ORIGINAL PAPER

Shigar valley gemstones, their chemical compositionand 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# Saudi Society for Geosciences 2013

Abstract Avariety of gemstones is being mined in the Shigarvalley, Skardu, Pakistan. These include beryl (goshenite andaquamarine), tourmaline (schorl), garnet (almandine–spessar-tine), apatite, topaz, fluorite, zoisite, clinozoisite, and axinite,mostly occurring in complex or zoned pegmatites and meta-morphic rocks. These have been analyzed using electronprobe micro-analyzer and X-ray diffractometer. The mineralchemistry of each gemstone is similar to its respective typicalgemstone variety with homogenous chemical composition.Field and chemical characteristics suggest that beryl, tourma-line, garnet, apatite, topaz, and fluorite are occurring in zonedpegmatites which are largely formed by magmatic hydrother-mal fluids in the cavities and vugs within the intermediatezone. However, zoisite, clinozoisite, and axinite may have ametamorphic and/or metasomatic origin.

Keywords Shigar valley . Skardu . Gemstones . Zonedpegmatites

Introduction

Shigar valley, located north of Skardu, is one of the most famousvalleys of the Gilgit-Baltistan region of Pakistan as it is thegateway for most of the expeditions to the K-2, the secondhighest peak of the world. In recent years, this valley receivedmuch attention due to gemstone occurrences. Pegmatites, whichare the hosts of gemstones, occur in Karakoram, Hindu Kush,and the Himalayan Mountains. Pegmatite related gemstoneshave also been reported from other localities of Pakistan suchas Shengus, Stak Nala, Garam Chasma by Kazmi et al. (1985)and Laurs et al. (1998). In addition, there are many pegmatitesworldwide, which are famous among the mineral and gemstonecollectors for the occurrence of various gemstones (e.g.,Rosenberg 1972; Shearer et al. 1984; London 1986; Viannaet al. 2002b; Peretyazhkoa et al. 2004). Shigar valley is uniquein this regard as many gemstones occur in pegmatites and themetamorphic rocks (Fig. 1). Hassan (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 ofmineralogy, internal structure, and texture, are complex andzoned. Unzoned and simple pegmatites are also not uncommonand are barren of the gemstones. The complex pegmatites showboth symmetrical and asymmetrical zoning. Each zone is litho-logically, texturally, and compositionally distinct from otherzone(s). The outermost zone is fine-grained, an intermediatecoarse-grained, and central blocky zones. Gemstones occur inthe central parts of the intermediate zone and/or at the core-margin zone. Gemstones are generally found in cavities usuallyrounded or ovoid in shape. The cavities are found tightly packedwith gemstones, usually surrounded by a light pink or whiteclayey material.

As a common observation during geological fieldwork, itwas noticed that the size of the gemstone crystals was directlyproportional to the size of the cavity as described elsewhere(e.g., London 1986, 1992). Various types of gemstones havealso been reported in different localities, including the Shigar

M. H. Agheem (*) :H. DarsCentre for Pure and Applied Geology, University of Sindh,Jamshoro, Sindh, Pakistane-mail: mhagheem@yahoo.com

