Accepted Manuscript

Reflections of the geological characteristics of Cyprus in soil rare earth element

patterns

Limin Ren, David R. Cohen, Neil F. Rutherford, Andreas M. Zissimos, Eleni

G. Morisseau

PII: S0883-2927(15)00042-6

DOI: http://dx.doi.org/10.1016/j.apgeochem.2015.02.011

Reference: AG 3429

To appear in: Applied Geochemistry

Please cite this article as: Ren, L., Cohen, D.R., Rutherford, N.F., Zissimos, A.M., Morisseau, E.G., Reflections of

the geological characteristics of Cyprus in soil rare earth element patterns, Applied Geochemistry (2015), doi: http://

dx.doi.org/10.1016/j.apgeochem.2015.02.011

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Reflections of the geological characteristics of Cyprus in soil rare earth element patterns

Limin Rena,b, David R. Cohena,*, Neil F. Rutherforda, Andreas M. Zissimosc and Eleni G. Morisseauc

a School of Biological, Earth and Environmental Sciences, University of New South Wales, 2052, NSW, Australia. b Faculty of Earth Science, China University of Geosciences, Wuhan, 430074, Hubei Province, China. c Cyprus Geological Survey, Ministry of Agriculture, Natural Resources and Environment, Lefkonos 1, Lefkosia

1415, Cyprus.

1 Corresponding author. Tel.: +61 2 93858084

E-mail: d.cohen@unsw.edu.au (D.R. Cohen)

Abstract

Rare earth elements (REEs) are used as indicators or proxies for a range of geological and

mineralogical processes due to their unique geochemical characteristics. Total and aqua regia-

extractable concentrations of REEs and 57 other elements have been determined for 5,350 soil

samples as part of the high sampling density Geochemical Atlas of Cyprus. The bedrock geology

of Cyprus is dominated by the sequence of ultramafic to mafic units formed at a spreading ridge

and subsequently obducted to form the Troodos Ophiolite (TO), and the surrounding carbonate-

rich Circum-Troodos Sedimentary Sequence (CTSS) deposited in environments ranging from deep

marine to sub-aerial. Total and aqua regia-extractable REE patterns are similar for each element

and are largely controlled by parent lithology. Soil-to-rock REE ratios are generally elevated in the

TO units (>4 for LREEs and 1.5–3 for HREEs) due to loss of more mobile elements during

weathering but are close to 1 in the CTSS units. HREEs are more elevated than LREEs in soils

derived from TO units with upper continental crust-normalised patterns indicating the main source

to be pyroxenes and zircon. Trace element trends indicate REEs in the CTSS were largely derived

from detrital material shedding off the TO and deposited in progressively shallowing basins under

largely anoxic conditions (absence of Ce4+ anomalies), with a minor contribution from seawater

via adsorption onto secondary Fe+Mn oxides or co-precipitation with carbonates. Heavy mineral-

associated elements such as Zr and Th display a relative consistent ratio in the CTSS soils. Peak

HREE concentrations occur in the mafic cumulates and intrusives where the median LaUCC/YbUCC

is ~0.12, whereas in CTSS units the LREEs are more elevated with a median LaUCC/YbUCC ~0.7.

Due to the strong lithogeochemical controls, soil REE spatial patterns reflect even subtle

mineralogical variations within the various TO units, the location of major transform faults and

other structures, and areas that have been affected by hydrothermal alteration.

Keywords: REE; partial extraction; Troodos; geochemical atlas

1. Introduction

Rare earth elements (REEs) are used as proxies for a range of geological and mineralogical

processes due to their unique geochemical characteristics and fractionation trends generated by the

lanthanide contraction and the multiple valencies for Ce and Eu (Henderson, 1984; Banfield and

Eggleton, 1987; Leybourne and Johannesson, 2008). Examples include modeling of magmatic and

crustal evolutionary processes, analysing water–rock–regolith interactions, and characterizing the

provenance of sedimentary rocks (McLennan, 1989; Elderfield et al., 1990; Sholkovitz and

Szymczak, 2000; Nyakairu and Koeberl, 2001; Leybourne et al., 2006; Antonina et al., 2013).

Hydrothermal alteration in particular may significantly alter REE patterns depending on

temperature, the source of fluids, host lithology, the extent of alteration and types of secondary

minerals formed, including depletion of LREEs (La to Eu) relative to HREEs (Gd to Lu) in

groundmass-replacement minerals and the converse in zeolites, carbonates and some secondary Fe

oxide minerals (Michard, 1989; Bau, 1991; Gillis et al., 1992; Wells et al., 1998; Guy et al., 1999).

In alteration involving seawater, including processes such as spilitization, LREE enrichment

occurs due to the higher stability constants and solubilities of most trivalent HREE phosphate,

carbonate, and hydroxyl species (Piepgras and Jacobsen, 1988; Lee and Byrne, 1992; Åström and

Corin, 2003). Under strongly reducing conditions and elevated temperature, hydrothermal fluids

emanating from mid-ocean ridges and back-arc spreading centers are characterized by elevated Eu

values (Michard et al., 1983; Sverjensky, 1984; Klinkhammer et al., 1994; Bierlein, 1995; Bau and

Dulski, 1999) due to higher solubility of Eu2+ compared with trivalent REEs and Ce4+ (Kamber,

2010). Associated massive sulfide deposits and related sediments commonly preserve the strongly

positive Eu anomaly of the precursor hydrothermal fluids (Peter et al., 2003; Leybourne et al.,

2006).

In sedimentary and weathering environments there are various factors that can influence REE

mobility and distribution patterns, including direct precipitation of carbonates, phosphates or

oxides, adsorption or co-precipitation with clays and secondary Fe+Mn oxyhydroxides, and the

influx of detrital material and REE-bearing heavy minerals. Accumulation of REEs in clay

exchange sites is the basis of some economic deposits (Hoatson et al., 2011; Kynicky et al., 2012;

Sadeghi et al., 2013b).

