Field-trip to epithermal and VMS mineralizations of the Rhodope Metallogenic Province (Greece-Bulgaria)

Introduction

On 15^th and 16^th October 2016 the AUTH SEG Student Chapter organized a field trip in Southern Bulgaria and Northeastern Greece (Fig. 1). A group of 20 members of the chapter, using 2 nine-seat vehicles and one car, visited a number of ore deposits of the Rhodope Metallogenic Province. The field trip was organized by Efi Petika, 2015-16 Chapter’s secretary, with the guidance of the Assistant Professor Vasilios Melfos, Academic Advisor of the chapter. In total 12 undergraduate students, 6 MSc students and 2 PhD students participated at this field trip.

Objectives

The field trip was focused on three significant ore deposits of Southern Rhodope Core Complex and on the abandoned processing plant of the Kirki mine (Thrace, Greece). The Tertiary Rhodope Metallogenic Province belongs to the Western Tethyan Metallogenic Belt and spreads to Bulgaria and Greece hosting several major ore deposits of various types. The AUTH SEG student chapter visited Ada Tepe, a sedimentary-hosted low-sulfidation epithermal gold deposit that in the present is operated by “Dundee Precious Metals”, the Perama Hill deposit, a high- and intermediate-sulfidation Au-Ag-Te-Se epithermal system owned by “Eldorado Gold”, the Xylagani Mesozoic gold-bearing Fe-Cu VMS deposit and the abandoned processing plant near Kirki of Alexandroupolis (Fig .1). The field trip was a great opportunity for the students to visit deposits of a great scientific importance, near our host Aristotle University of Thessaloniki. Furthermore, they got familiar with the regional geology, the ore deposit types and their ore paragenesis, and had the chance to explore the specific metallogenic and the structural control processes of these deposits.

Activities Program

The field trip started early in the morning, on Saturday 15^th October 2016, with three vehicles from Thessaloniki (Greece) to Krumovgrad (Bulgaria). After approximately 5 hours we arrived at the offices of “Dundee Precious Metals” in Krumovgrad. At our arrival the chief geologists of the company, Yaroslav Dintchev and Tsvetana Jeleva, waited for us and lead us to the presentation room, where we attended a presentation by Y. Dintchev about the activities of the mining company, the regional geology, the mining history of Ada Tepe deposit and its metallogenic and structural characteristics. Ada Tepe is a sedimentary-hosted detachment-associated low-sulfidation epithermal gold deposit. It is hosted in Maastrichtian–Paleocene sedimentary rocks above a detachment fault at the contact with the underlying Paleozoic metamorphic rocks. Dating of the ore mineralizing processes revealed older ages than the adjacent magmatic rocks. Gold mineralization is located in: (1) a massive, tabular ore body above the detachment fault; and (2) open space filling ores along predominantly east–west oriented listric faults. The ores are zones of intensive silicification and brecciation synchronous with the detachment faulting.

After the end of the presentation session, we discussed our questions and then visited the drilling cores (Fig. 2) where we could observe the ore minerals (including visible gold!), the ore textures (breccias, colloform, bladed and banded textures), the hydrothermal alterations (mainly alunite) and the host rocks.

After fruitful discussions with the two geologists we moved to the Ada Tepe hill with the company’s vehicles. We were excited with the prehistoric gold mines since 3^rd millennium BC. The mineralization with an intense silification was formed at the hanging wall of a long impressive detachment fault (Fig. 3). At this point, T. Jeleva explained us the regional geology and presented the Au and Ag grades of the deposit. We were also informed by the company geologists that the AUTH SEG student chapter was the last group visited the Ada Tepe Hill at the present situation, as in the following days the company started the infrastructures for the open pit!

Our last stop in Krumovgrad area was about a silica sinter and the breccia in the sinter mixed with sandstone of a low-sulfidation system. We really appreciate the effort of Y. Dintchev and T. Jeleva, who spent more than 6 hours with our chapter to present and explain all the details of the Ada Tepe ore deposit. We also thank the staff and the Directors of “Dundee Precious Metals” in Krumovgrad who helped in many ways this field trip in Bulgaria (Fig. 4).

Next day, on Sunday 16^th October, we drove from Krumovgrad to Komotini in Greece, and then to Perama Hill deposit (Fig. 1) owned by “Eldorado Gold”. It is a high- and intermediate-sulfidation Au-Ag-Te-Se epithermal system located at the eastern margin of the Petrota graben. The mineralization forms ore veins in the Oligocene silicified and argillic-altered andesite (33.1 and 30.8 Ma) and oxidized Au-rich mineralization in the overlying Eocene sedimentary rocks (Fig. 5, 6). The mineralization consists mainly of enargite-luzonite, tennantite, Au-Ag tellurides, and native gold. The deposit evolved from an early stage silica-pyrite rock and argillic alteration followed by the deposition of sulfide-, sulfosalt- and telluride-bearing quartz-barite veins and stockworks.