M. T. ShahNational Centre of Excellence in Geology, University of Peshawar,Peshawar, Pakistan

T. KhanDepartment of Earth and Environmental Sciences, Bahria University,Islamabad, Pakistan

M. MurataDepartment of Geosciences, Faculty of Science, Naruto Universityof Education, Naruto Tokushima 772-8502, Japan

M. ArifDepartment of Geology, University of Peshawar, Peshawar, Pakistan

Arab J GeosciDOI 10.1007/s12517-013-1045-8

Fig. 1 Location map of theShigar valley, Gilgit-Baltistan,Pakistan

Fig. 2 Map showing gemstone occurrences in the Shigar valley

Arab J Geosci

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

SiO2 65.13 65.35 65.02 63.91 63.55 63.64 65.33

TiO2 0.00 0.00 0.00 0.00 0.00 0.15 0.07

Al2O3 17.98 18.24 18.00 17.31 17.28 17.63 19.91

FeOt 0.14 0.28 0.20 0.69 0.77 3.92 0.50

MnO 0.12 0.00 0.00 0.04 0.01 0.13 0.06

MgO 0.00 0.01 0.04 0.00 0.00 0.01 0.11

CaO 0.00 0.01 0.01 0.00 0.00 2.34 0.48

Na2O 0.12 0.09 0.12 0.00 0.38 0.00 0.16

K2O 0.02 0.01 0.00 0.04 0.04 0.14 0.42

Cr2O3 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

Fe2 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 0.00 0.00 0.00 0.01 0.01 0.03 0.10

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

SiO2 33.51 34.75 35.06 34.52 33.16 33.47 34.25 33.55

TiO2 0.26 0.29 0.22 0.08 0.07 0.01 0.08 0.27

Al2O3 32.80 33.11 33.79 34.30 34.92 34.64 34.50 34.87

FeOt 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

Na2O 2.16 1.86 1.88 1.31 0.97 1.27 1.24 1.39

K2O 0.05 0.10 0.02 0.01 0.03 0.03 0.02 0.02

Cr2O3 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

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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

Fe2 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

SiO2 37.77 37.61 36.28 35.83

TiO2 0.00 0.00 0.00 0.05

Al2O3 23.72 23.42 24.95 20.73

FeOt 21.55 21.37 21.32 20.42

MnO 16.80 16.76 16.94 23.05

MgO 0.13 0.31 0.12 0.00

CaO 0.00 0.27 0.28 0.23

Na2O 0.02 0.17 0.00 0.02

K2O 0.03 0.00 0.00 0.00

Cr2O3 0.00 0.00 0.00 0.03

NiO 0.00 0.00 0.00 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

Fe2 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 0.00 0.00 0.00 0.00

Cr 0.00 0.00 0.00 0.00

Ni 0.00 0.00 0.00 0.00

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 0.00 0.00 0.00 0.09

Table 1 (continued)

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Apatite

Locality Yuno Kashmol

Sample 3 M 3C 9A 9B

Grain Core Rim Core Core Rim Core Rim

SiO2 0.34 0.21 0.18 0.55 0.29 0.37 0.25

TiO2 0.01 0.26 0.00 0.05 0.00 0.04 0.02

Al2O3 0.03 0.00 0.01 0.05 0.00 0.02 0.00

FeOt 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

Na2O 0.26 0.08 0.07 0.13 0.06 0.05 0.03

K2O 0.00 0.00 0.00 0.00 0.00 0.00 0.00

Cr2O3 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

P2O5 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

Fe2 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

SiO2 32.37 32.13 32.25 31.82 31.87 31.75

TiO2 0.00 0.00 0.00 0.00 0.00 0.00

Al2O3 55.12 55.45 57.16 55.12 56.73 56.65

FeOt 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

Na2O 0.02 0.00 0.03 0.00 0.00 0.00

K2O 0.05 0.01 0.13 0.06 0.01 0.02

Table 1 (continued)

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Cr2O3 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

Fe2 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

SiO2 0.28 0.14 0.21 0.13 0.20 0.26 0.34 0.18 0.30 0.17

TiO2 0.11 0.00 0.11 0.09 0.07 0.10 0.00 0.17 0.09 0.10

Al2O3 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

Na2O 0.01 0.00 0.00 0.04 0.02 0.02 0.00 0.00 0.00 0.02

K2O 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

Cr2O3 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

SiO2 39.89 39.67 39.88 39.65

TiO2 0.06 0.04 0.00 0.03

Al2O3 31.17 30.09 32.64 32.54

FeOt 1.89 2.23 2.40 2.16

Table 1 (continued)

Arab J Geosci

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

Na2O 0.05 0.00 0.00 0.00

K2O 0.00 0.00 0.00 0.00

Cr2O3 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

Fe2 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

SiO2 40.36 40.72 39.48 38.98 39.11 39.21

TiO2 0.09 0.21 0.14 0.18 0.15 0.14

Al2O3 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

Na2O 0.00 0.00 0.01 0.00 0.00 0.04

K2O 0.00 0.00 0.00 0.00 0.00 0.00

Cr2O3 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

Fe2 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)

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valley, of the Gilgit-Baltistan region of Pakistan by Blauwetet al. (1997, 2004). However, on the basis of field occurrenceand mineral chemistry, the gemstones of the area are discussedfor the first time for their origin (Fig. 2).

