A New Porphyry Mo Mineralization at Aisymi-Leptokarya, South-Eastern Rhodope, North-East Greece: Geological and Mineralogical Constraints

Abstract

A new porphyry Mo prospect has been discovered in the Aisymi-Leptokarya area, along the southern margin of the Byala Reka–Kechros metamorphic dome, south-eastern (SE) Rhodope metallogenic zone. The study area is dominated by an Oligocene felsic dike complex, which hosts the porphyry Mo mineralization and intrudes into upper Eocene sandstones-marls and the Leptokarya monzodiorite pluton. The Aisymi-Leptokarya felsic dike complex displays a rhyodacitic to dacitic composition with post-collisional affinities. The porphyry Mo mineralization occurs in the form of porphyry-style quartz stockworks in the felsic dike complex associated with potassic alteration characterized by hydrothermal K-feldspar. The ore minerals consist mainly of pyrite, molybdenite, kesterite, bismuthinite and galena within both the stockwork and the rock matrix. Bulk ore analyses indicate enrichment in Mo (up to 215 ppm), Se (up to 29 ppm), Bi (up to 8 ppm) and Sn (up to 14 ppm) in the porphyry quartz veins. Late-stage, north-east (NE-) and north-west (NW-)trending milky quartz intermediate-sulfidation epithermal veins with base metals, crosscut previous vein generations and are characterized by Ag, Sn and Te anomalies. The Aisymi-Leptokarya porphyry Mo prospect is set in a back-arc geotectonic regime and shares similarities to other post-subduction porphyry molybdenum deposits elsewhere.

1. Introduction

Porphyry-type deposits are the largest source of the world’s molybdenum. Currently, China, which hosts many porphyry Mo deposits is the most significant Mo producer [1]. Proven reserves are >25 Mt Mo metal (e.g., [2]) and comprise more than twice the rest world’s supplies [3].

Porphyry Mo deposits have been classified into three types [4]: (1) The Endako-type (or high-fluorine), which is related to subduction environments and hosted in calc-alkaline magmatic rocks [5]. These deposits are characterized by fluids with low CO₂/H₂O, F/Cl and K/Na ratios and a low Rb-Nb and moderate to high Sr signature. They were originally described from the Endako deposit, British Columbia, Canada [5]; (2) Climax-type (or low-fluorine) is rift related. This deposit type is characterized by a high F/Cl ratio and significant variations in their CO₂/H₂O and K/Na ratios [6]. They also display high Rb-Nb geochemical signatures; (3) Dabie-type was recently described by Mi et al. [7] named after the Dabie Shan orogenic belt, China and occurs in collision to post-collision environments. These deposits are genetically linked to high-K calc-alkaline to shoshonitic magmas, in syn- to post-collisional tectonic settings and are related to fluids with high CO₂/H₂O, F/Cl and K/Na ratios. The class is originally represented by the giant Qian’echong Mo deposit, east China [7]. Alteration patterns in porphyry Mo deposits usually comprise an internal zone dominated by potassic alteration, which grades outwards into silicic/sericitic, propylitic and more distally to argillic assemblages [8,9,10].

The Thrace metallogenic province in NE Greece hosts a number of mineralization types including porphyry, high/intermediate-sulfidation, epithermal and other intrusion related systems, containing significant amounts of precious and critical metals [11,12,13]. Among them, many porphyry-type deposits are enriched in molybdenum, along with other commodities (e.g., Cu, Au, Re). Characteristic examples are the Pagoni Rachi, Konos, Myli, Maronia and Melitena deposit/prospects [11,12,13,14,15,16].

A new porphyry Mo prospect was recently discovered [17] in the poorly studied Aisymi-Leptokarya area. The goal of the current contribution is to present results on the alteration, ore mineralogy and geochemistry of the porphyry Mo mineralization. We will also investigate its possible relationship to nearby mineralization and will try to establish any possible genetic links.

