Category Archives: Our activities

The traditional annual field trip (October 3-5, 2014) of our chapter has mainly focused on stratiform iron mineralization in the Neoproterozoic metasediments of the Děsná unit and iron mineralization of the Lahn-Dill type in the Devonian volcanosedimentary cover in the Jeseníky Mts., northeastern Bohemian Massif.

The main part of the excursion was designed as a transsect across the metamorphic and deformation gradient imposed on the same iron-bearing precursor of the Lahn-Dill type. We have thus investigated transition from jaspilites to metamorphosed magnetite ores as well as their banded magnetite-quartz counterparts. This provided many interesting examples, based on a number of small historically mined occurrences.

The 13 students participated in this 3-days excursion, which was led by David Dolejs.

SGA News no. 36 page 17

The SGA Student Chapter Prague organized one of its field trips to visit sedimentary iron mineralization in the Paleozoic volcanosedimentary sequences of the Prague Basin (Barrandian) in central Europe.

The Barrandian is a classical area of Neoproterozoic to Devonian volcanosedimentary strata, affected by the Variscan orogeny. In the Middle Cambrian through Ordovician, the deposition of predominantly shallow marine conglomerates, graywackes, mudrocks and shales was accompanied by intermittent volcanic activity of calc-alkaline basalts, andesites, rhyolites and their subaqueous pyroclastic products. Several of these volcanic centers were source of energy and chemical components for the formation of perivolcanic or hanging-wall iron-oxide mineralization. The formation of ironstones continued to stratigraphic hanging wall as well as more distal sedimentary settings, and gradually evolved into oolitic iron deposits, which occur as several horizons In the Ordovician siliciclastics. The deposition of these siderite-, chamosite- or hematite-bearing oolitic iron ores coincides with their worldwide formation on shallow marine continental shelves at this time interval. Ironstones in the Barrandian represent classical and previously economic accumulations, which were exploited from prehistoric times until 1960’s. The field stops offered a rich opportunity to compare volcanic and epiclastic products and several mineralization styles, which recorded different influences of volcanic activity, hydrothermal and subaquatic alteration and redox gradients during iron precipitation and diagenesis.

SGA News No 36 page 16

The second field trip organised by the SGA Student Chapter Prague in 2013 was aimed at Slovakia and Hungary. Purpose of this excursion was to get in touch with different geological settings than the Bohemian massif. Major part of Slovakia and the northern part of Hungary (Tokaj Mountains) are situated in the mountain range of Western Carpathians. This system evolved during the Alpine orogeny as the northern branch of the Alpine-Himalayan fold and thrust system called the Alpine belt.

SGA News no. 35

The first field trip organised by the SGA Student Chapter Prague in 2013 lead to the famous Alpine deposits Habachtal and Knappenwand in Austria. Habachtal emerald deposit has been known since the Roman times. This locality provides the best emeralds in Europe and it is the only location where emeralds of gem quality occur. The mine has been active until these days, where the Steiner family has been irregularly mining the precious stones using just a simple technology. Access to the adit collar is rather difficult requiring good physical conditions. The emerald deposit is located at the tectonic contact of ortho-gneiss and basic to ultrabasic metamorphosed rocks: amphibolite,mica schist, serpentine and talc schist. The most important emerald bearing rocks are biotite-, talc- and actinolite schists occurring at the margins of serpentine bodies. The emeralds mostly appear in the form of automorphic hexagonal columns in a size up to 4–5 cm. The emeralds can be found in the Habach valley under the adit where they are transported by water.

SGA News no. 34 

Main focus was on the origin of ore deposits in both the Czech and German parts of the Krusne hory/Erzgebirge Mts. The main attraction of the field trip was an underground visit in the historical mines of Ehrenfriedersdorf and Pöhla and at the Zlatý Kopec near Boží Dar (Gotesgab). The common feature of all localities is a widespread cassiterite mineralization related to the hydrothermal fluid flow from late Variscan biotite to topaz granites (327–312 Ma). The tin deposits are located in the paleoroof of the Krusne hory/Erzgebirge batholith formed by Neoproterozoic and Early Paleozoic supracrustal sequences: phyllites, micaschists, paragneisses, amphibolites, and marbles that were altered and host stratiform or disseminated mineralization. Altered rocks are also intersected by numerous ore-bearing veins. The highest abundances of economic minerals are concentrated in skarns that formed by replacement of dolomites or surrounding metasediments and metavolcanics. Therefore skarns were target of historical mining as well as post-war exploration and became the principal target of our field trip.

SGA News no. 33

As in the previous years, the autumn field trip of our Student Chapter represents the main annual educational event. This year, our target was to visit various products of volcanic activity in the Neogene arc in the Carpathians (Slovakia) and inspect their associated mineralization types, ranging from skarn to porphyry, mesothermal and epithermal styles.

During four days we were exploring different mineralization types associated with the evolution of the Miocene Štiavnica stratovolcano: gold mineralization of the intermediate-sulfidation type in Banska Štiavnica and Hodruša (museum and dump of the Rozália mine), magnetite skarns in Úškrtova Dolina, and secondary mineralization in L‘ubietová and Špania Dolina. We also had the opportunity to visit the secondary limnoquartzite deposits with plant remnants in the Kremnické Vrchy Mts.

The area is located in the western part of Slovakia. The Banska Štiavnica ore district is situated in the central zone of the largest stratovolcano in the Central Slovakian volcanic field of Neogene age, emplaced in the inner part of the Carpathian arc overlying the Hercynian basement. The volcanic activity was related to subduction of the flysch belt under the Carpathian arc and to subsequent back-arc extension.

An epithermal system related to the postcaldera uplift has the dominant significance in the metallogeny of the ore district. According to their ore assemblages, the epithermal veins were divided into three types:
1) base-metal veins
2) Au-Ag veins in the central or western part of the horst
3) Au-Ag veins related to marginal faults of the horst
Formation of the hydrothermal system and precipitation of Au mineralization is related to the initial stage of caldera subsidence that changed the hydrologic conditions.

SGA News No 32, page 3

The metamorphic complexes of the northwestern Bohemian Massif host several mineralization styles that span stratiform base-metal deposits, stratabound skarn mineralization as well as low-temperature hydrothermal veins.
During the second trip in 2012, our chapter visited several examples of these mineralization styles, exposed mainly in historical mines.

–The Mědník deposit near the village Měděnec: calcic-ferroan skarn with stratabound sulfide mineralization, produced silver, copper and iron since medieval times. We also visited a Země zaslíbená mine of this mineralization in Měděnec.

–Mýtinka location: about 4 km SW of Měděnec; a complicated fold structure containing migmatites, orthogneisses and mica schists intensely fractured and filled with quartz gangue. Quartz veins located at fault intersection are usually mineralized with hematite that formed from low-temperature hydrothermal fluids.

SGA News No 32, page 9

Our SGA Student Chapter devoted its first field trip in 2012 to cassiterite mineralization and associated alteration in the northwestern part of the Bohemian Massif. We visited the Hieronymus mine at Čistá and the active quarry at Krásno.

–The Čistá tin deposit:  the formation of postmagmatic greisens and late hydrothermal vein-type mineralization (Sn-W).

–The active quarry at Krásno: open pit exploits alkali feldspar granites and alkali feldspathites as raw materials for ceramic, glass and chemical industry.

SGA News No 32, page 1

Date: November 21, 2011
Program: visit to the Centrum black coal mine, the only underground mine in operation in the Czech Republic, visit to several mineral occurrences related to the Tertiary volcanic activity in the Northern Bohemia
Leader: Ing. Pavel Lička (North Bohemian Mining Corporation)