He only has one rock and said it is not worth doing a fire assay. If using cupellation he could lose any small amount of gold anyway:
Recently I leaned that fire assays using cupellation are inconsistent, and they absorb some of your precious metals! So I’m not a fan of that method.
Some people also use cupellation to remove impurities from gold.
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A great wee video - I enjoyed watching it even though I know this stuff. The man presents his statements clearly so that any novice can understand and get a really good idea of how to text a specimen…actually I like that specimena nd would love it for my rock collection!
I am not a fan of breaking apart a ri=ock specimen if it is proven to have gold in it because gold specimen rock is worth so much more than the gold value so my advice to anyone is that if they have a mineral specimen known to contain gold then keep it as it is.
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Just adding on another video with very clear up close view of ore specimens.
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Slightly off subject but pertinent i think… i have been told that at Macraes in central the gold in the quartz veins occurs as very small grains, generally totally enclosed in hard quartz. In addition, most of the gold is contained in sulphide minerals pyrite or arsenopyrite which are in turn totally enclosed in quartz… The main cause of gold loss was when gold was not liberated from the sulphide minerals, as it could not be dissolved in cyanide.The schist surface zone (upper 10-20 m) has been invaded by oxygen-bearing rain water which oxidized many of the original iron-bearing minerals leading to the brown colouring characteristic of Central Otago landscape. This oxidation affects sulphide minerals in quartz veins, and results in natural liberation of gold from the sulphides. Beneath this oxidized zone, schist is grey and sulphide minerals are intact. Early hard-rock miners extracted gold readily from the oxidised zone because of this natural liberation process, but gold returns dropped off dramatically when they penetrated into sulphide-bearing veins in the grey schist beneath. Hence, most historical gold mines became quickly uneconomic as they went deeper…Many of the hard rock mining undertaken in the old days gold loss was high.Even today Macraes loss is around 15+% …which makes the old piles of quartz chips and stones outside the early tunnels and battery sites worth inspection.
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Gold from Macraes is indeed microscopic. I have a pair of tiny ‘specimens’ each with a microscopic grain in which I got when I was a kid upwards of fifty years ago. I used to go there and chipped quartz from the pillars that held the roof up!
I know of another area in Central where good specimen gold can still be had and that included nuggets.
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