The geology, SHRIMP U-Pb geochronology and metallogenic significance of the Ankisatra-Besakay District, Andriamena belt, northern Madagascar

J. Kabete, David Groves, Neal Mcnaughton, Jan Dunphy

Research output: Contribution to journalArticle

20 Citations (Scopus)

Abstract

The Ankisatra-Besakay District (A-BD), located about 200 kin north of Antananarivo and 75 km cast of Maevatanana in central-northern Madagascar, hosts two historical mines, the Ankisatra Pb-Zn An and Besakay Pb-Ag mines. These shear-hosted en echelon quartz veins at Besakay and deformed tensional quartz veins at Ankisatra produced a total of 4446 t of lead and 156 t of zinc in the early 1940s. In addition, there is Pb-Zn-Cu mineralisation in both quartz-feldspar leucosome veins/bands and metasomatised granulite-facies mafic orthogneiss, Cu-Zn and associated Fe-Mn mineralisation in magnetite-pyrite enderbite breccia, and Cu-Zn mineralisation in retrograde shear zones in granulite-facies paragneiss in the A-BD. The country rocks in the A-BD consist of amphibolite to granulite-facies mafic and granitoid orthogneisses and paragneisses with horizons of silicate-facies BIF. The paragneissic rocks in the district tectonically overlie the biotite-granitoid hornfels and sub-volcanic mangeritic rocks, which are separated from amphibolite-facies alkali-feldspar granitoid and enderbitic rocks by a major structure. The A-BD is structurally characterised by: (1) E-W-trending tensional fractures, quartz veins and dolerite dykes; (2) buckling-related axial-planar fractures; and (3) N-S, NE-SW and NNE-SSW trending dextral strike-slip shear zones, dolerite sills and quartz veins in transpressional extensional zones.Uranium-Pb SHRIMP II geochronology of zircon constrains the peak of magmatic, metamorphic, deformational and metasomatic events in the A-BD. An important constraint is whether hosting terranes contain signatures of the ca. 1690-1590 Ma critical age window for world-class BHT Pb-Zn-Ag deposits elsewhere in the world. At least two magmatic events are recorded from the A-BD. An early magmatic event is recorded by a 2725 +/- 12 Ma single xenocrystic magmatic zircon in the > 2676 +/- 6 Ma precursor to the granulite-facies mafic orthogneiss. A ca. 2503-2460 Ma event is recorded by a 2465 6 Ma minimum age of magmatism for the precursor to metasomatised granulite-facies mafic orthogneiss and 2483 +/- 20 Ma for the precursor to biotite-granitoid hornfels. Zircons extracted from both the metasomatised and unaltered granulite-facies mafic orthogneisses record peak metamorphic ages of 2465 +/- 12 and 2390 +/- 10 Ma, probably representing compressional deformation, partial melting, and associated local magmatic events within the ca. 2475 +/- 2380 Ma period. Inherited zircons from the quartzo-feldspathic granulite-facies paragneisses return ages of protolithic supracrustal rocks ranging from ca. 2870 to 1700 Ma. A widespread period of rifting, anatectic magmatism, basic-ultrabasic and mangerite magmatism, and related granulite-facies metamorphism occurred between ca. 820 and 780 Ma. The possible exhalative units (silicate-facies BIF and metasomatic, garnet-quartz-plagioclase rock) are of late-Archaean to early-Palaeoproterozoic, rather than Mesoproterozoic age. The terrane lacks the critical evolution age window of ca. 1770-1550 Ma, characteristic of well-documented BHT Provinces in the Broken Hill Block and Mt. Isa Block, Australia and ca. 1959-1135 Ma from the Bushmanland Ore District, South Africa. This suggests that either such an event did not occur in the crust now forming the A-BD or that the equivalent supracrustal rocks containing these age signatures were eroded during Proterozoic times. It is less likely that the intense 780-820 Ma event destroyed evidence for their prior existence.The galenas from the Ankisatra and Besakay deposits have signatures characteristic of small-scale mineralised systems which derived most of their lead from local crustal rocks older than ca. > 2.7 Ga. They are thus atypical of BHT deposits and associated vein-style mineralisation from well-endowed terranes.It is concluded that there are neither direct signs nor indirect temporal signals of giant stratiform/stratabound BHT Pb-Zn-Ag mineralisation, nor clear evidence for the presence of characteristic transitional sequences and alteration styles associated with BHT mineralisation in the A-BD, thus downgrading its prospectivity. (c) 2006 Elsevier Ltd. All rights reserved.
Original languageEnglish
Pages (from-to)87-122
JournalJournal of African Earth Sciences
Volume45
Issue number1
DOIs
Publication statusPublished - 2006

