Mineralisering = generell term, koncentration av malmmineral

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Malmgeologi

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Malm - mineralisering

Malm = ekonomisk term, koncentration av malmmineral, som kan utvinnas med vinst

Mineralisering = generell term, koncentration av malmmineral

Kopparmalm:

 Malm för 100 år sedan 5 wt.% Cu

 Malm idag <0,5 wt.% Cu (5000 ppm)

På 100 år, har en kopparmalm 10 gånger lägre koncentration av Cu Den globala kopparreserven har ökat med en faktor på mellan 100 till 1000

En malmreserv är den kända mängden malm som finns i jordskorpan

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Malmbildning Källa

Transport

Avsättning

Hydrotermal Direkt magmatisk

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Anrikningsfaktorer till malm för några viktiga metaller

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Mineraliseringar - geologiska förutsättningar

Koncentrationen av ex. Cr and Ni varierar stort mellan olika typer av magmatiska bergarter.

Ultramafiska bergarter (tex peridotit):

Cr - 3000 ppm (anrikningsfaktor c.150) Ni - 2000 ppm

Basalt:

Cr - 270 ppm (anrikningsfaktor c. 1500) Ni - 130 ppm

Granit:

Cr - 10 ppm (anrikningsfaktor 40 000) Ni - 10 ppm

Alla Cr- och Ni-nickelmalmer förekommer i ultramafiska bergarter.

ppm=parts per million

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Viktiga malmmineral

Element Oxider

Sulfider

Guld, silver, platina Magnetit, hämatit (Fe) Kromit (Cr)

Ilmenit, rutil (Ti) Kassiterit (Sn) Kopparkis (Cu) Zinkblände (Zn) Blyglans (Pb)

Molybdenglans (Mo) Pentlandit (Ni)

Guld och silver är nästan alltid biprodukter vid brytning av sulfidmalmer.

Många sulfidmineral förekommer tillsammans i så kallade komplexmalmer.

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3 huvudgrupper av malmbildande processer

1. Direktmagmatiska (ortomagmatiska) malmer:

Malmer bildade direkt ur en magma genom separation

(kristallisationsfraktionering) eller i magmatiska restlösningar som anrikar vissa ovanliga element (tex i pegmatiter)

2. Hydrotermala malmer:

Malmer bildade ur heta lösningar, ofta associerade till vulkanisk eller annan magmatisk aktivitet

3. Sedimentära malmer:

Malmer som anrikats av ytnära vatten så som vaskning och vittring, och utfällning

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Ortomagmatiska malmbildande processer

Magmatisk kristallisationsdifferetiering:

Separering av tidigt kristalliserade, tunga mineral, pga

densitetsskillnader mellan smälta och kristaller (tex kromit).

Magmatisk likvation:

Separation av oxidrika och silikatrika smältor från en ursprunglig järn- och fosforrik magma (ger apatitjärnmalm).

Kromit i peridotit apatitjärnmalm

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Bushveld Cr+Ni+PGM mineralisering

En 2,0 Ga lagrad LIP- Large Igenous Province

PGM-Cu-Ni

PGM-Cr + Cu-Ni PGM-Cr + Cu-Ni

Ti-Fe 300 km

anortosit (basisk,Ca-plagioklasrik magmatisk djupbergart)

kromit

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Bushveld Cr+Ni+PGM mineralisering

En 2,0 Ga lagrad LIP- Large Igenous Province

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Ortomagmatisk malm Apatitjärnmalm

järnoxidsmälta

1000 m

Tex Kiruna, Malmberget, Grängesberg

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Senmagmatiska malmer (ortomagmatiska) magmatisk fraktionering

Pegmatiter kristalliserar sent i ett magmatiskt system  rika på kvarts, fältspat, muskovit som tillväxer till stora kristaller

Är anrikade på inkompatibla element som Li, Be, Cs, Sn, REE

Är också rika på volatila element som F, OH

Litiummalm, spodumen (LiAlSi₂O₆) – en litiumpyroxen

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3 huvudgrupper av malmbildande processer

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Hydrotermala och magmatiska mineraliseringar