2. Regional and Local Geology

Based on previous studies [18,19,20], the Rhodope metamorphic core complex in the NE Thrace region, comprises two metamorphic domes, the Kesebir-Kardamos to the east and the Byala Reka–Kechros to the west (Figure 1), which are bound by extensional detachment faults [19]. The tectonostratigraphic units in these domes are from bottom to top, a basal, high-grade unit of orthogenesis with Permo-Carboniferous protoliths, an overlying high-grade metamorphic unit of continental and oceanic affinities consisting of amphibolites, marbles, schists, gneisses and metaperidotitic bodies, with protoliths which range in age from the Neoproterozoic to Early Mesozoic. The upper part of the metamorphic dome is occupied by the metasedimentary lithologies of Circum-Rhodope Belt, namely the Makri and Drymos-Melia units.

The Makri unit consists of greenschist-facies metasedimentary lithologies and is tectonically overlain by the very low-grade to un-metamorphosed Drymos-Melia rocks [21], which include the Evros ophiolite. A nummulitic limestone overlies the metasedimentary sequence [22].

An extensional tectonic regime, established in the area since Eocene times, resulted in the opening of several, E-W and N-S trending supra-detachment basins, infilled by sedimentary and volcanic lithologies [19]. These basins consist of Priabonian marly sandstones and claystones interbedded with lava flows and domes, as well as plutonic rocks [23]. The plutonic rocks display calc-alkaline to shoshonitic affinities and are located along a NE-SW direction, subparallel to the northern margins of the Aisymi-Kirki basin, thus indicating a structurally-controlled emplacement [24,25].

The Aisymi-Leptokarya area is dominated by a felsic dike complex hosting the porphyry-Mo mineralization (Figure 2 and Figure 3), the Leptokarya pluton, a granodiorite porphyry in its southwestern part and Upper Eocene (Priabonian) volcano sedimentary rocks.

The felsic dike complex consists of a major NW trending intrusive body, up to hundreds of meters wide and several km long, which crosscuts all the other rocks in the area (Figure 2). Alfieris et al. [26] described acid dikes (e.g., quartz ± biotite porphyries) from the south-eastern part of the study area, with disseminated pyrite and base metal veins mineralization.

The Leptokarya pluton, forms part of a NE-trending intrusive belt that includes the Kassiteres, Kirki, Leptokarya and Tris Vrisses intrusions (Figure 1) and consists of quartz monzogabbros/monzodiorites predominantly along with tonalites and granodiorite [24,25,27,28]. Theses intrusive rocks are characterized by a medium-grained, granular to porphyritic texture consisting of plagioclase and variable amounts of pyroxene, amphibole, biotite and Fe–Ti oxides, with quartz and K-feldspar occurring as interstitial minerals. Radiometric data (Rb-Sr in biotite) yielded ages of 31.4 ± 0.7 to 31.9 ± 0.5 Ma [24]. Recently, Perkins et al. [28] provided a high precision age of 32.235 ± 0.026 Ma, based on Pb-U geochronology, for the Leptokarya pluton.

Finally, the sedimentary sequence in the area comprises marls and sandstones and is characterized by different degrees and styles of hydrothermal alteration.

3. Materials and Methods

A total of 33 rock and mineralized samples were collected from the Aisymi-Leptokarya prospect for petrographic, mineralogical and geochemical studies. From these rock samples, 10 thin sections, 16 polished-thin sections and 51 polished sections were made and underwent detailed mineralogical investigation using a Leica DM2500P optical microscopy mounted with a Nikon camera. All samples were pulverized using a tungsten carbide mill at −70 μm grain size and were scanned by X-ray diffraction, using a Bruker (Siemens, Munich, Germany) D-5005 X-ray diffractometer between 3° and 65° 2θ with 1°/min velocity using the Ka radiation of a Cu X-ray tube operated at a voltage of 40 kV and a current of 40 mA, in conjunction with the DIFFRACplus software. Results were evaluated using EVA 10.0 software at the Department of Mineralogy and Petrology, National and Kapodistrian University of Athens. Bulk chemical analyses of 12 samples (prepared according to the PUL85 analytical protocol of ACME) were performed using an XRF (X-Ray Fluorescence) instrument using the method LF700 (2015) for major elements and LF100 (2015) for trace elements at the ACME Laboratories, Canada. Trace elements for all samples were measured using ICP-MS (Inductively Coupled Plasma Mass Spectrometry) method AQ200 (2015) by ACME, Canada. Electron Probe Micro Analyses (EPMA) analyses of sulphides and sulfosalts in ten polished sections were carried out using a Superprobe JEOL JXA 8200 electron-microprobe (Eugen F. Stumpfl laboratory, Leoben University, Leoben, Austria). The operating conditions were: accelerating voltage 20 kV, beam current 10 nA, beam size ≈ 1 μm. Counting times were 20 s on the peak and 10 s on the right and left backgrounds for major elements. The counting times were increased up to 60 and 30 s for peak and background, respectively, to analyse the trace elements. The minerals were analysed using pure metals as the reference material for Ge, In, W and Re, synthetic Bi₂Te₃, GaAs, AgBiSe₂, cassiterite and electrum for Bi, Te, Ga, Se, As, Sn and Ag. Natural pyrite, chalcopyrite, sphalerite, molybdenite, stibnite and galena were used for Fe, Cu, Zn, Mo, Sb, Pb and S. In the following, the analytical lines and the diffracting crystals are listed for each analysed element: S = Kα, PETJ; Ag, Sb, Mo = Lα, PETJ; Bi, Re = Mα, PETJ; Fe, Cu, Zn = Kα, LIFH; As, Se, Ge = Lα, TAP; Te, In, Sn = Lα, PETH; Pb = Μα PETH; W = Lα, LIF; Ga = Kα, LIF.

