Geology and Origins of the Panjsher Valley Emerald Deposits of Afghanistan

The Panjsher Valley emerald, iron, and silver area of interest (AOI) lies in the Panjsher Valley in eastern Afghanistan. The main AOI, Panjsher Valley, is 958.68 square kilometers (km2) and a silver-iron subarea (111 km2) and emerald subarea (125 km2) lie within its central parts (Figure 1). The Panjsher Valley emerald, iron, and silver AOI lies within Parwan Province and includes the Hisa-e-Awal Panjsher District. Mineral deposit types in the AOI are emerald, hematite-magnetite ores, silver-bearing-iron ores, and polymetallic carbonate-hosted deposits. The Panjsher Valley emerald district contains the following emerald occurrences from the west to east: Khinj, Mikeni I, Mikeni II, Rewat, and Darun. The Buzmal’ Mine is located to the north, close to Panjsher Valley. There are three types of emerald mineralization: 1- mineralization within or adjacent to tectonized diorite dikes (parts of the western zone containing the Buzmal’, Khinj, and Rewat emerald occurrences); 2- mineralization within shear fractures in schist (locality in the eastern zone containing the Darun, Khinj, and Mikeni I and II emerald occurrences); and 3- mineralization in or adjacent to hydrothermally altered and albitized quartz porphyry dikes.

Detailed exploration has covered only small parts of the Panjsher Valley emerald deposits at Buzmal’ and Khinj, and the extension of the emerald-bearing zones at depth has been carried out only minimally at the Khinj emerald occurrence. Economic concentrations of emerald in the western zone at Khinj, estimated from exploration results, suggest that considerable resources of gemstone-grade emerald are likely to exist in the mining district.

Review of Previous Studies

Panjsher Valley emerald and iron deposits have been mined for thousands of years. Kusov and others [1] conducted exploration and mapping for the iron and silver ores in the Panjsher Valley, and Kafarsky and others [2] conducted field work in the emerald fields. Geological exploration and research studies conducted by Soviet and Afghan geologists between 1975 and 1976 were the first specialized studies on the emeralds. The exploration work, on the scale 1:25,000, covered an area of about 100 km2 and included a 5-kilometer (km)-wide and 20-km-long belt of metamorphic rocks along the Panjsher River as well as detailed exploration work at a scale of 1:2,000 that focused on the occurrences of Buzmal’ and Khinj. This work produced a schematic map of the Panjsher Valley emerald field at 1:25,000 scale and geological maps of the occurrences of Buzmal’ and Khinj at 1:2,000 scale, accompanied by detailed plans and profiles. This previous work was compiled by Abdullah and others [3], the United Nations Economic and Social Commission for Asia and the Pacific [4], the Metal Mining Agency of Japan [5], and Peters and others [6]. Additional field and laboratory work on the Panjsher Valley emeralds was conducted by Hammarstrom [7], Seal [8], Seal and others [9], and Bowersox and others [10]. The Afghanistan Geological Survey restarted work in 2009 in the Panjsher Valley, mostly to reassess the iron occurrences for silver.

Fieldwork Methodology

With the help of this method, the Panjsher Valley were first visited. In these areas, the geological characteristics of the area, their seam characteristics, have been studied. Also, sampling was done from Panjsher Valley and the samples were transferred to the thin Section laboratory of the Department of Geology, Faculty of Geoscience, Kabul University after scoring, height and coordinates.

Laboratory Analysis

we prepared thin Sections from the samples in the laboratory. After preparing the thin Sections, they were transferred to the microscopy laboratory of the Department of Geology, Faculty of Geoscience, Kabul University for comprehensive study.

The most favorable geological precondition for emerald mineralization is the presence of the granites of the Laghman Intrusive Complex. The emerald mineralization is localized along linear zones of slight fracturing and brecciation containing hydrothermally altered gabbro diorite dikes, marble, schist, and quartz porphyry. The emerald mineralization is present within a northwestern zone (Buzmal’) and a southeastern zone along the contact between the Silurian-Lower Carboniferous carbonate rocks and the Upper Carboniferous-Permian clastic rocks. The contact typically contains a series of closely spaced steep-dipping faults that contain complicated structural features, such as small-scale folding, fracturing, brecciation, boudinage, and cataclasis, as well as intense hydrothermal alteration that is marked by secondary biotite, phlogopite, epidote, albite, quartz, tourmaline, sulfide and carbonate minerals, chlorite, and muscovite .The beryllium mineralization, with gem-quality emeralds, is superimposed over these altered structural zones at the carbonate-clastic- rock contacts (Figure 5).

