Compiled by Salatiel Alves of Araújo, all reserved rights © 1996
AB'SABER (1988), in an extensive work on Pantanal Matogrossense's origin, it develops the idea that what today is a depression it would have been in the past a vast shield vault, that worked as area of supply detrítico for Grupo Bauru's sedimentary basins (High Paraná) and Parecis.
The vast vault of existent shield to the Cretaceous behaved later as emptied anticlinal, of great regional width. This would have happened because during the soerguimento powder-cretácico of group they would have happened in her important falhamentos facilitating its desventramento.
Today the Pantanal Matogrossense is characterized by extensive accumulation plains, with inferior quotas to 200 meters. Its past, current and future evolution is submitted to the conditions of the high areas that surround it, therefore these constitute its source of water and sediments (Godói Filho, 1986). This author presents some characteristic geológicas of the formations that you/they happen in the accumulation plains and of those that constitute its influence area: Complex Rio Apa, Complex Xingu, Group Rio Branco, Intrusive Suite Guapé, Grupo Cuiabá, Grupo Corumbá, Grupo Jacadigo, High Group Paraguay, Grupo Amoguijá, Intrusive Suite Alumiador, Intrusive Suite Rio Cheers and Grupo Aguapeí (Pré-Cambriano); Formations of the Sedimentary Basin of Paraná, Basalt of Tapirapuã, Formação Jauru and Intrusive Acid (Paelozóico and Mesozóico); Cobertura Detrito-laterítica, deposits detríticos, Formação Xaraiés and Formação Pantanal (Cenozóico).
Along the works of mapeamento geomorfológico accomplished through the Projeto RADAMBRASIL (Franco & Pinheiro, 1982) they were identified nine units geomorfológicas in the area, standing out the unit denominated Plains and Pantanais Matogrossense, that the authors described as being an enormous amphitheater gone back to west. This unit was subdivided at eight Swamplands, individualized by its characteristic morfogenéticas (relative altimetria, litologia and pedologia) and botanies: Swampland of Corixo Grande-Jauru-Paraguai, of the Cuiabá-Benedictine monk Gomes-Paraguaizinho, of Itiquira-São Lourenço - Cuiabá, of Taquari, of the Black, of the Miranda-Aquidauana, of Jacadigo-Nabileque, and of Paiaguás. The whole relative discussion to the incorrectness of the use of the term Swampland (once it is not an area with marshy characteristics) and to the different ones proposed of sub-divisions of the area it was told widely for of Silva (1990). The main fact is that although the whole area is submitted to a common genesis, characterized by the accumulation process, the different disposition of the sediments checks characteristics different to each subunidade.
The Grupo Cuiabá is the most important substratum of Benedictine monk Gomes' Basin. In agreement with Almeida (1948, mentioned by Franco & Pinheiro, 1982), the Grupo Cuiabá consists of rocks of low metamorfismo degree, constituted predominantly by filitos with quartzitos collations.
The dominant rocks in the area of Poconé are sedimentary, that suffered posterior metamorfismo (sequence metassedimentar detrítica of the Grupo Cuiabá). They are characterized by filitos sericíticos, grafitosos and piritosos. The filitos is usually cut for veins of quartz, that fill the zones of fraturamento of orientation N25-60W, and that can reach from few centimeters to decimeters of thickness. The gold is concentrated in these veins (Fernandes, 1989).
Second this same author, the processes of auriferous concentration in the fraturamento system were probably current of the action of having flowed hidrotermais. Flowed them they provoked the remobilização of the gold contained in the rocks encaixantes, represented by the filitos grafitosos e/ou sericíticos, mainly in the final apprenticeships of the last tectonic event that affected the units geológicas of the area.
Almeida (1965, apud Fernandes 1989), it considers this event as part of the Ciclo Brasiliano (900-600 million years). In this phase, the modifications of the terrestrial crust related to a tectonismo rígico provoked fraturamentos where in the zones of weakness, due to the relief of the pressure, they migrated them flowed hidrotermais that leached the gold disseminated in the encaixantes.
Light et alii (1980, apud Barros et alii 1982) they describe three manners different from occurrence of gold in the Grupo Cuiabá: in veins of quartz, in elúvio-coluviões and in alluviums. The gold that happens in veins of quartz, discussed previously, now is constituted as the main type in exploration. The occurrence of the type elúvio-coluvionar, of smaller importance in terms of available amount, supplies gold as by-product of the cascalho extraction for the civil construction. The type jazimento aluvionar constituted the main source of the metal garimpado in the past, for happening in the surface of the soils of the flood plains.
Computer science, Consulting and Training Paiaguás
Salatiel
Alves of Araújo - Geologist and Specialist in Remote Sensory
Comments for the author: salatiel@nutecnet.com.br
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