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A Scientific and mineralogical trip to the Iberian Pyrite Belt - (6)
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Cesar M. Salvan
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PostPosted: Mar 03, 2013 20:41    Post subject: A Scientific and mineralogical trip to the Iberian Pyrite Belt - (6)  

I want to share with the followers of the forum a brief overview on a topic I consider interesting that constituted a scientific interest for me during several years. Now, because the science cuts we suffered in Spain, that forced me to left my laboratory in stand-by (in an optimistic view…), I have enough time to let you know a little about our work.

Probably, all of you known the Iberian Pyrite Belt (IPB). Located in the SW of the Iberian Peninsula, constitutes one of the largest sulfur anomalies in Earth crust, in the form of at least 80 volcano-sedimentary massive sulfide deposits spread out in Portugal and Spain and that were mined since pre-roman times.

Roughly, we can divide the deposits in two groups:
- Northern IPB: Interpreted as replacive deposits hosted by the apical part of felsic domes, related with dacites and ryolites of early Visean age (Carboniferous). I think that the major and most interesting deposits are Aguasteñidas, La Zarza, Aljustrel and the beautiful San Miguel mines.
- Southern IPB: Includes the deposits of Neves-Corvo, Tharsis, Aznalcollar-Los Frailes, Las Cruces, Lousal, Valverde and Sotiel-Migollas mines. The massive sulfide is hosted by shale and of younger formation than the northern IPB sulfide (Fammenian age, Upper Devonian). The shale-hosted sulfide formation was interpreted as exhalative and formed in an anoxic basin.
Our interpretation is, in brief, the formation of seafloor hydrothermal vents and anoxic bottoms, in response to the crustal alteration and the onset of magmatism in the area, that generated hydrothermal cells that attacked the underlying shales and sandstones of the PQ group. The vented fluids were metal rich and poor in sulfur, so, where the sulfide come from?.

Interestingly, the formation of shale-hosted sulfide deposits in the southern-IPB coincides with the boundary between Devonian and Carboniferous, i.e. the DC boundary, marked by one of the major massive biological extinctions in the Earth history, characterized by the vanishing of about the 90% of terrestrial and the 21% of marine genera.

Coincidence or relation?. We think that the origin of sulfur and the paleogeographic changes and biological crisis of the DC boundary could be related. The sulfur isotopes on the pyrite and other geochemical proxies of anoxia and biological origin of the sulfur moved us to explore the IPB from a different point of view.

Tharsis mines

The Tharsis mines includes sixteen massive sulfide lenses aligned in three groups:

- Filon Norte, San Guillermo and Sierra Bullones pyrite masses, mined in the Filon Norte and Sierra Bullones open pits. About 40 Mt of pyritic ore have been mined here, that constitutes aprox the 45% of the estimated reserves.
- Filon Centro and Los Silillos
- Fion Sur and Esperanza mine

The Tharsis mines were worked by Romans and about 3,5 Mt of roman slags remains in the zone. In 1853, Ernesto Deligny rediscovered the mines and in 1867 were sold to the British company Tharsis Sulphur and Copper Company Ltd. The last active mine was Filon Norte, closed in December 2000 and the pyrite ore were used mainly for the sulfuric acid production.

Biological crisis and sulfide formation

One interesting feature of the Tharsis zone is that we can find a complete continuous sequence of shale, including the massive sulfide in the DC boundary. This allow us to study the vertical distribution of paleobiological proxies before, during and after the DC boundary. To test our hypothesis that the biological extinction drove the massive sulfide formation, we followed a falsation strategy: if there is no relation, we should not find evidences of the biological crisis associated with the mineralization. So, we focused the searching in the “molecular fossils”: molecules that contain information of the biological source. This was possible due to the relatively high content in organic matter of the dark shale that hosts the massive sulfide.
And what we found was awesome: exactly coincident with the anoxia and the formation of pyrite, we found a strong increase of the molecular fossils of vascular plants and terrigenous ecosystems. So, our interpretation was that the extinction of terrestrial ecosystems provides a lot of organic materials to the marine basin, which were used by anaerobic, sulfate reducing bacteria. The bacterial sulfide production lead to the precipitation of fine grained pyrite with the metal provided by hydrothermal vents.

Filon Norte, also, contains other interesting biological-mineralogical connections that are under study (currently stopped due to the terrific scientific policy of Spanish administration).

The genesis of the shale hosted massive sulfide, finally, appears to be connected directly to a biological event. This converts the Tharsis deposit in a unique formation.



