On International Environmental Law – Book Summary

On International Environmental Law – Book Summary
International Environmental Law in a Nutshell, which is written by Lakshman D. Guruswamy and Brent R. Hendricks, introduces the relevant concepts of international environmental law(IEL), contemplates the socio—scientific evidence confronting lawmakers and addresses the resulting corpus of substantive law. Expert authors cover international environmental problems such as

population, biodiversity, global climate change, ozone depletion, Antarctica, toxic and hazardous substances, land and vessel—based pollution, transboundary water pollution, desertification, and nuclear damage.

Generally, this book can be divided into three parts: Part one, which consists of Chapter one, two and three, discusses the basic concepts of the international environmental law, such as the definition of the international environmental law, the sources and forms of the international environmental law and so on. Part two, including fourteen chapters, from Chapter Four to Chapter Seventeen, emphasizes the specific international environmental problems, such as population, biodiversity, global climate change and etc. Part Three, the last part, Chapter Eighteen, draws the blueprint of the future of the international environmental law.

The first part of this book (Chapter one, two and three) illustrates the basic and important concepts of the international environmental law, which can help students, especially the ones who have not studied the IEL at all, clearly understand what the IEL is, what makes the IEL different from the other international laws, what constitutes the IEL and how the IEL become effective.

Although the definition of the IEL can be diverse, this book gives the most understandable one to the students. In the first page of this book, it is written that “International Environmental Law (IEL) bears a name that reflects the content. At its substantive core, IEL endeavors to control pollution and the depletion of natural resources within a framework of sustainable development… IEL is formally a branch of nation states for nation states, to govern problems that arise between nation states. ”

Then, the authors distinguish the IEL from traditional international law in two aspects. “First, its creation and vigorous, if uneven growth, owe much to national environmental laws and policies. Nation states frequently have entered into landmark international agreements and practices, driven largely by the momentum of law, regulation, and policies applicable to their own environmental problems, and not necessarily because of the gravity of international problems. Second, the law—making in IEL has been shaped primarily by bio—physical not geo—political forces, and this communal foundation has at times sheltered it from the disfiguring political dissension found in other areas of international law. These two factors have inevitably, albeit asymmetrically, infused the objectives of national environmental regulatory laws, and the conceptual frameworks of environmental sciences, into the corpus of IEL. ”

To wholly study IEL, it is crucial for students to grasp the substantive corpus of the IEL. And in authors’ view, there are several types of the sources of the IEL: treaties, customary law, general principles of law and judicial decisions. 1,Treaties “are written agreements governed by international law, entered into between two or more states, creating or restating legal rights and duties.” Treaties are the principle source of IEL, owing to the nature of environmental problems. “These problems range over a wide spectrum of future contingencies. Moreover, they demand continuous observation and monitoring, as well as quick legal action and implementation in response to ongoing and relatively rapid changes in scientific knowledge and conclusions… None of the four sources of IEL can fulfill all of these requirements…” And treaties, vague and nebulous, need to be interpreted so that they can be implemented. Usually, in the opinion of the authors, the International Court of Justice (ICJ) is perhaps the best known international courts, but the ICJ depends on the acquiescence of the parties for its jurisdiction. Also, the authors introduce the conflict between the treaties and other international laws. 2, Customary law “refers largely to unwritten law inferred from the conduct of states (practice) undertaken in the belief that they were bound to do so by law.” And customary law mainly comes from the forms, such as the national legislation, diplomatic notes and correspondence and statements and votes by governments in international organizations and forums of varying kinds and etc. One of the weaknesses of custom is that they are all unwritten and uncodified, so one way to remedy this shortcoming is to codify or re-state customary law, thus making it known and accessible. 3, General principles of law. It is of the great importance when some articles of a statute “need to be interpreted in accordance with its ordinary or plain meaning, in context, and in light of its object and purpose.” 4, Judicial decisions. “The statute of the ICJ restricts the role of judicial decisions to that of a ‘subsidiary means for the determination of riles of law’ however, judicial decisions still play an important role in any system of customary law by restating, codifying, and clarifying the often uncertain and usually unwritten customary law.” The authors also list the other sources of law, such as the writings of the most highly qualified publicists or scholars, resolutions, declarations, action plans and so on.

In the first part of this book, the authors introduce the landmark developments of IEL from 1972 to the present—the historical continuum, which helps us better understand the strengths and weaknesses of the subject. It includes five historical conferences that have influences on the development of the IEL; they are The 1972 Stockholm Conference on the Human Environment. The 1982 United Nation Convention on the Law of the Sea. The World Commission on Environment and Development. The 1992 United Nation Conference on Environment and Development. The 2002 World Summit on Sustainable Development.

What weights most in these three chapters is the implementation. It is said that “most international treaties require implementation within individual nation states. Implementation of treaty obligations, however, is hampered by the fact that the vertical command and control power structure governing domestic politics within nations is conspicuously absent within the international legal order. In international society, power or authority rests on a horizontal base made up of coequal sovereign states, and can be built into a pyramidal structure only if these nations consent to and join in such an endeavor. While piecemeal building upon the base has resulted in the substantive corpus of IEL noted in Chapter One, there is no overarching pyramid of authority consisting of law—making, law—interpreting, law—implementing, or law—enforcing institutions.” So, the authors start discussing the many international organizations that facilitate the implementation of IEL, the compliance mechanism, the diplomatic avenues and judicial remedies.

It is in the view of the authors that despite the impressive growth of IEL and its expanding domain, there is still no single institution or organization that serves environmental protection in the way that the World Trade Organization (WTO) advances, interprets, implements, and enforces the concept of free trade. The institutions and organizations enlisted to advance IEL are fractured, fragmented, and divided along functional, regional, bureaucratic, and geo—political lines. In the global area, there are institutions and organizations, such as the Food and Agricultural Organization (FAO), the International Labor Organization (ILO), the World Health Organization (WHO), the World Meteorological Organization (WMO), the International Maritime Organization (IMO), the UN Educational, Scientific, and Cultural Organization (UNESCO), the International Atomic Energy Agency (IAEA), the UN Development Program (UNDP), the World Bank, the International Finance Corporation (IFC), and so on. In the regional area, there are many institutions also become a part of role in developing IEL, and European Union (EU) is the most advanced form of international organization in the world and is evolving into a continent—wide political confederation. Still, many treaties have set up institutional arrangements (or rudimentary international organizations) for their implementation. For example, the sporadic conference of the parties under the Vienna Convention for the Protection of the Ozone Layer is one way to implement the treaties. And, the Non-governmental organizations (NGOs) are playing an increasingly important role in IEL, such as the World Wildlife Fund (WWF).

Although there are so many institutions and organizations in the World, they do not enjoy or exercise the power and authority of national legislative, executive, and judicial bodies that supervise and enforce the implementation of laws within nation states. Then, it is important that the substantive rules of international law should first possess an internal force or dynamic that makes sense to the parties and invokes an attitude of compliance rather than non-compliance. There are two ways that lead to compliance, first, treaty negotiators try to formulate and endow substantive rules with some compliance-generating character. Second, conventions or treaties also create institutions and techniques that induce compliance. The authors give some examples to illustrate how the two ways, especially latter way, form the compliance mechanism.

Many environmental treaties require that parties explore diplomatic and other means of settling their differences before resorting to judicial or quasi-judicial dispute settlement. Such as the International Convention for the Prevention of Pollution from Ships (MARPOL), the Convention on International Liability for Damage Caused by Space Objects and so on. Therefore, the diplomatic avenues become a way to settle the international environmental problems.

Apart from regulatory regimes supervised by or through agencies established by treaty, judicial enforcement provides another avenue for securing compliance with the law. Judicial remedies may be used to obtain specific items of compliance and can act as deterrents by bringing embarrassment, perhaps ignominy, to bear on wrongdoing states. More commonly judicial or quasi-judicial remedies within IEL are invoked through inter-state litigation, and are based on the grievance remedial principles of “state responsibility” or international trot law. And then, the authors explain in detail on the judicial avenue to resort the problems caused by the traditional ways. 1, Jurisdiction, jurisdiction can prove to be a difficult obstacle. In the Legality of the Use by a State of Nuclear Weapons in Armed Conflict case, the ICJ defined the concept to include legal capacity or status, and held that it lacked jurisdiction because the WHO was unable to demonstrate legal capacity. However, despite these defects, judicial remedies can prove to be an effective way of implementation the law if they are administered by a tribunal having compulsory and binding jurisdiction like the UNCLOS tribunals, and if the tribunals assume a more activist role in interpreting and applying the substantive law. 2, Accountability for transboundary environmental harms, in this part, the authors use the accountability for transboundary harms in 1955 to illustrate the specific way of how the ILC to deal with the codification of the law, including the application of SR, international liability for injurious consequences arising out of acts not prohibited by international law, civil liability, conclusion, the effectiveness of international environmental law, the relationship between IEL and domestic law,.

In the second part of this book, the authors detailedly enumerate the problems that facing people, such as population, biodiversity, global climate change, ozone depletion, Antarctica, toxic and hazardous substances, land and vessel—based pollution, transboundary water pollution, desertification, and nuclear damage. And in every single chapter, the authors usually illustrate in a way as the nature of the problem, and then the legal response.

