Mineralogical Study of Manganese Bearing Skarn Minerals and Manganese Content in Magnetite in the Dannemora Skarn Iron Ore Deposit

Examensarbete vid Institutionen för geovetenskaper

Degree Project at the Department of Earth Sciences

ISSN 1650-6553 Nr 336

Mineralogical Study of Manganese

Bearing Skarn Minerals and

Manganese Content in Magnetite in

the Dannemora Skarn Iron Ore Deposit

En mineralogisk studie av manganförande skarn-

mineral och manganhalt i magnetit i Dannemoras

skarn-järnmalmsfyndighet

Franz Åberg

INSTITUTIONEN FÖR GEOVETENSKAPER

Examensarbete vid Institutionen för geovetenskaper

Degree Project at the Department of Earth Sciences

ISSN 1650-6553 Nr 336

Mineralogical Study of Manganese

Bearing Skarn Minerals and

Manganese Content in Magnetite in

the Dannemora Skarn Iron Ore Deposit

En mineralogisk studie av manganförande skarn-

mineral och manganhalt i magnetit i Dannemoras

skarn-järnmalmsfyndighet

ISSN 1650-6553

Copyright © Franz Åberg and the Department of Earth Sciences, Uppsala University

Abstract

Mineralogical Study of Manganese Bearing Skarn Minerals and Manganese Content in

Magnetite in the Dannemora Skarn Iron Ore Deposit

Franz Åberg

The Dannemora skarn iron ore deposit is located in the northeastern part of Bergslagen. The deposit has been mined from the 1400’s and stopped in 1992, the mine was reopen in 2012 and it will close in 2015. The Dannemora deposit is hosted by 1.9 Ga old sedimentary and volcanic rocks. The deposit consists of both manganese rich and manganese poor iron ore. The purpose of this study is to investigate the controlling factors for manganese content in both magnetite and surrounding silicate minerals, especially when garnets is present. Also the mineral assemblage and association with different host rocks lithologies shall be investigated. Petrographical and chemical studies indicate the occurrence of both calcic amphibole and Mg-Fe-Mn-Li type amphibole. The calcic amphibole is found in the majority of the samples and is dominant in manganese poor samples where as Mg-Fe-Mn-Li-type amphibole is more abundant in the manganese rich samples. Generally in the manganese rich samples garnet and epidote become more abundant, particularly if the sample is taken close to a volcanic section.

Keywords:

Dannemora, ore, iron skarn, manganese, magnetite, skarn minerals Degree Project E1 in Earth Science, 1GV025, 30 credits

Supervisors: Elisabet Alm and Abigail Barker

Departmentof EarthSciences,UppsalaUniversity,Villavägen16, SE-75236 Uppsala (www.geo.uu.se) ISSN 1650-6553, Examensarbete vid Institutionen för geovetenskaper, No. 336, 2015

Populärvetenskaplig sammanfattning

En mineralogisk studie av manganförande skarn-mineral och manganhalt i magnetit i

Dannemoras skarn-järnmalmsfyndighet

Franz Åberg

Skarn-järnmalmsfyndigheten i Dannemora är belägen i den nordöstra delen av Bergslagen. Järnmalm och mindre sulfidmineraliseringar har blivit brutna sedan 1400-talet. Gruvan stängde 1992 men togs i produktion igen under 2012. Gruvan stängs återigen under 2015. Fyndigheten är omgiven av 1.9 Ga gamla sedimentära och vulkaniska bergarter. Järnmalmsfyndigheten innehåller både manganrika och manganfattiga järnmalmer. Syftet med denna studie är att undersöka varför fyndigheten har förhöjda halter av mangan. Förändringar av manganhalter och olika värdbergarter borde ge en annorlunda mineralsammansättning i de olika miljöerna. För att svara på dessa frågor skall både mikroskopiska och kemiska undersökningar göras för att bestämma och identifiera olika mineralogiska associationer. Petrografiska och kemiska studier indikerar två olika huvudtyper av amfiboler: kalciumhaltiga amfiboler och Mn-Li-amfiboler. Kalciumamfibolerna är generellt mer spridda i proverna medan Mg-Fe-Mn-Li-amfibolerna är mer koncentrerade till de mer manganrika sektionerna. När koncentrationen av mangan är högre blir granater och även epidot och olivin vanligare, speciellt närmare vulkaniska bergarter.

Nyckelord

: Dannemora, malm, järnskarn, mangan, magnetit, skarnmineral Examensarbete E1 i geovetenskap, 1GV025, 30 hp

Handledare: Elisabet Alm och Abigail Barker

Institutionen för geovetenskaper, Uppsala universitet, Villavägen 16, 752 36 Uppsala (www.geo.uu.se) ISSN 1650-6553, Examensarbete vid Institutionen för geovetenskaper, Nr 336, 2015

Table of Contents

1. Introduction ... 1

1.2.2 Skarn ores………....2

1.2.2 Fe-Skarn………..6

2. Geology...8

2.1 The Dannemora syncline ... 12

2.2 Dannemora skarn-iron ore ... 15

3. Methods ... 16 3.1 Sample collection/preparation ... 16 3.2 Electron microprobe ... 25 4. Result ... 26 4.1Petrography ... 26 4.2 Mineral chemistry ... 37 5. Discussion ... 66

5.1Host rock controls on skarn mineralogy ... 66

5.1.1 Skarn mineralogy at Svea 3208 ... 66

5.1.2 Skarn mineralogy at Norrnäs 3204 ... 68

5.1.3 Skarn mineralogy in Norrnäs 3088 ... 70

5.1.4 Skarn mineralogy at Konstäng 3167 ... 71

5.1.5 Skarn mineralogy in Konstäng 3170 ... 72

5.1.6 Skarn mineralogy in Kruthus 3175. ... 74

5.1.7 Summary ... 76

5.2 Origin of manganese in silicate minerals and magnetite ... 76

6. Conclusion ... 80

7. Acknowledgement ... 80

8. References ... 81

1

1. Introduction

The ore in Dannemora is of skarn iron type and co hosted by metavolcanic rocks and

limestones. The knowledge of the host rocks and their composition is of importance to

understand the mineral assemblages of the skarn and therefore the formation of the ore. The

motivation for Dannemora Magnetite AB is to produce as pure iron ore as possible without

unwanted elements like manganese when they sell they the product to the smelters.

The purpose of this study is to investigate two questions:

1. Dannemora iron ore incorporates high values of manganese both in magnetite and

surrounding minerals, but the values differ between different ore bodies. A controlling factor

for the manganese content in magnetite could be the presence of skarn minerals, in particular

garnet. Earlier studies carried out by Dannemora shows in general higher manganese content

where garnet is present in the rock.

2. Dannemora iron ore is hosted by skarn assemblages formed from interactions between

fluids, limestone and volcanic rocks. The assemblage of skarn minerals is controlled by the

different host rock lithologies and the mineral composition of the skarn should differs when in

contact with the different host rocks

To answer the problems microscopy studies will be a first approach to identify mineral

assemblages and electron microprobe will be used to analyze the different types of identified

minerals.

2

The Dannemora ore field is located in Östhammar municipality, 45 km NNE from

Uppsala and is the most important iron mineralization in the north eastern part of Uppland

(Figure 1). The mineralization has been known for over 500 years, and been mined for

hundreds of years until 1992 when the operation ended. During the early stages of the mine,

small amounts of sulphide mineralization were mined (Lager, 2001). The earliest evidence for

mining activities is from late 1400’s (Tegengren, 1924).

