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A special issue of Minerals (ISSN 2075-163X).

Deadline for manuscript submissions: closed (30 November 2017) | Viewed by 75657

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Dr. José António de Almeida

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Earth Sciences Department and GeoBioTec, FCT-NOVA University of Lisbon, 2829-516 Caparica, Portugal
Interests: geological modelling; geostatistics; data analysis; mineral resource assessment; circular economy
Special Issues, Collections and Topics in MDPI journals

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Dear Colleagues,

Geological modelling is a broad and multidisciplinary field that aims to build realistic computed representations (geological models) of geological features and structures, representing both morphology and properties. The information used to build such models is extremely heterogeneous, deriving from diverse sources including boreholes, geological field mapping, geophysical surveying, and physical and chemical measurements. Geological models are of paramount importance for activities at the earth's surface, such as in exploration and extraction of geological resources like raw materials, groundwater, oil and gas, geotechnical engineering (e.g. for excavation and foundations), remediation of soils and groundwater on contaminated sites, and risk analysis (e.g. slope instability and subsidence).

There are numerous tools available to build geological models, and for each project a workflow should be planned showing the tools and procedures to be employed. Although some modelling algorithms have reached a mature stage, there are still many areas where improvements are required, such as the combination of input data of different spatial resolutions, construction of high-resolution models for complex geological formations and high-density object-based models such as fractures and channels, and constraining properties to morphology. These issues continue to invigorate the research agenda.

Papers dealing with geological modelling, including original applications and directions in research, are welcome.

Prof. Dr. José António de Almeida
Guest Editor

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Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Minerals is an international peer-reviewed open access monthly journal published by MDPI.

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Keywords

3D/4D geological models
Applications of geological modelling
Genetic approaches
Geostatistics
High-resolution geological models
Integration of multiple data sources
Assessment of uncertainty
Object-based models
Realism

Related Special Issue

Geological Modelling, Volume II in Minerals (6 articles)

Published Papers (13 papers)

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Research

15 pages, 12057 KiB

Open AccessArticle

Estimating RMR Values for Underground Excavations in a Rock Mass

by Vítor Santos, Paula F. Da Silva and M. Graça Brito

Minerals 2018, 8(3), 78; https://doi.org/10.3390/min8030078 - 25 Feb 2018

Cited by 16 | Viewed by 5532

Abstract

During underground excavations for civil or mining engineering purposes, the variations in rock mass quality are important, especially for the design of the most suitable support to be applied to ensure stability. The aim of this investigation is to model the expected behavior of the ground, and thus to predict the scenarios indicating potential variations in the quality of the rock mass during underground excavation. When considering the rock mass rating (RMR) values observed at the excavation face in six study cases, which together total more than 27 km in length of underground excavation by drilling and blasting (D&B), and based on the observed RMR values at the face, the most probable value (1–100) is estimate for the RMR index at the five subsequent front advances. It is concluded that, up to about 20 m ahead of the current face, the quality of the rock mass for the next advances is close to the quality observed at the present face, and that, with increasing distance, there is a greater deviation of RMR values with respect to the quality observed at the current face. Full article

(This article belongs to the Special Issue Geological Modelling)

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28 pages, 41289 KiB

Open AccessArticle

Role of Volcano-Sedimentary Basins in the Formation of Greenstone-Granitoid Belts in the West African Craton: A Numerical Model

