Geochemistry and petrography of magnesium-rich intrusive rocks in
the Rompas-Rajapalot area, Peräpohja Belt, northern Finland
Miika Huttu
Master’s thesis
Geology and mineralogy
Oulu Mining School
University of Oulu
2014
Oulu Mining School
Maturity test for M.Sc.
(Appendix for M.Sc. thesis)
Major subject: Geology and mineralogy
Author (surname, forename)
Thesis’s number of
Huttu Miika
pages
62
Title
Geochemistry and petrography of magnesium-rich intrusive rocks in the Rompas-Rajapalot area,
Peräpohja Belt, northern Finland
Petrography, geochemistry, gabbro-wehrlite association, gold mineralization,
Paleoproterozoic, Rompas, Peräpohja Belt, northern Finland
Keywords:
Summary
The aim of this Master’s project was to describe high-MgO intrusive rocks from the RompasRajapalot area and to find potential analogues among known Paleoproterozoic mafic-ultramafic
intrusions that occur in the Karelian schist belts. The focus area of this study, the Rompas-Rajapalot
area, is situated in the Peräpohja Belt, northern Finland. The belt represents ~500-Ma-long geologic
history and supracrustal rocks that have been deformed in several tectonic events. The RompasRajapalot area is located at the northern margin of the Peräpohja Belt close to the Central Lapland
Granitoid Complex and the contact between these units is thought to be tectonic.
The sample material of this study was collected from three drillholes and two outcrops. Thin
sections of ultramafic were studied using polarization microscopy and whole-rock major and trace
element compositions were determined with X-ray Fluorescence Spectroscopy (XRF) and
Inductively Coupled Plasma-Mass Spectrometry (ICP-MS).
The primary mineral assemblage has been completely altered in all samples, and the secondary
minerals consist mainly of amphiboles (actinolite and tremolite), chlorite, biotite, plagioclase and
epidote. Accessory opaque minerals include ilmenite, magnetite, pyrite and pyrrhotite. Some
samples reveal clear “porphyritic-looking” texture, in which large clinopyroxene oikocrysts enclose
cumulus olivine grains. The presence of metamorphic olivine indicates peak metamorphic
conditions of amphibolite facies.
Whole-rock geochemistry shows that the parental magma had Al2O3/TiO2 of ~5.5, Ti/V of ~30, and
high LREE/HREE. This together with petrographical similarities suggests that the closest analogues
for the studied high-MgO rocks are ultramafic cumulates from the 2.22 Ga Gabbro-Wehrlite
Association intrusions. This conclusion has stratigraphic implications that calls for a reappraisal of
the structure of the northern part of the Peräpohja Belt.
Further information
Date: ________ / ________ 201______ Student’s signature:________________________________________________
Content
1
Introduction ....................................................................................................................................... 2
2
Regional geology ................................................................................................................................ 3
2.1
The Peräpohja belt ..................................................................................................................... 3
2.1.1
Kivalo Group ........................................................................................................................ 5
2.1.2
The Paakkola Group ............................................................................................................ 9
2.2
The Mellajoki Suite ................................................................................................................... 11
2.3
Intrusive rocks in the Peräpohja Belt ....................................................................................... 11
3
Paleoproterozoic mafic intrusions in Finland .................................................................................. 13
4
Local geology and sampling ............................................................................................................. 17
5
Methods ........................................................................................................................................... 25
6
Results.............................................................................................................................................. 27
6.1
Petrographical observations .................................................................................................... 27
6.2
Whole-rock geochemistry ........................................................................................................ 36
7
Discussion ........................................................................................................................................ 48
8
Conclusions ...................................................................................................................................... 57
9
Acknowledgements ......................................................................................................................... 58
10
References.................................................................................................................................... 59
Appendices
Appendix 1. Whole-rock analyses of drillcore PRAJ0032
Appendix 2. Whole-rock analyses of drillcore PRAJ0033
Appendix 3. Whole-rock analyses of drillcore ROM0026.
Appendix 4. Whole-rock analyses of the Rompas outcrops
Appendix 5. Trace element analyses of drillcore PRAJ0032
Appendix 6. Trace element analyses of drillcore PRAJ0033
Appendix 7. Trace element analyses of drillcore ROM0026
Appendix 8. Trace element analyses of outcrop PYX1
1 Introduction
The Canadian junior exploration company Mawson Resources Limited (Mawson) has been exploring
high-grade gold mineralization in the Rompas-Rajapalot prospect area since 2010. The prospect area
is part of the Paleoproterozoic Peräpohja Belt. It is located near the northern margin the belt and not
far from the Central Lapland Granitoid Complex. The Rompas high-grade gold and uranium
mineralization is hosted by strongly altered metabasalts and occur in hydrothermal carbonate-calcsilicate-quartz vein system. The Rompas mineralized area covers an area with a strike of ca. 6.0 km
strike and width of 200-250 m. In 2013, Mawson discovered a different kind of mineralization in the
Rajapalot area, ca. 6.0 km east of Rompas. The Rajapalot disseminated hydrothermal gold
mineralization is located in a contact zone between muscovite- and hematite-bearing, oxidized
quartzites and mafic rocks. The whole Rompas-Rajapalot prospect area covers an area of 10 x 10 km
(Hudson 2013a).
During the gold exploration in the Rompas area in the summer of 2014, drilling operation carried out
by the Mawson company intersected magnesium-rich rocks and pyroxenite outcrops were found in
some outcrops. Similar ultramafic rocks were also encountered in two drillholes in the Rajapalot area.
The main purpose of this Master’s project is to study the geochemistry and petrology of these maficultramafic rocks in the Rompas and the Hirvimaa areas (part of the Rajapalot area), in order to find
potential correlation between known barren and ore-bearing mafic-ultramafic rocks elsewhere in the
shield and provide new information for interpreting the structure and stratigraphy of the study area
and the northern part of the Peräpohja schist belt.
This work belongs to a series of Master’s theses that have been done on the Rompas-Rajapalot
prospect area at the University of Oulu. The previous ones focused on metavolcanic rocks (Mustonen
2012), U-Pb zircon dating (Ranta 2012), structural geology (Kinnunen 2013), and petrology of the
gold-uranium mineralization (Alaoja 2014).
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2 Regional geology
2.1 The Peräpohja belt
The Paleoproterozoic Peräpohja belt is located in the municipalities of Kemi, Keminmaa, Tornio,
Ylitornio, Ranua, Simo and Rovaniemi. The belt is triangular shape and it is 170 km long and 80 km
wide. It is represents a failed intercontinental rift (Kyläkoski et al. 2012) with a ~ 500 Ma long
geological history. The thickness of the stratigraphic succession reaches five kilometers (Kyläkoski et
al. 2012). The predominant rocks are supracrustal metasediments and mafic metavolcanics. These are
cut by mafic sills and dikes and felsic plutonic rocks. These latter can be correlated with the 18801890the Haaparanta suite and provide a minimum age for the Peräpohja belt (Perttunen and Vaasjoki
2001; Perttunen 2006).
The northern contact of the Peräpohja Belt to the Central Lapland Granitoid Complex is tectonic. In
the southeast, the Peräpohja belt is bordered by the Archean Pudasjärvi Basement Complex. The
Peräpohja belt lies partly on Paleoproterozoic layered mafic intrusion of the 300-km-long TornioNäränkävaara intrusion belt. In the west, it starts with the Tornio Kemi intrusions and continues to the
Portimo layered igneous complex beneath the Peräpohja belt
The supracrustal rocks of the Peräpohja belt are divided into two groups: the Kivalo and Paakkola
Groups (Perttunen and Hanski 2003). Both of them are further subdivided into several
lithostratigraphic formations (Table 1). The Kivalo Group represents an opening stage of the
intercontinental rift opened in the Archean basement. The sedimentary basin was shallow and
volcanic rocks extruded subaerially or in shallow water. In contrast, the depositional environment of
the Paakkola Group was a rapidly deepening ocean basin.
The degree of metamorphism increases in the Peräpohja Belt from the south to north. In general, the
metamorphic grade of the Peräpohja Belt is low in most of the area of map sheets 2613 (Ylitornio)
(Perttunen 2006) and 2631 and 2633 (Koivu and Törmäsjärvi) (Perttunen and Hanski 2003). The mafic
rocks show a typical greenschist facies assemblage: albite, actinolite, epidote and chlorite. The
3
metamorphic grade increase at the northern margin of the belt; in map sheet 3612 (Rovaniemi), for
example, peak P/T conditions reached amphibolite facies (Perttunen et al. 1996).
Table 1. Lithostratigraphy of the Peräpohja Belt after Hanski et al. (2003) and Kyläkoski et al (2012).
Group
Formation
Lithology
Age (Method)
Paakkola
Martimo
Mica and black schist
1.88–1.91 Ga (U-Pb)6
Pöyliövaara
Mica and black schist
Korkiavaara
Arkosite and mafic tuff
1975±10 Ma (U-Pb)3
Väystäjä
Mafic pillow lava, dolomite
2050±8 Ma (U-Pb)2
Lamulehto
Mafic tuffite
Rantamaa
Dolomite, quartzite
Hirsimaa
Mafic tuffite
Poikkimaa
Dolomite, phyllite
Tikanmaa
Mafic tuffite
Kvartsimaa
Quartzite, dolomite
Jouttiaapa
Amygdaloidal basalt
Kivalo
2106±8 Ma (U-Pb)4
2090±70 Ma (Sm-Nd)1,
correlated to 2140±11 Ma
(U-Pb) mafic sill5
Petäjäskoski
Mica-albite schist, dolomite,
quartzite
Palokivalo
Quartzite, mafic sill
> 2220 Ma (U-Pb)2
Runkaus
Amygdaloidal basalt
2330±180 Ma (Sm-Nd)1
Sompujärvi
Conglomerate
<2440 Ma (U-Pb)1
Age data from 1) Huhma et al. (1990), 2) Vaasjoki and Perttunen (2001), 3) Hanski et al. (2005), 4)
Karhu et al. (2007), 5) Kyläkoski et al. (2012) and 6) Ranta et al. (submitted).
4
2.1.1 Kivalo Group
The Sompujärvi formation
The lowermost unit of the Peräpohja belt, the Sompujärvi Formation, consists of conglomerates,
arkosites and quartzites. It overlies the Archean Pudasjärvi Basement Complex. The maximum age for
the Sompujärvi formation can be derived from its relationship to the ~2440 Ma mafic-ultramafic
layered intrusions (Perttunen and Vaasjoki 2001).
The Runkaus Formation
The first volcanic unit in the Peräpohja belt is the Runkaus Formation. The thicknesses of its
subaerially erupted lava flows are estimated to be between 100 and 200 m. Amygdaloidal basalt flows
are intervened with tuffitic layers and agglomerates. The rocks are composed of actinolite, albite,
epidote and chlorite. Minerals inside rounded amygdales include quartz, chlorite and calcite. The
timing of the volcanism is not yet precisely constrained. The Sm-Nd-method has yielded an age of
2332±180 Ma, whereas the U-Pb method has given an age of ~2250 Ma for secondary titanite (Huhma
et al. 1990).
The Palokivalo Formation
The Palokivalo Formation is a widespread quartzite formation with sporadic dolomitic interlayers. The
thickness of its quartzites is about one kilometer (Kyläkoski et al. 2012). Evidence for shallow water
deposition is well preserved: ripple marks and cross-bedding are common as well a as mud-cracks
indicating intermittent subaerial exposure. The dolomite interlayers show occasionally stromatolite
structures. In the western part of the Peräpohja belt, outcrops of the Palokivalo Formation are
exposed on the hills in the Törmäsjärvi and Koivu map-sheet areas.
5
Age constrains for the Palokivalo Formation are provided by mafic intrusions. Sills and dikes of the
gabbro-wehrlite association (GWA) intruding the lower part of the formation have been dated with
the U-Pb method at ~2220 Ma (Perttunen and Vaasjoki 2001; Hanski et al. 2005). Studies of detrital
zircon with ID-TIMS U-Pb suggest a solely Archean provenance for the quartzites of the Palokivalo
Formation (Perttunen and Vaasjoki 2001; Hanski et al. 2001a).
