TY  - GEN
A1  - Bobos, Iuliu
A1  - Goncalves, Ana
A1  - Lima, Luis
A1  - Noronha, Fernando
A1  - Sudo, Masafumi
T1  - Micas Ar-40/Ar-39 dating of hydrothermal events related with the post-orogenic W (+/- Sn), (Cu, Mo) mineralization from Borralha, Northern Portugal
T2  - Life with Ore Deposits on Earth – 15th SGA Biennial Meeting 2019,
N2  - Secondary mica minerals collected from the Santa Helena (W- (Cu) mineralization) and Venise (W-Mo mineralization) endogenic breccia structures were Ar-40/Ar-39 dated. The muscovite Ar-40/Ar-39 data yielded 286.8 +/- 1.2 (+/- 1 sigma) Ma (samples 6Ha and 11Ha) which reflect the age of secondary muscovite formation probably from magmatic biotite or feldspar alteration. Sericite Ar-40/Ar-39 data yielded 280.9 +/- 1.2 (+/- 1 sigma) Ma to 279.0 +/- 1.1 (+/- 1 sigma) Ma (samples 6Hb and 11Hb) reflecting the age of greisen alteration (T similar to 300 degrees C) where the W- disseminated mineralization occurs. The muscovite 40Ar/39Ar data of 277.3 +/- 1.3 (+/- 1 sigma) Ma and 281.3 +/- 1.2 (+/- 1 sigma) Ma (samples 5 and 6) also reflect the age of muscovite (selvage) crystallized adjacent to molybdenite veins within the Venise breccia. Geochronological data obtained confirmed that the W mineralization at Santa Helena breccia is older than Mo-mineralization at Venise breccia. Also, the timing of hydrothermal circulation and the cooling history for the W-stage deposition was no longer than 7 Ma and 4 Ma for Mo-deposition.
Y1  - 2019
UR  - https://www.researchgate.net/publication/337901420_Micas_40_Ar_39_Ar_dating_of_hydrothermal_events_related_with_the_post-orogenic_W_Sn_Cu_Mo_mineralization_from_Borralha_Northern_Portugal
IS  - 1
SP  - 353
EP  - 356
PB  - SGA Soc Geology Applied mineral  depositis
CY  - Geneva
ER  - 
TY  - JOUR
A1  - Trumbull, Robert B.
A1  - Sudo, Masafumi
A1  - Harris, C.
A1  - Armstrong, R. A.
A1  - de Beer, C. H.
T1  - The age of the Koegel Fontein anorogenic complex, South Africa, and its relationship to the regional timing of magmatism and breakup along the South Atlantic rifted margin
JF  - South African Journal of Geology
N2  - The early Cretaceous Koegel Fontein intrusive complex is situated near the Atlantic coast in South Africa, about 350 km northwest of Cape Town. The complex comprises felsic units of granite and syenite with compositionally related dykes, and a single intrusive plug of diorite. Existing zircon U-Pb ages of 144 +/- 2 Ma for the syenite and 133.9 +/- 1.3 Ma for the granite suggest that the emplacement of the complex took place over a period of about 10 My. This study provides additional and independent ages of the Koegel Fontein complex by Ar-40/Ar-39 dating to confirm the onset and duration of magmatism and better define the sequence of igneous units that comprise it. New laser step-heating Ar-40/Ar-3(9) ages on plagioclase and biotite from the main intrusive units in the complex are presented here, including samples previously dated by U-Pb dating. The Ar-40/Ar-39 ages for the granite and syenite units (131.1 +/- 0.9 Ma and 143.3 +/- 0.9, respectively) are in good agreement with the zircon U-Pb ages. Other units not previously dated include the Rooivleitjie alkaline granite (150.7 +/- 0.6 Ma), two quartz-porphyry dykes (143.0 +/- 0.9 and 139.4 +/- 1.7 Ma) and the Zout Rivier diorite plug (133.0 +/- 1.0 Ma). The new results confirm an early onset of magmatism at Koegel Fontein relative to that of the Etendeka Province some 1000 km to the north, which is consistent with the regional south-to-north propagation of South Atlantic rifting. The youngest Ar-40/Ar-3(9) ages at Koegel Fontein (134 to 131 Ma, Rietpoort Granite and 133 Ma, Zout Rivier diorite) correspond to the age of the first magnetic seafloor-spreading anomaly offshore, and we suggest that the longevity of Koegel Fontein magmatism relates to a superposition of pre-drift magmatism onshore and spreading-related magmatism as continental separation began.
Y1  - 2019
U6  - https://doi.org/10.25131/sajg.122.0007
SN  - 1012-0750
SN  - 1996-8590
VL  - 122
IS  - 1
SP  - 69
EP  - 78
PB  - Geological Society of South Africa
CY  - Marshalltown
ER  -