Minerals in Afghanistan

Rare Earth Elements

Introduction Rare Earth Elements (REE) have a wide variety of uses as catalysts, magnets, metallurgical alloys, phosphors for television and computer screens, glass and ceramics. China has the most abundant resources in the world and dominates the supply. The Bayan Obo bastnasite deposit is the world’s largest and contains reported reserves of >48 Mt at 6% REO (Rare Earth Oxides). Mineral exploration for REE is taking place throughout much of the world in an attempt to diversify supply. The Khanneshin area in Helmand Province was explored for REE, U and P deposits during the 1970’s by Afghan-Soviet Teams (Abdullah et al., 2008 and Cheremitsyn, and Yeremenko, 1976) but not brought into production. USGS teams have recently visited these deposits and re-evaluated the earlier data and produced several reports (Peters et al., 2011, Tucker et al., 2011, Department of Defense, 2011)

Geology of the Khanneshin Area

The Khanneshin carbonatite complex is the eroded core of an early Quaternary volcano and is situated in the Registan desert, Helmand Province, Southern Afghanistan (Figure 1). It is one of a number of similar volcanoes of on a SW-NE trend stretching from Iran, Pakistan and Afghanistan. A 4km diameter-wide central core of sövite and a ring dyke of alvikite forms the major part of the 700m high hill, and is surrounded by an apron of lavas and volcaniclastic sediments (Figure 2). The alvikites consist mainly of calcite, ankerite and dolomite but an unusual variety enriched in Ba and Sr crops out in the north-east of the marginal zone. In these rocks strontianite, barite, REE-minerals and celestite are common. The complex is intruded into Neogene sediments, which are strongly altered and brecciated, and radial dykes and volcanic plugs of alvikite are also present.

Figure 1. Google Earth image of the Khanneshin volcano, 3D-view from the south. The Central Vent forms the ele-vated area and the volcanic apron extends to the east. (©2011 Europa Technologies; ©2011 Cnes Spot Image;©2011 Digital Globe)

LREE Enriched Zone A high content of REE is characteristic of the sövitic rocks, as well as the barium- and strontium-rich ankerite-barite alvikites. In the 1970s, Soviet geologists identified a polygonal area of 0.64 km2 having extreme LREE enrichment in the northeast margin of the central vent (Figure 2). Two traverses were completed by USGS scientists across the northern and southern corners of the zone of REE enrichment. The traverses are indicated in figure 2. The traverse of August 2010 just touched the southern edge of the REE zone of mineralisation, and the traverse of February 2011 crossed the northern corner of the REE mineralization zone. In the course of this work, extremely unusual rocks and minerals were observed, some of them highly enriched in strontium, barium, and LREE, and more than 50 rock samples, representing the principal rocks of the mineralised zone, were collected for geochemical analysis and scanning electron microscopy. The result of the field and analytical work is summarized below and reported in Tucker et al. (2011).

Mineralisation Within the enriched zone two styles of REE mineralisation occur:

Type I Concordant mineralisation Occurs in symmetrically banded veins and seams (Figure 3), up to 0.5 to 0.7 m thick and several tens of meters long. The layers of REE enrichment consist of two outer bands of yellow-weathering minerals symmetrically disposed about a dark central band. The bands of yellow-weathering minerals consist of khanneshite-(Ce), barite, strontianite and secondary synchysite-(Ce), and parisite-(Ce). The central, dark-colored band consists primarily of ankeritic dolomite, barite, apatite, and strontianite, as well as trace khanneshite-(Ce). These symmetric bands of highly mineralised rock are layered with weakly mineralized ankerite-barite alvikite (that is, the host wall rock) for more than 150 m of exposed vertical section. Texturally, the REE carbonates formed late in the petrogenetic history, possibly from immiscible fluid droplets. Khanneshite-(Ce), the primary REE mineral, forms spheroidal mineral aggregates or late fibrous overgrowths on interstitial dolomite and calcite. The average diameter of the spheroidal aggregates, interpreted as REE-rich droplets of immiscible liquid, is 100 micrometers. In still other instances, REE-rich bands of barite, strontianite, and khanneshite-(Ce)

Figure 2. Geological map of the Khanneshin carbonatite complex (Tucker et al., 2011). The area of light rare earth element (LREE) enrichment is indicated (green box) to the north-east of the central vent, which is composed of sövite and alvikite (in red shades). Areas of uranium (U) and phosphate (P) enrichment are also shown in the SW quadrant.

appear to have crystallized from a fluid which was introduced into brecciated dolomitic ankerite of the host alvikite. In all examples, the REE minerals crystallized late in the mineral petrogenesis. In some veins the REE carbonate minerals form dense crystal aggregates comprising 50 percent (by volume) of the vein.

Figure 3. Type I Mineralisation. Photographs of (b) the concordant symmetric bands of mineralised alvikite and (c) partially rotated concordantly mineralised band .

Figure 4. Type II Mineralisation. An example of a fluo-rine-rich carbonatite dike, intruded into the banded alvikites of the marginal zone, central intrusive vent.

Figure 5. (a) Variation of La vs. Sr showing the correla-tion between LREE and Sr due to ability of the LREE to substitute for Sr in carbonates. Note the similar range of LREE to Bayan Obo rocks (green) and Mountain Pass (blue). Khanneshin Type 1 samples in filled purple cir-cles and Type 2 samples in open circles. (b) La vs Yb ratios are similar to those in Bayan Obo ores. (c) Rock/Chrondrite ratios are higher in HREE in the Khanneshin concordant bands than the ores at Bayan Obo or Mountain Pass. (Tucker et al., 2011).

