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The Application of Automated SEM-Based Identification of Detrital, Diagenetic and Indicator Mineral Phases

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A special issue of Minerals (ISSN 2075-163X). This special issue belongs to the section "Mineral Deposits".

Deadline for manuscript submissions: closed (15 September 2021) | Viewed by 19740

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Prof. Dr. Derek H. C. Wilton

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Guest Editor

Department of Earth Sciences, Memorial University of Newfoundland, St. John’s, NL A1B 3X5, Canada
Interests: metallogeny; mineral chemistry; automated mineral identifcation techniques; micro-analysis
Special Issues, Collections and Topics in MDPI journals

Dr. Gary Thompson

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Guest Editor

College of the North Atlantic, Prince Philip Drive, St John’s, NL, A1C 5P7, Canada
Interests: applied geochemistry; mineral exploration; mineralogy; Laser Induced Breakdown spectrometry (LIBS); hyperspectral imaging
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Automated SEM-based instruments (e.g., MLA-SEM, QEMSCAN) provide systematic and quantitative definition of minerals in a full range of sedimentary lithologies ranging from bedrock to surficial sediments; important data for both the petroleum and mining industries. Mapped minerals can include 1) detrital phases that provide data on provenance, 2) diagenetic phases and cements that provide data on physio-chemical conditions at depositional sites, or 3) in surficial sediments, indicator (proxy) minerals derived from source-hosted mineralization. Along with mineral identification, the analyses can furnish data on mineral properties including textures, intergrowths, shapes, and sizes.

The accurate, automated, and quantitative analyses of minerals provided by SEM-based mineral identification techniques essentially remove any inherent biases associated with human observation of the material. The technology fundamentally provides digital point counts of all mineral species present in material from sedimentary environments.

With sediment core or well cuttings, the technique can provide insight into the provenance and depositional environment of specific stratigraphic intervals, de-risking elements of petroleum systems in regions where little data exist. In surficial sediments, the technology defines the full range of mineral phases present, and specifically indicator minerals that are diagnostic of different types of mineral deposits.

Prof. Dr. Derek H. C. Wilton
Dr. Gary Thompson
Guest Editors

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Keywords

SEM-based mineral identification
MLA-SEM and QEMSCAN
Detrital minerals (automatic mapping)
Diagenetic minerals (automatic mapping)
Indicator Minerals (automatic mapping)
Bedrock mineral source tracing
Quantitative mineralogy of sediments, sedimentary rocks, surficial sediments
Mineral provenance
Diagenetic studies
Surficial sediment tracing

Related Special Issue

The Application of Automated SEM-Based Identification of Detrital, Diagenetic and Indicator Mineral Phases, Volume II in Minerals

Published Papers (7 papers)

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Research

28 pages, 90013 KiB

Open AccessArticle

MLA-SEM Characterization of Sulphide Weathering, Erosion, and Transport at the Voisey’s Bay Orthomagmatic Ni-Cu-Co Sulphide Mineralization, Labrador, Canada

by Derek H. C. Wilton, Gary M. Thompson and Dawn Evans-Lamswood

Minerals 2021, 11(11), 1224; https://0-doi-org.brum.beds.ac.uk/10.3390/min11111224 - 04 Nov 2021

Cited by 3 | Viewed by 2171

Abstract

The Voisey’s Bay nickel-copper-cobalt (Ni-Cu-Co) sulphide deposits constitute a significant resource of orthomagmatic mineralization. The deposits are not exposed at the surface except for in a small ferruginous gossan (Discovery Hill). The subsequent geophysical surveys and diamond drilling led to the discovery of the Ovoid ore body, buried beneath 20 m of till, and other deeper deposits in the bedrock. This study was initiated to characterize the sulphide mineralogy of these deposits through various stages of weathering, erosion, and transport. Because the samples ranged from bedrock through to a variety of surficial sediment types, the automated SEM-based identification provided by the MLA-SEM system was the ideal technique to quantitatively evaluate mineral distributions in the different media. The derived MLA-SEM data indicate that, aside from the Discovery Hill gossan, the surface sulphide mineralization at Voisey’s Bay was weathered in a pre-glaciation regolith at the Mini-Ovoid deposit and, on the surface of the Ovoid deposit, the massive sulphide was unoxidized due to a thin calcite-cemented clay cover. Pentlandite is very preferentially oxidized compared to other sulphides in the Voisey’s Bay ore, to depths of up to 10 m in bedrock. Conversely, within the coarse reject samples of crushed drill cores stored in sealed plastic bags, pyrrhotite was altered, whereas pentlandite and chalcopyrite are stable, presumably due to anaerobic reactions. The MLA-SEM detected trace amounts of minute sulphide grains in surficial sediments, but their contents abruptly decreased with distance from the sulphide mineralization. Microtextures such as troilite and pentlandite exsolution or twinning in pyrrhotite, however, could be observed in the fine sulphide grains from till, suggesting a derivation from orthomagmatic sulphide material, such as the Voisey’s Bay mineralization. Full article

