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Prospecting pegmatite for schorl: need help.
  
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cascaillou




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PostPosted: Dec 12, 2017 14:59    Post subject: Prospecting pegmatite for schorl: need help.  

Hi,
I found an outcrop of granitic pegmatite in the Pyrénées mountains, with some embedded Schorl (tiny broken prisms and anhedral ones). Indeed, in this area, pegmatites do not host pockets filled with crystals, instead the crystals are found directly embedded within the rock.
So, I wish I could find better Schorl crystals (meaning large and well crystallized) within this outcrop, but I'm not sure where to start digging:

Some parts of this pegmatite outcrop are rather fine grained (5mm to 1cm grains), while other parts are more coarse grained (1 to 4cm grains). Many parts of the pegmatite outcrop are mostly feldspatic (association of bluish grey and cream white feldspar grains) while other parts have more quartz, usually without major mica although a few areas do show large mica plates.

So, in your experience of European pegmatites, which parts of the outcrop sound more appropriate for nice Schorl crystals to occur?
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Peter




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PostPosted: Dec 12, 2017 16:24    Post subject: Re: Prospecting pegmatite for schorl: need help.  

cascaillou wrote:
So, in your experience of European pegmatites, which parts of the outcrop sound more appropriate for nice Schorl crystals to occur?


The larger the grain size the more interesting for larger tourmalines. That is basic. Now if you showed overview photo of this pegmatite we may sea bit more. Then in a pegmatite field of perhaps hundreds of pegmatites, perhaps only one or a few have some special mineralizations if you are lucky, and it is often these are not visible on the surface.

Good luck
Peter
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cascaillou




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PostPosted: Dec 13, 2017 08:02    Post subject: Re: Prospecting pegmatite for schorl: need help.  

I was wondering if Schorl is more likely to occur in the feldspatic part of the pegmatite outcrop, or rather in the part that has more quartz.
It would be difficult to take a picture due to thick vegetation and moss.
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Peter




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PostPosted: Dec 13, 2017 11:42    Post subject: Re: Prospecting pegmatite for schorl: need help.  

You may have in both.
The largest schorl I have seen occured in primarily feldspar blocky zone boardering the quartz core in very large pegmatites.
However the easiest schorls to recover complete with hammer and chisel, or perhaps you have access to more sophisticated tools, are in quartz.
Peter
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Peter Lemkin




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PostPosted: Dec 13, 2017 13:27    Post subject: Re: Prospecting pegmatite for schorl: need help.  

In the pegmatites I'm familiar with, the schorl will be more solid [less likely to easily crumble - but don't confuse this with weathering] as you get near the area of possible pockets. When you are very close to a pocket the tourmaline will actually have the XX oriented toward the core. So, I'd look for areas that have schorl that are more tough than others [don't break apart, but stay consolidated more often from the quartz]. There are other 'tricks' one learns in pegmatite areas...but you don't yet know if there are pockets or not. Pockets sometimes are penetrated by roots of trees/bushes.....but that is easier to find in semi-desert areas where there are not many plants. I'd also look for mica, especially lepidolite, lying on the ground in areas that might have pockets...but that is not 100% either. In each pegmatite area people learn the 'signs'...although there are a few that hold for most pegmatite areas. Not all pegmatites have pockets...in fact, most do not. Graphic granite is another thing I look for, as well as albite xx. Bigger and better garnet xx might be another indication. In some pegmatites, phosphate minerals, such as purpurite, are indications....I think you should do some research on the area you are exploring to see what has been found and what good signs are. If there are any ravines that water has moved materials down...walk back up and watch for xx that seem promising and find out where they might have come from. Look for others prospect holes, if any. See if any mining claims in the area and what kinds of minerals were on the claims. After years of searching pegmatites one gets a 'second sense' for where pockets are....and it is hard to explain to others [or one doesn't want to in very good areas ;-) ]
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Josele




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PostPosted: Dec 13, 2017 16:01    Post subject: Re: Prospecting pegmatite for schorl: need help.  

cascaillou wrote:
I was wondering if Schorl is more likely to occur in the feldspatic part of the pegmatite outcrop, or rather in the part that has more quartz. ...

In the pegmatites of Cap de Creus area (eastern end of Pyrenees) schorl (as the rest of associated minerals) is found mostly between feldspar in the intermediate zones and only occasionally into the quartz core.
Aside zonation, in the mentioned area schorl concentration is very variable from one outcrop to other, so this general rule is not a very useful trick for collectors.
On the other hand, these pegmatites are very old (syntectonic with Hercynian orogeny) and have suffered also the Alpine orogeny and related metamorphism, that's why crystals in these pegmatites are often distorted, broken and altered.

