just starting said:
Just another ...... rock ?
I was told colour in the quartz is an indicator of gold from the reef it came from and quartz that is just white with barely any colour to it won`t bare gold .
Is this likely to have come from deep in the ground or closer to the surface ? I am just trying to understand how to read the quartz.
Thanks .
FOZ
"Reading" the quartz is almost impossible. "I was told colour in the quartz is an indicator of gold from the reef it came from"
What do you mean by "color". Quartz itself can have colour (e.g. rose quartz, amethyst), but I suspect by colour you mean inclusions of other minerals. In some areas the presence of other SULPHIDE minerals - or graphite - can mean the quartz is more likely to contain gold. In others gold can just be in pure white quartz. Often there is a general rule for a particular goldfield. Pure transparent quartz like glass rarely contains gold.
"and quartz that is just white with barely any colour to it won`t bare gold" . Nope, not so - it can be loaded with gold - look at this sample:
There are reasons for some of these things. Quartz in pure form is transparent - however the quartz typical of quartz veins looks white because of all the little bubbles of the original fluid that formed it (and any gold in it) - they break up the light. Whether other minerals occur with gold depends a bit on the chemistry of the ore fluids that deposited the gold. Gold in quartz veins is often dissolved in a form attached to sulphur. If it hits carbon (graphite) the gold dumps out. If it hits iron minerals like magnetite it dumps out. And because of the sulphur in the ore solutions, often sulphide minerals dump out with (or near) the gold - copper sulphides like chalcopyrite, lead sulphides like galena, zinc sulphides like sphalerite, iron sulphides like pyrite, arsenic-iron sulphides like arsenopyrite, or antimony sulphides like stibnite. So this is why gold is often spatially associated with quartz that contains sulphide minerals or graphite.
However there is another way that gold can dump out, and in those places it may be just gold in quartz (as in the photo). But one process of dumping out gold will usually dominate in a particular goldfield, so you need to look at old ore on mine dumps (crack a few lumps of quartz ore). For example in Victoria, at Cassilis it will have lots of different sulphides, at Bethanga mostly lots of copper sulphides with some other sulphides, at St Arnaud or Percydale only moderate amounts of galena pyrite and arsenopyrite, at Ballarat just traces of sphalerite, pyrite and arsenopyrite. In general in central Victoria many goldfields only have traces of sulphides in white quartz, or just white quartz. But 99% of white quartz has no gold just the same....but it is more likely to contain gold than the surrounding rock, especially where there is no quartz gold will be unlikely.
This shows how the mineralogy of gold veins varies across the State of Victoria:
