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=Mineral separation=
 
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[[File:Mineral separation.png|250px|thumb]]
 
<div class="noautonum">__TOC__</div>
 
  
== Wozu werden Minerale aus Gestein abgeschieden?==
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<imagemap>
 
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Datei:PM Mineralseparation Schema.jpg|800px|center|thumb|Ablauf einer Mineralseparation
Die Separierung von Mineralen aus Gestein wird typischerweise aus einem der folgenden Gründen vorgenommen:
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rect 1977 189 2885 481 [[Vorbereitung eines Geländeaufenthalts]]
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rect 1845 545 3005 845[[Geologische Probenahme]]
{|  style= "text-align:left;"
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rect 1525 917 3333 1221 [[Gesteinsbeschreibung]]
|'''Industrie'''
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rect 1641 1289 3221 1685 [[Probenzerkleinerung]]
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</imagemap>
|'''Wissenschaft'''
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<br>
|-
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<br>
| - Apatit zur Düngemittelgewinnung
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<br>
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| - Chemische Analyse 
 
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| - Feldspat für Zement und Keramik
 
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| - Spektroskopie
 
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| - Metalle
 
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| - Stable isotope analysis
 
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| - Gold
 
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| - [[Radiometrische Datierung]]
 
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| - ...
 
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| - ...
 
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===Vorbereitung der Feldarbeit===
 
 
 
'''Geologischer Hintergrund'''
 
 
 
Um ein gutes Verständnis der Geologie des Untersuchungsgebietes zu erhalten, muss eine eingehende Auseinandersetzung mit der entsprechenden Literatur, vor allem in Form aktueller Paper, stattfinden. Nur so kann eine effektive und wissenschaftliche Feldarbeit gewährleistet werden.
 
 
 
'''Sammlung von Kartenmaterial, Konzeptkarte und Fernerkundung'''
 
 
 
Während der Forschungsphase werden alle verfügbaren Daten und alles Kartenmaterial des Untersuchungsgebiets gesammelt. Die Nutzung von Fernerkundungsdaten vor dem Beginn der Feldarbeit hilft bei der Organisation und von Feldkampagnen und ermöglicht einen Überblick über die geologischen Eigenschaften und Merkmale des Untersuchungsgebietes.
 
 
'''[[Vorbereitung von Geländeaufenthalt#Kleidung|Kleidung]]'''
 
 
Packing appropriate clothing for the anticipated weather conditions of the mapping area is essential for safety.
 
 
 
'''[[Vorbereitung von Geländeaufenthalt#Rucksack|Rucksack im Feld]]'''
 
 
 
Necessary tools for a field geologist to collect data in the field.
 
 
 
'''Reference materials'''
 
 
*  Barnes, J.W. and Lisle, R.J., 2004. Basic Geological Mapping (4th edition). John Wiley & Sons Ltd. 184p. 
Coe, A.L., 2010. Geological Field Techniques. Wiley-Blackwell/The Open University. 323p. 
Compton, R.R., 1985. Geology in the Field. John Wiley and Sons, 416pp. 

 
 
 
*  Fry, N., 1984. Field Description of Metamorphic Rocks. Geological Society of London Handbook Series. John Wiley and Sons, 110pp. 

 
 
 
*  McClay, K.R., 1987. The Mapping of Geological Structures. Geological Society of London Handbook Series. Open University Press, 161pp. 

 
 
 
*  Thorpe, R.S. and Brown, G.C., 1985. Field Description of Igneous Rocks. Geological Society of London Handbook Series. John Wiley and Sons, 154pp. 

 
 
 
*  Tucker, M.E., 2003. Sedimentary Rocks in the Field (3rd ed). Geological Field Guide Series. John Wiley and Sons, 244pp. 

 
 
 
* Pocket-sized reference books designed to be taken into the field.
 
 
 
===[[Probennahme]]===
 
 
 
The sampled rock has to be in-situ and fresh. The rock should not have alteration rims (can be removed in the lab with saw), weathering nor veins. The sample should be transported and stored in a dry environment. The labelling is usually a maximum of seven characters with two letters and five numbers (e.g. ID 12345). More information on the sampling methods is discussed [[Probennahme|here]].
 
 
 
===Sample size===
 
 
 
To separate minerals from a rock, you must have some prior knowledge about the relative abundance of that mineral in the rock, which would then serve as a guide as to how much of the rock sample you should process. Prior to beginning your work, you should also know (at least in a rough sense) the grain size of the minerals you wish to separate. A third piece of information is whether the mineral of interest contains any inclusions (as these are definitely not desired as they will interfere with most of your analyses). If the mineral is coarse grained, and is fairly abundant within the sample (modal content of > 10%), then a grapefruit sized sample is probably enough. On the other hand, if you are interested in separating an accessory mineral like sphene, zircon, or apatite, then your sample should be several kg in weight (minimum size that of a human head). Depending on the abundance of the available datable mineral the sample size will vary from 2-3 kg to 20-40 kg. Several points have to be taken into account such as:
 
 
 
- The yield of analysable material from a given sample is often unknown
 
 
 
- The bigger the sample the more options are given in selecting mineral grains for analysis
 
 
 
- Cost
 
 
 
===[[Probenzerkleinerung]]===
 
 
 
There are several techniques that can be used to crush rocks down to a desired size:
 
 
 
- hammer/chisel
 
 
 
- diamond saw
 
 
 
- [[Presse|hydraulic press]]
 
 
 
- [[Jaw crushers]]
 
 
 
- mills
 
 
 
===[[Sieve]]===
 
 
 
Sieving should be done with several sieves of different mesh sizes with the larger mesh at the top and the smallest mesh at the bottom of the tower. More information about the sieving steps can be found [[Sieve|here]].
 
