 7:3801–3814 3807

valley, of the Gilgit-Baltistan region of Pakistan by Blauwet
et al. (1997, 2004). However, on the basis of field occurrence
and mineral chemistry, the gemstones of the area are discussed
for the first time for their origin (Fig. 2).
Methodology
Forty crystals of different gemstones were collected from the
Shigar valley and identified with the help of their physical and
optical properties. In order to confirm their nomenclature, spot
chemical analyses were performed using the Jeol Super probe
Model JXA-8600 electron probe micro-analyzer (EPMA)
with wavelength dispersive system at the Naruto University
of Education, Japan. For this purpose, a small portion from
each gemstone was cut with a very fine diamond blade in the
Gems and Gemmological Institute of Pakistan, Peshawar.
These were mounted on glass slides and polished on an
automatic diamond polisher in the Mineral Testing
Laboratory, Peshawar. All the analyses were performed by
employing 15 kv accelerating voltage and 1.99–1.21 amp
current. The standards viz., wollastonite (Si and Ca), TiO
2
(Ti), corundum (Al), hematite (Fe), rhodonite (Mn), synthetic
MgO (Mg), microcline (K), albite (Na), synthetic Cr
2
O
3
(Cr),
and synthetic NiO (Ni) were used. X-ray diffraction analyses
were performed using Rigaku Corporation, Geigerflex D/Max
Series, X-ray diffractometer (XRD) at the National Centre of
Excellence in Geology, University of Peshawar.
Cr 0.00 0.00 0.00 0.00 0.00 0.00
Ni 0.00 0.00 0.00 0.00 0.00 0.00
Axinite
Locality Alchuri Hashupa
Sample 12A 12D 12F 12G 12H
Grain Core Rim Core Rim 2 3 4
SiO
2
43.93 42.58 42.58 43.30 43.04 43.12 44.64
TiO
2
0.00 0.00 0.07 0.00 0.00 0.02 0.00
Al
2
O
3
17.89 17.05 17.40 17.99 17.34 17.09 17.56
FeO 10.10 10.46 9.25 10.68 11.02 10.21 9.24
MnO 0.380.280.210.650.800.631.04
MgO 0.820.921.131.080.990.931.58
CaO 19.75 20.54 21.33 19.41 20.84 19.92 21.91
Na
2
O 0.000.000.000.000.000.000.00
K
2
O 0.000.000.000.000.000.000.00
Cr
2
O
3
0.00 0.06 0.03 0.00 0.00 0.00 0.00
NiO 0.020.110.000.020.000.050.08
Total 92.89 92.00 92.00 93.13 94.03 91.97 96.05
Structural formulas calculated on the basis of 32 oxygens
Si 9.15 9.03 9.01 9.03 8.96 9.12 9.07
Ti 0.00 0.00 0.01 0.00 0.00 0.00 0.00
Al 4.39 4.26 4.34 4.42 4.25 4.26 4.20
Fe
2
1.58 1.67 1.47 1.67 1.73 1.62 1.41
Mn 0.07 0.05 0.04 0.11 0.14 0.11 0.18
Mg 0.25 0.29 0.36 0.34 0.31 0.29 0.48
Ca 4.41 4.67 4.84 4.34 4.65 4.51 4.77
Na 0.00 0.00 0.00 0.00 0.00 0.00 0.00
K 0.000.000.000.000.000.000.00
Cr 0.00 0.01 0.01 0.00 0.00 0.00 0.00
Ni 0.00 0.02 0.00 0.00 0.00 0.01 0.01
Table 1 (continued)
3808 Arab J Geosci (2014) 7:3801–3814

Mineral chemistry
The representative chemical analyses of cores and rims
(margins) of individual gemstones from the Shigar valley are
given in Table 1. Based on EPMA and the XRD data
(Table 2), various gemstones have been identified, which are
described below.