The Kaisavaara Formation
Well exposed outcrops of the Kaisavaara hill have been assigned to a separate formation. Its
quartzites are sericite bearing and sedimentary textures are seldom visible. Perttunen and Hanski
(2003) suggested that Kaisavaara Formation correlates with the Palokivalo Formation and that
overlaying volcanic Santalampi Formation correlates with the Jouttiaapa Formation.
The Petäjäkoski Formation
Kyläkoski et al. (2012) distinguished a new basin-wide metasedimentary unit, which they named the
Petäjäkoski Formation. It is older than a crosscutting mafic sill dated by the U-Pb zircon method at
2140±11 Ma. On the other hand, ~2220 Ma differentiated GWA sills have not been found from the
Petäjäkoski Formation. Detrital zircon yielded Archean ages. The Petäjäskoski Formation is unique in
its geochemistry and mineral assemblage. They are moderate to high in MgO (~6-13 wt%), K2O (~3-8
wt%) and FeOtot (8-15 wt%) contents, low in CaO and Na2O and contain abundant phlogopite,
hematite and dravititic tourmaline. The rocks are classified as phlogopitic-sericitic schists and
hematite-rich albitic schists.
The Petäjäskoski Formation is defined as a claystone-siltstone-sandstone-dolostone association.
Pseudomorphic nodules after gypsum and anhydrite and well-preserved sedimentary structures and
textures suggest that the depositional basin wasn shallow-water to subaerial with evaporitic
conditions. The formation was metamorphosed in greenschist facies and the original structures have
been intensely deformed (Kyläkoski et al. 2012).
6
The Jouttiaapa Formation
The Petäjäkoski Formation is overlaid by a sequence of subaerially erupted continental flood basalt
flows. The thickness of the sequence is 300-1000 m and individual lava flows vary between 0.5 and 60
m in thickness. Between lava flows, there are sparse sediment and tuffite interlayers.
The size of amygdales in the lava flows ranges from 0.5 to 4.0 cm. Amygdales in the bottom part form
tubes perpendicular to the bedding. Amygdales in the upper parts of the lava flows have been
stretched during lava flow and are parallel to the lava layers. Amygdales are filled with calcite, quartz,
epidote and chlorite while the main minerals of the host rock are albite, actinolite, epidote and
chlorite (Perttunen and Hanski 2003; Perttunen 1991). Geochemically, the parental magma of the
formation is tholeiitic basalt. The rocks can be divided geochemically and stratigraphically into two
groups belong to the low-Ti and high-Ti series. The Jouttiaapa Formation basalts have an anomalously
high PGE content compared with typical flood basalts (Kyläkoski 2007). Lavas are strongly depleted in
incompatible elements and they are depleted LREE in comparison with MORB-type basalts (Hanski
and Perttunen 2003). Nd-Sm studies have yielded an age of 2090±70 Ma and positive initial εNd values
of +4.2±0.5 (Huhma et al. 1990). Kykäkoski et al. (2012) correlated the Jouttiaapa Formation with a
mafic sill dated at 2040±11 Ma. Clearly positive εNd values indicate derivation of the lavas from a
strongly depleted mantle with no or only very minor interaction of the magma with continental crust
during its ascent to the surface (Huhma et al., 1990, Kyläkoski 2007).
The Kvartsimaa Formation
The Kvartsimaa Formation consists of white or oxidized reddish granoblastic orthoquartzites. Ripple
marks and cross-bedding are visible in impure quartzite layers containing micas and carbonates. The
formation includes occasional dolomite and conglomerate interlayers (Perttunen and Hanski 2003).
7
The Tikanmaa Formation
The Jouttiaapa formation is overlain by a 200- to 300-m-thick sequence of fine-grained mafic tuffites
of the Tikanmaa Formation. Its bedding is commonly well-developed, with the thickness of single beds
ranging from 1 mm to dozens of centimeters. The mineral assemblage consists of metamorphic albite,
actinolite, chlorite and epidote. The magnetic susceptibility of the formation is high and this is clearly
visible in geomagnetic maps (Perttunen and Hanski 2003).
The Poikkimaa Formation
The Poikkimaa Formation is located between the magnetic Tikanmaa and Hirsimaa Formations. It is
poorly exposed and consists mainly of fine-grained dolomite with fyllite interlayers. Due to its poor
exposure, the extent of this formation has been approximated with help of aeromagnetic maps
(Perttunen and Hanski 2003).
The Hirsimaa Formation
The Hirsimaa Formation is a poorly exposed mafic tuffite formation. The formation has a high
magnetic susceptibility and its thickness has been assessed to be 100-400 m (Perttunen and Hanski
2003). U-Pb analysis on zircons has yielded a precise age of 2106±8 Ma for this formation (Karhu et al.
2007).
The Rantamaa Formation
The Rantamaa Formation is a fine-grained, yellowish or light gray, dolomite formation. Both
stromatolite structures and mud-cracks are clearly distinguishable in many outcrops. Quartz-rich
interlayers commonly display ripple marks and herring-bone structures. The total thickness of the
formation varies between 100 to 300 m (Perttunen and Hanski 2003). In his carbon isotope study of
Jatulian carbonate rocks, Karhu (1993) suggested that the Rantamaa Formation represents the 2200
8
to 2100 Ma sedimentation stage III due to its high δ13C values. The positive carbon isotope excursion
ended at >2050 Ma (Karhu 2005).
The Lamulehto Formation
The ca. 100-m-thick Lamulehto Formation consists of mafic tuffite. Its mineral assemblage is
amphiboles, plagioclase, chlorite and quartz. The formation is not exposed in the Peräpohja Belt, but
has been recognized by drilling (Perttunen and Hanski 2003).
2.1.2 The Paakkola Group
The Martimo Formation
The Martimo Formation represents the most wide-spread formation of the Paakkola Group. It
consists of metagraywackes, mica schists and black schists. Its black schists are graphite- and sulfidebearing and clearly visible in geophysical maps. The depositional environment was rapidly deepening
ocean basin and the characteristic feature of the formation is the presence of turbidites. Turbiditic
units are coarse-grained and typically contain oval-shaped, 5-20 cm sized concretions. The thickness
of the greywacke layers varies between 50 and 100 cm (Perttunen and Hanski 2003; Kyläkoski et al.
2012).
The stratigraphic position of the Martimo Formation is under discussion. A minimum age, ca. 1880
Ma, is determined by the U-Pb age of the Haaparanta Series plutons (Perttunen and Vaasjoki 2001).
Ranta (2012) measured U-Pb ages for detrital zircons from a mica schist sample. The youngest zircon
population turned out to be ca. 1.91 Ga in age indicating that at least some parts of the Martimo
Formation are relatively young and correspond to the Upper Kaleva (cf. Lahtinen et al., 2010).
9
The Väystäjä Formation
The Väystäjä Formation includes strongly deformed mafic volcanic rocks and dolomite and black
schist interlayers. Pillow lava structures are common, and chemically the volcanic rocks are tholeiitic
basalts. Felsic porphyries have yielded a zircon U-Pb age of 2050±8 Ma (Perttunen and Vaasjoki 2001).
Hanski et al. (2005) suggest that the Väystäjä Formation is an allochtonous unit and its contact with
the Martimo Formation is tectonic.
The Korkiavaara Formation
Kyläkoski et al (2012) incorporated the Korkiavaara Formation in the Paakkola Group. The formation
has been interpreted as a series of mafic and felsic tuffs. In-situ SIMS analyses of zircon grains have
yielded an age of 1975±10 Ma (Hanski et al. 2005).
The Pöyliövaara
The youngest supracrustal unit in the Peräpohja Belt is the Pöyliövaara Formation (Kyläkoski et al.
2012). The formation consists mainly of mica schists with a 1975±10 Ma detrital zircon population (UPb zircon data; Hanski et al. 2005).
10
2.2 The Mellajoki Suite
The western part of The Rompas area belongs to the Mellajoki Suite. Perttunen and Hanski (2003)
regarded the quartzites and mica schists as a lithodemic unit and part the Central Lapland Granitoid
Complex. In addition to quartzites, the formation consists of mica schists and quartz-feldspar
gneisses. Mica schists are strongly foliated and the quartzites folded and brecciated (Perttunen and
Hanski 2003). The recent detrital zircon study by Ranta (2012) only revealed Archean ages. Therefore
Ranta et al. (submitted) suggest that the Mellajoki Suite belongs to the Peräpohja Belt and is
potentially correlative with to the Palokivalo Formation of the Kivalo Group.
2.3 Intrusive rocks in the Peräpohja Belt
Mafic intrusions
Supracrustal rocks of the Peräpohja belt are commonly cross-cut by mafic intrusive dikes. The dikes
are divided into two major groups. The 2220 Ma gabbro-wehrlite association (GWA) intrusions occur
more often as sills than dikes. The sills are commonly gravity differentiated and occur within the
Palokivalo Formation quartzites (Hanski et al. 2010). 2.220 Ga GWA layered sills are discussed in more
detail in chapter 3. The second intrusion group is formed by younger, nondifferentiated series of
mafic intrusions cross-cutting the Petäjäkoski Formation. Kyläkoski et al. (2012) have dated the
Kuusivaara mafic sill at 2140±11 Ma.
Magnetic susceptibility is high and mafic intrusions are recognizable on aeromagnetic maps. Primary
minerals are almost completely replaced by secondary minerals. The present mineral assemblages in
mafic intrusions consist of albite and amphiboles, epidote, chlorite and magnetite (Perttunen and
Hanski 2003).
11
Felsic igneous rocks
Felsic igneous rocks from the Törmäsjärvi map sheet (2631) are divided into three groups: (1) small
dacitic or rhyolitic (1-3 m) dikes cutting the Martimo Formation, (2) the Aavasaksa granites and (3)
rhyolitic volcanic rocks of the Väystäjä Formation (Perttunen and Hanski 2003). The Ylitornio map
sheet (2613) also contains quartz monzodiorites and granodiorites of the Haaparanta Suite (Perttunen
2006). Perttunen and Vaasjoki (2001) dated zircons and titanites from the felsic intrusions of the
Haaparanta suite, obtaining ages of ~1.89 Ga.
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3 Paleoproterozoic mafic intrusions in Finland
2450 Ma dike swarms and layered intrusions
Several mafic igneous events are related to the geological history of the Peräpohja Belt. The first
igneous event, dated at ca.2450 Ma, consists of two types of magmas: boninite-norite and low-Ti
tholeiitic. Based on their geochemical characteristics and field relationship, they are divided into five
subgroup: (1) NE-trending boninite-noritic dikes, (2) NW-trending gabbronorite, (3) NW-trending
tholeiitic dikes, (4) NW- and E-trending Fe-tholeiitic dikes and (5) E-trending orthopyroxeneplagioclase-phyric dikes (Vuollo and Huhma 2005). The layered intrusions of the Tornio-Näränkävaara
belt are coeval with the igneous event at ~2450 Ma. The Tornio-Näränkävaara layered intrusions are
located at the margin of the Peräpohja Belt, except the Koilismaa layered igneous complex. Outside
the Peräpohja belt, the Paleoproterozoic Central Lapland Greenstone Belt (CLGB) includes the
Koitetelainen and Akanvaara layered intrusions. U-Pb zircon analyses of these gabbroic rocks have
yielded ages of 2439±3 and 2436±6 Ma (Mutanen and Huhma 2001).
