All the mines are found in the extreme north of the country in the Himalaya Mountains. A remarkable variety of gemstones occur in Swat valley. Mines are now being worked near Mingora, Gujar Killi, and Makhad on both sides of the Shangla Pass. The first area, the biggest one, is about 1.5 km N of Mingora.
In 1958 a few green crystal were found on the north of Mingora. They were brought to the local reigning sovereign, Prince Miagmul Jahanzeb. The prince showed the stones to some visitors from Bombay, who identified them as emeralds. The prince declared the hill forbidden territory and engaged workmen to search for more crystals on the surface.
After the 1968 the Industrial Development Corporation of Pakistan was given responsibility for mining.
In february 1979 the Gemstone Corporation of Pakistan was formed, and it reorganized mining according to modern principles.
All of the mines are owned by the state.
The emerald-bearing rocks overlie a dark mica schist and are covered by a lighter, green chlorite-tremolite schist. The chlorite-tremolite schist grades into talc schist beneath.
The emerald-bearing formation consist of dolomitic talc schist.
Lenses of ultamafic and talc-carbonate rocks are intercalated in the shear zone.
The thickness of talc-schist has been affected by rock movements.
A break is noted between the talc schist and mica schist: it consist primarily of a dark mica within layer of quartz and dark grey limestone.
Underneath, there are a sedimentary and calcareous layers: arenaceous, argillaceous and carbonatic rock. Underlying that is an older ultramafic dike of amphibolites and finally a younger intrusion of granodiorite called the Boner schistose group.
In the region of Mingora the schists are almost vertical.
The talc schist which hosts the emeralds is intruded by a series of serpentinized ultramafic dikes and, because of thrusting, it repeated four times. In the upper part there is a lack of emerald because there it lacks the quartz vein interlinked with calcite that characterizes the lower beds. This combination, quartz and calcite, becomes dominant in the lower part.
The quartz-calcite-beryl mineralization is hydrothermal, originating from granodiorite, which runs the full length of the talc schist. The chromium necessary for the emerald coloration was probably contained in the ascending solution as it passed through the ultramafic rocks that have been altered in serpentinites. Emeralds occur also in pockets associated with veins of quartz, calcite and talc. The emeralds found in quartz usually are broken whereas those found in carbonate-talc schist are normally intact and euhedral.
(Euhedral refers to well-formed crystals with sharp, easily-recognized faces. Normally, crystals do not form smooth faces or sharp crystal outlines. Many crystals grow from cooling liquid magma. As magma cools, the crystals grow, and they eventually touch each other, preventing crystal faces form forming properly or at all.
(However, when snowflakes crystallize, they do not touch each other. Thus, snowflakes form euhedral, six-sided twinned crystals. In rocks, the presence of euhedral crystals may signify that they formed early in the crystallization of a magma or perhaps crystallized in a cavity or vug, without hindrance from other crystals.
(Etymology: Euhedral is derived from the Greek hedron meaning shape.)
For each mine we calculated the medium value of chemical analyses (analysed 20 point ) by EMPA (Cameca CX 827).
Mn, Se, F, Rb are under detection limits except in few cases. Li and Be are not determined.
Chemical analyses have been normalized at 85%.
In this sample it is impossible to calculate the lattice parameter and water value because the analysis is destructive and the sample is worked.
Reflectance FTIR (Fourier Transform Infrared Spectra) of gemstones have been acquired using a microscope IRscopeII (Bruker) accumulating 200 scans with a resolution of a cm-1 or better, in the range 7000-600 cm-1. Here we give only the skeletal bands which lie in the interval 1500-600 cm-1.
When the samples were suitably cut in direction parallel or normal to the c axis, polarized spectra were also obtained on the pinacoid or on the basis respectively or both. According to the group theory 6A2u + 16 E1u infrared modes are predicted: the E1u modes are observed in the spectrum when the electric field is perpendicular to the c-axis (ordinary ray) and the A2u modes are observed for the extraordinary ray (E|| c). Therefore, non degenerate bands (A2u) are observed on pinacoids and show intensity changes in polarization, while degenerate bands (E1u) are detected on basis spectra and show only a lowering in intensity in polarized light.
1. Gubelin E. J. “Gemstones of Pakistan: Emerald, Ruby, and Spinel” Gems & Gemology Fall 1982 p. 123-139
2. Laurs B. M. and Dilles J. H. “Emerald Mineralization and Metasomatism of Amphibolite, Khaltaro Granitic Pegmatite-Hydrotherrmal Vein System, Haramosh Mountains, Northern Pakistan” The Canadian Mineralogist vol. 34 1996 p. 1253-1286
3. Sinkankas J. 1981 “Emeralds and Other Beryls” Pensylvania, Chilton Book Co. p.371-377