Barbara S. Kowalski MSc thesis abstract

The gold-bearing Metalore shear zone and Golden Highway quartz-carbonate vein in the Beardmore-Geraldton Archean Greenstone Belt occur along the Paint Lake splay faults at the contact between metavolcanic rocks and metaconglomerates intruded by pre-ore diorite.  The Metalore and Golden Highway deposits were emplaced during a late tectonic event.  They consist primarily of quartz, clinochlore, ankerite, potassium feldspars, sericite, pyrite, argentite and chalcopyrite with native gold.  The minerals have been deformed and are cut by at least three healed fractures by fluid inclusions.  Gold typically occurs in recrystallized quartz.  Microthermometric and Raman spectroscopy techniques were used to study fluid inclusions in quartz, calcite, ankerite, chlorites and potassium feldspars.

Six types of fluid inclusions were found to occur in three separate generations of hydrothermal fluid activity in the Metalore and Golden Highway.  The three generations of hydrothermal fluids represented by fluid inclusions are:  (1) pre-ore, low-salinity (<2wt.%) NaCl-CaCl₂ aqueous inclusions with small amounts of daughter mineral and H₂O-CO₂ inclusions with 10 and 40 mole percent CO₂ occurring in the Golden Highway and Metalore respectively; (2) syn-ore, MgCl₂ - H₂O-CO₂ aqueous and vapour rich inclusions with small amounts of daughter minerals with 50 and 80 mole percent in the Golden Highway and Metalore, respectively;  (3) post-ore, CO₂-H₂O liquid-vapour and CO₂ -rich liquid-vapour inclusion with variable CO₂ contents ranging from 10 to 50 mole percent CO₂.  Homogenization temperatures of pre-ore H₂O-CO₂ inclusions during are 220°-230°C and 356°C; syn-ore 266°C; and post-ore 21°C to 66°C.

The aqueous and CO₂-rich inclusions are interpreted to have been trapped as two immiscible phases in three separate generations.  Precipitation of gold may have been induced by pressure, temperature fluctuations and chemical changes from CO₂ effervescence.  Metamorphic fluids are the likely source for the onset of precious-metal deposition from reduced sulphur complexes along the Metalore splay fault and precious- and base-metal deposition from both reduced sulphur and chloride complexes along the Golden Highway splay fault.

A copy of the thesis can be downloaded here