λ SEG/SEGF Student Chapter Stewart R. Wallace Funding National and Kapodistrian University of Athens Faculty of Geology and Geoenvironment Field Trip Report Shallow submarine hydrothermal mineral deposits and mineralized geobiology systems in emergent volcanoes the example of the Milos natural paleogeothermal laboratory April 18 th -April 23 th 2017 The team at the top of Profitis Ilias Mountain. 1
Contents Introduction and Acknowledgments... 3 Geological Background... 4 Objectives... 5 Day 1:18th of April... 6 Day 2: 19 th of April... 7 Day 3: 20 th of April... 10 Day 4: 21 st of April... 13 Day 5: 22 nd of April... 17 Final Day: 23 rd of April... 20 2
Introduction and Acknowledgments The National and Kapodistrian University of Athens, SEG student chapter organized the field trip to Milos Island as a part of the Student Chapter Stewart R. Wallace Funding. The field trip was attended by 16 persons including the team's 2 leaders Professor Stephanos Kilias and Assoc. Professor Ariadne Argyraki, 2 MSc students, 11 BSc students and 1 exploration geologist currently working in the mining industry. Over the course of the field trip we had the chance to observe some of the most unique geological formations in the world and gain a great amount of knowledge over a wide variety of different geological fields of study and also mining. All the participants are very grateful for the financial support provided by the Society of Economic Geologists. Also the participants would like to thank Imerys S.A Industrial Minerals for their hospitality and the tour in the facilities of the company. Special thanks go to Mr. Petrakis, who was our guide throughout the day that we visited Imerys. 3
Geological Background Milos island is a recently emergent (<2 Ma) volcano in the active Pliocene modern Hellenic Volcanic Arc,Greece, where arc-volcanism and seafloor hydrothermal activity are occurring in thinned continental crust. Milos hosts one of the largest active mineralized shallow-submarine to coastal geothermal systems described to date, that has been operating for ~2 My. Milos forms a distinctive and renowned on-land natural laboratory for studying volcanic-hydrothermal and geothermal processes in a submarine setting and is identified as a new metallogenic environment namely shallow submarine epithermal-style mineralization associated with emergent volcanoes. In this rapidly evolving environment, heated seawater mixes with magmatic and meteoric waters, to produce young and extremely well preserved palaeogeothermal systems that give rise to hybrid VMS and epithermal mineralization (Au, Ag, Cu±Te), and industrial mineral deposits (i.e. bentonite, perlite, pozzolanes), as the driving volcanism changes from submarine to subaerial and the system becomes open to meteoric water. Furthermore, Milos provides a unique window into the interplay between volcanic-hydrothermal, metallogenic and biological processes, it hosts the first identified ~2.0 Ma unmetamorphosed, fossiliferous sedimentary iron formation (IF) comparable to Precambrian banded iron formations (BIFs), IF is spatially associated with sedimentary manganese oxide deposits of economic potential where biological processes may have played a major role in concentrating Mn. A number of large open pit bentonite and perlite mines are operational in Milos by S&B Industrial Minerals S.A./Imerys, the bentonite open pit is one of the biggest across the world. 4
Objectives This fieldtrip was designed to give students an opportunity to: A. Examine firsthand field characteristics of near surface and surface landscape products and structures that have been preserved in a range of epithermal-style precious metal mineralization in low relief (<750m), recently emergent (<2Ma) volcanoes, in tectonically active environments. Epithermal-type mineralization in the submarine environment is a developing field for mineral exploration and exploitation and is currently attracting significant international and national research funding to help secure the supply of a range of raw materials. Epithermal paleosurfaces, i.e. near surface and surface landscape products and structures resulting from the discharge of thermal fluids, can serve as vectors to mineralization, it is therefore expected this exercise to enrich the students field experience with direct application to mineral exploration. B. Visit the main operating bentonite open pit mine in Milos and processing facilities in order to familiarize the students with sustainable mining practices, and the flow sheet of material and the full production line from mine to port facilities, and monitoring equipment of loading and hauling operations. C. Acquaint field evidence for geobiological activity that contributes to the metals inventory and to mineralization processes in shallow-submarine paleo-geothermal and volcanichydrothermal systems. To this end students will examine field characteristics of the first identified modern analogue of Precambrian banded iron formations (BIFs) and spatially associated Mn ores with Microbially Induced Sedimentary Structures. D. Stimulate reflection and discussions on the sustainable case of modern Milos economy that is based on mining and tourism, activities that go hand-in-hand for the benefit of the local community that enjoys this fruitful and sustainable symbiosis. 5
Day 1:18 th of April Midday gathering in Piraeus port and travel by boat to Milos, talks for safety and logistics briefing. Arrival in Milos, Adamas port, after a 3-3.5 hours trip. The afternoon of the first day included a drive to Nychia obsidian deposit and the prehistoric obsidian quarries at Milos island. The obsidian of Nychia deposit. 6
