The transition from planar to en echelon morphology in a single vein in shale: Insights from X-ray computed tomography scanning

Abstract En echelon fractures and veins are among the most common and distinctive geological structures, yet their three-dimensional forms and relationships to surrounding structures are commonly unclear. X-ray computed tomography (CT) offers an unrivaled ability to examine structures within rocks in three dimensions, and it is applied here to a sample of drill core from the Marcellus Shale of southwestern Pennsylvania (USA). CT images yield qualitative and quantitative data on the transition from a pyrite-rich planar vein to an en echelon veinlet array, and on the heterogeneity of veinlets within the array. Using a combination of three- and two-dimensional images, geometric data, and traditional petrography, we identify a range of veinlet shapes consistent with deformation during formation of an antitaxial graphite-calcite-pyrite vein system. Each of the veinlets is rooted in the underlying planar vein where it is narrowest. The transition from planar vein to en echelon array coincides with a change in bedding, suggesting that competency contrasts between adjacent beds controlled the fracture morphology. Veinlets initiated as short, lenticular fractures at ∼45° to the planar vein before lengthening, dilating, and rotating. None of the veinlets are strongly sigmoidal, nor is there measurable offset across the margins of the planar vein; therefore, finite non-shear strain was very limited, and fluid overpressure–induced fracturing during burial and diagenesis is probably the most likely process for fracturing and vein formation.

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Gold Exploration in Two and Three Dimensions: Improved and Correlative Insights from Microscopy and X-Ray Computed Tomography

Minerals ◽

10.3390/min10050476 ◽

2020 ◽

Vol 10 (5) ◽

pp. 476

Author(s):

Joshua Chisambi ◽

Bjorn von der Heyden ◽

Muofhe Tshibalanganda ◽

Stephan Le Roux

Keyword(s):

Computed Tomography ◽

Spatial Distribution ◽

Gold Mineralization ◽

Three Dimensional ◽

Three Dimensions ◽

Low Grade ◽

X Ray ◽

3D Space ◽

X Ray Computed ◽

2D And 3D

In this contribution, we highlight a correlative approach in which three-dimensional structural/positional data are combined with two dimensional chemical and mineralogical data to understand a complex orogenic gold mineralization system; we use the Kirk Range (southern Malawi) as a case study. Three dimensional structures and semi-quantitative mineral distributions were evaluated using X-ray Computed Tomography (XCT) and this was augmented with textural, mineralogical and chemical imaging using Scanning Electron Microscopy (SEM) and optical microscopy as well as fire assay. Our results detail the utility of the correlative approach both for quantifying gold concentrations in core samples (which is often nuggety and may thus be misrepresented by quarter- or half-core assays), and for understanding the spatial distribution of gold and associated structures and microstructures in 3D space. This approach overlays complementary datasets from 2D and 3D analytical protocols, thereby allowing a better and more comprehensive understanding on the distribution and structures controlling gold mineralization. Combining 3D XCT analyses with conventional 2D microscopies derive the full value out of a given exploration drilling program and it provides an excellent tool for understanding gold mineralization. Understanding the spatial distribution of gold and associated structures and microstructures in 3D space holds vast potential for exploration practitioners, especially if the correlative approach can be automated and if the resultant spatially-constrained microstructural information can be fed directly into commercially available geological modelling software. The extra layers of information provided by using correlative 2D and 3D microscopies offer an exciting new tool to enhance and optimize mineral exploration workflows, given that modern exploration efforts are targeting increasingly complex and low-grade ore deposits.

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X-ray computed tomography study for drill core of the Drazhnoe orogenic-type gold deposit (Sakha (Yakutia), Russian Federation)

Ores and metals ◽

10.47765/0869-5997-2021-10027 ◽

2022 ◽

pp. 43-59

Author(s):

Victoria Chikatueva ◽

Nikita Stepanov ◽

Andrey Chitalin ◽

Dmitry Korost

Keyword(s):

Computed Tomography ◽

Three Dimensional ◽

Distribution Patterns ◽

Gold Deposits ◽

X Ray ◽

Vein Formation ◽

Study Results ◽

Ore Minerals ◽

Ore Mineralization ◽

X Ray Computed

Orogenic gold-quartz deposits have a clear structural control and are accompanied by wallrock metasomatic alteration. However, in detailed modeling of such deposits, there is often a mismatch between the structural plans for high-grade ore zone distribution and metasomatite zones, and the latter are not always associated with faults. This is explained by the evolution of the hydrothermal process and the pulsating nature of the development of the territory. In the early stages of the mineral deposit study, it is very important to reliably determine the distribution of ore zones, since the correct targeting of the drilling program and the economic deposit assessment depend on it. The problem can be solved using the method of X-ray computed tomography (СТ) in the core study. This paper presents the methodology of studying fullsize core samples of gold deposits by using CT. A core sample characterizing the central part of ore body of Drazhnoye deposit (Tarynskoye ore field, Republic of Sakha (Yakutia)) was used as the study material. The sample studied was scanned by a SIEMENS Somatom Perspective tomograph at two energies (80 and 130 keV). As a result, a detailed three-dimensional stereological model of the core was obtained, which made it possible not only to study the distribution of ore minerals in the volume of the entire sample, but also to identify vein bodies of different ages, as well as to study their morphology and trace the distribution patterns of ore mineralization in them. Based on the study results, we can offer a preliminary interpretation of ore mineralization and vein formation sequence.

