Fluid evolution in Tertiary magmatic-hydrothermal ore systems at the Rhodope metallogenic province, NE Greece. A review

Abstract

Characterization of various fluid parameters in magmatic-hydrothermal ore mineralizations is potentially essential for interpretation of the conditions of formation and therefore for mineral exploration. Fluid inclusions can provide a useful and promising tool in the research of the ore forming processes in these systems. This review focuses on the nature, composition and origin of magmatic-hydrothermal ore forming fluids involved in the formation of representative Tertiary ore deposits at the Rhodope metallogenic province in NE Greece. These deposits are spatially related to Tertiary magmatism in NE Greece. Case studies are presented here and include an intrusion-hosted sheeted vein system (Kavala), a Au-rich carbonate replacement and quartz-vein mineralization (Asimotrypes), mineralized veins in Eptadendro-Rachi and Thasos island (Kapsalina and Panagia), porphyry Cu-MoRe -Au deposits in Pagoni Rachi and Maronia and epithermal Au-Ag mineralizations in Perama and Loutros. Hydrothermal fluids rich in CO 2 together with elevated Au and Te content are common and occur at the Kavala intrusion hosted sheeted vein system, at the Asimotrypes Au-rich carbonate replacement mineralization and at the Panagia (Thasos) vein system. We classify all these ore mineralizations as intrusion-related gold systems (IRGS). Transport and precipitation of metals including Au and Te is favoured when CO 2 is present. Precipitation of the ore mineralization takes place due to the immiscibility of the carbonic and the aqueous fluids which have a magmatic origin with the contribution of meteoric water. Cooling of magmatic hydrothermal fluids and dilution with meteoric water is a common cause for ore mineral formation in the vein mineralizations of Eptadendro/ Rachi and Kapsalina Thasos. At the Pagoni Rachi and Maronia porphyry deposits, boiling and the high proportion of the vapour phase are the most essential fluid processes which affected ore formation. The epithermal veins overprinting the Pagoni Rachi and the Maronia porphyry systems and the HS-IS epithermal system in Perama Hill and the IS epithermal mineralization in Loutros are characterized by low to moderate temperatures and low to moderate salinities. Cooling and dilution of the ore fluids are the main process for gold precipitation. We conclude that the different fluid parameters and microthermometric data indicate a variety of fluid origin conditions and sources which can affect the strategy for exploration and prospecting for gold, rare and critical metals.

Metamorphic and Metasomatic Kyanite-Bearing Mineral Assemblages of Thassos Island (Rhodope, Greece)

“…Voudouris et al [20] documented at the top of the formation the presence of an orthogneiss at the contact with the paragneisses/mica schists. Although not exposed, a granitoid is considered to be genetically related to the widespread Miocene gold mineralization in the area [27].…”

“…The certified reference materials NIST SRM 610 and 612 (concentrations from Jochum et al [57]) were used as external standards for calibration of all analyses; they were analyzed twice at the beginning and at the end for each kyanite sample, following a bracketing standardization procedure. 27 Al and 29 Si were measured with a dwell-time of 10 ms; the following 17 isotopes were measured with a dwell-time of 20 ms for each: 7 Li (limit of detection of 20 ppm), 23 Na (70 ppm), 24 Mg (1 ppm), 39 K (50 ppm), 43 Ca (6000 ppm), 47 Ti (20 ppm), 51 V (1 ppm), 53 Cr (15 ppm), 55 Mn (15 ppm), 57 Fe (150 ppm), 63 Cu (10 ppm), 66 Zn (10 ppm), 88 Sr (0.5 ppm), 107 Ag (2 ppm), 137 Ba (3 ppm), 197 Au (1 ppm), and 208 Pb (0.5 ppm). All data were reduced off-line with the limits of detection calculated using the commercial version of Iolite (Version 3.71, https://iolite-software.com) data reduction software [58] running with Igor Pro.…”

“…The geology of Greece is marked by a recent alpine belt, which results in outstanding localities for minerals and gemstones owing to high PT metamorphic conditions and subsequent magmatism and hydrothermalism, e.g., [19][20][21][22][23]. Among these localities, the island of Thassos, in the Rhodope Belt, represents a unique mineralogical locality for kyanite and uncommon varieties of manganiferous/manganian and magnesian silicate and calc-silicate minerals, including garnet, andalusite and epidote among others [19,[24][25][26][27][28][29][30][31]. These crystals are often large (several centimeters long) and vividly colored, translucent but commonly fractured, which makes them usually inappropriate for faceting gemstones, but more proper for cabochon-shaped material.…”

Mn-Andalusite, Spessartine, Mn-Grossular, Piemontite and Mn-Zoisite/Clinozoisite From Trikorfo, Thassos Island, Greece

“…of the orthogneiss at Trikorfo is not known. Miocene granitoids are not exposed at Thassos Island, however a burried granitoid is considered by Melfos and Voudouris (2016) to be genetically related to the widespread Miocene intrusion-related gold mineralization in the area. Tourmaline at Trikorfo also occurs as a retrograde mineral, and according to van Hinsberg et al (2011) metasomatic introduction of boron on the retrograde path, is most commonly associated with the intrusion of late granites in orogenic belts.…”

Ore-forming fluids of the Fancha gold deposit, Lingbao, Henan Province

“…Fluid inclusions can preserve various geological and geochemical information during mineralization. Therefore, conducting a detailed physico-chemical and thermodynamic study of fluid inclusions can yield important data on the mineralization process, which may also inform and guide prospecting and exploration (LU, 2004;MELFOS et al, 2016;ROEDDER, 1984;TASEV et al, 2018). Therefore, our main objective focused on studying the Fancha gold deposits, and in particular, thoroughly investigating the geology, fluid inclusions and their stable isotope geochemistry.…”