Except where conditions are highly acidic, the aqueous solubilities of REEs are typically very

low (Wood, 1990). In marine environments, REEs, Th and most transition metals are more

strongly incorporated into Fe+Mn oxides rather than carbonates under oxic to sub-oxic conditions

across much of the Eh spectrum (Elderfield et al. 1981; Bayon et al. 2002; Koschinsky et al., 2003;

Négrel et al., 2006). LREEs tend to be more strongly adsorbed by authigenic Fe+Mn

oxyhydroxides than HREEs in marine sediments and soils (Caetano et al., 2009) although Mn

oxides have limited ability to incorporate trivalent REEs ions into their structure (Haley et al.,

2004). A change from anoxic to oxic conditions and conversion of Ce3+ to Ce4+ results in Ce

depletion in water and positive anomalies in the associated sediments (Shaw and Wasserberg,

1985; Pourret et al., 2008). Changes in redox conditions may occur in various settings such as

anoxic ground waters discharging to surface (Leybourne et al., 2000) or deep oceanic waters

welling up (Liu et al., 1988).

Lithological REE patterns (and those of other immobile elements such as Zr, Ti, Th and Hf) are

generally preserved during weathering and other regolith-forming processes especially where

REEs are hosted in resistate phases such as zircon and monazite. Total concentrations typically

increase due to mass loss during regolith formation, though there is a tendency for greater loss of

HREEs (Gregorauskienė and Kadūnas, 2006; Beyala et al., 2009). A number of studies have

investigated the behaviour of REEs under chemical weathering and subsequent transportation of

the dissolved and suspended REE fractions by separating various element-mineral associations

using a combination of total and partial geochemical extractions (Sholkovitz and Szymczak, 2000;

Leybourne and Johannesson, 2008; Galbarczyk-Gąsiorowska, 2010; Fu et al., 2011). Aqua regia

extractions in particular display similar chondrite-normalised trends to total REE patterns in

weathered materials but with a pronounced positive Gd anomaly (Marmolejo-Rodriguez et al.,

2007).

Along with other elements that display significant primary lithological variation and low

chemical mobility in surface environments, soil REE concentrations have been used to map

underlying parent lithologies (Halfpenny and Mazzucchelli, 1999; Mann, 2006) and other regolith-

landform patterns in a number of regional soil and sediment geochemical mapping projects (Xie

and Cheng, 2001; De Vos and Tarvainen, 2006; Klassen, 2009; Woodruff et al., 2009; Caritat and

Cooper, 2012).

This study draws on the extensive dataset derived from the high density soil Geochemical Atlas

of Cyprus (Cohen et al., 2011, 2012a, 2012b), to examine factors controlling the distribution of

REEs, including parent lithology, palaeo- and modern environmental conditions, land use and

regolith-landform settings.

2. Geological setting of Cyprus

2.1. Lithology

The geological development of Cyprus commenced in the Cretaceous with formation of a co-

magmatic vertical sequence of ultramafic and mafic cumulate units, basaltic to doleritic sheeted

dykes, overlying tholeiitic basaltic volcanic units (mainly pillow basalts) and associated chemical

sediments (Robertson and Hudson, 1973; Desmet 1976; Morris et al., 1998). This package of rocks,

formed as part of the oceanic lithosphere during sea floor spreading, was obducted in the late

Miocene to form the Troodos Ophiolite (TO) (Mukasa and Ludden, 1987; Robinson and Malpas,

1990; Fig. 1). Abutting the south-western side of the TO is the Mamonia Terrane which contains

tholeiitic to normal mid-ocean ridge basaltic volcanics (Malpas et al., 1992, 1993) and pelagic

sedimentary units containing limestones, mudstones, quartzose sandstones and small amounts of

metamorphic rocks (schists and marbles). The Kyreneia Terrane in the north is dominated by

carbonate-rich sedimentary units but contains some allocthonous clastic sedimentary units.

Zones of intense hydrothermal alteration occurred throughout the sheeted dyke complex

(Kelley and Robinson 1990) and probably indicate proximity to the feed vents that generated the

Cyprus-type Cu-Fe±Zn sulfide deposits and associated ferruginous sediments (Constantinou and

Govett, 1972; Friedrich et al., 1984). Along with spilitization, hydrothermal alteration has resulted

in a range of secondary minerals including chlorite, carbonates and zeolites. REE and Sr isotope

patterns of secondary minerals in these deposits demonstrate a predominantly seawater source

involving incorporation of the REEs with strong positive Ce anomalies into poorly crystalline Fe-

Mn oxyhydroxides and associated umbers including some amorphous high-Mn material

(Robertson, 1975; Robertson and Fleet, 1976; Chapman and Spooner, 1977; E. Morisseau,

unpublished data). Groundmass-replacing minerals such as chlorite typically have a similar REE

composition to the original host mafic rocks (Gillis et al., 1992). Glasses in the host rocks have

relatively low REE abundances, LREE depletion and a flat HREE profile typical of calcalkaline

and tholeiitic basalts (Thy et al., 1985; Rautenschlein et al., 1985). The composition of umbers and

other ferruginous sediments that overly the pillow basalts have elevated REEs and low Mn,

relative to the underlying basalts, with normalised patterns suggesting deposition in an oxygen-

poor marine environment (Robertson, 1978). Various geochemical and petrological indications of

penetrative hydrothermal alteration have been identified throughout much of the TO, especially in

the upper parts of the complex (Spooner, 1977).

Fig. 1. Simplified geological map of Cyprus with main depositional basins (based on the Geological Survey Department 2009 compilation and Eaton and Robertson, 1993), and inset showing soil sampling locations.

Subsequent obduction of the TO coincided with deposition of marine carbonates and

subordinate siliciclastics in progressively shallowing sedimentary basins on the TO flanks,

forming the Circum-Troodos Sedimentary Sequence (CTSS). The principal CTSS units are the

deep marine (2000-3000m) Lefkara Formation that is mainly composed of pelagic marls and

chalks, and the unconformably overlying shallow marine Pakhna Formation containing reefal

limestones, hemi-pelagic marls and chalks (Eaton and Robertson, 1993; Kähler and Stow, 1998).

