TY - JOUR
T1 - SHRIMP U-Pb dating of cassiterite
T2 - Insights into the timing of Rwandan tin mineralisation and associated tectonic processes
AU - Nambaje, Claude
AU - Williams, Ian S.
AU - Sajeev, K.
N1 - Publisher Copyright:
© 2021 Elsevier B.V.
PY - 2021/8
Y1 - 2021/8
N2 - Secondary Ionisation Mass Spectrometry (SIMS) U-Th-Pb dating of cassiterite with very low to sub-ppm U contents, zircon and monazite has provided direct measurements of the ages of Mesoproterozoic–Neoproterozoic pegmatite and quartz vein Sn mineralisation in the Karagwe–Ankole Belt (KAB), Rwanda, and through dates on local igneous rocks, helped to place the mineralisation in a tectonic context. Three generations of Sn mineralisation have been identified, each associated with magmatic and metamorphic processes during different periods of Rodinian and Gondwanan assembly. The first generation of mineralisation occurred in pegmatite at ca. 1145 Ma. The second generation, the main episode of Sn mineralisation, occurred from ca. 1090 to 960 Ma in quartz veins and intra-pegmatitic greisen. It started during the period ca. 1090–1040 Ma with fault-controlled Sn mineralisation in quartz veins hosted in quartzite and intra-pegmatitic greisen. This was mainly associated with the ca. 1078 Ma D2 orogenic event in the KAB during the final amalgamation of Rodinia. Peak Sn mineralisation occurred during the period ca. 1040–960 Ma in quartz veins hosted in mica schists related to shear zones. It was associated with G4 S-type granitic magmatism, with zircon U-Pb and monazite Th-Pb ages between 1011 ± 18 and 976 ± 11 Ma, possibly related to a late/-post-collisional setting linked to the amalgamation of Rodinia. The third and distinct generation of Sn mineralisation occurred at ca. 530 Ma in quartz veins hosted in mica schists within a shear zone located close to reworked basement rocks with meridional foliation. This Sn generation is attributed to hydrothermal fluids, possibly induced by a post-tectonic event associated with the emplacement of G5 S-type granite at 614 ± 9 Ma, during the Pan-African orogeny. Recognition of the nebulous Sn-mineralised, cross-structural, Satinsyi-Rutongo Fault Zone, and the links established between the mode of Sn mineralisation, its local geological setting, igneous activity and regional tectonism, will help in targeting exploration for ore-grade Sn deposits in Rwanda and nearby countries.
AB - Secondary Ionisation Mass Spectrometry (SIMS) U-Th-Pb dating of cassiterite with very low to sub-ppm U contents, zircon and monazite has provided direct measurements of the ages of Mesoproterozoic–Neoproterozoic pegmatite and quartz vein Sn mineralisation in the Karagwe–Ankole Belt (KAB), Rwanda, and through dates on local igneous rocks, helped to place the mineralisation in a tectonic context. Three generations of Sn mineralisation have been identified, each associated with magmatic and metamorphic processes during different periods of Rodinian and Gondwanan assembly. The first generation of mineralisation occurred in pegmatite at ca. 1145 Ma. The second generation, the main episode of Sn mineralisation, occurred from ca. 1090 to 960 Ma in quartz veins and intra-pegmatitic greisen. It started during the period ca. 1090–1040 Ma with fault-controlled Sn mineralisation in quartz veins hosted in quartzite and intra-pegmatitic greisen. This was mainly associated with the ca. 1078 Ma D2 orogenic event in the KAB during the final amalgamation of Rodinia. Peak Sn mineralisation occurred during the period ca. 1040–960 Ma in quartz veins hosted in mica schists related to shear zones. It was associated with G4 S-type granitic magmatism, with zircon U-Pb and monazite Th-Pb ages between 1011 ± 18 and 976 ± 11 Ma, possibly related to a late/-post-collisional setting linked to the amalgamation of Rodinia. The third and distinct generation of Sn mineralisation occurred at ca. 530 Ma in quartz veins hosted in mica schists within a shear zone located close to reworked basement rocks with meridional foliation. This Sn generation is attributed to hydrothermal fluids, possibly induced by a post-tectonic event associated with the emplacement of G5 S-type granite at 614 ± 9 Ma, during the Pan-African orogeny. Recognition of the nebulous Sn-mineralised, cross-structural, Satinsyi-Rutongo Fault Zone, and the links established between the mode of Sn mineralisation, its local geological setting, igneous activity and regional tectonism, will help in targeting exploration for ore-grade Sn deposits in Rwanda and nearby countries.
KW - Cassiterite U-Pb geochronology
KW - Karagwe–Ankole Belt
KW - Pan-African orogeny
KW - Rodinia assembly
KW - SHRIMP
KW - Sn mineralisation
UR - http://www.scopus.com/inward/record.url?scp=85105355327&partnerID=8YFLogxK
U2 - 10.1016/j.oregeorev.2021.104185
DO - 10.1016/j.oregeorev.2021.104185
M3 - Article
SN - 0169-1368
VL - 135
JO - Ore Geology Reviews
JF - Ore Geology Reviews
M1 - 104185
ER -