2300 Ma dike swarm and intrusions
In addition to the easily distinguishable ~2450 Ma and ~2200 Ma mafic dikes and sills, there are less
well-defined mafic magmatic events (Vuollo and Huhma 2005). The Runkaus Formation is younger
than the 2450 Ma layered intrusions but older than the 2200 Ma GWA sills (Pertunen and Vaasjoki
2001). Huhma et al. (1990) obtained a Sm-Nd isochron age of 2330±180 Ma for mafic dikes, whereas
Vuollo et al. (2000) determined a more precise age of 2332±18 Ma. Dikes of a similar age are also
present in Russia as shown by the recent study by Stepanova et al. (2014), which yielded U-Pb zircon
ages 2309±3 Ma and 2311±5 Ma for a mafic dike swarm not far from the Finnish border.
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2200 Ma layered sill and dikes
The wide-spread layered 2220 Ma mafic-ultramafic sills referred to as the gabbro-wehrlite association
(GWA) by Hanski (1984, 1986a, b, 1987). Later they have also been called karjalites (Vuollo and
Piirainen 1992). Vuollo and Piirainen (1992) proposed that the parental magma was low-Al-tholeiite.
The GWA sills in the Peräpohja Belt have dated at 2210-2220 Ma (Perttunen 1991; Perttunen and
Vaasjoki 2001). However, the total spread of the published zircon and baddeleyite dates is
considerable, which led Hanski et al. (2010) to undertake a single zircon SIMS study to look for the
reasons for the age scatter. Comparison of the SIMS and ID-TIMS results revealed the presence of
ubiquitous hydrothermal alteration of zircon grains in the GWA sills. It also showed that the original
magmatic event was a short-lived, but wide-spread magmatic episode. The GWA intrusions are
usually a few hundreds of meters in thickness and laterally that can be followed up to 150 kilometers.
Stratigraphically, the GWA sills are typically found close to unconformity between the Archean
basement and Paleoproterozoic metasediments. Later tectonic movements have deformed their
shape and size (Vuollo and Huhma 2005).
The Koli layered sill is one of the most prominent examples of the GWA sill (Hanski 1984, Vuollo and
Piirainen 1991). The Koli layered sill in northern Karelia is roughly 60 km long and 340 m thick unit.
This sill represents one single magma pulse and layered series formed by fractional crystallization
(Vuollo and Piirainen 1991).
The lowermost unit in the Koli layered sill is olivine-chromite cumulate and its composition is wehrlitic
(Streckeisen 1976). The cumulus minerals are olivine and euhedral chromite and the main
intercumulus minerals are clinopyroxene and edenitic hornblende. Magmatic Mg-rich mica,
phlogopite, is altered to chlorite. Chlorite also replaces clinopyroxene. Olivine is serpentinized and
clinopyroxenes altered to tremolite. Other secondary minerals are magnetite and carbonate (Vuollo
1988; Vuollo and Piirainen 1991).
14
The upper part of the ultramafic unit is formed by a ~2-m-thick olivine-clinopyroxene cumulate. This
unit shows rhythmic layering of olivine-clinopyroxene and clinopyroxene cumulates. The olivineclinopyroxene cumulate resembles underlying olivine cumulate with the only major difference
between them being the cumulus habit of clinopyroxene (Vuollo 1988; Vuollo and Piirainen 1991).
The thickest unit of the Koli sill is clinopyroxene cumulate. Clinopyroxene is the only cumulus mineral
in the unit. Intercumulus minerals are plagioclase (now albite) and brown hornblende. Plagioclase is
saussurized and some plagioclase grains are altered completely to epidote. Clinopyroxene is
metamorphosed to secondary amphiboles (actinolite / pargasitic hornblende) (Vuollo 1988). The
upper part of the clinopyroxene unit has also ilmenomagnetite as a cumulus mineral. This unit has
been defined as clinopyroxene-magnetite cumulate (Hanski, 1984, Vuollo 1988; Vuollo and Piirainen
1991).
When plagioclase becomes a cumulus mineral, the color of rock becomes lighter and its contrast to
the underlaying zone is sharp. The gabbroic upper part of the sill is formed by plagioclaseclinopyroxene-magnetite cumulates. Also minor intercumulus quartz appears in this unit. The
gabbroic unit grades gradually into the latest differentiate of quartz- and plagioclase-rich granophyre
(Vuollo and Piirainen 1991). The granophyre unit is characterized by granophyric intergrowth of
quartz and feldspars. Its minor primary minerals are hornblende, ilmenomagnetite, apatite, biotite,
titanite, allanite and zircon (Vuollo and Piirainen 1991).
The composition of parental magma can be obtained from a chilled margin. The parental magma of
the 2.22 Ga GWA layered sills is characterized by a relatively low Al2O3 (~10 wt%) and high FeO (~13
wt%) content and hence it has been called low-Al tholeiite. Low Al2O3 and moderately high TiO2
results in a low Al2O3/TiO2 ratio of 5-6, which is one of the most diagnostic chemical features of the
magma type. It is also enriched in LREE compared to HREE [(La/Yb)n = 5.8] (Vuollo and Huhma 2005).
Due to the low Al2O3 content, relatively high H2O and FeOtot, plagioclase appeared late as a liquidus
phase, allowing strong modal and chemical differentiation to take place in the sills (Hanski 2012).
15
2100 Ma dike swarms
Wide-spreading NW- and E-trending metadiabase dikes in northern and eastern Finland have been
dated between 2100 Ma and 1980 Ma. Their mineralogy and modal composition is homogenous, and
they consist mainly of hornblende and plagioclase.. Their parental magma composition is Fe-tholeiitic
(Vuollo and Huhma 2005)
2050 Ma intrusions in Lapland
Mafic intrusions with an age of ~2050 Ma exist in Lapland, particularly within the Savukoski Group.
Usually intrusions belonging to this age group occur as conformable or semiconformable dikes. The
thickness of these dikes is a few tens of meters. The Keivitsa and Satovaara intrusions are the only
prominent examples of differentiated layered intrusions of this age group. Keivitsa is a funnel-shaped
body with a surface area of ~ 16 km2 and estimated thickness of more than 2.5 km. The KeivitsaSatovaara complex includes also the Satovaara body. Probably they have been earlier one intrusive
body but were separated by later movements (Hanski and Huhma 2005).
The Keivitsa intrusion is divided into four zones: The Basal marginal chill zone, the ultramafic zone, the
gabbro zone and the granophyre. The ultramafic zone is the thickest, as much as 2 km or more. The
rock type in the ultramafic zone is defined as olivine-clinopyroxene-(orthopyroxene-) magnetite
cumulate. Table 4 shows element ratios from the basal marginal chill zone of the Keivitsa layered
intrusion, representing the composition of the parent magma (Mutanen 1997).
1980 Ma dike swarm
The 1980 dike swarm is less voluminous than the earlier 2100 Ma dike swarm. NW-trending and up to
70-m-wide dikes occur in the Archean Kuhmo block. The 1980 Ma dike swarm predates the 1950 Ma
ophiolites. The parental magma is Fe-tholeiitic to tholeiitic in composition (Vuollo and Huhma 2005).
16
4 Local geology and sampling
According to the DigiKP, the digital map database of the Geological Survey of Finland (Version 1.0,
available at http://www.geo.fi/en/bedrock.html), the Rompas prospect area consists of quartzites,
mica schists and arkose gneisses of the Mellajoki Suite (Fig 1). Mica schists on top of the hill where
PYX1 is located are strongly schistose and quartzites show clear foliation. Their typical dip direction is
to the southwest (avg. 260°) and dip angle is deep averaging. 81°.
Fieldwork of this study was carried out in 2014 in the Rompas area. During mapping, two outcrops of
ultramafic rocks were discovered within the area of the Mellajoki suite rocks. Outcrops PYX1 and
PYX2, which are shown in Fig. 1 and described below, were sampled for more detailed studies.
Ultramafic rocks were also found by drillhole ROM0026 located in the southern part of the Rompas
mineralized zone (Fig. 1).
The Hirvimaa area is located to northeast corner of the Rajapalot prospect area. According to the
DigiKP map database, the Hirvimaa area consists of rocks of the Korkiavaara, Jouttiaapa and
Pöyliövaara Formations (Fig. 1), i.e. the uppermost supracrustal rocks of the Peräpohja Belt.
Accordingly, rocks at the drilling are amphibolites, arkosites and mica schists of the Korkiavaara
Formation. In the south, there are the Jouttiaapa Formation mafic volcanic rocks. Mica schists of the
Pöyliövaara Formation are located in the northern part of the Hirvimaa area. However, new data
obtained in this study indicate that the geological map of the area needs to be updated. (see
Conclusions).
At Hirvimaa, several shallow drillholes were made and two of them, PRAJ0032 and PRAJ0033,
revealed the presence ultramafic rocks. The locations of these holes are shown in Fig. 1.
17
Figure 1. The Rompas prospect area (red ellipse on the left) and the Hirvimaa prospect area (red
ellipse on the right) as shown on the DigiKP, the digital bedrock database of the Geological Survey of
Finland (Version 1.0, available at http://www.geo.fi/en/bedrock.html).
18
Pyroxenite outcrop 1 (PYX1)
On top of small a hill is a pyroxenite outcrop, which is oval in shape, ca. 15 m long and ~10 m wide.
The outcrop is well exposed, except the east side (Fig. 2).
Figure 2. Outcrop PYX1 at in the Rompas area. Hammer at top of the outcrop is pointing to north,
handle length ~60cm (y = 3399858; x = 7375808).
The southern corner of the outcrop is strongly carbonized, coarse-grained amphibole-rich ultramafic
rock. Thin section PYX1-4 represents this part of the outcrop. The sample for thin section PYX1-1 was
taken from the middle part of the outcrop. Its fresh surface looks fine-grained and black while the
weathered surface is brown and pitted (Fig. 3). The texture of the rock in the northern corner of the
outcrop appears porphyritic: dark-colored phenocrysts in a greenish fine-grained groundmass (Fig 4).
The porphyritic part at the northern end of the outcrop is carbonitized.
19
Figure 3. Weathered surface of outcrop PYX1 and drillcore sample after gasoline powered rock
drilling. Rompas area. Diameter of drillcore ~2.5 cm.
Figure 4. Porphyritic looking texture in the northeastern part of outcrop PYX1 in the Rompas area.
20
Samples 221376, 241753 and 232890 for whole-rock analyses were collected from outcrop PYX1.
Sample 221376 was obtained earlier by Mawson field staff, while the rest of the samples was sampled
by me. Sample 232890 represents the coarse-grained north end (Fig. 4) and sample 241753 is ~100
cm to west from the sample 232890.
Pyroxenite outcrop 2 (PYX2)
Approximately 2 km to the north-west of outcrop PYX1, there is a ca. 30-m-wide, round-shaped
outcrop of ultramafic rock (PYX2). The northern end of this outcrop is coarse-grained and porphyritic
with a more fine-grained dark green groundmass enclosing large amphibole grains. Sample 232891
represents the northern end of the outcrop. The major part of the outcrop is homogenous, mediumgrained, black amphibolite rock, which is weakly and pervasively carbonitized. Sample 2328892 is
from the medium-grained part of the outcrop.
21
Figure 5. Outcrop PYX2 in the Rompas area. Rock hammer points to north, handle length is 60 cm (y = 3399858;
x =7375808).
The drillhole ROM0026 in the Rompas area
Drillhole ROM0026 is located near the margin of the Martimo Formation (Fig. 1). Mustonen (2012)
took one surface sample close to this drillhole. According to his interpretation, volcanic rocks of the
area can be correlated with the Runkaus Formation. The drillhole is adjacent to Mawson’s new
discovery, the Kaita prospect (Hudson 2013b).
The drillhole ROM0026 is 106.6 m long, with overburden of 12 meters. The first lithological unit is
quartzite, which is followed a brecciated fault zone. In this study, I concentrate on the mafic interval
between 28.2 and 78.7 m. This section was originally pyroxenite, but is now composed mainly of
amphiboles and chlorite. The section of the drillcore from 28.2 to 61.1 m is equigranular and mediumgrained. The section 61.1 – 78.7 m is strongly altered and cut by intensive carbonate veining.