2011-11-29 tharsis filon norte2.jpg
 Description:
Filón Norte, Tharsis, Alosno, Huelva, Spain
Old facilities at Filon Norte open pit
 Viewed:  35128 Time(s)

2011-11-29 tharsis filon norte2.jpg



2011-11-29 excursion faja piritica 015.JPG
 Description:
Filón Norte, Tharsis, Alosno, Huelva, Spain
Filon Norte open pit. At left, the PQ group. At center, the massive sulfide hosted in dark shale is visible.
 Viewed:  35154 Time(s)

2011-11-29 excursion faja piritica 015.JPG



2011-11-29 excursion faja piritica 018.JPG
 Description:
Filón Norte, Tharsis, Alosno, Huelva, Spain
Oxidized pyrite stockwork at Filon Norte.
 Viewed:  35153 Time(s)

2011-11-29 excursion faja piritica 018.JPG



2011-11-29 excursion faja piritica 013.JPG
 Description:
Melanterite
Filón Norte, Tharsis, Alosno, Huelva, Spain
The formation of beautiful melanterite in Filon Norte during cold days soon after raining, is an interesting phenomenon. Occasionally, the crystals are up to 5-10 cm., covering dozens of square meters of soil under the massive pyrite stockpiles.
 Viewed:  35149 Time(s)

2011-11-29 excursion faja piritica 013.JPG



2011-11-29 excursion faja piritica 021.JPG
 Description:
Filón Norte, Tharsis, Alosno, Huelva, Spain
iron oxide rich streams are common here. But, vascular plants appears not to be feared by the high metal content...
 Viewed:  35160 Time(s)

2011-11-29 excursion faja piritica 021.JPG


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PostPosted: Mar 03, 2013 21:31    Post subject: Re: A Scientific and mineralogical trip to the Iberian Pyrite Belt - (6)  

Filon Sur (Tharsis)

The Tharsis mines are probably one of the most beautiful and interesting groups of deposits on the IPB. The Filon Norte open pit contains a visible assemblage of massive sulfide hosted by dark shales, pyrite stockworks and a lot of very interesting structures (banded ore, carbonate ore...).

The Filon Sur open pit are composed by small lenticular massive pyrite masses and stockwork of primary ore. But the more interesting feature of Filon Sur is that hosts a potent gossan, that were systematically mines since Roman times. The gossan at Filon Sur is complex and very rich in valuable metals. The gossan has been worked for Ag-Au until recent times.
One of the gossan zones is a lead-rich beudantite-goethite gossan. This zone yielded a lot of interesting collectible mineral samples, including mimetite, cerussite, beudantite, iodargyrite and chlorargyrite.

The interpretation of the gossan suggest that the formation taken place in two stages: oxidation of underlying pyrite, with formation of jarosite group minerals, and second, weathering with formation of goethite and, in the latter phase, hematite.



varios 032.JPG
 Description:
Filón Sur, Tharsis, Alosno, Huelva, Spain
Filon Sur open pit overview. At left is located the lead rich gossan.
 Viewed:  35162 Time(s)

varios 032.JPG



mimetita+beudantita excursion nov.jpg
 Description:
Mimetite and Beudantite
Filón Sur, Tharsis, Alosno, Huelva, Spain
FOV 2.5 mm. Hexagonal mimetite crystals and minute beudantite
 Viewed:  35148 Time(s)

mimetita+beudantita excursion nov.jpg



mimetita filon sur dec12.jpg
 Description:
Mimetite
Filón Sur, Tharsis, Alosno, Huelva, Spain
Mimetite crystal 2 mm
 Viewed:  35124 Time(s)

mimetita filon sur dec12.jpg



varios 034.JPG
 Description:
Filón Sur, Tharsis, Alosno, Huelva, Spain
A pocket performed by rockhunters looking for the beautiful goethite of Filon Sur.
 Viewed:  35135 Time(s)

varios 034.JPG



cerusita tharsis.jpg
 Description:
Cerussite
Filón Sur, Tharsis, Alosno, Huelva, Spain
1 cm crystal
1 cm crystal of cerussite from the gossan of Filon Sur
 Viewed:  35149 Time(s)

cerusita tharsis.jpg



beudantita.jpg
 Description:
Beudantite
Filón Sur, Tharsis, Alosno, Huelva, Spain
FOV 1 mm
pseudocubic beudantite crystals from Filón Sur.
 Viewed:  35104 Time(s)

beudantita.jpg



clorargirita 3x.jpg
 Description:
Chlorargyrite
Filón Sur, Tharsis, Alosno, Huelva, Spain
FOV 2 mm
Chlorargyrite is relatively common in the gossan of Filon Sur.
 Viewed:  35128 Time(s)

clorargirita 3x.jpg



varios 039.JPG
 Description:
Filón Sur, Tharsis, Alosno, Huelva, Spain
It's me after 5 days outdoors and under a diet composed by ham and beer, in front of a Roman gallery. The space for oil lamps are visible.
 Viewed:  35129 Time(s)

varios 039.JPG



mimetita tharsis ultima salida.jpg
 Description:
Mimetite
Filón Sur, Tharsis, Alosno, Huelva, Spain
crystal max. 0.9 mm
Typical mimetite on goethite from Filon Sur.
 Viewed:  35116 Time(s)

mimetita tharsis ultima salida.jpg


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PostPosted: Mar 03, 2013 23:49    Post subject: Re: A Scientific and mineralogical trip to the Iberian Pyrite Belt - (6)  

