Quartz Crystal with Chlorite(?) intrusion

Found this on a large scale mine overburden dump a few years ago & am trying to identify it. After a bit of research it seems to be quartz with chlorite intrusion but I could be wrong. The crystals are very small, around the size of a match & the matrix seems to be sandstone. This is the only sample I could find, it could have come from an area over several square kilometers in size.

Hopefully some of the forum members might know what it is.

Gday Ditch! Nice find! To me, id say you have a quartz plate from an open cavity vein, meaning a thin quartz vein with a gap in the middle, but a tight gap. Most likely the vein had several plates like youve within the area, where some nice bigger crystals may appear! Is the host rock a sedimentary (like sandstone) or igneous rock? (granite)
The green tint may be where chlorite has been suggested

AtomRat said:

Gday Ditch! Nice find! To me, id say you have a quartz plate from an open cavity vein, meaning a thin quartz vein with a gap in the middle, but a tight gap. Most likely the vein had several plates like youve within the area, where some nice bigger crystals may appear! Is the host rock a sedimentary (like sandstone) or igneous rock? (granite)
The green tint may be where chlorite has been suggested

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Hi AtomRat,

The geology of the area (Woodsreef near Barraba) is quite confused, right on the eastern side of the Peel Fault. The host rock seems to be fine grained & very hard but I don't think it is granite. There is granite in the area but 20 km further to the east.

A Tertiary riverbed up to 20 meters thick is sitting on a lens of altered Harzburgite so the host rock could be metamorphic, but the Harzburgite was altered to Schistose Serpentinite around 300 million years ago & the tertiary deposits are around 65 million years old.

Bit hard to tell where the sample was originally situated as it was on top of around 70 million tons of overburden from the mine. It could have come from the Tertiary bed which they cut through, the lighter layer in the middle of the photo below looks to be same type & colour but I can`t get a closer look.



The area is not known for producing quartz crystals & I have never found any apart from this sample. It is a gold bearing area with a few reefs mainly associated with chert around the perimeter of the Serpentinite lens but gold has reportedly been found in the Tertiary gravels.

A close up of the host rock



A view of the surrounding area. The pit goes down another 10 levels under the water. Each level is around 10 meters high.



It has me stumped as I have not seen any other rocks like it in the area. A mate works for a drilling company so I might pass it on to him & have their Geo look at it.

Cheers.

No signs of quartz veins anywhere? Or is that what you mean by the reefs. If theres quartz, there will be crystals. Is it possible the host rock is limestone?

Nice mineral specimen whatever it may be.

AtomRat said:

No signs of quartz veins anywhere? Or is that what you mean by the reefs. If theres quartz, there will be crystals. Is it possible the host rock is limestone?

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Closest limestone that I know of is at Attunga, 60 km away. Plenty of quartz about the surrounding area, always picking up samples, but this is the first time I've seen crystals. Going to go out there for a bit of a fossick during the week & will keep an eye out for crystals.

Not much of a geologist, but this has sparked my interest, will have to do a bit more studying on the subject. Thanks for your input, much appreciated.

Some veins will be tightly sealed quartz matrix, but you can follow or locate seams that open up a little or a lot, especially in sandstones. Good luck mate, study the areas of serpentine as well and any pegmatite intrusions!

AtomRat said:

No signs of quartz veins anywhere? Or is that what you mean by the reefs. If theres quartz, there will be crystals. Is it possible the host rock is limestone?

Click to expand...

G`day AtomRat,

Looks like you may be right about the limestone. Had a good read of a Exploration survey for the area from 1982. Seems there is limestone at depth, explains why the sample was on top of the overburden. According to the report the limestone has been altered to Jasper at the surface which is full of quartz veins.



Also a high possibility that the intrusion is Chlorite. From a 1984 survey.



Going out for a dig tomorrow, will let you know how I go.

Cheers, Ditch