22
The next section between 78.7 and 97.9 m is fine-grained carbonate- and quartz-rich sedimentary
rock. Strongly cleaved carbonate schist with talc veins is the last lithological unit in the drillcore
between 97.9 – 106.6 meters. The main lithological units are listed in the Table 2.
Table 2. The main lithological units in drillcore ROM0026.
Depth from (m)
Depth to (m)
Lithology
0
12
Overburden
12
26.7
Quartzite
26.7
28.2
Fault zone. Strongly brecciated
28.2
61.1
Pyroxenite
61.1
78.7
Altered pyroxenite
78.7
97.9
Siltstone
97.9
106.6
Carbonate-rich schist
Drillholes PRAJ0032 and PRAJ0033 in the Hirvimaa area
The first ~5 meters in both drillholes is quartz-rich sedimentary rock. This study focuses on mafic rocks
from in the interval from ~5 to ~13 m in both drillholes. Figure 6 shows a half-cut drillcore from core
PRAJ0033. Minerals in both drillcores are mainly medium-grained amphiboles and the lower sections
of the drillcores (starting ~8 m) show a porphyritic-looking texture.
23
Figure 6. Photograph of drillcore PRAJ0033 consisting of medium-grained amphibolite. The lower
section of core shows dark oikocrysts.
24
5 Methods
Collecting samples
Field work for this study was carried out in 2014. Samples for whole-rock analysis and thin sections
were taken with a hammer from promising outcrops. Evenly rounded outcrops without sharp corners
were sampled with a gasoline-powered core drill. This drill was equipped with a 1-inch-diameter and
20-cm-long drill bit. In practice, the drillcore length was about 10 cm. The water supply for the drill
was a manually pressurized water pump can. An example of obtained drillcores is shown in Fig. 3.
Drillholes PRAJ0032 and PRAJ0033 were drilled with an in-house portable and low-impact rig. Drillhole
length was limited to 14 (PRAJ0032) and 12 (PRAJ0033) m.
Whole-rock geochemistry of the samples
The drillcore obtained by diamond drilling was cut into half and each sample length was measured to
be one meter. Samples for whole-rock analysis were sent to ALS global. Major elements were
determined by X-ray Fluorescence Spectroscopy (ALS method ME-XRF06). Trace elements were
analyzed with Inductively Coupled Plasma-Mass Spectrometry (ALS Method ME-MS61 and ME-MS81).
Platinum group elements and gold were analyzed with Inductively Coupled Plasma-Mass
Spectrometry (ALS Methods PGE-MS23L and Au-ICP22). Analytical data were processed and some
diagrams made with Excel (2010) software. Were drawn with GeoChemical Data toolkit (GDCkit
version 3.00) (Janoušek et al. 2006) and MinPet 2.0.
25
Petrographic studies
A thin section laboratory in France prepared a total of 11 thin sections. The samples for thin sections
were collected and prioritized based on their geochemistry with a special focus on magnesium-rich
lithologies in drillcores and outcrops.
Petrographic studies were carried out in the facilities of the University of Oulu. Petrographic
microscopes allowed using transmitting light for the inspection of silicate minerals and reflective light
for opaque minerals. Several photomicrographs were also taken using petrographic microscope
equipped with Canon powershot G10 digital camera. Photomicrographs from the thin sections were
edited when needed. Their cropping and adjustments of brightness and contrast were made with
Picasa (version 3.9.137) and Paint.net (version 4.0.3) software.
26
6 Results
6.1 Petrographical observations
PYX1-1 and PYX1-2
The thin section PYX1-1 is from the southern end of outcrop PYX1. The sample is composed of coarse
pseudomorphs of clinopyroxene oikocrysts, which enclose rounded chadacrysts of cumulus olivine.
Clinopyroxene and olivine are metamorphosed to secondary amphiboles, but original olivine grains
are visible by disseminated magnetite around olivine grains (Fig. 7A and 7B, Fig. 8A). The main
metamorphic minerals are pale blue, weakly pleochroic actinolite and chlorite. Accessory plagioclase
grains occur as small laths. Magnetite grains are associated sporadically with isotropic anhedral green
spinel.
Sample PYX1-2 is from the middle part of outcrop PYX1 (Fig 2 and 3). It is more fine-grained,
weathered and strongly carbonitized compared to thin section PYX1-1. Also its poikilitic texture is not
so clearly visible as in sample PYX1-1. In PYX1-2 tremolite is more abundant than actinolite and biotite
is common.
In outcrops PYX1 and PYX2, opaque minerals are mainly anhedral ilmenite and magnetite. Small iron
oxide-sulfide mixed grains are common (Fig. 8B and 8D). Sulfides are pyrrhotite and pentlandite and
minor chalcopyrite. Grayish-blue chromite cores are visible in some of the oxide grains while the
margin of the grains is altered to magnetite (Fig. 8C).
27
C
D
Figure 7. Photomicrographs of samples from aoutcrop PYX1 in the Rompas area. Photo width 4 mm.
A) Pseudomorph of cumulus olivine. Primary minerals are metamorphosed to secondary amphiboles;
the original cumulus texture is visible as magnetite coating around olivine grain. Sample PYX1-1,
cross-polarized light. B) Sample PYX1-1, plain-polarized light. C) Chlorite, carbonate and amphiboles in
sample PYX1-2, cross-polarized light. D) Sample PYX1-2, plain-polarized light.
28
Figure 8. Photomicrographs of samples from outcrop PYX1 in the Rompas area. A) Secondary
pseudomorph after a poikilitic clinopyroxene oikocryst containing rounded olivine chadacrysts.
Sample PYX1-1, cross-polarized light, photo width 4 mm. B) Magnetite and sulfide grains. Sulfides are
pyrrhotite and pentlandite and minor chalcopyrite. Sample PYX1-2, reflected light, photo width 1 mm.
C) Magnetite surrounding chromite. Sample PYX1-1, reflected light, photo width 1 mm. D) Magnetitesulfide mixed grain. Sample PYX1-1, reflected light, photo width 1 mm.
29
PRAJ0032-6.0
The most significant feature in sample PRAJ0032-6.0 is large (up to 5 mm) iddingsite pseudomorphs
after metamorphic olivine. Mineral assemblage consists of iddingsite, amphiboles, chlorite,
plagioclase and biotite. Sulfides (pyrrhotite, pentlandite and chalcopyrite) are often in mixed grains
with magnetite (Fig. 9A and 9B).
PRAJ0032-8.62
Sample PRAJ0032-8.62 represents a dark, ~50-cm-wide vein in the drillcore and consists of mainly
light brown mica and green, pleochroic tourmaline. The fine grained sample is cut by veins in which
biotite crystals are elongated. Accessory minerals are epidote and sporadic isotropic garnet. Oxide
minerals are absent, but a minor amount of sulfide (pyrite) is present (Fig. 9C and 9D).
PRAJ0032-9.75
Sample PRAJ0032 is mica rich and remnants of the original poikilitic textures are still visible. The
sample contains chlorite and amphiboles, mainly actinolite. Opaque minerals include euhedral
magnetite, minor amounts of pyrrhotite, pentlandite and chalcopyrite.
30
Figure 9. Photomicrographs of samples from drillcore PRAJ0032 from the Hirvimaa area. Photo width
4 mm. A) Large iddingsite crystal after metamorphic olivine. Sample PRAJ0032-6.0, plain-polarized
light. B) Large iddingsite crystal after metamorphic olivine. Sample PRAJ0032-6.0, cross-polarized
light. C and D) Tourmaline- and biotite-rich rock occurring as a vein, sample PRAJ0032-8.62, plainpolarized light.
31
PRAJ0033-9.22
Sample PRAJ0033-9.22 clearly shows the original poikilitic texture. Clinopyroxene oikocrysts including
rounded olivine intercumulus are altered to amphiboles, mainly actinolite. Between large oikocrysts
there are plagioclase, chlorite and mica. Ilmenite grains are enclosing magnetite and its sulfide
assemblage is pyrrhotite, pentlandite and a minor amount of chalcopyrite. The original texture is
partially disturbed by the growth of metamorphic olivine, which has later retrogressed to brownish
iddingsite (Fig. 10).
PRAJ0033-10.00
Sample PRAJ0033-10.00 is mainly composed of amphiboles and minor plagioclase and chlorite. Large
phenocrysts of iddingsite (pseudomorph after olivine) are typical for the sample (Fig. 10C). Carbonate
occurs in this sample as veins. The most abundant opaque mineral is ilmenite and sulfides are
intergrowths of pentlandite and pyrrhotite, with minor chalcopyrite.
PRAJ0033-13.13
Fine-grained chlorite, amphibole, mica and plagioclase ground mass are surrounding large (up to 3
mm) clinopyroxene oikocrysts. Clinopyroxene and olivine intercumulus crystals are metamorphosed
to secondary amphiboles. The opaque assemblage is similar to that in other samples: ilmenite,
magnetite, pyrrhotite, pentlandite and chalcopyrite. Magnetite-sulfide mixed grains are also common
in this sample.
32
Figure 10. Photomicrographs of samples from drillcore PRAJ0033 from the Hirvimaa area.A)
Amphibole pseudomorph after olivine. Magnetite coating reveals the original intercumulus texture.
Sample PRAJ0033-9.22, cross-polarized light, photo width 4 mm. B) Sample PRAJ0032-9.22, plainpolarized light, photo width 4 mm. C) Iddingsite after olivine, surrounded by amphibole and chlorite
ground mass. Sample PRAJ0032-10.0, cross-polarized light, photo width 4 mm. D) Oxide-sulfide mixed
grain. Sample PRAJ0032-9.22, reflected light, photo width 1 mm.
33
ROM0026-60
Sample ROM0026-60 is composed of amphibolites (actinolite and tremolite) and it has intense
carbonate, chlorite and epidote veining. The opaque minerals include ilmenite, magnetite, pyrrhotite,
pentlandite and chalcopyrite (Figs. 11A and 11B).
ROM0026-61
The most significant feature of sample ROM0026-61 is its blastomylonitic texture. A fine-grained
granoblastic matrix consists of biotite, epidote, chlorite and plagioclase. Up to 2-mm-wide
porphyroclasts are amphiboles. Amphibole crystals are more or less rounded and some grains are
almost round (Fig. 12).
ROM0026-78.8
Sample RO0026-78.8 is near the basal contact between quartz-rich country rock and high-MgO rocks.
The sample is strongly brecciated and its pseudomorphs after clinopyroxenes show characteristic 90°
cleavage (Figs. 11C and 11D). The mineral assemblage of the sample consists of amphiboles (tremolite
and actinolite), carbonates, chlorite and biotite.
34
Figure 11. Photomicrographs of samples from drillcore ROM0026 from the Rompas area. Photo width
4 mm. A). Sample ROM0026-60, cross-polarized light. B) Sample ROM0026-60, plain-polarized light. C
and D) Amphibolitized clinopyroxene cumulate, sample ROM0026-78.8, cross-polarized light.
Figure 12. Photomicrographs of samples from drillcore ROM0026 from the Rompas area. Cross
polarized light. A) Sample ROM0026-61, photo width 4mm. B) Sample ROM0026-61, photo width 14
mm.
35
6.2 Whole-rock geochemistry
Major elements
This study includes 3 samples of PYX1 outcrop, 2 samples of PYX2 outcrop, 9 whole-rock analyses
from drillcore PRAJ0032, 8 whole-rock analyses from PRAJ0033 and 52 analyses ROM0026
representing depth from 27 to 79 meter. Drillhole ROM0026 extends to both directions but quartz
rich rocks are excluded of this study. Assay results are available in Appendices 1 -13 and selected
chemical diagrams are shown in Figs. 13-22. In some of these diagrams, drillhole names of ROM0026,
PRAJ0032 and PRAJ0033 and abbreviated as Drillcores 26, 32 and 33, respectively. Major element
ranges are in Table 3.
Table 3. Range of selected major elements in ultramafic from drillcores and outcrops (wt%).