 
 
===[[Panning]]===
 
 
 
Panning is a quick and efficient method to separate the heavy fraction from the rest of the sample.
 
 
 
===[[Schütteltisch]]===
 
 
 
The Wilfley table is a type of shape/density separator and is used extensively to separate zircons for U-Pb dating, or heavy minerals (e.g native gold) for commercial use.
 
 
 
Nach der Justierung des Schütteltischs im benötigten Winkel und der Einstellung der Bewegungsgeschwindigkeit (Hubgeschwindigkeit, rpm), wird die Probe in den Vibrationsförderer gegeben der den Schütteltisch durch den Einspeisungskasten mit einer konstanten Rate speist (siehe Abbildung). Die Probe wird damit in drei Fraktionen geteilt:
 
 
 
====Schwere Fraktion====
 
 
 
The heavy mineral fraction is concentrated in minerals such as zircon, garnet, apatite, sphene, monazite...
 
 
 
Before proceeding to the picking of the desired mineral a magnetic separation is required to facilitate the picking.
 
 
 
If the heavy mineral fraction is still encumbered by lighter minerals such as quartz it is preferable to add a heavy liquid separation or a panning step to make the picking easier.
 
 
 
====Mittlere Fraktion====
 
 
 
The middle fraction is usually concentrated in minerals such as quartz, feldspars...
 
 
 
====Leichte Fraktion====
 
 
 
The light fraction is usually concentrated with minerals such as micas and clays...
 
 
 
===[[Isodynamischer Magnetabscheider]]===
 
 
 
====General Comments====
 
 
 
The Frantz Isodynamic Separator (FIS) separates minerals according to their magnetic susceptibility, and how the individual grains respond to the electromagnetic field versus gravity. It is a high precision, but very slow piece of equipment that is useful for processing and handling small quantities of your sample. It can only work with a grain size between 28 and 200 mesh. Samples larger than 28 mesh will clog the separator.
 
 
 
====Principle of operation====
 
 
 
''Magnetic properties of minerals''
 
 
 
Minerals are classified into four groups based on their attraction to a magnetic field (~magnetic susceptibility), namely:
 
 
 
1. diagmagnetic: repels a magnet, zero dipole moment
 
  
2. paramagnetic: random arrangement of magnetic dipoles in a crystal structure; drawn weakly to a magnet (e.g. olivine).
 
  
3. ferromagnetic: similar to paramagnetic but has domains that align easily in the presence of an external magnetic field; therefore strongly attracted to a magnet (e.g. Fe).
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{{Autor|1=D. Aßbichler, S. Prochaska}}
 
 
4. ferrimagnetic: antiparallel ionic spin moments; permanent magnetic domains are there (e.g. magnetite).
 
 
 
The FIS has a chute between the poles of an electromagnet. This chute is partitioned along its length. It can be tilted in two direction: forward (herein called slope), and sideways (herein called tilt). Forward slope controls the speed of movement of the grains down the chute, whereas tilt controls how well the minerals are separated according to their susceptibility. The FIS is typically set up with a slope of 15° and a tilt of 10 – 15° away from the operator. The electric current is then varied to separate the different minerals as they move down the chute.
 
 
 
===[[Schweretrennungsflüssigkeit]]===
 
 
 
===[[Picking]]===
 
 
 
<imagemap>
 
File:Mineral_separation_chart_2.png
 
 
 
circle 237 123 56 [[Kategorie:Mineral_separation#Vorbereitung der Feldarbeit|Vorbereitung der Feldarbeit]]
 
circle 421 123 56 [[Probennahme]]
 
circle 600 123 56 [[Kategorie:Mineral_separation#Sample size|Sample size]]
 
circle 421 278 56 [[Probenzerkleinerung]]
 
rect 187 320 294 465 [[Schütteltisch]]
 
rect 550 320 659 465 [[Panning]]
 
rect 447 485 499 518 [[Picking]]
 
circle 421 421 56 [[Analytik]]
 
rect 187 563 294 711 [[Kategorie:Mineral_separation#Schwere Fraktion|Schwere Fraktion]]
 
rect 367 563 475 711 [[Kategorie:Mineral_separation#Mittlere Fraktion|Mittlere Fraktion]]
 
rect 550 563 659 711 [[Kategorie:Mineral_separation#Leichte Fraktion|Leichte Fraktion]]
 
rect 164 791 310 901 [[Isodynamischer Magnetabscheider]]
 
rect 367 776 475 918 [[Schweretrennungsflüssigkeit]]
 
rect 527 806 675 896 [[Picking]]
 
circle 421 1021 56 [[Analytik]]
 
</imagemap>
 
  
[[Kategorie:Alle Methoden]]
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[[Kategorie:Probenaufbereitung Methoden]]
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[[Kategorie:Probenaufbereitung nach Präparationsmethode]]

Version vom 9. August 2020, 22:09 Uhr


Vorbereitung eines GeländeaufenthaltsGeologische ProbenahmeGesteinsbeschreibungProbenzerkleinerung
Ablauf einer Mineralseparation





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Dieser Artikel wurde geschrieben und gegengelesen von:
D. Aßbichler, S. Prochaska
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