The ore is hosted by 1.9 Ga old Svecofennian metavolcanic rocks that were previously

called the leptite group. The metavolcanic unit belongs to the same metavolcanic rock

formation that characterizes most of the metalliferous areas in Bergslagen. The limestones

have calcic and dolomitic compositions. The calcic limestones incorporate low concentrations

of Fe, Mg and Mn and the dolomitic limestones incorporate Fe contents between 5-30% and

Mn levels of 0.5-1-5% (Lager, 2001).

1.2.1 Skarn Ores

Skarn is a terminology from old Swedish miners that described Fe-rich calc-silicate gangue

materials. Distinguishing between different skarns can be done in different ways, one way is

to distinguish between reaction skarn and ore skarn. Reaction skarn is formed along the

contact between a shale and a limestone during metamorphism. Ore skarn is formed by

Figure 1: Map over the geology over Bergslagen that shows the Dannemora inlier, modified after Dahlin, Allen, &

3

infiltration of fluids driven from igneous intrusions (Pirajno, 2009). Classification can also be

done according to the rock types and the mineralogical association of the replaced rock.

Skarnification of igneous or aluminous and carbonate rock can be respectively divided into

endo- and exoskarn. Exoskarns are also separated in terms of their calc-silicates mineral

assemblages into calcic skarns and magnesian skarns. Calcic-skarn is associated with

replacement of limestones and common minerals are garnet (andradite-grossularite series),

clinopyroxene (diopside-hedenbergite series), wollastonite, scapolite, epidote and magnetite

(Pirajno, 2009). Magnesian skarn is formed from replacement of dolomitic limestones and

common minerals are diopside, forsterite, serpentine and talc in silica-poor environments, and

talc, tremolite-actinolite within silica-rich environments (Pirajno, 2009). This type of skarn is

rich in magnetite and relativity low in sulphides. The mineral composition of skarn is

relatively complex and the composition varies a lot in different types of skarn. A few

minerals, for example quartz and calcite are common in all types of skarn. The most common

minerals are given in Table 1. Within porphyry deposits a third type of skarn exists,

silica-pyrite skarns (Pirajno, 2009).

Skarn can also be classified with their associated metals: Fe skarns, Au skarns, W

skarns, Cu skarns, Zn-Pb skarns, Mo skarns and Sn skarns. Zn-Pb and Cu skarn are associated

with porphyry systems, more details are explained in Table 2 (Pirajno, 2009).

Table 1: Common skarn minerals, after Piranjo, 2009.

Mineral

End members

Mineral formula

Abbreviation

Garnet

Grossularite

Andradite

Spessartine

Almanidine

Pyrope

Ca

3

Al

2

Si

3

O

12

Ca

3

Fe

2

Al

2

Si

3

O

12

Mn

3

Al

2

Si

3

O

12

Fe

3

Al

2

Si

3

O

12

Mg

3

Al

2

Si

3

O

12

Gr

Ad

Sp

Al

Py

Pyroxene

Diopside

Hedenbergite

Johannsenite

Fassaite

CaMgSi

2

O

6

CaFeSi

2

O

6

CaMnSi

2

O

6

Ca(Mg,Fe,Al)(Si,Al)

2

O

6

Di

He

Jo

Fas

Olivine

Forsterite

Fayalite

Tephroite

Monticellite

Mg

2

SiO

4

Fe

2

SiO

4

Mn

2

SiO

4

Ca

2

SiO

4

Fo

Fa

Tp

Mc

Pyroxenoid

Ferrosilite

Rhodonite

Wollastonite

FeSiO

3

MnSiO

3

CaSiO

3

Fs

Rd

Wo

4

Mineral

End members

Mineral formula

Abbreviation

Amphibole

Tremolite

Ferroactinolite

Hornblende

Pargasite

Ferrohastingsite

Cummingtonite

Dannemorite

Grunerite

Ca

2

Mg

5

Si

8

O

22

(OH)

2

Ca

2

Fe

5

Si

8

O

22

(OH)

2

Ca

2

Mg

4

Al

2

Si

7

O

22

(OH)

2

NaCa

2

Mg

4

Al

3

Si

6

O

22

(OH)

2

NaCa

2

Fe

4

Al

3

Si

6

O

22

(OH)

2

Mg

5

Fe

2

Si

8

O

22

(OH)

2

Mn

2

Fe

5

Si

8

O

22

(OH)

2

Fe

7

Si

8

O

22

(OH)

2

Tr

Ft

Hb

Pg

Fh

Cm

Dm

Gru

Epidote

Piemontite

Allanite

Epidote

Pistacite

Clinozoisite

Ca

2

MnAl

2

Si

3

O

12

(OH)

(Ca,REE)

2

FeAl

2

Si

3

O

12

(OH)

Ca

2

FeAl

2

Si

3

O

12

(OH)

Ca

2

Fe

3

Si

3

O

12

(OH)

Ca

2

Al

3

Si

3

O

12

(OH)

Pm

All

Ep

Ps

Cz

Plagioclase

Anorthite

CaAl

2

Si

2

O

8

An

Scapolite

Meionite

Ca

4

Al

6

Si

6

O

24

(CO

3

,OH,ClSO

4

)

Me

Other

Vesuvianite

Prehnite

Axinite

Ca

10

(Mg,Fe,Mn)

2

Al

4

Si

9

O

34

(OH,Cl,F)

4

Ca

2

Al

2

Si

3

O

10

(OH)

2

(Ca,Mn,Fe)

3

Al

2

BO

3

Si

4

O

12

(OH)

Vs

Pr

Ax

Table 2: Characteristics of skarn ore deposits after Piranjo, 2009.

Fe

W

Sn-W

Mo

Cu

Zn-Pb

Size (Mt)

5-200

0,1-2

0,1-3

<0,1

1-400

0,2-3

Grade, %

40

0,5

0,-0,7

±0,1

1-2

9% Zn, 6%

Pb, ±15g/t

Ag

Associated

metals

Cu, Co,

Au

W, Mo, Cu,

Zn, Bi

Sn, F, W,

Cu, Zn

Cu, U, W,

Bi

Mo, Zn, W,

Ag

Ag, Cu, W

Igneous

rocks

Gabbro,

syneite,

diorite

Quartz-diorite,

quartz-monzonite

Granite

Granite,

quartz-monzonite

Granodiorit

equartz-monzonite

stock, dykes

and breccia

pipes

Granite,

diorite,

syenite,

stocks and

dykes

Ore

minerals

Magneti

te,

chalco-pyrite

cobalite

pyrrho-tite

Scheelite,

molybdenite

chalcopyrite

sphalerite,

magnetite,

pyrite,

bismuth

Cassiterite,

scheelite,

sphalerite,

pyrrhotite,

magnetite,

pyrite

Arseno-pyrite

Chalcopyrit

epyrite,

hematite,

magnetite,

pyrrhotite,

molybdenit

etennantite

Sphalerite,

galena,

pyrrhotite

pyrite,

magnetite

chalcopyrite

arseno-pyrite

5

Skarn occurs in several different

tectonic environments where magmatism and

carbonate lithologies are present. Four

different scenarios are mainly used to describe

the different environments: oceanic steep

subduction, transitional low-angle subduction,

continental subduction and continental rifting.

The details of associated mineralization are

shown in (Figure 2) (Pirajno, 2009).

Skarn minerals are in general zoned

and can show the fluid flow concentration and

scale between micrometer scale and kilometer

scale (Pirajno, 2009). Mineral zonation in

garnet and pyroxene, can give clues about the

evolution of the system when elements are

enriched or depleted in core to rim profiles.

Garnet growth can record the evolution of the

system where the core represents the

composition of the protolith and the rim

reflects the composition of the hydrothermal

fluid. The cores are often enriched in Ca, Al,

Ti and Mn and the rim is often enriched in Fe

and LREE (Meinert, et al., 2005).