All maps were made using ArcGIS 10.4 by ESRI.

4. Results and Discussion

4.1. Petrology and Geochemistry of the Aisymi-Leptokarya Magmatic Rocks

The Aisymi-Leptokarya felsic dike complex is texturally inhomogeneous and consists of at least two variants, both of which are hydrothermally altered: (a) a strongly silicified and sericitized equigranular to porphyritic variety, dominated by subhedral to anhedral quartz, K-feldspar (replaced by kaolinite) and sericite (pseudomorph after primary biotite) (Figure 4a). Spherulitic aggregates of quartz and K-feldspar are commonly present (Figure 4a), together with graphic textures of quartz and orthoclase; (b) a porphyritic variety, which includes quartz and K-feldspar phenocrysts embedded within a microcrystalline matrix of quartz and possible feldspars (Figure 4b). This variety resembles the acid dike rocks described by Alfieris et al. [26] and mostly occurs along the south-eastern margin of the Aisymi-Leptokarya felsic dike complex.

The Leptokarya pluton is a medium-grained, equigranular to porphyritic quartz monzodiorite, that contains plagioclase and variable amounts of pyroxene, amphibole, biotite and Fe-Ti oxides. Quartz and K-feldspar occur as interstitial minerals. In places, the monzodiorite is characterized by different styles of hydrothermal alteration (e.g., potassic alteration, Figure 4c).

Chemical compositions of the Aisymi-Leptokarya magmatic rocks are summarized in

Table 1. Chemical composition of rock samples from the Aisymi-Leptokarya prospect. Values are in wt.% for major elements (acquired by XRF) and in ppm for trace elements (acquired by ICP-MS).

