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Generalwhat does "supergene" zone mean??

8th Oct 2008 21:26 UTCAndy Givens

i am new to mineral collecting.....so bear with me ....i was reading an article talking about supergene zone and am having a hard time finding out what that means... can someone help out?

9th Oct 2008 11:44 UTCChris Stanley Expert

Andy, I think this from Wikipedia is a reasonable summary! Cheers

Chris S

"In ore deposit geology, supergene processes or enrichment occur relatively near the surface. Supergene processes include the predominance of meteoric water circulation with concomitant oxidation and chemical weathering. The descending meteoric waters oxidize the primary (hypogene) sulfide ore minerals and redistribute the metallic ore elements. Supergene enrichment occurs at the base of the oxidized portion of an ore deposit at which point the metals are redeposited on hypogene sulfides creating a zone of increased ore content. This is particularly noted in copper ore deposits where the copper sulfide minerals chalcocite, covellite, digenite, and djurleite are deposited by the descending surface waters".

12th Oct 2008 03:41 UTCAndrew G. Christy Manager

I've just partially rewritten the wiki article to make it even clearer:

"In ore deposit geology, supergene processes or enrichment occur relatively near the surface. Supergene processes include the predominance of meteoric water circulation with concomitant oxidation and chemical weathering. The descending meteoric waters oxidize the primary (hypogene) sulfide ore minerals and redistribute the metallic ore elements. Supergene enrichment occurs at the base of the oxidized portion of an ore deposit. Metals that have been leached from the oxidized ore are carried downward by percolating groundwater, and react with hypogene sulfides at the supergene-hypogene boundary. The reaction produces secondary sulfides with metal contents higher than those of the primary ore. This is particularly noted in copper ore deposits where the copper sulfide minerals chalcocite, covellite, digenite, and djurleite are deposited by the descending surface waters."

12th Oct 2008 06:11 UTCJesse Fisher Expert

Other minerals popular with collectors that are found in the supergene portion of ore deposits include azurite, malachite, cuprite, vanadanite, mimetite, wulfenite, adamite, smithsonite, hemimorphite, dioptase, among others.

12th Oct 2008 07:07 UTCCaleb Simkoff

so tsumeb and butte?

12th Oct 2008 18:35 UTCJesse Fisher Expert

Ore deposits can contain both supergene and hypogene portions, each with their own characteristic mineralogy. Tsumeb is famous not only for the diversity of the minerals from its supergene zone, but for the fact that it had two such zones. The near-surface one was mined out early on in the history of the mine, and a second one, below a stretch of hypogene mineralization was found later on. This one was created by a decending fracture zone in the country rock that carried oxygenated atmospheric water to depth, where it intersected the near-vertical ore vein. It was this lower supergene zone that produced much of the specimens we find on the market today. The primary (hypogene) ore minerals at Tsumeb included pyrite, chapcopyrite, sphalerite, galena, enargite, tennantite, and others. The secondary (supergene) minerals included dioptase, azurite, malachite, smithsonite, adamite, hemimorphite, duftite, wulfenite, mimetite and many, many others.

I am not so familiar with Butte, but there was an excellent issue of the MR devoted to it a few years back.

12th Oct 2008 20:40 UTCPavel Kartashov Manager

Hi, friends!

It seems to me, that you are overconcentrated on ore deposits.:) Wasn't formation of 300 m thick dolomite sediments covering all eastern Siberia supergene process? ;) Or pyrite oxidation into black Jurassic clays, which make almost unfit for drinking water in all SE part of Moscow region. Salt sedimentation in Dead Sea and many other places also supergene process. Hydratation of anhydrite layers, dissolving of carbonates with caves formation (karst), precepitation of Fe-Mn-concretions in deep sea waters, latherite and soil formation... In other words, all sedimentogenesis is supergene process.

