My study area is restricted to the central part of Singhbhum Craton surrounding by Iron Ore Group (IOG) belt in the Eastern India, India. In the mapped area meta-volcanic and meta-sedimentary units belongs to Iron Ore Group of rocks and are exposed along the Singhbhum Granite (SBG-B). In the western part, within Singhbhum Granite, older patches of hornblende-biotite gneiss (OMTG) are noted. These gneissic patches contain xenoliths of amphibolites of still older OMG. Youngest intrusives are marked as gabbro dykes, dolerite dykes, pyroxenite dykes and quartz reefs into all the rock units of the area. Laterite covering has formed at some places. In some thin sections, I have noticed the biotite, hornblende, sphene and apatite in the same granite. Is that possible the primary hornblende and biotite occurs together along with sphene, magnetite and apatite in the same granite?.
Dear Mr. Yadav,
a mineralogical association like that with predominantly hornblende, apatite and sphene besides some biotite I know from alkali granite or granites undergoing some kind of akali metasomatic alteration. I would favor the last option in your case
H.G.Dill.
Dear Pawan,
As I understood, your study area refers to a metamorphic zone and the presence of gneiss show medium to high grade metamorphism. Your granites are most likely S-type granite and the mentioned mineral assemblages can be occurred in this setting.
Regards,
Rahim
I do not think that gabbro or pyroxenite occur as dyke!
What is the problem in "biotite, hornblende, sphene and apatite in the same granite"? In addition, "Is that possible the primary hornblende and biotite occurs together along with sphene, magnetite and apatite in the same granite" - I think this is a primary assemblage in the Singhbhum Granite B.
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