by Xiaojun Feng, Enyuan Wang, Jérôme Ganne, Prince Amponsah and Roland Martin

Minerals 2018, 8(2), 73; https://doi.org/10.3390/min8020073 - 17 Feb 2018

Cited by 11 | Viewed by 6031

Abstract

Greenstone belts in the West African Craton (WAC) are separated by several generations of granitoids intruded at ca. 2.18–1.98 Ga. Simultaneous folding and exhumation play an important role in the formation of greenstone-granitoid belts. However, the overall tectonic regime and origin of granitoids remain controversial. In this study, we present the estimates of the mantle potential temperature (Tp) for the WAC, which yields values of about 1500–1600 °C, pressure estimates of initial and final melting yield values of about 3.7–5.2 GPa and 1–1.3 GPa, respectively. Subsequently, 2D thermo-mechanical models have been constructed to explore the width of volcano-sedimentary basin on spatial-temporal evolution of diapirs that emplaced in the lower-middle crust during compression. The models show that the width of the volcano-sediment layer plays an important role in the formation mechanisms of greenstone-granitoid belts. The lower crust beneath sedimentary sequences is deformed into a buckle fold during the first compressional stage, through which relief uplifts slowly. Subsequently, the buckle fold is further deformed into several individual folds. Diapirs made of lower crust rocks ascend and emplace in the middle-upper crust resulting from instability. Benefitting from the mantle temperature, the pressure estimates and the numerical modelling results, a new geodynamic model was constructed. This model indicates that a series of sheet-like granitoids possibly derived from either subducted mélanges, lower crust and/or mantle melting that are accumulated at depths of the subcontinental mantle would channel along diapirs before feeding the upper crust. When the granitoids arrive at the solidified lids of the diapirs, they would favour migrating horizontally and intrude into the upper crust through weakening zones between the diapirs. Our geodynamic model also suggests an asymmetry of structures between the upper and middle-lower crust, with the dome-like granitoids overlying high-grade sedimentary synforms and high-grade diapirs underlying low-grade greenstone belts. Full article

(This article belongs to the Special Issue Geological Modelling)

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19 pages, 3663 KiB

Open AccessArticle

Modelling Geotechnical Heterogeneities Using Geostatistical Simulation and Finite Differences Analysis

by Marisa Pinheiro, Xavier Emery, Tiago Miranda, Luís Lamas and Margarida Espada

Minerals 2018, 8(2), 52; https://doi.org/10.3390/min8020052 - 07 Feb 2018

Cited by 17 | Viewed by 4325

Abstract

Modelling a rock mass in an accurate and realistic way allows researchers to reduce the uncertainty associated with its characterisation and reproduce the intrinsic spatial variability and heterogeneities present in the rock mass. However, there is often a lack of a structured methodology to characterise heterogeneous rock masses using geotechnical information available from the prospection phase. This paper presents a characterization methodology based on the geostatistical simulation of geotechnical variables and the application of a scenario reduction technique aimed at selecting a reduced number of realisations able to statistically represent a large set of realisations obtained by the geostatistical approach. This type of information is useful for a further rock mass behaviour analysis. The methodology is applied to a gold deposit with the goal of understanding its main differences to traditional approaches based on a deterministic modelling of the rock mass. The obtained results show the suitability of the methodology to characterise heterogeneous rock masses, since there were considerable differences between the results of the proposed methodology, mainly concerning the theoretical tunnel displacements, and the ones obtained with a traditional approach. Full article

(This article belongs to the Special Issue Geological Modelling)

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17 pages, 1535 KiB

Open AccessArticle

Relating Topological and Electrical Properties of Fractured Porous Media: Insights into the Characterization of Rock Fracturing

by Delphine Roubinet, James Irving and Philippe A. Pezard

Minerals 2018, 8(1), 14; https://doi.org/10.3390/min8010014 - 10 Jan 2018

Cited by 16 | Viewed by 4006

Abstract

Numerous laboratory and field experiments suggest that electrical properties of fractured rocks may provide critical information regarding the topological properties of the underlying fracture networks. However, a lack of numerical studies dedicated to realistic fractured media prevents us from assessing, in a systematic manner, the relationships between electrical and topological properties in complex domains for which a representative elementary volume may not exist. To address this issue, we conduct an extended numerical analysis over a large range of realistic fractured porous media with an explicit description of the fractures that takes into account the fracture–matrix interactions. Our work shows that the fracture density determines the suitability of Archie’s law for describing effective electrical properties with complex behavior associated with small fracture densities. In particular, for fracture networks at the percolation threshold surrounded by a low-porosity matrix, the effective petrophysical relationships are impacted by the assumed fracture-length distribution and the exchange of electric current between the fractures and surrounding matrix. These results help in understanding experimental observations that were difficult to explain so far, suggesting that the effective electrical properties of fractured rock may be used to obtain insights into the properties of their geological structures. Full article

(This article belongs to the Special Issue Geological Modelling)