Methodology

Forty crystals of different gemstones were collected from theShigar valley and identified with the help of their physical andoptical properties. In order to confirm their nomenclature, spotchemical analyses were performed using the Jeol Super probeModel JXA-8600 electron probe micro-analyzer (EPMA)with wavelength dispersive system at the Naruto University

of Education, Japan. For this purpose, a small portion fromeach gemstone was cut with a very fine diamond blade in theGems and Gemmological Institute of Pakistan, Peshawar.These were mounted on glass slides and polished on anautomatic diamond polisher in the Mineral TestingLaboratory, Peshawar. All the analyses were performed byemploying 15 kv accelerating voltage and 1.99–1.21 ampcurrent. The standards viz., wollastonite (Si and Ca), TiO2

(Ti), corundum (Al), hematite (Fe), rhodonite (Mn), syntheticMgO (Mg), microcline (K), albite (Na), synthetic Cr2O3 (Cr),and synthetic NiO (Ni) were used. X-ray diffraction analyseswere performed using Rigaku Corporation, Geigerflex D/MaxSeries, X-ray diffractometer (XRD) at the National Centre ofExcellence 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

SiO2 43.93 42.58 42.58 43.30 43.04 43.12 44.64

TiO2 0.00 0.00 0.07 0.00 0.00 0.02 0.00

Al2O3 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 0.38 0.28 0.21 0.65 0.80 0.63 1.04

MgO 0.82 0.92 1.13 1.08 0.99 0.93 1.58

CaO 19.75 20.54 21.33 19.41 20.84 19.92 21.91

Na2O 0.00 0.00 0.00 0.00 0.00 0.00 0.00

K2O 0.00 0.00 0.00 0.00 0.00 0.00 0.00

Cr2O3 0.00 0.06 0.03 0.00 0.00 0.00 0.00

NiO 0.02 0.11 0.00 0.02 0.00 0.05 0.08

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

Fe2 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 0.00 0.00 0.00 0.00 0.00 0.00 0.00

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)

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Mineral chemistry

The representative chemical analyses of cores and rims(margins) of individual gemstones from the Shigar valley aregiven in Table 1. Based on EPMA and the XRD data(Table 2), various gemstones have been identified, which aredescribed below.

Beryl

The gem-quality beryl of the Shigar valley includes light todark blue aquamarine and colorless goshenite. The occurrenceof transparent light blue aquamarine crystals (5–15×1–7.5 cm)from the Dassu pegmatites was reported earlier (Middlemissand Parshad 1918). According to Kazmi et al. (1985), aqua-marine crystals up to 16 cm long and 7 cm wide from theDassu pegmatites have been included in the James A. Gibbscollection. 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 atthe core-margin zone, the gem-quality aquamarine crystalsmay occasionally occur in the coarse-grained intermediatezone 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 ofberyl are given in Table 1 and 2, respectively. Due to the

limitation of EPMA analysis, the BeO contents of the berylcrystals were not determined. Therefore, the total of eachanalysis is about 12–18 % low which can be attributed to thelack of determination of BeO and H2O contents in the studiedberyls. The major cations such as silicon and aluminum arewithin the range of normal aquamarine and goshenite analysis.Both these verities are chemically homogenous. The onlydifference in the chemical composition of both the verities isthe difference in FeO contents. The aquamarine has higheramount of FeO as compared to goshenite (Table 1). Therefore,the aquamarine has light blue color, while goshenite iscolorless.