The source of chromium, which gives beryl crystals the green color, is most likely from the hydrothermally altered phlogopitized and chloritized gabbro diorite dikes. The emerald mineralization rarely extends beyond the area of hydrothermally altered gabbro diorite dikes; emeralds are not present in all dikes, but are present typically only in large dikes in the southeastern zone. Within the dikes, the emeralds are most likely to occur in zones of albite and chlorite where they are cut by veins containing quartz and potassium-feldspar and carbonate and sulfide minerals or tourmaline. The beryl mineralization in hydrothermally altered rocks forms as small inclusions, individual crystals, or aggregates. This mineralization, commonly metasomatically, replaces yellow coarse-grained vein dolomite, or quartz, potassium-feldspar, or iron carbonate. These minerals are present in veinlets in the gabbro diorite, marble, schist, and rarely, quartz porphyry at the contact with gabbro diorite. As a rule, all the beryl crystal is strongly fractured, nontransparent, and no greater than 3.5 by 0.6 centimeters (cm) in size; commonly the beryl crystal is 1.0 to 1.5 by 0.2 to 0.1 cm or smaller. The color variations of the beryl stones mostly are bluish-green and, in some cases, blue or colorless and rarely emerald-green.

Regional Geologic Setting

The Panjsher Valley emerald, lies within a complex fault system that juxtaposes sedimentary rocks of presumed Paleozoic age that have been metamorphosed to upper greenschist facies against highgrade metamorphic schist and gneiss of presumed Precambrian age. Ultramafic rocks, both of presumed Carboniferous and Precambrian ages, form fault-bounded lozenges within the tectonic zone. The complex fault system is discussed by Chmyriov and others [11]. These authors suggest a Hercynian age (circa 300 million years ago) for much of the latest tectonic activity. A set of granitoid plutons and other igneous bodies of presumed Oligocene age (Laghman Intrusive Complex) were intruded into these older fault systems (Figure 2). Metamorphic rocks are prevalent in the Panjsher Valley emerald, but their age and origin is not well understood. Because of the lack of isotopic ages, scientists have expressed a low confidence in the ages assigned to metamorphic and plutonic rocks and to their assumed ages of tectonic activity (L.W. Snee, U.S. Geological Survey, 2005, written commun).

Strongly foliated, high-grade layered gneiss at the entrance into the valley contains color banding (Figure 3) and reflects compositional variation from felsic to mafic. Metasedimentary units form two extensively faulted sedimentary packages, one dominated by clastic and the other dominated by carbonate rocks (Figure 2). Fine-grained, thinly laminated carbonaceous phyllite (Figures 4a-4c) is interbedded with massive, up to 1-meter (m)- thick discontinuous sandstone layers. This low-grade carbonaceous phyllite contains angular quartz fragments in a fine-grained dark matrix that is dominated by graphite (Figure 4a). The more massive lenses in Figures 4b&4c are carbonate-cemented quartzrich sandstone blocks. At higher metamorphic grade, this rock underwent prograde metamorphism from spotted phyllite (Figure 4b) to schist (Figure 4c).

Metallogeny

The Panjsher Valley emerald, iron, and silver AOI lies within the Har-i-Rod-Panjsher Metallogenic Zone, which stretches from the western frontier eastward through the whole country as far as and beyond the upper reaches of the Panjsher River. The Hari- Rod-Panjsher Metallogenic Zone contains a variety of mineral occurrence types and commodities, including barite, emerald, gold, iron, lead, manganese, mercury, silver, sulfur, and zinc. The zone displays an extremely complex heterogeneous structure and contains Paleozoic, Mesozoic, and Cenozoic rocks belonging to different structural-formational zones. Proterozoic rocks also outcrop in upthrown blocks throughout much of the zone. Specific features of this metallogenic zone are extensive Paleozoic and Mesozoic nappe outliers and imbricate structure zones.