Interesting text and pictures. Thanks for this writeup.
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PostPosted: Mar 04, 2013 03:56    Post subject: Re: A Scientific and mineralogical trip to the Iberian Pyrite Belt - (6)  

Thank you very much, Cesar, for spending your "free" time in posting such an interesting report. I will "save" your pictures of the mimetites since I cannot take microphotographs myself!! :-)
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PostPosted: Mar 04, 2013 04:20    Post subject: Re: A Scientific and mineralogical trip to the Iberian Pyrite Belt  

Fascinating article! Is there anything more coming?
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PostPosted: Mar 04, 2013 09:26    Post subject: Re: A Scientific and mineralogical trip to the Iberian Pyrite Belt  

Amazing trip...
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PostPosted: Mar 04, 2013 15:43    Post subject: Re: A Scientific and mineralogical trip to the Iberian Pyrite Belt  

Thank you, Cesar, for your nice report and photos about this area. For some like myself, who are not terribly familar with these deposits in Spain, it provides a good enrichment of knowledge about them! To me, though I knew (to a very limited extent) that were numerous pyritic deposits in this part of Spain, the "Iberian pyrite deposits" mostly meant just "Rio Tinto", and I did not know anything about what other deposits existed or were being currently mined or explored. I did a little searching online after viewing your post, and I'm now aware that the old Rio Tinto deposit is in the eastern-most part of that northern pyrite belt, and it has been inactive since about 2001; and that there has been an attempt to renew mining there, but that has not been successful yet. One of the best maps I've found online showing the mines and deposits and geology in this belt is this one, from a mining investment company:
https://www.proactiveinvestors.com/genera/files/sponsor_extras/Image/Slide3.jpg
Best regards,
Pete Modreski
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PostPosted: Mar 04, 2013 15:51    Post subject: Re: A Scientific and mineralogical trip to the Iberian Pyrite Belt  

Thanks Cesar and Pete, the presentation was great, then as with probably many, the slide showing a geologic map of that part of Spain and Portugal was extremely interesting. Especially since I have an internet friend from the coast of Portugal on the western shore of the map area.

John

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PostPosted: Mar 15, 2013 18:59    Post subject: Re: A Scientific and mineralogical trip to the Iberian Pyrite Belt  

I want to continue with this brief revision with some Iberian Pyrite Belt deposits. Pete, I think is usual that people refers to the IPB just as Rio Tinto. It is not surprising, because some famous mines, as Atalaya and Cerro Colorado open pits belongs to Rio Tinto district. Atalaya open pit was famous because the awesome sulfates from the Alfredo underground workings. Other famous mine is Peña del Hierro, because in this zone some creeks converges to form the river Tinto. But the Rio Tinto mines, as you learned, are only one of several mining districts, which are at least equally important and interesting. If I can stimulate the curiosity about the IPB, this little effort in the forum will be a success!.
I began with the beautiful Tharsis mines, which complex and intriguing metallogeny is now under study. These mines belong to the southern IPB, characterized by the massive pyrite of DC-boundary age.

Now I will show you a beautiful open pit: the San Miguel mine (Almonaster la Real, Huelva, Spain). This constitutes the best example of the "northern IPB deposits" class, younger (Visean, Carboniferous) and with a completely different mineralization mechanism, basically replacive after volcanic rocks.

This mine, as usual in the IPB, show remains of Roman workings. The Romans were efficient miners, who oriented their work to the Ag and Au enrichment zone, in the contact between gossan and massive pyrite. Modern works began in 1851 and between 1859 and 1960 about 1.29Mt of pyritic ore with 2-3%Cu and 46%S were extracted. The copper grades were very irregular but with a significant enrichment towards the supergene zone. Most of the Au-bearing gossan has been recently removed by Minas de Rio Tinto S.A.L and treated in the plant at Rio Tinto. Luckily, a strong gossan and massive sulfide zone remains unexploited in a net, vertical cut that clearly shows the structure of the deposit and awesome pyrite replacement structures. Attempts for the protection of this open pit as a point of geological interest are now under development.
As usual in this kind of deposits of the IPB, the mineralogy is pretty monotonous, with a gossan very poor in supergenic species. It is interesting to note the presence of Baryte crystals, uncommon in other type of deposits.