Rock Type	Microgranite Porphyry									Monzodiorite
Sample	EG8	EG10	EG13	EG15	EG19	EG20	EG22	EG23	EG32	EG9	EG28
SiO2	78.6	83	79.2	80.6	80.5	82.8	76.3	72.5	82.9	58.2	55.8
TiO2	0.14	0.13	0.17	0.14	0.18	0.14	0.22	0.31	0.11	0.69	0.73
Al2O3	12.3	11.3	13.6	12.1	12.3	11.2	12.8	14.2	10.1	14.5	13.4
Fe2O3	0.27	0.18	0.15	0.23	0.35	0.24	0.33	1.11	1.16	5.71	8.62
MnO	bdl	bd	bd	bd	bd	bd	0.01	0.02	0.06	0.22	0.59
MgO	0.12	0.14	0.19	0.3	0.15	0.05	0.38	0.95	0.21	5.06	6.09
CaO	0.03	0.02	0.03	0.02	0.03	0.03	0.46	0.84	0.07	6.44	7.17
Na2O	0.12	bd	0.12	0.05	0.25	0.02	2.37	3.33	bd	2.88	2.3
K2O	5.19	0.81	1.54	2.87	3.43	0.51	4.93	4.68	0.99	2.32	1.32
P2O5	0.01	bd	bd	bd	0.02	0.01	bd	0.1	bd	0.15	0.3
LOI	2.48	3.82	4.1	2.61	1.76	4.16	1.31	1.34	3.74	2.83	3.24
Total	99.51	99.43	99.14	99.06	99.03	99.19	99.26	99.56	99.4	99.55	99.7
Ba	1351	91	187	299	776	146	1410	1067	188	750	417
Co	0.4	0.6	0.3	bd	0.3	0.7	0.5	1.5	1.8	19	23.6
Cs	4.1	3	3.6	10.3	1.5	3.4	0.5	1.4	4.2	2.2	9.6
Ga	9.9	9.6	10.1	10.2	12.7	6.8	10.1	12.9	6	14.1	15.6
Hf	2.8	2.2	2.8	2.9	3	2.5	3	3.6	2.1	1.7	2.9
Nb	9.6	8	8.9	9.7	9.3	8.9	10.3	9.9	7.9	7.8	8.5
Rb	141	44.8	76.1	130	123	24	134	116	56.6	60.7	54
Sn	2	4	4	6	34	2	2	3	2	6	7
Sr	81.5	12.7	28.3	7.4	13.7	23.1	227	235	19.5	309	445
Ta	0.8	0.8	0.8	0.9	0.8	0.9	1.3	1.4	0.8	0.7	0.7
Th	18.5	16.1	16	18.1	18	19	19.5	15.7	15	12.5	10.4
U	8.1	4.2	4.8	5.6	4.3	12.2	6.8	7.3	14.7	4.8	3
V	14	14	10	11	9	19	9	43	11	177	220
W	1.7	2.9	1.9	4.9	6.1	2.3	0.5	0.9	1.8	2.8	0.9
Zr	76.3	60.7	85.9	70	87	74.7	85.6	134	60.3	48	112.7
Y	14.2	11.7	12	16.9	16.8	20.4	14.3	17.6	13.6	18.7	24.5
La	22.3	19.6	25.3	28.8	28.1	27.1	25.6	15.5	22.3	24.9	24
Ce	41.8	37.5	46.7	52.2	52.7	49.9	44.7	31.6	42.5	49	53.1
Pr	4.08	3.41	4.44	5.22	5.3	4.82	4.47	3.64	4.18	5.13	5.96
Nd	14.3	11.9	15.1	18.6	18.2	16.5	15.5	13.9	14.1	19.7	23.1
Sm	2.3	2.1	2.48	2.97	3.52	2.83	2.66	3.08	2.4	3.72	4.77
Eu	0.41	0.33	0.38	0.37	0.39	0.37	0.3	0.5	0.34	0.87	0.87
Gd	2.05	1.86	2.21	2.53	2.83	2.68	2.24	2.72	2.07	3.66	4.81
Tb	0.32	0.3	0.3	0.38	0.45	0.42	0.36	0.46	0.34	0.54	0.71
Dy	2.1	2.11	2.01	2.47	2.95	2.81	2.32	3.04	2.24	3.23	4.25
Ho	0.44	0.41	0.4	0.53	0.52	0.62	0.48	0.64	0.47	0.66	0.92
Er	1.37	1.32	1.35	1.71	1.68	2.19	1.65	1.9	1.29	1.82	2.68
Tm	0.25	0.22	0.22	0.26	0.26	0.3	0.24	0.28	0.24	0.28	0.4
Yb	1.92	1.56	1.61	1.91	1.79	2.28	2	1.96	1.67	1.73	2.45
Lu	0.26	0.24	0.26	0.29	0.31	0.35	0.31	0.31	0.27	0.28	0.34
Mo	1	56.9	2.3	4.2	20.9	0.9	bd	0.1	2.9	1.1	1.1
Cu	8.2	12.2	15.5	2.6	5.8	2.7	3.7	3.9	4.5	89.1	2.9
Pb	32.9	13.1	97.1	9.9	7.9	11.7	2.7	5.3	20.7	12.3	4.4
Zn	249	6	6	4	4	3	17	402	72	120	157
Ni	0.7	2.8	1.5	0.2	0.1	0.8	0.4	13.2	3.1	42.6	73.5
As	2	4.4	1.8	0.8	1.1	1.2	bd	bd	1	2.9	0.6
Cd	1.6	bd	bd	bd	bd	bd	0.1	0.5	0.4	0.5	bd
Sc	0.5	0.4	0.6	0.3	0.3	0.5	0.6	1.9	0.6	4.3	3.7

bdl: below detection limit.