Beryl
The gem-quality beryl of the Shigar valley includes light to
dark blue aquamarine and colorless goshenite. The occurrence
of transparent light blue aquamarine crystals (5–15×1–7.5 cm)
from the Dassu pegmatites was reported earlier (Middlemiss
and Parshad 1918). According to Kazmi et al. (1985), aqua-
marine crystals up to 16 cm long and 7 cm wide from the
Dassu pegmatites have been included in the James A. Gibbs
collection. The light blue aquamarine and goshenite crystals,
ranging in size from 1 to 3 cm, are common in zoned pegma-
tites (Fig. 3a). Although largely concentrated in the cavities at
the core-margin zone, the gem-quality aquamarine crystals
may occasionally occur in the coarse-grained intermediate
zone within the host pegmatites. Albite, muscovite, and tour-
maline are commonly associated with aquamarine as matrix.
The EPMA and XRD data of all the analyzed crystals of
beryl are given in Table 1 and 2,respectively.Duetothe
limitation of EPMA analysis, the BeO contents of the beryl
crystals were not determined. Therefore, the total of each
analysis is about 12–18 % low which can be attributed to the
lack of determination of BeO and H
2
O contents in the studied
beryls. The major cations such as silicon and aluminum are
within the range of normal aquamarine and goshenite analysis.
Both these verities are chemically homogenous. The only
difference in the chemical composition of both the verities is
the difference in FeO contents. The aquamarine has higher
amount of FeO as compared to goshenite (Table 1). Therefore,
the aquamarine has light blue color, while goshenite is
colorless.
Tourmaline
Tourmaline is an ubiquitous mineral in the gem-bearing peg-
matites of the Shigar valley. It is scattered in the entire
groundmass of the pegmatite veins and dykes but mostly
concentrated either at the core-margin zone or in the border
zone of the host pegmatites. A gem-quality tourmaline crystal,
measuring 4×1 cm, was found in a pegmatite exposed at
Kashmol village (Fig. 3b). It is black in color with well-
developed faces of trigonal crystal system. Numerous stria-
tions are found parallel to the prismatic faces. Good quality
specimens of this kind are commonly associated with albite,
muscovite, aquamarine, and quartz (Hassan 2007). On the
basis of EPMA (Table 1) and XRD (Table 2) data, these
tourmaline crystals are classified as schorl having 13–15 %
FeO. These are generally homogenous both physically and
chemically. The total of the analysis of schorl crystals is 13–
16 % less than the typical analysis of schorl as B
2
O
3
and H
2
O
could not be determined by EPMA. However, all the other
main constituent oxides such as SiO
2
,Al
2
O
3
, and FeO and
minor oxides (Table 1) are consistent with the typical analysis
of schorl (Deer et al. 1966).
Garnet
The occurrence of gem-quality garnet as large crystals is rare;
however, minute crystals (<2 cm) of this sort do occur in the
gem-bearing pegmatites in the Dassu and Yuno areas of the
Shigar valley. These pegmatites are extensively mined for
well-developed euhedral crystals of garnet and other gem-
stones (Fig 3c, e). The gem-quality garnets collected during
the fieldwork are usually >0.5 cm in diameter, translucent, and
reddish brown in color and display the typical dodecahedral
form of cubic crystal system. The chemical analysis of the
studied gem-quality garnet crystals along with their end-
member compositions are given in Table 1. The relative
proportions of the calculated end-members suggest that the
studied garnets are generally almandine–spessartine with
Table 2 XRD data of the gemstones of different localities of Shigar
Valley with three major d values
Sample No. Name of the Locality d−1 d−2 d−3 Gemstone
4A Yuno 2.85 3.24 7.89 Beryl
16B Yuno 2.843.227.89Beryl
16C Kashmol 2.85 3.23 7.89 Beryl
50 Nyit 2.88 3.27 7.92 Beryl
15M Kashmol 3.45 2.57 6.32 Schorl
20A Dassu 3.45 2.56 6.33 Schorl
20B Dassu 3.45 2.56 6.32 Schorl
5 Yuno 2.542.831.51Almandine
20H Dassu 2.56 1.56 1.54 Almandine
3M Yuno 2.78 3.41 2.71 Apatite
6 Yuno 2.923.023.65Topaz
19 Kashmol 2.91 3.17 3.65 Topaz
1CM Yuno 3.131.921.64Fluorite
21C Kashmol 3.13 1.96 1.64 Fluorite
26M Goyungo 3.13 1.92 1.64 Fluorite
11AM Alchuri 2.682.024.03Zoisite
13C Alchuri 2.87 2.78 2.65 Clinozoisite
10C Alchuri 2.88 2.66 2.59 Clinozoisite
22 Hashupa 2.57 3.96 2.88 Clinozoisite
Arab J Geosci (2014) 7:3801–3814 3809

3810 Arab J Geosci (2014) 7:3801–3814
Fig. 3 Photographs of various gemstones from Shigar valley. a
Goshenite and aquamarine from various pegmatites of the Shigar valley.
