Welcome to opalholicsanonymous.com where opal season lasts forever.

Pertinent scientific papers doing analysis like this one are where I get my answers off the top of my head.
My Google Alert failed again to notify me of publishing's after rewording what I requested apparently. I found this out of images on a separate search.
(hard to work with broken tools, but if controlling access to information is the goal, the tools are working well)

... "Taken together, we consider this evidence to indicate a Neogene age for Lightning Ridge opalization and by inference for the opalization of the extensive opal deposits of the Great Artesian Basin in Australia."....

Im going to make you go give George a click too. https://www.mdpi.com/2075-163X/13/12/1471
Its worth making a stop at the paper publisher for the pictures alone. I downloaded the paper for the science of our beloved Gems. from my files of woods I donated to his research on opal formation.

https://www.mdpi.com/2075-163X/13/12/1471

great - thanks for posting mate

I have couple interesting fossils from LR which I'm trying to ID and there is a lot of good info (still reading)
*btw. watch the video I posted about the growing opals

The one place Mead dug here, other than up by Fossil in the John Day Beds, they discovered dozens of new species that were not the same as John Day or were found here first. A lot of students screening and using magnifying glasses around the feet of the deposits or old bench placers. The best Ive seen come out were two cat teeth and he looked for 10 years between the two of them without another.