In the next part I will show more minerals, I swear...



sketch tharsis.jpg
 Description:
Sketch that shows our model for the origin of the mineral from southern IPB deposits (in this case, Tharsis). The formation of mineral is dependent on the end Devonian biological crisis.
 Viewed:  34507 Time(s)

sketch tharsis.jpg



2008-09-29_0016.JPG
 Description:
Pyrite-Siderite
Filón Norte, Tharsis, Alosno, Huelva, Spain
May be not very interesting for the typical mineral collector, but this kind of mineral, called "carbonate ore" and formed by alternating layers of siderite and pyrite, is one of the most interesting minerals to be found in Filón Norte open pit.
 Viewed:  34471 Time(s)

2008-09-29_0016.JPG



2011-11-27 excursion faja piritica 008.JPG
 Description:
old shaft in Peña del Hierro (Nerva, Huelva, Spain). The origin of the famous river Tinto is in the vicinity...All this zone is famous because the Astrobiology work performed here. The zone has been considered a "Mars analog" on Earth and the study of extremophile organisms received a lot of attention here.
 Viewed:  34483 Time(s)

2011-11-27 excursion faja piritica 008.JPG



2008-09-29_0006.JPG
 Description:
The extremophiles paradise: biogenic terraces in the acidic waters of the river Tinto. The yellow material in the shore is biogenic sulfur.
 Viewed:  34496 Time(s)

2008-09-29_0006.JPG



2008-09-28_0004.JPG
 Description:
The famous Atalaya open pit, (Rio Tinto, Huelva, Spain)...
 Viewed:  34507 Time(s)

2008-09-28_0004.JPG



azufre atalaya fov 5 mm 2.jpg
 Description:
Sulfur and Covellite
Corta Atalaya, Rio Tinto, Huelva, Spain
FOV 5 mm
and one mineral from Atalaya mine. Sulfur on covellite from the copper enrichment zone of the mine.
 Viewed:  34616 Time(s)

azufre atalaya fov 5 mm 2.jpg



2011-11-29 excursion faja piritica 053.JPG
 Description:
A beautiful scenery in San Miguel open pit: Dramatic contact between gossan, in the uppermost zone, and the underlying semimasive, replacive pyrite.
 Viewed:  34526 Time(s)

2011-11-29 excursion faja piritica 053.JPG



2011-11-29 excursion faja piritica 051.JPG
 Description:
San Miguel mine: awesome replacive texture. The hydrothermal fluid flowed left to right in the image, giving to the original volcanic rock a characteristic spindle form.
 Viewed:  34504 Time(s)

2011-11-29 excursion faja piritica 051.JPG



san miguel barita3.jpg
 Description:
Baryte
San Miguel mine, Almonaster la Real, Huelva, Spain
Crystal 1 mm.
The only mineral that could sate my micromount hunger is the Baryte, very extended in the gossan of San Miguel.
 Viewed:  34492 Time(s)

san miguel barita3.jpg



2011-11-29 excursion faja piritica 054.JPG
 Description:
View of the miners ghost town in the entrance of San Miguel mine, abandoned between 1920 and 1930.
 Viewed:  34461 Time(s)

2011-11-29 excursion faja piritica 054.JPG


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PostPosted: Mar 16, 2013 06:22    Post subject: Re: A Scientific and mineralogical trip to the Iberian Pyrite Belt  

Superb César. Please more...! ;-)
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PostPosted: Mar 26, 2013 09:28    Post subject: Re: A Scientific and mineralogical trip to the Iberian Pyrite Belt  

The last deposit we will review in this brief introduction to the Iberian Pyrite Belt is the Las Cruces mine, in Gerena, near Seville. The Las Cruces mine ise the easternmost in the IPB and is a very interesting mine from a mining, geological and mineralogical point of view. The mine is fully active and, to the date, is the richest active copper deposit in the world, with estimated 16 Mt of a supergene enrichment zone ore containing 7% copper and 5 Mt of a cupriferous stockwork with estimated 3% on copper. Overlying, the deposit has an Au-Ag rich gossan and, underlying, a 30 Mt massive sulfide lens, in part of exhalative origin, that are waiting for mining, with metal contents of about 1% copper, 2% lead, 4 % zinc and economically significant quantities of Ag and Au. The massive sulfide, called ‘polymetallic ore’ included in the Volcanosedimentary complex, is of Devonian-Carboniferous boundary age.

Thanks to the thick Tertiary and Quaternary sediments of the Guadalquivir basin, that buried the deposit about 150 meters subsurface, the deposit was discovered in 1994 and the Las Cruces open pit began the copper production in 2009. Luckily for me, because it was an opportunity to get involved in the scientific and mineralogical study of a very interesting mine and, moreover, near home….

