Heavy Mineral - Sedimentology - Lecture Slides, Slides of Geology

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Heavy mineral analysis and

Provenance

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Objectives :

1. To separation of heavy minerals from light

minerals.

2. To studying the mineralogy in detail, which can

learn much more about the history of a sediment.

3. To determine rock type or source material (source

area) is known as provenance.

4. To understand the simple sedimentary processes of

weathering, transportation, and deposition.

5. Textural maturity, which is a measure of

distance/time from the source area to the

depositional site, of sediments is determined

largely in terms of grain size, sorting and

roundedness. Docsity.com

Introduction

 Heavy minerals are those minerals which have specific gravity greater than 2.9.  They are a group of minerals found in some kinds of sedimentary rocks: o as a small quantity or o as an ore minerals or o as placer deposits.  In sandstone rocks they make up more than one percent of the rock.  The extent that the heavy minerals survive the intensity of weathering, transportations and diagenesis and to the degree that they occur in a restricted range of provenance types, they are most useful for source rock interpretation. Docsity.com

 Heavy minerals may be concentrated to form placer deposits like monazite sands of India.  Common heavy minerals range from (3 to 5) in specific gravity.  Because of heaviness they usually travel with quartz with the size (0.5 to 1Ø).  Shapes of heavy minerals are sensitive indicators to the intensity of abrasion.  For example angular and rounded tourmaline in the same sample indicates a multiple source.

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 Pyrite is not a rock-forming mineral, but it is commonly present in sedimentary rocks that formed in or near seawater (oceans, lagoons, and coastal swamps).

 Olivine, pyroxene, plagioclase, amphibole, and biotite are uncommon in sedimentary rocks.

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Equipment and materials

o Heavy liquid-tetrabromethane (C 2 H 2 Br 4 ), about 10 ml per sample. o Acetone. o Hand magnet, for removal of magnetic mineral particles o Separatory funnels and ring stand. o Analytical Balance o Wire-mesh sieves o Brush for cleaning sieves. o Glass slides and cover glasses. o Filter paper. o Magnetic-separator apparatus. o Bottles for collecting used heavy liquid and fluid waste o Watch glass to cover separatory funnel Docsity.com

2. Magnetic methods

This method depends on magnetic susceptibility of the heavy minerals. Depending on this property heavy mineral divided into: a) Mineral with high magnetic susceptibility , include: magnetite, hematite, ilmenite, and pyrrhotite. b) Mineral with medium magnetic susceptibility , include: amphibole, biotite, and chromite. c) Mineral with low magnetic susceptibility , include: epidote, rutile, garnet, olivine, and pyroxene. d) Non-magnetic minerals include: galena, apatite, pyrite, and zircon.

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In this method we can separate the heavy minerals in two different ways:

a) Manual method: b) Electrical magnetic method:

a) Manual method: In which a normal hand magnetic grains and the high magnetic susceptibility grains will be attracted by the hand magnet.

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o The prepared sample or crushed sample will be placed on the free moving stage, o first the high magnetic susceptibility grains can be removed by passing low electric current, o then by increasing the current the force of the magnet will be increased and the medium magnetic susceptibility grains will be removed (at the time of separation free moving stage will be moved upward, downward, and in all directions). o For separation of low magnetic susceptibility the force of the magnet must be increased by increasing the electric current. o Finally the non-magnetic grains will be remained. Each group of the minerals must be studied under microscope for reorganization and to obtain the provenance. Docsity.com

Minerals that are Magnetic at Various Amperages

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Procedure:

1. The prepared sample must be sieved in order to obtain grains with (1-4Ø) or (1/2-1/16mm) in size.
2. Weigh (20gm) of the sample.
3. Pour tetrabromoethane (bromoform) into upper (separatory) funnel, (Fig.2). The funnel should be about ½ full [carry out this and all following operations under a well ventilated hood] the heavy liquid and its funnels are toxic.
4. Pour the sample into the bromoform and stir thoroughly in order to make all the particles wet and disperse air bubbles.
5. Allow the particles to settle, stir periodically so that particles will not adhere to funnel wall. Cover the funnel with watch glass to reduce heavy liquid evaporation. Docsity.com

6. When heavy minerals have settled to bottom of separatory funnel, open pinch-cock and allow heavy mineral particles to drop onto filter paper in lower funnel. Close pinch-cock so that minerals floating in remaining heavy liquid will remain in the separatory funnel.
7. After heavy liquid has drained from filter paper into used heavy liquid bottle below, remove paper and place upside down in porcelain dish or large watch glass containing acetone. If necessary, use plastic squeeze bottle containing acetone to wash into the dish any particles which adhere to the filter paper, decant excess acetone into fluid waste container.

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