Day 2: 19 th of April The second day was devoted to Kalamos active volcanic fumarole field, and the Paleochori coastal geothermal field in the south coast, this drive crosscuts a small shallow crater built by subaerial block-and-ash flow deposits generated by explosive eruptions at the Firiplaka rhyolitic complex. The Kalamos Palaeochori Bay in an active volcanic-hydrothermal and geothermal field. Active seafloor hydrothermal venting is manifested at Paleochori Bay as extensive areas of diffusively venting CO2 rich gas fluids,microbial mats and Mn(Fe) and As rich hydrothermal precipitates fossil hydrothermal vents with advanced argillic alteration minerals and native sulfur deposits, are exposed along the Paleochori beach. Active fumaroles depositing native sulfur occur in biotite-quartz-phyric rhyolite in Kalamos. After Paleochori Bay we visited the abandoned sulfur quarries where we observed the white vuggy silica cap and the extensive advanced argillic alteration. A subaerial volcano-sedimentary formation on the way to Kalamos Bay. 7
The active geothermal field of Kalamos. Banded multicolored tuffs near the Kalamos active geothermal field. 8
The Paleochori Beach coastal geothermal field and the altered rock as a result of the geothermal and hydrothermal activity. 9
Day 3: 20 th of April The third day was devoted to visiting the Profitis Ilias-Chondro Vouno Au-Ag epithermal deposit and the silica sinter outcrops. The Profitis Ilias Chondro Vouno (PI-CV) epithermal Ag Au deposit constitutes a 20 km 2 epithermal system with a combined resource of 0.8 Moz gold and 12.4 Moz silver. Mineralization is hosted by altered rhyolitic pumiceous tuffs-ignimbrites and consists of crustiform/colloform-banded quartz-chalcedony veins related to quartz, adularia, sericite wallrock alteration. Mineralized steep vein system extend to depths of at least 300 m below the current surface (~600 m above sea level). Metallic minerals include pyrite, galena, chalcopyrite, sphalerite, marcasite, tetrahedrite, native gold/electrum, silver halogenides (chlorargyrite, iodargyrite), atacamite, and trace petzite. Sulfides mainly occur deep in the system as disseminated stockwork mineralization of unknown vertical extent. The PI-CV deposit is geographically associated with characteristic epithermal paleosurface features. These include hot spring silica (chalcedony) sinter accumulations, apron facies silica sinter and sinter mounds around geyser vents. Fossilized silica bubble at the silica sinter formation. 10
The view of Adamantas Bay from the top of Profitis Ilias Mountain Au bearing quartz veins at Profitis Ilias Mountain. 11
Au bearing quartz veins at Profitis Ilias Mountain. 12
Day 4: 21 st of April The fourth day was dedicated to visiting the premises and mining zones of S&B Industrial Minerals SA/Imerys at Voudia (NE Milos), the Aggeria operating bentonite open pit mine and processing facilities, the flow sheet of material and the full production line from mine to port facilities, and monitoring equipment of loading and hauling operations. The Aggeria Bentonite open pit mine that has been in continuous operation since 1968, is one of the largest in the world. Aggeria mine is 700 m wide, and is the main of three mines of a large bentonite deposit which extends over an E-W distance of 2.5 km. Milos produces ~1/10 of the world bentonite production (~1.1. million tons). Bentonite deposit formed from the alteration of pyroclastic flows that took place in a marine environment. The deposit may exceed 60 m in thickness in a series of successive flows. Red marl overlies the bentonite. The final stop of the day was at the sub-volcanic dacite intrusion at the Filakopi area. The Aggeria Bentonite Mine. 13
The team in the pit of the mine. Briefing at the HQ of Imerys. 14
Imerys S.A. Voudia processing plant. Barite at the abandoned barite mine. 15
The dacite sub-volcanic intrusion. 16
Day 5: 22 nd of April The final day included a visit to the Cape Vani Mn-Fe (-Ba) deposit, the old abandoned Mn mine and surrounding area. The Cape Vani Mn Fe(Ba) deposit. Manganese ore Cape Vani operated as Mn mine during two periods: 1886-1909 and 1916-1928. In the first period 220, 000 tons of manganese ore have been produced. Reserves amount to 2.1 million tons at 14.4 % Mn. Beneficiation studies that were conducted for barite-bearing rocks have resulted in high-grade barite concentrate. Ore-grade beds have mean composition: 14.6% Mn, 12.8% BaSO4, 62% SiO2, and 7.5% Fe2O3. Manganese ore occurs in siliciclastic sequence of the the Pliocene-Pleistocene Cape Vani sedimentary basin (CVSB) that is nested by submarine dacitic/andesitic lava domes and consists chiefly of todorokite, hollandite and manjiroite that cement volcaniclastic sandstone/sandy tuff. Ore formation took place in a volcanic-tectonically uplifted, sunlit and oxidizing paleoenvironment of interacting shallow-marine/tidal-flat sedimentation, microbial ecosystem, and hydrothermal vent-sourced metals (Mn 2+ ) and bioessential elements. Mn oxides formation at Cape Vani. 17
Iron formation Submarine hydrothermal iron formation (IF) in the CVSB occurs within the Cape Vani siliciclastics sequence in association with the Mn ore. The IF displays banded rhythmicity of alternating Fe(hematite)- and Si-rich bands analogous to Precambrian banded iron formations (BIF) and earlier reports showed association with anoxygenic phototrophic biofilms and abundant microbial fossil assemblages. Iron formation sample from Cape Vani. 18
Amorphous silica at Cape Vani. 19
Final Day: 23 rd of April Prior to our departure we visited the Sarakiniko area. The Sarakiniko area is formed by layers of pumice tuff formations. In the area there is also an extensive ignimbrite formation as well as active faulting that can be clearly observed in the formations of the area. The lunar landscape of Sarakiniko hosts some of the most beautiful beaches of the Aegean Sea. Faulting is clearly observed in the formations of the area. 20
Ignimbrite formations in the area. 21
The blue waters of the Aegean Sea at Sarakiniko. 22