I was kindly gifted a couple of flats of (mostly) copper sulphide specimens in thumbnail boxes recently. These were all collected in the Cattle Grid Deposit, Mount Gunson, Pernatty Lagoon, South Australia, by the late South Australian mineral collector, Mal Annells.
The copper ores that were mined there, mostly chalcocite and bornite, occur in fracture-filling veins in a coarse grained sandstone and breccia.
Mindat lists 38 minerals, including 21 that contain copper, 12 of which are copper sulphides and sulphosalts. There are 7 sulphides and sulphosalts that do not contain copper in their formula.
Here is where it gets interesting. And frustrating.
Very few of the boxes are labelled, and some that are labelled are incorrect.
The copper sulphides that occur there are not necessarily easily distinguished visually from others. And there may be some that are present that are not recorded in Mindat too.
As I have now gone through all of the specimens, I am in the process of regifting duplicates (via the latest Mineral Matters Sales #30 post). A number are already set aside, but there are still some left.
The problem is that I can’t necessarily identify all of the specimens. So I will be at least sharing here what I know, or suspect, over the coming days.
The first one is an unusual habit, reminiscent of marcasite. On broken surfaces, some of the cores look like typical chalcopyrite yellow, some look like bornite “Peacock Ore” (note: fresh surfaces, not weathered or treated).
My tentative identification is as follows: Chalcocite or bornite coating chalcopyrite or bornite. If anyone has seen this habit before, even from other localities, I’d like to hear about it.
Below: Chalcocite or bornite over chalcopyrite or bornite, Cattle Grid Deposit, Mount Gunson Copper Mines, Pernatty Lagoon, South Australia. Width of view 9mm.