13th Oct 2008 00:02 UTCRob Woodside 🌟 Manager

The supergene process was first recognized as the origin of the Bristol, Connecticut Chalcocites back in the 19th Century. Then the common view was that stuff came up from below and if you hadn't found it, you merely hadn't dug deep enough. This brilliant stratigy resulted in the discovery of some of the largest Swiss smokies, the Ogalla Aquifer, the gold at Barkerville, etc. The surprising thing about the supergene process was that the enrichment came from above. The economic importance of supergene metallic ores may have blinded people to physically identcal processes in non economic circumstances. As I understand it, the key ideas are the downward circulation of eroding rainwaters carrying ions that enrich the concentration of these ions occuring at depth.

So Pavlov. Did the Siberian dolomites arise by the downward percolation of magnesium into limestone? That would certainly be supergene as I understand it. My geology is weak, so I don't know how dolomites are formed but I could imagine Magnesium comming from below or a lot of magnesium concentrating shells precipitating from above. That later suggestion does seem supergene, but rain water would not be involved. Does the iron increase in concentration in the Moscow black clays? I wasn't aware that the salt pans under the Dead Sea or the Mediterrean resulted from and enrichment due to downward flow. I thought the salt merely precipitated where it could as the sea evaporated. Hydration of anhydrite to gypsum certainly seems supergene as I guess would be the formation of Stalagmites and Stalactites in caves. I would throw out"precepitation of Fe-Mn-concretions in deep sea waters," as the sea waters do not have the erosional characteristic of rain water. Bauxites, Laterites and soils are all economically important and arise from a supergene process as I understand it. As I see it all supergene processes are all sedimentogenesis but some sedimentogenesis does not happen with a supergene process.

Andy's description starts with, "In ore deposit geology..." so he doesn't have to rewrite it.

13th Oct 2008 00:30 UTCRalph S Bottrill 🌟 Manager

I think most geologists usually differentiate supergene alteration of rocks from the sedimentation, diagenesis and other low-temperature processes predating sedimentary rock formation (at least where I have worked and studied).

Sedimentary dolomites (or strictly dolostones) are usually considered to be formed mostly by diagenesis of limestones, i.e. between the burial of the limey sediments and their compaction and metamorphism.

Oxidation of sulphidic mudstones is certainly supergene.

Salt formation is mostly sedimentary as Rob suggests, but some can form by rising groundwaters in arid areas also.

Hydration of anhydrite layers: supergene

Caves formation (karst): supergene

Precepitation of Fe-Mn-concretions in deep sea waters: sedimentary

Laterite: supergene

Soil formation: mostly supergene

14th Oct 2008 12:21 UTCRalph S Bottrill 🌟 Manager

Supergene enrichment should happen at or neat the water table, by downward-percolating groundwater, and is characterised by a narrow near-horizontal zone with (in copper deposits) fine grained chalcocite, bornite, digenite, etc replacing chalcopyrite in the zone of supergene enrichment, overlying relatively unaltered chalcopyrite. Overlying this is a rough zonation from native copper to cuprite and copper carbonates and phosphates etc at higher levels.

Its possible that in some deposits supposed "supergene" minerals may actually be formed by ascending fluids, which may be due to deeply convecting groundwater, being heated at depth and rising along fault systems, giving the nice big chalcocites, azurites at deep levels, etc.

14th Oct 2008 14:33 UTCjacques jedwab

According to the "Glossary of Geology & Related Sciences-Amer. Geol. Institute, 1957", "supergene" relates to ore deposits and minerals, and is put in a semantic pair (opposition) with/to "hypogene" ores, minerals, processes. Sedimentary processes are thus not included.

The funny thing is that, since the discovery of the "Unconformity-related ore deposits" (circa 1980; Cox and Singer Model 37a), concepts have become more fuzzy, and ores, minerals or parageneses of "clear" hypogene affiliation are now interpreted as formed per descensum. In such cases, the important factor is the alternation of oxygenated/reduced layers, as in Katanga, Namibia, Saskatchewan, Austr. North Territories, with their minerals which were considered as "hypogene", not so long ago. One has thus to consider an additional circumstance to classify a given deposit .

