Orogenic gold ores in three-dimensions: A case study of distinct mineralization styles at the world-class Cuiabá deposit, Brazil, using high-resolution X-ray computed tomography on gold particles
Orogenic gold ores in three-dimensions: A case study of distinct mineralization styles at the world-class Cuiabá deposit, Brazil, using high-resolution X-ray computed tomography on gold particles
复制标题
三维造山金矿石：使用金颗粒高分辨率 X 射线计算机断层扫描对巴西世界级 Cuiabá 矿床的不同矿化类型进行案例研究
DOI：
10.1016/j.oregeorev.2021.104584
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发表时间：
2022
影响因子：
3.3
通讯作者：
Fernandes, Raphael C.
中科院分区：
文献类型：
--
作者：
Ferraz da Costa, Marília;Kyle, J. Richard;Lobato, Lydia M.;Ketcham, Richard A.;Figueiredo e Silva, Rosaline C.;Fernandes, Raphael C.
用传统的岩石学方法研究矿石有一个固有的局限性，即必须通过二维观测和测量来推断空间(三维、三维)分布、方向、形状和矿物组合。此外，对于金矿来说，开发具有统计意义的数据集尤其困难，因为即使在高品位的矿石中，黄金的粒度也很细，金的丰度也很低。我们使用高分辨率X射线计算机层析成像(HRXCT)和改进的处理方法来提供矿石结构和原位金粒的三维数据，以识别矿化类型和提高矿石回收率。这是巴西最大的地下矿山QuadriláTero Ferrífero省太古宙世界级Cuiabá造山金矿的案例研究。选定的样品代表了Cuiabá矿不同的矿化类型：BIF赋存的矿石来自Fonte Grande Sul(FGS)矿体，含金的石英-碳酸盐矿脉赋存于Veio de Quartzo(VQZ)矿体的变质单元中。这项研究描述了16,000多个金颗粒的形状、大小、取向和矿物组合。由于金粒子的粒度很小，因此对其进行分割和定量测量尤其具有挑战性。这个问题是使用最近形式化的部分体积和模糊(PVB)方法来解决的。金矿化类型在三维结构和数量方面不同，包括大小和空间分布。对VQZ样品的分析表明，金颗粒主要以游离状态存在于石英-碳酸盐基质中，许多颗粒与多种硫化物矿物组合直接接触。赋存于BIF中的FGS矿石中的金颗粒与富铁碳酸盐带中的高磁黄铁矿带伴生。PVB分析表明，两种矿石中测量到的颗粒长轴范围为∼25~μm~1.4 mm，中值约为115μm。较大颗粒主要为近等长球体，较小颗粒主要为近等粒至等粒。HRXCT数据揭示了运动过程对金的形状和取向的影响，并表明了变形在颗粒尺度上的影响。
Ore studies using conventional petrographic methods have an intrinsic limitation that spatial (three-dimensional, 3-D) distribution, orientation, shape and mineral associations have to be inferred by 2-D observations and measurements. Further, developing statistically significant data sets is particularly difficult for gold ores, given the fine grain size and low gold abundance even in high-grade ores. We use high-resolution X-ray computed tomography (HRXCT) and improved processing methods to provide 3-D data of ore textures and in-situ gold particles to discern mineralization styles and improve ore recovery. This is a case study of the Archean, world-class Cuiabá orogenic gold deposit in the Quadrilátero Ferrífero province, the largest underground mine in Brazil.Selected samples represent distinct mineralization styles at the Cuiabá mine: BIF-hosted ore from the Fonte Grande Sul (FGS) orebody, and gold-bearing quartz-carbonate veins hosted in a metamafic unit from the Veio de Quartzo (VQZ) orebody. This study characterizes shape, size, orientation and mineral associations of over 16,000 gold particles. Segmentation and quantitative measurements of gold particles are particularly challenging due to their small grain size. This issue is addressed using the recently formalized partial volume and blurring (PVB) method. Gold mineralization styles differ in 3-D textural and quantitative aspects including size and spatial distribution. Analysis of the VQZ sample shows that gold particles are mainly free in the quartz-carbonate matrix, with many particles in direct contact with a diverse sulfide mineral assemblage. Gold particles in the BIF-hosted FGS ore form bands in association with high pyrrhotite zones within iron carbonate-rich bands. PVB analysis show that the long axis of measured particles in both ore types ranges from ∼25 μm to 1.4 mm, with median values around 115 μm. Larger particles dominantly are sub-equant to prolate spheroids, with smaller particles appearing to be dominantly sub-equant to equant grains. The HRXCT data reveal that the kinematic processes affect gold shape and orientation and indicate the influence of deformation at the grain scale.