Can see a report of these pegmatites here: Pegmatitas del Cap de Creus



pegmatite structure.jpg
 Description:
Mineralization distribution in different pegmatite types. Schorl is represented as black triangles.

image © Pura Alfonso - J. C. Melgarejo, 2000, Boron vs. Phosphorus in granitic pegmatites: the Cap de Creus case, modified from J. Carreras (1975)
 Viewed:  683 Time(s)

pegmatite structure.jpg



pegmatite boudin.jpg
 Description:
When the pegmatite body is "boudinated" (very usual in syntectonic pegmatites as these ones) schorl is concentrated on the sides of the constrictions:

image © Pura Alfonso - J. C. Melgarejo (2000) Boron vs. Phosphorus in granitic pegmatites: the Cap de Creus case
 Viewed:  685 Time(s)

pegmatite boudin.jpg



P1160233.jpg
 Mineral: Schorl
 Locality:
Cap de Creus, Cadaqués - Port de La Selva - Roses, Comarca Alt Empordà, Girona/Gerona, Catalonia, Spain
 Dimensions: Up to 10 cm
 Description:
Schorl grouping surrounded by feldspar:
 Viewed:  661 Time(s)

P1160233.jpg



405P1160229 copia.jpg
 Mineral: Schorl
 Locality:
Cap de Creus, Cadaqués - Port de La Selva - Roses, Comarca Alt Empordà, Girona/Gerona, Catalonia, Spain
 Dimensions: Diameter up to 5 cm
 Description:
Crystals are always embedded, The only miarolitic cavities I have found in these pegmatites were very small and containing just quartz.
 Viewed:  664 Time(s)

405P1160229 copia.jpg



P1080952.jpg
 Mineral: Schorl
 Locality:
Cap de Creus, Cadaqués - Port de La Selva - Roses, Comarca Alt Empordà, Girona/Gerona, Catalonia, Spain
 Dimensions: 20 x 13 x 12 mm
 Description:
Found on the floor as result of feldspar weathering.
 Viewed:  657 Time(s)

P1080952.jpg


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cascaillou




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PostPosted: Dec 13, 2017 17:59    Post subject: Re: Prospecting pegmatite for schorl: need help.  

Thanks guys, great contributions!
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Philippe Durand




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PostPosted: Dec 14, 2017 12:17    Post subject: Re: Prospecting pegmatite for schorl: need help.  

I have a little experience of french pegmatites south of massif central.
I have found some schorls ;
but I have worked the ground around and down at the foot of the pegmatites or on altered pegmatites; it is far easier to work, and to find crystals naturally free from the quartz and
feldspath.

examples that can be found



E41.JPG
 Mineral: schorl
 Locality:
La Salvetat-sur-Agout, Saint-Pons-de-Thomières, Béziers District, Hérault, Occitanie, France
 Dimensions: 80mm
 Description:
 Viewed:  557 Time(s)

E41.JPG



DSC03936.JPG
 Mineral: Schorl
 Locality:
La Salvetat-sur-Agout, Saint-Pons-de-Thomières, Béziers District, Hérault, Occitanie, France
 Dimensions: 20mm
 Description:
 Viewed:  559 Time(s)

DSC03936.JPG


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cascaillou




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PostPosted: Dec 14, 2017 14:11    Post subject: Re: Prospecting pegmatite for schorl: need help.  

Well I spent the all day there but couldn't find anything interesting.
Still here are a few pictures. The first pic shows the host rock surrounding the pegmatite lodes. The other pics show the pegmatites.



IMG_20171214_152745.jpg
 Mineral: Host rock
 Description:
 Viewed:  537 Time(s)

IMG_20171214_152745.jpg



IMG_20171214_155539.jpg
 Mineral: Peg 1
 Description:
 Viewed:  533 Time(s)

IMG_20171214_155539.jpg



IMG_20171214_153324.jpg
 Mineral: Peg 2
 Description:
 Viewed:  538 Time(s)

IMG_20171214_153324.jpg



IMG_20171214_140955.jpg
 Mineral: Peg 3
 Description:
 Viewed:  536 Time(s)

IMG_20171214_140955.jpg



IMG_20171214_132109.jpg
 Mineral: Peg 4
 Description:
 Viewed:  537 Time(s)

IMG_20171214_132109.jpg



IMG_20171214_132127.jpg
 Mineral: Peg 5
 Description:
 Viewed:  532 Time(s)

IMG_20171214_132127.jpg


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