Soil sampling sites

Pafos

Polis Lefkosia (Nicosia)

Lemesos

Kokkinochoria

Ammochostos

Larnaca

Keryneia

0 20km

KhalassaBasin

(Mio-Plio)

PolemiBasin(Mess)

PissouriBasin(Mess)

MaroniBasin

(Mio-Mess)LimassolSub-basin

(Mess)

Polis Basin(Mio-Plio)

Mesaoria Basin(Mio-Plio)

N

Keryneia Terrane

Mamonia Terrane

Troodos Ophiolite Circum-Troodos Sedimentary Sequence

mafic intrusive unitsbasaltic lavas and sediments

other CTSS sedimentary unitsQuaternary sediments

mafic cumulate unitsultramafic units

Pakhna FormationLefkara Formation

The Pakhna Formation was deposited during a period of more rapid tectonic uplift of the TO,

resulting in a higher detrital component from the TO than in the Lefkara Formation. Sea levels in

the Mediterranean dropped rapidly in the late Miocene leading to the Messinian “salinity crisis”

(Rouchy et al., 2001), exposing both sediments and the TO sub-aerially, allowing formation of

palaeosols. The subsequent Pliocene marine transgression resulted in deposition of sediments in

more oxygenated marine waters than the Pakhna Formation (di Stefano et al., 1999). A component

of clastic sediments containing TO-derived materials, was deposited in these marine basins on the

northern and southern flanks of the TO and may represent different seismogenic events in the

uplift and erosional history of the TO (Lord et al., 2009). The CTSS sedimentary facies

stratigraphy is summarised in Fig. 2 (Malpas et al., 1992). Large volumes of erosional products

were transported by colluvial and alluvial processes to form the heavy mineral-enriched

fanglomerates, Pliocene-Recent valley fill sediments and the sediments of the Mesaoria and

Coastal Plains.

Fig. 2. Stratigraphic and palaeodepositional environments of the main CTSS units (after Malpas et al., 1992).

2.2. Tectonic Setting and Structure

The post-formational tectonics affecting the TO and, subsequently, the overlying CTSS units

were dominantly compressional strike-slip based on kinematic models for the entire Eastern

Mediterranean (Spray and Roddick, 1981; Lundgren et al., 1998; Papazachos and

Papaioannou1999; Harrison et al., 2004). The main structural features are summarised in Fig. 3.

Lithology Depositional EnvironmentFormation

Shallow marine /terrestrial

Gravel, sand and silt

Calcarenite, sandstones

Quaternary

PleistoceneAthalassa

Gypsum and carbonates

Marls, sandstones and gravelsNicosia

Kalavasos

Pliocene

MessinianReefal limestone

Chalk, marl and calcarenite

Reefal limestone

Shallow marine (<1000m depth)

PakhnaMiocene

Bentonite, sandstone, silt

Radiolarites, bentonite, umber

Kannaviou

Perapedhi

Upper Pillow Lavas

Cretaceous

V VV V

V V

Deep marine(2000 – 3000m)

Marl and chalky marl

Massive chalk

Chalk and chert

Marl

Lefkara

Oligocene

Eocene

Palaeocene

Palaeosols

Palaeomagnetic data indicates that the late Cretaceous (Campanian) was a time of rapid rotation of

the Troodos microplate, with up to 45° of anticlockwise rotation and intracrustal clockwise

rotations of small fault-bounded blocks within the southern Troodos Transform Zone (Abrahamsen

and Schonharting, 1987; Morris et al., 1990). During the late Pliocene to early Quaternary,

regional extension in the Aegean Province generated grabens (possibly contributing to exposure of

the ultramafic TO core), although the same rotational forces that caused right-lateral shear were

still present (Glover and Robertson, 1998). Additionally, older structures were tectonically

reactivated during the Miocene (Eatonand Robertson 1993).

Fig. 3. Simplified plate tectonic model for the Eastern Mediterranean (based on Robertson and Grasso, 1995; Glover and Robertson, 1998; Harrison et al., 2004; Ergün et al., 2005; Papadimitriou and Karakostas, 2006).

2.3. Soils

The soil characteristics in Cyprus reflect the young age of the terrain (exposure from Mid-

Miocene) and rapid tectonic uplift (Vita-Finzi, 1990) that has limited the development and

preservation of deep weathering profiles. In the upper parts of the Troodos Massif the soils tend to

be skeletal, with Fe-rich residual weathered profiles exposed at various locations. There are

pockets of colluvium and alluvium in the valley floors on the deeply dissected Troodos flanks,

where the CTSS units crop out. The CTSS units weather to carbonate-rich soils with terra rossa

development in the Kokkinochoria area and other areas with exposed carbonates. Around the

boundary between the TO and CTSS units, thin layers of colluvium and gravel containing clastic

material derived from the TO (elevated Cr, Ni and Mg) overly weathered CTSS bedrock. The

coastal areas, especially the beaches, display accumulation of resistate heavy minerals such as

TartusRidge

Cyprian Arc

EratosthenesSeamount

Ovgos FaultZone

Misis-KyreniaFault Zone

FlorenceRise

PaphosTransform

Fault

Cyprus

ArabianPlate

AfricanPlate

Eurasian Plate

sinistralshear

0 50km N

magnetite and chromite along with some mobile ions associated with salt lakes and groundwater

seepages (Cohen et al., 2012a; Zissimos et al. 2014).

3. Dataset

3.1 Sampling and Processing

The sampling and analytical protocols for the Geochemical Atlas of Cyprus were based on

those of IGCP Project 360 and the Geochemical Atlas of Europe protocols (Darnley et al., 1997;

Salminen et al., 2005; Sandström et al., 2007). Top soils (0–20 cm depth) and sub soils (50–75 cm)

were collected on a nominal 1 km2 grid (1.4 km2 in central Troodos) and sieved to <2 mm. Various

field data, including the lithology of any adjacent outcropping bedrock and land use, were also

collected. The resulting suite of soil samples from 5,350 sites were milled in mild-Cr steel.

For a small sub-set of the samples, heavy minerals in the non-magnetic unmilled fraction were

separated out using Li-polytungstate solution (ρ=2.9 g/cm3) in separating funnels and

representative sub-samples made into polished blocks.