Sample
SiO2*
TiO2
Al2O3
FeO
MgO
CaO
K2O
Na2O
PRAJ0032
48.3–51.01
0.56-0.86
3.42-8.62
9.28-13.38
16.5-23.13
4.95-9.44
0.18-2.73
0.27-85
PRAJ0033
48.71-55.10
0.66-1.57
3.68-5.54
9.64-12.99
15.22-25.7+
5.43-10.84
0.19-1.36
0.16-0.66
ROM0026
44.58-57.62
0.46-1.20
2.61-7.48
5.22-15.50
10.43-19.32
8.66-23.93
0.10-1.75
0.07-1.59
PYX1
48.21-51.30
0.29-0.75
2.44-4.44
9.65-12.29
22.22-26.03
5.60-9.23
0.02-0.05
0.11-0.20
49.71-52.43
0.60-0.77
3.55-4.44
10.16-12.36
19,57-25.79
4.53-11.15
0.04-0.08
0.11-0.28
outcrop
PYX2
outcrop
(* Calculated)
Magnesium number, Mg#, ranges in drillcores PRAJ0032 and PRAJ0033 between 60 and 67. In
ROM0026 Mg# scatter is between 53 and 73 in lower parts, decreasing to 54 in the upper part of the
drillcore. Figure 15 shows variation diagrams with MgO on X-axis. Scattering of major elements can
be a result of both magmatic and metamorphic processes.
36
Geochemical results show a differentiation trend in drillcore ROM0026 (Figs. 14 and 16). Petrographic
studies reveal porphyritic affinity of the rocks and drillcore is strongly altered and carbonized between
61-79 m.
In layered sills, CaO content varies as a function of the modal content of clinopyroxene. Figure 13
shows how CaO and MgO contents change during crystallization. Anomalous CaO contents drillcore
ROM0026 are results of carbonitization. Drillcore ROM0026 shows a similar deviation from the GWA
reference data in a CMA diagram (Fig. 14).
Selected major elements vs. depth in drillhole ROM0026 are present in Figure 16. An evolving trend is
clear for each element regardless of the significant scattering in bottom parts of the drillhole. The
MgO trend shows two peaks at depths of 60 m and 78 m. Other major oxides behave more linearly as
a function of depth. In this drillcore, CaO shows highest contents roughly between 65 and 75 m.
Drillcore ROM0026 is strongly carbonitized between ca. 45 – 78 m..
Figure 13. MgO vs. CaO plot for Rompas and Hirsimaa samples and reference data of GWA intrusions
from eastern and northern Finland.
37
Figure 14. CMA diagram for Rompas and Hirsimaa samples and reference data of GWA intrusions
from eastern and northern Finland.
38
Figure 135. Major elements vs. MgO plots. Red circle PRAJ0032. Blue triangle PRAJ0033, green square
ROM0026 magenta circle PYX1-outcrop and grey square PYX2 outcrop.
39
Figure 146. Selected elements plotted against height in drillcore ROM0026.
40
Trace elements
Chromium contents in drillholes PRAJ0032 and PRAJ0033 are in the range of 0.11 – 0.22 wt%. The
outcrops of the Rompas area show similar contents, which are PYX1: 0.16 – 0.22 wt% and PYX2: 0.14
– 0.21 wt%. The Ni content of drillcores PRAJ0032 and PRAJ0033 is between 405 and 1220 ppm, while
ROM0026 is less rich in nickel, with the Ni content ranging between 127 and 658 ppm. Sulfur varies
strongly; from below of detection limit up to 1.45 wt%. An average and median sulfur contents is
0.149 0.065 wt%. In addition to the strong scatter, the sulfur content does not show correlation with
any other element. In drillcore PRAJ0032, the average sulfur content is 0.47 wt% and the median
content is 0.42 wt%. Rocks intersected with drillhole PRAJ0033 are lower in sulfur, averaging 0.19
wt%.
The nickel content of the samples shows an almost linear correlation with MgO (Fig. 17) due to olivine
crystallization. The strong deletion of Cr with decreasing MgO as shown in Fig. 18 is a result the
crystallization sequence olivine+chromite, clinopyroxene+olivine, and clinopyroxene
41
Figure 157. Relationship between MgO and Ni. Samples of drillholes PRAJ0032, PRAJ0033, ROM0026
and the Rompas outcrops are included in diagram.
Figure 168. Relationship between MgO and Ni. Samples of drillholes PRAJ0032, PRAJ0033, ROM0026
and the Rompas outcrops are included in diagram.
42
Variation of selected trace elements in drillcore ROM0026 is shown in Fig. 19. Especially nickel and
chromium have two decreasing trends from the bottom part to upper parts. The first one starts from
~80 m (drillcore depth from surface) and reaches its minimum at around 65 m. The second maximum
in Ni and Cr is between 60 and 62 m. The Ni and Cr content drops rapidly and then decreases steadily
until having less significant local peak value at 30 meters. It looks that the core has two magmatic
cycles but brecciated zone in drillcore support idea of tectonic break.
43
Figure 19. Selected minor elements vs. depth in the drillhole ROM0026.
44
Figure 20 represents chondrite-normalized rare earth element (REE) patterns of the studied samples.
All patterns are enriched in light rare earth elements (LREE) compared to heavy rare earth elements
(HREE) and have (La/Yb)CN values in the range of 2.6-5.9. Both drillcores PRAJ0032 and PRAJ0033 have
a sample that is more enriched in REE than the rest of the samples (Fig. 20). Sample 238992 from
drillcore PRAJ0033 has a high TiO2 content of ca. 2 wt% (Fig. 15) and relatively low in Cr and Ni.
Another anomalous REE-rich sample, 238980 from the drillcore PRAJ0032, has no clear anomalies in
geochemistry. Logging of drillcores does not show obvious explanation for the extra REE enrichment.
45
Figure 20. Chondrite-normalized REE patterns Rompas and Hirsimaa samples and reference data of
GWA intrusions from Koli and Kuhmo sills. In the Koli and Kuhmo sills, open symbols are for gabbroic
rocks and closed symbols for ultramafic rocks. Normalizing values after Sun and McDonough (1989).
Figure 21 displays mutual plots of Th, Nb and U in samples from the Rompas and Hirvimaa areas and
GWA intrusions from eastern and northern Finland. The diagram reveals interesting features.
Immobile elements Nb and Th seem to behave coherently with all samples having approximately the
same Th/Nb ratio. In contrast, a large scatter appears when generally mobile U is involved, but not in
46
all cases. The U/Nb ratio is still more or less uniform at ca. 0.07 in the Hirvimaa area, but is increased
in the Rompas area, reaching values up to ca. 3.0. An average U/Nb ratio in ROM0026 is 0.47 and in
Rompas outcrops 0.37. This demonstrates the presence of strong U metasomatism in the Rompas
area, which is seen in both the drill core ROM0026 and outcrop samples. It seems that elevated U is
linked to carbonate veins.
Figure 21. Th-U-Nb relations in the samples of this study compared to samples from GWA intrusions
elsewhere in Finland. The Th/Nb ratio of primitive mantle taken from Sun and McDonough (1989).
47
7 Discussion
Petrographical and geochemical data show that all studied samples are magnesium-rich ultramafic
rocks, with most MgO-rich rocks being located in the outcrops in the Rompas area and drillcores
PRAJ0032 and PRAJ0033 in the Rajapalot area. These are very similar in mineralogy and geochemistry
and easily correlated with each other. While SiO2 content of the samples varies in the range of 48 and
52 wt%, alkalis are relatively low; Na2O + K2O rarely exceeds 2 wt%.
Jensen’s (1976) cation plot is used for classifying subalkalic volcanic rocks. Samples of this study plot
in the komatiite and the komatiitic basalt fields (Fig. 18). The IUGS classification defines komatiites as
rocks having MgO >18%, TiO2 <1%, SiO2 <52 % and Na2O + K2O <2% and picrites having MgO >12 %
and Na2O + K2O <3% (Le Bas 2000). In this sense, most of samples from PRAJ0032, PRAJ0033 and
outcrops are komatiitic. However, the use of Jensen’s (1976) cation plot or the IUGS classification of
the high-Mg rocks is problematic in our case, because the rocks are cumulates and do not represent
magma compositions with the exception of ratios defined by incompatible, immobile elements such
as Al2O3 and TiO2. Thus we can conclude that the parental magma of the ultramafic rocks had a low
Al2O3/TiO2 ratio of 5-6, which is much lower than in komatiitic rocks in general (cf. Hanski et al.
2001b).
Mafic-ultramafic rocks intersected by drillhole ROM0026 show a significant differentiation trend with
MgO and Ni varying between ca. 19 to 10 wt% and 100 to 658 ppm, respectively. Although the
carbonate metasomatism is very strong in the core, the carbonate alteration cannot solely explain the
decrease in the content of compatible elements but magmatic differentiation must be involved. It
seems that the carbonate alteration has attacked more preferentially the most differentiated parts of
the drillcore.
As shown in Fig. 21, all ultramafic bodies studied in this work show similar Th/Nb, which is also similar
to that of the GWA intrusions. The ratio is higher than that in primitive mantle indicating interaction
of the magma with continental crust. The trace element ratios involving U show much variation,
especially in the Rompas area, which is compatible with the occurrence of U-bearing carbonate veins
48
in the Rompas area. In drillcore ROM0026, the U enrichment seems to be linked to the CaO
enrichment (Fig. 16).
Correlation with known igneous occurrences
The poikilitic textures, mineralogy, differentiation trends in drillcore PRAJ0026 and low TiO2/Al2O3
ratio and Ti/V ratio (avg. of all samples 29.13) of the studied rocks strongly support correlation with
the Paleoproterozoic differentiated sills of the 2.22 Ga Gabbro-Wehrlite Association (GWA). The most
prominent example of the GWA intrusions is the Koli layered sill, which shares common features with
the high-Mg rocks in the Rompas and the Hirvimaa areas, including low Al2O3/TiO2 of 5-6 and Ti/V of
31 (Vuollo 1994). The original mineralogical composition is not preserved in the Rompas and the
Hirvimaa samples but pseudomorphic poikilitic textures are very similar to those in the olivine or
olivine-pyroxene cumulates of the GWA as described by Hanski (1984) and Vuollo (1994). Typically,
large clinopyroxene oikocrysts enclose cumulus olivine grains and are in turn surrounded by
intercumulus magmatic brown amphibole. In Fig. 23, textures of olivine cumulates from the Koli sill
and drillcore PRAJ0033 are compared. Sample PRAJ0033-9.55 is more altered than the sample from
the Koli sill. The primary minerals are not present anymore but the cumulus texture is well preserved.
Altered clinopyroxene grains have got an opaque dissemination emphasizing the original porphyriticlooking texture of the rock.
49
Figure 23. Photographs of scanned thin sections. A: Olivine-clinopyroxene cumulate from the Koli sill.
Clinopyroxene (with opaque pigment) oikocrysts and poikilitic brown primary magmatic amphibole
enclosing cumulus olivine grains. B: Sample PRAJ0033-9.55 from the Hirvimaa area. Yellow mineral is
iddingsite after metamorphic olivine.
50
Also whole-rock major and trace element geochemistry reveals similarities between the GWA sills and
the Rompas and Hirvimaa high-Mg rocks. Reference data shown in Figs. 24-25 come from the Kuhmo
Greenstone Belt (Ensilä), Central Lapland Greenstone Belt (Silmäsvaara, Haaskalehto), Peräpohja
Schist Belt (Runkausvaara) and North Karelia Belt (Koli), and Kuusamo Belt. Figure 24 presents an
Al2O3/TiO2 vs. MgO diagram showing that when MgO content rises above ~10 wt%, Al2O3/TiO2
remains roughly constant at 5-6. Low MgO rocks represent upper part of the intrusions in which Al2O3
Al2O3/TiO2 rise rapidly when plagioclase becomes a cumulus phase. A strongly curved trend in Figs. 13
and 14 is created when the MgO content of the rocks decreases and CaO increases at the same time
as olivine-dominated cumulates change first to clinopyroxene-dominates ones and then to gabbroic
rocks during fractionating crystallization. The CaO content steadily decreases and aluminum content
increased in clinopyroxene-plagioclase-magnetite cumulates.
