Sapphire Formation and Deposit Theory

[Twapster]

This one has been bugging me. My last hunt revealed what I beleived to be a "water worn" sapphire, only to find "shards" of several other sapphires in the same spot. My first reaction was...id like to find where daddy was for the nice broken off pieces were, and why they appeared not water worn.

Then doing some research on how Sapphires are formed, how they are deposited and how far they travel etc to get a better understanding of where to look for them, im now not beleiving theory that they have travelled at all.

http://www.australiansapphire.com/sapphire_formation_theory.htm

The above article validates some of the questions that were in my head

Every rockhound knows that if you put a sapphire crystal in a tumbling machine with grinding compound and let it run for even I0 weeks the sapphire will probably still have it's corners still visible. If you do the sum for a 500mm diameter tumbler doing 40 revs per minute, for 60 mins/hour, 24 hrs/day, 7days/week, for 10 weeks - you will find that your sapphire has traveled some 6,000 kilometres in a dry abrasive environment - but is still not reduced to a round pebble.

and this part

Shape of Sapphire Crystals.

Conventional wisdom has it that sapphire forms in the shape of double-terminated "dogs teeth", or at very least a single dogs tooth form.

Having studied tens of thousands of pieces of sapphire from out mining operations, Jenny can assure you that very little of the sapphire found is actually broken, and that most of the pieces actually are the entire crystal as it was formed.

This "as formed" crystal shape can be chunky, but irregular, or flat like a sapphire platelet - but they all are fully developed crystals without being broken off a larger piece. Many miners, when finding a large piece which is apparently the broken-off centre section of a dogs tooth have been known to exclaim that they wish that they could find the rest of the crystal - when , in reality, they do have the entire crystal.

and this point

We tried some mining techniques which would have had conventional miners questioning our sanity - but they worked, and we found sapphire! We left the alluvial systems and started mining the huge deposits of volcanic ash which blanket the area - and we found excellent sapphire.

I believe that the sapphire was produced from a large number of smaller vents which are located throughout the sapphire producing areas, and that the sapphire never moves, any significant distance from its point of origin at the surface.


Anyway, some interesting reading. Im wondering if anyone has noted these sort of findings in their own gem travels which make you question where and how you should be digging etc.

 

[KarlS]

Intresting article, thanks for posting.
Karl

 

[Twapster]

Makes me think digging a hole straight down in the right spot is the way to go. Unfortunately thats not what most of us want to hear. I can see that anything can travel some distance but really....im starting to think that if you find a GOOD SAPPHIRE, go back several metres and dig to china! lol

 

[Heatho]

In places like Inverell you could pretty much dig a hole straight down anywhere between there and Glen Innes and find Sapphires though the overburden in some places is way too deep. Other places there it's between say 30cm and 5-6m down, though they can be found anywhere between the surface and bedrock but are concentrated on the decomposing bedrock among the Billy Boulders. There are areas of Basalt caps where there would have to be good Sapphire beneath but probably too expensive to remove it.

Dry sieving in the dust up there even smells volcanic and ashy. The dust is Grey and almost as fine as Bulldust. The deposits up there are massive but same as anywhere they seem to concentrate in certain spots, certain colours also only seem to come in certain sizes. I'll take some pics of different layers down to bedrock next time. Just wandering around up there you are likely to find nice stones, they can be sitting anywhere even nowhere near the creek. Could even be really good specking around the higher terraces at places like GG BS and PR after rain.
https://www.prospectingaustralia.com/forum/viewtopic.php?id=2906&p=3
In my Inverell thread you can see what's going into the washplant and it's the Grey Volcanic ashy stuff with small boulders and a bit of Clay. Also at the wash tub area you can see the view behind is pretty flat, that is all flood plain of Frazers Creek, the Creek has probably changed course numerous times over that floodplain over 100 000 years, totally different to GG, being so flat, GG is a very hilly area.

All very interesting stuff.

 

[snafu]

Gday Twapster,

I have been mining sapphires here on the Central Qld Gemfields for the past 25 years and I have known Jim Elliot (the author of the article in your post) for most of that time. It would be an understatement to say that his knowledge & expertise in relation to sapphires is second to none and I think a lot of other miners out here would agree.

Until he actually came up with his theory that sapphires dont move very far from the original source I had not given much thought to the possibility that they rose to the surface through vents rather than 1 or 2 major volcanic events such as Mt Leura (west of Rubyvale) and Mt Ball (north of Rubyvale).

During the late 80s I spoke to a couple of geologists who were working here at the time and they both agreed that the source of all sapphires here was undoubtedly the Mt Leura activity and that the crystals moved with the lava flows to cover a large area until finally erosion formed gravels and so on.

I dont think anybody would have disputed this rather simple explanation until Jim came up with his theory and now a lot of us do believe that he is correct. I have mined in many areas out here and have been puzzled at times as to why there was a large concentration of crystals in particular locations without the obvious associated worn gravels that would indicate an alluvial flow.