Zonation can also reflect the

oxidation state of the skarn system. The

oxidation state can be determined by the ratio

between Fe

2

O

3

/(Fe

2

O

3

+FeO), for example

when Fe

3+

_{is enriched in garnets and Mg is}

enriched in pyroxene indicating an oxidized

environment, or presence or absence of minerals, more details are shown in (Figure 3)

(Pirajno, 2009). Using the ratio between distal pyroxene, often of hedenbergite and

johannsenite type, and proximal garnets, commonly iron rich, can give a rough indication of

the oxidation state of the system and interpretation about contribution from plutons, wall rock

Figure 2: The tectonic settings and their associated

mineralization, A) Steep subduction under an island arc, B) shallow subduction under an island arc, C) subduction under a continent, D) continental rift setting associated with a mantle plume (Pirajno, 2009).

6

and the depth of the formation. This relationship is not completely reliable, for example if the

wall rock is reduced it can hide the true oxidation state of the fluid. A reduced assemblages is

expected to have lower garnet/pyroxene ratios and relatively Fe poor garnets and Fe rich

pyroxenes (Meinert, et al., 2005).

1.2.2 Fe-Skarn

The largest skarn deposit in the world consist of Fe-skarns and they are mined for magnetite

with smaller amounts of Cu, Co, Ni and Au. The deposits are very large, with some having

tonnages of >500 Mt. The ore consists mainly of magnetite with smaller amounts of gangue

minerals. A few deposits contains higher abundance of Cu and are transitional to Cu-skarns

(Pirajno, 2009).

Calcic Fe-skarn is generally associated with oceanic island arcs. Plutons that are

enriched in Fe intrude limestone and volcanic wall rocks. This type of terrane occurs in the

Urals, the Philippines, Japan, Cuba and in the northern Cordillera, Canada. The intrusions are

commonly of dioritic composition, but can also have gabbro or syenite composition (Pirajno,

2009). Skarn mineralogy commonly consists of ferrosalite, salite, garnet, epidote and

actinolite, and all of them are rich in iron. The retrograde assemblages are amphibole, chlorite

and ilvaite. The igneous rocks are commonly altered and veins of albite, orthoclase, scapolite

and other replacements are formed. Two examples of mines that are mining calcic Fe-skarns

are the Empire mine in Vancouver Canada, and Larap in the Philippines (Pirajno, 2009).

Figure 3: Oxidation states of skarn systems. The Fe2O3/(Fe2O3+FeO) ratio shows the causative oxidation of

7

Magnesian skarn is typically associated with monzogranite and granodiorite stocks

and dykes. This type occurs most commonly in dolomitic limestone settings. The skarn

minerals consist of forsterite, diopside, periclase, talc and serpentine. They are not as rich in

iron as the calcic Fe-skarns, here the iron is more restricted to the magnetite. The ore strata of

magnetite can reach up to several hundreds of meters in thickness and several km in length.

The biggest mineralization is found in Russia the Teya deposit at 144 Mt with 33% Fe and the

Sheregosh deposit at 234 Mt with 35%Fe (Pirajno, 2009).

Fe-skarn deposits are also divided into poor and rich deposits. In the

Mn-poor deposits, the ore occurs as thin stratabound to stratiform lenses that stretch laterally and

are hosted by volcanic rocks. The mineralogy of Mn-poor skarn deposits consist of magnetite,

actinolite, epidote, andrandite garnet and hedenbergite. Amphibole and garnet are in general

the most dominant calc-silicates in Mn-poor Fe-skarn deposits. Mn-rich deposits occur at

higher stratigraphic levels and are hosted by crystalline carbonate rocks. The carbonate rocks

incorporate MnO levels around 1% but locally MnCO

3

levels of 10% can occur. Mn-rich

deposits are also stratabound to stratiform lenses that incorporate magnetite and

manganiferous silicates. Generally the high levels of manganese are incorporated in

calc-silicates and not in the magnetite where the levels are low to very low (Stephens, 2013). Some

authors have reclassified some iron skarn deposits into Cu-Au-REE-Fe oxide deposits

(Meinert, et al., 2005).

8

2. Geology

The bergslagen region is located in the southwestern part of Svecokarelian Domain, one of the

four different domains in the Baltic shield which result from different orogenic episodes (Gaál

& Gorbatschev, 1987). The four different domains are the Archean Domain, Svecokarelian

Domain, Sveconorwegian Domain and the Caledonian Domain. The Archean domain in the

northeastern part, is the oldest (2.5-2.8 Ga). The Svecokarelian Domain (2.3-1.8 Ga) reaches

from the northern part of Sweden outside the Caledonides down to the eastern part of

Svealand (central part of Sweden) (Gaál & Gorbatschev, 1987). The Svecokarelian Domain is

divided into two different domains, Svecofennian and Karelian-Lopian Domain (Loberg,

1993). The Sveconorwegian Domain (1.05-0.9 Ga) in Sweden reaches from the western part

of Götaland (southern Sweden) to the western part of Svealand. The youngest domain is the

Swedish-Norwegian mountain chain the Caledonides (0.5-0.425 Ga) that defines the

boundary of the Baltic shield to the West (Gaál & Gorbatschev, 1987) (Figure 4).

Figure 4: The major geological units of the Fennoscandian Shield. Bergslagen and Dannemora inlier is marked

9

The Svecofennian sub-Domain, that part Bergslagen belongs to, incorporates three

different regions: the northern volcanic region, the central region and the southern volcanic

region (Gaál & Gorbatschev, 1987). The northern volcanic region incorporates most of the

massive formations of felsic to intermediate volcanic rocks with intercalations of sedimentary

units. Around Kiruna, mighty porphyry are deposited on a conglomerate. The border between

a syenite porphyry and a quartz porphyry is the location of the famous Kiirunavaara-ore. The

southern volcanic region is where the Skellefte-field is located and consists mostly of

intermediate rocks. Stratigraphically under the volcanic formation sedimentary units that

belong to Härnö-formation occur (Loberg, 1993).

The central volcanic region incorporates most of the Bothnian Basin where

migmatised metagreywacke’s belong to the Härnö-formation. Intercalation of basic volcanic

rocks are found in the migmatised metagreywacke’s that have been deposited in a sub-aquatic

environment (Loberg, 1993). The magmatic rocks in the area are dated to 1.9-1.8 Ga (Gaál &

Gorbatschev, 1987).

Bergslagen is located in the southern part of the Svecofennian sub-Domain. The

western part of Bergslagen is dominated by metavolcanic rocks that are overlain by

meta-sediments but to the East the layering is inverted (Lundström, 1987). The metavolcanic rock

layers are up to 8 km thick and are dominated by ignimbrites, meaning they have been

deposited by pyroclastic flows (Allen, et al., 1996). The marble is intercalated with the

metavolcanic rocks. The ignimbrites are poorly sorted mixtures of ash, pumice and lapilli.

The chemistry of the metavolcanic rocks is subalkaline to calc-alkaline, with an andesitic to

rhyolitic composition (Allen, et al., 1996). The complete characteristics of the region have

proposed that Bergslagen formed in an environment similar to an extensional back-arc region

close to a continental margin because of a broad area of subsidence features and evidence of

intense volcanism. Comparison has been made between the volcanic rocks in Bergslagen area,

and rocks in the active volcanic area Taupo, in New Zealand (Allen et al., 1996).

The evolution of the volcanic rocks in the area is separated into two main facies. It is

initiated by an explosive magmatic period in an extensional environment. During the

following episode the magmatism declined, and the tectonic environment changed more to a

compressional regime and metamorphism occurred later (Allen et al., 1996).

