Mineralogical and beneficiation studies of the Fe-Cu ores of Dammal Nisar, Chitral, NW Himalayas Pakistan
Keywords:
Iron and copper ores; skarn mineralogy; beneficiation; Dammal Nisar; Chitral.Abstract
Medium-grade iron and copper ore deposits occur in the Dammal Nisar area of southern Chitral, NW Pakistan. They are distributed as 20 to 200m2 size lens-shaped bodies in the metavolcanic and metasedimentary rocks of the Gawuch Formation along the eastern contact of the arc–related Mirkani granitoids. Detailed mineralogical investigation using petrographic, X-ray Diffraction and SEM-EDX techniques shows that these deposits consist of magnetite, hematite and malachite as the principal ore minerals while occasional chalcopyrite and pyrite are also observed. Quartz, garnet, olivine, epidote, calcite, pectolite, serpentine and foshagite occur as the associated gangue phases. Two main paragenetic stages can be recognized in these deposits based on petrographic and field observations. Olivine and garnet represent the prograde skarn mineralogy while retrograde mineral assemblage is characterized by epidote, amphibole and serpentine. On the basis of proximity to the Mirkani granitoids and prograde and retrograde skarn mineralogy, the studied ore bodies may be classified as skarn-type magnetite deposits.
Being medium-grade in their current form, different beneficiation techniques including gravity separation, magnetic separation and froth flotation were employed to assess the up-gradation potentials of the Dammal Nisar ores. The results reveal that an average Fe2O3 concentrate of 89.15 wt. % at 48% recovery and 90.7 wt. % at 55% recovery are obtainable through a combination of gravity and magnetic separation techniques after sample feeds with 72-75 wt. % Fe2O3 contents are pulverised at 20 and 25 minutes, respectively. As such, the studied ores can be utilized in steel manufacturing. Furthermore, average product of 1.91 and 5.55 wt. % Cu is obtainable through froth flotation, from the studied ore samples showing 0.28 to 0.68 wt. % Cu. Besides, more than 60% of the samples grain size is reduced to <106 microns, when subjected to a grinding interval of up to 25 minutes thereby enhancing liberation of ores from their associated gangue phases. The better liberation results in a relatively higher recovery of both iron and copper minerals.
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