Tourmaline

Tourmaline is an ubiquitous mineral in the gem-bearing peg-matites of the Shigar valley. It is scattered in the entiregroundmass of the pegmatite veins and dykes but mostlyconcentrated either at the core-margin zone or in the borderzone of the host pegmatites. A gem-quality tourmaline crystal,measuring 4×1 cm, was found in a pegmatite exposed atKashmol 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 qualityspecimens of this kind are commonly associated with albite,muscovite, aquamarine, and quartz (Hassan 2007). On thebasis of EPMA (Table 1) and XRD (Table 2) data, thesetourmaline crystals are classified as schorl having 13–15 %FeO. These are generally homogenous both physically andchemically. The total of the analysis of schorl crystals is 13–16 % less than the typical analysis of schorl as B2O3 and H2Ocould not be determined by EPMA. However, all the othermain constituent oxides such as SiO2, Al2O3, and FeO andminor oxides (Table 1) are consistent with the typical analysisof 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 thegem-bearing pegmatites in the Dassu and Yuno areas of theShigar valley. These pegmatites are extensively mined forwell-developed euhedral crystals of garnet and other gem-stones (Fig 3c, e). The gem-quality garnets collected duringthe fieldwork are usually >0.5 cm in diameter, translucent, andreddish brown in color and display the typical dodecahedralform of cubic crystal system. The chemical analysis of thestudied gem-quality garnet crystals along with their end-member compositions are given in Table 1. The relativeproportions of the calculated end-members suggest that thestudied garnets are generally almandine–spessartine with

Table 2 XRD data of the gemstones of different localities of ShigarValley 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 2.84 3.22 7.89 Beryl

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 2.54 2.83 1.51 Almandine

20H Dassu 2.56 1.56 1.54 Almandine

3M Yuno 2.78 3.41 2.71 Apatite

6 Yuno 2.92 3.02 3.65 Topaz

19 Kashmol 2.91 3.17 3.65 Topaz

1CM Yuno 3.13 1.92 1.64 Fluorite

21C Kashmol 3.13 1.96 1.64 Fluorite

26M Goyungo 3.13 1.92 1.64 Fluorite

11AM Alchuri 2.68 2.02 4.03 Zoisite

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

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Fig. 3 Photographs of various gemstones from Shigar valley. aGoshenite and aquamarine from various pegmatites of the Shigar valley.The colorless, transparent crystals are of goshenite while the pale blueones with rectangular prism faces are aquamarine; b A crystal of blacktourmaline (schorl) from the Kashmol pegmatite, Shigar valley. Striationsalong the prism faces are visible; c a crystal of reddish brown garnet fromthe Yuno pegmatite mine. An aggregate of yellowish white calcite crys-tals from the same pegmatite is also shown; d an aggregate of light pinkapatite crystals from the Yuno mine, Shigar valley; e Specimen showingan aggregate of light pink apatite, green fluorite, reddish garnet, and large

books or sheets of muscovite from the Yuno mine, Shigar valley; fcolorless, transparent crystal of topaz (∼1–2 cm across) from the Kashmolpegmatite; g three light green to green crystals of fluorite collected frompegmatite at Kashmol, Shigar valley; h a transparent light green fluoritecrystal (∼2 cm across) represents the Yuno mine, Shigar valley; i twocrystals of zoisite from Alchuri, Shigar valley; j an aggregate of darkbrown crystals of clinozoisite fromHashupa, Shigar valley; k light brownto greenish brown crystals of clinozoisites (epidote), Alchuri, Shigarvalley. A twinned crystal of clinozoisite can be seen near the top of thepicture; l brown crystals of axinite from Alchuri, Shigar valley

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more than 46% of spessartine component. However, the XRDdata (Table 2) classified these as almandine garnet. A garnetcrystal collected from Yuno is showing homogenous compo-sition, but the one collected from Dassu is having increasingMnO content from core to rim suggesting the increase in thespessartine component. However, the core of garnet collectedfrom Dassu has similar composition as that of Yuno (Table 1).

