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post-mineralization alteration during the intervals of 2.2-2.1 Ga, 2.1-2.0 Ga, 2.0-1.9 Ga,
1.9-1.8 Ga, and 1.6 Ga (Table 2.1 and Appendix 1).
2.4.4.1.2. Geochronology of the early tensional vein-type ±U 2
U 2 uraninite gives a discordant U-Pb upper-intercept age of 1594±95 Ma and a lower
intercept of 89±670 Ma (Fig. 2.11B). The oldest 207 Pb/ 206 Pb age of 2289±20 Ma is
interpreted as a minimum crystallization age. The 207 Pb/ 206 Pb system shows alteration
events at ca. 2.2-2.1 Ga, 2.1-2.0 Ga, 2.0-1.9 Ga, 1.9-1.8 Ga, and 1.6 Ga (Table 2.1, Fig.
2.11, and Appendix 1).
2.4.4.1.3. Geochronology of the granite-related metasomatic-type U 3 in Gunnar
U/Pb isotopic ratios of U 3 are discordant with very low Pb/U ratios that indicate
significant Pb loss. Ages obtained in the U/Pb system range between 1550 to 10 Ma
(Tables 2.1b and 2.2b) and do not reflect the formation age of the granite-related
metasomatic-type U mineralization because of substantial Pb loss. Rather they reflect
periods of alteration that have significantly affected U 3 subsequent to its formation.
2.4.4.1.4. Geochronology of the breccia-type U 4
U/Pb isotopic ratios of U 4 , which reflect the major uranium mineralizing event, are
discordant and yield a U-Pb upper-intercept age of 1857±170 Ma (2σ, MSWD: 0.5) and a
lower intercept of 42±350 (Fig. 2.11C). The oldest 207 Pb/ 206 Pb age of 1848±5 Ma records
the minimum crystallization age. Post-mineralization alteration recorded in the 207 Pb/ 206 Pb
ratios occur at ca. 1.8 Ga, 1.4-1.3 Ga, 1.2-0.9 Ga, 0.8 Ga and 0.5 Ga (Table 2.1).
2.4.4.1.5. Geochronology of the volcanic-type ±U 5
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