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Identity HelpQueensland secondary mineral roundup

18th Mar 2009 04:20 UTCRyan Eagle Expert

Hi all, I have a bunch of secondary minerals that I need some help with:

1. George Fisher mine, Mount Isa, Queensland, Australia. Yellowish mineral growing on quartz, could be anglesite?

2. Another from Mount Isa, growing on galena. Pyromorphite-Mimetite or one of the silver minerals such as pyrargyrite that occur there?

3. Barbara copper mine, Mount Isa. Much the same type of mineralisation as any of the other copper mines in the area, not much info on this specific mine though. The reddish-brown alteration surrounding chalcopyrite. Initially, without a microscope, I suspected massive chalcocite but I'm not very confident of that getting up close.

18th Mar 2009 05:27 UTCRob Woodside 🌟 Manager

I demur to others who know more, but the first might be anglesite. However 2) has red black octos and looks like cuprite. In 3) the red brown surrounds the chalcopyrite and borders on the malachite. It is probably a mixture of limonite and cuprite from oxidizing the chalco. the Malachite is the result of further oxidation.

18th Mar 2009 05:47 UTCRalph S Bottrill 🌟 Manager

I agree with Rob on 1 & 3, but could 2 be sphalerite? We need a closer look at the crystals for form and colour. I recall when I was working at Mt Isa 25 yrs ago we thought we had lots of secondary silver minerals in fractures, but I think most turned out to be sphalerite, galena and other common minerals.

Ralph

18th Mar 2009 06:09 UTCRob Woodside 🌟 Manager

I know what Ralph is saying. I used to complain when people saw triangles and said octos, especially with sphalerite. Sphalerite is a tetrahedral mineral not an octahedral mineral!!! Then Robbie Belcher had a specimen from Naica in just the size I collected. On a mound of galena was perched an octahedron of Sphalerite!!! Shortly after I saw the Bulgarian Sphalerites were also octahedral!!! A positive and negative terahedron in equal devlopment make an octahedron and this can happen with sphalerite!!! This is somewhat rare so I thought the octos in your photo were cuprite. Maybe Mt Isa produces octohedral spalerites. The streak will tell.

18th Mar 2009 06:16 UTCRyan Eagle Expert

I'm quite sure I have seen miniscule cuprite crystals elsewhere on 3, so a limonite/cuprite mix sounds good. Number 2 though, I can't really get in any closer or clearer, those crystals are about a mm across. Doubt I'll get a better picture of them until I can get a micro focus rack for the camera, it's taking a very steady hand to push the camera along just enough to overlap the focus already! I have included a few more views of the same thing here though. They seem to mostly be six sided, with flat tops, however they vary a bit. It's quite different to most of the sphalerite at Handlebar Hill, I don't think we ever really saw/noticed well formed crystals outside of the later carbonate veins. Though the siderite buff altered ore bodies often had pinkish sphalerite in them.

18th Mar 2009 07:40 UTCRyan Eagle Expert

Managed to get some better photos, they are pretty complex. They seem to be altering to limonite in some places.

18th Mar 2009 07:58 UTCRob Woodside 🌟 Manager

Ralf has better eyes than I do!!! They are not octos. Brown translucent xls with trigonal symmetry altering to limonite. Maybe Jarosite???

PS I didn't want to increase thread length, but Ralf that was agreat job you did on Crocoite on the best stuff board!!!

18th Mar 2009 08:45 UTCUwe Kolitsch Manager

The first one reminded me also of sulphur (try hot needle test).

2: I'd vote for pyromorphite-mimetite (rosette-like aggregates of tabular xls).

18th Mar 2009 08:54 UTCRob Woodside 🌟 Manager

The mosaic faces of the brown translucent are very reminiscent of Pyromorphite/Mimetite

18th Mar 2009 09:02 UTCRyan Eagle Expert

The sulphur at Handlebar Hill tends to occurr as light yellow-green indistinct crystals, I think these are fairly different. Could well be though... (edit, red hot needle has no effect)

As for jarosite, I knew we had found it somewhere in the pit before, so I dug through my piles of rocks and found a bit. The crystals are even smaller than the things in the number 2 photo, so it's a pretty atrocious photo, it literally has a 1mm field of view. I am quite confident of these ones being jarosite, they were well in the oxidised zone, before we hit sulphides. Matches up well with the images in the database.

One thing that suprised me at Handlebar Hill was the almost complete absence of secondary zinc minerals... they really were scarce, but the one piece of smithsonite I picked up was pretty spectacular on the small scale.

edit: closer photo of the 'anglesite', these things are impossible to make look good. ordering my micro focus rack right NOW.

18th Mar 2009 09:42 UTCSebastian Möller Expert

Hello,

1. Anglesite or cerussite then (try to dissolve in hydrochloric acid, cerussite will do with giving lead chloride)

3. Limonite with possibly cuprite

2. all minerals mentioned seem reasonable to me without cuprite. It is clearly brownish, whereas most cuprites show a red colour. First I thought sphalerite, but this could really be some alunite group mineral such as jarosite.

Regards,

Sebastian Möller

18th Mar 2009 11:28 UTCRalph S Bottrill 🌟 Manager

#2 is probably mimetite, but maybe either pyromorphite or maybe a jarosite group mineral.

Thanks Rob for the compliments, I hope to get a few more up soon.

Ralph

18th Mar 2009 12:20 UTCRyan Eagle Expert

Definitely going to run with the mimetite-pyromorphite call here I think, a visit to the Campylite variety page here has several dead ringers, and many really do have a six sided barrel shape, even though it isn't that obvious in the photos. I will try to get a microprobe analysis on them some time in the future to determine the species. Thanks for everybody's help!

18th Mar 2009 20:04 UTCRob Woodside 🌟 Manager

Could there be two minerals here??? The hexagonal prisms are probably Pyromorphite/Mimetite, but what is the brown translucent? Is it even trigonal?

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