One, Population.
Needless to say, the growth of global population has dramatically increased to an extent that the earth we live can no longer afford. On the basis of the statistics, “it took until approximately 1804 for the global population to reach 1 billion, this figure doubled to 2 billion by 1927—a span of only 123 years. The global population reached 3 billion in 1960 (33years); 4 billion in 1974 (14year); and 5 billion in 1987 (13year). It then took a mere 12 years for the global population to reach the current level of approximately 6 billion people in 1999.” And without doubt, the numbers will continue rising in the future, so what directly induces from the unchecked population growth is that the resources on the earth will not meet the need of everyone. Meantime, the environmental impacts of population growth are ubiquitous and universal. For instance, population growth has a direct impact on agricultural resources. The demand for food created from population growth has necessitated an increase in required cropland area at the expense of natural ecosystems such as forests, grasslands, and wetlands.

In order to introduce the remedial objectives, the authors first illustrate the theories on population growth. They are the Malthusian apocalypse and neo-Malthusian, economic transition and redistributional theories of population growth. Although the two theories are poles apart, they both seriously believe that the growth of population must be checked.

So, the authors relate on the legal response on the growth of population. The approach fashioned and proclaimed at the “Earth Summit” the 1992 United Nations Conference on Environment and Development (UNCED), and the World Summit on Sustainable Development (WSSD), hopes to integrate economic development, social development and environmental protection without compromising the needs of present and future generations. In the 1994 United Nations International Conference on Population and Development, the result is a comprehensive plan that incorporates ideas from many theories. Though there is controversy in this Program of Action, this is one big step of humans to give methods on balancing the growth of population and other problems.

Two, Biodiversity
Biodiversity sustains life on earth by maintaining atmospheric quality, regulating local climates, absorbing pollutants, protecting watersheds, and generating and maintaining soils. Despite the fact that biodiversity plays an important role in the humans life, it is suffering from loss, and mainly based on the “use-value” of species and ecosystems, within economic, ecological, and aesthetic frameworks, also on ethical values, which are different than use-values and arises from a belief in the intrinsic worth of a species. The primary cause of the loss of biodiversity is habitat destruction resulting from the expansion of human population and activities. And other direct causes include invasion by introduced species, over-exploitation of biological resources, industrial agriculture and forestry, pollution, and potentially, global climate change.

In order to meet people’s needs for biological resources while ensuring that those resources last indefinitely, it is crucial for all the humans to conserve the species biodiversity, and it must be based on global frameworks of equity and justices as well as sustainable development.

And the legal response to the conservation includes the Convention on Biological Diversity (CBD), Cartagena Protocol on Biosafety, and International Treaties Related to Biological Diversity, Regional Treaties and Agreements Related to Biodiversity. The CBD is a framework treaty which possesses only the power to seek appropriate forms of cooperation with the executive bodies of other biodiversity conventions. And in order to fully understand this treaty, the authors bring us to the two overriding principles in this framework convention: (1) Equity and Resources Transfers, (2) Sustainable Development (Conservation and Sustainable Use). After the authors pay more attention to detailedly illustrate the two principles and thus we can see how important these two principles are in the framework treaty. The Cartagena Protocol on Biodiversity is a supplementary agreement to the CBD, which acted upon the Art 19(3) of CBD: “The parties shall consider the need for and modalities of a protocol setting out appropriate procedures, including, in particular, advance informed agreement, in the field of the safe transfer, handling and use of any living modified organism resulting from biotechnology that may have adverse effect on the conservation and sustainable use of biological diversity.” And thus the protocol aims at the detailed aspect on the biotechnology which can make a contribution towards achieving the objectives of the Convention if developed and used with adequate safety measures for the environment and human health. The International Treaties Related to Biological Diversity includes: The 1973 Convention on International Trade in Endangered Species of Fauna and Flora (CITES), The 1972 UNESCO Convention Concerning the Protection of the World Cultural and Natural Heritage (World Heritage Convention), The 1971 Convention on Wetlands of International Importance, Especially as Waterfowl Habitat (Ramsar Convention), The 1979 Convention on the Conservation of Migratory Species of Wild Animals (Bonn Conservation). The Regional Treaties and Agreements Related to Biodiversity. They include a cluster of treaties protecting the Antarctic and so on.

Three, Global Climate Change
When referring to the global climate, one will mention the Greenhouse gases (GHGs), and the past several years had witnessed the on and on discharging of carbon dioxide, and significant quantities of other GHGs such as methane and nitrous oxide, all of these have altered the natural distribution of atmospheric gases that blanket the earth. According to the statistics, the atmospheric CO levels will increase to between 540 ppm to 970 ppm by2100, which is respectively 90% to 250% higher than the concentration in the late 1700s. Today’s CO concentration of approximately 370 ppm is about 95 ppm greater than the pre-industrial concentration. This could correspond to a mean global temperature increase from 1.4? to 5.8?,an increase range that is two to ten times larger than the central value of observed warming over the 20th century. And scientists predict that if the trend continues in the future, the global climate will be changed greatly that cannot be reversed, and will do harm to not only the humans themselves, but also the plants and animals living on the earth, maybe one day what happened in the science fiction will come true.

Then a cluster of remedies objectives have been set forth in the United Nations Framework Conventions on Climate Changes (UNFCCC), and the ultimate objective is to achieve “…stabilization of greenhouse gas concentration in the atmosphere at a level that would present dangerous anthropogenic interference with the climate system. Such a level should be ecosystems to adapt naturally to climate change, to ensure that food production is not threatened and to enable economic development to proceed in a sustainable manner. ”

The international legal responses to the threat of climate change or global warming are not only found in the UNFCCC, but also in the Tokyo protocol to the UNFCCC. On the basis of the UNFCCC and the Tokyo protocol, the authors discussed the substantive obligations, institutions and implementation, outstanding issues, and implications. 1, Substantive obligations. It is important not only for the developed countries but also the less-developed countries to cooperate together to solve the climate problems.2, Institutions and implementation. The authors specifically introduce how to implement the convention; they are conference of the parties, secretariat, subsidiary body for scientific and technological advice, subsidiary body for implementation, financial mechanism. 3, Outstanding issues. In this part, the authors quote the famous issues concerning the implementation, such as joint implementation, technology transfer and financing, adaptation, and costs?benefits. 4, Implications. The authors talked about the small problems involving the implementation, and give some suggestions.

Four, Ozone Depletion
Ozone is a shield to protect living organisms and humans on earth from exposing to a range of adverse consequences. However, research data has largely concluded that human activities are causing the ozone depletion.

In order to restore the ozone shield and prevent the future enlarging of the ozone hole, it is necessary to prohibit the use of damaging chemicals. And legal responses to this include the Vienna Ozone Convention, the Montreal Protocol, adjustments and amendments, transfers, trade restrictions, technological and financial assistance, and the impact of the regime. There are abundant ideas in this part and this will help students to better understand the problem of the ozone depletion.

Five, Antarctica
Antarctica is the coldest, windiest, iciest, driest and highest major landmass on earth. The fifth largest continent in the world, Antarctica comprises around 9% of the earth’s continental crust and is approximately twice the size of Australia. However, only a tiny fraction of the continent itself is visible, as 98% of its 5.4 million square miles is buried beneath an immense sheet of ice.

Antarctica means to humans not only the scientific and archeological importance but also the economic and political consequence. Unfortunately, over the last half of the 20th century, the Antarctic Peninsula region has grown warmer. Given that the 90% of the world’s ice located in Antarctica, were this ice to melt the sea level would rise some 200feet—dramatically impacting human and other forms of life across the entire planet.

Considering the threat to the Antarctica, in 1959 the 12 claimant and nonclaimant states met to resolve the problem and eventually sighing a compromise treaty—the Antarctica Treaty. Within the 1959 Antarctica Treaty area, the 1972 Convention for the Conservation of Antarctica Seals limits harvesting of three species of seals. And 1980 Convention on the Conservation of Antarctic marine living resources aims to conserve all living resources found south of the Antarctic Convergence. And 1988 Antarctic Mineral Resources Convention. 1991 Antarctic Environment Protocol chose to create an environmental protocol to the 1959 treaty.

Six, Toxic and Hazardous Substances
Toxic and hazardous substances can cause significant damage in small, even minuscule, amounts. They are among the pollutants responsible for transboundary air and water pollution, as well as land-based pollution and dumping. About 95% of all hazardous pollutants are created by industries that generate four primary groups of toxic and hazardous chemicals. They are toxic metals, petrochemicals, pesticides and radioactive materials. Toxics often impact ecological food chains by bio-accumulating in the tissues of aquatic organisms and this does harm to the humans and living organisms deeply.

Legal responses to the toxic and hazardous substances include toxic and hazardous substances in general, before 1998, no international treaty existed regarding the distribution and use of hazardous substances across all media. In the absence of such a treaty, the FAO and UNEP filled this gap with two sets of voluntary guidelines. After there is prior informed consent, such as 2002 FAO International Code of Conduct on the Distribution and Use of Pesticides, 1987 UNEP London Guidelines for the Exchange of information on Chemicals in International Trade, Rotterdam Convention on the Prior Informed Consent Procedure for Certain Hazardous Chemicals and Pesticides in International Trade. In light of hazardous wastes, the Basel Convention on the Control of Transboundary Movements of Hazardous Wastes and Their Disposal, the Convention on the Ban of Imports Into Africa and the Control of Transboundary Movement and Management of Hazardous Wastes Within Africa, the International Convention on Liability and Compensation for damage in Connection with the Carriage of Hazardous and Noxious Substances by Sea.

