To try and understand the intense decrepitation of many samples between 200 and 300 C, 5 samples were observed on a petrographic microscope as grain mounts in RI oil.

One of these samples had extremely high intensity low temperature decrepitation  ( J279)
One sample had very high low temperature decrepitation and was from a productive lode (J270)
One sample had very high low temperature decrepitation  (J276)
One sample had very high low temperature decrepitation and complex decrepitation and was deconvoluted to gaussian component populations (J286)
One sample lacked any low temperature decrepitation (J277)

All of the observations were made at a room temperature of 30 C, which is above the critical Temperature of CO₂, so  liquid CO₂ phases would NOT occur or be visible


J279

numerous FI  smaller ones are 2-5u, typically 2 phase 50% vapour, some have 90% vapour
equant, rounded or -ve crystal euhedral
Numerous very large FI  10-25u, very irregular shapes, empty or gas filled only
some have large bubble - high RI - CO₂?
No CO₂ liquid phase could be observed because the observation temperature was above the critical temperature of CO₂.

J276

numerous FI, 2-5u, equant, subhedral 2 phase 50% vapour
less numerous large 15-20u irregular inclusions
majority are 2 phase, some are empty or gas filled

J270

numerous inclusions smaller 2-5u are equant 2phase, 50% vapour
many larger FI, 5-15u, 2phase, 80% vapour, very irregular with high RI bubble

J277

very numerous FI almost always about 2u size, equant, 2 phase, 10-20% vapour
No or only very rare larger FI, no high RI bubbles

J286  To examine the very wide population in the gaussian fit (image below)

observed at room temp 28 C
very numerous FI, size from <2u to >20
some grains have mostly larger inclusions with few small ones, lower no. of FI
some grains heve extreme numbers of Fi, but smaller, 2-5 u dominate
Multiple quartz generations present?
FI <5u, typically 50% V 2phase, typically equant
also many larger FI (20u) often 2ph with 20% vap bubble, often irregular shape
many larger FI seem to be single phase - high CO₂?
no clear C0₂ liquid phase - too hot at 28 C, but some dark bubbles - CO₂?

De-convolution of sample J276 to 4 component skew-gaussian populations. Black dots are the observed original data points. Yellow curve is the sum of component curves.