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.
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.