Seven, Land-based pollution
At least 80% of all marine pollution comes from sources that are located on land, and it has loomed more problematic to the extent that urban growth has departed from principles of sustainable development, and environmental protection has been ignored or minimized by economic growth. In general, there are eight groups of pollutants that are deposited into the ocean from land-based sources: chemical nutrients, sewage and bacterial agents, oil, organic chemicals, metals, sediments and litter, radioactive substances, heat.

Though land-based sources contribute the highest percentage of marine pollution, the international commitment to controlling these wastes remains understandably low. Only the United Nations Convention on the Law of the Sea, Montreal Guidelines for the Protection of the Marine Environment Against Pollution from Land-based Sources, the Global Program of Action for the Protection of the Marine Environment from Land-based Activities and the Washington Declaration on Protection of the Marine Environment from Land-based Activities.

Eight, Vessel-based Pollution
The transportation of crude oil or refined products results in the release of approximately 136,000 tons of petroleum per year into the oceans of the world. And this will cause harm not only to the sea itself but also the humans and the living organisms.

International law has responded to the harms, the 1973/1978 International Convention for the Prevention of Pollution from Ships, the United Nations Convention on the Law of the Sea, International Convention on Oil Pollution Preparedness, Response and Co-operation, International Convention Relating to Intervention on the High Seas In Cases of Oil Pollution Casualties, Protocol on Preparedness, Response and Cooperation for Pollution Incidents by Hazardous and Noxious Substances, 2000.

Nine, Dumping
Many types of wastes that are difficult to dispose of on land have traditionally been dumped directly into oceans and rivers without regulation. This includes many hazardous materials, such as sewage, industrial effluents, sludges, radioactive wastes and polluted dredged spoils.

Thus, to reduce the harm, international legal responses include United Nations Convention on the Law of the Sea, Convention on the Prevention of Marine Pollution by Dumping of Wastes and Other Matter, 1996 Protocol to the Convention on the Prevention of Marine Pollution by Dumping of Wastes and Other Matter.

Ten, Conservation of Marine Living Resources
The Oceans cover 75% of the earth’s surface and human depend on the oceans for their living, however, without protection, the oceans will not be capable for the future of the next generation, so, it is the time to protect the oceans.

The legal responses to the protection of the Oceans include United Nations Convention on the Law of the Sea, UNEP regional seas programme, International Convention for the Regulation of Whalting.

Eleven, Transboundary Air Pollution
Human demands lead to a number of physical processes and activities that convert raw materials, energy, and labor into desired finished products. Diverse pollutants are introduced into the environment during various stages of these production and consumption cycles.

In this part, the authors mention the famous case—1941Trail Smelter Arbitration. This case has since become the basis for the general prohibition against transboundary environment harm that was definitely restated in the 1992 Rio Declaration: States have , in accordance with the Charter of the United Nations and the principles of international law, the sovereign right to exploit their own resources pursuant to their own environmental and developmental policies, and the responsibility to ensure that activities within their jurisdiction or control do not cause damage to the environment of other States or of areas beyond the limits of national jurisdiction. Also, Convention on Long-range Transboundary Air Pollution is the treaty that regulates the transboundary pollution.

Twelve, Transboundary Water Pollution
Waters cover the face of the earth. And we have seen that the environmental health of the oceans is critical to humanity. However, the healthy waters have become polluted because of human activities. Meantime, pollution introduces into rivers, watercourses, and coastal waters of one state can affect another through transport, diffusion or dispersion.

International and Regional ways include Convention on the Law of the Non-Navigational Uses of International Watercourses, 1992 ECE Convention on the Protection and Use of Transboundary Watercourses and Lakes. And also the authors mention some famous cases on the transboundary water pollution, which become the rules for the future solving problems.

Thirteen, Desertification
Desertification refers to the process of climate change and human impacts that create desert environments in “drylands”—the arid, semi-arid, or dry sub-humid regions of the world. Human activities, driven by population growth, energy needs, and the lack of land have led to over-cultivation—the farming of land beyond its sustainable fertility.

Desertification raises questions common to other international environmental problems, and must be addressed within the conceptual framework of sustainable development. In 1992, the United Nations Conference on Environment and development adopted Agenda 21, a program for sustainable development, which recommended preventive measures for threatened or slightly degraded drylands and rehabilitative measures for moderately or severely degraded drylands.

Fourteen, Nuclear Damage
The military use of nuclear bombs can lead to unparalleled suffering, especially the radiation, radiation can cause destructive chemical changes, and when harmful radiation strikes human tissue, it strips electrons or neutrons of the molecules and atoms and thereby kills or damages human cells. And it has the power to destroy all civilization and the entire ecosystems of the planet. So, fear of such destruction has led the international community to seek way of containing and eliminating the nuclear threat from both military and civilian sources.

To ban all together the nuclear weapons and find other ways to substitute for the civilian nuclear uses are the best method to control the nuclear damage, however, it is unreal to realize this, so the authors discuss the international way concerning the protection from the nuclear damage.

The last part of this book mainly talks on the future of the international environmental law, although the international community has done much concerning the protection of our environment, the road ahead still in the twists and turns.

International Environmental Law in a Nutshell is a very useful book that not only for the students, who study the IEL, but also the handbook to the teachers and students who have well known the IEL.


Gold deposits are not uniformly distributed along major faults due to complex (and long-debated) interactions between seismicity, hydrothermalism, and structural heterogeneities. Here, we use static stress modelling (SSM) to quantitatively investigate these interactions, by exploring the role of Cadillac-Larder Lake Fault (CLLF) Archean seismicity in the genesis of the regional goldfields. Various rheological factors are evaluated for optimizing the models’ ability to reproduce known gold occurrences, regarded as the fossil primary markers of synkinematic hydrothermal systems. We propose that the marked structural heterogeneities of the CLLF induced persistent seismic segmentation and recurrent ruptures of the same fault windows that arrested on robust node points. These ruptures favour repeated occurrences of seismically triggered hydrothermalism along long-existing fluid pathways having an enhanced permeability and iterative ore formation into supracrustal discharge zones by means of episodic drops and build-ups of pressure. Two-dimensional SSM permits the predictive mapping of these high-potential zones. These modelled zones correlate positively with the actual observed gold distribution. We demonstrate that the ruptures along the Joannes Segment arresting on the Davidson Fault and Lapa’s bend can explain the occurrence and location of the Rouyn and Malartic goldfields; the models’ validity is improved by implementing regional geological constraints; and the distant gold occurrences from the CLLF, including the Bourlamaque field, can be explained by doublet seismic events along the Rivière-Héva and Lapause subsidiary faults. Our results provide new perspectives from a fundamental standpoint and for exploration purposes.

1. Introduction

Mesothermal gold deposits are developed by the discrete circulation of mineralized fluid flows that are controlled by structural frameworks (e.g., [15]). The channeling and concentrating of the fluids are important for gold endowment. The role of fault seismicity in such processes has been discussed over the last three decades [610]. Yet, quantifying the regional-scale interplay between seismicity, crustal permeability, and hydrothermal ore genesis remains an open question requiring multidisciplinary efforts that involve both active and fossil systems. Addressing these issues from a mechanical modelling perspective is particularly challenging in fossil systems due to the lack of quantifiable evidence. The complex distribution of gold deposits along regional-scale faults has long been a major focus for understanding the controls on mesothermal gold mineralization processes [1113]. Recent studies have shown that the nonuniform distributions of gold endowments are correlated to variations in fault geometry, including deviations from its main trend [1416]. Most faults can be divided into several segments characterized by constant attitude. The segments are separated from each other by bending step-overs, hard links, or gaps [17]. These large fault segments play a critical role in seismic behaviour, displacement, and failure propagation. Historically, segmentation has been a major focus of seismology for understanding seismic hazards around existing active fault zones. This has produced the aftershocks theory; this idea involves the geomechanical modelling of static stress changes around a ruptured segment for predictive mapping of coseismic activity and aftershock triggering zones. The zones are generally referred to as coseismic damage zones (San Andreas Fault, California [1820]; North Anatolian Fault, Turkey [21]). The approach has been validated using modern active faults, and the modelled zones correspond to actual aftershock locations 65% to 85% of the time [20, 22, 23].