3.2 Analysis

Samples were subjected to a heated HNO3-rich aqua regia digestion for 8 hours on a 20:1

reagent:solid ratio with ICP-MS analysis, including the full REE suite. Totals analysis was

performed using INAA for which for the only REEs reported were La, Ce, Nd, Sm, Eu, Yb and

Lu. These analyses were performed by Actlabs-Pacific Ltd. Major oxides were analysed by

laboratory XRF at the Geological Survey Department of Cyprus laboratories. A representative

suite of 350 top soil samples from across the study area was analysed using an Innov-X Delta

Premium field portable XRF using the “soils” mode to provide data on total Zr.

Soil mineralogy on selected samples was determined using a combination of Siroquant XRD

analysis of pressed powders using a Panalytical Empyrean II XRD and SEDNORM (Cohen and

Ward, 1992; Ward et al., 1999). Samples collected from two traverses across the study area (near

Pafos to Lefkosia and from near Polis to Kokkinochoria) and various mining areas were subjected

to two selective geochemical digestions - ammonium acetate in pH 5 acetic acid (discarded) to

remove mobile metals and carbonate-hosted elements, sequentially followed by 1M

hydroxylamine.HCl in pH 1 HCl to extract secondary Fe+Mn-oxyhydroxide hosted elements

(Cohen et al., 1998; Mokhtari et al., 2015) with the resulting solution analysed by ICP-MS. Trace

elements of some of the mounted zircons were analysed using LA-ICPMS and SEM at the UNSW

Analytical Centre.

Analytical quality control was monitored using a series of soil reference materials, blanks and

duplicates. Reference materials included two materials used by Actlabs (including OREAS 45P

ferruginous soil) and three project in-house reference materials developed from soils derived from

calcarenite, basalt and pyroxenite respectively, and which were analysed by a number of

commercial laboratories to determine expected aqua regia-extractable ICP-MS element values.

INAA analyses were monitored using soil reference material USGS GXR-6 (Gouveia et al. 1994)

and four Actlabs in-house till reference materials. Field-portable XRF analyses were monitored

using synthetic reference material SynTerm 12 (Cohen and Beck, 1994) and USGS GXR-6.

Detection limits are listed in Table S1. Analytical precision was monitored using a large number of site and sub-sample duplicates. Analytical precision was better than ±10% and accuracy better than

±5% at 10 times the detection limits.

3.3 Map presentation

Given the density of the data points, geochemical maps were produced following gridding of the data and interpolation by inverse-distance weighting (IDW) within MapInfo™ and ArcGIS™. Following extensive testing of various parameters, the IDW model selected had a grid-cell size of

0.33 km, a distance weighting exponent of 1.6 and a maximum search radius from the centre of

each grid-cell of 2 km.

4. Results

4.1. Soil Mineralogy

Soils derived from the ultramafic units are dominated by ferromagnesian minerals (mainly Fe-

oxyhydroxides such as goethite, but including detrital magnetite and chromite) with various

phyllosilicates such as talc and montmorillonite (Fig. 4). Soils derived from the TO mafic intrusive

and basaltic volcanic units contain residual feldspar and weathered derivatives of the feldspar and

ferromagnesian minerals such as montmorillonitic clays, as well as crystalline silica whose

content is typically higher in the top soils. The Lefkara and Pakhna Formations soils are dominated

by carbonates with a minor amount of quartz and Fe oxyhydroxides. The coastal plains, terrace

deposits and alluvial areas contain a mixture of material representing the TO and CTSS end-

members. Due to the presence of Mg and Ca and lack of organic material in the soils, pH values

typically range from 7.5 to 9.5, with acidic pH restricted to the sulfide mining areas.

Zircons extracted from the soils are typically <1mm in size and rounded with some resorption

textures and variably frosted surfaces. The samples from the REE-rich Mesaoria Plain contain both

a greater abundance of zircons as well as more angular and glassy grains, in addition to rare apatite

grains. REE concentrations displayed no relative zonation within the zircons but the normal HREE

enrichment.

Fig. 4. Mean Siroquant quantitative XRD mineral compositions of a representative suite of soil samples and lithological groupings.

4.2. General REE Patterns in Soils

Description of the main REE spatial patterns for the total (tot-) and aqua regia extractable (ar-)

metal values will focus on La and Ce representing the LREEs, Eu the MREEs and Yb the HREEs.

Cerium and Eu are also important given their redox conditions-dependent behaviour. Various REE

parameters for the soil samples, divided by the main parent lithological groups, are summarised in

Table 1. It is noted that aqua regia typically extracts only a small percentage of REEs, Zr and other

heavy elements associated with resistate minerals zircon and monazite, as well as feldspar,

pyroxene and a number of other silicates.

Other

Talc

Montmorillonite

Kaolinite + illite

Ferromagnesian minerals, goethite and hematite

Feldspar

Carbonate

Quartz / crystalline silica

0%

25%

50%

75%

100%

Ultramafic units

Basaltic volcanics

Lefkara & Pakhna Fmns

Mafic intrusives

Cu

mu

lati

ve %

of

min

eral

s

Table 1. Median REE concentrations for the main lithological groups and other ratios. Values in mg/kg.

Ultramafic units

Mafic intrusives

Basaltic volcanics

LefkaraFormation

Pakhna Formation

Other CTSS

N = 187 640 929 609 1059 105

Aqua regia extractable values (ar-)

La 5.25 2.60 3.05 10.40 7.90 7.90Ce 10.00 6.00 6.60 13.10 13.00 13.20Pr 1.20 0.80 0.90 2.00 1.70 1.70

Nd 4.65 3.43 4.15 8.07 6.53 6.51Sm 1.10 1.10 1.30 1.90 1.60 1.60Eu 0.30 0.40 0.40 0.40 0.40 0.50Gd 1.30 1.80 2.20 2.50 2.20 2.30Tb 0.20 0.30 0.30 0.30 0.30 0.30Dy 0.93 1.62 2.07 1.76 1.60 1.80Ho 0.20 0.30 0.40 0.40 0.30 0.40Er 0.50 1.00 1.30 1.00 0.90 1.00

Tm 0.10 0.10 0.20 0.10 0.10 0.10Yb 0.45 0.90 1.20 0.90 0.80 0.90Lu 0.05 0.10 0.20 0.10 0.10 0.10

LaUCC/ YbUCC

1.03 0.18 0.13 0.81 0.89 0.73

EuUCC* 1.12 1.30 1.18 1.06 1.03 1.10CeUCC* 0.98 0.95 0.91 0.83 0.76 0.88

Total values

(tot-)

La 9.05 4.80 4.30 13.10 11.50 11.40Ce 22.00 13.00 12.00 20.00 22.00 23.00Nd 3.00 3.00 3.00 10.00 9.00 8.00Sm 1.70 2.00 1.90 2.30 2.10 2.30Eu 0.40 0.70 0.70 0.60 0.60 0.70Tb 0.30 0.30 0.30 0.30 0.30 0.30Yb 1.00 2.40 2.10 1.30 1.30 1.80Lu 0.15 0.35 0.32 0.20 0.19 0.25

LaUCC/ YbUCC

0.87 0.12 0.12 0.70 0.77 0.65

ar- / tot- ratio

La 0.57 0.54 0.69 0.80 0.71 0.68Ce 0.52 0.45 0.58 0.66 0.61 0.60Sm 0.62 0.53 0.70 0.84 0.75 0.69Eu 0.83 0.60 0.75 0.80 0.77 0.66Yb 0.50 0.40 0.63 0.66 0.60 0.51Lu 0.38 0.38 0.59 0.62 0.52 0.45

UCC = Upper continental crust values based on the data of Taylor and McLennan (1985). CeUCC*=CeUCC/ (LaUCC*PrUCC) 0.5; EuUCC* =EuUCC/ (SmUCC*GdUCC) 0.5

As with nearly all other elements in this high density soil survey (including Ca, Ba, Cr, Cu, Fe,

Mg and U), the most striking feature is the spatial continuity in the geochemical data and the sharp

boundaries that generally follow major changes in underlying lithology and/or palaeo or modern

depositional environments (Fig. 5). The spatial distribution of the REE concentrations varies

substantially from LREEs to HREEs. Soil tot-La and tot-Ce display near-identical patterns with

more elevated values in soils derived from the carbonate-rich Lefkara Formation and areas within

the Pakhna Formation, the Mamonia Terrane ferruginous sediments, the fanglomerates and other

recent sediments in the Polis and the Kokkinochoria areas where tot-La commonly exceeds 50

mg/kg, tot-Ce 100 mg/kg and other heavy mineral-hosted elements such as Cr are also elevated.

Apart from Ce, all REEs are low in soils derived from the ultramafic units that crop out in central

and south-eastern Troodos. Lanthanum is relatively depleted within the mafic intrusive and

basaltic volcanics, whereas Yb is enriched relative to the CTSS units and its distribution displays

only a faint spatial echo of the La pattern outside TO. Europium follows the La trends to some

extent but is more elevated in the basaltic volcanic units and a 20km-wide north-south zone that

crosses the western side of the TO within the sheeted dykes.

Fig. 5. Distribution of total (tot-) and aqua regia (ar-) extractable La, Ce, Eu and Yb in the soils of Cyprus. Data were gridded using IDW with the grid cells designed to limit the number of neighbouring points to a maximum of 2. The colour symboling divisions are based on deciles even where the overall range within each variable is relatively low. For explanation of zone bounded by dashed lines see caption for Fig 9.

40181412

82

30.011.29.67.85.20.5

6020151310

2

9035252015

2

1.80.70.60.50.40.2

2.000.980.820.700.580.30

3.01.41.21.00.90.5

tot-La ar-La

ar-Cetot-Ce

ar-Eutot-Eu

ar-Ybtot-Yb

6.02.82.31.91.71.1

Pafos

Lefkosia

Larnaca

Lemesos

Polis

AkrotiriPenin.

KokkinochoriaTroodos

0 20km

N

Valuesin mg/kg

The ar-REE patterns mimic those of the tot-REE data, although zones with relatively higher

REE values scattered throughout the carbonate units and ar-La particularly high in the Lefkara

Formation (as is Bi, Ba and Mo). The lowest ar-HREE values occur in the ultramafic intrusives in

the core of the TO and the axis of the original rifting system from which the TO sequence was

derived. Elevated ar-Yb values are generally restricted to the basalts rather than other mafic

intrusive units, except for the zone of elevated REE concentrations on the western side of Troodos

as indicated for tot-Eu. Urbanization, proximity to the major sulfide mineralization or former mine

sites, and different agricultural activities do not appear to influence REE patterns.

Irrespective of underlying lithology, there is a high correlation between top soil and sub soil

REE concentrations for both the ar- and tot- data (Fig. 6). The increased scatter in the Lefkara and

Pakhna Formation samples compared with the TO unit soils is attributed to sample representivity

in the distribution of REE-bearing heavy minerals or to some top soil samples being derived from

transported regolith (e.g. thin colluvium derived from TO materials overlying CTSS carbonates)

and the sub soil sample from saprolite.

Fig. 6. Comparison between ar- contents of La, Ce and Yb of top soil and sub soil samples (with equivalence line plotted) and the ar- and tot- contents of top soil samples (with 50, 75 and 100% ratios for ar-/tot- plotted).

Soil tot-REE values are similar to those reported on whole-rock analyses of corresponding

CTSS lithologies (Table 2). Samples from the TO display a wide variation in enrichment values

between ultramafic and mafic units and between elements. In the pyroxene-rich ultramafic units,

soil values range from 1–10 times the REE contents of the rocks, which may be attributed to both

TO units

Lefkara & Pakhna Fmns

ar-R

EE

in t

op

soil

ar-REE in sub soil

Yb

0 2 4 60

2

4

6La

25 50 750

25

50

75

0

Ce

40 80 1200

40

80

0

120

ar-R

EE

in t

op

so

il

tot-REE in top soil

La

25 50 750

25

50

75

0

Ce

40 80 1200

40

80

0

120 Yb

0 2 4 60

2

4

6

1:1

100%

75%

50%

Values in mg/kg

hydromorphic and mechanical loss of other elements during weathering and erosion and

indications of the immobility of the REEs. The enrichments are greatest for peridotite. The mafic

intrusives and basaltic volcanics display similar enrichments of 1–3 times, except in the case of

highly altered and mineralized basalts where enrichment is higher, reflecting REE enrichment in

secondary minerals (Gillis et al., 1992).