I think that the most interesting feature of Las Cruces is the big secondary enrichment zone and the complex boundary between this zone and the gossan. I cannot give a lot of details about this intriguing structure because it is under study, with some findings waiting for publication. But, in brief, the boundary contains a zone, called “black gossan”, composed of galena and siderite, with features that suggest that it is the product of biogenic reduction of the gossan. Locally, it is rich in native silver and silver minerals, mainly proustite, in crystals up to centimetre size. The “yellow gossan” is formed by siderite, goethite, cerussite and anglesite (that form occasionally very good crystals) and minor galena and the gossan sensu stricto, composed by hematite, siderite, quartz and goethite. The gossan zone is interesting for the presence of marine meso and macrofossils mineralized with siderite or galena.

The secondary enrichment zone is composed mainly of a copper sulfide assemblage of the Chalcocite-Digenite mineral group, with neoformed pyrite and earlier and supergene bornite, chalcopyrite, enargite, tennantite and pearceite. Late hydrothermal alteration in the supergene zone formed a complex structure of fractures covered with calcite and with beautiful Chalcocite crystals, recrystallized after copper remobilization by hydrothermal fluids.

The Chalcocite crystals of the Las Cruces mine yielded, probably, the best chalcocite specimens in Europe and I saw some world-class specimens in the mine that are now part of good collections. Apart from the interesting mineral specimens and the economic importance of Las Cruces mine, at a scientific level the deposit has features that make it a unique deposit in the world. A very unusual and intriguing secondary and supergenic processing of the primary mineral that converts the Las Cruces deposit in a very important point in the study of the geology of mineral deposits and the interactions between biology and geological materials.

If readers of the forum are interested and wish to read more on the IPB, I can share some bibliography.



figura3.JPG
 Description:
Las Cruces mine, Gerena, Seville, Spain
Las Cruces open pit in 2010
 Viewed:  34221 Time(s)

figura3.JPG



DSCN0229.JPG
 Description:
Las Cruces mine, Gerena, Seville, Spain
Beautiful perspective of the open pit in 2010. The secondary enrichment zone is visible at the bottom, with black chalcocite rich ore and galena rich ore. Overlying, the thick sedimentary cover (marls and calcarenites) of Guadalquivir basin.
 Viewed:  34164 Time(s)

DSCN0229.JPG



DSCN0239.JPG
 Description:
Las Cruces mine, Gerena, Seville, Spain
View of the contact zone between yellow gossan, black gossan and secondary copper sulfide ore
 Viewed:  34164 Time(s)

DSCN0239.JPG



calcosina5 FOV 15 mm.jpg
 Description:
Chalcocite
Las Cruces mine, Gerena, Seville, Andalusia, Spain
FOV 1.5 cm
Beautiful crystal on calcite. Typical late hydrothermal chalcocite.
 Viewed:  34167 Time(s)

calcosina5 FOV 15 mm.jpg



calcosina xtal 3mm 4.jpg
 Description:
Chalcocite
Las Cruces mine, Gerena, Seville, Andalusia, Spain
Crystal 3 mm
Pseudohexagonal twinning in chalcocite.
 Viewed:  34170 Time(s)

calcosina xtal 3mm 4.jpg



DSCN0246.JPG
 Description:
Las Cruces mine, Gerena, Seville, Andalusia, Spain
It's me collecting in the copper sulfide ore at Las Cruces. In my hand, the specimen pictured previously. See the calcite filled fractures, in whose cavities the chalcocite crystals grow.
 Viewed:  34190 Time(s)

DSCN0246.JPG



pearceita3 copia.jpg
 Description:
Pearceite
Las Cruces mine, Gerena, Seville, Andalusia, Spain
FOV 1.5 mm
Beautiful pearceite crystal, with harmotome (upper right). The matrix is chalcocite-djurleite.
 Viewed:  34175 Time(s)

pearceita3 copia.jpg



siderita.jpg
 Description:
Siderite
Las Cruces mine, Gerena, Seville, Andalusia, Spain
FOV 5 mm
Siderite crystals and a curious biogenic galena developed in a fossil shell in the Las Cruces gossan.
 Viewed:  34168 Time(s)

siderita.jpg



proustita2.jpg
 Description:
Proustite
Las Cruces mine, Gerena, Seville, Andalusia, Spain
crystal 1 cm
centimetric crystal in pulverulent galena.
 Viewed:  34198 Time(s)

proustita2.jpg



xantoconita copia2.jpg
 Description:
Xanthoconite
Las Cruces mine, Gerena, Seville, Andalusia, Spain
FOV 1 mm
 Viewed:  34157 Time(s)

xantoconita copia2.jpg



cerusita4 FOV 3.4 mm.jpg
 Description:
Cerussite
Las Cruces mine, Gerena, Seville, Andalusia, Spain
FOv 3.4 mm
Cerussite and anglesite crystals are relatively common in the lead rich gossan.
 Viewed:  34157 Time(s)

cerusita4 FOV 3.4 mm.jpg



calcosina prisma FOV 7mm.jpg
 Description:
Chalcocite
Las Cruces mine, Gerena, Seville, Andalusia, Spain
FOV 7 mm
Finishing this post with a beautiful chalcocite crystal on calcite.
 Viewed:  34193 Time(s)

calcosina prisma FOV 7mm.jpg


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Mark Ost




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PostPosted: Mar 26, 2013 13:47    Post subject: Re: A Scientific and mineralogical trip to the Iberian Pyrite Belt  

