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silcrete

Mining Opalised Fossils 20M (60 Feet) Underground

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silcrete

I love the useful information on the fossil forum. For something different I have posted some pictures of where I "mine" fossils from 20m underground in an old opal mine. I am extending an old mine tunnel to find occaisional opalised fossils.

The first picture below shows my current tunnel and the second picture the "rock" layer that contains traces of opal and opalised fossils. The rock is quite weathered and can be dug out with an electric jack pick.

The majority of fossils that I find do not have gem opal colour play, but they do have exceptional presevation.

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Edited by silcrete

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silcrete

Below are some pictures of an opalised turtle shell fragment that I found last weekend. The first picture shows the specimen as it was found, while the others show the staged process of cleaning it with a microabrasive blaster.

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glacialerratic

Super cool!

Thanks for sharing & please keep us posted!

(remember the "Show us your blue fossils" thread in Member's Collections)

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Vordigern

always fascinated by opalised fossils but I dont think I could work 60 ft down in a space that cramped :) cant wait to see what you find next

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Auspex

Thank you for the peek inside these legendary digs!

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CH4ShotCaller

Excellent place to collect! Do you use the mine as a residence? I remember an article of some who made the mine their home, a great idea!

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Crinoid Queen

That is neat! I love opalised fossils they are some of my favorites! I agree though I could not work down there can you say claustrophobia!

-CQ

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silcrete

Thanks for the feedback everyone.

Vordigem & Crinoid Queen - the space is reasonable in the tunnel I am working on. It is about 2m high and 1m wide. I could make it bigger, but I would have to dig out a lot more rock that appears to be barren. I am fundamentally lazy and this is a labour intensive process, hence I am sticking to a relatively narrow tunnel for the mean time. Ironically it will widen itself over time as the clay walls dry out, shrink and fragments fall off. I will then have to shovel up any loose pieces to maintain access to the tunnel.

CH4Shot caller - I live in a house. As far as I know there is no one living underground in Lightning Ridge (there was one family some years ago). Lots of people do live underground in Australia on opal fields at White Cliffs, NSW and various South Australian fields.

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Terry Dactyll

WOW... What a great way to collect... Your never going to run out of finds...

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silcrete

Terry Dactyll - It is great when you actually find something. The yields are generally very, or extremely, low compared to my experiences with finding fossils nearly anywhere else in the east coast of Australia.

A typical fossil recovery cycle consists of three days work, as follows:

  • Day one - mining barren rock from below the fossil layer. This rock (weathered claystone and sandstone) appears to be barren apart from very rare poor quality partially opalised plant stems and occaisional thin seam opal traces (common opal with no colour). The seam opal sometimes coats fault planes. I excavate about 1 cubic metre of barren rock with a jack pick, shovel and wheelbarrow. The rock is dumped (backstowed) in old mine tunnels.

  • Day two - carefully excavating the fossil layer. A jack pick is used to break out the fossil layer. The rock is then broken apart further by hand and, where necessary, with a geological hammer. Any pieces of potch (common opal) observed are packaged and hauled out of the mine at the end of the day.

Generally I avoid putting the jack pick directly into the fossil layer to avoid damaging any fossils, but now and again it is the only way that the rock can be excavated. Murphy's law says that the layer will be barren until you put the pick in it. I have seen some evidence that this is true (a small broken opalised bone fragment that I never found the rest of, as shown in the second picture below!!!).
  • Day three - microabrasive preparation. At home the samples recovered from the mine are washed with a hose. This removes any loose clay and sometimes makes it easier to see fossils within the rock. Areas of 'rock' that may be obscuring a fossil are highlighted with a texta (see previous pictures) then microabraded under magnification to expose any fossils that may be present. Most of the time microabrasion shows that the samples consist of insignificant opal traces or poorly preserved plant stems. In my recent experience somewhere around 1 to 5% of samples will be a fossil that is worth keeping.

The first picture below shows four yabby (freshwater crayfish) gastroliths resulting from a three day work cycle as described above. Three are in matrix and one is loose. They were the only specimens found.

As far as I know crayfish gastroliths have never been found opalised anywhere in the world other than in the Lightning Ridge region. Historically most potch (common opal) gastroliths were discarded as valueless, while the specimens with colour were cut into cabochons. One miner has told me that he liked gastroliths with colour play because they nearly always polished into good quality clean (sand free) cabochons.

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Roz

I love opal fossils but I had no idea of how much work was involved.. You have earned them..