. Due to strong hydrothermal alteration, discrimination diagrams for granitoids are not suitable for the studied samples. Using the immobile element Zr/TiO₂ versus Nb/Y diagram [29] the felsic dike samples show a rhyodacitic to dacitic composition (in accordance with previous studies by Alfieris et al. [26]), with some samples plotting in the trachyandesitic field, possibly due to hydrothermal alteration (Figure 5a). Accordingly, these rocks can be regarded as microgranite porphyries. In the Zr/TiO₂ versus Nb/Y diagram samples from the Leptokarya pluton plot in or near the andesite field. Accordingly, the Leptokarya pluton is a monzodiorite. In the Rb versus Y + Nb diagram [30,31], the magmatic rocks are mostly characterized by post-collisional affinities (Figure 5b). Compositional variations in the felsic dike samples, could be attributed to hydrothermal alteration, which could result in erroneously low values of Rb for these rocks.

The microgranite porphyry and the Leptokarya monzodiorite display different chondrite-normalized rare earth element (REE) (Figure 5c) and mantle-normalized trace element patterns (Figure 5d). The microgranite samples have subparallel chondrite-normalized REE patterns and show strong light REE enrichment (La/Sm = 3.14–6.37) but almost unfractionated heavy REEs (Tb/Y = 0.74–1.12). They also display a negative Eu anomaly (Eu/√(Sm + Gd) = 0.37–0.58). The Eu anomalies are chiefly controlled by feldspars, particularly in felsic magmas, thus the removal of feldspar from felsic melt by crystal fractionation or partial melting of the rock will give rise to a negative Eu anomaly. The monzodiorite samples have subparallel patterns with the microgranite porphyry but are more enriched in all REEs.

In Figure 5d, the samples of microgranite display enrichment of LILE relative to HSFE, negative anomalies of Nb, Ta, P, Ti and positive anomalies of K, Zr and Pb, typical for convergent boundaries magmatism, which is consistent with the findings in previous studies for igneous rocks in the Evros area by Christofides et al. [34]. Compositional variations in the microgranite samples within for same element, can be attributed to different degrees of hydrothermal alteration (e.g., Ba, Rb). The monzodiorite, displays quite the opposite geochemical features, as it appears enriched in HSFE and relatively depleted in LILE, always compared to the microgranite samples.

4.2. Mineralization and Alteration

Mineralization comprises: (a) porphyry-type quartz stockworks (A- and D-type veins according to Seedorf et al. [35] in the microgranite porphyry and partly in the monzodiorite; (b) sulphide disseminations hosted in both magmatic rocks; and (c) base metal veins (E-type veins), which crosscut the previous styles of mineralization.

The A-type veins in the core of the system are associated with potassic (hydrothermal K-feldspar) alteration (Figure 3b,c and Figure 4d,e;

Table 2. Mineralogical content of selected hydrothermally-altered samples defined by X-ray diffraction (XRD) analyses.

Sample	Lithology	Alteration	Qz	K-fs	Pl	Hbl	Bt	Chl	Ser
EG06	Microgranite porphyry	potassic	+	+
EG08		potassic	+	+
EG15		potassic/phyllic	+	+					+
EG16		potassic/phyllic	+	+					+
EG21		potassic/phyllic	+						+
EG9	Monzodiorite	propylitic	+	+	+	+	+	+
EG28		potassic/sodic	+		+		+

Abbreviations: Qz = quartz; K-fs = K-feldspar; Pl = plagioclase; Hbl = hornblende; Bt = biotite; Chl = chlorite; Ser = sericite.

). In places, D-type veins are associated with phyllic alteration (Figure 4b,f; Table 2) and overprint earlier style of mineralization and alteration. Localized potassic-sodic alteration characterized by hydrothermal biotite and albite (Figure 4c) is also present within the Leptokarya monzodiorite.