Table 2. Mean tot-REEs for various lithologies in Cyprus and soil/rock ratios.

Harzburgites and wehrlites

Peridotite Mafic intrusives

Pillow lavas and basaltic volcanics

Mineralised basalt

CTSS carbonates

This study Kay and Senechal (1976)

This study Robertson and Fleet

(1976)

This study

Robertson (1978)

This study

Average rock

values

(mg/kg)

La 0.85 0.015 1.67 3.5 2.37 0.8 9.86

Ce 2.66 0.04 5.64 4.4 4.53 1.2 17.8

Nd 3.0 0.025 3.92 4.0 4.0 0.6 8.6

Sm 0.2 0.01 1.56 1.4 0.94 0.3 2.02

Eu 0.16 0.007 0.64 0.5 0.35 0.04 0.55

Yb 0.6 0.02 2.17 1.9 1.42 0.6 1.29

Soil/rock ratios

La 10.6 603 2.9 1.2 1.8 5.4 1.2

Ce 8.3 550 2.3 2.7 2.6 10.0 1.2

Nd 1.0 120 0.8 0.8 0.8 5.0 1.1

Sm 8.5 170 1.3 1.4 2.0 6.3 1.1

Eu 2.5 62 1.1 1.4 2.0 17.5 1.1

Yb 1.7 50 1.1 1.1 1.5 3.5 1.0

For the majority of samples, ar-La and ar-Ce exceed 50% of the tot- concentrations (most

observations clustered along the 75% extraction line).Ytterbium and other HREEs display a lower

ar- extractable proportion, though most values range between 25 and 80% extraction. Although

hxl- extracted around 50% of the ar-Mn, it extracted <1% of the ar-Fe. In the Fe-rich TO soils,

hxl- extracted up to 10% of the ar-REE but <5% in the carbonate-rich CTSS soils.

To further examine the nature of the distribution of the REEs (specifically whether the CTSS

signatures are derived from continental weathering and transportation of detrital materials), the

data were normalised to the upper continental crust (UCC) values of Taylor and McLennan (1985).

The ar-REEUCC values for the main geological groups are presented in Fig. 7 and key parameters

summarised in Table 1. The ultramafic units display flat REE patterns, with general depletion. The

mafic intrusive and basaltic volcanic units have similar depleted LREE values but higher HREE

values. The patterns for the Pakhna and Lefkara Formation carbonates are similar, with moderately

depleted LREEs and HREEs but less depletion within the MREEs. The Lefkara Formation

displays a weak negative Ce anomaly. Whereas the Lefkara Formation and overlying Pakhna

Formation have similar HREE distributions, the Lefkara Formation has lower average CeUCC* and

EuUCC* anomaly values than the Pakhna Formation but otherwise higher LREEs.

Fig. 7. Interquartile spread for aqua-regia (ar-) extractable REEs in the soils from the main geological units in Cyprus, normalized to UCC average values. Late Kimmeridgian Formation (LKF) sediments of the Paris Basin based on data from Négrel et al. (2006).

4.3. Inter-element relationships

There is no correlation between tot-La and either Ca or Fe in the TO soils and even a weak

negative correlation with Ca in the CTSS units (Fig. 8). There is strong correlation between La and

Fe in the CTSS units and between La and Th in all units, with the trends corresponding closely to

the respective UCC ratios of 8.8 and 2.8. There are distinct correlation trends between tot- Yb and

La in the TO and the CTSS soils, with the latter following the UCC trend. ar-Ce and ar-La display

two correlation trends against ar-Mn in the Pakhna Formation (the main one corresponding being

the UCC trend) but only weak correlation in the Lefkara Formation (Fig. S1).

UC

C n

orm

alis

ed v

alu

e

La

0.9

0.7

0.8

0.5

0.0

0.2

0.6

0.4

0.1

0.3

CTSS

TO

Ce Pr Nd Eu Gd DyTb Er YbHoSm

0.9

0.7

0.8

0.5

0.0

0.2

0.6

0.4

0.1

0.3

Ultramafic units

Mafic intrusive units

Basaltic volcanic units

LKF Paris Basin

Lefkara Fmn carbonates

Pakhna Fmn carbonates

Fig. 8. Scatterplots of tot- Ca, Fe, Th and Yb versus La in top soils derived from the TO and the Lefkara and Pakhna formations with UCC.

For most samples, between 1% and 10% of the total Zr is extractable by aqua regia, with some

samples having up to 25% (Fig. S2). There is low correlation between ar-Zr and tot-Zr, but the

highest ar-Zr/tot-Zr ratios occur in soils derived from the basaltic volcanic units. Thorium and Zr

are uncorrelated in tot-or ar-data, even at higher concentrations. Bismuth and Th display very

similar spatial patterns to La (Figs. 5 and 9). Whereas the ar-Zr distribution is very close to the

HREEs such as Yb, U is largely unrelated and displays very strong spatial anti-correlation with Bi

in the CTSS units. The REE data from the few zircons extracted from the basaltic soils display a

similar UCC-normalised profile to the basaltic soils in general.

tot-Th(mg/kg)

TO units

tot-Fe(%)

tot-Ca(%)

Lefkara + Pakhna Fmns

tot-Yb(mg/kg)

tot-La (mg/kg) tot-La (mg/kg)

6

12

0

6

12

0

20

40

0

4

8

00 20 40 0 20 40

(UCC trend)

The Lefkara Formation displays consistently high ar-La/tot-La ratios. The zone in the western

end of the sheeted dykes, containing slightly elevated ar-REEs, corresponds with a zone of

elevated soil ar-Cu (>140 mg/kg) and weak hydrothermal alteration with secondary Cu minerals

observed in outcrops.

