Thomas Chudy, PhD student, University of British Columbia



My geological career commenced in October 2002 at the Institute for Geology and Palaeontology at the Julius-Maximilian University of Wuerzburg (Germany). After five years of undergraduate and graduate studies I received my diploma degree in Geology in the winter of 2007. While my undergraduate studies emphasized geological mapping, structural analysis and petrography, my focus turned to economic geology and mineralogy after my pre-diploma. As an undergraduate student I completed a geological and structural mapping project around a diatreme in southern Germany for the County of Bad Kissingen under the supervision of Prof. Volker Lorenz. Shortly after my pre-diploma, I went to South Africa to conduct a two-month mapping project as partial fulfillment of the diploma degree. This was supervised by Prof. Reiner Klemd (University of Wuerzburg, Germany) and Prof. Jay Barton (then Rand Afrikaans University, South Africa) and was sponsored by DeBeers Consolidated Mines. The goal was to investigate the regional (structural) geology surrounding the DeBeers Venetia kimberlite pipes, which are situated within locally confined nappe structures in the high-grade gneisses of the Limpopo Belt. After this mapping project, and before commencing my diploma thesis, I spent time as an intern at the Federal Institute for Geosciences and Natural Resources in Hannover (Germany). Here, I was responsible for the petrologic characterization and classification of (historic) PGE-bearing samples from ultramafic pipes from the Bushveld Complex (South Africa), with an emphasis on the mode and occurrence of the PGE-alloys. Subsequently I focused on my diploma thesis, which dealt with the tectonometamorphic evolution of my mapping area. Detailed petrographic examination in conjunction with thermodynamic calculations (P-T pseudosections) allowed me to construct pressure-temperature paths for three different lithologies from this area. The scope of the thesis was extended and geochemical investigations of amphibolites and geochronological studies of metamorphic monazite were included to cover all aspects of the geological record. Based on my experiences in the industry during my studies I decided to continue my career in a direction where I can combine academic research with the mining industry. My current PhD project is an academia — industry liaison in which financial and technical support is provided by the sponsoring company (Commerce Resources Corp. and Zimtu Capital Corp.) as well as NSERC. My proposed and partly completed research (see below) is congruent with the knowledge sought by the industrial partner at the various stages of exploration and facilitates the resource development as well as further exploration. Any findings from my PhD research are continuously evaluated and implemented by the project geologists (Dahrouge Geological Consulting) which facilitates the advancement of the project in areas such as structural modelling, resource model and metallurgy.

After my Ph.D. I plan to continue my career in a similar manner in British Columbia where all requirements for an interesting future are met including the rocks, a growing academic expertise, an active geological survey and the mining industry.

Project: The Petrogenesis of the Fir Carbonatite System, East-Central British Columbia

In my Ph.D. project I am investigating the petrogenesis of the Blue River carbonatites (BRC) that are situated within the Monashee Mountains of the Omineca Belt, south-eastern British Columbia. They intruded metamorphosed clastic sediments and amphibolites of the Late Proterozoic (Hadrynian) Horsethief Creek group and now form variably deformed and folded lenses and sills of up to 80 meter in thickness.

Carbonatite-alkaline rock complexes are known to host a range of commodities and they attracted much notice in the past four years because of the strong demand for rare earths elements. The main focus of my studies lies on the Fir carbonatite system which stands out in particular for its high Ta content (weighted average of 200 ppm Ta) which is unmatched by any other carbonatite occurrence in the Canadian Carbonatite belt or even worldwide, at least with respect to the consistency of grade.

The accumulation of particular elements in a carbonatite is controlled by a variety of magmatic processes and the tectonic setting in which their parental melts are generated. Contrary to the widely known textbook opinion, which chiefly describes a central-type complex of carbonatites and associated ultramafic-alkaline rocks that intruded along crustal-scale lineaments within a consolidated craton (e.g., Winter, 2001), a steadily growing number of different tectonic settings has been discovered to host carbonatite complexes (e.g., Chakhmouradian et al., 2008). Further diversification of our carbonatite understanding provided a mineralogic-petrogenetic classification which is based on the distinction of several different clans, all described by a particular mineralogy/mineralization (e.g., Mitchell, 2005). This diversity obviously precludes a generalization of the petrogenesis of carbonatites which is particularly true with regard to the geochemistry and the mineral chemistry (for latter see Reguir et al., 2011). It is thus necessary to investigate each occurrence on its own merits in order to establish potential links or indicators for the enrichment of strategically important metals.

My petrogenetic-mineralogic investigations encompass (1) the petrography of all units potentially related to the Fir carbonatite system including various types of fenites and carbonatites, (2) a fabric analysis of the carbonatite textures, (3) (limited) whole rock geochemistry of various carbonatite units and fenites, and (4) the mineral chemistry of rock-forming and accessory phases with an emphasis on the Nb-Ta mineralization.

The high degree of deformation in the Canadian Carbonatite belt certainly adds more complexity to the matter and has been addressed in the first part of the Ph.D. project. Through petrographic investigations focusing on the (micro-)fabric evolution a general sequence of events has been inferred. The oldest texture reflects a high-grade metamorphic event which transformed the carbonatite into a gneissic rock. This texture has been overprinted by retrograde shearing and folding which resulted in strongly mylonitized rocks. The mylonitic shear zones are a very important piece of information that can help unravel the complex deformational history of this carbonatite system which is also a requirement for a realistic deposit model.

The petrographic findings have been followed up by geochemical investigations, which focused on mineralogically different units (e.g., calcite vs. dolomite carbonatite) but included also the textural aspect (e.g., gneissic vs. foliated). One interesting outcome of this investigation is that mylonitic shear zones are preferentially developed in a dolomite carbonatite unit with a particular geochemical composition and mineralization, which is not easily detectable in hand specimen.

Mineralogical investigations including microprobe analyses revealed that the differences in the major carbonatite units are also reflected at the accessory level as evidenced by variations in the composition of the Nb-Ta phases and their paragenesis. This knowledge allows a discrimination of various ore-type zones at the deposit scale by using specific geochemical signatures and it allows to evaluate these variations with regard to the magmatic evolution.

The results from the different parts of this Ph.D. project are already a valuable contribution to the continuous improvement of the exploration process and resource development including metallurgy, since they directly relate to aspects such as structural modelling of the deposit, ore-type distribution and ore composition. Another important aspect is the potential alteration accompanying high-grade deformation and mylonitization, which directly relates to the ore distribution, especially in deposits in the Canadian Carbonatite belt. These results are also very encouraging from the academic point of view and implicate further detailed petrogenetic studies. The goal is to elaborate the mineralogical characteristics and a potential clan association of this carbonatite system in order to propose a genetic model and improve future exploration for strategic metals.

Roundup 2013 Poster: The Petrography, Geochemistry and Mineral Chemistry of the Fir Carbonatite System, east-central British Columbia: An Update of Current Knowledge with Implications for Deposit Modelling