Igneous Rock Associations 14. The Volcanic Setting of VMS and SMS Deposits: A Review

Volcanogenic massive sulphide (VMS) deposits and seafloor massive sulphide (SMS) deposits have a spatial and genetic connection with contemporaneous volcanism. The control exerted by the volcanic succession (e.g. rock type, architecture and facies) on the nature and style of the ore and alteration (e.g. subsea-floor replacement vs. exhalative, or discordant vs. conformable) is significant, making it imperative to understand the local volcanology in developing better genetic and exploration models. Three VMS deposit groupings collectively represent a high proportion of cases: (1) deposits associated with complexes of submarine felsic domes, cryptodomes, lobe-hyaloclastite flows and/or blocky lavas, and their reworked equivalents; (2) deposits associated with thick piles of pumiceous felsic pyroclastic rocks, suggesting a caldera context; and (3) deposits associated with mafic volcanic footwalls and/or with sedimentary hosts, including significant deposits such as Windy Craggy (~300 Mt) in British Columbia. With regard to number (2) above, demonstrating the presence of a caldera in ancient successions can be difficult because silicic calderas tend to be large and exceed the limits of deposit-scale investigations. Furthermore, there is no consensus regarding what a large submarine caldera should look like, i.e., no accepted facies model exists showing the distribution of rock types. But without thick piles of pumiceous felsic pyroclastic deposits, arguing for a large submarine caldera is a challenge.SOMMAIRELes gisements de sulfures massifs volcanogènes (SMV) et leurs équivalents actuels au fonds des mers ont une connexion spatiale et génétique avec le volcanisme. La succession volcanique – composition, architecture, faciès – exerce un contrôle important sur la nature et le style de minéralisation et d’altération hydrothermale (p. ex. minéralisation mise en place par remplacement sous le fond marin vs. exhalative; altération discordante ou plus concordante). Il est donc impératif de connaître la volcanologie des roches encaissantes pour développer de meilleurs modèles génétiques et d’exploration. Trois groupes de gisements couvrant collectivement une grande proportion des cas sont discutés ici. Premièrement, plusieurs gisements sont associés à des complexes de dômes felsiques sous-marins, des cryptodômes, des coulées de type lobes-hyaloclastite et/ou des laves en blocs, ou leur équivalents resédimentés. Deuxièmement, certains gisements sont associés à d’épaisses séquences de roches pyroclastiques felsiques ponceuses, suggérant un contexte de caldeira. Troisièmement, plusieurs gisements sont associés avec des roches volcaniques mafiques et/ou avec des roches sédimentaires, par exemple l’important dépôt de Windy Craggy (~300 Mt) en Colombie-Britannique. Concernant les contextes de type 2, la démonstration d’une caldeira peut être difficile dans les successions anciennes, car les caldeiras felsiques sont de grandes dimensions, excédant les limites des études à l’échelle du gîte. De plus, il n’existe pas de consensus sur un modèle de faciès pour une grande caldeira sous-marine. Mais sans la présence d’épais empilements de roches pyroclastiques felsiques ponceuses, il est difficile d’argumenter en faveur d’une caldeira sous-marine

Rockburst in underground excavations: A review of mechanism, classification, and prediction methods

Technical challenges have always been part of underground mining activities, however, some of these challenges grow in complexity as mining occurs in deeper and deeper settings. One such challenge is rock mass stability and the risk of rockburst events. To overcome these challenges, and to limit the risks and impacts of events such as rockbursts, advanced solutions must be developed and best practices implemented. Rockbursts are common in underground mines and substantially threaten the safety of personnel and equipment, and can cause major disruptions in mine development and operations. Rockbursts consist of violent wall rock failures associated with high energy rock projections in response to the instantaneous stress release in rock mass under high strain conditions. Therefore, it is necessary to develop a good understanding of the conditions and mechanisms leading to a rockburst, and to improve risk assessment methods. The capacity to properly estimate the risks of rockburst occurrence is essential in underground operations. However, a limited number of studies have examined and compared yet different empirical methods of rockburst. The current understanding of this important hazard in the mining industry is summarized in this paper to provide the necessary perspective or tools to best assess the risks of rockburst occurrence in deep mines. The various classifications of rockbursts and their mechanisms are discussed. The paper also reviews the current empirical methods of rockburst prediction, which are mostly dependent on geomechanical parameters of the rock such as uniaxial compressive strength of the rock, as well as its tensile strength and elasticity modulus. At the end of this paper, some current achievements and limitations of empirical methods are discussed