Fingerprint

granulite facies
geochronology
geology
mineralization
quartz vein
granitoid
orthogneiss
zircon
hornfels
magmatism
terrane
supracrustal rock
diabase
rock
shear zone
biotite
silicate
quartz
leucosome
alkali feldspar

Cite this

@article{7abe92b4d081431f9b65061f81c2be83,
title = "The geology, SHRIMP U-Pb geochronology and metallogenic significance of the Ankisatra-Besakay District, Andriamena belt, northern Madagascar",
abstract = "The Ankisatra-Besakay District (A-BD), located about 200 kin north of Antananarivo and 75 km cast of Maevatanana in central-northern Madagascar, hosts two historical mines, the Ankisatra Pb-Zn An and Besakay Pb-Ag mines. These shear-hosted en echelon quartz veins at Besakay and deformed tensional quartz veins at Ankisatra produced a total of 4446 t of lead and 156 t of zinc in the early 1940s. In addition, there is Pb-Zn-Cu mineralisation in both quartz-feldspar leucosome veins/bands and metasomatised granulite-facies mafic orthogneiss, Cu-Zn and associated Fe-Mn mineralisation in magnetite-pyrite enderbite breccia, and Cu-Zn mineralisation in retrograde shear zones in granulite-facies paragneiss in the A-BD. The country rocks in the A-BD consist of amphibolite to granulite-facies mafic and granitoid orthogneisses and paragneisses with horizons of silicate-facies BIF. The paragneissic rocks in the district tectonically overlie the biotite-granitoid hornfels and sub-volcanic mangeritic rocks, which are separated from amphibolite-facies alkali-feldspar granitoid and enderbitic rocks by a major structure. The A-BD is structurally characterised by: (1) E-W-trending tensional fractures, quartz veins and dolerite dykes; (2) buckling-related axial-planar fractures; and (3) N-S, NE-SW and NNE-SSW trending dextral strike-slip shear zones, dolerite sills and quartz veins in transpressional extensional zones.Uranium-Pb SHRIMP II geochronology of zircon constrains the peak of magmatic, metamorphic, deformational and metasomatic events in the A-BD. An important constraint is whether hosting terranes contain signatures of the ca. 1690-1590 Ma critical age window for world-class BHT Pb-Zn-Ag deposits elsewhere in the world. At least two magmatic events are recorded from the A-BD. An early magmatic event is recorded by a 2725 +/- 12 Ma single xenocrystic magmatic zircon in the > 2676 +/- 6 Ma precursor to the granulite-facies mafic orthogneiss. A ca. 2503-2460 Ma event is recorded by a 2465 6 Ma minimum age of magmatism for the precursor to metasomatised granulite-facies mafic orthogneiss and 2483 +/- 20 Ma for the precursor to biotite-granitoid hornfels. Zircons extracted from both the metasomatised and unaltered granulite-facies mafic orthogneisses record peak metamorphic ages of 2465 +/- 12 and 2390 +/- 10 Ma, probably representing compressional deformation, partial melting, and associated local magmatic events within the ca. 2475 +/- 2380 Ma period. Inherited zircons from the quartzo-feldspathic granulite-facies paragneisses return ages of protolithic supracrustal rocks ranging from ca. 2870 to 1700 Ma. A widespread period of rifting, anatectic magmatism, basic-ultrabasic and mangerite magmatism, and related granulite-facies metamorphism occurred between ca. 820 and 780 Ma. The possible exhalative units (silicate-facies BIF and metasomatic, garnet-quartz-plagioclase rock) are of late-Archaean to early-Palaeoproterozoic, rather than Mesoproterozoic age. The terrane lacks the critical evolution age window of ca. 1770-1550 Ma, characteristic of well-documented BHT Provinces in the Broken Hill Block and Mt. Isa Block, Australia and ca. 1959-1135 Ma from the Bushmanland Ore District, South Africa. This suggests that either such an event did not occur in the crust now forming the A-BD or that the equivalent supracrustal rocks containing these age signatures were eroded during Proterozoic times. It is less likely that the intense 780-820 Ma event destroyed evidence for their prior existence.The galenas from the Ankisatra and Besakay deposits have signatures characteristic of small-scale mineralised systems which derived most of their lead from local crustal rocks older than ca. > 2.7 Ga. They are thus atypical of BHT deposits and associated vein-style mineralisation from well-endowed terranes.It is concluded that there are neither direct signs nor indirect temporal signals of giant stratiform/stratabound BHT Pb-Zn-Ag mineralisation, nor clear evidence for the presence of characteristic transitional sequences and alteration styles associated with BHT mineralisation in the A-BD, thus downgrading its prospectivity. (c) 2006 Elsevier Ltd. All rights reserved.",
author = "J. Kabete and David Groves and Neal Mcnaughton and Jan Dunphy",
year = "2006",
doi = "10.1016/j.jafrearsci.2006.01.008",
language = "English",
volume = "45",
pages = "87--122",
journal = "Journal of African Earth Science",
issn = "1464-343X",
publisher = "Elsevier",
number = "1",

}

TY - JOUR

T1 - The geology, SHRIMP U-Pb geochronology and metallogenic significance of the Ankisatra-Besakay District, Andriamena belt, northern Madagascar

AU - Kabete, J.