A large volume of plutonic rocks, mostly granitoids, occurs with the supracrustal

rocks. The plutonic rocks are divided into four different groups, early orogenic, late orogenic,

post orogenic and anorogenic (Lindström, et al., 2000). The early orogenic intrusives were

emplaced before the main deformation and the regional deformation, the result is that there

10

are heavily metamorphosed or migmatised. The chemistry of the early orogenic intrusives are

calc-alkaline. The late orogenic intrusives are associated with pegmatites and they are

intruded later during the Svecokarelian orogeny, and there for the intrusives are mainly

undeformed. The post orogenic intrusive are younger than the Svecokarelian orogeny. The

late- and post orogenic intrusives are commonly assembled in to one group, late- to post

orogenic group, because of their similar age (Lindström, et al., 2000). They are further

classified as S-type and I-type granitoids. S-type granites are pegmatite rich and are formed

by partial melting of sedimentary rocks. The I-type granites (sometimes called A-type) are

formed by fractional crystallisation processes of magmas. The anorogenic intrusives mainly

consist of the Rapakivi granites and are connected to the basic plutonic rocks and diabases.

The Rapakivi granite are connected to late rifting during the Sveconorwegian orogeny and the

formation of the southwest Scandinavian province (Lindström et al., 2000).

The early orogenic granitoids, mostly consist of granodiorite and tonalite, which are

very common in Bergslagen, except for the most western part. The rocks have an intrusive

relationship to the early Svecofennian shallow rocks. Some have intruded quite early during

the orogeny and come into an erosional position, remnants are found in the conglomerates

(Lindström et al., 2000).

The oldest rocks, supracrustal rocks and early orogenic intrusions, have been

metamorphosed under amphibolite facies at low pressure and high temperatures. Migmatites

(vein gneiss and schollen migmatite) are also common in the area, in particular in the

sedimentary units where the dehydration has lowered the melting point (Lindström et al.,

2000).

The felsic metavolcanic that belong to the leptite group, are exposed as a curve from

the northern part of Uppland to the southern part of Gästrikland, into the eastern part of

Dalarna, western Västmanland, Närke and southeast Värmland. The volcanites are in general

metamorphosed under low grades (green schist- to amphibolite facies) and still show primary

structures. The felsic metavolcanics often show sodic or potassic alteration due to

hydrothermal fluids (Lindström, et al., 2000). Magnesium metasomatic alteration is also

common, causing the feldspar to be replaced by chlorite, phlogopite, anthophyllite, sericite

and cordierite. Also the younger metamorphosed diabases have been affected by some

metasomatic alteration, resulting in some veins, breccia networks and some spots of

actinolite-tremolite alteration (Lindström et al., 2000).

Late orogenic granite intrusions, S-type, are produced by melting of the middle crust.

Sodic and potassic values are enriched. Related pegmatites are rich in muscovite and quite

11

rich in tourmaline. The age of the late- and pos-torogenic granites are 1.81-1.75 Ga, and they

are common in Bergslagen (Lindström et al., 2000).

Pegmatites that are older or younger than the late- and post orogenic intrusives occur,

the older pegmatites can be a result of early orogenic granite magma, but the occurrence is

quite limited. Some pegmatites have been produced during vein gneiss alteration during the

Svecokarelian regional metamorphic event (Lindström et al., 2000).

The composition of the pegmatites is simple and consists of quartz, feldspar and

mica. Some pegmatites have more complex compositions and are divided into two groups:

NYF-type (niobium, yttrium and fluorine) and LCT-type (lithium, cesium and tantalum)

(Lindström et al., 2000).

Iron oxide and sulfide mineralization is common in Bergslagen. The iron oxide

mineralization is divided into quartz banded iron ore, skarn iron ore and apatite iron ore.

Quartz banded iron ore consists of bands of hematite and secondary magnetite interlayered

with quartz (Loberg, 1993), small amounts of skarn minerals are also present. The iron

content of the banded iron ore is 30-50% (Lindström et al., 2000).

The skarn iron ores are often associated with the banded iron ores, and therefore they

probably also have a supracrustal origin. In additional to carbonates and Ca and Fe-rich fluids

acidic Si-rich fluids has also been present for the skarn reactions to occur during regional

metamorphism (Loberg, 1993).

The iron content of the skarn iron ore is 35-50% and consists of magnetite and skarn

minerals that gradually turn into limestone hosted iron ore. Skarn iron ore is divided into

manganese rich (1-8% Mn) and manganese poor (<1% Mn) ores, and the manganese are often

hosted by different silica minerals (Lindström et al., 2000). The manganese poor or crystalline

carbonate hosted (skarn iron ore) is the dominant type of iron oxide mineralization in

Bergslagen, up to 50% of all iron oxide deposited in Bergslagen is of this type. Mineralization

is more dominant in the western and central part of Bergslagen. Some examples of this type of

deposit are the Persberg ore field, Nordmark and Riddarhyttan. Persberg is the “birthplace” of

the skarn concept (Stephens, et al., 2009).

The mineralization of manganese poor iron ore is thin and stratiform, but they are

laterally extensive. The age of the mineralization is considered to be the same as the

metavolcanic host rocks 1.91-1.89Ga. The tonnage of the deposits varies from 1 Mt up to the

Riddarhyttan ore field, at 15 Mt and the iron content varies from 30% to 50%. The minerals in

the deposits are magnetite, hedenbergeite, andradite, garnet and epidote. Manganese is mostly

restricted to the skarn or carbonate minerals (Stephens, et al., 2009).

12

The third type of iron ore is the apatite iron ore. The ore minerals are magnetite and

hematite. The mineralization is genetically connected to the metavolcanites. The full scaled

understanding of the formation is heavily discussed. One solution is that anatectic processes

partially or completely melted sedimentary iron accumulations driven by volcanic activity.

Other theories are the ore is directly connected to the magma or formed by hydrothermal

fluids in subaquatic environment (Loberg, 1993, Jonsson, et al., 2013).

Sulfide mineralization in Bergslagen is in general classified as a VMS-type

(Volcanic massive sulfide deposit), earlier called Kuroko-type (Loberg, 1993). The ore has a

complex structure and consists of pyrite, chalcopyrite, sphalerite and galena. The ore is often

stratified, and is often connected to a certain layer of the metavolcanics (Loberg, 1993).

2.1 The Dannemora syncline

The Dannemora syncline that bears the carbonates and the ore body is 3 km long and around

400-800 m wide (Figure 5). The syncline consists of two limbs that are both steeply dipping

but the WNW-limb is overturned to the East (Lager, 2001). The thickness of the formation is

estimated by Lager, (2001) to 700-800 m Dahlin, (2014) estimate the formation is not thicker

than 600-700 m. The Dannemora syncline is divided into the lower and upper formation

(Lager, 2001), and they are correlated with two different volcanic stages of the evolution of

Bergslagen area (Dahlin, 2014). The lower formation is composed by primary pyroclastic and

redeposited pyroclastic rocks (Lager, 2001) and has a thickness of 500-600 m (Dahlin, et al.,

2012), and represents a more intense stage, whereas the upper formation represents a waning

stage. Dahlin, (2014) divided the lower formation into subunit 1 and subunit 2, both consist of

a bottom flow deposit and at top air-fall deposit with accretionary lapilli (Dahlin & Sjöström,

2014). The whole inlier is surrounded by intrusives of the GDG-unit (granite-diorite-gabbro)

(Dahlin, 2014).