Porphyry-style mineralization consists mainly of pyrite, molybdenite, magnetite, kesterite, bismuthinite and galena within the A-type veins and as disseminations in the rock matrix. Pyrite is present in anhedral crystals in all samples, whereas molybdenite occurs as isolated flakes in both the quartz veins and the microgranite (Figure 6a). Kesterite, (Cu₂(Zn,Fe)SnS₄), a relatively rare member of the stannite group, is also present in porphyry-style veins. It is included in pyrite either as isolated grains, or associated with bismuthinite (Figure 6b,c). Bismuthinite forms small blebs in pyrite (Figure 6d). D-type veins host pyrite mineralization associated with sericitic alteration in both the microgranite and the monzodiorite. In the elevated part of the prospect, oxidation of ore minerals, most probably argentiferous galena, resulted in the formation of supergene acanthite (Figure 6e).

Late-stage, NE- and NW-trending, epithermal-style (E-type), milky quartz veins with base metal sulphides crosscut all earlier-formed vein generations and are associated with sericite-rich alteration assemblages (Figure 3e,f). Mineralization is composed of early pyrite followed by sphalerite and then by galena (Figure 3l). Fahlores (zincian tennantite) and minor chalcopyrite are also present.

4.3. Mineral Chemistry

Molybdenite is characterized by varying rhenium concentration from below detection to 0.3 wt.%. Electron-microprobe data of molybdenite compositions are presented in

Table 3. EPMA data of molybdenite from porphyry-style mineralization of the Aisymi-Leptokarya prospect.

Sample	EG16 (n = 64)				EG3 (n = 10)
wt.%	Min	Max	Mean	1σ	wt.%	Min	Max	Mean	1σ
Mo	58.8	60.8	59.9	0.34	Mo	58.6	60.3	59.8	0.39
W	bdl	0.08	0.01	0.02	W	bdl	0.07	0.01	0.02
Re	bdl	0.14	0.02	0.03	Re	bdl	0.31	0.08	0.07
Sn	bdl	0.02	0.002	0.01	Sn	bdl	0.01	0.000	0.001
Se	bdl	0.04	0.004	0.01	Se	bdl	0.03	0.003	0.01
S	39.6	40.9	40.2	0.29	S	39.6	40.8	40.1	0.34
Total	99.1	100.5	100.2	0.30	Total	99.4	100.4	100.1	0.27
apfu	3
	Min	Max	Mean	1σ		Min	Max	Mean	1σ
Mo	0.982	1.018	0.996	0.007	Mo	0.973	1.010	0.997	0.009
W	-	0.001	-	-	W	-	0.001	0.000	0.000
Re	-	0.001	-	-	Re	-	0.003	0.001	0.001
Sn	-	-	-	-	Sn	-	-	-	-
Se	-	0.001	-	-	Se	-	0.001	-	-
S	1.98	2.02	2.00	0.007	S	1.988	2.027	2.002	0.009

bdl: Below detection limit.

and all data are plotted in a binary Re versus Mo diagram (Figure 7). Minor amounts of Sn and W were also identified (up to 0.08 and 0.02 wt.% respectively). Finally, traces of Se (up to 0.04 wt.%) substitute S in the structure of the molybdenite.

Kesterite revealed almost stoichiometric composition, with a minor substitution of Sn by In (values up to 0.70 wt.%) (Figure 8).

Galena is generally characterized by very low values of trace elements (Se up to 0.05 wt.% and Sb p to 0.02 wt.% respectively (

Table 4. EPMA data of galena and sphalerite from base metals veins of the Aisymi-Leptokarya prospect.

Sample EG1	Galena (n = 8)				Sphalerite (n = 12)
wt.%	Min	Max	Mean	1σ	wt.%	Min	Max	Mean	1σ
Pb	86.6	87.1	86.8	0.19	Fe	0.51	1.00	0.79	0.16
Se	0.01	0.02	0.01	0.004	Zn	65.4	67.2	66.3	0.54
Sb	0.02	0.05	0.03	0.01	S	32.5	33.3	32.9	0.24
S	13.2	13.6	13.4	0.14	Total	99.5	100.5	100.1	0.37
Total	100.0	100.5	100.3	0.175
apfu	2
	Min	Max	Mean	1σ		Min	Max	Mean	1σ
Pb	0.993	1.008	1.001	0.006	Fe	0.009	0.017	0.013	0.003
Se	0.000	0.000	0.000	0.000	Zn	0.973	1.000	0.986	0.008
Sb	0.000	0.001	0.000	0.000	S	0.988	1.010	1.000	0.006
S	0.991	1.007	0.998	0.006

).

