首页> 外文期刊>Acta crystallographica. Section F, Structural biology communications >Metal source and fluid-rock interaction in the Archean BIF-hosted Lamego gold mineralization: Microthermometric and LA-ICP-MS analyses of fluid inclusions in quartz veins, Rio das Velhas greenstone belt, Brazil
【24h】

Metal source and fluid-rock interaction in the Archean BIF-hosted Lamego gold mineralization: Microthermometric and LA-ICP-MS analyses of fluid inclusions in quartz veins, Rio das Velhas greenstone belt, Brazil

机译:Archean Bif-Hosted Lamego金矿化中的金属源和流体岩石互动:石英静脉中的微液和LA-ICP-MS分析石英静脉,Rio Das Velhas Greenstone Belt,巴西

获取原文
获取原文并翻译 | 示例
获取外文期刊封面目录资料

摘要

The Lamego orogenic gold deposit (440,742 oz gold measured reserves and 2.4 million t measured resources, with an average grade of 5.71 g/t Au and a cut-off grade of 2.15 g/t Au; AngloGold Ashanti Corrego do Sitio Mineracao S/A (AGA) personal communication, 2014) is located in the 5 km-long trend that includes the world-class Cuiaba deposit. It is hosted in the Neoarchean metavolcano-sedimentary rocks of the Rio das Velhas greenstone belt, Quadrilatero Ferrifero, Brazil. Mineralization is associated mainly with metachert-banded iron formation (BIF) and carbonaceous phyllites in the reclined Lamego fold, in which the Cabeca de Pedra orebody represents the hinge zone. Mineralization is concentrated in silicification zones and their quartz veins, as well as in sulfide minerals, product of BIF sulfidation. Hydrothermal alteration varies according to host rock, with abundant sulfide-carbonate in BIF, and sericite-chlorite in carbonaceous phyllite. Quartz vein classification according to structural relationships and host rocks identified three vein systems. The V1 system, mainly composed of smoky quartz (Qtz I) and pyrite, is extensional, crosscuts the bedding plane So of BIF, and is parallel to the fold axis. The V2 system, of the same composition, is represented by veins that are parallel to the S1-2 foliation and S-0. This system is also characterized by silicification zones in the BIF-carbonaceous phyllite contact that has its maximum expression in the hinge zone of folds. The V3 system has milky quartz (Qtz II) veins, which result from the reciystallization of smoky quartz, located mainly in shear zones and faults; these veins form structures en echelon and vein arrays. The most common ore minerals are pyrite, As-pyrite and arsenopyrite. Fluid inclusion-Ft trapped in all quartz veins present composition in the H2O-CO2 +/- CH4-NaCl system. Fluid evolution can be interpreted in two stages: i) aqueous-carbonic fluid trapped in Qtz I, of low salinity (similar to 2% equiv. wt.% NaCl), and ii) carbonic-aqueous fluid, of moderate salinity (average 9 eq. wt.