(This article belongs to the Special Issue The Application of Automated SEM-Based Identification of Detrital, Diagenetic and Indicator Mineral Phases)

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11 pages, 1424 KiB

Open AccessArticle

Linking Automated Scanning Electron Microscope Based Investigations to Chemical Analysis for an Improved Understanding of Ash Characteristics

by Andrea C. Guhl, Sandra Pavón, Bernhard Schulz and Martin Bertau

Minerals 2021, 11(11), 1182; https://0-doi-org.brum.beds.ac.uk/10.3390/min11111182 - 26 Oct 2021

Cited by 1 | Viewed by 1586

Abstract

The movements and efforts of a circular economy, aiming to tap into the resource potential of ash, require an intimate knowledge of the material; often, target elements within this material are part of complex ash phases. This work shows how automated SEM investigations measure up to other laboratory techniques for the analysis of elemental composition and particle size. Three sewage sludge ash (SSA) samples have been studied in this comparison, showing material variation for SSA and highlighting the strengths and shortcomings of the methods chosen. Inductively coupled plasma optical emission spectroscopy (ICP-OES), X-ray fluorescence (XRF) and scanning electron microscopy with energy dispersive X-ray analysis (SEM-EDX) show relevant phosphate phases, but also a number of other elements. The extent of the accompanying elements, most likely hindering efficient phosphorus (P) recovery, varies. Propensities for detection in fine-grained and largely amorphous material such as ash vary, as is explored in this thorough comparison. ICP-OES data suffers from incomplete sample mobilization, and XRF-derived values suffer from matrix effects. Both are the only techniques studied which show trace elements, such as potentially toxic elements. SEM-EDX automated mineralogy delivers more reliable data for main elements while not reporting traces. By showing SEM-EDX automated mineralogy particle size distributions, alongside laser diffraction derived particle size distributions, the extent of the strain ash puts on traditional techniques is visible. Ashes tend to agglomerate, and the porous nature of particles hinders accurate detection. This work highlights where SSA recycling needs to be careful and hints at the extent of discrepancies between different methods. When understanding ash as a potential resource and designing efficient extraction strategies, this knowledge is crucial. Full article

(This article belongs to the Special Issue The Application of Automated SEM-Based Identification of Detrital, Diagenetic and Indicator Mineral Phases)

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31 pages, 8403 KiB

Open AccessEditor’s ChoiceArticle

Automated Gold Grain Counting. Part 2: What a Gold Grain Size and Shape Can Tell!

by Réjean Girard, Jonathan Tremblay, Alexandre Néron, Hugues Longuépée and Sheida Makvandi

Minerals 2021, 11(4), 379; https://0-doi-org.brum.beds.ac.uk/10.3390/min11040379 - 02 Apr 2021

Cited by 3 | Viewed by 2728

Abstract

Glacial drift exploration methods are well established and widely used by mineral industry exploring for blind deposit in northern territories, and rely on the dispersion of mineral or chemical signal in sediments derived from an eroded mineralized source. Gold grains themselves are the prime indicator minerals to be used for the detection of blind gold deposits. Surprisingly, very little attention has been dedicated to the information that size and shape of gold grain can provide, other than a simple shape classification based on modification affecting the grains that are induced in the course of sediment transport. With the advent of automated scanning electron microscope (SEM)-based gold grain detection, high magnification backscattered electron images of each grain are routinely acquired, which can be used for accurate size measurement and shape analysis. A library with 88,613 gold grain images has been accumulated from various glacial sediment surveys on the Canadian Shield and used to detect trends in grains size and shape. A series of conclusions are drawn: (1) grain size distribution is consistent among various surveys and areas, (2) there is no measurable fine-grained gold loss due to natural elutriation in ablation or reworked till, or during the course of reverse circulation drilling, (3) there is no grain size sorting during glacial transport, severing small grains from large ones, (4) shape modification induced by transport is highly dependent on grain size and original shapes, and (5) the use of grain shape inherited from neighboring minerals in the source rocks is a useful feature when assessing deposit types and developing exploration strategies. Full article