As illustrated in Fig. 20, chondrite-normalized REE patterns in the studied ultramafic rocks LREEenriched and similar to those of ultramafic cumulates of the GWA intrusions. It is evident that the
parental magma for the Rompas and Hirvimaa rocks had moderately high LREE/HREE as is the case for
the GWA intrusions. Other incompatible, immobile element ratios, such Th/Nb (Fig. 21), provide
evidence for the common parental magma type.
51
Figure 24. MgO vs. Al2O3 diagram for ultramafic rocks of this study and rocks from GWA intrusions
(reference data from E. Hanski, pers. comm). Mineral symbols refer to cumulus phases at each stage
of fractionation in the GWA intrusions (Ol = olivine, Cpx = clinopyroxene, Chr = chromite, Mgt =
magnetite, Plag =plagioclase).
52
Figure 25. MgO vs. Al2O3/TiO2 plot for Rompas-Rajapalot rocks and some other Paleoproterozoic
mafic-ultramafic intrusions from northern Finland (reference data from E. Hanski, pers. comm and
Suvanto 2013.)
In Figure 25, samples from other Paleoproterozoic mafic-ultramafic intrusions are compared with
Rompas and Hirvimaa samples on an Al2O3/TiO2 vs. MgO diagram. The closest analogues are found in
the Keivitsa layered intrusion. Zr/TiO2 and TiO2/V ratios (Table 4) from a chilled margin of the Keivitsa
layered intrusions are relatively close to the values in the samples of the Rompas and Hirvimaa areas.
In contrast, CaO/Al2O3 and Al2O3/TiO2 in the Keivitsa intrusion differ from the samples of this study (Fig
25 and Table 4). We can conclude the chemistry of the Rompas and Hirvimaa ultramafic rocks most
closely matches with that of the ultramafic parts of the 2.22 Ga differentiated sills.
53
Table 4. Element ratios from the basal marginal chill zone of the Keivitsa (Mutanen 2007).
Al2O3/TiO2
13.4
CaO/Al2O3
0.79
Zr/TiO2
94.38
TiO2/V
33.09
Stratigraphic position of samples and correlation with the Koli layered sill
The poikilitic texture of the studied samples (especially samples PYX1-1 and PRAJ0032-9.22) is similar
to the olivine cumulates in the GWA layered sills. On the other hand, some samples from the Rompas
outcrops are likely analogues of olivine-pyroxene cumulates in the Koli sill. The thin sections from
drillcore ROM0026 are limited to depths 78.8 m, 61 m and 60 m. Despite the strong carbonate
alteration, the partly preserved textures indicate that the rocks were originally olivine-pyroxene
cumulates in the bottom part of the core and pyroxene cumulates elsewhere.
In the Koli layered sill, the olivine-clinopyroxene cumulate is a kind boundary zone where the
composition of rocks change dramatically. The compositions of the rocks are the following: MgO is
~30 wt% in olivine cumulates, when clinopyroxene appears as a cumulus mineral, MgO decreases to
~25 wt%, and after olivine has disappeared, MgO drops to down 15 wt%. The CaO content follows the
modal abundance of clinopyroxene; in olivine cumulates, CaO is low (3 – 5 wt%). The rapid increase to
~17 % happens after clinopyroxene had become a cumulus phase. This is followed by the steady
decrease of CaO, which can go below 10 wt%. The amounts of Cr and Ni are high in olivine cumulates
(up to 0.4 wt% and 0.12 wt%, respectively) and they decrease down to ~500 ppm and 190 – 360 ppm
in clinopyroxene cumulates (Vuollo 1988).
Observations made from the major element content and petrographic findings from the Hirvimaa
area drillcores (PRAJ0032 and PRAJ0033) and the Rompas area outcrops (PYX1 and PYX2) suggest that
the stratigraphic position of the ultramafic rocks correspond to olivine– and olivine clinopyroxene
cumulates in the GWA sills and the mafic-ultramafic section of drillcore ROM0026 mostly resembles
clinopyroxene cumulates. The MgO and Ni peaks at around 60 m and 78 m indicate a minor presence
54
of olivine-clinopyroxene cumulate. This raises the question of the apparent absence of gabbroic
differentiates in the studied magmatic bodies. The potential reasons may be that the gabbroic rocks
are not exposed or do not exists because the bodies were tectonically dismembered. The latter option
is supported in the case of drillcore ROM0026 by the presence of a breccia zone between the
magmatic body and the overlying sedimentary rocks.
Stratigraphic implications
The occurrence of 2.22 Ga GWA intrusions in the Rompas area is plausible. Ranta (2012) obtained
exclusively Archean ages for detrital zircons from Mellajoki Suite quartzites close to the Rompas area
and regarded the suite potentially as a correlative to the Palokivalo Formation. Based on
geochemistry, Mustonen (2012) suggested a correlation between the Rompas area volcanic rocks and
the Runkaus volcanic Formation. The Runkausvaara 2.22 Ga sill at the SE margin of the Peräpohja Belt
occurs in close spatial association with the Runkaus Formation volcanic rocks and Palokivalo
quartzites and hence mimic the situation in the Rompas area. However, the whole structure of the
bedrock in the Rompas area is more complicated because the youngest supracrustal rocks of the
Peräpohja Belt, represented by some parts of the Martimo Formation, occur south of Rompas, not far
from the mineralized zone (Ranta, 2012).
The relationship of drillholes PRAJ0032 and PRAJ0033 to the surrounding country rocks is more
problematic. The bedrock map places the Hirvimaa area in an environment composed of the
Korkiavaara, Pöyliövaara, and Jouttiaapa Formation rocks, which belong to the upper and middle part
of the stratigraphy of the Peräpohja Belt. The limited amount of drilling and field data do not allow
establishment of the character of the immediate country rocks of the MgO-rich intrusive rocks.
Nevertheless, the apparent occurrence of 2.22 Ga GWA affinity rocks in the Hirvimaa area suggests
major tectonic disturbances in the northern part of the Peräpohja Belt.
55
Economic implications
No economically significant ore deposits are known to occur in the 2.22 Ga GWA intrusions, with the
exception of one small Au-Cu deposit at Kivimaa in the municipality of Tervola (Rouhunkoski and
Isokangas 1974). The gold-copper mineralization is related to a 1-6 m wide, >350 m long quartz vein in
an E-W trending dip-slip fault in a pyroxenite. Pre-mining resource estimate included 106 kg of gold
and 1160 t of copper. In 1969, Outokumpu Oy mined 18600 t of ore, but the recovery of gold and
copper were low, only 7 kg Au and 223 t Cu.
It seems that the potential for the occurrence of Ni-Cu sulphide mineralization in the studied
ultramafic rocks is low. Nevertheless, the occurrence of the GWA intrusions sheds new light on the
tectonic history of the study area, implying major thrust and fault zones which were potentially linked
to the formation of the gold mineralization. Also, based on the more well-preserved analogies
elsewhere, the knowledge of the original chemical composition of the ultramafic rocks can be used to
evaluate the chemical alteration processes that have taken place in the mineralized area.
Metamorphism
Mustonen (2013) interpreted that the rocks of the Rompas area was metamorphosed in amphibolite
facies. This interpretation was supported by Alaoja (2014). His study included rocks from the
Rajapalot and there the intensity of metamorphosis is lower greenschist-amphibolite facies. Mineral
assemblage in this study (epidote, chlorite and amphiboles are mainly actinolite and tremolite)
indicates greenschist facies. However, the presence of metamorphic olivine in the ultramafic rocks
indicates that the peak metamorphic conditions reached the amphibolite facies (Blatt et al. 2006).
56
8 Conclusions
Geochemical and petrographic observations suggest that the studied ultramafic rocks belong to the
2.22 Ga Gabbro-Wehrlite Association. Outcrops and drillholes in the Rompas area and the Hirvimaa
(PRAJ0032 and PRAJ0033) represent olivine and olivine-clinopyroxene cumulate units in the
stratigraphy of typical GWA sills. Petrographic studies indicate olivine as a cumulus mineral in most
Mg-rich rocks (for example PRAJ0032-6.0), and on the other hand, the rocks with the lowest MgO
content (sample 238992 from drillcore PRAJ0033) indicates clinopyroxene as a sole cumulus phase.
Drillhole ROM0026 from the Rompas area intersects rocks which mostly represent clinopyroxene
cumulates. Normally, the GWA differentiated sills also contain a gabbro unit, which has not been
encountered in this study. In drillcore ROM0026, the contact zone between pyroxenite and overlaying
quartzite is strongly brecciated and may present a tectonic break.
Establishing the presence of a 2.22 Ga GWA sill in the Rompas are supports the idea of correlating the
Mellajoki Suite with the Palokivalo Formation and volcanic rocks of the area with the Runkaus
Formation. On the other hand, the spatial relationship of the rocks in the Hirvimaa area and their
relation to enclosing host rocks is problematic. The Korkiavaara and Pöyliövaara Formations are
younger than the 2.22 Ga GWA layered sills. The long and intense deformation history of the
Peräpohja Belt and its closeness of the tectonic contact to the Central Lapland Granitoid Complex
could explain the occurrence of GWA sills. Tectonic disturbance has emplaced remnants of GWA sill to
the middle of the younger sedimentary units or stratigraphy at the Hirvimaa area is more
complicated.
The presence of brown iddingsite after metamorphic olivine suggests that peak metamorphic
conditions reached the amphibolite facies. This finding is coherent with earlier studies in the Rompas
area.
The studied ultramafic rocks are not potential exploration targets for Ni-Cu deposits. However, this
study shows that the tectonic history of the Rompas-Hirvimaa area is complicated. Tectonic fault
zones are present, which potentially acted as fluid channels in the genesis of the gold mineralization.
57
9 Acknowledgements
I am grateful to Mawson and especially Dr. Nick Cook who provided me the possibility of doing this
thesis. Whole Mawson team has been great support and especially MSc. Janne Kinnunen has been of
great help with needed data.
I would like to express my gratitude professor Eero Hanski for supervising my work and for providing
reference samples and data.
I would also like to thank my wife for all the support during my studies. My children, Mimosa, Simeon
and Werneri, I thank you for being there for me but apology on my own behalf- although I have been
home, I have been absent-minded during this intensive thesis project.
58
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62
Appendices
Appendix 1. Whole-rock analyses of drillcore PRAJ0032.
SampleID
238980 238981 238982 238983 238984 238985 238986 238987 238988
DepthFrom
5
6
7
8
9
10
11
12
13
DepthTo
6
7
8
9
10
11
12
13
13,8
SiO2*
52,44
50,58
50,79
54,52
48,88
49,25
51,01
50,39
48,37
TiO2
0,56
0,66
0,58
0,60
0,86
0,78
0,72
0,81
0,79
Al2O3
3,42
4,10
3,55
8,62
8,05
5,04
4,59
4,86
4,91
FeO
11,14
11,27
11,40
9,28
10,32
10,96
10,20
11,12
13,38
MnO
0,15
0,16
0,19
0,14
0,18
0,21
0,20
0,20
0,21
MgO
23,13
21,72
21,39
16,50
19,07
20,23
20,65
21,31
21,39
CaO
5,61
6,93
8,44
4,95
6,65
9,44
9,23
8,44
7,99
Na2O
0,27
0,35
0,32
0,73
0,85
0,65
0,51
0,35
0,31
K2O
0,82
1,22
0,65
2,13
2,73
0,92
0,53
0,18
0,06
P2O5
0,05
0,15
0,05
0,11
0,10
0,06
0,05
0,05
0,06
S
0,41
0,86
0,64
0,42
0,32
0,46
0,30
0,30
0,53
Cr_pct
0,171
0,168
0,177
0,0914
0,17
0,19
0,174
0,199
0,22
V_ppm
116
114
124
133
147
146
136
149
175
Ni_ppm
1130,00
980,00 1080,00
533,00
939,00 1020,00
948,00 1080,00 1210,00
Cu_ppm
63,1
52,7
59,4
21,4
23,5
45,2
36,9
57,3
75,2
Zn_ppm
91
88
89
88
111
95
89
95
109
S_ppm
4100
8600
6400
4200
3200
4600
3000
3000
5300
Zr_ppm
24,2
24,7
19,4
99,7
38,1
25,2
21,9
23,6
21,4
(* calculated)
63
Appendix 2. Whole-rock analyses of drillcore PRAJ0033.