Cesar
Congratulations on a superb post. The pictures, combined with the geologic discussion, are excellent. I have never seen these colors of red before, not in our Triassic fault basins of the east coast or the clays of the southeast U.S. . Lovely. This is a really nice reference for those unfamiliar with this deposit. Thanks.
Mark
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Roger Warin




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PostPosted: Mar 26, 2013 15:25    Post subject: Re: A Scientific and mineralogical trip to the Iberian Pyrite Belt  

Extraordinary report and great pictures, thank you for sharing your knowledge and aesthetic sense.
All the best for Spain and you,
Roger.
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Cesar M. Salvan
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PostPosted: Mar 27, 2013 12:42    Post subject: Re: A Scientific and mineralogical trip to the Iberian Pyrite Belt  

Mark, Roger,

Thank you for your interest and kind words.
Mark, indeed the red color of the iron oxide gossan is impressive in live view. Especially in the beautiful San Miguel open pit, that preserved intact the contact between the primary ore and the paprika-red hematite rich gossan. My goal was to introduce the IPB deposits to those who are unfamiliar with them, as it is, probably, the most important mining district in the Iberian peninsula from a global perspective.



proustita11.jpg
 Description:
Proustite
Las Cruces mine, Gerena, Seville, Andalusia, Spain
0.7 cm crystals
The association of proustite (a hidrothermal mineral formed at relatively high temperature) with the secondary, pulverulent and possibly biogenic galena in Las Cruces is intriguing.
 Viewed:  33902 Time(s)

proustita11.jpg



calcosina 1.jpg
 Description:
Chalcocite
Las Cruces mine, Gerena, Seville, Andalusia, Spain
2 cm crystal
It is not usual in the IPB to find centimetric crystals of sulfide minerals. I recovered this specimen in 2010, just after the beginning of copper production.
 Viewed:  33924 Time(s)

calcosina 1.jpg



DSCN0738.JPG
 Description:
Chalcocite
Las Cruces mine, Gerena, Seville, Andalusia, Spain
Chalcocite crystal photographed in situ
 Viewed:  33910 Time(s)

DSCN0738.JPG



varios 007.JPG
 Description:
Las Cruces mine, Gerena, Seville, Andalusia, Spain
From the mineral to the market: pure copper slabs prepared for shipping. The hydrometallurgy process of Las Cruces mine is efficient and allow to obtain highly purity copper.
 Viewed:  33912 Time(s)

varios 007.JPG


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Mark Ost




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PostPosted: Mar 27, 2013 15:11    Post subject: Re: A Scientific and mineralogical trip to the Iberian Pyrite Belt - (6)  

You are doing a fine job of it. Your micro photography is very good. I would almost call the colors vermilion.........................almost, because; as a man I can only really recognize primary colors! We need our painter here to weigh in on color. I'll bet those copper sheets are heavy. Keep it coming. I love this thread.
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jorge santos garcia




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PostPosted: Apr 09, 2013 18:05    Post subject: Re: A Scientific and mineralogical trip to the Iberian Pyrite Belt - (6)  

Let me share some information about the Iberian Pyrite Belt, as well, complementing the previous data posted by César:

The Iberian Pyrite Belt (IPB) corresponds to an area of Devonian-Carboniferous Superior (380 to 290 million years) volcanic and sedimentary rocks containing massive polymetallic sulfide deposits. This area forms a belt, about 250 km long and up to 60 km wide, trending westwards from near Seville in Spain to west-northwest in South Portugal. Both the eastward and westward extents of the belt are covered by Tertiary sedimentary rocks.

The IPB is arguably the largest and most important volcanogenic massive sulfide metallogenic province in the world. Some of its mineral deposits have been known and mined since the Chalcolithic era such as the Rio Tinto deposit, reaching a high peak of exploitation at roman times, such as in Aljustrel.

Only after the discovery of the large and rich copper-tin orebody of Neves-Corvo (Southern Portugal) in 1977, has the true importance and potential of the IPB become fully appreciated.

The original, pre-erosional amount of sulfides concentrated in about 90 known deposits are estimated at more than 1.7 billion tons. Of this amount, about 20 percent has been mined. This impressive amount of metals, in concentrations that range from small lenses with thousands of tons to giant bodies with hundreds of millions of tons, in such a relatively small area, represents an outstanding global geochemical anomaly of S, Fe, Zn, Cu, Pb, Sn and several other metals.