The most common rock types in the syncline are primary supracrustal rocks

(volcaniclastic and carbonate rocks), diagenetically and hydrothermally altered supracrustal

rocks, for example chlorite hornfels, skarn and the iron and sulphide ores (Lager, 2001). The

lower formation consists mostly of ignimbrites and lacks any known mineralization. The

upper formation contains more of fine-grained reworked volcanic metasedimentary rocks and

metalimestones that can be associated with waning volcanic stages. It is in this member the

iron ore is hosted (Dahlin, 2014; Dahlin, et al., 2012).

The reworked fine-grained volcanic metasedimentary rocks are overlain by

metalimestones that incoporate pseudomorphs of gypsum, halite and stromatolites. Millimeter

13

to meter thick layers of siltstone and conglomerate with crystals of quartz are sometimes

intercalated within the metalimestones. The reworked fine-grained volcanic metasedimentary

rocks are interpreted to originate as volcaniclastic turbidity events or tempestites (Dahlin,

2014; Dahlin, et al., 2012).

Evaporites, with pseudomorphs of gypsum and halite are suggested to have formed

in an open sabkha or a closed saline environment, and are intercalated with the volcaniclastic

turbidites or tempestites. Turbidites and tempestites are formed much deeper than an open

sabkha or a closed salina environment. Dahlin (2012) suggested these “turbidites” are more

likely a result of air-fall and pyroclastic flow deposits that have been reworked and locally

covered the stromatolites and evaporites. No evidence of erosional features and presence of

interbedded hemipelagic mudstones have been observed that would support the theory of a

deep water environment (Dahlin, 2014; Dahlin, et al., 2012).

The lower formation ends with skarn layers that are covered by a weakly normally

graded ash-siltstone with accretionary lapilli. The siltstone is interpreted as a subaerial air-fall

deposit, but the layering, normal grading and the presence of accretionary lapilli is not limited

to a subaerial deposit, it can also result from a subaqueous deposit (Dahlin, 2014; Dahlin, et

al., 2012).

The rocks in the the Dannemora syncline are in general metamorphosed under

greenschist or lower amphibolite facies within the hydrothermally altered zones (Lager,

2001). Dahlin, (2014) on the other hand suggest that the metamorphic grade never exceeded

greenschist facies. The area has probably been affected by the Svecokarelian orogeny and the

resulting mineral parageneses changed. The primary structures are well preserved so the

post-depositional processes are assumed to be isochemical. Therefore the mineralogical

composition of the skarns and the chlorite hornfelses reflects the geochemical alteration that

has been produced by the syndepositional, diagenetic or hydrothermal processes (Lager,

2001).

At least two fold phases have affected the Dannemora inlier with a result of two

clearly separated cleavages (S

1

and S

2

) with a dominating L

2

-lineation. F

1

-folds were detected

by stratigraphic data and by bedding and cleavage relationships that indicated shifting

younging direction in the stratigraphic column. The F

1

-folds are isoclinal to tight and are

upright on a km-scale (Dahlin, 2014).

A few of the rocks have been dated by Stephens, et al., 2009. Zircons from the upper

part of the lower formation give a U-Pb zircon TIMS age of 1894±4 Ma (Stephens, et al.,

2009).

14

15

2.2 Dannemora skarn-iron ore

Dannemora skarn hosted iron ore is located in the northeastern part of Bergslagen. The iron

ore appears in massive strata-bound bodies, connected to dolomitic limestones or skarn.

Tectonic events possibly separated the ore into 25 different bodies (Lager, 2001)

The ore consists mostly of magnetite. The ore is divided into Mn-rich and Mn-poor

magnetite. Mn-rich iron ore is connected with skarn and manganese levels are 1-6% and the

iron content is 30-50% (Lager, 2001). Skarn minerals act like aggregates in the ore, typical

minerals are knebelite, dannemorite, diopside, actinolite, chlorite and serpentine. Mn-poor

iron ore is connected both to the skarn and carbonate rocks. The manganese levels are <1%,

and the iron content is 30-50% (Lager, 2001).

Electron microprobe analysis done by the Geological Survey of Sweden suggest that

most of the manganese is hosted by minerals other than in magnetite, except for Konstäng 2

where the MnO content of the magnetite is 3.1% in the magnetite (Table 3) (Lager, 2001).

The manganese rich iron ore is probably a result of iron- and manganese-rich

hydrothermal fluids. The fluids needed to be quite warm to alter the silica-rich units.

Alteration decreased with stratigraphic depth suggesting that transport of iron and manganese

not has been vertical, instead it has probably been transported laterally (Lager, 2001). Iron and

manganese rich fluids are likely transported from the hinterland towards more low-lying areas

and deposited in a basin. Smaller amounts of the iron oxide are deposited in the carbonates.

The fluids get concentrated in evaporites, which were favorable for dissolution, precipitation

and re-distribution of materials. In some of the iron-ore stromatolite-like structures and

pseudomorphs of evaporite structures are visible (Lager, 2001).

Magnetite is also found as vugs and veins in dolomitic limestone outside the main

ore-zone, but it never exceeds 30% of iron. The magnetite veins are 1 cm to 2 m thick. The

vugs and veins not only consist of magnetite, but earlier carbonate is also observed. A theory

is that cavities were formed during dissolution and have been filled by carbonates, and later

magnetite filled the remaining cavities. Remnant carbonate structures are visible as small

spots in the magnetite matrix (Lager, 2001). For theskarn-spotted iron ores the skarn

represents more altered remnants of an overlying, aeolian volcanic sediments that has

collapsed (Lager, 2001).

16

Table 3: Manganese content from microprobe analyses done by SGU of five different ore bodies, table after

(Lager, 2001).

Ore bodies

Mn% in ore sample

Mn% in magnetite

Svea

3.90

0.42

Konstäng 2

3.40

3.10

Konstäng 4

0.75

0.33

Kruthus

0.43

0.10

Norrnäs

1.90

0.17

3. Methods

3.1 Sample collection and preparation

Samples were collected from Dannemora Mineral AB drill core archive. Twenty four

different samples were chosen from four different ore bodies and 6 different drill cores (Svea

3208, Norrnäs 3088 and 3204, Konstäng 3170 and 3167, and Kruthus 3175). The focus was to

get representative samples of different skarn assemblages. The range of lithologies are, skarn

assemblages with limestones or volcanic rocks, and magnetite rich samples to investigate

manganese content in magnetite and skarn minerals. Dannemora Mineral AB has done

chemical analyses that gave indications of the manganese content in the drill core that helped

to choose different representative samples with above named minerals assemblages into focus

on the manganese content. Another feature that was of importance, was the presence of

garnet, particularly yellow garnets because manganese rich garnet is commonly yellow.

Seven samples were selected from the Svea ore body drill hole at 3208, 161.42,

163.36, 169.41, 171.91, 180.82, 200.49 and 215.20 meter downhole depth. The samples

161.42 and 163.36 are taken from a skarn section with limestone origin with high

concentrations of manganese (same chemical analyses). The difference between the samples

is visible garnet contents. 169.41 is a ore section of the limestone skarn origin. This section

also incorporates high amounts of manganese. 171.91 is also an ore section with a limestone

skarn origin showing high levels of manganese. 180.82 is a limestone skarn sample after a

section of low concentrations of manganese. 200.49 is a skarn sample that is in contact with a

volcanic section. The last sample (215.20) is a limestone sample with skarn and magnetite.