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Hydrotermala malmer

VMS

Volcanic hosted Massive Sulfide deposits

Vid oceaniska spridningszoner och vid subduktionszoner

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Hydrotermala malmer

Volcanic hosted Massive Sulfide deposits - cyperntyp (koppar) -

oceanisk spridningszon

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Hydrotermala malmer

Volcanic hosted Massive Sulfide deposits - cyperntyp (koppar) -

oceanisk spridningszon

pyrit kopparkis

(Loberg, 1993)

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Hydrotermala malmer

Volcanic hosted Massive Sulfide deposits - cyperntyp (koppar) -

oceanisk spridningszon

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Hydrotermala malmer

Volcanic hosted Massive Sulfide deposits - cyperntyp (koppar) -

oceanisk spridningszon

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Hydrotermala malmer

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kuroko besshi

Cu, Pb, Zn

kuroko skarn

Hydrotermala malmer

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Hydrotermala malmer

Volcanic hosted Massive Sulfide deposits - Kurokotyp (Cu, Pb, Zn) -

Magmatiska bågen

Back-arc Hav

Tex Falun, Zinkgruvan, Kristineberg

(Loberg, 1993)

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Hydrotermala malmer

Volcanic hosted Massive Sulfide deposits

- Kurokotyp (Cu, Pb, Zn) -

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kuroko besshi

Cu, Pb, Zn

skarn

Hydrotermala malmer

VMS + järnoxider

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Hydrotermala malmer Skarnjärnmalm

Fe

kalkutfällning +

stromatoliter Avtagande vulkanisk aktivitet (långt mellan utbrotten) Hydrotermala celler med utfällning av Fe±Mg

Utfällning av kalkslam och tillväxt av stromatoliter

Reaktion mellan kalksten, vulkaniska utbrottsprodukter och hydrotermala lösningar

skarn (kalcium-magnesium-järnsilikater)

Tex Dannemora, Persberg, Nordmark, Långban

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Hydrotermala malmer Skarnjärnmalm

Kalkstenshorionter ersätts av skarn genom Si+Mg-Fe-rika lösningar

Felsisk vulkanit

Hydrotermala lösningar

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Hydrotermala malmer Skarnjärnmalm

Kalkstenshorionter ersätts av skarn genom Si+Mg-Fe-rika lösningar

Kalcitmarmor Zinkblände

Granat Pyrit

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kuroko besshi

Cu, Pb, Zn

skarn

Hydrotermala malmer

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Hydrotermala malmer Porfyrkopparmalmer

(tex Aitik)

Kopparmalm (± Mo, Au)

Fattiga (0,3 wt.% Cu), men stora

60 % av den globala kopparproduktionen

(Loberg, 1993)

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Bingham Canyon open-pit mine

Porfyrkopparmalm

Bingham Canyon, världen största porfyrkoppargruva

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Porfyrkopparmalm

Bingham Canyon, världen största porfyrkoppargruva

Kopparmalm

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Porfyrkopparmalm

Bingham Canyon, världen största porfyrkoppargruva

Jordskred 18/4 2013

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Hydrotermala malmer

Porfyrkopparmalmer

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kuroko besshi

Cu, Pb, Zn

skarn

Hydrotermala malmer

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Hydrotermala malmer Orogent guld

(tex Björkdal, Svartliden)

ex. Boliden, Björkdal

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3 huvudgrupper av malmbildande processer

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Sedimentära malmer

Banded Iron Formation (BIF)

Fotosyntetiserande cyanobakterier 3,5 Ga producerade syre Det tidiga syret oxiderade lättlöslig Fe²⁺ till svårlöst Fe³⁺

Järnoxid (Fe₃O₄, Fe₂O₃) och järnhyrdoxid (FeOOH) fälldes ut och sedimenterade

Cykliskt förlopp

BIF bildades mellan 3,5 och 1,7 Ga, maximum mellan 2,6 och 2,3 Ga

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Sedimentära malmer

Banded Iron Formation (BIF)

Tex Striberg

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Sedimentära malmer Vaskförekomster