From a hydrothermal standpoint, damage zones undergo a temporary and dramatic increase in structural permeability related to the opening of fracture networks where aftershocks are triggered [6, 24]. This results in the activation of second-order faults that lead to the draining of deep-seated fluid reservoirs [25] and a greatly increased hydrothermal circulation [8, 10]. The repeated failure of the same fault segment (hundreds to thousands of times), combined with the cyclic draining of pressurized fluids, allows for the iterative enrichment of gold deposits by the repeated circulation of large volumes of metal-rich fluids within a restrained area [7, 15]. From the perspective of gold metallogeny and prospection, predicting the spatial distribution of these potentially auriferous coseismic discharge zones—by means of a static stress modelling approach as analogous to seismological studies on present-day active faults—is a highly valuable and relevant approach. Micklethwaite and Cox [15, 26] pioneered this approach by applying it to the analysis of gold deposition near auriferous Archaean faults. They established that the activation of favourably oriented segments along the Black Flag and Boulder-Lefroy faults, Western Australia, yielded coseismic damage zones that were positively correlated with gold distribution; these zones include the world-class St. Yves and Mt. Pleasant deposits. Moreover, Micklethwaite and Cox [26] suggested that static stress changes from the mainshock combined with doublet aftershocks enhance the precision when delineating damage zones. These studies have focused mainly on the impact of some intrinsic characteristics of the main fault such as its geometry [14], permeability [27], and links between segments [28]. However, it is likely that the regional geological background (structural framework and lithologies) in the vicinity of the main fault greatly interferes with the coseismic propagation of stress and strain. This, along with the influence of preexisting, low-strength regional fabrics on coseismic stress patterns, remains an unaddressed first-order parameter. Although they play an important role in the spatial distribution of damage zones, the trends of the primary failing planes at any point near the ruptured main segment have also been given little attention [20]. Moreover, the validation of static stress models using ancient fault systems represents a major challenge [29] due to the absence of direct aftershock records. On the other hand, mesothermal gold mineralization located near fault areas represents reliable markers of seismically triggered fossil hydrothermalism occurring within damage zones. This study thus follows the premise used in previous studies (e.g., [9, 15, 26]) that, through a classic inverse approach, the validity of various models can be evaluated by comparing the simulated coseismic damage zones to the spatial distribution of actual goldfields.

This study aims to identify the role of Archean seismicity along the Cadillac-Larder Lake Fault (CLLF) on gold deposition in the Abitibi greenstone belt, Québec, Canada. Numerical geomechanical modelling is used to establish static stress changes subsequent to mainshocks along the fault. Emphasis is placed on testing the incorporation of regional geological inputs as mechanical and rheological constraints for refining the models.

The CLLF is a 250 km long east-striking structure associated with several clusters of gold deposits, which represent 25% of all gold produced in Canada [5]. The Abitibi Subprovince is characterized by numerous anastomosing faults dominated by east- and southeast trends [35, 36]. Rabeau [37] performed pioneer geomechanical modelling attempts in the Rouyn-Noranda region, using a strain propagation approach in a 3D elastic space. Dextral-reverse finite-displacement was applied on a 25 km long portion of the CLLF and subsidiary Wasa Fault, combined to compressive far-field boundaries conditions. Several methodological aspects deeply differ from the present study: the input kinematics combine strain fields related to different tectonic events, with likely different faults deformational regimes, and fluid-focusing zones were tracked by mapping high bulk volumetric changes while the present study computes the stress fields applied on fractures in order to track structural permeability enhancement in damage zones. Rafini [38] modelled damage zones of the CLLF during the late dextral strike-slip. The present study builds upon this latter modelling attempt. A century of gold exploration in the region has yielded considerable knowledge regarding the geological framework, including the architecture of major structures and lithologies. Therefore, this environment is well suited for testing the impact of contrasting lithologies and subsidiary faults on the geometry of stress change following displacement along a main fault such as the CLLF.

2. Geological Setting and Timing Relationships between Deformation and Gold Mineralization

2.1. Regional Geology

The Abitibi Subprovince is an Archean greenstone belt dominated by volcanosedimentary rocks and sedimentary basins intruded by several types of granitoid rocks (Figure 1). The Southern Volcanic Zone of the Abitibi Subprovince [39] is separated from the Pontiac Subprovince to the south by the CLLF. The Pontiac Subprovince is mainly composed of sedimentary and granitoid rocks. The CLLF can be separated into several 30–40 km long segments of constant attitude despite having geometric variations (azimuth, dip) between them (see [40, 41] for details). Tips between segments include abrupt and gentle bends as well as hard links such as second-order faults (Figure 1).

The Abitibi and Pontiac Subprovinces have experienced prolonged deformational events and are characterized by highly developed structural features. Rock assemblages are tilted prior to ductile deformation events [40, 42]. Although there is no consensus on the interpretation of the structural evolution of the study area, it is commonly accepted that a major N–S shortening event was responsible for most of the finite deformational framework. This was followed by a dextral strike-slip along east-striking faults during a subsequent NW–SE shortening (e.g., [40, 41, 4345]). Most of the contacts between rock groups have been activated as first- and second-order faults [35, 42], as illustrated in Figure 2. Rocks are affected by a predominantly east-striking vertical foliation related to shortening. Regional metamorphism is mostly at a greenschist grade, but ranges locally from subgreenschist to amphibolite facies [46, 47]. This metamorphism grade is consistent with the lower levels of a seismogenic crust [6]. The exposed portion of the CLLF experienced a frictional rheological mode and seismic cyclic activation that appeared to have been simultaneous with more viscous, probably aseismic, deformational modes (ductile creep). This transitional rheological context, which was contemporary to gold deposition, is supported by field evidence including brittle–ductile auriferous faults (with low- mylonitization) as well as cross-cutting relationships between pure tensile gold-bearing veins and ductile features (folding on various scales and boudinage). The cyclic deformational mode is convincingly indicated by the heterogeneous distribution of fluid inclusions in quartz veins [7] and the ubiquitous occurrence of crack-and-seal textured veins. The successive mineral ribbons in these veins reflect stress and fluid pressure fluctuations as well as repeated opening and precipitation/closure stages induced by seismic cycles [8, 48].

2.2. Relationship to Mineralization

The CLLF contains many gold deposits distributed mostly in clusters that are historical mining districts, most notably the Val-d’Or, Malartic, and Kerr Addison districts [5]. Spatially, they are located next to the CLLF, but not directly upon the fault, and correlate with the major structural segments as described by Bedeaux et al. [41]. Smaller gold deposits also occur along the fault but remain marginal compared to the tonnage found in the clusters (Figure 1(b)). Rafini [30] pointed out in his metallogenic synthesis of the CLLF that these clusters regroup gold deposits having similar characteristics in regard to sulfides abundance and type, alteration, and vein paragenesis as well as orebody shape (see [41] for the English version). This typology of deposits showed the existence of “metallogenic fields” along the CLLF. Several deposits highlight the various parameters, originating either locally or distally, that influenced the deposits. These parameters include fluid origin and chemistry [49, 50], contribution of magmatism [51], host rock geochemistry [52], pervasive primary permeability, and the local structural framework (fracture-related permeability, rheological contrasts, and dilation [49]).

Great effort has been made to place a date on gold mineralization, especially the timing of deformation. At a district scale, gold mineralization appears to have occurred over several events [5356]. Hydrothermalism was globally active over a long period (tens of millions of years), exceeding the duration of deformation [57]. Still, several authors suggest that a dominant gold deposition event is associated with the late NW–SE shortening event [45, 49, 5861] expressed predominantly as a dextral strike-slip.

3. Theoretical Background and Methodology

Several models were created to assess the impact of the subsidiary fault framework surrounding the CLLF, the preexisting structural fabrics such as the ubiquitous regional penetrative foliation, the rheological contrasts between lithological units, and the doublet aftershocks.

3.1. Segmentation

During an earthquake, the propagation of slip from the epicentre throughout the rupturing fault window is extremely sensitive to the geometry of the fault [17]. Slip is confined to major segments having consistent geometry and it diminishes drastically approaching the tips [62]. Major segments can also be identified using the slip distributions of modern active faults [17]. Tips of segments occur as either soft links (i.e., gaps or step-overs) or hard links (changes in orientation of fault trace, connecting faults, ramps). During the seismic activation of a fault, these terminations can act as barriers—or rupture arrest points [17, 63]—especially if the termination is a misoriented feature or denotes an abrupt change in geometry. A strong rupture arrest point will therefore recurrently restrain slip propagation and influence static stress distribution and the aftershock location. This will also focus hydrothermal pathways over specific damage zones allowing iterative gold endowment and the formation of deposit clusters. At the scale of the fault, the numerous gold deposit clusters will be related to the repeated failure of several segments [26].

3.2. Static Stress Changes and the Coulomb Criterion

Following a major rupture, the distribution of elastic strain is drastically modified around the displaced fault segment. Corollary changes in stress fields bring some regions closer to a critical failure state, which become the loci of coseismic activity, episodic hydrothermal pathways, and discharge zones [15, 26], while other regions are seismically silent. Geomechanical numeric codes permit simulating, at any point in the model, these static stress changes, induced by sudden displacement, onto a given segment of a main fault and also permit calculating the associated changes in the Coulomb failure stress (e.g., [20, 21]).

The Coulomb-Navier failure criterion is a common empirical measure of the static frictional strength of a fracture. The Coulomb failure stress (CFS) is given bywhere is the change in CFS, is the change in shear stress, is the change in normal stress, is the fluid pressure, and is the friction coefficient. We use the convention that compression stresses are positive. It is a common approximation that, after a seismic rupture, the fluid pressure at any nearby location is not connected to far-field conditions, but rather it is a fraction of normal stress [23, 64]. This theory is referred to as the undrained crust hypothesis, which essentially relies on the fact that static stress transfer is much faster than pore pressure diffusion. This is expressed through the empirical Skempton coefficient :where (2) can now be written:where The Skempton coefficient tends toward 1 when the angle between sigma 1 and the fracture network decreases [65]. The value of μ′ is expected to range from 0.2 to 0.8 [20, 21, 26, 66, 67].