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10535 KiB

Open AccessArticle

Geological Modelling and Validation of Geological Interpretations via Simulation and Classification of Quantitative Covariates

by Amir Adeli, Xavier Emery and Peter Dowd

Minerals 2018, 8(1), 7; https://doi.org/10.3390/min8010007 - 29 Dec 2017

Cited by 26 | Viewed by 6022

Abstract

This paper proposes a geostatistical approach for geological modelling and for validating an interpreted geological model, by identifying the areas of an ore deposit with a high probability of being misinterpreted, based on quantitative coregionalised covariates correlated with the geological categories. This proposal is presented through a case study of an iron ore deposit at a stage where the only available data are from exploration drill holes. This study consists of jointly simulating the quantitative covariates with no previous geological domaining. A change of variables is used to account for stoichiometric closure, followed by projection pursuit multivariate transformation, multivariate Gaussian simulation, and conditioning to the drill hole data. Subsequently, a decision tree classification algorithm is used to convert the simulated values into a geological category for each target block and realisation. The determination of the prior (ignoring drill hole data) and posterior (conditioned to drill hole data) probabilities of categories provides a means of identifying the blocks for which the interpreted category disagrees with the simulated quantitative covariates. Full article

(This article belongs to the Special Issue Geological Modelling)

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20667 KiB

Open AccessArticle

Integrated 3D Geological Modeling to Gain Insight in the Effects of Hydrothermal Alteration on Post-Ore Deformation Style and Strain Localization in the Flin Flon Volcanogenic Massive Sulfide Ore System

by Ernst Schetselaar, Doreen Ames and Eric Grunsky

Minerals 2018, 8(1), 3; https://doi.org/10.3390/min8010003 - 25 Dec 2017

Cited by 6 | Viewed by 5877

Abstract

3D geological modeling of lithogeochemical and geological data provides insight into the role of the sulfide ore horizon and associated footwall hydrothermal alteration in localizing shear strain in the Flin Flon volcanogenic massive sulfide deposits, Canada, as deformation evolved from brittle-ductile to ductile regimes during collisional stages of the 1.9–1.8 Ga Trans-Hudson orogeny. 3D spatial characterization of hydrothermal alteration based on the Ishikawa index (AI) and normative corundum percentages outline sericite + chlorite-rich high strain zones, consisting of Al-enriched and Na-depleted felsic and mafic volcanic rocks in the footwall of the sulfide ore horizon. The hydrothermal vent complex, from which these sheared alteration zones originated, was stacked together with the ore horizon by W-vergent thrust faults during an early collisional deformation regime, imbricating molasse-type clastic sediments with the ore-hosting volcanic and volcaniclastic rocks of the Flin Flon arc assemblage. Chlorite-rich planar zones marked by high values of the Carbonate–chlorite–pyrite index (CCPI) are laterally more extensive and outline a later system of ductile shear zones, in which phyllosilicates, quartz and chalcopyrite in stringer zones localized shear strain and enhanced transposition of the hydrothermal vent stockwork. The contrasting deformation styles of these two thrusting events and their localization within the ore horizon and hydrothermal vent stockwork have important implications for vectoring towards undiscovered ore in this mature mining camp that are possibly also relevant to other strongly deformed VMS ore systems. Full article

(This article belongs to the Special Issue Geological Modelling)

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13432 KiB

Open AccessArticle

Joint Application of Fractal Analysis and Weights-of-Evidence Method for Revealing the Geological Controls on Regional-Scale Tungsten Mineralization in Southern Jiangxi Province, China

by Tao Sun, Kaixing Wu, Lingkang Chen, Weiming Liu, Yun Wang and Cisheng Zhang

Minerals 2017, 7(12), 243; https://doi.org/10.3390/min7120243 - 11 Dec 2017

Cited by 13 | Viewed by 4263

Abstract

The Southern Jiangxi Province (SJP) hosts one of the best known districts of tungsten deposits in the world. Delineating spatial complexities of geological features and their controls on regional-scale tungsten mineralization by using an integrated fractal and weights-of-evidence (WofE) method can provide insights into the understanding of ore genesis and facilitate further prospecting in this area. The box-counting fractal analysis shows that most of the tungsten occurrences are distributed in regions with high fractal dimensions of faults and fault intersections, suggesting ore-forming favorability of areas with highly complex structural patterns. The WofE-derived indices are employed to quantitatively measure the controls of analyzed features on mineralization, which illustrate that tungsten anomalies, faults, Yanshanian granites, and manganese anomalies have high contrast values, implying a spatially strong correlation of these features with tungsten occurrences. In particular, high manganese anomalies in host rock may provide a novel indication for mineral prospecting in this area. A predictive map is extracted based on the combination of fractal and WofE results, providing intuitive guides for future prospectivity in this area. Regions identified by high posterior probability in conjunction with high fractal dimensions of both faults and fault intersections are evaluated as the most favorable targets. Full article

