Jordan Pawlowski, MSc

Pyrite (FeS₂), Earth's most abundant sulfide mineral, forms under a diverse range of conditions. Contained within pyrite are trace elements incorporated either as part of the crystal lattice, or as nano-inclusions. Trace elements hosted in pyrite include precious metals, heavy metals, and metalloids. Despite the role of pyrite as a common host mineral in many economically important ore deposits such as orogenic gold, epithermal, and porphyry deposits, there is limited experimental data that measures how trace elements are distributed between pyrite and hydrothermal fluids. 

We have employed experimental methods to equilibrate pyrite with simulated ore-forming hydrothermal fluids from which we can measure partition coefficients systematically. Our approach comprises a sealed silica glass ampule containing a trace element standard solution, NaCl, water, and a pyrite-pyrrhotite-magnetite buffer mixture. A coarser grained pyrite seed is also added, and physically separated from the buffer using silica sand. Ampules are sealed under low vacuum, then placed in a box furnace and heated from ~50 °C to the intended run temperature over a period of 1 to 2 hours. Samples are then held at high temperature until equilibrium is achieved. Run temperatures will be consistent with those seen in ore-forming hydrothermal fluids, approximately 200-400 °C. Once quenched, the experimental run product fluids and pyrite seed will be separated and prepared for SN-ICPMS (fluid), LA-ICPMS, EMPA and SEM (pyrite) analysis. Work to-date has focused on refining the experimental design to maximize the achievable temperature. 

Partition coefficients will be calculated for each element from both direct measurements of the pyrite and fluid compositions, as well as using a mass-balance method that relies solely on LA-ICPMS measurement of the pyrite phase. Results will provide a new constraint on pyrite-fluid partitioning that can be used to illuminate the conditions of mineralization.