Combining paleofluid chemistry and rock characterization to constrain genetic processes in tungsten deposits.

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Ore deposits are major geochemical anomalies. Precipitation of metal-bearing phases can be spatially and temporally localized. However, the geochemical processes that lead to metal precipitation can leave signatures over ranges of several kilometers and over thousands to millions of years. The systematic spatial and temporal variability in these systems provides indication of which are the main geochemical processes at work and what are potential good indicators of mineralization and vectors toward fluid and heat sources. The main objective of this research program is to combine the chemistry of ore fluids with the chemical and mineralogical composition of host rocks to constrain some of the major controls in ore deposit formation. In the next five years I will focus on studying tungsten deposits. Tungsten is a critical metal, with Canada being one of the five major producers worldwide and NWT being a major exporter historically. The conditions under which tungsten occur geologically are fairly common (thick metasedimentary packages with associated reduced magmatism). However tungsten deposits are highly localized. In particular the Tungsten belt in the border between NWT and YK constitutes the only major tungsten-producing province in western North America. Therefore this program will focus on (1) determining whether tungsten fertility is controlled at the hydrothermal stage or at an earlier stage (at fluid-melt partitioning or melt source) and the implications for global distribution, (2) determining the hydrology of hydrothermal systems formed at deep conditions using tungsten deposits as an example and (3) define which elements characterize tungsten mineralizing fluids and at which scale they are likely to cause anomalies.The approaches used in this project towards chemical characterization of fluids will include petrography, fluid inclusion thermometry and laser ablation inductively coupled plasma mass spectrometry. These techniques will provide information on how the PT conditions of entrapment, volatile and cation content of the fluid vary in tungsten-rich vs tungsten-poor systems and how they change with time and space. Combination with secondary electron microscopy and ion microprobe will provide paired information on how changes in the source of fluids may influence the evolution of paragenesis and fluid chemistry over time. Further characterization of fluid-rock interaction in the host rocks will be achieved through portable techniques (X-ray fluorescence), whole rock analyses through conventional XRF and digestion methods, XRD and SEM. Combination of fluid chemistry with hand sample and ore scale mineralogy and chemistry will provide information on which elements are likely to be buffered locally and which ones are likely to cause distal anomalies associated with these deposit types.