Dear Christopher, In addition to the valuable observations already made I would like to point out that jīrṇa here probably refers (indeed) to the or a saṁskāra of jāraṇa having been performed, (however) with jāraṇa not in the sense of māraṇa (which is often [partly] parallel to what was called calcination in the past: heating leading to oxidation in the case of metals, to elimination of CO2 and or H2O etc. in the case of some minerals) but very precisely in the sense of swallowing or digestion or assimilation (as mercury is able to dissolve metals including gold but also minerals such as abhra or mica: initially the mercury remains as fluid as before it started to "eat" the gold etc. but at a certain point its viscosity increases significantly).
In Abhinavagupta's "fourth state" the objectivity of śūnyādi-deha-dhātv-antaṃ "permeated" by "consciousness" (having undergone the procedure or saṁskāra of vedha by "consciousness") starts to fall away as it were,
in the "state beyond the fourth" that objectivity is entirely "swallowed" / "dissolved" by consciousness just as gold is entirely "swallowed" by the fluid rasa i.e. mercury.
The tertium comparationis in the case of gold would then not be its beauty or shiny nature but its capability of being "swallowed" by mercury (which remains fluid or druta as long as it is not saturated).
I also agree that the already mentioned rich, encyclopedic Woerterbuch of Oliver Hellwig (Wörterbuch der mittelalterlichen indischen Alchemie. Groningen 2009 Supplements to eJournal for Indian Medicine, 2) is a must for a fullfledged analysis of the fascinating passage you cite as it shows with numerous citations and translations that major texts may differ considerably in the concepts and procedures they accept.
Regarding vedha and its application to the human body (dehavedha) you may also wish to consult Gordon White's The Alchemical Body Chicago 1996.
Jan Houben