Sphalerite has very low Fe content (up to 1.0 wt.%) and is generally devoid of any trace elements (Table 4).

4.4. Bulk Ore Geochemistry

The Aisymi-Leptokarya prospect has not yet been drilled or has been the subject of exploration utilizing modern techniques. Preliminary bulk ore analyses of surface samples from the porphyry-style veins revealed a significant enrichment in Mo, with values up to 215 ppm (

Table 5. Selected bulk-ore trace elements analyses (acquired by ICP-MS) from porphyry-style and base metals veins from the Aisymi-Leptokarya prospect. Concentrations are in ppm, except for gold in ppb.

Sample	EG2	EG3	EG6	EG14	EG16b	EG27	EG29	EG31	EG1	EG11	EG25
	Porphyry-Style Veins								Base Metal Veins
Au	4.1	0.8	5.3	5.9	1.1	1.3	7.9	7.1	<0.5	4.6	23.5
Ag	1.2	0.5	0.9	0.2	<0.1	0.7	1	1.3	3.9	8.6	7.9
Mo	38.6	182	114	65.3	150	215	96.3	20.3	20.2	0.5	1.2
Se	1	29	2.2	0.8	<0.5	0.5	<0.5	<0.5	4.6	4.5	<0.5
Te	<1	<1	<1	<1	<1	<1	<1	<1	3	<1	3
Bi	2.3	1.4	8.2	4.8	0.7	0.8	1.1	0.8	3.4	16.4	0.8
Sn	6	13	5	13	2	3	14	2	6	17	1
Sb	1.7	1.2	1.4	0.4	0.3	0.1	1.1	10.6	6.1	0.3	9.8
Pb	94.5	16.6	28.7	18.4	8.7	10.8	31.5	25.1	>10,000	5258	996
Zn	58	10	4	38	6	9	2	10	>10,000	789	71
Cu	9.8	3.2	1	6.8	3.3	18.3	2	49.2	277	379	23.5
As	1.6	<0.5	18.7	45.6	2.7	6.2	20	24.8	13.7	40.4	31.1

), with a mean of 110 ppm. It must be noted that elevated Mo concentrations lacks correlation with any other element such as Cu or Au, which characterizes mineralization elsewhere in the nearby area [15]. Selenium is also enriched, up to 29 ppm, whereas Bi and Sn display relatively elevated concentrations (up to 8 and 14 ppm, respectively). Gold and Ag content is rather insignificant.

The base metal veins are characterized by enrichment in Bi and Sn, with values up to 16 and 17 ppm, respectively. Mo displays elevated concentration as well (up to 20 ppm). Au and Ag values reach up to 24 ppb and 9 ppm respectively.

4.5. Genetic Implications

This study demonstrates a new porphyry-style prospect in the Kassiteres-Leptokarya magmatic suite, located in the Aisymi-Leptokarya area. The studied mineralization is hosted in an Oligocene felsic dike complex, which intrudes into upper Eocene volcanoclastic sediments and the Leptokarya pluton. The felsic dike complex displays a rhyodacitic to dacitic composition with post-collisional geochemical signature. Mineralization is composed by porphyry-style quartz stockwork in the felsic dike complex and is associated with potassic alteration, dominated by K-feldspar, which grades outwards into propylitic assemblages. Early alteration and mineralization are overprinted by D-type veins and late-stage, base metal veins associated with quartz-sericite±carbonate alteration assemblages. Ore minerals within the porphyry stockworks consist mainly of pyrite, molybdenite, kesterite, bismuthinite and galena. Late base-metal veins are dominated by sphalerite, galena, chalcopyrite and tennantite.

The absence of drilling data and the altered nature of the analysed samples, make it difficult to classify the studied mineralization. Preliminary bulk ore analyses showed that the Aisymi-Leptokarya porphyry deposit is characterized by an enrichment in Mo, which lacks correlation with any other commodities (e.g., Cu, Au), thus it should be possibly considered as a porphyry-Mo prospect.

The magmatic rocks hosting the Aisymi-Leptokarya porphyry Mo deposit were emplaced in a back-arc geotectonic regime according to Menant et al. [36].

