Hi everyone,
I'm hoping we can discuss and share knowledge relating to what geological features to look for when out fossicking.
I live in Central QLD and we have quite a lot of minerals and gems that occur in the area.
I know of a quartz crystal deposit located within 15min drive of Rockhampton, Lowmead Amethyst which is around 2.5hr drive, Mt Hay Thundereggs - 45min drive, Marlborough Chrysoprase - 1hr drive, not to mention the petrified wood, chalcedony and agates you can find in creek gravels.
Now I've been trying to do some research, to find some new ground to potentially look around on, and I've started at the "top" by looking at Geology maps and the type of Rock deposits in those areas. I've plotted the known deposits on a map and then overlayed the geology map to determine the rock types this formed in.
Given we are only "surface" fossicking, I have only considered the surface geology.
I've got a hunch I should be able to find some quartz crystal deposits in my area so I'm going to use that to base my next line of questioning.
Disclaimer - I'm no expert, so please correct the below if it is wrong.
Quartz crystals are generally formed inside igneous rock or with geothermal water. With igneous rock, as the magma body cools slowly, larger crystals are able to form. (Bigger crystals form due to slower cooling of the rock - geology 101).
The geothermal water scenario is when silica dioxide dissolves in water at high temperature and pressure, and as it cools / pressure drops, crystals can start to form.
The CQ area was very volcanic in the past, judging by all the fault lines and extinct volcanic plugs littering the landscape. I know of a few spots where marine fossils are found, so its also pretty likely there was geothermal water in the area at some point in the past. (bit of an assumption there i know).
Now quartz being a high silica content mineral, would be more "likely" to occur in Felsic (high silica content) rocks - such as Granite. I'm pretty sure the Lowmead amethyst deposit mentioned above formed in granite rock, and is now shedding the crystals due to decomposition of the granite.
So after looking at the maps and geology, I have narrowed down areas where large granitic rock intrusions have occurred, alongside known crystal deposits. How do we go about further narrowing the field of search?
Currently only using the 1:2M Surface Geology overlay.
Apart from getting out and wandering the hills looking for something that would suggest larger crystals formed in the rock, what other things should I be on the lookout for?
I'm hoping we can discuss and share knowledge relating to what geological features to look for when out fossicking.
I live in Central QLD and we have quite a lot of minerals and gems that occur in the area.
I know of a quartz crystal deposit located within 15min drive of Rockhampton, Lowmead Amethyst which is around 2.5hr drive, Mt Hay Thundereggs - 45min drive, Marlborough Chrysoprase - 1hr drive, not to mention the petrified wood, chalcedony and agates you can find in creek gravels.
Now I've been trying to do some research, to find some new ground to potentially look around on, and I've started at the "top" by looking at Geology maps and the type of Rock deposits in those areas. I've plotted the known deposits on a map and then overlayed the geology map to determine the rock types this formed in.
Given we are only "surface" fossicking, I have only considered the surface geology.
I've got a hunch I should be able to find some quartz crystal deposits in my area so I'm going to use that to base my next line of questioning.
Disclaimer - I'm no expert, so please correct the below if it is wrong.
Quartz crystals are generally formed inside igneous rock or with geothermal water. With igneous rock, as the magma body cools slowly, larger crystals are able to form. (Bigger crystals form due to slower cooling of the rock - geology 101).
The geothermal water scenario is when silica dioxide dissolves in water at high temperature and pressure, and as it cools / pressure drops, crystals can start to form.
The CQ area was very volcanic in the past, judging by all the fault lines and extinct volcanic plugs littering the landscape. I know of a few spots where marine fossils are found, so its also pretty likely there was geothermal water in the area at some point in the past. (bit of an assumption there i know).
Now quartz being a high silica content mineral, would be more "likely" to occur in Felsic (high silica content) rocks - such as Granite. I'm pretty sure the Lowmead amethyst deposit mentioned above formed in granite rock, and is now shedding the crystals due to decomposition of the granite.
So after looking at the maps and geology, I have narrowed down areas where large granitic rock intrusions have occurred, alongside known crystal deposits. How do we go about further narrowing the field of search?
Currently only using the 1:2M Surface Geology overlay.
Apart from getting out and wandering the hills looking for something that would suggest larger crystals formed in the rock, what other things should I be on the lookout for?
I’m always looking for signs of crystal points popping up in the earth and then trying to follow them to more concentrated sources. The one time I’ve had success finding a spot to dig where no one else has dug before was when I found a big Quartz vein that opened up into a crevice within a boulder which I’ve started prying open. I’m not sure if this is a pegmatite I found? Or if pegs and veins are different? I’m still learning and finding it hard to hold all the new words and concepts in my brain 