AU - Groves, David

AU - Mcnaughton, Neal

AU - Dunphy, Jan

PY - 2006

Y1 - 2006

N2 - The Ankisatra-Besakay District (A-BD), located about 200 kin north of Antananarivo and 75 km cast of Maevatanana in central-northern Madagascar, hosts two historical mines, the Ankisatra Pb-Zn An and Besakay Pb-Ag mines. These shear-hosted en echelon quartz veins at Besakay and deformed tensional quartz veins at Ankisatra produced a total of 4446 t of lead and 156 t of zinc in the early 1940s. In addition, there is Pb-Zn-Cu mineralisation in both quartz-feldspar leucosome veins/bands and metasomatised granulite-facies mafic orthogneiss, Cu-Zn and associated Fe-Mn mineralisation in magnetite-pyrite enderbite breccia, and Cu-Zn mineralisation in retrograde shear zones in granulite-facies paragneiss in the A-BD. The country rocks in the A-BD consist of amphibolite to granulite-facies mafic and granitoid orthogneisses and paragneisses with horizons of silicate-facies BIF. The paragneissic rocks in the district tectonically overlie the biotite-granitoid hornfels and sub-volcanic mangeritic rocks, which are separated from amphibolite-facies alkali-feldspar granitoid and enderbitic rocks by a major structure. The A-BD is structurally characterised by: (1) E-W-trending tensional fractures, quartz veins and dolerite dykes; (2) buckling-related axial-planar fractures; and (3) N-S, NE-SW and NNE-SSW trending dextral strike-slip shear zones, dolerite sills and quartz veins in transpressional extensional zones.Uranium-Pb SHRIMP II geochronology of zircon constrains the peak of magmatic, metamorphic, deformational and metasomatic events in the A-BD. An important constraint is whether hosting terranes contain signatures of the ca. 1690-1590 Ma critical age window for world-class BHT Pb-Zn-Ag deposits elsewhere in the world. At least two magmatic events are recorded from the A-BD. An early magmatic event is recorded by a 2725 +/- 12 Ma single xenocrystic magmatic zircon in the > 2676 +/- 6 Ma precursor to the granulite-facies mafic orthogneiss. A ca. 2503-2460 Ma event is recorded by a 2465 6 Ma minimum age of magmatism for the precursor to metasomatised granulite-facies mafic orthogneiss and 2483 +/- 20 Ma for the precursor to biotite-granitoid hornfels. Zircons extracted from both the metasomatised and unaltered granulite-facies mafic orthogneisses record peak metamorphic ages of 2465 +/- 12 and 2390 +/- 10 Ma, probably representing compressional deformation, partial melting, and associated local magmatic events within the ca. 2475 +/- 2380 Ma period. Inherited zircons from the quartzo-feldspathic granulite-facies paragneisses return ages of protolithic supracrustal rocks ranging from ca. 2870 to 1700 Ma. A widespread period of rifting, anatectic magmatism, basic-ultrabasic and mangerite magmatism, and related granulite-facies metamorphism occurred between ca. 820 and 780 Ma. The possible exhalative units (silicate-facies BIF and metasomatic, garnet-quartz-plagioclase rock) are of late-Archaean to early-Palaeoproterozoic, rather than Mesoproterozoic age. The terrane lacks the critical evolution age window of ca. 1770-1550 Ma, characteristic of well-documented BHT Provinces in the Broken Hill Block and Mt. Isa Block, Australia and ca. 1959-1135 Ma from the Bushmanland Ore District, South Africa. This suggests that either such an event did not occur in the crust now forming the A-BD or that the equivalent supracrustal rocks containing these age signatures were eroded during Proterozoic times. It is less likely that the intense 780-820 Ma event destroyed evidence for their prior existence.The galenas from the Ankisatra and Besakay deposits have signatures characteristic of small-scale mineralised systems which derived most of their lead from local crustal rocks older than ca. > 2.7 Ga. They are thus atypical of BHT deposits and associated vein-style mineralisation from well-endowed terranes.It is concluded that there are neither direct signs nor indirect temporal signals of giant stratiform/stratabound BHT Pb-Zn-Ag mineralisation, nor clear evidence for the presence of characteristic transitional sequences and alteration styles associated with BHT mineralisation in the A-BD, thus downgrading its prospectivity. (c) 2006 Elsevier Ltd. All rights reserved.