(This article belongs to the Special Issue The Application of Automated SEM-Based Identification of Detrital, Diagenetic and Indicator Mineral Phases)

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27 pages, 77690 KiB

Open AccessFeature PaperArticle

Automated Gold Grain Counting. Part 1: Why Counts Matter!

by Réjean Girard, Jonathan Tremblay, Alexandre Néron and Hugues Longuépée

Minerals 2021, 11(4), 337; https://0-doi-org.brum.beds.ac.uk/10.3390/min11040337 - 24 Mar 2021

Cited by 6 | Viewed by 3245

Abstract

The quantitative and qualitative assessment of gold grains from samples of glacial till is a well-established method for exploring gold deposits hidden under glaciated cover. This method, which is widely used in the industry and has resulted in numerous successes in locating gold deposits in glaciated terrain, is still based on artisanal gravity separation techniques and visual identification. However, being artisanal, it is limited by inconsistent recoveries and difficulties associated with visually identifying the predominantly small gold grains. These limitations hinder its capacity to decipher subtle or complex signals. To improve detection limits through the recovery of small gold grains, a new approach has recently been introduced into the industry, which is commercially referred to as the “ARTGold” procedure. This procedure involves the use of an optimized miniature sluice box coupled with an automated scanning electron microscopy routine. The capabilities of this improved method were highlighted in this study by comparing till surveys conducted around the Borden gold deposit (Ontario, Canada) using the conventional and improved methods at both local and regional scales. Relative to that with the conventional approach, the improved method increased the recovery of gold grains from samples (regional and down-ice mineralization) by almost one order of magnitude. (regional and down-ice mineralization), dominantly in regard of the small size fractions. Increasing the counts in low-abundance regional samples allows for a better discrimination between background signals and significant dispersions. The described method offers an alternative for improving the characterization of gold dispersal in glaciated terrain and related gold deposit footprints. Full article

(This article belongs to the Special Issue The Application of Automated SEM-Based Identification of Detrital, Diagenetic and Indicator Mineral Phases)

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12 pages, 3076 KiB

Open AccessArticle

Application of SEM Imaging and MLA Mapping Method as a Tool for Wettability Restoration in Reservoir Core Samples for SCAL Experiments

by Edison Sripal, David Grant and Lesley James

Minerals 2021, 11(3), 285; https://0-doi-org.brum.beds.ac.uk/10.3390/min11030285 - 10 Mar 2021

Cited by 2 | Viewed by 1782

Abstract

In reservoir engineering, special core analysis experiments (SCAL) are performed in the lab to evaluate the production capabilities of an oil reservoir. A critical component of SCAL experiments is core wettability restoration to its original wettability, i.e., oil wet condition. Typically, aging is performed by saturating the core with oil and aging at reservoir temperature where time is the variable in question dictating whether the resulting restored core is strongly or weakly oil-wet. In the lab, core wettability is often experimentally validated using contact angle measurements or USBM (United States Bureau of Mines) wettability tests, which are often time consuming, expensive and prone to error. In this study we developed a novel method by using Scanning Electron Microscope (SEM) and mineral liberation analysis (MLA) imaging (at low vacuum conditions) to determine the wettability of rocks saturated with reservoir fluids such as oil and brine. For this work a systematic approach was applied with comparing the SEM-MLA method against conventional methods to quantify the degree of uncertainty linked to a) wettability estimation and b) the aging time. We have used a comprehensive suite of core samples such as Berea, Silurian Dolomite and Chalk to represent the bulk of oil reservoirs in the world. Full article

(This article belongs to the Special Issue The Application of Automated SEM-Based Identification of Detrital, Diagenetic and Indicator Mineral Phases)

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32 pages, 14820 KiB

Open AccessArticle

A Provenance Study of Upper Jurassic Hydrocarbon Source Rocks of the Flemish Pass Basin and Central Ridge, Offshore Newfoundland, Canada

by Matthew Scott, Paul J. Sylvester and Derek H. C. Wilton

Minerals 2021, 11(3), 265; https://0-doi-org.brum.beds.ac.uk/10.3390/min11030265 - 04 Mar 2021