Apatite

Pink and light pink apatite occurring in the Shigar valleypegmatites is of gem quality (Fig. 3d, e). On the basis ofchemical analysis of the studied apatite crystals, thesehave been classified as apatite and mangano-apatite(Table 1). Their EPMA data (Table 1) confirm that theapatite crystals are stoichiometrically pure, and the sum ofthe reported weight percent oxides is about 100 withoutincluding chlorine, fluorine, hydroxyl, and carbonatethereby signifying that the latter components may occurin trace amounts if present. One apatite crystal fromKashmol is enriched in MnO (up to 7.36 wt%) and there-fore is classified as mangano-apatite (Table 1). However,apatite crystals of Kashmol are having higher amount ofMnO and FeOt as compared to that of Yuno (Table 1). TheEPMA data further suggest that the studied apatite crystalsare chemically homogenous. The XRD data (Table 2) alsoconfirmed that the studied crystals are of apatite.

Topaz

The occurrence of two varieties of topaz (i.e., colorless andlight yellow) is reported from pegmatites at Yuno, Kashmol,Dassu, Nyit Bruk, and Goyungo in the Shigar valley (Kazmiand Donoghue 1990). However, during this study, only threecolorless crystals of topaz (∼1×3 cm), one each fromKashmol, Yuno, and Goyungo were collected (Fig. 3f).These topaz crystals are usually associated with albite–quartz–muscovite matrix.

The EPMA analysis of the studied topaz crystals are givenin Table 1. Stoichiometrically, the chemical composition, es-pecially the amount of F (∼19 wt%), of the analyzed topaz isanalogous to the typical topaz found in miarolitic pegmatites(Colombo et al. 2009). The higher amount of F in the studiedtopaz 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 belowthe detection limit while K reaches to 0.13 wt% (Table 1). Thestudied topaz crystals from all the three localities are similar inchemical composition and are homogenous in composition asno significant chemical difference is noticed between theircores and margins (Table 1). Light yellow topaz is relatively

enriched in Cr, Co, Mn, and V and the blue color topaz isenriched in Ni while the colorless topaz is without theseimpurities (Rosenberg 1972). Therefore, due to the negligibleamount of Mn, Cr, and Ni in the studied topaz crystals, theseare colorless in nature. The XRD data (Table 2) also con-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. Theaverage size of the collected crystals is 2×3 cm, and these aretypically associated with tourmaline, beryl, quartz, topaz, andmuscovite in cavities (Fig. 3g, h, and e). The EPMA analyses,given in Table 1, suggest that the large gem-quality greencolor fluorites are stoichiometrically pure CaF2 and have thesame 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 ofSi, Al, and Mg may exist in fluorites either as inclusions and/or impurities or may replace some of the Ca. In the studiedfluorites, no such replacement, substitution, and inclusionswere observed except for silica, which is present up to0.34 wt%. The XRD data also confirmed that the studiedcrystals are of fluorite (Table 2).

Zoisite

Gem-quality zoisite, found in the Alchuri area of the Shigarvalley, is colorless to light green in color. The local miners andgem dealers call it tanzanite (Fig. 3i). The EPMA chemicaldata of the studied zoisite crystals are given in Table 1. All ofthe major oxides such as the SiO2, Al2O3, FeOt, and CaO arein the range of a typical chemical analysis of a zoisitesuggesting that these are stoichiometrically pure zoisites(Table 1). On the basis of XRD data (Table 2), these crystalsare also identified as zoisite.

Clinozoisite

Various varieties of gem-quality clinozoisite were collectedfrom the Alchuri and Hashupa areas in the Shigar valley.Clinozoisite occurs as veins and fracture-filled material withinthe metamorphic rocks (Fig. 3). The color and size of thecollected crystals are variable. Most of the crystals are darkbrown and opaque but transparent to translucent greenishbrown to light brown or yellowish green varieties are alsocommon (Fig. 3j, k). The EPMA data of the studied crystals ofclinozoisite are given in Table 1. The chemical data suggest

