Geology and Genesis of Hajigak Iron Ore Deposit Bamyan, Central Afghanistan

2011

Universität Bonn

H. Malistani

Progress Report

Geology and Genesis of Hajigak Iron Ore Deposit, Bamyan, Central Afghanistan

Introduction

Hajigak Iron ore deposit is situated in the eastern part of Baba mountain range nearby the Hajigak pass (34°43N,

68°01E) in Bamyan province, about 200km west of Kabul (Fig.1). It is the largest iron ore reserve located in

Afghanistan. There exists some previous exploration in the Hajigak area for iron deposits in 1960s and 1970s by

Russian, Afghan and French geologists. However, little is known about the formation and the age of

mineralization/host rocks of the deposit and therefore this giant deposit is not developed for exploitation until

now. Several large to medium size and numerous smaller ore bodies occur in a North-East to South-West

directed band within a major fault zone (Herat fault) as sub-concordant sheets and lenses in Proterozoic (?) meta-

sedimentary and meta-volcanic rocks. The study in the 1960s demonstrated the mineral potential of the region,

and estimated for the immediate Hajigak deposit resources of 1800 million tons of iron ore with a concentration

of approximately 62 % Fe. This assessment ranks the Hajigak deposit as world-class and comparable with large

iron deposits in the world.

Geology of the region

The oldest rocks of the region belong to the Paleo-Proterozoic Paymuri Group located 5km northwest of the

deposit and composed of gneiss, crystalline schist, marble and amphibolite. Mesoproterozoic rocks of the Jawkul

Formation (1000m) composed of crystalline schist, quartzite and marble overly the Paymuri Group. They are

located in the footwall of deposit (Fig.1).

All ore bodies of Hajigak deposit are located inside of metavolcano-sedimentary series named Kalu Group that

built up by three major units. The Kab Formation (3500m) in the footwall of the main ore bodies and the

Awband Formation (300-1000m), the main host of the iron ore bodies, which are bedded in slate, phyllite, schist,

dolomitic marble and quartzite. The Green Schist Formation (700m) mainly consisting of meta-andesitic

volcanics and doleritic sill and dikes, forms part of the hanging wall of the deposits. It is overlain by the Hajigak

Formation (900m), composed of limestone, dolomite, sandy limestone and conglomerate. Brachiopods found

allow dating the formation into Upper Devonian. The Upper Carboniferous Kharzar Formation (2500m) with

pelitic schists, conglomerates and quartzites, unconformably overlies the Hajigak Formation. Finally, a large

complex of tertiary Kuhe Baba Granitoids intruded the older rocks of the region a few kilometeres south of the

deposit alongside of a major fault. Many mafic sills and dikes (gabbro and dolerite) in different generations

intruded these formations; especially the upper part of the Kalu Group (Green Schist Formation) and some of

these intrusions are near to ore bodies. Underlying and overlying rocks are almost everywhere in sharp contact

with iron ores and in the most areas the ore bodies lay conformably in these host rocks. There is no agreement

concerning the age of this group. Some former workers based on stratigraphy assumed a lower paleozoic age

(Kusov etal, 1964, Bouladon and de Lapparent, 1975) but other Afghan-Russian workers based on regional

geology and correlation with eastern and western formations believed on early new-proterozoic age (Abdullah

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and Chemyriov, 1980). No radiometric age determination has been done until now and the question remained

unclear. Due to metamorphism and hydrothermal alteration of these rocks, the age determination is difficult and

needs using some advanced but expensive methods and techniques of analyses, for example precise radiometric

dating.

Figure 1: Location map of Hajigak and structure of Afghanistan (up) and geologic map of the main

deposits (down). Modified and redrawn after Afghanistan Geological Survey work (Kusov et al,

1965).

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Fieldwork

In August and September 2010 extensive fieldwork were conducted in the deposit area by the applicant and

the main work was done in the central part of Hajigak region. Short visits were done in the eastern and western

remote areas. During these fieldworks, including sampling, all important geological data have been taken and all

formations and stratigraphic units have been mapped. In turn to get fresh material, the samples were taken from

less altered outcrops and from former exploration holes, shafts, trenches and adits. The most important results of

these fieldworks that will help our project greatly are as follows:

-     First time sampling from a newly discovered iron ore deposit of Hajigak type alongside of the Herat

fault in far west of the province in Siahdarra, Yakawlang district.

-      Detection of a new and important outcrop of iron oxide pillow like structures inside of the main

Hajigak deposit.

-   Detection and sampling of less altered outcrops of magnetite -pyrite ore type and of banded hematite-

quartz ores.   