Geology

The Panjsher Valley emerald, iron, and silver AOI lies adjacent to the Hari-Rod fault that trends westward into western Afghanistan (Figure 2). This entire fault structure crosses Afghanistan and is one of the most significant and complex in Afghanistan. In the Panjsher Valley, high-grade metamorphic rocks on both sides of this fault are separated from each other by a thin, up to 5-km-wide belt of low-grade metasedimentary rocks consisting of graphitic schist and marble. Scattered throughout the terrane are fault-bounded lozenges of ultramafic rocks (L.W. Snee, U.S. Geological Survey, 2005, written commun). Mineral deposit models for emerald deposits include the emerald veins as well as metasomatic or shear zone models discussed in Peters and others [6]. The bestknown emerald deposits of the Panjsher Valley lie along the valley’s southeastern side near the village of Khinj; although emeralds also have been reported on the northwestern side of the valley.

The emerald mineralization is localized along linear zones that contain fracturing and brecciation of hydrothermally altered gabbro diorite dikes, marble, schist and quartz porphyry. Emeralds are present in two zones [in a northwestern zone (Buzmal’ locality) and in a southeastern zone (the other occurrences)] and are located near the contacts between Silurian-Lower Carboniferous carbonate rocks and Upper Carboniferous-Permian clastic rocks. Along the contacts, a series of closely spaced, steep-dipping faults contain zones of fracturing, brecciation, boudinage, and cataclasis as well as intensely hydrothermally altered rock (including secondary biotite, phlogopite, epidote, albite, potassium-feldspar, quartz, tourmaline, sulfide and carbonate minerals, chlorite, and muscovite). The beryllium mineralization in the zones that contain the emeralds is superimposed on a complex system of fractures in hydrothermally altered (carbonate-sulfide) rocks (gabbro diorite, marble, schist), especially near hydrothermally altered phlogopitized and chloritized diorite dikes (gabbro diorites).

Geologic Character of the Panjsher Valley Emerald Deposits

The emerald-bearing zones occupy an area about 3 km wide and 20 km long in the Panjsher Valley emerald, that trends northwest and is confined to the southeastern side of the Panjsher River. The mountain ridge that parallels the Panjsher River rises steeply in elevation from about 2,200 m in the valley to almost 5,500 m in the peaks to the southeast. The primary emerald- bearing zones are a few miles to the east of the Panjsher River at about 3,200 m elevation but as high as 4,000 m. Access to the mineralized areas is by footpaths, generally following the streams (19;20;21). The rocks in this emerald-rich belt consist of highly faulted carbonate and clastic sedimentary rocks, which are variably metamorphosed to phyllite, schist, and marble. Intruded into these units are mafic gabbro diorite and felsic quartz porphyry bodies. Within this belt, seven emerald-bearing zones have been defined; three of these occurrences—Khinj (western zone), Buzmal’, and Rewat—are in carbonate host rocks, and the other four—Khinj (eastern zone), Mikeni I, Mikeni II, and Darun—are in clastic host rocks.

All these occurrences lie along the fractured and altered contact between the carbonate and clastic units The best emeralds are from the Khinj and Mikeni occurrences. Remnants of cavities in the quartz, potassium-feldspar, and carbonate veins are thought to be the principal repositories of the emerald mineralization and are interpreted to be the latest hydrothermal events in the host zones. Veinlets of carbonate (with specular hematite in places; Figures 5&6), quartz, quartz-carbonate, pyrite-carbonate, and quartz and tourmaline-carbonate are common. Tourmaline and albite carbonate and iron oxide alteration is common (Figures 8a- 8c). Microcline, white mica, and biotite or phlogopite also form alteration products. Beryl crystal forms in clusters within the alteration and in veinlets. Evidence for post depositional fracturing is exhibited by some beryl crystals (Figure 8d). The quality of the emerald crystals varies from mine to mine. Most miners believe that the highest quality crystals come from the Mikeni and Khinj localities. Crystals are transparent to translucent or opaque and generally range from 4 to 5 carats, although a 190-carat crystal was reported by Bowersox [12,13].