A post-subduction tectonic environment of porphyry formation has been recognized for porphyry deposits worldwide [37] and has implications for some porphyry molybdenum deposits such as the 27 Ma old Quartz Hill, Alaska (USA) [38], the 33 Ma old Mačkatica (Serbia) [39], the 18 Ma old Pinarbaşi (Turkey) [40], the 4 Ma old Malala (Indonesia) [41] and the Shapinggou and Tianmugou, China, which were formed in a post collisional tectonic setting [42].

These post-subduction porphyry Mo deposits, as well as the studied Aisymi-Leptokarya porphyry Mo deposit, share common features with the arc-related, or Endako-type and the collision to post-collision–related, or Dabie Shan, porphyry Mo deposits, as for example the low Nb and Rb contents in the causative intrusion [43]. Despite its post-subduction geochemical affinities, it cannot be classified as Climax-type porphyry Mo deposit, since the hosting intrusives display no features of anorogenic magmatism.

The Re anomalies in the analysed molybdenite are in accordance with the observations of Voudouris et al. [15], who reported moderate to extremely-high Re content in molybdenites from a number of porphyry-type deposits in Greece.

The enrichment of Bi, Pb and Zn in the polymetallic veins in the studied prospect is also a common feature of many porphyry Mo deposits worldwide [38]. Furthermore, these deposits are known to be enriched in elements like Sn, Bi, Zn, Pb and Ag [38,44]. This is consistent with the presence of kesterite, bismuthinite, sphalerite and galena in the studied prospect.

Aplitic textures in the microgranite porphyry, which include micrographic and spherulitic quartz-feldspar intergrowths, are common in many porphyry Mo deposits [38,45]. According to Taylor et al. [38] the formation of aplitic texture is regarded as a quenching feature because of rapid ascent and loss of volatiles from the magma due to rapid crystallization of the viscous melt. Candela [45] considered textural variants like those present at Aisymi-Leptokarya microgranite (i.e., porphyritic, aplitic, micrographic and dendritic, acicular and/or skeletal crystals) to be indicative of undercooling, volatile exsolution and ore formation.

Recently, Perkins et al. [28], extending previous studies of Del Moro et al. [24], classified the magmatic rocks of the Maronia-Leptokarya corridor, into two, temporally and geochemically distinct, magmatic complexes, the Kassiteres–Leptokarya magmatic suite and the Maronia plutonic complex respectively. Both complexes comprise magmatic rocks with calc-alkaline to shoshonitic compositions and post-collisional affinities. Porphyry-style Cu-Mo-Au-Re mineralization, has been recognized in both magmatic complexes and has been attributed to three mineralizing events [15,16]. These events are related to granodiorite- and microdiorite porphyries in the Kassiteres-Leptokarya complex (e.g., the Pagoni Rachi and Konos Hill porphyry-epithermal deposits) and to granite porphyry in the Maronia complex.

The igneous rock hosting the studied mineralization is a microgranite porphyry, similar in composition to that hosting the Maronia porphyry Cu-Mo deposit. However, the studied porphyry event lacks any enrichment in Au, Cu and Re.

Further field and laboratory work aims to establish the mechanism for elemental enrichment in the studied mineralization, by testing the hypothesis of vapor versus fluid transportation as has been observed in both active volcanoes (e.g., Etna, Italy, Lewotolo and Merapi, Indonesia, Kudryavy, Russia) and magmatic-hydrothermal systems (porphyry and epithermal systems) [46,47,48,49,50,51,52].

5. Conclusions

The newly-described porphyry Mo prospect in the Aisymi-Leptokarya area, is hosted within a hydrothermally-altered microgranite porphyry and to a lesser extent in the Leptokarya monzodiorite, emplaced in a back-arc geotectonic regime. Hydrothermal alteration includes potassic rimmed by propylitic, overprinted by silicic/sericitic assemblages. Mineralization is found in the form of quartz stockwork veins as well as disseminations in the host rocks. It comprises pyrite, molybdenite, kesterite, bismuthinite and galena. Base metal veins overprint and occur peripherally to the porphyry style mineralization and are associated with sericitic alteration. Bulk ore analyses from porphyry-style mineralized samples yielded very high Mo values. Se, Bi, Sn are also enriched, while the base metal veins are characterized by enrichment in Bi, Sn and Ag.

The studied mineralization shares similarities to other porphyry Mo deposits emplaced in post-subduction settings elsewhere.