J.J.

15th Oct 2008 03:16 UTCRalph S Bottrill 🌟 Manager

I suspect between us all, we have completely confused poor Andy by now! (Such a simple question...)

18th Oct 2008 03:01 UTCAndy Givens

for real!!!

18th Oct 2008 07:17 UTCRalph S Bottrill 🌟 Manager

I guess in simplest terms it is just the oxidised part of a sulphide orebody, above the water table, usually an iron rich gossan containing often colourful oxysalt minerals like malachite, azurite, crocoite, anglesite, cerussite, etc

18th Oct 2008 13:14 UTCDavid Von Bargen Manager

No, it also includes the zone where sulfides are redeposited (usually just below the water table).

20th Oct 2008 05:17 UTCRalph S Bottrill 🌟 Manager

True but I was trying to keep it very simple and supergene enrichment is a complex process and its not significant in most deposits, excpet some copper deposits

20th Oct 2008 05:33 UTCRob Woodside 🌟 Manager

I'm very embaressed, if I was confusing.

20th Oct 2008 06:46 UTCRalph S Bottrill 🌟 Manager

Hi rob

I found your post and others very interesting but them rememebered the original poster said he was new to minerals, so I suspect some of us went a bit over this head.

20th Oct 2008 18:32 UTCRob Woodside 🌟 Manager

Thanks for the kind words Ralph. The first paragraph I wrote here was for Andy Givens and the second was for Pavel who knows far more about these things than I and always has interesting comments. It is my experience that Russian geologists are very strong, but sometimes have a different take on things than North Americans. Like you I was wondering if his equating sedimentogenesis with supergene was one of these different takes. Thanks for the explanation of Dolostone.

21st Oct 2008 02:34 UTCHoward Heitner

I would like to follow up on the previous post by Rob Woodside. Chalcocite and covellite are copper rich minerals usually formed in the supergene zone of ore deposits where the primary copper mineral is chalcopyrite. The deposit at Bristol, Connecticut is known for the magnificent crystals of chalcocite found in the 1840's. Work by Alan Bateman of Yale on ore samples obtained after the mine closed, showed that chalcocite was the primary copper mineral, making this deposit an exception to the usual case.

21st Oct 2008 17:37 UTCRob Woodside 🌟 Manager

Thanks Howard, I wasn't aware of that.

22nd Oct 2008 02:55 UTCAndy Givens

i am new and a lot of these has gone over my head but i still appriciate it all. thanks again.

22nd Oct 2008 03:20 UTCRalph S Bottrill 🌟 Manager

(Sorry Andy, here we go again) I suspect most well crystallised chalcocites are probably primary rather than supergene (but am happy to be shown otherwise). Supergene chalcocite is usually fine grained, mixed with bornite, digenite, djurleite, chalcocite etc. Chalcocite can form in epithermal (low temperature) hydrothermal deposits. as well as the supergene zone.

+

11th Jan 2016 14:07 UTCPaty

I would like to learn about the alteration secuence from sulphide copper minerals primary (Chalcopyrite and bornite) to supergene copper minerals (chalcocite, digenite, covelite). maybe Chalcopyrite-bornite-digenite-chalcosite???

11th Jan 2016 15:54 UTCWilliam C. van Laer Expert

Jesse:

I hate to say this, but the article in the Mineralogical Record about Butte was full of flaws, errors, omissions, and photos of minerals either so bad as to be embarrassing or some of minerals that were not even from Butte. A good example of a poorly-researched and badly edited article, literally an unreliable article. Most Butte collectors just ignore it.

Chris

12th Jan 2016 09:55 UTCRalph S Bottrill 🌟 Manager

Paty

thats about right, normally something like:

Chalcopyrite->bornite->digenite/djurleite/chalcocite->covellite

Its essentially a matter of increasing Cu/S with increasing oxidation and preferential removal of Fe and S.

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