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Geochronology, mineral chemistry and genesis of REE mineralization in alkaline rocks from the Kohistan Island Arc, Pakistan

Geochronology, mineral chemistry and genesis of REE mineralization in alkaline rocks from the Kohistan Island Arc, Pakistan
Geochronology, mineral chemistry and genesis of REE mineralization in alkaline rocks from the Kohistan Island Arc, Pakistan

Alkaline igneous-related rare earth element (REE) deposits constitute a major global economic resource of REE. However, our understanding of their geodynamic settings and magmatic-hydrothermal processes remains uncertain. Here, we present an investigation of petrography, geochronology and mineral chemistry of newly discovered REE mineralization in the alkaline syenite and pegmatite from the Kohistan Batholith in the Kohistan Island Arc, Pakistan. The pegmatite contains abundant chevkinite and monazite (up to 10–35% in volume), which formed from crystallization of a REE-oversaturated evolved melt and are the main REE-bearing phases. U-Th-Pb isotopic dating of zircon from the syenite yields the emplacement age of 31.2 ± 0.3 Ma, which closely matches the ages of zircon and monazite from the pegmatite (30.1 ± 0.3 Ma and 30.9 ± 0.3 Ma, respectively). Zircons from the syenite and the pegmatite have similar ɛ Hf(t) values, ranging from + 0.2 to + 2.5, indicating that the syenite and the pegmatite are co-magmatic in origin. The alkaline magma likely formed by partial melting of the enriched lithospheric mantle induced by the asthenospheric upwelling, which was related to slab break-off at the post-collisional stage following the collision of the Kohistan Island Arc with the Indian Plate. Zircons show the evolutional trend in trace element compositions from the syenite to the pegmatite, marked by increases in REE, Hf, Y, U, volatiles and fo 2. These changes reflect prolonged fractional crystallization processes of the alkaline magma, which were responsible for the REE enrichment in the residual pegmatitic melt. Post-collisional alkaline magmatic rocks are widely distributed in many places along the Tethyan orogenic belt. These observations suggest that these post-collisional alkaline rocks may be good targets for REE exploration.

Kohistan Island Arc, Pakistan, Pegmatite, REE mineralization, Syenite
0169-1368
Hussain, Amjad
a02898d1-2903-488f-a705-bee9b061b15a
Zhao, Kui-dong
bd5bd864-d7d0-40b4-ae43-37cdc7632a37
Arif, Mohammad
fd6899e5-31f5-4ea3-be4d-3de3cf1fefc7
Palmer, Martin R.
d2e60e81-5d6e-4ddb-a243-602537286080
Chen, Wei
86fa29ef-acf8-4208-ac52-d29afb220702
Zhang, Qiang
a956c138-e3b3-4305-b8ce-8776c5e124f4
Li, Qian
2691bb40-fffc-439e-ba9f-e465be89358a
Jiang, Shao-yong
dc929006-69ac-4366-bf2b-dc97527602d3
Bala Girei, Musa
5502e508-6bb7-43b6-b87f-29792b689464
Hussain, Amjad
a02898d1-2903-488f-a705-bee9b061b15a
Zhao, Kui-dong
bd5bd864-d7d0-40b4-ae43-37cdc7632a37
Arif, Mohammad
fd6899e5-31f5-4ea3-be4d-3de3cf1fefc7
Palmer, Martin R.
d2e60e81-5d6e-4ddb-a243-602537286080
Chen, Wei
86fa29ef-acf8-4208-ac52-d29afb220702
Zhang, Qiang
a956c138-e3b3-4305-b8ce-8776c5e124f4
Li, Qian
2691bb40-fffc-439e-ba9f-e465be89358a
Jiang, Shao-yong
dc929006-69ac-4366-bf2b-dc97527602d3
Bala Girei, Musa
5502e508-6bb7-43b6-b87f-29792b689464

Hussain, Amjad, Zhao, Kui-dong, Arif, Mohammad, Palmer, Martin R., Chen, Wei, Zhang, Qiang, Li, Qian, Jiang, Shao-yong and Bala Girei, Musa (2020) Geochronology, mineral chemistry and genesis of REE mineralization in alkaline rocks from the Kohistan Island Arc, Pakistan. Ore Geology Reviews, 126, [103749]. (doi:10.1016/j.oregeorev.2020.103749).

Record type: Article

Abstract

Alkaline igneous-related rare earth element (REE) deposits constitute a major global economic resource of REE. However, our understanding of their geodynamic settings and magmatic-hydrothermal processes remains uncertain. Here, we present an investigation of petrography, geochronology and mineral chemistry of newly discovered REE mineralization in the alkaline syenite and pegmatite from the Kohistan Batholith in the Kohistan Island Arc, Pakistan. The pegmatite contains abundant chevkinite and monazite (up to 10–35% in volume), which formed from crystallization of a REE-oversaturated evolved melt and are the main REE-bearing phases. U-Th-Pb isotopic dating of zircon from the syenite yields the emplacement age of 31.2 ± 0.3 Ma, which closely matches the ages of zircon and monazite from the pegmatite (30.1 ± 0.3 Ma and 30.9 ± 0.3 Ma, respectively). Zircons from the syenite and the pegmatite have similar ɛ Hf(t) values, ranging from + 0.2 to + 2.5, indicating that the syenite and the pegmatite are co-magmatic in origin. The alkaline magma likely formed by partial melting of the enriched lithospheric mantle induced by the asthenospheric upwelling, which was related to slab break-off at the post-collisional stage following the collision of the Kohistan Island Arc with the Indian Plate. Zircons show the evolutional trend in trace element compositions from the syenite to the pegmatite, marked by increases in REE, Hf, Y, U, volatiles and fo 2. These changes reflect prolonged fractional crystallization processes of the alkaline magma, which were responsible for the REE enrichment in the residual pegmatitic melt. Post-collisional alkaline magmatic rocks are widely distributed in many places along the Tethyan orogenic belt. These observations suggest that these post-collisional alkaline rocks may be good targets for REE exploration.

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More information

Accepted/In Press date: 28 August 2020
e-pub ahead of print date: 6 September 2020
Published date: 1 November 2020
Keywords: Kohistan Island Arc, Pakistan, Pegmatite, REE mineralization, Syenite

Identifiers

Local EPrints ID: 444349
URI: http://eprints.soton.ac.uk/id/eprint/444349
ISSN: 0169-1368
PURE UUID: 5dd83fbd-24a5-49eb-a7e0-d533a7537859

Catalogue record

Date deposited: 14 Oct 2020 16:30
Last modified: 14 Oct 2020 16:30

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