The colorless, transparent crystals are of goshenite while the pale blue
ones with rectangular prism faces are aquamarine; b A crystal of black
tourmaline (schorl) from the Kashmol pegmatite, Shigar valley. Striations
along the prism faces are visible; c a crystal of reddish brown garnet from
the Yuno pegmatite mine. An aggregate of yellowish white calcite crys-
tals from the same pegmatite is also shown; d an aggregate of light pink
apatite crystals from the Yuno mine, Shigar valley; e Specimen showing
an aggregate of light pink apatite, green fluorite, reddish garnet, and large
books or sheets of muscovite from the Yuno mine, Shigar valley; f
colorless, transparent crystal of topaz (∼1–2 cm across) from the Kashmol
pegmatite; g three light green to green crystals of fluorite collected from
pegmatite at Kashmol, Shigar valley; h a transparent light green fluorite
crystal (∼2 cm across) represents the Yuno mine, Shigar valley; i two
crystals of zoisite from Alchuri, Shigar valley; j an aggregate of dark
brown crystals of clinozoisite from Hashupa, Shigar valley; k light brown
to greenish brown crystals of clinozoisites (epidote), Alchuri, Shigar
valley. A twinned crystal of clinozoisite can be seen near the top of the
picture; l brown crystals of axinite from Alchuri, Shigar valley

more than 46 % of spessartine component. However, the XRD
data (Table 2) classified these as almandine garnet. A garnet
crystal collected from Yuno is showing homogenous compo-
sition, but the one collected from Dassu is having increasing
MnO content from core to rim suggesting the increase in the
spessartine component. However, the core of garnet collected
from Dassu has similar composition as that of Yuno (Table 1).
Apatite
Pink and light pink apatite occurring in the Shigar v alley
pegmatites is of gem quality (Fig. 3d, e). On the basis of
chemical analysis of the studied apatite crystals, these
have been cl assified as apatite and mangano-apatite
(Table 1). Their EPMA data (Table 1) confirm that the
apatite crystals are stoichiometrically pure, and the sum of
the reported weight percent oxides is about 100 without
including chlorine, fluorine, hydroxyl, and carbonate
thereby signifying that the latter components may occur
in trace amounts i f present. One apat ite crystal from
KashmolisenrichedinMnO(upto7.36wt%)andthere-
fore is classified as mangano-apatite (Table 1). However,
apatite crystals of Kashmol are having higher amount of
MnO and FeO
t
as compared to that of Yuno (Table 1). The
EPMA data further suggest that the studied apatite crystals
are chemically homogenous. The XRD data (Table 2)also
confirmed that the studied crystals are of apatite.
Topaz
The occurrence of two varieties of topaz (i.e., colorless and
light yellow) is reported from pegmatites at Yuno, Kashmol,
Dassu, Nyit Bruk, and Goyungo in the Shigar valley (Kazmi
and Donoghue 1990). However, during this study, only three
colorless crystals of topaz (∼1×3cm),oneeachfrom
Kashmol, Yuno, and Goyungo were collected (Fig. 3f).
These t opaz crystals are usually associated with albite–
quartz–muscovite matrix.
The EPMA analysis of the studied topaz crystals are given
in Table 1. Stoichiometrically, the chemical composition, es-
pecially the amount of F (∼19 wt%), of the analyzed topaz is
analogous to the typical topaz found in miarolitic pegmatites
(Colombo et al. 2009). The higher amount of F in the studied
topaz is also the characteristic of topaz found in rhyolites
(Foord et al. 1990). Among the trace elements Ti, Fe, Mn,
Mg, Ca, Cr , and Ni are either in negligible amount or below
the detection limit while K reaches to 0.13 wt% (Table 1). The
studied topaz crystals from all the three localities are similar in
chemical composition and are homogenous in composition as
no significant chemical difference is noticed between their
cores and margins (Table 1). Light yellow topaz is relatively
enriched in Cr, Co, Mn, and V and the blue color topaz is
enriched in Ni while the colorless topaz is without these
impurities (Rosenberg 1972). Therefore, due to the negligible
amount of Mn, Cr, and Ni in the studied topaz crystals, these
are colorless in nature. The XRD data (Table 2)alsocon-
firmed that the analyzed crystals are of topaz (Table 2).
