How to identify argentiferous galena?

I've read accounts of the old-time mineral explorers finding galena and stating that it was argentiferous, based simply on appearance. What were they seeing? I've heard that argentiferous galena is shinier than pure galena, and also that the crystal faces are curved on the silver-bearing mineral. Any truth to either?

Thanks!

Dan, I've assayed a lot of galena, some highly argentiferous but most barren. I've not seen any correlation between appearance and silver content and, since I heard the same things about galena many years ago, I been particularly careful to note in my lab notebooks the physical characteristics of my pyrite, chalcopyrite and galena samples sent for assay.

Don

I grew up at a silver mine and remember the miners referring to the high grade as "steel galena". It was generally finer grained and often slightly banded. This is anecdotal and may not apply to other deposits. I do have some high grade silver-bearing galena from Keno Hill and it has this fine gained banded appearance. I suspect some inclusions of fine freibergite may contribute. The finer grain/higher grade may be a result of faster cooling and co-precipitation. Slower cooling larger resulting in coarser galena may also result in greater separation of silver and lead minerals.
I admit this is somewhat idle speculation, but could get more discussion going (especially if I'm wrong )

Dan;
I brought this up before about bluish galena crystals with barrel shaped faces and was told pretty much the same thing Don pointed out. It may have been Don that pointed it out. I was wondering if these things are a localized phenomenum or simply legend, or if its something like Alex said. The galena I'm talking about (Sullivan Mine ore) can be very banded and relatively fine grained
Gord

I've also heard that argentiferous galena supposedly has a slightly curved cleavage (silver distorts the structure of the galena). I don't have any empirical evidence to back this up, just one of those thing I head somewhere along the way. Does anyone (Don) know if this is true?

I've been dealing with the "argentiferous galena" situation for many years.

I always find that "argentiferous galena" is really galena with "invisible" silver mineral inclusions such as matildite and silver bearing lillianite homologues. The actual mode of occurrence of the silver in galena doesn't really matter to the mine operator. The ultra fine grained silver minerals in galena can not be isolated for the purposes of recovery and silver reports with the galena concentrate.

There are a few competent researchers who believe that galena can dissolove silver, but I don't think that the texture of galena is related to silver concentration.

Bart

Thanks everybody for the input. I suspect that most of the guys who said the galena appeared to be argentiferous where probably basing this assumption on optimism.

Yesterday I spoke with the guy who I consider the World's leading expert on this subject. Richard O. Sack.

He has published many papers on ore mineralogy and is very opinionated about how tetrahedrite, tennantite and friebergite are illusory minerals and should CLUMPED into one classification : FAHLORE.

He insists that galena itself never contains solid solution silver. In the evolution of most ore systems the silver gets sucked up by associated minerals, such as the various FAHLORES, and included sulfosalts.

His papers are way over my head. They are all ternary diagrams and chemical reaction series that I can't really comprehend.

We have many long discussions, but they are mostly about canine behavior. Another subject that can't be fathomed. We are both dog nuts.

Bart

"[...] about how tetrahedrite, tennantite and friebergite are illusory minerals."

Referring to end-member compositions, likely yes. But minerals are not defined as end-members.

Silver in galena is like gold in pyrite: mostly it's in microscopic to submicroscopic inclusions but there are some circumstances where it does appear to be in a true solid solution.

Steely galena does seem to be commonly rich in sulphosalts, it's thought to be due to relatively low temperature, deformation-induced remobilisation of ductile sulphides, relatively rich in Pb, Sb and Ag.

And calling the fahlore endmembers illusory is like calling siderite, rhodochrosite, magnesite etc are illusory because the form solid solutions.

Regards,
Ralph

Ralph, Peter,

There is much more to Richard Sacks position than I can state. Look up his papers. He is on the next level up from the rest of us. I will provide a listing of his work. Mind you, I don't agree with him. If either of you come to Seattle, I would love to see you participate in a roundtable with him.

Peter,

I don't understand your statement that "end members" do not define a mineral species.

If the composition of end member grossular, spessartine or andradite are not the definition of those mineral species, then I completely give up and will only accept quartz as a true mineral species.

Bart

Bart
I think Peter meant that most minerals do not have endmember compositions, they usually fall in the grey areas with various substitutions in different sites indicating they are members of various solid solutions.

I am quite familiar with Richards work, which is excellent for sulphosalts, but I not sure of his expertise in mineral classification & dont think we need to be too intimidated by anyone's expertise in one specific area of mineralogy; most of us can bamboozle an expert by talking of our own particular passions (and vice versa).

Regards,
Ralph

The composition of a mineral is defined by a hyperplane in the phase diagram. This plane is bounded by lines denoting first and second order phase transitions, and can be further sub-divided by definition (e.g. the dominant constituent rule in case of solid solution series). It is not defined by a formula, which always represents only one of an infinite number of possible compositions.