There are large operational quarries out here that have enormous deposits of well-rounded worn gravels, but no sapphires. These deposits were the result of great ancient floods that moved gigantic amounts of water and one would assume that sapphires, zircons and other gem crystals would have moved with the flow, but according to the quarry workers it is not so or maybe they are not telling us the real story.

Jeff

 

[Wally69]

Tested some theories of my own out last week and then dismissed them all.

Found sapphire in all quadrants around a big granite boulder. Some worn, some perfect crystals, some fractured chips, some big some small, some in the topsoil above the ash layer, some mid ash and some on the clay layer interface below and the odd one a bit into the clay( but did not generally work this). Was expecting a concentration in one of the quadrants indicating ash layer had been mobile but it was not to be. But then again the zircon and ironstone were rounded.

Then did about 2m3 of river gravel in another location with only a couple of clean fractured small chips.

My current theory is that sapphire was thrown into the air and is evenly distributed in this particular ash layer, with some working its way to the underlying interface and some long eroded layers ending up in the topsoil deposits. Sandblasted surface on some may be from a superheated dust up with ash/glass instead of travelling far, but who knows? Who am I kidding......I really am left not understanding the geology at all.

No doubt there is a honey hole in a nearby creek that I could exploit that fits my traditional view of where to find sapphires and I hope that this theory supports the story of my next trip.

In the New England region, I think the best theory to follow is find a known ash area and dig volume.

My experience at GG is it is more of an alluvial deposit but I did ask myself when I was there, where is the source?

 

[charlie123]

My understanding of sapphire or diamond is they are damn near impossible to track or loam to the source and that the majority of miners on sapphire or diamond are following ancient alluvial beds, either close to the surface or 30 feet down. I agree with the fact that if a sapphire diamond is harder than anything in the river than it would have to be impossible to wear down, wich means they are they shape they were formed as, I also know that you can break the sapphire or diamond just with your shovel with enough force. The old ways of africa diamond mining would smash potential diamonds with hammer to see if they were they were the real thing. My beliefe is that after a volcano thousands of years ago that old rivers may have flown through the bassalt and broken down the rock that holds the sapphire then depossiting it else where. I also find it very hard to understand where a river might have run even 500 years ago let alone 100,000 yrs

 

[Kingsolomon]

I wholeheartedly agree with above article. Although I have found ( not the best photo) two pieces within a few metres off each other , what I think is the same crystal . All the corners line up .. Look the same , maybe coincidence ?

 

[Heatho]

Also one of the fellas a BB was saying part of a Geode type of formation with Sapphires had been found in another country somewhere. Makes you wonder if each Geode type structure had the same colour stones within it.

 

[charlie123]

They say that sapphire colour is caused my the minerals that surrounded them either during or after formation, wich i then thought i could source red/green/blue coloured sapphires from geology maps that show copper/titanium and other minerals mines in the area, but every single sapphire i have found are never the exact same colour out of thousands, the blues can be very similar. crystalized sapphire geode would have to be so rare it is a collectors item, i would say priceless, diamond geode would have to be even better, cut it open and pure light would come out

 

[Kingsolomon]

I saw an epic double dogtooth at inverell , about 15-20 k , clear as the sky . Wish I took a photo to share! And for me . Don't think he's letting it go , so ill take a pic in a couple off weeks to post . Best looking crystal I've seen so far...ill get a photo of the 134 k I saw my friend up there find . Think he will die with that stone in his pocket.. None of these sapphire guys seem to let much go.

 

[Twapster]

Pics would be great. 15k clear, and a stone at 134k...would be an unbelievable find!

 

[Lefty]

Hi all. This is a facinating area, sapphire formation and deposition.

My father had two claims at Russian gully near Rubyvale about 30 years ago and I have just recently pegged in Reward which begins near the town of Rubyvale and runs all the way out to near the Drummond range. I think Jim Elliot's theory makes a lot of sense - for starters, the stones we dug from Russian gully years ago were predominately blue while all the stones I have so far found at the far end of Reward - the opposite end of the field - have so far been green. I am only just starting out but have been told by people who have worked the area for a long time that green stones seem to predominate in my spot. I have also heard of a spot where yellow stones supposedly predominate - you would not expect that alluvial action could sort them out by colour groupings, if they had been transported by water you would expect the different colours to be fairly evenly mixed.

Same goes for Jim's observations regarding the quartzite boulders known locally here as "billy boulders". Jim rejects the idea that their shape is due to stream wear and insists that is the result of being heat-glazed in the volcanic tubes. I have uncovered a large one in my hole - about a quarter of a tonne - and when I was looking at it closely the other week I could only agree with Jim that the surface has a distinct "melted" appearence rather than water-worn.

Very close by, just over the fossicking area boundary fence is the small extinct volcanic cone known as Mount Pleasant - I tend to think that it is the source of my stones rather than the much larger and further away Mount Leura. The mostly blue stones from our old place at Russian gully probably came from a different vent such as Policeman knob perhaps.