54772-04-2Relevant articles and documents
Geology and Pb-Pb Geochrology of Paleoproterozic Volcanic and Grantic Rocks of Pitanga Province, Amozian Craton Northern Brazil
Costi,Dall'Agnol, Roberto,Moura
, p. 832 - 849 (2007/10/06)
Pinga Province is one of the main tin provinces of the Amazonian craton. The oldest unit in the studied area is the Iricoume Group, which consists of rhyolites and rhyodacites with a 207Pb/206Pb zircon age of 1888 ± 3 Ma. This volcanic sequence is intruded by five-A-type granite plutons. The studied portion of the Eropa pluton is homogeneous, and composed of a peralkaline alkali-amphibole hypersolvus granite that yielded a 207Pb/206Pb zircon age 1829 ± 1 Ma. The early facies of the Madeira pluton consists of a metaluminous amphibole-biotite synogranite (rapakivi facies) with a 207Pb/206Pb zircon age of 1824 ± 2 Ma. It is intruded by 1822 ± 1 Ma, mildly peraluminous biotite syenogranite. The later facies of this pluton consist of a porphyritic, hypersolvus, alkali-feldspar granite and an albite granite. Field relationships and an extensive drilling survey indicate that these two facies are sheet-shaped and were emplaced almost simulteneuosly. The hypersolvus alkali-feldspar granite has a 207Pb/206Pb zircon age of 1818 ± 2 Ma. Taking in account its field relationships with the albite granite, a similar age is assumed for the latter. The albite granite intrudes the biotite granite and rapakivi granite facies of the Madeira pluton, which was emplaced by shallow-level cauldron subsidence. The albite granite is sheet shaped and consists of a magmatic peralkaline cryolite-bearing core facies partially surrounded by an autometasomatic peraluminious flourite-bearing border facies. Both albite granite facies are strongly tin-mineralized and display anomalous contents of Nb, Rb, Zr, and REE. A massive body of cryolite and permatitic rocks is associated with the albite granite. The contrast in age between the Iricoume Group and the Europa + Madeira granites demonstrates that the plutons are not subvolcanic intrusions related to the extrusives. The ages of 1824 ± 2 Ma, 1822 ± 2 Ma, and 1818 ± 2 Ma obtained, repectively, for the amphilole + biolite syenogranite, biotite granite, and porphyritic hypersolvus granite of the Madeira pluton are consistent with the emplacement sequence inferred for these facies. These ages indicate that the Madeira pluton was emplaced in a relatively short time. Its facies are a little younger than the peralkaline granite of the Europa pluton, suggesting that the latter is not coeval with the Madeira peralkaline albite granite.