Three types of sulfide mineralization occur in the IPB: stratiform polymetallic massive sulfide bodies, with pyrite predominant (35-51 % S or 66-96% pyrite equivalent); disseminated polymetallic pyrite bodies usually with less than 35% S, and generally associated with the stratiform orebodies, stockwork, stringer or fissural ore, distinguished by the relative proportion of sulfides and silicates, and with sulfur contents from 5-25% (10-25% pyrite equivalent).

Among the very large deposits, several are considered giant (more than 50 million tons), such are the cases of Tharsis (>100), La Zarza (>100), Los Frailes-Aznalcóllar (>110), Sotiel-Migollas (>100); and three super-giants (more than 200 million tons): Rio Tinto (>290), Neves-Corvo (>270) and Aljustrel (>230).

The average composition of known resources and reserves is: Cu - 1.3%; Zn - 2.0%; Pb - 0.7%; Au - 0.5 g/t; Ag - 26 g/t; S - 45%; Fe - 40%.

The bulk of the mineralogy in massive sulfide bodies comprises fine to medium grained pyrite, with variable amounts of sphalerite, chalcopyrite, galena (and cassiterite at Neves-Corvo). Tetrahedrite-tennantite, arsenopyrite, bournonite and pyrrhotite are common, and many other minerals have been identified in small and trace amounts. Tin minerals, cassiterite and Cu-Zn-Sn sulfides (stannite-kesterite, mawsonite and stannoidite) are present in most deposits, and reach extremely high concentrations in the tin and copper-tin ores at Neves-Corvo.

This information was based on: Introduction to the Iberian Pyrite Belt. Fernando J.A.S. Barriga, Delfim de Carvalho and António Ribeiro. F.J.A.S. Barriga and D. Carvalho,eds
Geology and VMS Deposits of the Iberian Pyrite Belt. SEG Neves Corvo Field Conference 1997. Guidebook Series Volume 27. © Society of Economic Geologists 1997
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jorge santos garcia




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PostPosted: Apr 10, 2013 16:41    Post subject: Re: A Scientific and mineralogical trip to the Iberian Pyrite Belt - (6)  

Some information about Aljustrel mines:
The polymetallic sulphide ore are mainly iron sulphides (pyrite -> 70%) that associate varying proportions of sulfides of copper (chalcopyrite), zinc (sphalerite) and lead (galena). Tetraedrite and arsenopyrite rarely appear. The main gangue minerals are quartz, carbonates and Baryte. There are six mineralized orebodies discovered so far - São João do Deserto, Algares, Moinho, Feitais, Estação and Gavião, occurring in two parallel alignments. The southern alignment is composed by the deposits Gavião, São João do Deserto, Moinho and Algares and the southern alignment is composed of deposits of Feitais and Estação. All this geological structure is cut by the Fault of Messejana, the biggest of the Iberian Peninsula.
The mining activity in Aljustrel goes back at least to Roman times. There’s evidence that at the time of Emperor Adriano (117-138 AD) exploitation was in full operation.
Between 1876 and 1906 a series of bronze plaques were discovered - the Tables of Vipasca (former name of Aljustrel) - dating from 173 AD. They are a code and the laws for operating the mines, having regulations on the administration of mining, the exploitation regime, fines and technical exploitation guidelines.
The Romans and possibly the people who preceded them exploited the masses and surface gossan of São João do Deserto and Algares. This exploitation was so intense that it is known that in some periods of the second and third centuries, during Roman rule, workers at Vipasca Mines reached about 2000 people.
During the Middle Ages the mine was largely abandoned, having been resumed operation in 1845. At the beginning of the 20th century, the operation aimed mainly at obtaining sulfur used to produce sulfuric acid and fertilizers. Copper and silver and gold was also produced.
The orebodies of São João do Deserto and Algares have been exploited during the 1960s, the last one being depleted. In the 1950s was discovered the orebody of Moinho, in 1964 the orebody of Feitais, in 1969 the orebody of estação and in 1970 the orebody of Gavião. The orebodies of Feitais and Moinho were exploited until 1993, the year the mines closed. The veins of Estação and Gavião were never explored.
Feitais orebody is being exploited since 2008 for copper and zinc concentrates.



Picture3.jpg
 Description:
Vipasca shaft. Doesn't work anymore. It was recovered for future memory
 Viewed:  33381 Time(s)

Picture3.jpg



Picture4.jpg
 Description:
Old cementation tanks for obtaining sulfur and copper.
 Viewed:  33381 Time(s)

Picture4.jpg


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jorge santos garcia




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PostPosted: Apr 10, 2013 17:03    Post subject: Re: A Scientific and mineralogical trip to the Iberian Pyrite Belt - (6)  

A few more photos.