Fluorite
The pale to dark green fluorite occurs in pegmatites at Yuno,
Mungo, Kashmol, Baha, and Nyit Bruk of Shigar valley. The
average size of the collected crystals is 2×3 cm, and these are
typically associated with tourmaline, beryl, quartz, topaz, and
muscovite in cavities (Fig. 3g, h, and e). The EPMA analyses,
given in Table 1, suggest that the large gem-quality green
color fluorites are stoichiometrically pure CaF
2
and have the
same chemical composition as the tiny fluorite grains previ-
ously reported from the Shigar valley pegmatites by Hassan
(2007). All the crystals of fluorite are found chemically homo-
genous (Table 1). According to Saito (1950), some amounts of
Si, Al, and Mg may exist in fluorites either as inclusions and/
or impurities or may replace some of the Ca. In the studied
fluorites, no such replacement, substitution, and inclusions
were observed except for silica, which is present up to
0.34 wt%. The XRD data also confirmed that the studied
crystals are of fluorite (Table 2).
Zoisite
Gem-quality zoisite, found in the Alchuri area of the Shigar
valley, is colorless to light green in color. The local miners and
gem dealers call it tanzanite (Fig. 3i). The EPMA chemical
data of the studied zoisite crystals are given in Table 1. All of
the major oxides such as the SiO
2
,Al
2
O
3
,FeO
t
,andCaOare
in the range of a t ypical chemical analysis of a zoisite
suggesting that these are stoichiometrically pure zoisites
(Table 1). On the basis of XRD data (Table 2), these crystals
are also identified as zoisite.
Clinozoisite
Various varieties of gem-quality clinozoisite were collected
from the Alchuri and Hashupa areas in the Shigar valley.
Clinozoisite occurs as veins and fracture-filled material within
the metamorphic rocks (Fig. 3). The color and size of the
collected crystals are variable. Most of the crystals are dark
brown and opaque but transparent to translucent greenish
brown to light brown or yellowish green varieties are also
common (Fig. 3j, k). The EPMA data of the studied crystals of
clinozoisite are given in Table 1. The chemical data suggest
Arab J Geosci (2014) 7:3801–3814 3811

that these are stoichiometrically pure clinozoisites. These con-
tain SiO
2
(37.75–40.78 wt%), Al
2
O
3
(25.89–28.92 wt%),
CaO (20.58–24.68 wt%), and FeO (5.07–8.73 wt%) and a
number of other oxides which occur in insignificant amounts
(Table 1). The insignificant nature of chemical variation with-
in individual crystals indicates their homogenous nature. The
same crystals were also analyzed on XRD, which has con-
firmed these as clinozoisite (Table 2).
Axinite
Axinite occurs at Alchuri and Hashupa areas as veins in
greenschist to epidote–amphibolite facies metamorphic rocks
in the Shigar valley (Fig. 1). Their color varies between light
pink and brown (Fig. 3l). The chemical analyses of various
crystals of axinite are given in Table 1. Due to limitation of the
EPMA analysis, the Be
2
O
3
and H
2
O could not be determined
which resulted in the lower total (91.97–96.05 wt%). The rest
of the major oxides such as SiO
2
,Al
2
O
3
,FeO
t
, MnO, MgO,
and CaO have similar concentration as of typical axinite. The
chemical analyses indicate that all the studied crystals of
axinite have Ca>1.5 and Fe>Mn which can be classified as
ferroaxinites (Pringle and Kawachi 1980). In terms of chem-
ical composition, the studied ferroaxinites are very similar to
those reported from Sri Lanka (Han ni and Gunawardene
1982), New Jersey (Pohl et al. 1982), and New Melones
Lake, California (Cummings 1983).
Discussion
Mineralogical and geochemical studies play a vital role in
understanding the petrogenesis of any rock type. In case of
pegmatites, especially the granitic pegmatites generally have a
very complex mineralogy and internal structure (Ćerný 1982,
1991). The granitic pegmatites have been classified on the
basis of various parameters such as the occurrences of rare
metals, gemstones, presence or absence of cavities or vugs,
and zoning and relationships with the nearby plutonic bodies
(Ćerný 1982, 1991). Geochemically, the Shigar valley peg-
matites are granitic and belong to the two main categories, i.e.,
the simple and complex pegmatites (Hassan 2007). Further,
on the basis of presence of cavities and vugs, the complex
pegmatites are classified as gemstone-bearing miarolitic
pegmatites.
The variation in the color of beryl generally reflects varia-
tion in composition (Hammarstrom 1989). The blue color in
aquamarine is more commonly caused by Fe
+2
(Vianna et al.
2002a, b; Mihalynuk and Lett 2003; Beal and Lentz 2010),
but variable Fe
+3
/Fe
+2
ratio in aquamarines has been reported
by Figueiredo et al. (2008). Therefore, the blue color of the
studied aquamarine, containing relatively high FeO, can be
attributed to Fe
+2
. Beryl mineralization generally but by no
means exclusively occurs in the complex or zoned type of
pegmatites (Ćerný 1982, 1991). It may even occur in simple
pegmatites where metas omatic repla cement has occurr ed.
Various studies have indicated that the alkali content of beryl
from Li pegmatites is mostly higher than that occurring in
non-lithium pegmatites (Gallagher 1975). Correspondingly,
the studied beryls are very poor in alkalis since the Li content
of their parent pegmatites is low (e.g., Hassan 2007).
Although the studied aquamarines and goshenites are mostly
associated with the minerals of pneumatolytic or fluid phase
stage found in cavities and vugs, some of the non-gem beryl
crystals also occur in the intermediate zone. This indicates that
the crystallization of beryl started during the solidification of
the intermediate zone and matured in the core-margin zone till
the formation of vugs and cavities.
In terms of occurrence, the most important compositional
varieties of tourmaline group are the iron tourmalines or
schorl, the alkali tourmalines or elbaites, and the magnesian
tourmalines or dravites. In these varieties, the Y sites are
mostly occupied by Fe
2+
, Li, and Mg, respectively. Various
studies have revealed that different types of tourmalines may
be present even in a single pegmatitic body as reported from
the Black Hills, South Dakota (Shearer et al. 1984) and from
theStakNalapegmatites(Laursetal.1998). On the other
hand, some specific types of tourmalines may be present in a
particular type of pegmatite. Two genetically different types of
tourmalines occur in the Shigar valley pegmatites: (a) primary,
i.e., the ones formed during the main phase of the host peg-
matite evolution and (b) secondary, which appear to have
formed during a later hydrothermal or pneumatolytic action
(Hassan 2007). The studied tourmalines (schorl in composi-
tion) also occur in the intermediate zone and even in the
border zone, but the gem-grade crystals are associated only
with other gemstones of pneumatolytic or cavity formation
stage near the core-margin zone. The presence of tourmalines
in the intermediate or border zone may be the result of a
fracture-filling process, which commonly occurs in certain
pegmatites after the formation of cavities or vugs near the
core-margin zone.
The garnets of the gem-bearing pegmatites of the Shigar
valley are neither pure almandine nor spessartine, although the
occurrence of pure spessartine has been reported from differ-
ent pegmatites elsewhere in the world (Strock 1930; Hall
1965;Gresens1966). Hall (1965) suggested that if the micas,
especially muscovite in granitic aplites or pegmatites are poor
in MnO (containing 0.06–0.08 wt% MnO), then there are
chances of manganese accumulation in the residual magma
until the formation of garnet of almandine–spessartine com-
position. The MnO content of the studied muscovites from the
Shigar valley pegmatites is low (0.03–0.09 wt%, Hassan
2007). It is, therefore, possible that the manganese was
retained by the residual magma until the formation of garnets
3812 Arab J Geosci (2014) 7:3801–3814

of almandine–spessartine composition near the core-margin
zone within the Shigar valley pegmatites. The occurrence of
garnets either in the wall zone or intermediate zone supports
the idea that in the paragenetic sequence of gemstones, they
formed relatively earlier, i.e., before the saturation of fluids
and the resulting formation of the corresponding gemstones
such as the fluorite, schorl, and topaz.