SampleID 238991
DepthFrom
3,85
DepthTo
4,85
SiO2*
50,62
TiO2
1,34
Al2O3
5,42
FeO
10,95
MnO
0,23
MgO
16,83
CaO
10,84
Na2O
0,92
K2O
0,48
P2O5
0,08
S
0,28
Cr_pct
0,142
V_ppm
178
Ni_ppm
455,00
Cu_ppm
52
Zn_ppm
168
S_ppm
2800
Zr_ppm
60,6
238992 238993 238994 238995 238996 238997 238998
4,85
5,35
6,35
7,35
8,35
9,35
10,35
5,35
6,35
7,35
8,35
9,35
10,35
11,55
55,10
51,80
51,19
49,52
50,00
50,99
48,71
1,57
0,75
0,78
0,85
0,76
0,68
0,66
5,54
4,89
4,19
4,50
4,08
3,68
3,72
9,64
11,01
10,95
11,57
11,26
12,32
12,99
0,19
0,22
0,22
0,20
0,19
0,19
0,19
15,22
17,83
19,90
21,64
22,14
22,72
25,70
8,49
9,82
9,77
8,84
8,40
6,20
5,43
0,59
0,66
0,50
0,32
0,30
0,26
0,16
1,36
0,73
0,36
0,34
0,64
0,70
0,19
0,14
0,05
0,05
0,05
0,04
0,05
0,05
0,15
0,23
0,09
0,17
0,19
0,21
0,19
0,106
0,156
0,149
0,156
0,155
0,18
0,192
142
154
138
140
130
129
122
405,00
620,00
760,00
837,00
848,00 1090,00 1220,00
30,5
67,5
49,8
44,8
63,4
75,4
73
143
163
148
128
96
113
114
1500
2300
900
1700
1900
2100
1900
82,6
33,7
25,9
22,3
18,5
23,5
22,8
(* calculated)
64
Appendix 3. Whole-rock analyses of drillcore ROM0026.
SampleID 224617 224618 224619 224620 224621 224622 224623 224624 224626
DepthFrom
27
28
29
30
31
32
33
34
35
DepthTo
28
29
30
31
32
33
34
35
36
SiO2*
57,62
56,02
55,21
52,75
54,56
54,26
55,92
55,72
55,55
TiO2
0,86
0,75
0,74
0,77
0,88
0,98
0,90
0,88
0,82
Al2O3
4,97
3,99
4,74
4,55
4,57
5,27
4,84
4,63
4,36
FeO
7,94
11,50
11,35
11,71
11,31
10,07
9,26
9,02
8,53
MnO
0,60
0,26
0,13
0,12
0,12
0,13
0,12
0,12
0,13
MgO
12,62
13,76
14,33
14,96
13,91
14,64
14,28
14,68
14,36
CaO
12,76
10,24
9,42
11,03
10,82
10,62
10,75
11,18
12,83
Na2O
0,07
0,38
0,85
0,90
1,16
1,51
1,21
1,00
0,82
K2O
0,49
0,77
1,01
1,05
0,58
0,48
0,66
0,72
0,55
P2O5
0,04
0,02
0,03
0,02
0,02
0,03
0,02
0,02
0,02
S
0,04
0,31
0,20
0,13
0,07
0,01
0,03
0,03
0,03
Cr_pct
0,0781
0,0848
0,0942
0,0981
0,0485
0,0324
0,0349
0,035
0,0367
V_ppm
227
175
161
167
192
209
198
192
188
Ni_ppm
217
289
307
337
266
245
245
249
246
Cu_ppm
91,1
96,4
67,8
94,3
60,7
80,3
57,8
80,8
123
Zn_ppm
38
329
72
27
30
49
47
46
42
S_ppm
400
3100
2000
1300
700
100
300
300
300
Zr_ppm
75,6
50,2
62,8
70,7
66,8
72,9
65,9
60,4
52,7
(* calculated)
65
Appendix 3. Whole-rock analyses of drillcore ROM0026 (continued).
SampleID 224627 224628 224629 224630 224631 224632 224633 224634 224635
DepthFrom
36
37
38
39
40
41
42
43
44
DepthTo
37
38
39
40
41
42
43
44
45
SiO2*
56,51
52,91
55,37
54,71
52,68
53,69
53,89
53,55
54,35
TiO2
0,80
0,83
0,90
1,08
0,94
0,99
0,93
0,85
0,87
Al2O3
4,14
4,35
4,25
5,14
4,42
4,95
4,82
4,40
4,59
FeO
8,54
9,16
8,52
9,53
9,01
9,42
9,28
8,98
9,21
MnO
0,12
0,14
0,14
0,12
0,16
0,13
0,14
0,14
0,13
MgO
14,34
15,17
13,47
13,88
13,43
14,48
14,34
14,36
14,41
CaO
12,33
14,13
13,98
11,78
15,95
12,87
13,08
14,27
12,82
Na2O
0,96
1,13
1,24
1,51
1,24
1,29
1,19
1,27
1,46
K2O
0,23
0,16
0,12
0,20
0,13
0,14
0,29
0,14
0,13
P2O5
0,02
0,02
0,02
0,02
0,02
0,02
0,02
0,02
0,02
S
0,01
0,01
0,01
0,02
0,02
0,01
0,02
0,01
0,01
Cr_pct
0,0371
0,0369
0,0328
0,0345
0,0375
0,0335
0,0353
0,0368
0,0366
V_ppm
185
193
192
218
196
211
205
190
191
Ni_ppm
252
274
243
259
245
266
264
263
280
Cu_ppm
34,4
20,1
16,8
65,7
12,7
20,3
50
18,6
30,9
Zn_ppm
40
40
40
43
42
46
50
46
45
S_ppm
100
100
100
200
200
100
200
100
100
Zr_ppm
39,9
33,2
42,9
60,4
53,5
38,4
32,6
38,5
40
(* calculated)
66
Appendix 3. Whole-rock analyses of drillcore ROM0026 (continued).
SampleID 224636 224637 224638 224639 224640 224641 224642 224643 224644
DepthFrom
45
46
47
48
49
50
51
52
53
DepthTo
46
47
48
49
50
51
52
53
54
SiO2*
53,31
51,22
53,04
53,46
55,12
53,81
52,62
53,01
52,13
TiO2
0,90
0,84
0,77
0,75
0,78
0,80
0,68
0,77
0,80
Al2O3
4,46
4,33
3,99
3,82
4,02
4,23
3,72
3,97
4,02
FeO
8,92
9,61
8,63
8,74
8,22
9,46
8,41
8,39
8,54
MnO
0,13
0,15
0,15
0,15
0,14
0,13
0,16
0,14
0,15
MgO
14,76
14,64
14,29
15,34
14,29
15,41
13,75
15,67
15,79
CaO
13,99
15,53
15,53
14,06
13,88
12,68
17,42
14,69
15,11
Na2O
1,33
1,28
1,25
0,98
1,13
1,01
1,00
1,02
0,81
K2O
0,17
0,22
0,20
0,51
0,37
0,45
0,23
0,30
0,63
P2O5
0,02
0,02
0,02
0,02
0,02
0,02
0,02
0,02
0,02
S
0,01
0,16
0,12
0,18
0,02
0,01
0,00
0,01
0,00
Cr_pct
0,0403
0,0408
0,0397
0,0403
0,0515
0,0686
0,074
0,0548
0,0579
V_ppm
204
196
182
185
170
177
158
172
178
Ni_ppm
282
298
270
265
284
320
290
308
321
Cu_ppm
23,9
203
138,5
196
75,7
42
24,3
34,1
28
Zn_ppm
42
45
44
49
43
47
43
46
50
S_ppm
100
1600
1200
1800
200
100
0
100
0
Zr_ppm
33
43,3
39
39,3
42,7
41,3
34,2
37,5
39,9
(* calculated)
67
Appendix 3. Whole-rock analyses of drillcore ROM0026 (continued).
SampleID 224645 224646 224647 224648 224650 224651 224652 224653 224654
DepthFrom
54
55
56
57
58
59
60
61
62
DepthTo
55
56
57
58
59
60
61
62
63
SiO2*
51,36
52,29
51,34
52,57
52,55
50,91
50,63
51,25
51,49
TiO2
0,76
0,74
0,79
0,64
0,63
0,57
0,81
0,66
0,79
Al2O3
3,82
3,89
4,52
3,40
3,31
3,16
4,46
3,48
4,72
FeO
9,19
9,78
9,70
7,60
7,98
8,67
10,47
9,98
7,19
MnO
0,16
0,14
0,14
0,15
0,16
0,28
0,17
0,15
0,16
MgO
15,84
16,67
16,83
16,52
18,41
16,75
19,32
18,99
14,06
CaO
15,39
13,00
12,87
16,09
14,20
16,65
10,87
12,34
17,49
Na2O
0,74
0,71
0,71
0,61
0,62
0,46
0,63
0,57
1,59
K2O
0,55
0,71
0,98
0,39
0,10
0,43
0,52
0,46
0,40
P2O5
0,02
0,02
0,02
0,02
0,01
0,02
0,02
0,02
0,03
S
0,19
0,05
0,10
0,02
0,04
0,11
0,09
0,10
0,08
Cr_pct
0,0611
0,126
0,124
0,154
0,144
0,125
0,161
0,143
0,0425
V_ppm
174
153
160
154
134
124
163
141
133
Ni_ppm
325
419
411
489
491
394
644
577
198,5
Cu_ppm
55,8
54,4
379
33,3
40,4
33,1
93,3
68
26,4
Zn_ppm
52
47
51
55
84
84
79
49
38
S_ppm
1900
500
1000
200
400
1100
900
1000
800
Zr_ppm
39,3
43,1
47,3
35,2
34,5
32,8
52,5
39,6
54,7
(* calculated)
68
Appendix 3. Whole-rock analyses of drillcore ROM0026 (continued).
SampleID 224655 224656 224657 224658 224659 224660 224661 224662 224663
DepthFrom
63
64
65
66
67
68
69
70
71
DepthTo
64
65
66
67
68
69
70
71
72
SiO2*
50,55
51,92
48,63
47,71
51,30
53,20
56,13
50,18
51,69
TiO2
0,63
0,79
0,58
0,47
0,73
0,79
0,64
0,76
0,46
Al2O3
3,38
4,33
3,27
2,61
4,25
4,38
3,57
4,19
2,61
FeO
6,25
7,01
5,22
6,16
6,57
6,78
6,93
9,19
5,49
MnO
0,19
0,20
0,20
0,21
0,16
0,17
0,15
0,15
0,17
MgO
13,91
13,15
14,73
15,72
13,91
11,84
10,43
11,69
13,93
CaO
21,69
18,47
23,86
23,93
19,38
18,12
17,35
18,26
22,25
Na2O
1,02
1,16
1,27
0,66
1,11
1,50
1,50
1,40
1,05
K2O
0,23
0,69
0,23
0,30
0,41
0,55
0,35
0,61
0,27
P2O5
0,02
0,02
0,02
0,02
0,02
0,02
0,02
0,02
0,02
S
0,13
0,26
0,01
0,22
0,15
0,64
0,93
1,54
0,07
Cr_pct
0,0196
0,0261
0,0177
0,0182
0,031
0,0334
0,035
0,0366
0,0446
V_ppm
117
170
111
89
165
169
167
175
122
Ni_ppm
127
133,5
101,5
107,5
158
165,5
137,5
160,5
137,5
Cu_ppm
19,2
31,3
3,9
4,3
5,1
16,8
8,5
16,9
4,5
Zn_ppm
36
51
38
59
42
25
21
24
40
S_ppm
1300
2600
100
2200
1500
6400
9300
15400
700
Zr_ppm
33,6
50,8
32,9
29,3
43,1
47,7
39,1
39,5
24,4
(* calculated)
69
Appendix 3. Whole-rock analyses of drillcore ROM0026 (continued).