3.3. Doublet

Major tremors are followed by numerous aftershocks that decrease in intensity over time. Aftershocks having magnitude roughly similar to the mainshock are designated as doublets. The segment triggered by this aftershock will in turn influence the local stress field. Thus, the Coulomb stress field can be considerably modified in areas situated far from the mainshock location. An earthquake can be considered a doublet aftershock if [34, 68, 69] the segment experiencing the aftershock is located inside the damage zone related to the mainshock, the two earthquakes have similar magnitude, they have close spatial relationships, and both have close temporal relationships.

3.4. The Numerical Code

The geomechanical simulations were carried out using the UDEC (Universal Distinct Element Code) [70], a finite element code that has the singular ability to interactively simulate internal block deformations as well as displacement along discontinuities that separate these blocks. Although it was developed for engineering purposes, its application to geological problems has proved successful [71, 72]. The 2D model is divided into blocks separated by rheological boundaries that allow the representation of regions having various mechanical properties and discontinuities such as faults and contacts. Internal boundary initial conditions are displacement imposed on the failing fault segment, while far-field boundaries are free. In other words, these conditions are strain-only and there are no stresses applied to the system. The influence of the regional stress state hence is not considered, for the purpose of investigating the coseismic-only stresses and elastic strain, that is, exclusively those propagating from the rupturing segment. Implementing any regional stress field indeed is not relevant to coseismic stress propagation modelling at this stage: either the regional stress field would be presumed initially homogeneous in the entire domain, which implies no relative impact on the results, or the time-dependent and heterogeneous modifications of the stress tensor during the seismic loading-discharge cycle in the vicinity of the fault are modelled, which is a nonvaluable increase of complexity and uncertainty to the scope of this study.

Static stress modelling is a relatively straightforward method where stress and strain are calculated at any point from the derivative of the displacement field converted into the elastic strain field ,and then into the stress field by means of the elastic constitutive law (Hooke’s laws): where and are the Lamé coefficient (Pa) and the shear modulus (Pa), respectively. The symbol represents the Kronecker delta, which is 0 or 1 if . Finally, the resulting stress field is converted into forces applied at each node of the spatial discretization, from which the next-step displacement field is calculated using Newton’s laws.

Finally, the assumption of elastic-only rheological mode into the blocks is a common and consensual first-order approximation [15, 26], highly suitable for the purposes of this modelling. Implementing elastoplastic deformational mode would increase complexity and require additional, weakly constrained, rheological parameters, inducing a barely calibrated and incidentally low (from our testing) influence on the results and then increasing uncertainty in a nonvaluable fashion.

3.5. Geomechanical Parameters

Coulomb stress changes during the failure of the CLLF were modelled in several stages, from simple to more complex and multiparameter model configurations by incrementally including the various geomechanical parameters (Table 1). The simplest model includes only the CLLF (model 1). A structural framework is then added (model 2.a), followed by the integration of failure planes having variable orientations (model 2.b). The influence of potential doublets is finally considered (models 3 and 4). At each stage, the vertical, east-striking Joannes Segment is triggered during the mainshock. This segment was chosen because of its homogeneous geometry and its optimal orientation with respect to the late NW–SE shortening deformation event. Moreover, the segment is clearly delimited by the Davidson Fault to the west and the abrupt bend of the CLLF to the east. Both features constitute well defined and highly plausible rupture arrest points. The Joannes Segment is also located between the Rouyn and Malartic districts, two well-documented areas after decades of exploration. This 41 km long segment is expected to experience earthquakes having 6.6 to 7.0 magnitude associated with 1.4 m maximum lateral offset based on the log-normal empirical relationships established between the earthquake magnitude, the length of the ruptured segment, and the offset (Figure 3, [31, 32, 73, 74]).

In each model, blocks are assigned geomechanical properties corresponding to their dominant lithology (sedimentary, volcanic, or granitoid rocks). These are based on the abundant experimental data available in the literature [7578]. Block boundary properties are also determined according to their structural nature: major faults, second-order faults, third-order faults, or simple contacts (Figure 2). Such a hierarchical assignment of properties is designed to depict the actual relative importance of every contact in the deformational framework, based on an extensive knowledge of the field area obtained over several decades of observations in southern Abitibi [4045, 79, 80].

The CFS may be calculated for any point from the projection of the local stress tensor along the failure plane of interest. Consequently, a critical parameter is the orientation of failure planes, which relies on various structural assumptions. A common assumption is to consider primary failing planes as being oriented optimally at every point of the model to maximize Coulomb stress [20, 22, 23]. This means setting the angle of as constant and equal to 45–0.5 atan (μ) (i.e., to 29.5° for ). This method can be suitable if the model includes isotropic rocks having no preferential failure plane and if regional stress tensors are well defined. In the case of the CLLF, the late strike-slip event is related to a general NW–SE shortening event where the exact orientation is not defined. This means that the optimal failure plane orientation can only be estimated, and this estimate can range from N090° to N120° with respect to the direction that can range from N300° to N330°. An alternative assumption is that preexisting, low-strength fabrics preferentially undergo failures. Around the CLLF, such fabric corresponds to the ubiquitous and highly penetrative regional foliation, which is mostly east-striking and globally parallel to bedding and faults [36, 41]. Its similarity to the optimal orientation makes it a reasonable failure plane alternative, and this is supported by field evidence showing reactivation during late strike-slip events [41, 49]. Moreover, the existing surface geology in southern Abitibi corresponds to a crustal level close to the one experiencing high-magnitude earthquakes when the CLLF was active. In an initial stage, failure planes were set as east-striking by default. In a second stage, the refinements to the model obtained through implementing foliation fabric orientations at any point were investigated through the use of an interpolation of the numerous available foliation measurements (Figure 2). For calculating the CFS, a value of 0.4 was used for μ′ based on previous modelling attempts [20, 26, 29].

The final investigated parameter was the influence of doublet aftershocks. In the vicinity of the CLLF, the Rivière-Héva and Lapause second-order faults are high-potential doublet segments using empirical criteria based on present-day seismic observations: location in a zone of positive CFS change and close proximity to and similar segment length as the Joannes Segment experiencing the mainshock. The first segment considered to be able to produce a doublet aftershock is associated with the Lapause Fault, which marks the boundary between sedimentary and volcanic rocks in the eastern part of the CLLF (Figure 2). The 24 km long segment trends at 120° and is delimited by an abrupt change in azimuth in the northwest; it intersects the third-order Parfouru Fault in the southeast. Coseismic failure along this segment is expected to yield 1.3 m of dextral displacement based on its length (Table 1). The other segment is related to the Rivière-Héva second-order fault, a recently discovered structure in the volcanic rocks of the Malartic Group, which has significant importance in the local stratigraphy [79, 80]. The selected segment strikes 115° to southeast and is bounded on each tip by an abrupt change in azimuth to the east. Its length of 29 km corresponds to dextral displacement of 1.4 m for one earthquake.

4. Results

Static stress change mapping around the CLLF was done by the testing of seven models (Table 1 and Figure 2). Three models involve failure on the Joannes Segment of the CLLF with extra parameters added. The first model uses only the CLLF. The second model adds the geological and structural frameworks of southern Abitibi, that is, additional faults, contacts, and major lithological assemblages. The third builds on the second model with the addition of variable orientations of the failure planes for CFS calculations. Potential doublets along the Lapause and Rivière-Héva Faults were initially tested using the geological and structural frameworks of Abitibi and then again tested with the addition of variable failure plane orientations. Models involving doublets are combined with the CFS calculations from the Joannes Segment failure.

4.1. Cadillac-Larder Lake Fault Failure (Model 1)

In the generic model 1.a, including only the CLLF, lobate areas representing positive and negative change in Coulomb stress are distributed in a symmetric pattern, similar to the results obtained by King et al. [20]. Positive lobes, corresponding to predicted damage zones, are distributed at the tips of the fault failure plane. Negative lobes are located on each side of the Joannes Segment (Figure 4(a)). The eastern positive lobe is well developed with an ESE trend, although the W-trending western lobe is less developed.

Model 1.b (Figure 4(b)) incorporates southern Abitibi geological and structural frameworks. Lobes are generally smaller than those within the generic model. The main difference with the first model is that lobe boundaries are heavily influenced by contacts and faults. In addition, lateral positive lobes are absent. The western positive lobe is delimited by the Davidson Fault to the east and covers a larger area than in the generic model. It also extends farther west along the CLLF.

The final model (model 1.c) to represent the main rupture along the Joannes Segment displays the most important variations from the classic geometry of Coulomb stress change only when the preexisting low-strength fabrics are included as the primary potentially failing planes (Figure 4(c)). Taking into consideration the variable orientation of the failure planes induces a locally important increase or decrease of Coulomb stress change. The eastern lobe strikes SE and shows a restricted width and length. It lies close to the CLLF next to the tip of the Joannes Segment. The western damage zone is larger than those within the previous models and is well developed next to the intersection between the Davidson Fault and the CLLF. In contrast with other models, it extends to the south of the CLLF instead of being mostly confined to the north of the fault.