% NaCl) hosted in Qtz II. Both stages are characterized by decrepitation temperatures in the range of 200 to 300 degrees C, and suggest a fluid of metamorphic origin. Applying an arsenopyrite geothermometer, the calculated formation temperature for the Cabeca de Pedra orebody is 300 to 375 degrees C. The vertical intersection of the isochors allows a minimum pressure calculation of 2.6 kbar. The composition of individual Fls of this orebody, obtained by LA-ICP-MS analyses, compared with results of Fls for the Carvoaria Velha deposit, Corrego do Sitio lineament, highlights a standard composition typical of metamorphic fluids with Na K Ca Mg, which increase or decrease in concentration as a function of salinity in both deposits. Trace elements vary according to fluid-rock reactions, and are directly related to the host rock composition. The comparison of data sets of the two deposits shows that the Cabeca de Pedra Fls have a higher enrichment in Zn, while Cu, As and Sb are richer in Carvoaria Velha, suggesting influence of the host rock geochemistry. The suggested mechanisms for gold precipitation at the Cabeca de Pedra orebody, Lamego gold deposit are: i) hydrolysis of the carbonaceous matter of phyllite and BIF, affecting fO(2), destabilizing sulfur complexes and enhancing gold precipitation; ii) replacement of BIF iron carbonates by sulfides; and iii) continuous pressure changes that lead to silica precipitation and free gold.
机译:Lamego Orengenic金矿床(440,742盎司金币储量和240万吨测量资源,平均5.71克/吨Au等级,截止等级为2.15克/ T Au; Anglogold Ashanti Correogo Do Sitio Mineracao S / A. (AGA)个人沟通,2014年)位于5公里长的趋势,包括世界一流的库亚巴存款。它托管在Rio Das Velhas Greenstone Belt,Quadrilatero Ferrififero,巴​​西里约热内卢的Neoarchean Metavolcano - 沉积岩石中。矿化主要与斜倚的Lamego折叠中的MetaChert带状铁形成(BIF)和碳质阈值相关联,其中Cabeca de Pedra Osebody代表铰链区。矿化在硅化区及其石英脉中集中,以及硫化物矿物质,BIF硫化产物。水热改变根据宿主岩,BIF中具有丰富的硫化物 - 碳酸盐和碳质植物的绢云母。根据结构关系和主体岩石的石英静脉分类确定了三个静脉系统。 V1系统主要由烟熏石英(QTZ I)和硫铁矿组成,是宽泛的,横切平面为BIF,并且与折叠轴平行。相同的组合物的V2系统由与S1-2叶子和S-0平行的静脉表示。该系统的特征还在于BIF-碳质的硅藻土中的硅化区,其在折叠的铰链区中具有其最大表达。 V3系统具有乳白色石英(QTZ II)静脉,由烟熏石英的循环化引起,主要位于剪切区和故障中;这些静脉形成结构EN梯队和静脉阵列。最常见的矿石矿物质是硫铁矿,黄铁矿和砷黄石。在H 2 O-CO 2 +/-CH 4-NaCl系统中捕获的所有石英脉冲中捕获的液体夹杂物。流体进化可以在两个阶段解释:i)捕获QTZ I的水性碳酸盐,低盐度(类似于2%当量的2%NaCl)和II)碳碳酸盐水溶液(平均9 QTZ II中托管的%NaCl)。两个阶段的特征在于200至&gt的衰减温度范围为300摄氏度,并提出了变形源的流体。施加亚苯甲酸盐地热计,Cabeca de Pedra Osebody的计算温度为300至375摄氏度。等分组的垂直交叉点允许最小的压力计算2.6 kbar。通过La-ICP-MS分析获得的该矿体的个体杂种的组成与Corrego Do Sitio Lineament的FLS的结果相比,Corrego Do Sitio LineAment突出了一种标准组成,典型的变质液与Na& k& CA& Mg,其浓度增加或降低,作为沉积物中的盐度的函数。微量元素根据流体岩体反应而变化,并且与宿主岩体组合物直接相关。两种沉积物的数据集的比较表明,Cabeca de Pedra FLS在Zn中具有更高的富集,而Cu,As和Sb在Carvoaria Velha中富裕,暗示了主岩地球化学的影响。 Cabeca de Pedra Osebody,Lamego金沉积的金沉淀的建议机制是:i)植物碱和BIF的碳质物质水解,影响FO(2),稳定硫络合物并增强金沉淀; ii)通过硫化物替换BIF铁碳酸盐;和III)导致二氧化硅沉淀和自由金的连续压力变化。

著录项

相似文献

  • 外文文献
  • 中文文献
获取原文

客服邮箱:kefu@zhangqiaokeyan.com

京公网安备:11010802029741号 ICP备案号:京ICP备15016152号-6 六维联合信息科技 (北京) 有限公司©版权所有
  • 客服微信

  • 服务号