A new geological map of the Lau Basin (southwestern Pacific Ocean) reveals crustal growth processes in arc-backarc systems

A 1:1,000,000-scale lithostratigraphic assemblage map of the Lau Basin (southwestern Pacific Ocean) has been created using remote predictive mapping (RPM) techniques developed by geological surveys on land. Formation-level geological units were identified in training sets at scales of 1:100,000–1:200,000 in different parts of the basin and then extrapolated to the areas where geological data are sparse. The final compilation is presented together with a quantitative analysis of assemblage-level crustal growth based on area-age relationships of the assigned units. The data sets used to develop mapping criteria and an internally consistent legend for the compilation included high-resolution ship-based multibeam, satellite- and ship-based gravity, magnetics, seafloor imaging, and sampling data. The correlation of units was informed by published geochronological information and kinematic models of basin opening. The map covers >1,000,000 km2 of the Lau-Tonga arc-backarc system, subdivided into nine assemblage types: forearc crust (9% by area), crust of the active volcanic arc (7%), backarc rifts and spreading centers (20%), transitional arc-backarc crust (13%), relict arc crust (38%), relict backarc crust (8%), and undivided arc-backarc assemblages (<5%), plus oceanic assemblages, intraplate volcanoes, and carbonate platforms. Major differences in the proportions of assemblage types compared to other intraoceanic subduction systems (e.g., Mariana backarc, North Fiji Basin) underscore the complex geological makeup of the Lau Basin. Backarc crust formed and is forming simultaneously at 12 different locations in the basin in response to widely distributed extension, and this is considered to be a dominant pattern of crustal accretion in large arc-backarc systems. Accelerated basin opening and a microplate breakout north of the Peggy Ridge has been accommodated by seven different spreading centers. The result is an intricate mosaic of small intact assemblages in the north of the basin, compared to fewer and larger assemblages in the south. Although the oldest rocks are Eocene (~40 m.y. old basement of the Lau and Tonga Ridges), half of the backarc crust in the map area formed within the last 3 m.y. and therefore represents some of the fastest growing crust on Earth, associated with prolific magmatic and hydro-thermal activity. These observations provide important clues to the geological evolution and makeup of ancient backarc basins and to processes of crustal growth that ultimately lead to the emergence of continents

Les minéralisations aurifères au sein de la tonalite de La Grande-Sud, Baie-James, Québec

