Download Minerals in Afghanistan

Minerals in
Afghanistan
Rare Earth Elements
Figure 1. Google Earth image of the Khanneshin volcano, 3D-view from the south. The Central Vent forms the elevated area and the volcanic apron extends to the east. (©2011 Europa Technologies; ©2011 Cnes Spot Image;©2011
Digital Globe)
Introduction
Geology of the Khanneshin Area
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)
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 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.
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, darkcolored 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)
appear to have crystallized from a fluid which was Chemistry
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 fluorine-rich carbonatite dike, intruded into the banded
alvikites of the marginal zone, central intrusive vent.
Type II Discordant mineralisation
Type II REE mineralisation occurs in discordant dikes
and tabular sheets , up to tens of meters thick and hundreds of meters long, which are filled with primary
igneous minerals that crystallized directly from magma
or a late-stage hydrothermal fluid. These REEenriched igneous rocks are of two types; those enriched 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), bastnäsite-(Ce), and calkinsite-(Ce) of likely secondary
(alteration) origin. The igneous rocks enriched in phosphorus have as their REE-bearing minerals idiomorphic phenocrysts of carbocernaite-(Ce), together with
parisite-(Ce) of secondary origin.
Figure 5. (a) Variation of La vs. Sr showing the correlation 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 circles 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).
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
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).
Khanneshin LREE Deposit Summary
Deposit name: Khanneshin, Helmand Province
Deposit style: Igneous Carbonatite-related
Host geology: Ankerite-barite-alvikites
Deposit geology: Type 1 Semi-concordant
bands and veins in alvikite; Type 2 Discordant dykes and sheets enriched in F or P.
Ore minerals: 1 khanneshite-(Ce) and secondary 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
Table 1 Estimated grade and tonnage of the
ΣLREE resources (after Tucker et al., 2011)
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
218.3
2.775
1: Total
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
15.4
3.282
2: Total
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
Contact Details
For More Information Please Contact:
Investment Promotion Directorate
Ministry of Mines
Kabul, Afghanistan
Telephone: +93 (0) 752 076 483
E-Mail: [email protected]
Website: http://www.mom.gov.af
©Afghanistan Geological Survey
Director General
Afghanistan Geological Survey,
Kabul, Afghanistan
Tel: +93 (0) 75 200 1714
E-mail: [email protected]
PMU Director
Afghanistan Geological Survey
Kabul, Afghanistan
Tel: +93 (0)796 216 251