One sample was selected from drill hole 3088 Norrnäs, sample 598.15 is a skarn sample of

magnetite ore origin with an anomalously high manganese content. Five samples were

collected from drill hole 3204 Norrnäs, taken from a section with alternating limestone and

volcanic rocks. Sample 121.92 has a limestone skarn origin with garnet and a medium-high

concentration of manganese. The following section 123.05 has lower concentration of

manganese but incorporates magnetite. Samples 135.93 and 136.37 are taken from the same

17

chemical analysis but the samples differ in the amounts of visible garnet. One sample from

drill hole Konstäng 3170 60.72, is taken from a limestone skarn origin section with

anomalously high concentration of manganese. Five samples from drill hole Konstäng 3167

were collected, sample 30.36 from Konstäng 3167 is taken from a limestone origin skarn

section with high concentration of manganese. The following sample comes from the same

area but dominated by magnetite. Sample 43.10 the “garnets” looked more yellowish than the

other samples and it has an intermediate concentration of manganese. Sample 104.80 is a

limestone skarn sample with garnets and low levels of manganese. The last sample of

Konstäng 3167, 106.25 is a magnetite dominated sample from the same chemical analysis as

104.80. Five samples were selected from drill hole Kruthus 3175, sample 24.53 is a

garnet-rich sample taken from a skarn section with limestone origin. Sample 28.31 is a magnetite

spotted sample with low concentration of manganese. Sample 34.55 is a skarn sample with

limestone origin and yellow garnets. Sample 45.65 is a skarn sample with volcanic origin and

the last sample 47.90 is a limestone skarn sample. More info in Table 4 and Figure 6. For

preparation of this sections the samples were sent to Slovakia.

18

Table 4: The table is showing the investigated samples with descriptions, the four first number in the sample

number stands for drill hole and the last number are in cm

Sample number

Description

Ore body

3208-161.42

Skarn sample with 7.2 %Mn, garnet rich

Svea

3208-163.36

Skarn sample with 7,2 %Mn with small content

of garnets

Svea

3208-169.41

Magnetite sample with 7,94 %Mn to see Mn

difference between the more skarn rich last

sample

Svea

3208-171.91

Skarn sample with 7,94 %Mn

Svea

3208-180.82

Skarn sample

Svea

3208-200.49

Skarn sample with contact to volcanic rocks

Svea

3208-215.20

Limestone sample with magnetite + skarn

Svea

3088-598.15

Skarn sections in magnetite section with 13,98

%Mn

Norrnäs

3204-120.28

Switching between limestone and volcanic

rocks

Norrnäs

3204-121.92

Skarn with rich in garnets + magnetite in veins,

4,45 %Mn

Norrnas

3204-123.05

Magnetite rich sample with 4,45 %Mn

Norrnäs

3204-135.93

Skarn sample with lesser amounts of visible

garnet with the eyes, 3,67 %Mn

Norrnäs

3204-136.37

Skarn sample with garnets, with 3,67 %Mn

Norrnäs

3170-60.72

Skarn sample with small amount of garnet and

with 14,67 %Mn

Konstäng

3167-30.36

Limestone skarn sample with 5,61 %Mn

Konstäng

3167-31.74

Magnetite sample with 5,61 % Mn

Konstäng

3167-43.10

Skarn with lots of, in that time interpreted as

yellow garnets, with 3,73 %Mn

Konstäng

3167-104.80

Skarn with garnet, with 1,615 %Mn

Konstäng

3167-106.25

Magnetite and limestone sample with

1,615%Mn

Konstäng

3175-24.53

Garnet rich skarn with 1.06 %Mn

Kruthus

3175-28.31

Magnetite spotted with skarn with 0,489 %Mn

Kruthus

3175-34.55

Skarn with yellow garnet, 1,086 %Mn

Kruthus

3175-45.65

Skarn with volcanic origin

Kruthus

24

Figure 6:Summary drillcore logs. Mn concentrations from chemical analyses from Dannemora Mineral AB.

25

3.2 Electron microprobe

In this study a Jeol-JXA8530F Hyperprobe electron microprobe at Uppsala University was

used. The beam was 10 nA and a current accelerating voltage of 15 kV was used. For the

calibration of the instrument different minerals were used as standards; Si and Ca

(wollastonite), Na (albite), K (orthoclase), Mn and Ti (pyrophanite) and metal oxides Fe –

Fe

2

O

3

, Cr – Cr

2

O

3

, Al – Al

2

O

3

, Mg – MgO.

A scanning electron microscope uses a high energy electron beam that creates

variation of signals on the surface of the polished sample. The difference in signals is for

example caused by different texture, chemical composition, structure of the crystals and the

orientation. The signals includes secondary electrons, backscattered electrons, diffracted

electrons, photons, heat and visible light. BSE (back scattered electrons) are used for example

for BSE images in this report (Reed, 2005). A BSE detector collect this signal from

electron-sample interaction. The signals is produced by inelastic and elastic collision during the electron-sample

interactions, and larger atoms tends to produce elastic collision because of their larger

cross-sectional area and more backscattered electrons are picked up by the detector than the smaller

atoms. This leads to a brighter image for the larger atoms (Reed, 2005).

Wavelength-dispersive-spectometer (WDS) using the Bragg reflection law,

employing a crystal that operates in a serial mode and the spectrometer is turned on to only to

one wavelength at the time (Reed, 2005).

26

4.Results

4.1 Petrography

Svea

Seven samples from Svea are investigated. The most common silicate minerals in this section

are garnet, amphibole and chlorite. Amphibole and chlorite are commonly intergrown with

each other (Figure 7). The grain size of amphibole is in general small and it is hard to see any

cleavage, the color is colorless to weak green. The pleochroism of the amphibole is weak

green to green-brown. The grain size of amphibole increases closer to the volcanic section

that occurs in the end of this drill hole (Figure 7). The other sections are closer to limestone.

Calcite occurs sparingly in Svea, only in thin section 200.49 is calcite present and it occurs in

cracks with amphibole between magnetite crystals. Garnet occurs only in two sections.

Olivine is visible in 161.42 (Figure 7, Figure 8).

27

Figure 7: Petrographic pictures of A: green pleochroic amphibole from 161.42 B: A under crossed nicols. C:

28

Figure 8: Petrographic pictures of A: Olivine in 161.42 B: A under crossed nicols C: Garnet from 161.42 D: C

under crossed nicols.

Magnetite is the dominant iron oxide and occurs through the sections and sample

169.41 and 215.20 are dominated by magnetite. In these sections the silicates occurs in cracks

in the ore. Smaller amounts of sulphides occur, dominantly of pyrite and pyrrhotite.

Norrnäs

Five samples from drill core 3204 and one from 3088. Sample 3088 comes from a skarn

section within magnetite with anomalously high Mn content (Table 4). The sample consists of

big amphibole that show cleavage. The amphibole show from colourless into weak green

pleochroismand the birefringence is high. Small ammounts of garnet are present (Figure 9).

29

Figure 9: Petrographic pictures from Norrnäs 3088. A and C large amphibole crystals. B and D are under

30

In Norrnäs drillcore 3204 the samples are more influenced by calcite. Amphibole are

in general small, particularly when garnet and calcite are present. The amphibole are colorless

to weak green with weak greenish pleochroism. Magnetite is the dominant mineral in 121.92

and 123.05 (Figure 10).

31

Figure 10: Petrographic pictures of Norrnäs 3204. A: Amphibole and calcite from 120.28. B: A under crossed

nicols. C amphibole and garnet from 136.37. D: C under crossed nicols. E amphibole and garnet in a vein in the magnetite sample 121.92. F: E under crossed nicols.

32

Kruthus

The amphibole at Kruthus differs from Norrnäs and Svea in that they have a stronger green

color with a pleochroism in green, brown and blue green color. Garnets are also more sparely

present. The volcanic sample 45.65 consists of quartz and K-feldspar phenocrysts and

chlorite, calcite, amphibole, quartz and K-feldspar in the matrix (Figure 11).

33

Figure 11: Petrographic pictures of Kruthus. A: Amphibole from 24.53. B: A under crossed nicols. C Garnet

surrounding by amphibole and calcite from 34.55. D: C under crossed nicols. E Quartz and K-feldspar grain in matrix of amphibole, quartz, k-feldspars and chlorite. F: E under crossed nicols.