The proven and probable reserves are 975,000 oz Au @ 3.13 g/t and the measured and indicated resources 1,382,000 oz Au @ 3.46 g/t, whereas the inferred resources are 554,000 oz Au @ 1.96 g/t (Eldorado Gold 2016).We would like to thank “Eldorado Gold” for the permission to visit Perama Hill and for the continuous support of the AUTH SEG student chapter activities.

Our next stop was at the abandoned hydrometallurgy plant of the Kirki Pb-Zn sulfides mines, where numerous old tailing ponds and mine wastes (Fig. 7) have caused permanent problems due to acid mine drainage and the subsequent contamination of the ground water. The Kirki flotation plant operated between 1973 and 1992, without any Environmental Impact Assessment. It comprises eight tailings ponds close to the factory at morphologically favorable locations, requiring the minimum earthworks. They were excavated along valleys or in the flat areas surrounding the two main streams (Kirkalon and Eirini streams), without taking into consideration the effects of surface water flow. We had the opportunity to see the details of the effects caused from mine wastes and hydrometallurgy products left in situ without any environmental consideration by the state and the local authorities.

Our last target was the Xylagani Mesozoic gold-bearing Fe-Cu volcanogenic massive sulfide (VMS) deposit (Fig. 8). The mineralization shares many common features with the Cyprus-type mineralizations. It is hosted in Mesozoic meta-volcanic rocks (lavas and tuffs) which belong to the Circum Rhodope belt and have been metamorphosed to very low to low grade stage. Lensoidal silicified mineralized bodies are hosted in the metavolcanic rocks. On the basis of textural features, five types of mineralization are recognized: thin layered, disseminated, disseminated to massive and massive sulfide (pyrite or chalcopyrite-pyrite) mineralization as well as quartz veins poor in sulfides. The ore mineral assemblage consists of framboidal pyrite, pyrite, chalcopyrite, sphalerite, galena, pyrrhotite, tennantite and gold. The main gangue minerals are quartz, white mica and chlorite. VMS deposits are not so common in Greece and they are mostly of Mesozoic age. The students were introduced by the academic advisor, V. Melfos, who studied this mineralization for his PhD in early 1990’s and showed the various mineralization textures and types and their relation to the host rocks.

Acknowledgements

This field trip was a conclusion for the second year of operation of AUTH SEG student chapter. The Executive Committee would like to thank the Society of Economic Geologists for the overall support and trust provided through the 2014-2015 academic year. In addition we would like to exceptionally thank the Student Chapter Stewart R. Wallace Funding Program of the Society of Economic Geologists for the provided financial support regarding the field trip expenses. Special thanks are due to “Dundee Precious Metals” and “Eldorado Gold” for the permission to visit Ada Tepe and Perama Hill deposits, respectively.

Photos

Figure 1. Simplified map displaying the distribution of the ore deposits within the Rhodope and the Serbomacedonian metallogenic provinces in the southern Balkan peninsula. RM Rhodope Massif, SMM Serbomacedonian Massif, CRB Circum Rhodope Belt, AZ Axios (Vardar) Zone, SG Srednogorie Zone. 1. Ada Tepe; 2. Perama Hill; 3. Kirki; 4. Xylagani. (Melfos et al. 2002)

Figure 2. Drill cores from the Ada Tepe at the “Dundee Precious Metals”.

 Figure 3. The AUTH SEG Student Chapter in front of the hanging wall of the detachment fault of the Ada Tepe deposit accompanied by the geologists  Yaroslav Dintchev and Tsvetana Jeleva.

Figure 4. The AUTH SEG Student Chapter  in front of the “Dundee Precious Metals” offices in Krumovgrad, Bulgaria.

Figure 5. The AUTH SEG student chapter in front of the Au-bearing quartz-barite veins crosscuting Eocene sandstones at the Perama Hill deposit of “Eldorado Gold”.

Figure 6. The Au-bearing sandstones of Perama hill deposit that host part of the ore mineralization.

Figure 7. The AUTH SEG student chapter with the academic advisor, Prof. V. Melfos, standing on a tailing pond with acid drainage of the abandoned hydrometallurgy plant at the Kirki mines.

Figure 8. Members of the AUTH SEG student chapter investigating the ore mineralization textures at the Xylagani VMS deposit.

Submitted on behalf of

the AUTh SEG Student Chapter Executive Committee by

Margarita Melfou

 2016-2017 President