Crystals normally are euhedral and prismatic, although in some places, crystals have been naturally etched by later reactive fluids. Color zoning is common, and interiors are pale and exteriors are dark green. The green color of all emeralds is the result of a small amount of chromium or vanadium instead of aluminum in the beryl crystal structure. In Panjsher Valley emeralds, chromium concentrations range up to 19,180 parts per million (ppm), and vanadium concentrations range up to 690 ppm according to measurements by neutron activation. Hammarstrom [7] measured chromium concentrations up to 13,700 ppm and vanadium concentrations up to 3,100 ppm by electron microprobe and also showed that the brightly colored green areas of emerald are enriched with chromium. Chemically, Panjsher Valley emeralds fall within the range expected for natural emeralds but appear to be most similar to Colombian emeralds. They are easily distinguished from Pakistani emeralds and other world emerald deposits by differences in trace element content.

Origins of the Panjsher Valley Emerald Deposits

Emerald is one of the rarest and most precious gemstones because unusual circumstances are necessary to combine chromium and beryllium together in the natural environment. Emerald results when aluminum in the beryl crystal structure is substituted with a small amount of chromium or vanadium. Beryllium and chromium are geochemically incompatible because beryllium has a very small atomic radius (0.3 angstrom). Therefore, beryllium is excluded from the crystal structure of most minerals, but it remains in fluid or magma until the last stages of the magmatic processes. Beryllium also has a small crustal abundance (5 ppm or less). Thus, beryllium- bearing minerals generally are only found in late-stage igneous rocks, such as pegmatite, or form from beryllium that has been scavenged from beryllium-bearing source rocks by hydrothermal processes. Chromium, on the other hand, is found in significant amounts in ultramafic and some “primitive” mafic rocks. Ultramafic rocks crystallize early in magmatic processes and are at the opposite end of the geological spectrum from those that carry beryllium.

Chromium also is found in significant amounts, up to 5,000 ppm, in some black shale; the vanadium content of some black shale can be as high as 14,000 ppm reference. The source of the high concentrations of chromium and vanadium in black shale is uncertain, but Krauskopf recognizes the importance of provenance, and Snee and Kazmi [14] suggest that a high chromium content could reflect the presence of ultramafic and chromium-rich mafic rocks in the source area of the shale. The favorable conditions for the formation of Panjsher Valley emeralds include: 1-nearby occurrence of the rare-metal-enriched granites of the Laghman Complex,2- zones of tectonic disturbance and shearing, -hydrothermally altered biotitized (phlogopitized) and chloritized gabbro diorite dikes, marble, schist, and quartz porphyry,4- the contact between the carbonate and clastic sedimentary rocks. Distinct sources for both chromium and beryllium are needed; the chromium source for Panjsher Valley emeralds is from mafic (gabbro diorite) igneous rocks.

Beryllium is transported along faults and fractures to the chromium-bearing host rocks by hydrothermal fluids that are derived during magmatic processes derived from the emplacement of the Laghman Igneous Complex. Aside from quartz porphyry dikes, no chemically evolved igneous rocks or pegmatites exist in the mineralized area of the Panjsher Valley. Laghman Complex granitoids are located to the east, in Nuristan, where they are the host rock and likely source for numerous rare-metal pegmatites, some of which contain beryl. In recent years, work done on Colombian emeralds by Beus [15], Giuliani and others [16], and Ottaway and others [17] has resulted in an alternative hypothesis for the source of beryllium and chromium in Colombian emerald deposits. In the Colombian model, beryllium and chromium are derived from organic-rich black shale, which is exposed within the sedimentary units that host the emeralds.

As noted earlier in this report, black shale in some parts of the world contains a significant abundance of chromium and vanadium, but near the Colombian emerald deposits, chromium abundance is only on the order of 30 to 40 ppm. In the Colombian model, hydrothermal brines derived from the dissolution of evaporates transported sulfate to the black shale along fractures and faults. The sulfate then reacted with the organic matter in the shale and released beryllium, chromium, and vanadium, which ultimately precipitated as emerald. Considering the very low concentrations of beryllium, chromium, and vanadium in the host rock shale, this process must have been highly efficient. Sabot and others [18] have proposed a similar model for the formation of the Panjsher Valley emeralds and report, as did Seal [19] and Bowersox and others [20], the presence of high-salinity inclusions. The inclusions in Panjsher Valley emeralds are very similar to those of Colombian emeralds [21-24].

