@phdthesis{oai:air.repo.nii.ac.jp:00003305,
 author = {MUHAMMAD, TAHIR},
 month = {Sep},
 note = {Talc occurs as economic deposits in amphibolite facies metamorphosed dolomite marble and magnesite rocks in the Spinghar Fault Block in Afghanistan. This block is composed of various Proterozoic gneisses, schists, quartzites, marbles and amphibolites metamorphosed to amphibolite facies which were intruded by Early Cretaceous igneous rocks such as migmatite-granite and gabbro-monzonite-diorite. Eight deposits and two prospects were chosen from three areas. Six quarries and outcrops among ten from the western part i.e., Anarokas, Kherwasti, Dar, Janinaw, Kotikhel (Dawood mine and Noor mine), three from the middle part i.e., Wachalgad, Lesho, Sargare and one from the most eastern part i.e., Mamond dara in Spinghar Fault Block were studied. The objective of this study is to understand the talc mineralization and formation processes in these areas on the basis of field relations, petrography, X-ray diffractometry (XRD), X-ray fluorescence spectroscopy (XRF), inductively coupled plasma mass spectrometry (ICP-MS), scanning electron microscope energy-dispersive X-ray spectroscopy (SEM-EDX) and electron probe micro analysis (EPMA).
In this block, talc ore bodies occur parallel to subparallel to host magnesite rocks, dolomite marble and gneiss. Intrusive rocks such as dolerite and diorite cross cut the talc ore bodies, host carbonate rocks and gneiss, and are also parallel to sub parallel to the beddings of host carbonate rocks and talc ore bodies. Tremolite was observed with most of talc, and  antigorite (serpentine) in the altered dolerite and host carbonate rocks. Quartz veins follow the gneissosity of gneiss all over the study areas. Quartz veins were cross cut by granitic rocks at Anarokas. Talc was mainly formed by alteration of magnesite and tremolite in Kherwasti, Anarokas, Dar, Wachalgad, Lesho and Sargare, while in Janinaw, Kotikhel and Mamond dara, talc was formed by alteration of dolomite and tremolite. Common mineral assemblages in the study area of talc ores are (a) talc + magnesite, (b) talc + tremolite, in magnesite rocks (c) magnesite ± olivine and (d) magnesite + antigorite in Dar, Anarokas and Kherwasti, (e) talc + magnesite , in talc ores and (f) dolomite + calcite + tremolite in dolomite marble in Wachalgad, (g) talc + magnesite, in talc ores, (h) dolomite + tremolite ± talc in dolomite marble, and (i) hornblende + quartz + plagioclase in amphibolites in Lesho and Sargare, (j) talc + dolomite, in talc ores, (k) tremolite + dolomite in dolomite marble and (l) quartz + talc in quartz veins in Kotikhel and Janinaw, and (m) dolomite + talc + quartz ± calcite, in host dolomite marble (n) quartz + microcline + muscovite + biotite + allanite in gneiss in Mamond dara, and (o) quartz + muscovite + biotite in gneiss in Anarokas, Wachalgad and Kotikhel. On the basis of the mineral assemblages, the formation temperatures of different minerals such as talc, tremolite and antigorite were estimated. In Mamond dara, the temperature ranged from 360 to 460℃. In Anarokas, Dar and Kherwasti, the temperature was 380 to 460℃. In Janinaw and Kotikhel, it ranged from 405 to 500℃. 
The SiO₂ contents of talc rocks from all deposits range from 56.1 to 65.1 wt% and carbonate rocks of Kotikhel are 16.2 wt%, those from Kherwasti range from 1.6 to 25.8 wt%, Anarokas range from 16.6 to 45.5 wt%, Dar range from 6.9 to 8.9 wt%, Wachalgad range from 5.6 to 22.2 wt%, Lesho are 31.0 wt%, Sargare range from 9.6 to 13.9 wt% and Mamond dara range from 10.9 to 15.7 wt%. It is evident that SiO₂ content increased to form talc from magnesite rocks and dolomite marble. The whole-rock MgO contents of those range from 30.2 to 35.5 wt% and 27.1 wt%, from 25.1 to 46.3 wt%, from 37.3 to 47.7 wt%, from 43.7 to 46.0 wt%, 23.1 to 53.5 wt%, 37.5 wt%, 26.2 to 48.1 wt%, and 19.3 to 21.9 wt%, respectively. The whole-rock CaO contents of talc rocks and magnesite rocks of all deposits are less than 1 wt%, while those of dolomite marbles of Kotikhel, Kherwasti, Wachalgad, Sargare and Mamond dara range from 17.0 to 33.5 wt%. The ƩREE contents of talc rocks, magnesite rocks and dolomite marbles in Wachalgad and Sargare are 0.4, 1.3, 3.5 ppm and 2.1, 1.7 and 6.6 ppm respectively. The ƩREE contents of talc rocks and magnesite rocks in Kherwasti range from 0.2 to 1.2 ppm, 0.7 to 18.6 ppm respectively, in Anarokas 0.5 ppm, 1.0 to 4.2 ppm respectively, in Dar from 0.2 to 0.8 ppm, 1.1 to 4.7 ppm respectively and in Lesho 2.6 ppm and 13.0 ppm respectively. The ƩREE contents of talc rocks and dolomite marble in Kotikhel are 0.12 ppm and 14.0 ppm respectively, in Janinaw from 0.08 to 6.6 ppm and 2.5 ppm respectively, while in Mamond dara it ranges from 0.04 to 3.2 ppm and 23.5 ppm respectively. EPMA analysis of carbonate minerals from all deposits shows that dolomite and magnesite compositions are close to the ideal composition with FeCO₃ ranging from 0.2 to 0.6 wt% and from 0.2 to 0.5 wt%, and MnCO₃ ranging from 0.02 to 0.06 wt% and from 0.01 to 0.09 wt%, respectively. The chemical compositions of talc and tremolite slightly deviate from ideal compositions with FeO, Na₂O, K₂O, MnO, Al₂O₃, TiO₂ and Cr₂O₃ contents less than 1 wt%. Concentrations of Al, Ta, Th, Cr, Ni, Co and ƩREE in talc ores and carbonates rocks are comparatively very low with mafic and ultramafic rocks, so inconsistent with mafic and ultramafic rocks protolith. Therefore, the metamorphosed sedimentary carbonate rocks were likely the protolith of talc ores. Magnesium has been derived from pre-existing Mg-rich carbonate host rocks, i.e., magnesite and dolomite marbles.},
 school = {秋田大学},
 title = {Ore Genesis and Geochemical Characteristics of Carbonate-hosted Talc Deposits in Nangarhar Province, Afganistan.},
 year = {2018}
}