(This article belongs to the Special Issue Geological Modelling)

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5240 KiB

Open AccessArticle

Indicator Variograms as an Aid for Geological Interpretation and Modeling of Ore Deposits

by Mohammad Maleki, Xavier Emery and Nadia Mery

Minerals 2017, 7(12), 241; https://doi.org/10.3390/min7120241 - 05 Dec 2017

Cited by 14 | Viewed by 5376

Abstract

Geostatistics offers a set of methods for modeling, predicting, or simulating geological domains in space. In addition of being an input of some of these methods, indicator direct and cross-variograms convey valuable information on the geometry of the domain layouts and on their contact relationships, in particular, on the surface area of a domain boundary, on the surface area of the contact between two domains, on the propensity for a domain to be in contact with, or separated from, another domain, and on the minimum and maximum distances between points from two domains. Accordingly, the indicator variograms inferred from sparse sampling data can be used to determine whether or not an interpreted model of the subsurface is consistent with the sampling information. The previous concepts are illustrated through a case study corresponding to a porphyry copper deposit. Full article

(This article belongs to the Special Issue Geological Modelling)

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8087 KiB

Open AccessArticle

Geostatistical Methodology to Characterize Volcanogenic Massive and Stockwork Ore Deposits

by David Silva and José Almeida

Minerals 2017, 7(12), 238; https://doi.org/10.3390/min7120238 - 30 Nov 2017

Cited by 6 | Viewed by 5460

Abstract

The Zambujal ore deposit, Neves-Corvo mine, is a zoned volcanogenic sulfide deposit of copper and zinc, with massive ores at the top and stockwork ores at the bottom. Metal grades are strongly zoned by ore types. The main methodology hereby proposed combines geostatistical techniques so that an improved stochastic geological model of the Zambujal deposit encompassing morphology and grades is presented. The model of the morphology was made in two main steps. First, a 3D solid of the boundaries was created and then a 3D grid model of the local sulfide proportion was simulated. This latter variable was modeled by using rock specific gravity as a proxy. After that, a conditional grid model of relative copper grades, i.e., recalculated metal grades assuming only the sulfide content, is also simulated in accordance with the morphology. At the end, the new tool, metal tonnage cut-off surface, is proposed, which combines copper grades within massive ores and stockwork ores. To validate the results found, the global tonnages of copper obtained by Ordinary Kriging and the proposed methodology are compared. Full article

(This article belongs to the Special Issue Geological Modelling)

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18009 KiB

Open AccessArticle

A 3D Geological Model of a Vein Deposit Built by Aggregating Morphological and Mineral Grade Data

by André Sanches, José Almeida, Paulo Sá Caetano and Romeu Vieira

Minerals 2017, 7(12), 234; https://doi.org/10.3390/min7120234 - 26 Nov 2017

Cited by 3 | Viewed by 7484

Abstract

The objective of this study was to establish a methodology for building a 3D geological model of a mineral vein deposit, encompassing morphology and wolframite content. The available data set includes stope data (vein thickness and wolframite quantity) and borehole data (vein thickness and wolframite modal classes). The data captured from boreholes and stopes differ in terms of their spatial distribution and clustering as well as the size and shape of each sample. Therefore, a specific methodology was designed to combine these two sources of information. The morphology model mapped vein thickness as a vein proportion variable, by applying a two-phase Direct Sequential Simulation (DSS) locally conditioned to borehole data. Regarding the evaluation of wolframite content, the variables are unable to be related directly to each other and are non-co-located. Therefore, a proximity study was made using DSS to build local conditional cumulative histograms (by borehole class and by mine level). The final model of wolframite quantity was generated using Probability Field Simulation. The proposed approach considers the initially identified problems, allowing the mineral potential of the deposit to be quantified by integrating the results of the two independent methodologies. Full article

(This article belongs to the Special Issue Geological Modelling)