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that these are stoichiometrically pure clinozoisites. These con-tain SiO2 (37.75–40.78 wt%), Al2O3 (25.89–28.92 wt%),CaO (20.58–24.68 wt%), and FeO (5.07–8.73 wt%) and anumber of other oxides which occur in insignificant amounts(Table 1). The insignificant nature of chemical variation with-in individual crystals indicates their homogenous nature. Thesame 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 ingreenschist to epidote–amphibolite facies metamorphic rocksin the Shigar valley (Fig. 1). Their color varies between lightpink and brown (Fig. 3l). The chemical analyses of variouscrystals of axinite are given in Table 1. Due to limitation of theEPMA analysis, the Be2O3 and H2O could not be determinedwhich resulted in the lower total (91.97–96.05 wt%). The restof the major oxides such as SiO2, Al2O3, FeOt, MnO, MgO,and CaO have similar concentration as of typical axinite. Thechemical analyses indicate that all the studied crystals ofaxinite have Ca>1.5 and Fe>Mn which can be classified asferroaxinites (Pringle and Kawachi 1980). In terms of chem-ical composition, the studied ferroaxinites are very similar tothose reported from Sri Lanka (Hanni and Gunawardene1982), New Jersey (Pohl et al. 1982), and New MelonesLake, California (Cummings 1983).

Discussion

Mineralogical and geochemical studies play a vital role inunderstanding the petrogenesis of any rock type. In case ofpegmatites, especially the granitic pegmatites generally have avery complex mineralogy and internal structure (Ćerný 1982,1991). The granitic pegmatites have been classified on thebasis of various parameters such as the occurrences of raremetals, 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 complexpegmatites are classified as gemstone-bearing miaroliticpegmatites.

The variation in the color of beryl generally reflects varia-tion in composition (Hammarstrom 1989). The blue color inaquamarine 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 reportedby Figueiredo et al. (2008). Therefore, the blue color of thestudied aquamarine, containing relatively high FeO, can be

attributed to Fe+2. Beryl mineralization generally but by nomeans exclusively occurs in the complex or zoned type ofpegmatites (Ćerný 1982, 1991). It may even occur in simplepegmatites where metasomatic replacement has occurred.Various studies have indicated that the alkali content of berylfrom Li pegmatites is mostly higher than that occurring innon-lithium pegmatites (Gallagher 1975). Correspondingly,the studied beryls are very poor in alkalis since the Li contentof their parent pegmatites is low (e.g., Hassan 2007).Although the studied aquamarines and goshenites are mostlyassociated with the minerals of pneumatolytic or fluid phasestage found in cavities and vugs, some of the non-gem berylcrystals also occur in the intermediate zone. This indicates thatthe crystallization of beryl started during the solidification ofthe intermediate zone and matured in the core-margin zone tillthe formation of vugs and cavities.

In terms of occurrence, the most important compositionalvarieties of tourmaline group are the iron tourmalines orschorl, the alkali tourmalines or elbaites, and the magnesiantourmalines or dravites. In these varieties, the Y sites aremostly occupied by Fe2+, Li, and Mg, respectively. Variousstudies have revealed that different types of tourmalines maybe present even in a single pegmatitic body as reported fromthe Black Hills, South Dakota (Shearer et al. 1984) and fromthe Stak Nala pegmatites (Laurs et al. 1998). On the otherhand, some specific types of tourmalines may be present in aparticular type of pegmatite. Two genetically different types oftourmalines 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 haveformed 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 theborder zone, but the gem-grade crystals are associated onlywith other gemstones of pneumatolytic or cavity formationstage near the core-margin zone. The presence of tourmalinesin the intermediate or border zone may be the result of afracture-filling process, which commonly occurs in certainpegmatites after the formation of cavities or vugs near thecore-margin zone.