4.2. Doublet-Lapause Fault (Model 2)

Model 2.a includes the geological and structural framework and generates numerous lateral positive lobes in addition to lobes located at the tip of the ruptured segment (Figure 5(a)). High positive CFS occurs between the Joannes and Lapause Segments. The eastern lobe covers a larger area and is east-striking. Lateral lobes are north-striking and are also associated with southeast-striking faults proximal to the Lapause Fault.

Model 2.b involves variable failure plane orientations (not shown). Positive CFS changes are significantly affected by variations in the orientation of the failure planes and are mostly confined to the tip of the segment. The eastern lobe strikes WNW and is developed along the east-striking faults to the north of the CLLF. The western lobe is nearly absent and is confined to the SE-trending section of the CLLF.

4.3. Doublet-Rivière-Héva Fault (Model 3)

In model 3.a (Figure 5(b)), only the lobes at the tip of the Rivière-Héva segment are developed. The western lobe is east-striking and delimited to the south of the Rivière-Héva Fault and reaches the tip of the Joannes Segment. The eastern lobe closely follows the east-striking splay fault of the Rivière-Héva Fault.

In the final model, the positive lobe between the Joannes and Rivière-Héva Segments is poorly developed and is confined to the SE-trending portion of the CLLF (not shown). The eastern lobe is much more developed and covers the area between both splay faults of the Rivière-Héva Fault. A N-trending lateral lobe is also well developed from the western tip.

5. Discussion

In this section, we review the validity of the method and compare results of models among each other. We also discuss implications for gold metallogeny and exploration in southern Abitibi.

5.1. Validation of Methods
5.1.1. Frequency-Magnitude Diagrams

Following ruptures in the main fault segment, lower-scale displacement and lower-magnitude seismicity are expected to occur along major adjoining and surrounding fault segments [21]. Simulations integrating the structural framework partially allow this slip in accordance with the faults’ relative importance as determined from field observations. This suggests implicitly that failure conditions are reached on these faults. Displacement fields calculated on contacts in the entire domain following the main rupture are converted to frequency-magnitude profiles by means of classical empirical relationships [31, 32]. The profiles obtained from simulations are then compared to actual profiles to confirm the mechanical validity of the models (Figure 6). Frequency-magnitude profiles are commonly represented by the Gutenberg–Richter relationships:where is the number of rupture events with moment magnitude greater than and and are constants [29, 33, 81]. This power law behaviour was shown to be related to elastic interactions within a heterogeneous medium (e.g., [82]), with increasing with heterogeneity. The value of has been the focus of extensive interest, primarily for seismic hazard prediction, as it was recognized early as a highly sensitive parameter in crustal rheology. At the scale of the fault system, it is expected to vary between 0.6 and 1.2 depending on various factors including temporality relative to the seismic cycle (e.g., [29, 8385]). Other controlling factors are more context-related and are of greater interest in validating our models: the stress regime such as type of fault, depth [86], and the slipping mode—notably the creeping mode which increases [33]. We reviewed values recorded on large transcrustal active strike-slip faults in oblique convergent margins, which may be considered as modern analogues of the Archean CLLF deformations modelled in our study: the San Andreas Fault ( and [87, 88], resp.), the North Anatolian Fault ( [88]), the Central Japanese Median Tectonic Line ( [87]), and the Sagaing Fault area, Myanmar ( [85]). Perceptible variations are observed partly due to methodological bias, but recorded values consistently trend below unity, mostly ranging from 0.5 to 0.9. Simulated profiles display values ranging from approximately 0.79 to 0.84 (Figure 6), which are similar to actual trends, indicating that our models reliably reproduce natural frequency-magnitude distributions for the targeted context. Although this mechanical validation attempt is conclusive, it overrides the temporality of values when aftershock sequences are compared to historical records. This is an issue requiring a verification in future work.

5.1.2. Correlation with Known Gold Deposits

Gold deposits in southern Abitibi are clustered near the CLLF, forming several goldfields as illustrated in Figure 1. Damage zones are identified as a critical control in the generation of gold deposits as they allow sustained fluid flow while allowing precipitation of gold-related minerals [15, 24, 29]. Previous static stress mapping studies in the Archean goldfields in Australia have shown that the clustered distribution of gold deposits along major fault systems can be correlated to positive CFS changes, a proxy for damage zones, following failure along specific fault segments (e.g., [9, 26]). In southern Abitibi, exploration for gold deposits has been carried out to various degrees using geological features such as major faults as criteria for gold prospecting. This yielded abundant documentation, sampling, and drill hole surveys as shown in Figure 7. This figure displays fewer exploration studies in the Pontiac Subprovince due to a thick glacial overburden and exploration strategies traditionally favouring volcanic rocks that are largely absent south of the CLLF. Only a few, less than a kilometre wide areas have been explored in detail; all correspond to gold deposits and gold mines (i.e., the Joanna gold deposit, Sigma-Lamaque, Canadian Malartic, Lapa, and Laronde gold mines). Overall, the known distribution of gold north of the CLLF does not correlate with the intensity of exploration studies. Moreover, these are well-studied regions, as there are no areas lacking in data, as shown in Figure 7. As such, the present-day spatial distribution of gold deposits and tonnage can be realistically considered as unbiased indicators of fossil auriferous hydrothermalism north of the CLLF and in its nearby southern vicinity. Thus, these are reliable validation variables for the models.

Models can be compared in regard to their ability to match the distribution of existing gold deposits and tonnage. For a model to be deemed a good fit, it is expected that damage zones correlate with known gold occurrence. The detailed results of this validation analysis are given in Table 2. Positive CFS changes are considered significant when above 30 kPa [20, 21].

The Rouyn goldfield is only reproduced by damage zones induced by rupturing of the Joannes Segment. In all simulations involving failure of the Joannes Segment, 73% of the Rouyn goldfield deposits are successfully predicted as they are correlated to significant positive CFS change. However, models 1.b and 1.c offer a better tonnage correlation, accounting for 48% of the existing tonnage. The Bousquet goldfield is poorly explained by the Joannes Segment failure, with only two deposits (11%) located west of the goldfield covered by the damage zones. Such results were expected, as the triggered segment (containing the Bousquet district) experiences an important stress drop following failure [20]. In addition, the Bousquet goldfield is located quite distant from doublet segments.

The Malartic goldfield shows a greater variability between models. The model that includes only the CLLF produces a correlation with 90% of existing deposits. On the other hand, the model incorporating the Abitibi structural framework and the doublet aftershock on the Lapause Fault can account for only 67% of existing gold deposits, suggesting these factors are not significantly involved in gold genesis in this area. In all cases, tonnage correlations to damage zones in the Malartic goldfield are markedly low. This is attributed to a bias due to the important proportion of gold contributed by the Canadian Malartic mine, a dominant intrusion-related deposit accounting for 67.5% of the total Malartic goldfield tonnage. Smaller deposits located over a wide area along the CLLF still occur in positive lobes.

In all three models involving only the Joannes Segment, the Bourlamaque and Val-d’Or goldfields remain largely unexplained by static stress changes. Moreover, static stress is expected to be modified only 10–20 km away from the failing segment [20, 26]. This means that gold deposits in the Val-d’Or and Bourlamaque districts cannot be explained solely by failure of the Joannes Segment as they are too far away from this segment. In the case of the Val-d’Or segment, the doublet failure of the Lapause segment matches 38% of existing gold deposits and 95% of the goldfield tonnage in both models 3.a and 3.b, revealing the importance of this segment for explaining the eastern deposits along the CLLF. More precisely, this doublet rupture corroborates Val-d’Or goldfield’s most important deposits such as Sigma-Lamaque, Goldex, and Kiena. It is worth noting that the cluster of deposits located near the recently developed Marban deposit is also remarkably well predicted. Doublet rupture along the Rivière-Héva Fault yields damage zones containing 40% of gold deposits in the Bourlamaque district and 50% when the variable orientation of regional foliation is integrated (model 3.b). These results illustrate how the doublet seismic activation of the Rivière-Héva Fault—a subsidiary of the CLLF—extends the influence of the CLLF laterally and permits gold occurrences in the Bourlamaque district despite being located quite distant from the CLLF.

In summary, the scenario involving the sole failure of the Joannes Segment produces a good correlation with deposits in the Malartic and Rouyn districts. However, a combined model that simulates successive rupturing of the Cadillac-Larder Lake and Lapause and Rivière-Héva Faults produces the best results for explaining the occurrence of gold in regard to the number of deposits and related tonnage. During a deformational event, faults will be active over millions of years, involving multiple repetitions of displacement during rupture events. Each of these events will trigger neighbouring major and second-order fault segments, including doublet aftershock ruptures on the Lapause and Rivière-Héva Faults. Over time, fluid flow will be focused along the same pathways, progressively developing and endowing gold deposits. In southern Abitibi, repeated doublet triggering of second-order faults by mainshocks on the Joannes Segment allows gold deposition to occur in areas farther away from the CLLF. It is thought to be possible that some gold deposits were developed by this combination of several failing segments repeated over time. These models demonstrate the significant role of the regional geological framework and orientation of the regional foliation on the spatial distribution of the positive lobes and how doublet aftershocks play a significant role in explaining the location and endowment of existing goldfields.