SampleID 224664 224665 224666 224667 224668 224669 224670
DepthFrom
72
73
74
75
76
77
78
DepthTo
73
74
75
76
77
78
79
SiO2*
49,94
54,72
48,40
49,28
49,26
49,15
44,58
TiO2
0,55
0,70
0,65
0,68
0,84
0,82
1,20
Al2O3
2,97
3,87
3,57
3,53
4,53
4,86
7,48
FeO
6,39
8,40
7,92
7,76
12,29
11,68
15,50
MnO
0,18
0,13
0,20
0,22
0,14
0,12
0,12
MgO
14,38
12,34
14,19
14,26
16,58
18,82
17,74
CaO
22,04
15,18
20,78
20,78
12,21
11,04
8,66
Na2O
1,12
0,98
0,70
0,50
0,39
0,43
0,53
K2O
0,34
1,33
1,39
0,95
1,22
1,00
1,75
P2O5
0,02
0,02
0,02
0,02
0,02
0,03
0,05
S
0,09
0,32
0,17
0,02
0,51
0,06
0,39
Cr_pct
0,0583
0,0823 0,0732 0,0806
0,12
0,134
0,132
V_ppm
152
186
155
200
190
168
212
Ni_ppm
167
205
202
205
368
554
658
Cu_ppm
4,7
6,2
5,4
4
67,6
17,2
113
Zn_ppm
53
36
34
31
41
37
36
S_ppm
900
3200
1700
200
5100
600
3900
Zr_ppm
38,1
48,3
42,8
50,7
54,5
59,5
104
(* calculated)
70
Appendix 4. Whole-rock analyses of the Rompas outcrops.
PYX1
SampleID
SiO2*
TiO2
Al2O3
FeO
MnO
MgO
CaO
Na2O
K2O
P2O5
S
Cr_pct
V_ppm
Ni_ppm
Cu_ppm
Zn_ppm
S_ppm
Zr_ppm
221376
51,30
0,29
2,44
9,65
0,27
26,03
7,85
0,11
0,02
0,02
0,02
0,102
64
756
7,4
108
200
19,5
PYX1
241753
48,21
0,64
3,84
12,29
0,21
26,95
5,60
0,11
0,05
0,01
0,11
0,22
116,00
1235,00
43,60
107,00
1100,00
28,60
PYX1
232890
50,11
0,75
4,40
10,60
0,27
22,22
9,23
0,20
0,04
0,03
0,15
0,16
130,00
959,00
64,40
85,00
1500,00
59,50
PYX2
232892
52,43
0,60
3,55
10,16
0,12
19,57
11,15
0,28
0,08
0,02
0,03
0,14
125,00
725,00
53,20
68,00
300,00
18,60
PYX2
232891
49,71
0,77
4,44
12,36
0,15
25,79
4,53
0,11
0,04
0,02
0,08
0,22
136,00
1220,00
44,70
109,00
800,00
24,90
(* calculated)
71
Appendix 5. Trace element analyses of drillcore PRAJ0032.
Sample Id
(ppm)
Ba
Ce
Cs
Dy
Er
Eu
Ga
Gd
Hf
Ho
La
Lu
Nb
Nd
Pr
Rb
Sm
Sn
Sr
Ta
Tb
Th
Tm
U
V
W
Y
Yb
Zr
Au_ppb
Pt _ppb
Pd_ppb
238980
68,3
20,3
5,1
2,17
1,09
0,5
7,8
2,43
1,3
0,35
11,3
0,12
2,9
12
2,56
28
2,57
1
45,8
<0.1
0,33
1,34
0,11
0,3
164
<1
9,9
0,88
49
1
4,1
4,1
238981
99,3
8,5
5,6
2,15
1,15
0,56
9,4
2,53
1,5
0,39
4,1
0,13
2,7
6,8
1,36
38,7
2,25
1
63,3
<0.1
0,38
0,98
0,13
0,26
139
<1
10,6
0,8
56
2
5,2
7,2
238982
64
6,7
2,7
1,64
0,78
0,58
8,8
1,88
1,3
0,33
3,4
0,09
2,6
5,6
1,06
19,9
1,7
1
32,9
<0.1
0,28
0,95
0,09
0,24
126
<1
7,4
0,74
46
1
4,2
3,2
238986
35,5
14,1
1,92
2,44
1,1
0,91
10
2,53
1,4
0,41
6,1
0,13
3
9,8
2,07
13,1
2,53
3
31,4
<0.1
0,4
1,16
0,17
0,26
163
<1
11
0,91
53
<1
4,9
4,6
238987
15
11
0,7
2,26
1,32
0,87
10,8
2,41
1,6
0,41
5,2
0,15
3,4
8,4
1,62
4
2,38
1
32,7
<0.1
0,36
1,22
0,14
0,33
167
<1
11,3
1,01
62
<1
5,6
4,9
72
238988
8,9
13,9
0,23
2,67
1,3
0,74
11,4
2,76
1,7
0,46
6,4
0,17
5,4
8,8
1,91
1,6
2,19
1
35,8
0,4
0,41
1,62
0,18
0,41
254
1
11,8
1,1
63
1
5,5
4,5
Appendix 6. Trace element analyses of drillcore PRAJ0033.
Sample Id
(ppm)
Ba
Ce
Cs
Dy
Er
Eu
Ga
Gd
Hf
Ho
La
Lu
Nb
Nd
Pr
Rb
Sm
Sn
Sr
Ta
Tb
Th
Tm
U
V
W
Y
Yb
Zr
Au_ppb
Pt _ppb
Pd_ppb
238992
152
36,4
5,81
5,49
2,73
1,85
10,2
5,77
3,7
0,96
16,5
0,31
8
21,6
4,78
55,5
5,58
1
33,3
0,8
0,91
2,58
0,34
0,48
211
1
24,7
2,02
146
<1
4,4
0,9
238994
28,1
11,5
1,45
2,35
1,09
1,07
7,6
2,45
1,3
0,38
4,9
0,13
3,7
8,3
1,7
10
2,27
1
25,5
0,4
0,4
0,96
0,13
0,3
171
1
10,4
0,95
50
<1
4
3,5
238995
34,2
13,3
1,81
2,42
1,13
0,79
7,9
2,75
1,3
0,41
6
0,14
3,4
9,2
1,93
9,5
2,36
1
31,3
0,3
0,36
1,11
0,14
0,25
165
3
10,1
0,85
52
<1
4,3
3,7
238996
91,1
12,9
3,35
2,01
0,93
0,68
9
2,23
1,3
0,36
6,2
0,15
3,4
8,4
1,79
20,8
2,12
1
44,5
0,7
0,35
0,87
0,14
0,2
178
1
9,1
0,81
51
<1
3,4
2,2
73
238997
67,8
8,5
7,27
1,94
1,03
0,55
8,3
1,92
1,3
0,33
4
0,12
3,3
6,4
1,31
21,3
1,82
1
43,2
0,3
0,31
0,86
0,08
0,23
160
1
9
0,69
47
<1
3,9
2,7
238998
17,5
11,3
2,06
2,06
1,08
0,46
7,9
2,32
1,3
0,39
4,9
0,12
3,5
7,9
1,56
5,6
2,15
1
61,9
0,1
0,3
0,93
0,11
0,21
136
1
10,1
0,95
57
1
4,1
3,5
Appendix 7. Trace element analyses of drillcore ROM0026.
Sample Id
(ppm)
Ba
Ce
Cs
Dy
Er
Eu
Ga
Gd
Hf
Ho
La
Lu
Nb
Nd
Pr
Rb
Sm
Sn
Sr
Ta
Tb
Th
Tm
U
V
W
Y
Yb
Zr
Au_ppb
Pt _ppb
Pd_ppb
224643
33,6
17
0,29
2,99
1,44
0,9
8,1
3,16
1,4
0,5
7,8
0,16
2,5
11,8
2,4
7,9
2,93
<1
59
0,1
0,47
0,85
0,18
0,72
195
1
13
1,03
46
1
2,9
2,5
224644
59,4
12,4
0,88
2,51
1,08
0,73
7,7
2,68
1,3
0,41
5,9
0,13
2,2
8,7
1,9
18,9
2,57
1
58,7
0,2
0,42
0,86
0,15
0,52
187
<1
11,1
0,9
44
1
2,9
2,5
224648
32,2
10,1
0,5
2,16
1,04
0,64
7,3
2,4
1,2
0,35
4,7
0,11
2
7,7
1,44
12,2
2,05
1
51
<0.1
0,34
0,74
0,17
0,78
161
1
9,8
0,8
39
1
2,5
2,1
224651
29
10,8
1,29
2,28
1,13
0,75
6,6
2,43
1,1
0,37
5,7
0,12
2,1
7,1
1,48
15,9
1,85
<1
45,2
<0.1
0,35
0,58
0,14
1,12
132
1
11,4
0,84
37
2
2,5
2,1
224652
18,9
11,5
2,01
2,25
1,07
0,7
9,3
2,9
1,5
0,39
5,1
0,13
4,4
8,3
1,72
15,7
2,34
1
21,9
1
0,37
1,08
0,15
0,6
180
1
10,7
0,9
53
16
3,5
3,6
74
224653
16,2
11,2
1,68
1,96
1,04
0,7
7,5
2,45
1,2
0,38
5,2
0,12
2,6
7,8
1,59
15
2,04
1
28,6
0,2
0,36
0,86
0,1
0,69
157
<1
9,5
0,75
42
4
2,9
2,6
224658
8,5
9,1
0,48
1,43
0,7
0,41
5,2
1,72
0,9
0,24
5,1
0,07
1,9
5,3
1,19
8,9
1,28
<1
44,4
<0.1
0,23
0,64
0,09
1,37
89
1
7,7
0,67
30
1
2
2
224668
62
21,6
1,42
3,11
1,41
0,99
10,3
3,39
1,5
0,44
11
0,17
3
12,2
2,72
39,9
3,13
3
18,6
0,3
0,5
1,06
0,15
1,04
195
1
13,5
1,06
50
<1
3,4
3,1
224669
40,8
24,1
1,3
2,65
1,32
0,8
10
3,62
1,6
0,48
11
0,15
3,2
14,6
3,17
29,6
3,53
2
15,2
0,5
0,44
1,15
0,16
1,18
182
1
12,9
1,02
53
<1
4,1
3,5
Appendix 8. Trace element analyses of outcrop PYX1.
Sample Id
(ppm)
Ba
Ce
Cs
Dy
Er
Eu
Ga
Gd
Hf
Ho
La
Lu
Nb
Nd
Pr
Rb
Sm
Sn
Sr
Ta
Tb
Th
Tm
U
V
W
Y
Yb
Zr
Au_ppb
Pt _ppb
Pd_ppb
241753
5,3
10,7
0,05
1,69
0,93
0,37
7,2
2,03
1,3
0,3
4,8
0,11
3
7,3
1,51
1,1
1,64
<1
100,5
0,2
0,29
0,8
0,11
0,72
125
1
8,9
0,78
45
<1
4,5
3,6
232890
17,1
9,5
0,05
2,57
1,27
0,54
10
2,66
1,5
0,48
4
0,16
4,2
7,2
1,45
1,1
2,17
1
53,1
0,5
0,43
1,36
0,16
2,83
140
1
12,3
1,09
57
<1
5,9
5,4
75