Applied Mineral Exploration
Discussion and research relevant to mineral
exploration. Baro Acoustic decrepitation ONLY detects pressure pulses from fluid inclusions.
It cannot and does not detect crystal transition events.
The counts detected by the instrument are in fact pressure
pulses which arise as fluid inclusions burst open when they reach
sufficient internal pressure to overcome the confining strength of the
host mineral. These pressure pulses are caused either by the release of
gases such as CO2, or by the explosive boiling of
superheated water into steam as the superheated water at high pressure
is suddenly released into the 1 atmosphere environment in the
apparatus. The sensor used is sensitive to pressure pulses in the air
column of some 8 cm which separates the sample from the sensor.
Because the pathway between the sample and the sensor is through
air, a fluid, shear waves generated by crystalline transitions in the
sample are not detected. This is beneficial as it ensures that ONLY
pressure pulses from the gas expansion as fluid inclusions explode are measured.
There have been comments made that the baro-acoustic decrepitation method only measures crystal restructuring events, such as dauphine twinning transitions in quartz. Such comments are completely wrong as crystalline transitions cause only shear waves in the quartz. And shear waves cannot be transmitted through the fluid (air) which isolates the sample from the sensor. Crystalline transitions cause only minute volume changes in the crystal which translate into minute pressure changes which are well below the detection limit of the pressure sensor.
There have been comments made that the baro-acoustic decrepitation method only measures crystal restructuring events, such as dauphine twinning transitions in quartz. Such comments are completely wrong as crystalline transitions cause only shear waves in the quartz. And shear waves cannot be transmitted through the fluid (air) which isolates the sample from the sensor. Crystalline transitions cause only minute volume changes in the crystal which translate into minute pressure changes which are well below the detection limit of the pressure sensor.
July 2011