Advice on gold recovered (or not) from mineralised quartz vein

[vcubitt]

I have a property not far from Majors Creek NSW, with basically the same geology. The property has a quartz vein extending across it for some 400 metres above the surface and under a hill where it disappears. At its most eroded extent it is about 50cm above the surface and eroded components of the vein extended only some ten metres downslope of the vein, which I think indicates that the vein has not been above the surface for too long. There is mineralisation along the observable length of the vein with some major quartz veins and stockworks along it. I have had rock samples from the vein assayed and it came back 2.2 g/t Silver and 0.1 g/t Gold. The only method I used in collecting rock samples was to pick the most mineralised I could find on the surface or up to 30cm subsurface after breaking through weathered rock. I had tried crushing some similar samples and found only a very small gold which I recall appeared wiry and which at the time I put down to contamination from panning in the nearby Shoalhaven River. More recently I have done more research and learned that gold tends to form in certain parts of a vein, particularly where the vein meets with the altered country rock, so I went back to the vein and gathered some more samples. I crushed a very small amount, a handfull and panned out the attached (which are magnified up to 200x). I am certain they are not contamination this time, but the gold does bear a striking similarity to alluvial gold in the nearby Shoalhaven River - perhaps being from the same geology?

Can anyone with prior experience of gold in granite / quartz veins tell me whether the gold in the attached photo looks like the kind of stuff crushed and panned? I have read that vein gold should be more "nuggety" or rough, but a couple of these pieces appear flat, which could also be a result of the sledge hammer i suppose.... I look forward to hearing from anyone with experience in this, and what steps I should take next. Although it is not enough gold to even weigh, it is literally from only a small handful of rocks - if it is not contamination that is!. Thanks.

 

[SWright]

G'Day

I know the Majors Creek area fairly well. As a geologist I would say the the gold in the photo is likely to have been flattened by the crushing. That said it is also unlikely that its contamination as there would be similar accumulations elsewhere in the area irrespective of there being a quartz vein or not. If there are any alluvial deposits near the vein such as rounded pebbles or sand/grit deposits where the vein is located then there may have been contamination. The Shoalhaven gold is generally very fine and any "nuggets" have grown in the soil, not transported. Also while flattened the shapes are irregular indicating that it has not traveled far.

Araluen

 

[vcubitt]

Thanks for the reply Araluen!

I have tried several more crushing but failed to yield any results - though admittedly I am not crushing very much at all really, just handfuls of rock from different parts of the vein, and if the gold is concentrated rather than finely spread then I may have to do a lot of crushing to find another concentration. My property is 60m (compared to sea level) above Majors Creek, and from what I have read, lies on top of the same geology as Majors Creek (long flat volcanics), but the geology dips to the west and the majors Creek area has been much more eroded over time and shed gold which may still lay under the western areas waiting for erosion to release. I am sure that the vein on my property has broken the surface only in recent times (geologically speaking).

My property is perched above a major tributary of the Shoalhaven and is entirely granite (kain porphyry and toggannogera rhyolite - a lot of it altered) with no alluvial deposits. Strangely enough though several times I have come across rounded stones in decomposed granite up to 50cm below the topsoil when digging postholes in the past - we are 45 metres above the tributary and the Shoalhaven but perhaps these are part of the long since dried up ancient riverbed where river stones have become trapped in rock crevices??? That's the only explanation I can think of... they are not very common though but I am certain they were not put there by human hands.

I have taken some magnified shots (7 photos) of fine gold I have panned from the Shoalhaven - it looks very different to the Gold I (hopefully) crushed out of the vein, to me anyway. Shoalhaven gold is very flat or rounded. Then I have magnified shots of the Gold from the vein crushings (5 photos) - it seems to be to be more edged... the "long" piece in particular is odd to me as I have never found anything "long" like that when panning - I would have thought the river would have broken it down long ago. The last photo is a strange "conglomeration" in one of the rocks - which doesn't look bright enough to me to be gold, but if its not I have no idea what it is. This piece of rock was in the crushing that panned out the gold, along with other small rocks.

Appreciate any more thoughts you may have - particularly on where I should take my next sample from. I have read about hanging walls and all this sort of thing, but i am not very geology savvy! Many thanks.

 

[Ship of fools]

Is it just me or is this very exciting!
Matt T

 

[vcubitt]

Found five more teeny tiny "nuggets" after crushing some more ore ... when I say tiny, I mean tiny - these photos are 100x magnification! I lost three of the "nuggets" being they were even smaller.

Both are really interesting because they are like tiny specimen nuggets - it looks like a bit of quartz and iron still in the bigger one and a small bit of iron on the conical one. Interesting because I have never panned a spec out of the Shoalhaven River with other minerals still attached like that. I am guessing this could give a clue to where the gold particles are sitting in this ore, ie with the iron? The "nuggets" look like gold that has never seen a creek or river - they don't look water worn at all. I have never done any hard rock mining before, so I am pretty confident these are not bits left over from prior pannings / sluicings...

Perhaps I would get more gold out of my chrushings if I had a mechanical rock crusher rather than a dolly pot. The dolly pot leaves most of the rock uncrushed and I wonder how much still trapped gold I might be panning out. Any ideas would be welcome?

Are there any geology heads, or hard rock miners around Canberra who might want to help explore the vein a bit more?