Haapala (1974) has attempted to differentiate topaz-bearing
granites from the normal and rapakivi type granites merely on
the basis of trace element geochemistry. He mentioned that the
topaz-bearing granites have relatively high values of Be, Li, F,
Rb, Sn, Ga, and Nb and low values of Fe, Mg, Ti, Ba, Sr, and
Zr. The co ncentration of some of these elements, e.g., Be, Sn,
and Li in the Shigar valley pegmatites was not determined, but
their whole rock chemistry indicates that they are rich in F, Rb,
and Nb and poor in Mg, Ti, Ba, Fe, Sr, and Zr (Hassan 2007).
Consequently, these pegmatites host gem-quality topaz along
with other fluorine-bearing and or other volatile (B, H
2
O)-
saturated gemstones. Some of the topaz crystals from a zoned
pegmatite near Yuno occur at the base of a core-margin zone
thereby suggesting their formation during the pneumatolytic
stage. The occurrence of such type of mineralization has also
been reported from the Bro wn Derby grani tic pegmatite,
Gunnison County, and Colorado (Rosen berg 1972). The fluo-
rine content of the studied topaz crystals (Table 1)canbe
correlated with the Brown Derby granitic pegmatites that are
believed to have formed at ∼750 °C and 2,000 Kbar.
Various parageneses have been documented for the for-
mation of fluorite. Its formation as a vein mineral and
through pneumatolytic process in granites and pegmatites
are the most common cases, but it may also be one of the
metasomatic minerals (Deer et al. 1966). Hassan (2007)has
correlated the formation of various gemstones in the Shigar
valley pegmatites to the hydrothermal activity. The presence
of fluorite in these pegmatites is another evidence for the
occurrence of such a process because the fluorite is most
likely formed in the last stages of hydrothermal activity
within the pegmatites at t he time o f saturation o f fluids
(Peretyazhkoa et al. 2004).
All the reported gemstones from the Shigar valley are not of
pegmatitic origin, some are either the product of metasomatism
or metamorphism. The axinite, zoisite, and clinozoisite seem to
be of the later paragenesis. The Hashupa and Alchu ri areas of
the Shigar valley, where the mines of axinite, zoisite, and
clinozoisites are located, lack pegmatitic intrusions. These are
mineralized along joints or fractures within greenschist or
epidote–amph ibolite facies metamorphic rocks of the Bauma-
Harel formation. This area is highly deformed due to the
Northern Suture or the Main Karakoram Thrust. This major
tectonic activity may have played a key role in the deformation
of the rock strata to provide channels for the hot solutions to
interact with the host rock to form axinite, zoisite, and
clinozoisites.
Conclusions
A variety of gemstones having homogeneous chemical com-
position are found in the Shigar valley. These are mainly
confined to the cavities and vugs within the zoned pegmatites
and hence appear to be of hydrothermal or pneumatolytic
origin. Those gemstones which are not confined to the zoned
pegmatites are considered to be formed due to metamorphism
and or metasomatism. The compositions of studied garnets
indicate that these are almandine–spessartine garnets and are
magmatic in origin rather than being xenocrysts due to assim-
ilation from the host rock. Gemstone assemblage of the Shigar
valley pegmatites suggest that the source rock was significant-
ly enriched in B, F, Cl, H
2
O, and other volatiles and was
depleted in Li because no lithium-bearing mineral (e.g., lepid-
olite, zinnwaldite, spodumene) has so far identified these
pegmatites.
Acknowledgments All the authors say thanks to Director NCE in
Geology, University of Peshawar for the financial support during field
and laboratory work. The first author says special thanks to the adminis-
tration of the University of Sindh, Jamshoro for granting the study leave
for Ph.D., and we also extend our thanks to the Department of
Geosciences, Naruto University of Education, Japan for availing their
analytical facilities. Mr. Mohammad (driver) is highly thanked for nicely
driving in such a hard mountainous terrain during field.
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