There was no correlation in the CTSS soils between any of the REEs and Fe under hxl-

extractions and a weak correlation between the LREEs and both Al and Mn for hxl- (the Al

associated with the Fe+Mn oxides rather than clays under the hxl- extraction used; Dalrymple et al.,

2005). There was a weak correlation between hxl-REE and Fe in the TO samples.

Fig. 9. Distribution of the ar-La/tot-La ratios and the ar- extractable distributions for Cu, Zr and various redox-sensitive elements in the top soils of Cyprus. Zone of elevated Cu in western TO mafic intrusive units shown in dashed lines.

1.000.980.820.700.580.30

40181412

82

4,0001,2501,050

900750300

9.06.05.23.82.50.7

ar-Latot-La

ar-Cu

ar-Mn

ar-Fe ar-Th

7.001.901.321.120.750.25

9035252015

2ar-U

30.08.56.24.83.21.0ar-Zr

6.02.82.31.91.71.1ar-Bi

0 20km

N

mg/kg

mg/kg

% mg/kg

mg/kg

mg/kg

mg/kg

5. Discussion

5.1. Primary controls on REE distributions

The main control on the distribution of REEs in the soils of Cyprus is parental geology, as

observed for most other elements in the Cyprus dataset (Cohen et al., 2011). This is consistent with

the results of a number of previous regional soil and sediment geochemical surveys including the

low sampling density atlas of Europe for which REEs in soils and sediments are completely

attributed to geological controls (Fedele et al., 2008; Sadeghi et al., 2013b).

Changes in the relative abundance of the REEs in soils between different lithologies in the TO

units, the high aqua regia extractability and UCC-normalised patterns indicate the REEs are

largely derived from pyroxenes, which favour HREE partitioning (peak concentrations of Yb

occurring in the gabbroic sheeted dykes), rather than olivine, which strongly partitions LREEs or

plagioclase, which both favours LREEs and typically displays a strong positive Eu anomaly

(Taylor and McLennan, 1985; Hoatson et al., 2011) or resistate minerals. This also yields a

progressive HREE enrichment from ultramafic units to the basaltic volcanics as observed in other

systems (Brophy, 2008). The high spatial correlation between soil ar-Zr and ar-HREEs indicates a

significant contribution by zircon or secondary Zr-bearing phases in the soils.

A lack of correlation between ar-P and LREEs in soils from any of the TO but a weak

correlation between ar-P and HREEs in the mafic intrusive units may indicate some contribution

to the total REE content by apatite or other primary or secondary REE phosphates (though few of

these minerals were found in soil heavy mineral concentrates). A general correlation between Zr

and REEs (especially with ar-Yb), along with the HREE enrichment relative to LREE in soils

derived from the basalts, also indicates the influence of zircons.

There are no strong indications of significant alteration of the basaltic REE patterns by seawater

alteration of the pillow basalts. Hydrothermal alteration associated with development of VMS and

related deposits commonly causes enrichment in LREEs, especially Eu, in alteration minerals

(Wells et al., 1998; Douville et al., 1999; Hongo et al., 2007) and highly altered basalts and

associated Fe+Mn-rich sediments typically have elevated REE concentrations (Ravizza et

al.,1999). Yet, even in the vicinity of the major Cyprus-style Cu deposits and mining operations,

there is little to differentiate the REE patterns with soils derived from average tholeiitic basalts.

The source of the REEs in soils derived from the CTSS units may also be attributed to various

processes. The transition from the deep water anoxic Lefkara Formation to the oxic to suboxic

shallow marine Pakhna Formation and younger CTSS units is reflected in trace element patterns

(Cohen et al., 2011) including a moderate increase in U and U/Th and progressively more negative

CeUCC* anomalies. Apart from Ce, REE concentrations in seawater tend to increase towards the

base of deep ocean basins (e.g. Nozaki et al., 1999) and, while this may increase incorporation of

REEs into carbonates, the negative correlation between Ca and the REEs indicates that co-

precipitation with carbonates is only a minor contributor to the higher REE values in the Lefkara

Formation soils. Adsorption or co-precipitation of REEs onto Fe and Mn oxides may exert

significant control on REE concentrations in sedimentary units and soil profiles (with Mn more

important than Fe and clays); however, the hxl- extraction data indicated only a weak association

between LREEs and Mn, and no correlation between REEs and Fe. The UCC-normalised hxl-data

displays similar patterns to the ar- data except for a strongly positive Eu anomaly for Lefkara

Formation soils. The lack of positive Ce anomalies in the Pakhna Formation further points to

adsorption onto Fe+Mn oxides as a minor contributor to total REEs in the shallow marine CTSS

units.

The UCC-normalised patterns in the ar- and hxl- data point to terrestrial detrital signals and not

to precipitation with authigenic minerals in the CTSS sediments. These results are similar to those

for the Eastern Paris Basin (Négrel et al., 2006) and the Venetian region of northern Italy

(Bellanca et al., 1997). They also support the conclusions of Dill et al. (2009) who showed that

mineral assemblages and Ca isotope abundances indicated a significant proportion of detrital

material in the CTSS sediment to have been derived from mafic igneous sources.

5.2. Spatial REE patterns and structures

In addition to changes in parental lithology, the spatial patterns in the REE data can be linked to

various structural features of Cyprus. As an example, the chondrite normalised pattern for Ce (ar-

CeCN* ) displays a series of sharp NE-trending boundaries which divide the TO into a series of

blocks (Fig. 10). This is accentuated by the negative Ce anomalies in the CTSS units (especially

the Lefkara Formation) and weak positive Ce anomalies in the mafic intrusives. These blocks cut

across a series of smaller NW-trending faults and the boundaries are parallel to other NE-trending

faults. They also mark the boundary between units within the TO and between the TO and CTSS.