The garnets of the gem-bearing pegmatites of the Shigarvalley are neither pure almandine nor spessartine, although theoccurrence of pure spessartine has been reported from differ-ent pegmatites elsewhere in the world (Strock 1930; Hall1965; Gresens 1966). Hall (1965) suggested that if the micas,especially muscovite in granitic aplites or pegmatites are poorin MnO (containing 0.06–0.08 wt% MnO), then there arechances of manganese accumulation in the residual magmauntil the formation of garnet of almandine–spessartine com-position. TheMnO content of the studied muscovites from theShigar valley pegmatites is low (0.03–0.09 wt%, Hassan2007). It is, therefore, possible that the manganese wasretained by the residual magma until the formation of garnets

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of almandine–spessartine composition near the core-marginzone within the Shigar valley pegmatites. The occurrence ofgarnets either in the wall zone or intermediate zone supportsthe idea that in the paragenetic sequence of gemstones, theyformed relatively earlier, i.e., before the saturation of fluidsand the resulting formation of the corresponding gemstonessuch as the fluorite, schorl, and topaz.

Haapala (1974) has attempted to differentiate topaz-bearinggranites from the normal and rapakivi type granites merely onthe basis of trace element geochemistry. He mentioned that thetopaz-bearing granites have relatively high values of Be, Li, F,Rb, Sn, Ga, and Nb and low values of Fe, Mg, Ti, Ba, Sr, andZr. The concentration of some of these elements, e.g., Be, Sn,and Li in the Shigar valley pegmatites was not determined, buttheir 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 alongwith other fluorine-bearing and or other volatile (B, H2O)-saturated gemstones. Some of the topaz crystals from a zonedpegmatite near Yuno occur at the base of a core-margin zonethereby suggesting their formation during the pneumatolyticstage. The occurrence of such type of mineralization has alsobeen reported from the Brown Derby granitic pegmatite,Gunnison County, and Colorado (Rosenberg 1972). The fluo-rine content of the studied topaz crystals (Table 1) can becorrelated with the Brown Derby granitic pegmatites that arebelieved 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 andthrough pneumatolytic process in granites and pegmatitesare the most common cases, but it may also be one of themetasomatic minerals (Deer et al. 1966). Hassan (2007) hascorrelated the formation of various gemstones in the Shigarvalley pegmatites to the hydrothermal activity. The presenceof fluorite in these pegmatites is another evidence for theoccurrence of such a process because the fluorite is mostlikely formed in the last stages of hydrothermal activitywithin the pegmatites at the time of saturation of fluids(Peretyazhkoa et al. 2004).

All the reported gemstones from the Shigar valley are not ofpegmatitic origin, some are either the product of metasomatismor metamorphism. The axinite, zoisite, and clinozoisite seem tobe of the later paragenesis. The Hashupa and Alchuri areas ofthe Shigar valley, where the mines of axinite, zoisite, andclinozoisites are located, lack pegmatitic intrusions. These aremineralized along joints or fractures within greenschist orepidote–amphibolite facies metamorphic rocks of the Bauma-Harel formation. This area is highly deformed due to theNorthern Suture or the Main Karakoram Thrust. This majortectonic activity may have played a key role in the deformationof the rock strata to provide channels for the hot solutions tointeract with the host rock to form axinite, zoisite, andclinozoisites.

Conclusions

A variety of gemstones having homogeneous chemical com-position are found in the Shigar valley. These are mainlyconfined to the cavities and vugs within the zoned pegmatitesand hence appear to be of hydrothermal or pneumatolyticorigin. Those gemstones which are not confined to the zonedpegmatites are considered to be formed due to metamorphismand or metasomatism. The compositions of studied garnetsindicate that these are almandine–spessartine garnets and aremagmatic in origin rather than being xenocrysts due to assim-ilation from the host rock. Gemstone assemblage of the Shigarvalley pegmatites suggest that the source rock was significant-ly enriched in B, F, Cl, H2O, and other volatiles and wasdepleted in Li because no lithium-bearing mineral (e.g., lepid-olite, zinnwaldite, spodumene) has so far identified thesepegmatites.

Acknowledgments All the authors say thanks to Director NCE inGeology, University of Peshawar for the financial support during fieldand laboratory work. The first author says special thanks to the adminis-tration of the University of Sindh, Jamshoro for granting the study leavefor Ph.D., and we also extend our thanks to the Department ofGeosciences, Naruto University of Education, Japan for availing theiranalytical facilities. Mr. Mohammad (driver) is highly thanked for nicelydriving in such a hard mountainous terrain during field.

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