5.2. Hydrothermal Fields Validation

In a continued effort to constrain the models’ validity, this section explores the spatial correlation between hydrothermal fields derived from geochemical and mineralogical data and the modelled damage zones expected to be triggered due to coseismic permeability enhancement. A critical control for gold precipitation is the destabilization triggered by wall-rock chemical interactions [89, 90] and by fluid pressure changes induced by fault cycling [6, 29], as explained in Section 5.5. Mesothermal gold-bearing fluids are in a geochemical disequilibrium with the host rocks [10, 24, 28], resulting in fluid-rock interactions that primarily include transfers of H, C, and S elements from the fluid to the wall rock by replacement or mineral precipitation. These exchanges cause substantial hydration, carbonation, and, to a lesser extent, pyritization. These common reactions, along with silicification, albitization, and potassic alterations, mobilize major cations (Ca2+, Mg2+, Fe2+, Si4+, Na+, and K+), which are derived either from the in situ destabilization of wall-rock minerals (e.g., [89, 91]) or from external metasomatic input supplied by the fluids. Finite-state absolute gains and losses therefore provide, to some degree, records of the composition of the hydrothermal fluids that percolated over time. Thus, attempts to identify different signatures of fluids and delineate distinct hydrothermal fields are made possible by calculating multielement mass balances on a regional scale from existing lithogeochemical databases.

Absolute gains or losses of Na and K have been found by Bigot [92] to bear the highest potential for ore classification in southern Abitibi, since most mesothermal gold deposits exhibit significant enrichments in either Na or K, although rarely both. Carbonatization and silicification, for instance, are ubiquitous in the CLLF’s surroundings. Na-K metasomatism is seemingly more limited in space and time and is related to auriferous hydrothermalism. Rafini [30] mapped Na and K mass balances in the Malartic and Val-d’Or districts using a compilation of 3488 whole-rock analyses of mafic to felsic igneous rock samples from government (SIGEOM), academic, and industry databases. Mass balance calculations use the precursor-modelling method [93], in which major cation compositions of fresh rocks are predicted for each sample using the ratios of immobile elements Al, Ti, Y, and Zr based on relationships established by neural networks on a large worldwide reference database of unaltered rocks. This method is analogous to isocon in that immobile elements permit predicting cations gains or losses, yet the precursor (unaltered) rock composition is modelled rather than measured (sampling unaltered rocks is not required). The results (Figure 8) suggest logically organized zones that evoke distinct hydrothermal fields, yet their delineation is not straightforward. This is partly due to a highly heterogeneous sampling coverage; a given cell value may correspond either to a single sample or to a predominant trend derived from fifty samples. Moreover, strong local-scale variations are visible, which plausibly reflect the superposed footprints of several alteration events associated with the long-lived CLLF hydrothermal system. Notwithstanding these reservations, such analysis of the finite-state metasomatic regional footprint provides a valuable overview of the predominant hydrothermal events. Eastern regions, where structural fabrics (stratification and schistosity) are east-striking, record large-scale Na-K losses along with very strong local-scale K-gain zones; these patterns have been interpreted as representing a volcanogenic footprint [30]. It is interesting that this metasomatic pattern changes drastically west of the “axial zone” where structural fabrics shift from E- to ESE-striking. Our numerical simulations predict that the influence of the Joannes Segment ruptures ends approximately in this “axial zone” (Figure 4). This suggests that fluid flow triggered by persistent rupture arresting at the Lapa bend would not reach the regions east of the “axial zone,” hence predicting a geographical break in the metasomatic record that is consistent with these observations. This also echoes the fact that Val-d’Or and Bourlamaque goldfields, which are east of the “axial zone,” show apparently distinctive structural characteristics, with the predominance of subhorizontal tensile veins associated with E–W auriferous faults (discussed in Section 5.3). West of the “axial zone,” the presence of distinct ESE-oriented fields north and south of the Lapause Fault is noticeable: the latter exhibits a drastic K-gain corroborated by recurrent microcline occurrences in mineralized rock samples as well as a weaker and less ubiquitous Na-gain. In contrast, the former shows a large K-loss associated with a strong and widespread Na-gain that superposes markedly on deposits where a significant albitization is reported in mineralized veins. These hydrothermal fields match the geometry of the damage zones obtained from our doublet rupture simulations along the Lapause Fault (models 2.a and 2.b, Figure 5(a)). These models predict a dissociation in space and time between hydrothermalisms occurring north (deposits proximal to the Marban mine) and south (deposits proximal to Malartic mine) of the Lapause Fault. These models reflect the occurrence of distinct metasomatic signatures along these two areas.

5.3. Comparison with Other Ore-Targeting Models and Limits

This study focused on modelling CLLF seismic activity using existing geological knowledge. In doing so, several assumptions were made, which limited our results although they offer potential future research topics. Modelling late strike-slip events ensures that fault geometries remained largely unmodified at a regional scale. However, the model remains largely dependent on our current knowledge of regional geology, most notably the traces of faults and their relative importance. In particular, the geometry of southern Abitibi at depth remains largely speculative and will remain an obstacle for precise and representative 3D modelling of fluid circulation and its influence on potential discharge areas. Another critical limitation is the orientation of failure planes. Even if foliation planes surrounding the CLLF are mostly east-striking, variations can still occur at a local scale along shear zones, contacts, and disrupted foliations, which are not accounted for in our interpolation.

Several deposits in the Val-d’Or and Bourlamaque districts (including Sigma-Lamaque), correlating with predicted damage zones, have previously been interpreted as formed during reverse movement on E–W faults associated with N–S shortening [9496]. However, faults recorded in these deposits mostly display oblique reverse movements that are compatible with NW–SE shortening [97, 98], meaning that part of the mineralization in these districts can be related to the late dextral strike-slip deformational event. Moreover, damage zones in Val-d’Or and Bourlamaque districts are triggered by the Rivière-Héva and Lapause Faults, both of which are southeast-striking and steeply dipping. It is thus possible that these two faults were also triggered as dextral faults during N–S shortening.

The model that integrates the regional framework, failure along the main fault, and seismic doublet on second-order faults explains very well the distribution of gold deposits in the Rouyn, Malartic, Bourlamaque, and Val-d’Or districts. However, the Bousquet district remains largely unrelated to positive CFS changes in a dextral strike-slip fault system. Gold deposits in this district are distributed more homogeneously along the CLLF, which obviously differ from the other districts in which most of the deposits are in the surroundings of the CLLF. This likely reflects another form of structural control in the Bousquet district, which comforts the hypothesis that the Joannes Segment is the rupturing master segment exerting a prevailing control on the formation of goldfields at a regional scale. This also corroborates our results in that no damage zone is generated along the rupturing segment itself, which explains why no deposit formed around the fault in the Joannes Segment.

5.4. Coseismic Release of Deep-Seated CO2 Reservoirs

In seismically triggered hydrothermal systems, the episodic enhancement of permeability along crustal-scale fault drains creates a transient hydraulic continuity between overpressured, sublithostatic deep reservoirs and possibly hydrostatic, supracrustal fluids (e.g., [26, 99]) (Figure 9). Supracrustal levels are the locations of orebody formation. In the CLLF area, deep-rooted connections between faults have been tentatively documented [52, 98]. Failure can thus reach deep pressurized reservoirs and release fluid flows through the entire fault system.

Carbon-dioxide-rich metamorphic fluids have deep sources originating from crustal devolatilization (likely from tectonically buried carbonate sediments) during prograde metamorphism [100, 101]. The high CO2 content in gold-bearing fluids, commonly from 5 to 20 mol%, has been reported extensively from fluid inclusion analyses [2, 101103], including into deposits related to the CLLF [48, 104, 105]. These fluids are associated either with late orogenic midcrust reheating or with subduction-related processes and subsequent fluid entrapment in the mantle wedge [5]. In the region of the CLLF, it is likely that the abundant CO2 inflow, reflected by ubiquitous carbonate alterations (e.g., [40, 98, 106, 107]), is supplied by vertical fluid transfers from subamphibolite devolatilized Pontiac sediments enrooted at the CLLF’s footwall (Figure 9), as suggested by the LITHOPROBE profiles [108]. It is worth noting, however, that both midcrust and mantle fluid source models are remarkably well supported by present-day observations of crustal fluid transfers following major earthquakes in active convergent zones. Husen and Kissling [109] and Nippress and Rietbrock [110] reported the upwelling of a fluid mass and a fluid pressure front, respectively, through the entire crust thickness following major thrust-fault earthquakes in Chile. Miller et al. [111], Antonioli et al. [112], and Terakawa et al. [113] observed that the seismic activation of major faults in Switzerland and Italy consistently triggered the release of entrapped CO2-rich overpressured fluids from the base of the seismogenic crust to the upper levels; the poroelastic diffusion of these fronts is considered to be a first-order control on aftershock spatiotemporal sequences. Such cyclic CO2 pulses agree remarkably well with the genetic model of mesothermal gold deposits, in which veins develop from pulsatile infilling of CO2-rich multiphase fluids, as well as with the extensive carbonatization associated with fossil hydrothermal gold systems.