Vittrat berg (källa) transporteras av vatten

När vattens energi minskar kan tunga mineral, text guld, platina (diamant) sedimentera (avsättas)

Detta sker vid:

1.skyddade lägen 2.nedström biflöden

3.bakom tex större stenar och block 4.nedanför vattenfall

5.i meandrande floders innerkurvor

(Loberg, 1993)

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kuroko besshi

Cu, Pb, Zn

Fe-skarn

Malm i Sverige

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Kalderabildning

(explosiv vulkanism) i grunda havsbassänger

Kontinentkant

Back-arc miljö

ZnPbAgCu-sulfider som är utfälld i kalksten-skarn i anslutning till vulkanismen. Lagerbundna.

ZnPbAg-sulfider som fälls ut på eller under havsbotten i

pyroklastiskt material (i anslutning till vulkanismen). Stratiforma.

Malmbildning i Bergslagen

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Garpenberg VMS

Kontinental back-arcmiljö

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Malmbildning i Norrbotten

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Från malm till gruva

Prospektering är dyrt!

Regional skala: geofysik (magnetometri, gravimetri), geokemi, existerande geologiska kartor och borrkärnor

Lokal skala: Berggrundskartering

Borrning (hammar- och kärnborrning) Borrkärnekartering - mineralogi -petrologi Geokemi

Undersökningstillstånd från Bergsstaten Prövning av Mark och miljödomstolen Infrastrukturuppbyggnad

Brytning

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Sveriges produktion i förhållande till EU

Au 24%

Ag 17%

Cu 10%

Zn 23%

Pb 39%

Fe 91%

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Many geologists say this is the most impressive geological formation of all.

It covers the central parts of RSA, has a surface extension of about 300x300 km and is the major source of both Cr and Platinum Group Elements (PGE) on

Earth. One hypothesis says that around 2 Ga ago a big meteorite struck planet Earth on a ”Protocontinent” which much later became South Africa. Before

impact, the heavenly body broke into three pieces which struck down close to each other, forming a three-lobed structure. The crust cracked all the way down to the mantle and heavy molten magma welled up. Subsequently a big magma chamber formed at a depth of a few km and the magma started to slowly cool.

The first minerals to crystallize were heavy chromite (FeCr₂O₄), pyroxene etc., which sank to the floor of the magma chamber forming bands of alternating black chromite and yellow pyroxene (see the ore samples showing

pseudostratification!!). Individual less than meter-thick layers can be followed for up to 90 km in Bushveld. The whole layered complex is saucer-shaped because it is so heavy compared with the surrounding continental granites and gneisses that the central portion sags down.

The Bushveld ultramafic layered complex.

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VMS deposits

VMS stands for Volcanogenic Massive Sulfide deposits. The

word ”Massive” means that the content of sulfide minerals (mostly pyrite) is much more than 50% giving the ore a massive appearance. They are believed to be associated with volcanoes and subduction and are

consequently found:

1) in geologically young rocks along the periphery of the Pacific Ocean (The Girdle of Fire) etc.

2) associated with fold belts in older geological formations.

Formation of a typical VMS deposit can be explained as follows: On the flank of an active volcano at the coast, groundwater is forced upwards- outwards to escape the heat. Water has to be replaced, and water from the ocean is forced down into the sediments and volcanic rocks nearby.

Convection of hot water starts and since this water is charged with salts from the ocean, it has the power to dissolve and pick up heavy metals from the porous rock-pile it encounters. As the hot circulating water,

driven by the volcanic heat, encounters the ocean floor from below (in the form of a hot spring or Black Smoker!) it suddenly cools from some 300- 500°C to almost zero. This forces the heavy elements to precipitate out as sulfides and a compact ore deposit will form with high contents of Cu, Zn, Pb etc. These ores are relatively common, found on all continents and represent the whole history of planet Earth.

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Porphyry copper ores

These subvolcanic sulfide ores are typically confined to active subduction zones

(geologically young rocks) and are especially abundant around the Pacific Ocean (the Girdle of Fire).

They are the biggest copper ores and in order to understand their genesis the amount of copper they contain must be explained.

