June 9th 2017
Mining in Bavaria – Exploration, exploitation and usage by Bernhard Ratzke
Bergbau in Bayern – Exploration, Gewinnung und Anwendung
Bergbau in Bayern – Exploration, Gewinnung und Anwendung
In the introduction Mr. Ratzke stated that bentonite - named after Fort Benton - is a wrongly labled, industrial mineral which composition is mainly of montmorillonite, kaolinite, feldspar, mica, calcite, quartz, illite and cristobalite and can be found in the regions between Ulm, Augsburg and Passau and in the triangle made up by Moosburg, Mainburg and Landshut, in which the Clariant Produkte GmbH is mining their bentonite. Following the introduction it was explained, that there are two types of bentonite: the Na-rich and the Ca-rich ‚bavarian type‘, which is less reactive than the previously mentioned Na-bentonite and therefore usually chemically activated. This activation is either done acetous by hydrochloric acid and used for the food industry afterwards, or alkaline by sodium bicarbonate and then used for the casting or drilling industry. The speaker then talked in detail about the steps necessary to open a new mine. At first the Bergamt Süd-Bayern (Mining authority of southern Bavaria) has to issue a drilling license, after which the landowner has to give his permission for drilling on his property before exploration itself can start. For exploration sampling-holes are drilled by a vehicle-mounted drilling rig to the upper boundary of the bentonite, out of which samples are taken by a twist drill. These sampling-holes are drilled in a distance of approximately 80-100 m and when Bentonit is found the distance is lowered to create a more accurate representation of the deposit, the so called „Lagerstättenplan“, which is the next step on the way to a new mine. According to this „Lagerstättenplan“ the area of mining is determined, followed by the aquisition of the needed land. Before mining can begin, an operating-plan has to be established, in which size and position of the mining area, the thickness of the bentonitelayer, overburden, recultivation, biology, archaeology and many more topics have to be detailed. After mining has ended the area is recultivated and given back to the previous owner. At the end Mr. Ratzke stated that on average there are 11 m of overburden and only 1.5 m of
bentonite in the six active mines the Werk Bergbau Clariant Produkte GmbH currently opertes, which produce 340‘000 tonnes of bentonite each year. Also there are currently two mines in preperation and six in recultivation. On our field trip to the Werk Bergbau Clariant Produkte GmbH on the 9th of June 2017 we were able to attend the drilling process during the last few meters of drilling and the taking of the samples, of which we were allowed to take some with us. During drilling it was stated that the well trained drilling rig operator is able to notice the upper boundary of the bentonite due to a slight rise in pressure needed to pierce the bentonite, in comparison to the pressure needed to drill through sand and gravel. Right after that we visited one of the six active mines, where Mr. Ratzke gave a short overview over the different qualities of the bentonite and the process of its mining. After that we had some time to take a look around the mine, which luckily was not operating this day.
You can also see some pictures of our fieldtrip when you click here.
December 13th 2016
"Fluid-mediated metal transport in subduction zones and its link to arc-related giant ore deposits: Constraints from a sulfide-bearing HP vein in lawsonite eclogite (Tianshan, China)“ by Dr. Reiner Klemd, professor of geochemistry and economic geology at the Geozentrum Erlangen-Nürnberg
In the research area he proved a continous slab watering and fluid flow through and out the slab, so there was a clear transition from the H2O-rich, ‘wet’ blueschist to the ‚dry‘ eclogite formed by devolatilization. This process leads to a reduction of porosity and permeability. Subsequently he distinguished two different forms of fluid-transport: first the pervasive form within a dihedral angle of at most 60o, which always needs a fluid for dissolving, transport and precipitation. If the angle is bigger than 60o – as in this example – , no fluid flow is possible. Secondly the channelized fluid flow along fractions oft he slab (dehydration embrittlements), which is considerably stronger.
In the mesozoic Tianshan-area the biggest accessible open blueschist can be found in the so called eclogitic belt, which is generally dominated by HP pelitic-felsic schists. After the disappearance oft he glaciers, glaucophane and omphazite are located next to each other, differentiated in pillows and venes. Furthermore Klemd recognized, that the p-T-pathes were strongly different in the same zone, probably arised out of the location at a subduction zone where the rock was altered. He reasoned that the eclogite-front moves forward and replaces the glaucophane, whilst the freed H2O escaped via veins, the ‚fluid-highways‘. This and the metasomatized upper mantle are leading to a strong enrichment of Sr, Pb (300%; circa 110% in the eclogitic selvage) and metals like Cu, Au and Ga.
November 14th 2016
"Ore formation and hydrothermal processes in Schwarzwald" by Prof. Gregor Markl
In the introduction Prof. Markl gave a short overview on the geographic and geological situation of the Schwarzwald, which is located in the south-west of Germany, and therefore mentioned that about 1000 hydrothermal veins - formed during the Jurassic and Cretaceous - can be found there. Unfortunately it is only visible in one active mine and one that will open in the upcoming years in that region.
He then continued with the explanation of the general forming of ore deposits by mixing of fluids from the sediment and basement aquifer in the area around the active Klara-mine and stated for this purpose that fluid-mobilisation and previous forming of salt-deposits is necesarry because the Cl-ions in the fluid increase the dissolubility of e.g. copper and silver.
To prove this concept Prof. Markl showed that the possible fluid-mobilisation by heating, salt-enrichment or diagenese only occur in an area between 6 and 12 cubic kilometers, then mentioned that the fluid-volume in Schwarzwald was somewhere around 11 cubic kilometers and concluded that the process of fluid-mixing is therefore possible.
The average composition of this hydrothermal veins with a volume of about 10,000,000 m³ had a percentage of 46% fluorite, 35% quarz and 19% barite and depict a perfect record of palaeo-fluid-flows.
With 26 visitors the talk was well attended.