Cited by 4 | Viewed by 2359

Abstract

A number of hydrocarbon discoveries have been made recently in the Flemish Pass Basin and Central Ridge, offshore Newfoundland, Canada, but there is only limited geological information available. The primary goal of this study was to determine the sedimentary provenance and paleodrainage patterns of mudstones and sandstones from the Upper Jurassic Rankin Formation, including the Upper and Lower Kimmeridgian Source Rock (organic-rich shale) members and Upper and Lower Tempest Sandstone Member reservoirs, in this area. A combination of heavy mineral analysis, whole-rock geochemistry and detrital zircon U-Pb geochronology was determined from cores and cuttings from four offshore wells in an attempt to decipher provenance. Detrital heavy minerals in 20 cuttings samples from the studied geologic units are dominated by either rutile + zircon + apatite ± chromite or rutile + apatite + tourmaline, with minor zircon, indicating diverse source lithologies. Whole rock Zr-Th-Sc trends suggest significant zircon recycling in both mudstones and sandstones. Detrital zircon U-Pb ages were determined in two mudstone and four sandstone samples from the four wells. Five major U-Pb age groups of grains were found: A Late Jurassic group that represents an unknown source of syn-sedimentary magmatism, a Permian–Carboniferous age group which is interpreted to be derived from Iberia, a Cambrian–Devonian group derived from the Central Mobile Belt of the Newfoundland–Ireland conjugate margin, and two older age groups (late Neoproterozoic and >1 Ga) linked to Avalonia. The Iberian detritus is abundant in the Central Ridge and southern Flemish Pass region and units containing sizable populations of these grains are interpreted to be derived from the east whereas units lacking this population are interpreted to be sourced from the northeast and possibly also the west. The Upper Tempest Sandstone contains Mesozoic zircons, which constrain the depositional age of this unit to be no older than Late Tithonian. Full article

(This article belongs to the Special Issue The Application of Automated SEM-Based Identification of Detrital, Diagenetic and Indicator Mineral Phases)

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28 pages, 9495 KiB

Open AccessArticle

Exploration for Platinum-Group Minerals in Till: A New Approach to the Recovery, Counting, Mineral Identification and Chemical Characterization

by Sheida Makvandi, Philippe Pagé, Jonathan Tremblay and Réjean Girard

Minerals 2021, 11(3), 264; https://0-doi-org.brum.beds.ac.uk/10.3390/min11030264 - 04 Mar 2021

Cited by 12 | Viewed by 4819

Abstract

The discovery of new mineral deposits contributes to the sustainable mineral industrial development, which is essential to satisfy global resource demands. The exploration for new mineral resources is challenging in Canada since its vast lands are mostly covered by a thick layer of Quaternary sediments that obscure bedrock geology. In the course of the recent decades, indicator minerals recovered from till heavy mineral concentrates have been effectively used to prospect for a broad range of mineral deposits including diamond, gold, and base metals. However, these methods traditionally focus on (visual) investigation of the 0.25–2.0 mm grain-size fraction of unconsolidated sediments, whilst our observations emphasize on higher abundance, or sometimes unique occurrence of precious metal (Au, Ag, and platinum-group elements) minerals in the finer-grained fractions (<0.25 mm). This study aims to present the advantages of applying a mineral detection routine initially developed for gold grains counting and characterization, to platinum-group minerals in <50 µm till heavy mineral concentrates. This technique, which uses an automated scanning electron microscopy (SEM) equipped with an energy dispersive spectrometer, can provide quantitative mineralogical and semi-quantitative chemical data of heavy minerals of interest, simultaneously. This work presents the mineralogical and chemical characteristics, the grain size distribution, and the surface textures of 2664 discrete platinum-group mineral grains recovered from the processing of 5194 glacial sediment samples collected from different zones in the Canadian Shield (mostly Quebec and Ontario provinces). Fifty-eight different platinum-group mineral species have been identified to date, among which sperrylite (PtAs₂) is by far the most abundant (n = 1488; 55.86%). Textural and mineral-chemical data suggest that detrital platinum-group minerals in the studied samples have been derived, at least in part, from Au-rich ore systems. Full article

(This article belongs to the Special Issue The Application of Automated SEM-Based Identification of Detrital, Diagenetic and Indicator Mineral Phases)

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