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|Type:||Artigo de periódico|
|Title:||Structural Controls On Gold Mineralisation And The Nature Of Related Fluids Of The Paiol Gold Deposit, Almas Greenstone Belt, Brazil|
|Abstract:||Chemical analyses suggest that the metavolcanic rocks of the Almas Greenstone Belt (AGB), Tocantins State, Brazil have a continental affinity, possibly related to a continental rift environment. They were metamorphosed to amphibolite facies during a regional tectono-metamorphic event (Dn), retrogressed to greenschist facies assemblages and then hydrothermally altered within dextral strike-slip shear zones (Dn+1). Fracture sets related to Dn+2 intersect Sn+1. The Paiol Gold Mine is one of several mineralised zones within metabasic and meta-intermediate rocks of the AGB. It exploits shoots of sulphide-Au-quartz mineralisation that occupy dilational zones approximately perpendicular to an elongation lineation (Ln+1) within mylonitic foliation Sn+1 (Sn+1=S within the S-C fabric). The dilational zones probably formed due to dextral displacement on sinistrally en echelon C surfaces. Minor amounts of gold may have been introduced or remobilised during Dn+2.Coexisting primary and pseudosecondary fluid inclusions in mineralised quartz veins from ore shoots comprise a high-salinity three-phase type (Type II) and a lower salinity two-phase type (Type I). Homogenisation temperatures for Type II inclusions range from 200 to 410 °C and Type I from 90 to 320 °C. The inclusions and their temperature ranges are believed to reflect heat exchange and some mixing between the two fluid types under relatively constant ambient temperatures, but variable (though broadly declining) fluid temperatures. This took place late in Dn+1 in conjunction with greenschist facies retrogression and localised hydrothermally induced metasomatism. © 2003 Elsevier B.V. All rights reserved.|
|Appears in Collections:||Unicamp - Artigos e Outros Documentos|
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