Structural Geology Applied to Mineral Exploration
Monday, November 18
8:30 a.m. to 4:30 p.m. – Room 309A
Regular rate: $450
Student rate: $75
Workshop Organizer: Les chapitres étudiants SEG du Québec
Structure exerts critical control over many types of mineralization, at both the scale of the deposit and of the geological provinces. This workshop will address the concepts of structural geology and Archean and modern geodynamics, with an emphasis on economic geology, in order to provide participants with concrete tools for exploration. Case studies of major Quebec and international deposits will also be presented.
8:30 a.m. – Important structural concepts and their application to gold deposits – François Robert (FR Geo-consult)
Abstract:
This two-parts presentation is intended as a practical review of structural elements that are important in exploration. The emphasis is placed on field and drill core observations, and their application at different scales. A sample suite will be available during the breaks to illustrate some of the concepts discussed.
The first part will introduce a few fundamental concepts and will discuss the following structural elements: foliation, lineation, shear zone, and veins. The influence of anisotropy and competency contrast on the development of these structural elements will also be addressed. The objective is to ensure rigorous application in the field.
The second part focuses on the application of these structural elements in a greenstone belt context, supported by examples covering a range of styles of gold mineralization. We will illustrate how the different structural elements can be integrated in the analysis (or prediction) of deposit-scale geometric architecture and structural controls of mineralization. The effects of overprinting deformation on mineralization will also be discussed.
10:15 a.m. – Break
10:30 a.m. – Important structural concepts and their application to gold deposits – following – François Robert
12:00 p.m. – Lunch
1:30 p.m. – Deformation and Modification of Volcanogenic Massive Sulphide Deposits – Bruno Lafrance (Université Laurentienne)
Abstract:
Volcanogenic massive sulphide (VMS) deposits are formed in a variety of geodynamic environments, including arcs and back-arc basins. Many of these deposits were deformed during the closure of these basins by continental collisions. The volcanic and hydrothermal architecture of these deposits, along with their composition, have influenced the development of deformation structures. Consequently, VMS clusters are typically less competent than the surrounding volcanic rocks. During the deformation process, stress is concentrated in the sericite and chlorite alteration envelopes that surround the massive sulphide clusters. These clusters subsequently become shear zones and creep towards the regional fold hinge or are deformed in parallel with the stretching lineation. In and around the clusters, foliation may occur as a result of the flattening of primary heterogeneities and the transposition of sulphide-rich beds. As the host rocks are more competent than the sulphide clusters, piercement and Durchbewegung (sulphide breccia) structures can also form at the contact between these units. Certain features of VMS, such as the telescoping of massive sulphide lenses or the elongation of lenses, may have a tectonic or primary origin. In order to reconstruct the volcanic, hydrothermal and structural architecture of VMS, it is therefore necessary to undertake a detailed analysis of the primary and secondary structures. This is all the more important as the structural analysis of VMS is hampered by the dynamic recrystallization of sulphides at low temperatures, which tends to obliterate pre-existing structures, by the limited development of foliations in the surrounding volcanic rocks and the pronounced localization of deformation in mineralized zones. During this course, the formation of primary and secondary structures in VMS will be discussed in order to facilitate the reconstruction of their volcanic environment and their modification during deformation episodes.
2:30 p.m. – Break
2:45 p.m. – Structural Geology and Evolution of the Upper Beaver Gold-Copper Deposit, Ontario – Ruth Orlóci-Goodison (Université Laval)
Abstract:
The Upper Beaver deposit is a ca. 2680 Ma intrusion-related gold-copper deposit located in the Abitibi Greenstone Belt, Ontario. The deposit is associated with the Upper Beaver Intrusive Complex, which was emplaced in the hanging wall of an extensional listric fault rooted in metavolcanic rocks of the 2704-2695 Ma Blake River assemblage. The fault likely formed during the development of an overlying sedimentary basin into which the fluvial sedimentary rocks of the 2679-2669 Ma Timiskaming assemblage was deposited. The Upper Beaver deposit was rotated to its current position during the formation of a post-Timiskaming fold, the Spectacle Lakes Anticline, during an episode of deformation associated with the development of the Larder Lake-Cadillac Deformation Zone, located 7 km to the south. The Upper Beaver deposit is overprinted by the axial planar cleavage of the anticline but is less deformed than other gold deposits located along the deformation zone. Alteration and other pre-existing planar anisotropies enhanced strain partitioning and the development of folds and fabrics in strained mineralized zones. Steeply-dipping, sericite-altered mineralized zones developed a continuous foliation surrounding boudinaged and recrystallized quartz-calcite-anhydrite veins, whereas strong, shallowly-dipping, stratiform, skarnoid mineralized zones developed a wavy disjunctive cleavage and deformed mainly by folding. The mineralized zones acted as pre-existing anisotropies during deformation, and their orientation and composition were key factors in the development of structures at the Upper Beaver deposit, which can be used as a guide for interpreting the development of structures in similar but more complexly deformed deposits along major deformation zones. This presentation will serve as an individual case study in the application of structural geology to the understanding of ore deposits.
3:30 p.m. – Structural Controls on Emplacement and Modification of Ni-Cu-PGE Deposits – Carol-Anne Généreux (Terrane géoscience)
Abstract:
This presentation will focus on the effects of deformation and metamorphism on the formation and modification of Ni-Cu-PGE deposits. A brief summary of Ni-Cu-PGE deposits will be presented, with a focus on the primary features that are critical to a comprehensive interpretation of deformation history. Various case studies will be presented to illustrate how structural and metamorphic processes can affect Ni-Cu-PGE deposits at various scales. Emphasis will be put on the interpretation of field and drill core observations, such as structural fabrics, sulphide mineral assemblages, base and precious metal distribution, and deposit geometry.