AB - The Ankisatra-Besakay District (A-BD), located about 200 kin north of Antananarivo and 75 km cast of Maevatanana in central-northern Madagascar, hosts two historical mines, the Ankisatra Pb-Zn An and Besakay Pb-Ag mines. These shear-hosted en echelon quartz veins at Besakay and deformed tensional quartz veins at Ankisatra produced a total of 4446 t of lead and 156 t of zinc in the early 1940s. In addition, there is Pb-Zn-Cu mineralisation in both quartz-feldspar leucosome veins/bands and metasomatised granulite-facies mafic orthogneiss, Cu-Zn and associated Fe-Mn mineralisation in magnetite-pyrite enderbite breccia, and Cu-Zn mineralisation in retrograde shear zones in granulite-facies paragneiss in the A-BD. The country rocks in the A-BD consist of amphibolite to granulite-facies mafic and granitoid orthogneisses and paragneisses with horizons of silicate-facies BIF. The paragneissic rocks in the district tectonically overlie the biotite-granitoid hornfels and sub-volcanic mangeritic rocks, which are separated from amphibolite-facies alkali-feldspar granitoid and enderbitic rocks by a major structure. The A-BD is structurally characterised by: (1) E-W-trending tensional fractures, quartz veins and dolerite dykes; (2) buckling-related axial-planar fractures; and (3) N-S, NE-SW and NNE-SSW trending dextral strike-slip shear zones, dolerite sills and quartz veins in transpressional extensional zones.Uranium-Pb SHRIMP II geochronology of zircon constrains the peak of magmatic, metamorphic, deformational and metasomatic events in the A-BD. An important constraint is whether hosting terranes contain signatures of the ca. 1690-1590 Ma critical age window for world-class BHT Pb-Zn-Ag deposits elsewhere in the world. At least two magmatic events are recorded from the A-BD. An early magmatic event is recorded by a 2725 +/- 12 Ma single xenocrystic magmatic zircon in the > 2676 +/- 6 Ma precursor to the granulite-facies mafic orthogneiss. A ca. 2503-2460 Ma event is recorded by a 2465 6 Ma minimum age of magmatism for the precursor to metasomatised granulite-facies mafic orthogneiss and 2483 +/- 20 Ma for the precursor to biotite-granitoid hornfels. Zircons extracted from both the metasomatised and unaltered granulite-facies mafic orthogneisses record peak metamorphic ages of 2465 +/- 12 and 2390 +/- 10 Ma, probably representing compressional deformation, partial melting, and associated local magmatic events within the ca. 2475 +/- 2380 Ma period. Inherited zircons from the quartzo-feldspathic granulite-facies paragneisses return ages of protolithic supracrustal rocks ranging from ca. 2870 to 1700 Ma. A widespread period of rifting, anatectic magmatism, basic-ultrabasic and mangerite magmatism, and related granulite-facies metamorphism occurred between ca. 820 and 780 Ma. The possible exhalative units (silicate-facies BIF and metasomatic, garnet-quartz-plagioclase rock) are of late-Archaean to early-Palaeoproterozoic, rather than Mesoproterozoic age. The terrane lacks the critical evolution age window of ca. 1770-1550 Ma, characteristic of well-documented BHT Provinces in the Broken Hill Block and Mt. Isa Block, Australia and ca. 1959-1135 Ma from the Bushmanland Ore District, South Africa. This suggests that either such an event did not occur in the crust now forming the A-BD or that the equivalent supracrustal rocks containing these age signatures were eroded during Proterozoic times. It is less likely that the intense 780-820 Ma event destroyed evidence for their prior existence.The galenas from the Ankisatra and Besakay deposits have signatures characteristic of small-scale mineralised systems which derived most of their lead from local crustal rocks older than ca. > 2.7 Ga. They are thus atypical of BHT deposits and associated vein-style mineralisation from well-endowed terranes.It is concluded that there are neither direct signs nor indirect temporal signals of giant stratiform/stratabound BHT Pb-Zn-Ag mineralisation, nor clear evidence for the presence of characteristic transitional sequences and alteration styles associated with BHT mineralisation in the A-BD, thus downgrading its prospectivity. (c) 2006 Elsevier Ltd. All rights reserved.

U2 - 10.1016/j.jafrearsci.2006.01.008

DO - 10.1016/j.jafrearsci.2006.01.008

M3 - Article

VL - 45

SP - 87

EP - 122

JO - Journal of African Earth Science

JF - Journal of African Earth Science

SN - 1464-343X

IS - 1

ER -