34

Konstäng

The sample from 3170 consists of garnet and epidote with a matrix of amphibole and chlorite.

The amphibole has a white – green color with a green pleochroism (Figure 12).

Figure 12: Petrographic pictures of Konstäng 3170. A Garnet with matrix of chlorite and green amphibole. B: A

under crossed nicols. C: Epidote. D: Epidote under crossed nicols.

Samples from 3167 consist of colorless - green amphibole with green – brown

pleochroism. Epidote is present in sample 43.10 and garnet is only present in sample 104.80.

This sample is special as the amphibole grains are little larger than usual when garnet is

present (Figure 13, Figure 14).

35

Figure 13: Petrographic pictures from Konstäng 3167. A: Epidote from 43.10. B: Epidote under crossed nicols.

C: Amphibole from 43.10. D: C under crossed nicols. E: Amphibole and calcite from106.25. F: E under crossed nicols.

36

Figure 14: Petrographic pictures of 104.80 at Konstäng 3167. A: Large green amphibole. B: A under crossed

37

4.2 Mineral chemistry

Svea 3208 – amphibole

Four samples from Svea (161.42, 163.36, 169.41 and 171.91) were investigated. The

amphibole composition have been calculated according to Leake et al., (1997). In sample

161.42 and 171.91 two different types of amphibole are present, calcic amphibole and

Mg-Fe-Mn-Li amphibole. The definition of calcic amphibole are that (Ca+Na)

B

is >1 and usually Na

B

is 0.50-1.50 and Ca

B

is > 1.50. Mg-Fe-Mn-Li amphibole instead has (Ca+Na)

B

<1 and (Mg,

Fe, Mn, Li)

B

>1 (Leake, et al., 1997).

Leake et al. (1997) describes two groups of calcic amphibole types in addition to

(Na+K)

A

<0.5 or >0.5, the (Na+K)

A

values of 0.5 are also found in the investigated

amphibole. The calcic amphibole in 161.42 was of ferroactinolite type, with a representative

chemical formula:

□(Ca

1.7

Mg

0.3

)(Fe

3.9

Mn

0.7,

Mg

0.3

Al

0.1

)(Si

7.8

Al

0.2

O

22

)(OH)

2

(Figure 16). In the

171.91 sample the calcic amphibole is of actinolite type with a representative chemical

formula: □(Ca

1.8

Mn

0.2

)(Mg

3.4

Fe

1.4

Mn

0.1

)(SiO

4

)

8

(OH)

2

(Figure 16).

Mg-Fe-Mn-Li-amphibole is present in samples 161.42 and 171.91. Leake, et al.,

(1997) describe two different conditions with regards to the Lithium content. Lithium wasn’t

measured so the cummingtonite and grunerite series was chosen. But in a paper written by

Hawthorne et al, (2012) renaming of amphibole is proposed due to new types of amphibole

that have been detected since 1997 and Leake rules about prefixes no longer apply anymore.

In particular for this report the new rules of how to use the mangano prefix. Hawthorne et al,

(2012) use the mangano prefix when Mn

2+

is dominating in the C site (Figure 15). By

Hawthorne et al, (2012) rules manganogrunerite will be called ferrogrunerite instead. The

chemical formula for manganogrunerite is Mn

2+2

Fe

2+5

(Si

8

O

22

)(OH)

2

with Mn in the B site,

when

Hawthorne et al, (2012)

suppose the chemical formula should be

Mn

2+

2

(Mn

2+2,5

Fe

2+2,5

)(Si

8

O

22

)(OH)

2

.

I will be consistent and classify my manganese rich

38

reasoning is applied for classifying and use of the manganoprefix for cummingtonite.

Figure 15: Using prefix mangano according to Hawthorne, et al., (2012.)

The amphibole of Mg-Fe-Mn-Li-type in sample 161.42 are of grunerite type with Mn

over 1 (apfu) so the complete name is manganogrunerite or dannemorite (Figure 17, Figure

18). The representative chemical formula for manganogrunerite in sample 161.42 is

(Ca

0.2

)(Mn

1.5

Mg

0.5

)(Fe

4.6

Mn

0.2

Al

0.2

)(Si

8

O

22

)(OH)

2

. Plots of the amphibole in sample 161.42

can be seen in Figure 17 and of the prefix condition (Figure 18).

In sample 171.91 the Mg-Fe-Mn-Li-amphibole are scattered over the diagram, both

in the cummingtonite and a few in the grunerite field (Figure 17). Also the manganese content

changes a lot, from under 1 to 5 (apfu) into the permangano field (Figure 18). A

representative chemical formula for permanganocummingtonite is

□(Mn

1.7

)(Mg

1.8

Mn

1.7

Fe

1.4

Al

0.1

)(Si

8

O

22

)(OH)

2

and a representavie for manganocummingtonite is

□(Mn

1.4

Fe

0.4

Ca

0.2

)

(Mg

2.7,

Fe

2.3

)(Si

8

O

22

)(OH)

2

, for the manganogrunerite

□(Mn

1.6

Mg

0.2

Ca

0.1

Na

0.1

)(Fe

4.6

Mg

.4

)

39

Figure 16: Plots of calcic amphibole in Svea samples 161.42 n=7 and 171.91 n=60.

40

Figure 18:Prefixes of naming Mg-Mn-Li-amphibole with respect to manganese content in Svea samples 161.42

(n=4) and 171.91 (n=33).

Svea 3208 – garnet

To calculate garnet I followed Locock, (2008). Garnets were investigated in samples 161.42

and 163.36 and the result can be seen in Figure 19. In both of the samples the garnets are

trending up towards spessartine composition, but where in sample 163.36 the spessartine

composition varies most, in sample 161.42 the grossular and almandine content varies most.

A representative chemical formula of a garnet from sample 161.42 (Mn

2+1.7

Fe

2+0.4

Ca

0.8

)

(Al

1.9

Fe

3+0.1

)(SiO

4

)

3

, and a representative chemical formula for garnet in sample 163.36 is

41

Figure 19: Spessartine-Grossular-Almandine triangular diagram for Svea samples 161.42 (n=5) and 163.36

(n=7) garnets.

Svea 3208 – olivine

Olivine was calculated according to Brady et al. (2012). Olivine exists in samples 161.42 and

171.91 (Figure 20). The olivine data plots away from fayalite towards tephroite and in the

fayalite-tephroite series an intermediate manganese-iron olivine called knebelite exists with a

recommended chemical formula between (Fe

1.5

Mn

0.5

)

2

SiO

4

to (Mn

1.5

Fe

0.5

)

2

SiO

4

.

A representative chemical formula for olivine in sample 161.42 (Fe

2+

1.2

Mn

0.8

)(SiO

4

) and for

42

Figure 20: Triangular diagram between Tephroite-Fayalite-Fosterite that plot olivine from Svea 161.42 (n=2)

and 171.91 (n=50).

Svea 3208 – magnetite

Calculation was made following Lepage (2003). The magnetite in Svea sample 169.41

incorporates very little manganese, the mean value of manganese in the magnetite is 0.71 wt%

MnO (Figure 21).

43

Figure 21: Triangluar diagram between Ti+Al-Mn-Fe of magnetite from Svea sample 169.41 n=102.

Norrnäs 3204 – amphibole

The investigated samples in Norrnäs 3204 are 121.92, 123.05 and136.37. Calcic amphibole is

present in samples 123.05 and 136.37 (Figure 22). Sample 136.37 consists of only actinolite

with a representative formula of

□(Ca

1.7

Mn

0.3

)(Mg

3.6

Fe

1.3

Mn

0.1

)(Si

8

O

22

)(OH)

2

.

