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Mark Ost
Joined: 18 Mar 2013
Posts: 516
Location: Virginia Beach
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Posted: Apr 17, 2013 20:43 Post subject: Re: A Scientific and mineralogical trip to the Iberian Pyrite Belt - (6) |
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The Baryte is beautiful. Thanks for tour.
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Cesar M. Salvan
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Joined: 09 Jun 2008
Posts: 126
Location: Alcalá de Henares
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Posted: Jul 07, 2013 22:13 Post subject: Re: A Scientific and mineralogical trip to the Iberian Pyrite Belt - (6) |
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Here, I pick the tour through IPB up from the last addition about the interesting Neves-Corvo deposit.
As I explained in the beginning of this thread, the IPB deposits could be divided in two types, well differentiated in age and origin of the main mineralization. The Neves-Corvo deposit belong to the "Southern" class of volcano-sedimentary massive sulfide deposits in the IPB. This class of deposit is of interest to our research team, because of its main characteristics:
-shale hosted deposit: The mineralized massive sulfide bodies are included in the VSC (volcano-sedimentary complex), a complex formation that include dacitic-rhyolitic domes, sills, lava flows and volcanoclastics units interbedded with detrital sedimentary rocks, formed between 360-330 Ma.
- Age: The formation of the sulfides begun during late Fammenian (Devonian), in a black mud in a submarine environment and are coincident with the major biological crisis of the D-C boundary.
The origin of the mineral in this type of deposit is still a matter of debate. Some authors suggest that is exhalative, but some evidences suggest that is a brine pool type: the volcanic activity were formed in a small basin that suffered an anoxic episode due to the displacement of seawater by dense and saline hydrothermal fluids. This leads to the precipitation of sulfide, generated by the activity of anaerobic sulfate-reducing bacteria, among others parallel phenomena, as the formation of rich stockworks. The formation of pyrite in the form of fall-out of a very tiny crystals is the explanation to the extraordinary thin grain of massive pyrite in this type of deposits.
The deposits as Neves-Corvo and Tharsis show us a dramatic episode during Earth history: the volcanic activity and climate changes lead to a major ecological crisis and geochemical change that left the massive sulfide deposits as a generous clue.
The Neves-Corvo deposit has some particular features, that differentiate it from others deposits of similar origin, as Tharsis. For example, the contribution of magmatic-hydrothermal fluids to the mineralization, that generate an unique mineral assemblage, very rich in tin (with the presence of about 300000 tons of metal), associated with copper minerals in form of stannite and casiterite, among others rarer minerals. The origin and accumulation of tin is still a not fully resolved question, anyway.
Also, Neves-Corvo is a source of "high-tech" metals, particularly indium and germanium. The chalcopyrite and sphalerite of Neves-Corvo is one of the richest indium sources and this metal is recovered mainly from zinc concentrates. Despite of this indium richness, this metal rarely form visible minerals, observable at microscopic level (roquesite).
Other curiosity: the 23th april of 2013, the mine reached 1000 m deep, being the deepest mine workings in the IPB. To visit this mine is a exciting experience, although, as usual in active mining operations, is not easy to obtain permissions.
Anyway, as usual also in the IPB mines and in general in all volcano-sedimentary deposits, to obtain collectible specimens is very difficult, as Jorge Santos said. The Neves-Corvo mine was a unique case and beautiful crystals of tetrahedrite-group minerals, chalcopyrite, galena and Baryte occasionally appear.
...next chapters: Lousal mine, converted in a beautiful educational and divulgative initiative, and revisiting the most intriguing and complex deposit of IPB: Las Cruces.
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Neves-Corvo Mine, Santa Bárbara de Padrőes, Castro Verde, Beja District, Portugal The impressive headframe of Santa Barbara shaft, used for the extraction of mineral. |
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Neves-Corvo Mine, Santa Bárbara de Padrőes, Castro Verde, Beja District, Portugal The shores of hell: plaque remembering the day the miners reached the -1000 m level. The climate at that depth is oppressive: 50şC and 120% humidity in a mist, dark and suffocating atmosphere in spite of air circulation system. |
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Tetrahedrite group Neves-Corvo Mine, Santa Bárbara de Padrőes, Castro Verde, Beja District, Portugal aprox. 10 cm FOV Tetrahedrite group mineral taken in situ. The presence of tetrahedrite, tennantite and freibergite (usually in intermediate composition) has been reported. Without analysis of the sample, the correct label is tetrahedrite group or tetrahedrite-tennantite. |
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Chalcopyrite Neves-Corvo Mine, Santa Bárbara de Padrőes, Castro Verde, Beja District, Portugal View of a chalcopyrite stockwork in the Lombador orebody. Occasionally, epithermal veins and deformation fractures lead to the formation of crystals of chalcopyrite and other sulfides. |
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Chalcopyrite Neves-Corvo Mine, Santa Bárbara de Padrőes, Castro Verde, Beja District, Portugal crystal 4.7 mm Chalcopyrite and carbonate crystals in a closed fracture in shale hosted pyrite stockwork from Corvo orebody. Chalcopyrite is a plastic mineral and tends to flow and recrystallize in fractures. |
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Tetrahedrite group Neves-Corvo Mine, Santa Bárbara de Padrőes, Castro Verde, Beja District, Portugal crystal 2 mm Tetrahedrite-tennantite crystal surrounded by galena. Some authors suggest that these assemblages in volcanogenic sulfide deposits come from the mixing of hydrothermal fluids with cold seawater, with precipitation of galena-tetrahedrite group association. |
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Cesar M. Salvan
Site Admin
Joined: 09 Jun 2008
Posts: 126
Location: Alcalá de Henares
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Posted: Jul 12, 2013 19:15 Post subject: Re: A Scientific and mineralogical trip to the Iberian Pyrite Belt - (6) |
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And a little bit more on Neves Corvo mine...we found some rare secondary copper minerals in small fractures in chalcopyrite.
