Direct dating of gold by radiogenic helium: Testing the method on gold from Diamantina, Minas Gerais, Brazil

Geology (Impact Factor: 4.64). 01/2013; 41:163-166. DOI: 10.1130/G33751.1

ABSTRACT New analytical developments have made radiogenic helium (He-4) applicable to archeological gold artifacts for age determinations. Here we report the application of the U/Th-He-4 method to the direct dating of gold from the historically important gold deposit in Diamantina, Minas Gerais, Brazil. The U/Th-He-4 age of 515 +/- 55 Ma for the Diamantina gold is corroborated by a new U/Pb age of 524 +/- 16 Ma for rutile recovered from auriferous pockets. These ages tie the Diamantina gold mineralization to the Brasiliano orogenic event, in the context of the Gondwana amalgamation. Our results indicate that U/Th-He-4 dating of gold is possible, opening new perspectives for the dating of gold deposits without assuming contemporaneity between gold and datable hydrothermal minerals.

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    ABSTRACT: zircon and cassiterite U–Pb, molybdenite Re–Os and muscovite 40 Ar– 39 Ar ages on multiple generations of granitic magmatism and related W–Sn mineralization in the Wangxianling area, Nanling Range, South China: Zircon U–Pb age molybdenite Re–Os age cassiterite U–Pb age muscovite 40 Ar– 39 Ar age W and Sn mineralization Wangxianling Nanling Range South China The Nanling Range in South China hosts numerous W–Sn–rare metal deposits associated with several cycles of polygenetic granitic intrusions. In the Wangxianling area of the middle Nanling Range, igneous intrusions include the Wangxianling and Hehuaping granite plutons and more than 20 granite porphyry dykes. The Wangxianling pluton has a central phase of medium-grained tourmaline two-mica granite and a marginal phase of medium-grained tourmaline muscovite granite. The pluton hosts several tungsten deposits including Shuiyuanshan and Yejiwo. Mineralization type is dominantly scheelite greisen, with subordinate scheelite skarn and wolframite– quartz veins. The Hehuaping pluton composed of coarse-grained biotite granite and granite porphyry dykes to the east of the Wangxianling pluton have an associated Hehuaping tin deposit with tin skarn and subordinate porphyry and greisen mineralization. In situ zircon and cassiterite U–Pb dating, molybdenite Re–Os and muscovite 40 Ar– 39 Ar dating techniques are used to refine the age spectra of granitic rocks and W–Sn mineralization in the Wangxianling area. Granites of the Wangxianling pluton have zircon U–Pb ages of ~ 224 Ma. Tungsten-bearing quartz veins from both the Shuiyuanshan and Yejiwo tungsten deposits have an average molybdenite Re–Os isochron age of ~ 224 Ma, and muscovite of scheelite greisen from the Shuiyuanshan tungsten deposit yields a 40 Ar– 39 Ar plateau age of 214 Ma. The two mineralization ages are consistent with the zircon U-Pb age of the Wangxianling pluton indicat-ing a close association between pluton emplacement and W mineralization in the Late Triassic. Both the Hehuaping pluton and granite porphyry dykes have zircon U–Pb ages of ~156 Ma. In situ LA–ICP–MS U–Pb dating of cassiterite in both the tin skarn and tin greisen yields an average age of ~156 Ma, showing that the Sn miner-alization occurred at a similar time to the Late Jurassic granitic magmatism. Thus, two mineralization events are identified in the Wangxianling area, and include an earlier W dominant mineralization event and a later Sn dominant mineralization event. The earlier event is related both spatially and temporally to intrusion of the Late Triassic S-type Wangxianling granite pluton, whereas the later mineralization is associated both spatially and temporally with intrusion of the Late Jurassic Hehuaping A 2 -type granite pluton and A 2 -type granite porphyry dykes.
    Ore Geology Reviews 09/2014; 65(4):1021-1042. · 3.38 Impact Factor


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Dec 15, 2014