In sample 123.05 the calcic amphibole trend from actinolite up to tremolite (Figure

22). These amphibole incorporate fluorine in high enough concentrations to use the prefix

fluoro, the correct name of this type of tremolite is fluorotremolite, and a representative

chemical formula for this mineral is

(Ca

0.2

Na

0.1

)(Ca

1.6

Mn

0.3

Fe

2+0.1)

)(Mg

4.4

Fe

2+0.2

Fe3

+0.1

Al

0.1

)(Si

8

O

22

)(F

1.1

OH

0.9

). Also the actinolite

in this sample has high fluorine content so the correct name with prefix is fluoroactinolite, and

a representative chemical formula is

□(Ca

1.8

Mn

0.2

)(Mg

4.3

Fe

0.5

Mn

0.1

Al

0.1

)(Si

8

O

22

)(F

1.1

OH

0.9

).

The trend of the fluorine content seems to slightly increase when silica content decreases

(Figure 23).

44

Figure 22: Diagram of calcic amphibole in Norrnäs 3204 drillcore. Sample 123.05 (n=49) and sample 136.37

(n=5).

Figure 23: F against Si diagram of Norrnäs 123.05 calcic amphibole.

Mg-Fe-Mn-Li-amphibole is detected in samples 121.92 and 136.37. The types are

distinctly separated between cummingtonite type and grunerite type by sample, but the trend

of manganese is the same from less than 1 up to 1.5-2 apfu (Figure 24, Figure 25).

45

The Mg-Fe-Mn-Li amphibole in sample 121.92 consists completely of grunerite type

and mostly of manganese content over 1 apfu so the prefix mangano shall be used.

Manganogrunerite with a representative chemical formula

□(Mn

1

.

3

Fe

0.4

Ca

0.2

)(Fe

2.9

Mg

2.1

)

(Si

8

O

22

)(OH)

2

. The 136.37 amphibole consist only by Cummingtonite type and also here most

of them incorporates over 1 apfu manganese and the prefix mangano is used (Figure 24,

Figure 25). A representative chemical formula of manganocummingtonite

(Ca

0.1

)(Mn

1

.

4

Fe

0.5

Ca

0.1

)(Fe

2

Mg

3

)(Si

8

O

22

)(OH)

2

.

46

Figure 25: Diagram of the prefix with respect to manganese content in Norrnäs 3204 samples 121.92 and

136.37.

Norrnäs 3204 – garnet

Garnet is investigated in samples 121.92 and 136.37 . Both of the samples are dominated by

spessartine but they differ in grossular-almandine composition. Sample 121.92 is more

enriched in almandine where sample 136.37 is more enriched in grossular (Figure 26). A

representative chemical formula of a garnet from sample 121.92 (Mn

2+1.6

Ca

0.7

Fe

2+0.7

)

(Al

1.9

Fe

3+0.1

)(SiO

4

)

3

, and a representative chemical formula of a garnet in sample 136.37

47

Figure 26: Spessartine-grossular-almandine triangular diagram of Norrnäs 3204 samples 121.92 (n=98) and

136.37 (n=77).

Norrnäs 3204 – magnetite

48

Figure 27: Triangular diagram over Ti+Al-Fe-Mn content in Norrnäs 3204 sample 121.92 (n=135).

Norrnäs 3088 – amphibole

The amphibole in sample 598.15 is of grunerite type that incorporates high manganese

content ~3.5 apfu. With more than 3 apfu Mn the prefix permangano shall be used (Figure 28,

Figure 29). These amphibole incorporate significant amounts of chlorine, up to 4.56%, so a

second prefix chloro shall also be used. The chlorine content seems to follow the levels of

manganese and silica, when manganese content is high the chlorine levels are also high, and

the opposite with silica, when silica is low the chlorine levels are high (Figure 30, Figure 31).

Chloro-permanganogrunerite is named after Leake et al. (1997) rules, and a representative

chemical formula is (Mn

1.3

)(Fe

3+0.7

Fe

2+1.9

Mn

2.1

Mg

0.3

)(Fe

3+2

Si

6

O

22

)(Cl)

2

.

49

Figure 28: Diagram of Mg-Fe-Mn-Li-amphibole in Norrnäs 3088 sample 598.15 (n=35).

50

Figure 30: Manganese vs Chlorine in Norrnäs 3088 sample 598.15.

Figure 31: Silica vs Chlorine in Norrnäs 3088 sample 598.15.

The prefix naming procedure of this type of amphibole is a little complex, after

Leake et al. (1997) rules the amphibole would be called chloro-permanganogrunerite. But the

prefix permangano is not accepted and using Hawthorne et al. (2012) nomenclature for

amphibole it would probably be chloro-ferro/manganogrunerite. The representative chemical

formula (Mn

1.3

)(Fe

3+0.7

Fe

2+1.9

Mn

2.1

Mg

0.3

)(Fe

3+2

Si

6

O

22

)(Cl)

2

indicates both manganese in the B

and C sites. The Hawthorne et al. (2012) rules for mangano prefix is not completely fulfilled,

it lacks a few percent of manganese (Figure 15). To be consistent, Leake et al. (1997) rules

are followed.

51

Norrnäs 3088 – garnet

High spessartine content in the garnet also reflect the anomalous high levels of manganese

that can be seen in the amphibole of this section (Figure 32), and has a representative

chemical formula (Mn

2+1.6

Fe

2+0.8

Ca

0.6

)(Al

1.9

Mg

0.1

)(SiO

4

)

3

.

Figure 32: Triangular diagram of spessartine-grossular-almandine in Norrnäs 3088 sample 598.15 (n=65).

Norrnäs 3088 – other minerals

A few grains of a manganese titanium mineral called pyrophanite with a chemical formula of

MnTiO

3

have been found (Figure 33). This mineral incorporates iron substituting for

52

53

Konstäng 3167 – amphibole

Calcic amphibole are present in the two samples 43.10 and 104.80. Sample 43.10 plots around

the line between tremolite and magnesiohornblende (Figure 34). A representative chemical

formula for the mineral is magnesiohornblende because of the high content of Mg and

presence of Fe

3+

with generally less than 7.5 apfu Si, giving a formula of

(Ca

0.4

)(Ca

2

)(Ca

1.3

Mg

2

Fe

3+1

Mn

0.6

Fe

2+0,1

)(Si

7,5

O

22

)(OH)

2

.

The calcic amphibole in sample 104.80 trend from ferroactinolite to

ferrohornblende and ends in ferrotschermakite (Figure 34). The dominating composition is of

ferrohornblende type with a representative chemical formula

(K

0.1

)(Ca

1.8

Na

0.2

) (Fe

2+2.2

Mg

1.5

Fe

3+1

Mn

0.2

Ca

0.1

)(Si

7.2

)(OH)

2

.

Figure 34: Diagram of calcic amphibole in Konstäng 3167 samples 43.10 (n=16) and 104.80 (n=30).

Mg-Fe-Mn-Li-amphibole occurs sparsely in this section and only four grains were

detected. They are of grunerite type with less than 1 apfu manganese (Figure 35, Figure 36).

A representative chemical formula is (K

0.6

)(Mn

0.7

Na

0.1

)(Fe

3.8

Mg

1.1

Mn

0.1

)(Si

8

O

22

)(OH)

2

.

54

Figure 35: Mg-Fe-Mn-Li-amphibole diagram of Konstäng 3167 sample 140.80 (n=4).

Figure 36: Mg-Fe-Mn-Li-amphibole in Konstäng 3167 sample 140.80 with regarding prefix use for manganese