Thanks for sharing what's involved.. Opened up an unknown world to me..

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silcrete

Once in a while I have a good day mining for fossils, especially when I find an opalised bone like those shown below.

  • First bone - Part of a vertebrae which was photographed wet to highlight the purple colour play. It is about 15mm across.

  • Second bone - About 50mm long and I have photographed it from four sides. It is nearly complete, but unfortunately one end appears to have been naturally shattered and crumbled during excavation. This is not uncommon for opalised fossils, especially when they are found in friable rock and/or there is significant joints or faults in the rock.

Presumably the second bone is some sort of leg bone. Well informed comments on which one it is, and what it might be from, would be apreciated.

Thanks

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jpc

Great tale. Keep up the hard work. So, what do you do with the potch?

I was at Lightning Ridge many many years ago (1989) and fossicked a biyt on the spoils piles. Lots of potch, but I found a few bits of color. They are still one of the highlights of my copllection... and they are not even fossils. The day I was there the gift shop with the opalized plesioasur was closed... dangitall.

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silcrete

Hello jpc,

The potch where I am mining tends to be grey and opaque as shown in the picture below (highlighted with green circles). I just throw it in with the mullock (waste rock) unless it is a reasonable fossil. Most of the opal which shows colour play I keep, like the piece in the second photo (about 80mm long).

Like you, I have bits of potch and colour that I have found on spoil (mullock) piles. I tend to focus my attention on ones that have fossil fragments in them. Opalised plant stems are the easiest fossils to find, then shells and very rarely vertebrate fossils. Finding some fossil fragments amongst the mullock can be a pain, because then you start to wonder what else might lie undiscovered in the mine! It takes significant amounts of time and money to reopen an old mine based on the hope that you will find some interesting fossils.

I am sure that the plesiosaur that you mention actually came from Andamooka in South Australia. The lady that owned the shop had mined there decades earlier. Plesiosaur bones and teeth are also found at Lightning Ridge, but they are nearly always completely disarticulated, like all vertebrate fossils in the area.

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Edited by silcrete

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jpc

Thanks for the explanantion...

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silcrete

Recently I went back to mining fossils in the area which produced the fossils described above. After several days of work, the finds have been a bit sparse.

The first example is an opalised sharks tooth about 8mm high by 13mm wide, found in September 2014. The tip is missing, but it is still interesting because they are quite rare at Lightning Ridge.

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Next specimen was the right femur of a hypsilophodontid like dinosaur, found in October 2014. The first picture shows the specimen after excavation from the mine. The second shows it after it has been microabraded then repaired with paraloid B-72. It is about 80mm long, and 70% complete. The remaining 30% was broken off prior to fossilisation.

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jpc

More really cool stuff. Thanks for sharing.

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kauffy

Wicked cool fossils, nice insight too.

Thanks for sharing.

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Paleoworld-101

OMG!!

They are fantastic! Wow, i am stunned.

:goodjob:

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silcrete

I agree with the cool comments, but 'fantastic' only really happens when the specimen is all precious opal! I'll just have to keep digging and hope that the fantastic specimens are still hidden in the mine somewhere???

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Paleoworld-101

I disagree. Any Australian dinosaur material is fantastic, the holy grail of fossil collecting down under for me. Being opalised (precious or not) is just a bonus. You are very lucky indeed.

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Down under fossil hunter

Kudos, on a fantastic find!

this stuff is always really cool to see.

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Mike from North Queensland

Silcrete - Nice and interesting finds, something I would like to try one day. :envy:

Do you ever look for macro fossils in the slurry after washing ?

Mike

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silcrete

Hello Mike,

I have tried that with mixed results. Generally speaking the concrete agitators that are used to wash the opal bearing claystone tend to cause abrasion damage to most opalised fossils. It is quite rare to see an undamaged specimen recovered this way.

As a general rule, the least damaged pieces are recovered at the face while digging. A further complication is that some mines only produce fossils that have been quite weathered and/or waterworn prior to opalisation. Others produce material that shows exceptional 'fresh' preservation, presumably from being buried shortly after an animal's death. Some mines even show a mix of weathered and fresh preservation.

Matthew

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Plantguy

Hey Matthew, thats some stunning stuff you are finding-congrats! Is the material all Mesozoic aged stuff? I remember seeing examples of opalized belemnites years ago and dont remember where they came from exactly. Anything like that nearby or is that also further south?

Thanks for showing us those unique finds. Regards, Chris

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