Le but de cette étude menée par le CERM en partenariat avec le MRNQ et la compagnie Mines d'Or Virginia (détenteur de la propriété) a été de mettre en relation la magmatisme, l'hydrothermalisme, la déformation et les minéralisations nouvellement découvertes au sein de la Tonalité de La-Grande-Sud (LGS). Cette tonalité est une petite intrusion elliptique faisant 600 m de largeur sur 1500 m de longueur se retrouvant au sein d'un assemblage volcano-sédimentaire archéen métamorphisé au faciès des schistes verts supérieurs. Cette ceinture de roches vertes fait partie de la sous-province de La Grande, laquelle se trouve à l'est de la Baie-James dans le secteur sud du réservoir Robert-Bourassa. Cinq indices aurifères principaux sont localisés dans la Tonalité LGS : Zone 32, Mico-Milan, Pari, Brèche et Zone Veine. La Zone 32 a fait l'objet de calculs de ressources (avril 1999) et les résultats obtenus sont de 6,5 Mt à 1,52 g/t Au et 0,2% Cu à une teneur de coupure de 0,5 g/t Au. La signature géochimique de la tonalité a permis de déduire qu'il s'agit d'une intrusion trondhjémitique d'affinité calco-alcaline peralumineuse formée probablement dans un environnement d'îles-en-arc. De plus, une datation selon la méthode U-Pb a rapporté un âge de 2734 + 2 Ma comparable à celui des roches volcaniques encaissantes, appuyant une origine syn-volcanique pour la Tonalité LGS. Deux phases principales de déformation sont observées dans le secteur et à l'intérieur de la Tonalité LGS. La première phase (Dl) est à l'origine de la schistosité N-S ayant transposé les unités volcano-sédimentaires et étiré les grains de quartz dans la tonalité. La seconde phase (D2) se signale par une crénulation E-0 à l'origine du plissement du litage et de la première fabrique ainsi que par des zones de déformation intense E-0 dans lesquelles des bandes de cisaillement bien développées indiquent une composante de mouvement dextre tardive. Plusieurs zones d'altération auxquelles sont associés différents types de minéralisations sont reconnues à l'intérieur de la Tonalité LGS. Le coeur de l'intrusion correspond à une zone d'altération potassique caractérisée par l'assemblage (BO-AB-CC-EP) avec de la PY disséminée en traces. Cette zone passe graduellement vers les bordures à une zone d'altération propylitique montrant l'assemblage (CL-AB-SR-CC+EP) avec PY+CP disséminées en traces. Des zones métriques à décamétriques d'altération séricitique sont également observées, la Zone 32 se trouvant dans une de ces zones, lesquelles sont caractérisées par la présence de séricite abondante, de quartz, de chlorite, de sulfures disséminés (PY-CP+SP) et de filonets à sulfures ou à QZ-TL et sulfures. La minéralisation de type disséminé, où les sulfures peuvent former jusqu'à 5 % de la roche, est la forme de minéralisation aurifère la plus importante dans la Tonalité LGS. Des brèches à biotite et carbonates minéralisées sont également reconnues. Elles se retrouvent dans la tonalité près des bordures et se sont mises en place avant ou pendant l'épisode de déformation Dl. Une altération carbonatée (AK) est observée à certains endroits dans la tonalité et se superpose sur les autres assemblages pour former des veinules à carbonates irrégulières contenant localement du quartz, de la séricite et des sulfures (PY-CP-AS) disséminés ou en veinules. Des veines à quartz et tourmaline tardives (syn-tectonisme) subhorizontales et subverticales sont également rencontrées dans la tonalité. L'or est communément associé aux sulfures, soit en inclusions, soit en grains libres dans les zones à sulfures ou dans les veines tardives. La séquence évolutive proposée pour expliquer les observations faites dans le secteur à l'étude implique la mise en place d'un système minéralisateur hydrothermal aurifère de type porphyre à l'origine de la zonation des altérations potassique, propylitique et séricitique et de l'apparition des minéralisations disséminées sur lesquelles ont pu se superposer un ou plusieurs épisodes hydrothermaux aurifères ou remobilisateurs associés aux événements de déformation (Dl et D2) à l'origine des remobilisations, des veinules à sulfures et des veines à quartz et tourmaline et de l'altération carbonatée

A Review of Relationship between Texture Characteristic and Mechanical Properties of Rock

The textural characteristics of rocks influence their petrophysical and mechanical properties. Such parameters largely control rock mass stability. The ability to evaluate both immediate and long-term rock behaviors based on the interaction between various parameters of rock texture, petrophysical and mechanical properties is therefore crucial to many geoengineering facilities. However, due to the common lack of high-quality core samples for geomechanics and rock texture laboratory tests, single and multivariable regression analyses are conducted between mechanical properties and textural characteristics based on experimental test data. This study presents a review of how rock texture characteristics influence the geomechanical properties of a rock, and summarizes the regression equations between two aspects. More specifically, a review of the available literature on the effects of mineralogy, grain size, grain shape, packing density, foliation index, porosity, degree of weathering, and other rock physical characteristics on geomechanics is presented. Similarly, a review of the literature discussing the failure criteria of anisotropic rocks, both continuous and discontinuous, is also presented. These reviews are accompanied by a comparison of the fundamentals of these methods, describing their equations and discussing their advantages and disadvantages. This exercise has the objective of providing better guidelines on how to use these criteria, allowing for safer underground excavations via an improved understanding of how rock texture parameters affects the mechanical behavior of rocks