Along some of these boundaries, there are variations in the REE patterns relative to adjacent

lithologies, including lower CeCN* values. The orientation of these boundaries is consistent with

the sinistral shearing orientation (Fig. 3) that has developed due to the rotation of Cyprus and

along which the block containing the ultramafic core of the TO has likely been vertically shifted to

expose it in the centre of the Troodos Mountains. In the southern TO, there is some local

counterclockwise rotation due to the dextral strike fault between them. This was also shown by

palaeomagnetic data in the south of the TO by Morris et al. (1990, 1998). The basin boundaries

also coincide with a number of these boundaries (again showing up as very distinct changes in

REE patterns).

At a broader scale, there is some correlation between elevated Cu and Eu concentrations in

soils derived from sheeted dykes on the western side of Troodos and the location of these inferred

major faults or structures. This is consistent with the extensive hydrothermal fluid circulation

through the basalts and mafic intrusive units that generated the seafloor and sub-seafloor Cyprus-

type Cu deposits (Chapman and Spooner, 1977).

Fig. 10. Map of tot-CeCN* with interpretive structures of Cyprus. Main structural units based on Eaton and Robertson (1993) and Lagroix and Borradaile (2000), and the Geological Survey Department of Cyprus digital mapping compilation of 2009.

5.3. Regolith and landform controls on REE distributions

Apart from the general increase in REE values in soils relative to parental lithology due to loss

of mobile elements, there appear to be only limited regolith controls on REEs and other low-

mobility element abundances. The close correlation between top soil and sub soil REE

concentrations mirrors that of other large-scale soil geochemical mapping programs (De Vos and

Tarvainen, 2006). These results again emphasise that under typical weathering conditions, across a

wide spectrum of common rock types, REEs are only weakly mobile and that secondary phases

such as clays and Fe+Mn oxides are LREE-enriched due to the slightly higher mobility of the

small HREE trivalent ions (Daux et al., 1994; Ridley et al., 1994). Whereas total REE

concentrations generally increase, the LREE/HREE ratios increase due to the greater mobility of

HREEs. This is particularly the case for carbonate rocks and the formation of terra rossa (Temur et

al., 2009) as shown in the Kokinnochoria area. The tendency towards slightly higher ar-REE

ar-CeCN*

1.17

1.03

0.93

0.84

0.72

0.57

Faults (inferred)

ObservedArakapas t’form

Faults

Troodos Ophiolite (TO)0 20km

N

values in the top soils may relate to accumulation of REE-bearing phases in the top soil due to loss

of more mobile elements and/or elutriation of REE-poor clays.

REE patterns tend to be similar across a range of mineral forms in soils (from adsorbed, to Mn-

Fe oxide hosted) as shown by various selective extraction methods (Galbarczyk-Gąsiorowska,

2010). The weathered profile pH does not influence REE distributions significantly until it is low

enough to begin dissolving primary REE-bearing phases in the original rock such as apatite and

allanite (Braun et al., 1993). Again, the comparison of ar- and hxl- indicates only a weak

association between the REEs and minerals expected to dissolve in hxl- such as δMnO2 and

goethite.

A lack of Ce anomalies in the Cyprus soils related to precipitation of Ce4+ species in strongly

oxidizing conditions (Jaireth et al., 2014) further indicates a significant proportion of the REEs are

hosted in chemically resistate phases which contributes to retention of primary lithological patterns

in the weathered environment (Linnen et al., 2014). Yet, the high ar-/tot- ratio for most REEs

would indicate a significant source of REEs to be unstable primary phases (e.g. pyroxene in the

TO).

Unlike Cr (as chromite), there appears to have been little mechanical dispersion of REEs, Th, or

Zr and accumulation along the coastal areas. This again would suggest a limited contribution from

heavy minerals such as zircon to the REE content of the soils in those areas. The accumulation of

REEs and other heavy mineral-associated elements in the Kokkinochoria area that is on the eastern

edge of the Mesaoria Basin units, however, indicate a source of REEs (possibly zircon) derived

from the Keryneia Terrane in the north of Cyprus or even from the European mainland into the

former Mesaoria Basin.

6. Conclusions

Due to immobility of the REEs during weathering, the REE pattern in the soils of Cyprus

closely reflects the geochemistry of the parental rocks, allowing mapping of subtle variations in

lithology, large-scale structures and depositional environment. Troodos Ophiolite units have

elevated HREEs relative to LREEs reflecting pyroxene and, to a lesser extent, zircon and apatite in

the basalts as the main primary lithological hosts. Despite significant variations in physico-

chemical conditions indicated by various trace elements with redox-controlled mobility, the CTSS

displays UCC-normalised patterns for total analyses that indicate detrital material derived from

mafic lithologies (probably the TO) to be the main source of REEs in the CTSS units, with

selective geochemical extraction data indicating minor contribution from adsorption of REEs to

Mn+Fe oxides and little indication of co-precipitation with carbonates. Large-scale hydrothermal

alteration zones in western Troodos and along large slip-strike faults correspond with enrichment

or depletion in various REEs and related elements. There is little influence of land use on REE

patterns. This study reinforces the value of high density geochemical mapping in detecting the

effects of subtle variations in geology, depositional environment and regolith on soil geochemistry.

Acknowledgements

The authors acknowledge the funding, technical and logistical support for the project provided

by the Geological Survey Department of the Republic of Cyprus, and the provision of analytical

services through Actlabs. E. Cohen is thanked for assistance in the heavy mineral separations. The

visiting fellowship to UNSW for L. Ren was provided by China University of Geosciences,

Wuhan. The authors are grateful for criticism of the manuscript by I.T. Graham and three other

reviewers.

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Graphical abstract

TroodosOphioliteComplex 40 ppm

18

14

12

8

2

tot-La

tot-Yb

6.0 ppm

2.8

2.3

1.9

1.7

1.1

Circum-TroodosSedimentarySuccession

Top soil samples

Highlights

► REE patterns in the soils of Cyprus are dominated by parent lithology and indicate low REE

mobility during weathering

► REE in the Troodos Ophiolite are mainly derived from pyroxene and zircon and are HREE-

enriched

► Circum-Troodos Sedimentary Succession carbonate REE are mainly derived from continental

crust detritus and are LREE-enriched

► Hydrothermal alteration along major faults and other structural features is reflected in soil

REE patterns