In principle:

Basalt (Cu-rich rock type) dominates among rock types on the ocean floor. When the water-rich ocean plate goes down the subduction zone it eventually loses its water (as well as copper!) which become incorporated in the melts which form above the

subduction zone and which subsequently results in widespread volcanism in the island arcs and continents surrounding the Pacific Ocean. Eventually a series of Cu-rich rock types form, for example up in the Andes, of which porphyry copper ores are the most prominent. Thus, the huge amount of copper present in these ores can be explained if we allow for all the copper of the ocean floor to be processed and concentrated along a few narrow strips, along the periphery of the ocean! This is the reason why Chile is the number one copper exporter of the world by far, and it also explains why the Bingham Canyon (outside Salt Lake City), with a diameter of 4 km and a depth of 800 m, is the biggest man-made hole in the ground.

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The solubility of Fe

²⁺

(ferrous iron) in seawater is much higher than the solubility of Fe

³⁺

(ferric iron). Fe

²⁺

is stable in a reduced environment, Fe

³⁺

in an oxidizing environment.

The early Earth atmosphere contained no free oxygen and was thus

strongly reducing. Under these circumstances the oceans contained a lot of dissolved iron. When life and photosynthesis commenced some 3.5 billion years (3.5 Ga) ago the action of bluegreen algae in the shallow waters of the oceans resulted in oxidation of Fe

²⁺

to Fe

³⁺

, followed by precipitation of iron oxide (magnetite or hematite, depending on local

circumstances). Enormous amounts of sedimentary iron ores formed (the so called Banded Iron Formation - BIF) in the time interval 3.8 - 1.7 Ga, with a strong maximum at 2.2 Ga.

This demonstrated the importance of solubility (Fe

²⁺

under reducing conditions) and concentration (precipitation of iron-oxide on the ocean floor).

BIF I

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BIF II

These ores were already discussed above in connection with solubility and oxidation of Fe²⁺ to Fe³⁺ (and insoluable Fe-oxide) in the early oceans. However, a few points deserve to be added. BIFs have been found on all continents with ”old” enough rocks. The names differ but the formations in principle always consist of a package of alternating iron- oxide(s) and quartz layers. The packages may contain thousands of layers and be several hundred kms in the longest direction. They are often referred to as taconite in North America, itabarite in Brazil,

hematite-quartzite in India, banded jaspilite in Australia, banded ironstone in South Africa, and quartz-banded ore in Scandinavia.

One popular idea concerning the actual banding is that the bluegreen algae oxygen-poisoned themselves when their concentration exceeded a certain limit and they became almost extinct. Thus iron oxide

precipitation stopped and the conditions became reducing again.

Eventually, algae production started again and the whole process was repeated. And so on.

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Formation of a placer deposit of gold shows the importance of instantaneous deposition. Particles of gold are extracted from the source rocks during weathering and erosion (of e.g. volcanic rocks charged with numerous small gold-quartz veins.) The

heavy gold particles are transported in streams and rapids downstream from the source region. In rapids the water has enough power to transport both gold and gravel, but whenever the stream slackens the gold particles settle on the floor of the stream channel, forming a placer deposit.

In this way the classical gold-fields of California (1849) and SE Australia (1851) were formed.

Placer deposits

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Mineral resources and igneous processes

• Hydrothermal solutions

– Among the best known and important ore deposits – Majority originate from hot, metal-rich fluids that are

remnants of late-stage magmatic processes

– Move along fractures, cools, and precipitates the

metallic ions to produce vein deposits

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Kimberlites

Open pit mine near Yakutsk (Siberia)

Kimberlite is a type of potassic volcanic rock best known for diamonds occurence. It is named after the town of Kimberley in South Africa.

Kimberlite occurs in the Earth's crust in vertical structures known as kimberlite pipes.

The consensus on kimberlites is that they are formed deep within the mantle.

Formation occurs at depths between 150 and 450 kilometres, from anomalously

enriched exotic mantle compositions, and are erupted rapidly and violently, often with considerable carbon dioxide and other volatile components. It is this depth of melting and generation which makes kimberlites prone to hosting diamond xenocrysts.