The gold content of volcanogenic massive sulfide deposits

Volcanogenic massive sulfide deposits contain variable amounts of gold, both in terms of average grade and total gold content, with some VMS deposits hosting world-class gold mines with more than 100t Au. Previous studies have identified gold-rich VMS as having an average gold grade, expressed in g/t, exceeding the total abundance of base metals, expressed in wt.%. However, statistically meaningful criteria for the identification of truly anomalous deposits have not been established. This paper presents a more extensive analysis of gold grades and tonnages of 513 VMS deposits worldwide, revealing a number of important features in the distribution of the data. A large proportion of deposits are characterized by a relatively low gold grade (<2g/t), with a gradual decrease in frequency towards maximum gold grades, defining a log-normal distribution. In the analysis presented in this paper, the geometric mean and geometric standard deviation appear to be the simplest metric for identifying subclasses of VMS deposits based on gold grade, especially when comparing deposits within individual belts and districts. The geometric mean gold grade of 513 VMS deposits worldwide is 0.76g/t; the geometric standard deviation is +2.70g/t Au. In this analysis, deposits with more than 3.46g/t Au (geometric mean plus one geometric standard deviation) are considered auriferous. The geometric mean gold content is 4.7t Au, with a geometric standard deviation of +26.3t Au. Deposits containing 31t Au or more (geometric mean plus one geometric standard deviation) are also considered to be anomalous in terms of gold content, irrespective of the gold grade. Deposits with more than 3.46g/t Au and 31t Au are considered gold-rich VMS. A large proportion of the total gold hosted in VMS worldwide is found in a relatively small number of such deposits. The identification of these truly anomalous systems helps shed light on the geological parameters that control unusual enrichment of gold inVMS. At the district scale, the gold-rich deposits occupy a stratigraphic position and volcanic setting that commonly differs from other deposits of the district possibly due to a step change in the geodynamic and magmatic evolution of local volcanic complexes. The gold-rich VMS are commonly associated with transitional to calc-alkaline intermediate to felsic volcanic rocks, which may reflect a particularly fertile geodynamic setting and/or timing (e.g., early arc rifting or rifting front). At the deposit scale, uncommon alteration assemblages (e.g., advanced argillic, aluminous, strongly siliceous, or potassium feldspar alteration) and trace element signatures may be recognized (e.g., Au–Ag–As–Sb ± Bi–Hg–Te), suggesting a direct magmatic input in some systems

High-Temperature Ionic-Conducting Material: Advanced Structure and Improved Performance

A new composite proton-conducting material based on the association of an ionic liquid and a porous polymer support was prepared with the aim of applying it as an electrolyte in a proton exchange membrane fuel cell (PEMFC) at elevated temperature (130 °C). The porous support was made from a high glass-transition temperature polymer (<i>T</i>g) by using the vapor-induced phase separation (VIPS) method in conditions leading to highly interconnected porous films. The ionic liquid tested was obtained by the reaction of a sulfonic acid with a tertiary amine and presents enough high-temperature stability to be used at elevated temperatures. Composite samples were prepared by immersing pieces of porous film in the ionic liquids under test. The porous support was characterized by scanning electron microscopy (SEM), gas permeation, and thermogravimetric analysis (TGA) tests, and the composite samples were characterized by mechanical and proton-conduction measurements. At 130 °C, this new material exhibits proton conductivity (20 mS cm^–1) below, but very close to, that of the pure ionic liquid (31 mS cm^–1) and presents, up to at least 150 °C, a storage modulus exceeding 200 MPa. This is very promising considering the PEMFC applications