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X-ray computed tomography reveals that grain protrusion controls critical shear stress for entrainment of fluvial gravels

Geology ◽

10.1130/g46883.1 ◽

2019 ◽

Vol 48 (2) ◽

pp. 149-153 ◽

Cited By ~ 4

Author(s):

Rebecca A. Hodge ◽

Hal Voepel ◽

Julian Leyland ◽

David A. Sear ◽

Sharif Ahmed

Keyword(s):

Computed Tomography ◽

Shear Stress ◽

Three Dimensional ◽

Critical Shear Stress ◽

Bedload Transport ◽

Flow Profile ◽

X Ray ◽

Computed Tomography Scanning ◽

X Ray Computed ◽

Bed Stability

Abstract The critical shear stress (τc) for grain entrainment is a poorly constrained control on bedload transport rates in rivers. Direct calculations of τc have been hindered by the inability to measure the geometry of in situ grains; i.e., the shape and location of each grain relative to surrounding grains and the bed surface. We present the first complete suite of three-dimensional (3-D) grain geometry parameters for 1055 water-worked grains, and use these to parameterize a new 3-D grain entrainment model and hence estimate τc. The 3-D data were collected using X-ray computed tomography scanning of sediment samples extracted from a prototype scale flume experiment. We find that (1) parameters including pivot angle and proportional grain exposure do not vary systematically with relative grain size; (2) τc is primarily controlled by grain protrusion, not pivot angle; and (3) larger grains experience larger forces as a result of projecting higher into the flow profile, producing equal mobility. We suggest that grain protrusion is a suitable proxy for assessing gravel-bed stability.

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Three‐dimensional X‐ray‐computed tomography of 3300‐ to 6000‐year‐old Citrullus seeds from Libya and Egypt compared to extant seeds throws doubts on species assignments

Plants People Planet ◽

10.1002/ppp3.10220 ◽

2021 ◽

Author(s):

Katherine A. Wolcott ◽

Guillaume Chomicki ◽

Yannick M. Staedler ◽

Krystyna Wasylikowa ◽

Mark Nesbitt ◽

...

Keyword(s):

Computed Tomography ◽

Three Dimensional ◽

X Ray ◽

X Ray Computed

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Cover Feature: Non‐Destructive Three‐Dimensional Imaging of Metal Organic Framework Mixed Matrix Membranes using Lab‐based X‐ray Computed Tomography (Chemistry ‐ Methods 5/2021)

Chemistry–Methods ◽

10.1002/cmtd.202100034 ◽

2021 ◽

Vol 1 (5) ◽

pp. 202-202

Author(s):

Anton Jansson ◽

Ignacio Luz ◽

Ching‐Chang Chung ◽

Mustapha Soukri

Keyword(s):

Computed Tomography ◽

Metal Organic Framework ◽

Three Dimensional ◽

Mixed Matrix Membranes ◽

Mixed Matrix ◽

Three Dimensional Imaging ◽

X Ray ◽

Metal Organic ◽

X Ray Computed ◽

Non Destructive

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Visualizing Fluid Flows With X-Rays

Volume 1: Symposia, Parts A and B ◽

10.1115/fedsm2007-37023 ◽

2007 ◽

Cited By ~ 4

Author(s):

Theodore J. Heindel ◽

Terrence C. Jensen ◽

Joseph N. Gray

Keyword(s):

Computed Tomography ◽

Flow Visualization ◽

Three Dimensional ◽

Fluid Flows ◽

X Rays ◽

Radiographic Images ◽

Optical Access ◽

X Ray ◽

X Ray Computed ◽

Density Map

There are several methods available to visualize fluid flows when one has optical access. However, when optical access is limited to near the boundaries or not available at all, alternative visualization methods are required. This paper will describe flow visualization using an X-ray system that is capable of digital X-ray radiography, digital X-ray stereography, and digital X-ray computed tomography (CT). The unique X-ray flow visualization facility will be briefly described, and then flow visualization of various systems will be shown. Radiographs provide a two-dimensional density map of a three dimensional process or object. Radiographic images of various multiphase flows will be presented. When two X-ray sources and detectors simultaneously acquire images of the same process or object from different orientations, stereographic imaging can be completed; this type of imaging will be demonstrated by trickling water through packed columns and by absorbing water in a porous medium. Finally, local time-averaged phase distributions can be determined from X-ray computed tomography (CT) imaging, and this will be shown by comparing CT images from two different gas-liquid sparged columns.

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