    After primary evaluation of data and examination of samples, 150 representatives and less altered samples

were selected for chemical laboratory analyses and transported to Steinmann Institute (Bonn University).

Laboratory work

From October 2010 to April 2011, the following laboratory works have been done in Steinmann Institute of

Bonn University:

-    120 samples prepared for geochemical and mineralogical analyses -   Textural and micro structural study of thin sections by polarization microscopy

-    Textural and mineralogical study of polished sections by reflected light microscopy

-    X-Ray Fluorescence (XRF) analyses for trace and major elements of all samples

-    X-Ray Diffraction (XRD) analyses for all samples

- Electron microprobe analyses (EMPA) of some selected samples

- Elemental analyses of selected samples for Carbon and Sulphur content (CNS)

- Correcting and redrawing geological map of study area

Petrography and mineralogy

Mineralogy and petrology of ores and host rocks were studied by reflection, transmission and EMPA

microscopy and were determined by XRD. Based on these studies, mineralogical compositions of the deposit are

as follows:

Main ore minerals: Magnetite (Fe3O4), Hematite and Martite (Fe2O3), Goethite (FeOOH).

Minor ore minerals: Ankerite (CaFe(CO3)2), Siderite (FeCO3), Barite (BaSO4),Pyrite (FeS2),

Pyrrhotite (FeS ), Chalcopyrite (CuFeS2), Chamosite (Fe2+, Mg, Al, Fe3+) 6(Si, Al)4O10(OH,O)8.

Gangue minerals: Quartz and Chert (SiO2), Calcite (CaCO3), Dolomite (CaMg (CO3)2, some other minor/trace

phases like mica (sericite), albite, talc, and clay minerals. Some of these phases are enriched in iron.

Ore textures are massive, semi-banded and fine to medium granular. Replacement textures and evidence of

hypogene and supergene alterations are observed in most of the samples.

The composition of the host rocks shows a stronger variation due to the differences in age and type. However,

in almost all of them iron bearing minerals are present and sometimes reach to more than 10 % of the total

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mineral content. The Awband Formation, the main host rock, is composed of quartz-sericite schist, derived from

clayey material, quartz-sericite-chlorite schist, derived from mafic to intermediate tuffs, quartzite chert) and

calcite-dolomite marble.

Geochemistry

XRF analyses of 153 samples and EMPA analyses of some selected ones have been effectuated. A

comparison of the results reveals that the deposit composition in major elements is comparable with some well

known high grade iron ore deposits from around the world however with higher S but lower P and Ti content

(Fig.2). In trace elements composition (Fig.3), it shows enrichment in some elements like Mn, Ba, Sr, Zn, Pb,V,

W and light REE (Ce) but depletion in Cr, Co, Ni, Rb and heavy REE (Yb).

Figure 2. Comparison of major oxides and LOI of high grade iron ores from Hajigak deposit with other important iron ore

deposits: Hamersley, Minas gerais (Superior type), Orissa (Algoma type), Rapitan BIF and Gol Gohar (Rapitan type).

Figure 3. Average whole rock XRF analysed trace element compositions of different ore types of Hajigak deposit.

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From the geochemical and microscopical results we can conclude some preliminary aspects of formation of

the deposit as below. However, more detailed analyses are needed for the final development of a genetic model

for the deposit. Isotope analyses are also necessary to precise the origin and age of iron ore formation.

One of the big challenges for this project is that until now Hajigak iron ore deposit not exactly fits to any

available metallogenic model. Numerous papers and models about different iron ore deposits from around the

world have been reviewed, but still with these results, it remains difficult to describe the formation of the

deposit. However, XRF whole rock trace elements and EMPA analyses of magnetite and hematite ores of

Hajigak deposit show some correlation with chemical sedimentary (BIF) and hydrothermal related (IOCG) iron

ore deposits (Fig.4).

Figure 4. Ca+Al+Mn vs. Ti+V discriminant diagram for average compositions of magnetite and hematite in various ore bodies of Hajigak deposit. Each magnetite and hematite point represents the average composition that was analysed by EMPA in one sample. (Border lines from Dupuis and Beaudoin, 2011).

Future works

According to attached timetable, the future plan for next year is as follow:

- Completing current geochemical analyses.- Fieldwork (summer 2011).- Detailed geochemical analyses of REE and some other trace elements with ICP-Ms.- Sample preparation and analyses of new samples (September-October 2011).- Stable isotope analyses (O, S and Fe).- Geochronology and radiometric isotope analyses.- Data interpretation (October-January 2011).- Writing thesis, papers and posters (January to December 2012).

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