EOSC 545 · Advanced Models in Mineral Deposits

Learning Goals

Overview of the roles rock deformation and the development of geological structures play in the genesis of, and exploration for, ore deposits. Offered in alternate years (credits: 3)

Rationale for Course

The rationale behind this course is to give graduate students an overview of the role deformation plays in the genesis and spatial distribution of ore deposits. The course will also review structural geology techniques used to aid our understanding of, and exploration for, ore deposits. The overall focus of the course will depend on the technical background of the students, and the concepts and skills most relevant to their research interests and needs.

Course style and assessment

The course will be a combination of: (i) seminar-style classes with readings and student presentations; (ii) lab style exercises; and (iii) a term paper. All students will be expected to be able to lead the discussion of assigned readings. Students will develop skills related to asking and assessing scientific questions, synthesizing and presenting the results of scientific studies, and debating the assumptions and validity of conclusions outlined in published papers.

Instructors

Kenneth Hickey

Textbook

There is not set textbook for this course, but good review texts include:

Structural Controls on ore genesis, J. P. Richards and R. M. Tosdal, Reviews in Economic Geology, v. 14

Microtectonics by C. W. Passchier

Structural Geology, by H. Fossen

Rock fractures in geological processes, by A. Gudmundsson

Course Content

Structural geology is commonly cited in the minerals industry as being the most critical component to understanding any hydrothermal ore deposit. Structural geology involves the geometric, kinematic and mechanical analysis of rock deformation. There are several ways in which rock deformation is relevant to the understanding of, and exploration for, ore deposits

1. Syn-mineralization deformation
   Deformation can have a direct role in the formation of an ore deposit, particularly in the generation of permeability enabling the flow of hydrothermal fluids through rocks. Deformation also tends to create new rocks surfaces (walls of faults, fractures and microfractures) enabling greater chemical and thermal exchange between fluid and rock (fluid:rock interaction). In some environments deformation can have a significant control on fluid pressure and this effects fluid flow, metal solubility, and phase equilibria.
2. Pre-mineralization deformation
   This primarily involves ground preparation for subsequent fluid flow and fluid:rock interaction. Again, the primary role is determining regions of enhanced permeability for mineralizing hydrothermal fluids. The preferential reactivation of faults along which fluid flow is concentrated is a very important feature in the genesis of many deposits. Another important role is the juxtaposition (by faulting or folding) of chemically, and/or rheologically different units that control permeability or fluid chemistry in later mineralizing hydrothermal events.
3. Post-mineralization deformation
   The deformation of an ore deposit can have a variety of effects. Firstly, it can dismember and rearrange internal elements of a deposit making it difficult to use geological models of ore formation to help exploration (geometric “scrambling” of a deposit). In some cases deformation might completely remove part of a deposit by displacing it great distances laterally or vertically – potentially leading to its preferential erosion. Such geometric “scrambling” is particularly relevant in many VMS deposits as they form in oceanic environments and require deformation to be incorporated into the  continental environment where most exploration and mining occurs. Geometric “scrambling of a deposit is not always detrimental, in some situations deformation can lead to the upgrading of a deposit by structurally stacking ore lenses (via thrusting or tight folding); such an upgrading is a factor in making some iron-ore and SEDEX deposits economically viable. Secondly, post-mineralization deformation can lead to the egress of secondary fluids through a deposit. Such fluids are unlikely to be in chemical (Eh, pH, cation-chemistry etc) or thermal equilibrium with the deposit and can lead to its chemical and mineralogical modification. Such changes can result in the upgrading or downgrading of a deposit. Finally, in some high-temperature metamorphic environments sulfide masses might flow by intracrystalline deformation processes and move laterally or vertically to new structurally controlled locations. This remobilization typically leads to an upgrading of the deposit. At a smaller scale, in somewhat lower metamorphic grade environments, deformation induced dissolution may lead to local mass transfer and “remobilization” of metals and sulfides (“dissolution-precipitation” processes).

The application of structural geology to ore deposits at the most basic level (but not necessarily the least relevant from an exploration or mining perspective) involves unraveling the 3D geometry of an ore deposit. This geometric analysis is “bread and butter” structural geology, but in many deposits it is a critical component to the modeling of a deposit for resource extraction (e.g., many iron-ore deposits). In the simplest case it is about projection of planes and lines in space. In more complex cases it involved kinematic analysis to unravel overprinting paths of deformation and help make predictions about 3D geometry. Kinematic analysis involves understanding the motion taken by all particles from a non-deformed to a deformed state – i.e., deformation paths. It is not concerned with mechanics of how or why motion occurred in anything but a qualitative sense. In its most complex application, structural geology involves the development of mechanical models of rock deformation and ore genesis. Mechanical models of rock deformation incorporate mathematical relationship of forces and loads to deformation paths (and ultimately to geometry). Such models make use of fundamental rheological properties of rocks and rock masses.

Lecture Topics - see UBC Connect course website