Experimental analysis of Panjsher Valley inclusion fluids showed them to be highly saline with chlorine content of more than 200,000 ppm, sodium more than 73,000 ppm, potassium nearly 20,000 ppm, and very low bromine abundance, indicating derivation from the dissolution of halite. The stable isotope analyses suggested that sulfur and boron were derived from an evaporite source [25-29].

Known Deposits

The known emerald deposits of the Panjsher Valley lie along the valley’s southeastern side near the village of Khinj, although emeralds also are present on the northwestern side of the valley (Figure 9). The largest and most well-known area is the Khinj emerald prospect area, which has both surface and underground excavations [30-35]. The Khinj emerald prospect contains two emerald- bearing zones, the western and eastern zones. The western zone consists of a series of steep-dipping en echelon dikes of gabbro diorite, within which the emerald-bearing mineralization occurs in quartz-carbonate and quartz-microcline veinlets that are developed in the albitized and biotitized rocks. The eastern Khinj zone consists of a system of hydrothermally altered shear zones in schist, typically containing secondary albite, carbonate, and quartz [36-39]. Emerald occurrences are also present in a number of other localities in the Panjsher Valley AOI, such as at Buzmal’, Mikeni, Darun, and Rewat (Figure 9).

The Rewat emerald district is located along the Panjsher River. Beryl mineralization, including emerald, lies along a strip extending for about 15 km [40-44]. The mineralization consists of albite, tourmaline, pyrite, and silicified rocks in a fault zone that offsets Silurian-Lower Carboniferous carbonate rocks from Carboniferous- Lower Permian siliceous-shaly rocks. The favorable zone encloses a great number of gabbro diorite and quartz porphyry veins and dikes [45-48]. The orebodies are small, emerald-bearing quartz- ankerite and dolomite veins and stringers that commonly are contained in metasomatically altered gabbro diorite, dolomitic marl, quartzbiotite schist, and quartz porphyry. High-grade emeralds are most abundant in the altered gabbro diorite dikes (Figure 9).

Detailed exploration has covered only a small part of the Panjsher Valley emerald deposits at Buzmal’ and Khinj, and the extension of the emerald-bearing zones at depth has been done only in a small way at the Khinj occurrence. Economic concentrations of emerald in the western zone at the Khinj emerald mining district, resulting from exploration, suggest considerable resources of gemstone-grade emerald are likely in the mining district. Bowersox and others [10] estimated that, the annual production of emeralds in the Panjsher Valley area was worth $10 million in 1991, when 5,000 villagers were engaged in emerald mining. With peace, technical assistance, proper equipment, local support, and training, the potential for $300 million to $400 million per year in 10 years may be possible. Emerald miners in the Panjsher Valley generally excavate into the contact zone between carbonate and clastic host rocks; dynamite commonly is used, to the detriment of the crystals. Mining activity was reported at the Khinj and Mikeni localities. Miners follow yellow hydrothermal alteration zones and veins in search of emeralds.

Some tunnels extend only a few meters into the hillside; but some extend more than 200 m underground. Tunnels do not contain structural reinforcements. An important consideration to be addressed is the future of the Panjsher Valley emerald deposits. This concern applies to several aspects. First, the mining techniques used in the Panjsher Valley endanger the stones and the miners. Explosives are commonly used; mines are holes into the Earth that are not reinforced. The miners would benefit from training in modern gemstone mining techniques and mine safety as well as knowledge of current mining equipment and procedures. Consideration should be given to developing a plan that allows the primary resource planning and extraction to remain with the Afghan miners, with minimal damage to the mineral resources and maximum output for the world market. The preparation and exportation of the gemstones needs to be carefully considered. Currently, most emeralds leave the country without being registered or reported as exports. Afghanistan could potentially benefit from developing a domestic cutting and exporting industry.

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