Picture5.jpg
 Description:
Acidified rain water by running on contaminated soil (pH 1,5 - 3), coloured red by dissolved iron.
 Viewed:  33387 Time(s)

Picture5.jpg



Picture6.jpg
 Description:
Melanterite stalactites to 50cm high on old adit of Algares Mine.
 Viewed:  33377 Time(s)

Picture6.jpg



Picture2.jpg
 Description:
Blue green melanterite, brownish copiapite, white halotrichite-pickeringite crusts on old adit on Algares Mine. FOV +- 20cm.
 Viewed:  33356 Time(s)

Picture2.jpg



minerais antigos aljustrel.jpg
 Description:
Old specimens at the head office, collected on Feitais Mine (gypsum crystal with almost 20cm, single Baryte crystal on the right with 12-15 cm).
 Viewed:  33370 Time(s)

minerais antigos aljustrel.jpg



Picture11.jpg
 Description:
Collecting 330m deep, Feitais mine.
 Viewed:  33365 Time(s)

Picture11.jpg



503-DIV_2.jpg
 Description:
Some of the result - dog tooth calcite crystals to 1,5cm on brownish red dolomite
 Viewed:  33378 Time(s)

503-DIV_2.jpg



Picture10.jpg
 Description:
1.5 to 2m high fault mirror (slikenside) on chalcopyrite rich massive sulfide ore, 250m deep. Feitais mine.
 Viewed:  33360 Time(s)

Picture10.jpg


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Josele




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PostPosted: Apr 10, 2013 18:11    Post subject: Re: A Scientific and mineralogical trip to the Iberian Pyrite Belt - (6)  

Excellent report and very interesting hypothesis for the origin of these deposits, thank you César.
Thanks also to Jorge, your inputs of the Portuguese side provide an overview of the IPB.

_________________
Josele
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jorge santos garcia




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PostPosted: Apr 17, 2013 19:47    Post subject: Re: A Scientific and mineralogical trip to the Iberian Pyrite Belt - (6)  

Thank you Josele.

And now some information about Neves-Corvo mine:
Neves-Corvo is a modern mine, whose sulphide orebodies of Neves and Corvo where discovered in 1977. It’s exploitation started in 1988. The complex massive sulphide mineralization is constituted mainly by pyrite, chalcopyrite, sphalerite, galena, stannite, tennantite-tetrahedrite and by an array of others sulfosalts. Because the small granulometry of the sulphide massive mineralization, crystals are very rare, and because of the mechanical exploitation the recovery of specimens are even rarer. But sometimes the mine provide beautiful honey coloured baryte crystals, white dolomite and chalcopyrite, tennantite-tetrahedrite and pyrite crystals.

There are 5 orebodies discovered so far:
Corvo is 230m deep and has 1100m long by 600m wide and a maximum of 95m thick. It was discovered in 1977.

Graça is linked to Corvo and has 700m by 500m and a maximum thickness of 80m. it was discovered in 1978 and is mined out. It is exhausted and was the supplier of tin, which is not produced nowadays.

Neves has 1200m by 700m by 55m. it was also discovered in 1977.

Zambujal is a small lenses, discovered in 1979, with low levels of copper and zinc.

Lombador was discovered only in 1988. It goes to 1000m deep and has 750m long and 65m thick. It will be in exploitation very soon and will supply almost only zinc.

There are two more possible orebodies in study – Semblana and Monte Branco.



Picture7.jpg
 Description:
Copper rich sulphide wall (FOV 3-4m), 550m deep.
 Viewed:  33069 Time(s)

Picture7.jpg



26-NC_2.jpg
 Description:
7 cm specimen of white dolomite with brassy yellow chalcopyrite and greyish pyrite crystals.
 Viewed:  33051 Time(s)

26-NC_2.jpg



490-DIV.jpg
 Description:
Massive chalcopyrite with a spot of massive galena. 8,5cm
 Viewed:  33073 Time(s)

490-DIV.jpg



494-DIV.jpg
 Description:
Stockwork sample of chalcopyrite veinlets on schist. 6,5cm.
 Viewed:  33052 Time(s)

494-DIV.jpg



16-NC_3.jpg
 Description:
Chalcopyrite crystals with 4mm with white flattened rhombohedral dolomite crystals. FOV - 3cm.
 Viewed:  33046 Time(s)

16-NC_3.jpg



27-NC_3.jpg
 Description:
Strange baryte crystal with 4x4cm and an unusual pattern: a bottom rhombus dark golden, two sided light golden rhombus and a white top rhombus.
 Viewed:  33056 Time(s)

27-NC_3.jpg



468-DIV_2.jpg
 Description:
Golden baryte crystals. FOV 9cm.
 Viewed:  33048 Time(s)

468-DIV_2.jpg



470-DIV_1.jpg
 Description:
Golden baryte crystals specimen with 17cm.
 Viewed:  33051 Time(s)

470-DIV_1.jpg



470-DIV_3.jpg
 Description:
Baryte crystal with 2 cm high.
 Viewed:  33064 Time(s)

470-DIV_3.jpg


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