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5747 KiB

Open AccessArticle

BBUNS: Bluetooth Beacon-Based Underground Navigation System to Support Mine Haulage Operations

by Jieun Baek, Yosoon Choi, Chaeyoung Lee, Jangwon Suh and Sangho Lee

Minerals 2017, 7(11), 228; https://doi.org/10.3390/min7110228 - 21 Nov 2017

Cited by 32 | Viewed by 7976

Abstract

A Bluetooth beacon-based underground navigation system (BBUNS) was developed to identify the optimal haul road in an underground mine, track the locations of dump trucks, and display this information on mobile devices. A three-dimensional (3-D) geographic information system (GIS) database of the haul roads in an underground mine was constructed, and the travel time for each section was calculated. A GIS database was also constructed for 50 Bluetooth beacons that were installed along the haul roads. An Android-based BBUNS application was developed to visualize the current location of each dump truck and the optimal haul road to the destination on mobile devices, using the Bluetooth beacon system that was installed in the underground mine. Whenever the BBUNS recognized all of the Bluetooth beacons installed in the underground mine, it could provide the dump truck drivers with information on the current location and the two-dimensional (2-D) and 3-D haul road properties. The operating time of each dump truck and the time spent on each unit task could be analyzed using recorded data on the times when Bluetooth beacon signals were recognized by the BBUNS. The underground mine navigation system that was developed in this study can contribute to the improvement of haul operation efficiency and productivity. Full article

(This article belongs to the Special Issue Geological Modelling)

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8185 KiB

Open AccessArticle

UMineAR: Mobile-Tablet-Based Abandoned Mine Hazard Site Investigation Support System Using Augmented Reality

by Jangwon Suh, Sangho Lee and Yosoon Choi

Minerals 2017, 7(10), 198; https://doi.org/10.3390/min7100198 - 18 Oct 2017

Cited by 8 | Viewed by 5630

Abstract

Conventional mine site investigation has difficulties in fostering location awareness and understanding the subsurface environment; moreover, it produces a large amount of hardcopy data. To overcome these limitations, the UMineAR mobile tablet application was developed. It enables users to rapidly identify underground mine objects (drifts, entrances, boreholes, hazards) and intuitively visualize them in 3D using a mobile augmented reality (AR) technique. To design UMineAR, South Korean georeferenced standard-mine geographic information system (GIS) databases were employed. A web database system was designed to access via a tablet groundwater-level data measured every hour by sensors installed in boreholes. UMineAR consists of search, AR, map, and database modules. The search module provides data retrieval and visualization options/functions. The AR module provides 3D interactive visualization of mine GIS data and camera imagery on the tablet screen. The map module shows the locations of corresponding borehole data on a 2D map. The database module provides mine GIS database management functions. A case study showed that the proposed application is suitable for onsite visualization of high-volume mine GIS data based on geolocations; no specialized equipment or skills are required to understand the underground mine environment. UMineAR can be used to support abandoned-mine hazard site investigations. Full article

(This article belongs to the Special Issue Geological Modelling)

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2216 KiB

Open AccessArticle

Near-Infrared Spectroscopy of Limestone Ore for CaO Estimation under Dry and Wet Conditions

by Sungchan Oh, Chang-Uk Hyun and Hyeong-Dong Park

Minerals 2017, 7(10), 193; https://doi.org/10.3390/min7100193 - 13 Oct 2017

Cited by 5 | Viewed by 5761

Abstract

Quantitative analysis of CaO in limestone mining is mandatory, not only for ore exploration, but also for grade control. A partial least squares regression (PLSR) CaO estimation technique was developed for limestone mining. The proposed near-infrared spectroscopy (NIR)-based method uses reflectance spectra of the rock sample surface in the visible to short-wave infrared wavelength regions (350–2500 nm (4000–28,571 cm⁻¹)) without the need to crush and pulverize the rock samples. The root mean square (RMS) error of CaO estimation using limestone ore fragment was 1.2%. The CaO content estimated by the PLSR method was used to predict average CaO content of composite samples with a sample size of 15, which resulted in an RMS error of 0.3%. The prediction accuracy with moisture on sample surfaces was also examined to find out if the NIR-based method showed a similar RMS error. Results suggest that the NIR technique can be used as a rapid assaying method in limestone workings with or without the presence of groundwater. Full article

(This article belongs to the Special Issue Geological Modelling)

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