5.5. Multiphase Fluid Flow and Metal Deposition

Phase separation likely takes place during hydrothermal coseismic triggering and the transient upward migration of metamorphic fluids. Phase separation has been proposed as a first-order mechanism in mineralization processes related to hydrothermalism [114, 115], primarily magmatic-hydrothermal systems [116], and mesothermal gold [24, 117, 118]. During the seismic cycle, deep-seated fluids undergo drastic adiabatic depressurization associated with its migration through brittle crustal levels, which triggers phase separation and the partitioning of the CO2-rich vapor phase. Experimental works demonstrated that the fluid’s CO2 content exerts a significant control on the temperature and pressure of phase separation [115, 119], which may hence play a governing role in the depth of gold precipitation. These authors indeed highlighted that CO2-free fluids would undergo phase separation at higher crustal levels than that commonly reported for mesothermal gold deposits. Pokrovski et al. [119] concluded from thermodynamic constraints that Au is partitioned into the vapor phase in the presence of reduced sulfur in acidic-to-neutral conditions, a possible enrichment process associated with phase separation [115]. Zezin et al. [120] demonstrated that the gold solubility in the vapor phase is due to hydrated sulfide complexes, whose stability is closely dependent on H2O partial pressure. In contrast, Hodkiewicz et al. [117] submitted a possible gold precipitation trigger related to phase separation where the partitioning of reduced gas in the vapor phase modifies the oxidation state of the liquid, which destabilized bisulfide complexes and hence gold solubility. Additionally, as a possible gold precipitation trigger, the partitioning of reduced sulfur in the vapor during phase separation would induce a drop in sulfur fugacity which would also destabilize Au bisulfide species from the liquid. Other recent works have documented the decrease in noble metals solubility as a direct consequence of fluid pressure drop and phase separation [24, 121].

In this system, the vaporization of fluids induced by pressure drop in damage zones is a plausible process exerting control on Au solubility and gold deposition, possibly involving changes in oxygen fugacity as explained above. It is worth noting that other parameters have the ability to trigger Au deposition: any change in pH, oxygen, sulfur, or hydrogen fugacity related to wall-rock chemical interactions [89, 90] would tend to destabilize gold complexes either from the liquid or from the vapor phase (e.g., [5, 101, 117]). Although the detailed distinct implication of these various processes and their interrelationships in the formation of mesothermal gold ore still give rise to discussions, it is likely that several processes rather than a sole one are involved at a district scale [30] and even at a deposit scale.

5.6. Poroelastic Modelling

This study focused on the role of coseismic static stress changes in the genesis of hydrothermal gold deposition by hypothesizing a role for undrained crust conditions. However, another aspect is the influence of the transient diffusion of fluid pressure triggered by earthquakes. Indeed, seismically triggered fluid circulation is expected to result in marked pore pressure variations that also modify the stress field and the geometry of potential fluid discharge zones. This presumably also triggers aftershocks in areas not experiencing sufficient positive CFS change [23, 111, 122]. Such conceptual statements about the coseismic interactions between an overpressured diffusive fluid and the triggering of aftershocks are remarkably well corroborated by recent work in seismology. The observation of present-day seismic events from various geodynamic environments demonstrates that the outward propagation of the triggering front from the main rupture zone is governed by the transient diffusion of overpressured fluid [111, 112, 123126]. This was strongly suggested by records of the spatiotemporal propagation of triggering fronts in several present-day seismic events (Umbria Earthquake, Italy, 1999; Vogtland Swarm, Eastern Europe, 2000; Northern Apennines Sequence, 2000; Antofagasta Earthquake, Chile, 1995). The distance travelled by these fronts exhibits a square root relationship to time, reflecting a classical diffusive law [123]. This indicates that the spatial distribution of aftershocks is at least partially controlled by midcrustal fluid pressure diffusion. A consequence is that the undrained crust hypothesis, related to the use of Skempton’s parameter (see (2)), may not hold on the time scale of aftershock occurrences (weeks, months, etc.). Static stress transfers are practically instantaneous whereas the fluid pressure relaxation extends over months and clearly reproduces the observed time decay of aftershocks triggering. As a result, the maintaining of enhanced permeability—and related hydrothermal fluid transfers—near the main rupture zone may actually be the result of coupled effects of purely static stress transfers and stresses related to the transient diffusion of fluid pressure. This is the proper definition of the poroelastic approach [23]. Based on the Landers 1992 earthquake dataset, these authors demonstrated that poroelastic models provided stress mapping having a slightly better agreement with real aftershock locations than did the static stress models (87% versus 65% of epicentres were located in positive Coulomb stress change zones). However, due to the configuration of the poroelastic model and the close interactions between both stress propagation mechanisms, the two models displayed strong similarities. In conclusion, even though static stress models may explain, to a large extent, the spatial distribution of aftershocks [127], further study should consider incorporating poroelastic relaxation into the modelling of coseismic stress mapping in an attempt to better reproduce fossil hydrothermal fields.

6. Conclusion

This study proposes a quantitative framework where repeated seismic ruptures of a crustal window recurrently trigger fluid ascent through temporarily permeable damage zones via the breaching of the fluid pressure differential between the deeper and the upper crustal levels (Figure 9). These zones are located all around the ruptured surface (that extends over the entire seismogenic crust width for earthquakes , [32]). Iterative ore deposition is produced from repeated fluid discharges into the affected areas and is also related to persistent rupturing of the same fault window. This occurs when the fault shows a strong structural segmentation, leading to rupture arrest points on both extremities that remain constant over multiple seismic events. In the Joannes Segment, such robust rupture arrest points are the drastic inflexion of the CLLF around the Lapa deposit (east tip) and the early offset on the Davidson Fault (west tip). Our models markedly suggest that these structural barriers are responsible for the formation of goldfields in the Malartic and Rouyn districts.

The influence of various mechanical and rheological factors on the spatial distribution of coseismic damage zones was also investigated. The role of these factors in coseismic gold mineralizing processes was evaluated through the ability of the models to corroborate known deposit locations. The models tested in this paper explained the distribution of many gold deposits spatially associated with the CLLF: 60% of all gold deposits, including 90% and 73% of the Malartic and Rouyn goldfield deposits, respectively, and 48% of the total gold tonnage, including 95% and 71% of Val-d’Or and Bourlamaque goldfield tonnage, respectively. Implementing geological and structural frameworks improves the models’ correlation with known gold deposits producing a more detailed delineation of zones of hydrothermalism triggering. Doublet seismic ruptures along second-order faults are shown to be important factors in the genesis of goldfields at distances away from the CLLF. It is shown that the combined seismic events along the CLLF and, alternately, the Lapause and Rivière-Héva Faults produce extended damage zones, which explain gold deposition in the Bourlamaque, North-Malartic, and Val-d’Or areas, including the Sigma-Lamaque, Goldex, and Marban major deposits.

Identified hydrothermalism triggering zones, as predicted by the various combinations of main or doublet rupturing segments, show compelling geographical similarities to hydrothermal fields identified through the analysis of the regional metasomatic footprint using mass balance calculations and mineralogical observations. This provides a first-order, valuable validation of the submitted concepts.

The Malartic and Val-d’Or/Bourlamaque goldfields, that is, located, respectively, west and east of an axial “kink” zone where the structural fabric trends change from ESE–WNW to E–W, relate to distinct hydrothermal systems in time and space. This is suggested by the coseismic damage influence of the Joannes Segment rupture ending up at this axial zone. This gives perspective to the fact that Val-d’Or and Bourlamaque goldfields differ from the Malartic goldfield in terms of bulk metasomatic footprint and structural features.

The models are geomechanically validated by calibrating frequency-magnitude seismic distributions of the simulated aftershock sequences with that of actual datasets from analogous active major strike-slip faults such as San Andreas and the North Anatolian systems.

Finally, a likely source of the seismically migrating fluids is the devolatilization of the Pontiac carbonaceous platform that is enrooted at the CLLF’s footwall in supra-amphibolite crustal levels; this matches recent conclusions by Gaboury [105] and Leventis [128].

The promoted coseismic hydrothermal plumbing system was quantified and validated based only on its superior expression. Further work will benefit from the ongoing deep crustal geological acquisition programs (Metal Earth Project) to investigate this model over extended crustal windows owing to reliable constraints on the deep geology of the Superior craton.

Additional Points

Highlights. (i) The role of large Archean earthquakes in the genesis of mesothermal goldfields is investigated in southern Abitibi. (ii) Coseismic fluid-focusing damage zones induced by ruptures of the Cadillac-Larder Lake Fault (CLLF) are simulated using static stress modelling. (iii) Persistent seismic ruptures along the Joannes Segment exert a large control on the deposition of the Rouyn and Malartic goldfields. (iv) Seismic doublets along subsidiary faults are shown to be prime factors in generating goldfields geographically distant to the CLLF. (v) Simulated damage zones correlate well with the distribution of gold deposits and the regional metasomatic footprint.

Conflicts of Interest

This paper forms part of the first author’s Ph.D. thesis carried out at the Université du Québec à Chicoutimi. The work was supported by CONSOREM, the Mineral Research Exploration Consortium, which provided financial and logistical support, and by the Ministère de l’Énergie et des Ressources Naturelles, Québec, Canada.