Type II Discordant mineralisation Type II REE mineralisation occurs in discordant dikes and tabular sheets , up to tens of meters thick and hun-dreds of meters long, which are filled with primary igneous minerals that crystallized directly from magma or a late-stage hydrothermal fluid. These REE-enriched igneous rocks are of two types; those en-riched in fluorine, and those enriched in phosphorus. The igneous rocks enriched in fluorine have as their REE-bearing minerals idiomorphic phenocrysts of khanneshite-(Ce), together with synchysite-(Ce), bast-näsite-(Ce), and calkinsite-(Ce) of likely secondary (alteration) origin. The igneous rocks enriched in phos-phorus have as their REE-bearing minerals idiomor-phic phenocrysts of carbocernaite-(Ce), together with parisite-(Ce) of secondary origin.

Some REE Carbonate Mineral Compositions Khanneshite: (Na,Ca)3 (Ce,Ba,Sr)3(CO3)5 Synchysite: Ca(Ce,La)(CO3)2F Bastnäsite: (Ce, La) CO3 F Parisite: Ca(Ce,La)2(CO3)3F2

Chemistry

Sources of Information Abdullah S. H., et al., 1980, Geology and Mineral Resources of Afghanistan. 2 volumes. English Version, Republished in 2008 by British Geological Survey Occasional Publication No.15. 292pp. British Geological Survey, 2010 Rare Earth Elements: Mineral Profile. 45pp. Download from http://www.bgs.ac.uk/ mineralsuk/home.html Cheremitsyn, V.G., and Yeremenko, G.K., 1976, Report of the Hanneshin crew on the results of prospecting and evaluational activity for 1976 [in Russian]: AGS Report 1142, 84p. scale 1:10,000. Department of Defense, 2011. Mineral Resource Team 2010 Activities Summary. Task Force for Business and Stability Operations,Washington,DC,20301, 49pp. Peters, S.G., King, T.V.V., Mack, T.J., Chornack, M.P., eds., 2011, Summaries of important areas for mineral investment and production opportunities of nonfuel minerals in Afghanistan: USGS Open-File Report 2011–1204. Tucker, R.D., Belkin, H.E., Schulz, K.J., Peters, S.G., and Buttleman, K.P., 2011, Rare earth element mineralogy, geochemistry, and preliminary resource

Khanneshin LREE Deposit Summary Deposit name: Khanneshin, Helmand Prov-

ince

Deposit style: Igneous Carbonatite-related

Host geology: Ankerite-barite-alvikites

Deposit geology: Type 1 Semi-concordant

bands and veins in alvikite; Type 2 Discor-

dant dykes and sheets enriched in F or P.

Ore minerals: 1 khanneshite-(Ce) and sec-

ondary LREE minerals; 2 khanneshite-(Ce),

monazite-(Ce), synchysite-(Ce).

Metal content: Type 1: 218 Mt @ 2.77%

ΣLREE; Type 2: 15 Mt @ 3.28% ΣLREE

Estimated to depth of 150m

Resource Estimation Because the rocks with REE enrichment have not been mapped in detail, drilled for exploration, or investigated using modern geophysical methods, the resource estimation (Table 1) is hypothetical and assumes a depth of 150m, a density of 2.94 g/cm3 and uses an average grade of ΣLREE enrichment (sum of La, Ce, Pr, and Nd). The actual workable grade may be lower than this assuming a 10:1 wall rock dilution in the Type 1 mineralisation. Both types of LREE-enriched rocks are comparable in grade to the world-class Bayan Obo (China) and Mountain Pass, California (United States) deposits, which are also enriched in LREE. On the basis of several assumptions and employing a simple geometry for the zone of LREE enrichment, USGS estimates that at least 1 Mt of LREE may be present in the Khanneshin Area of Interest. This comports well with the probabilistic estimate of 1.4 Mt of undiscovered REE resources in all of south Afghanistan (Peters and others, 2007). In addition to LREE, the Khanneshin carbonatite is also enriched in barium (>10 wt. percent), strontium (>6 wt. percent), phosphorus (~2 wt. percent), and uranium (>0.05 wt. percent).

Type : Zone Length (m)

Width (m)

Mt ΣLREE grade %

1: Lower zone 750 550 181.9 2.775

1: Upper zone 330 250 36.4 2.775

1: Total 218.3 2.775

2: Dyke 1 50 20 0.4 3.282

2: Dyke 2 500 40 8.8 3.282

2: Dyke 3 400 35 6.2 3.282

2: Total 15.4 3.282

Table 1 Estimated grade and tonnage of the ΣLREE resources (after Tucker et al., 2011)

©Afghanistan Geological Survey

Contact Details

For More Information Please Contact: Investment Promotion Directorate Ministry of Mines Kabul, Afghanistan Telephone: +93 (0) 752 076 483 E-Mail: miningenquiries@mom.gov.af Website: http://www.mom.gov.af

Director General Afghanistan Geological Survey, Kabul, Afghanistan Tel: +93 (0) 75 200 1714 E-mail: ags@mom.gov.af

PMU Director Afghanistan Geological Survey Kabul, Afghanistan Tel: +93 (0)796 216 251