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Chalcopyrite, Redgillite Neves-Corvo Mine, Santa Bárbara de Padrőes, Castro Verde, Beja District, Portugal FOV 0.9 mm Small balls (aggregates of lath like crystals) of the rare sulfate Redgillite, found in a small fracture of massive Chalcopyrite of Corvo mass. |
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Chalcopyrite+undetermined chloride Neves-Corvo Mine, Santa Bárbara de Padrőes, Castro Verde, Beja District, Portugal FOV 0.9 mm Crystals of a not fully determined copper chloride (Botallackite?, Bobkingite?) on chalcopyrite. Corvo orebody. |
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Dolomite Neves-Corvo Mine, Santa Bárbara de Padrőes, Castro Verde, Beja District, Portugal A beautiful SEM image: dolomite, brochantite and copper chloride (Botallackite? Bobkingite?) on chalcopyrite. From the Corvo orebody. |
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Galena Neves-Corvo Mine, Santa Bárbara de Padrőes, Castro Verde, Beja District, Portugal FOV 2.5 mm |
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Chalcopyrite Neves-Corvo Mine, Santa Bárbara de Padrőes, Castro Verde, Beja District, Portugal Usually is not the underground workings the best place to study the metallogeny of a mine. Instead, the drill cores gives us better and more complete information about the geology and mineralogy of a mine. In the picture, a chalcopyrite stockwork (a network of ore veins) |
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Cesar M. Salvan
Site Admin
Joined: 09 Jun 2008
Posts: 126
Location: Alcalá de Henares
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Posted: Aug 23, 2013 07:57 Post subject: Re: A Scientific and mineralogical trip to the Iberian Pyrite Belt - (6) |
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As promised in the latest post, I continue here with this brief trip along the Iberian Pyrite Belt, with the, by far, most interesting deposit of the belt from both a mineralogical and general scientific point of view: the Las Cruces mine (Gerena, Sevilla, Spain).
As the audience here seems to have a low interest in the metallogenic and ore deposit geological aspects, I will not annoy with long explanations. Instead, I will complete the glimpse of the deposit's mineralogy.
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Bornite Las Cruces mine, Gerena, Seville, Andalusia, Spain FOV 2 mm A recent novelty in the mine: beautiful (although small) pseudo-cubic crystals of bornite. |
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Bornite Las Cruces mine, Gerena, Seville, Andalusia, Spain FOV 2 mm Another view of the bornite crystals |
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Chalcocite Las Cruces mine, Gerena, Seville, Andalusia, Spain 4 mm crystal. Beautiful chalcocite crystal on calcite. The bests crystals have been recovered from recrystallization on fractures and hydrothermal veins, usually covered with carbonates. |
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Harmotome Las Cruces mine, Gerena, Seville, Andalusia, Spain FOV 2 mm This low temperature barium zeolite is widespread along the hydrothermal veins and fractures that cut the secondary enrichment zone, giving clues on the complex processes that happened here. |
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Harmotome Las Cruces mine, Gerena, Seville, Andalusia, Spain FOV 5 mm Harmotome radial groups, with pearceite on chalcocite matrix. |
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Tennantite Las Cruces mine, Gerena, Seville, Andalusia, Spain FOV 1.6 mm The tennantite is a frequent mineral, although is rare in crystals higher than 1 mm. When crystallized, always form perfect tetrahedrons, usually covered with other minerals, in this case chalcocite in spheroidal groups of very tiny tabular crystals. |
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Galena Las Cruces mine, Gerena, Seville, Andalusia, Spain Fast Sulphur sobresaturation in a zone of the deposit lead to interesting galena forms. |
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Silver Las Cruces mine, Gerena, Seville, Andalusia, Spain FOV 1.2 mm Native silver is a very rare mineral in Las Cruces, as expected given the mineralization processes. But, is occassionally found as small wires, usually accompanied by proustite. |
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amigo
Joined: 03 Feb 2017
Posts: 1
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Posted: Feb 08, 2017 22:24 Post subject: Re: A Scientific and mineralogical trip to the Iberian Pyrite Belt - (6) |
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hello, what a great site. Does anyone have any information or pictures of Lomero Poyatos mine. Australian mining company Winmar Resources has commenced drilling today. Would be very keen and interested if anyone could offer their thoughts on Lomero. Thankyou
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Jordi Fabre
Overall coordinator of the Forum
Joined: 07 Aug 2006
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Location: Barcelona
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