Conference Agenda

The Werra Potash District is located on the border of the federal states of Thuringia and Hesse. Mining has taken place in this area for more than 125 years. The mined area is larger than the city of Munich. The two potash seams in this area, called the Thuringia and Hesse Potash Seams, are generally between 3 and 5 meters thick and are located in the Werra Salt, which is 300 m thick. There are two active mines, Hattorf-Wintershall and Unterbreizbach, in which approximately 19 million tonnes of raw salt are mined annually. Exploration is very important for mining in terms of being able to forecast and obtain information about the thickness and mineralogy of the potash seams, the presence of basalt dikes and areas with hydrogeological risks or gas hazard areas.

In general, exploration can be divided into two categories: surface exploration and underground exploration.

Surface exploration: there are many surface drill holes and shafts from the last century that allow conclusions to be drawn about the geology and mineralogy of the potash seams and the overburden.

In addition, numerous geophysical measurements are carried out like seismic surveying, gravimetric surveying and geomagnetic measurements.

Underground exploration: in the two active mines, underground drilling with a length of more than 80 km per year is carried out. All underground drill holes are measured using 3D radar. All geological data are processed in a 3D geological model, which enables forecasts for mine planning, resource estimation as well as geomechanical modeling.

In-mine seismics provide a better resolution and spatial coverage than surface exploration methods such as 2D or 3D seismics, enhancing the exploration around underground facilities. Over the past decades, seismic exploration techniques have been developed to address challenges in exploring ahead and around tunnels and mines. Methods such as reflection seismics and tomography are applied, taking into account the constraints on resolution and exploration range due to the distribution, accessibility, and shape of in-ground cavities.

The major challenges for the application of underground seismic exploration include avoiding cost-intensive downtimes of construction and production, as well as minimizing risks to underground facilities for safety reasons. The Integrated Seismic Imaging System (ISIS) largely integrates seismic exploration into the workflow of tunnel construction. ISIS has been improved to 3D underground seismics within the Helmholtz Innovation Lab 3D-Underground Seismics. For a detailed seismic exploration, seismic sources and receivers are used in all accessible underground spaces. The exploration capabilities were enhanced with a seismic borehole tool for exploration ahead, a borehole receiver chain, and a borehole source in exploration boreholes.

With efficient impact hammers or magnetostrictive vibrators as sources and three-component receivers, our 3D underground seismics can resolve and image 3D structures in underground with reconnaissance depths up to several hundred meters and resolutions of dm to m. Especially for exploration in clay-bearing salt reservoirs 3D underground seismics is an alternative to the established GPR. We present the components of our 3D-underground seismics and discuss their applications based on case studies in various salt mines.

We explore this question using the example of salt structures in Northern Germany. The salt mines in the North German basin are among the best explored in the world. The question now arises as to whether findings on the internal structure of these salt structures also allow conclusions to be drawn about previously unexplored diapirs. BGR worked on the crucial question posed by BGE on the prediction of homogeneous salt volumes in saline rocks. However, improvements in the prognosis could also support the exploration and possible future economic use (as storage caverns) of underexplored salt structures, for example in the German North Sea. Our method is based on the definition of several basin-wide assessable proxies, which suggest an influence on the internal structure and its variability with regard to the utilization of the salt structure. Furthermore, additional findings on genesis, kinematics or the detailed internal structure are discussed which cannot be directly transferred into a basin-wide proxy but can contribute to the evaluation of the variability of the internal structure. Due to the wide range of influencing factors to be discussed, our presentation will focus in particular on new findings on salt tectonics from the comparison of the analyzed structures, but also on the given limitations of a prediction of the internal structure. In summary, certain types of salt structures that have passed through certain evolutionary stages indicate a higher probability of larger salt homogeneous volumes in economically exploitable depths.

Rock salt is a valuable commodity for the food and fertiliser industries. It is also used as a host for artificial underground structures, such as caverns. As part of Germany's transition to net-zero energy by 2045, rock salt caverns will continue to be needed, but they must be suitable for storing green hydrogen. Salt deposits could also provide a potential source of lithium, with German demand currently being met by imports. However, more information is required to understand the potential of rock salt deposits and to decipher their suitability.

Several stratigraphic salt horizons occur in the geological record of Schleswig-Holstein, ranging in age from the Triassic (Keuper, Muschelkalk, Bunter) to the Permian (Zechstein, Rotliegend). The economically exploited horizons are of Zechstein and Rotliegend ages and often form salt domes and walls. A special feature is the so-called "Doppelsalinare", where older Rotliegend salt is intruded into younger Zechstein salt due to rheological processes.

The aim of this study was to characterise the different salt horizons in terms of their mineralogy and geochemistry and to identify any potential lithium resources. To achieve this, rock salt samples were examined by polarised microscopy, quantitative mineralogy was determined by X-ray diffraction, while geochemistry was analysed by X-ray fluorescence and inductively coupled plasma mass spectrometry.

Our results show that each stratigraphic salt horizon is characterised by a unique Br-Cl spectrum, with lithium and other trace elements also showing distinct patterns.

Two significant potash-bearing basins occur within Central Asia. The Pricaspian Basin refers to an approximately 600 km wide (east-west) structure at the northern end of the Caspian Sea. This structure is filled with up to 4.5 km thick Permian (Kungurian and Roadian (Kazanian)) evaporite rocks and covered mainly by clastic sediments. Due to the large thickness of overlying sediments, diapirism of the salt rocks started with an initial movement phase between the late Permian and the Triassic and a later movement phase in the period between the Juraissic to the Neogene. Several hundreds of salt structure, that bring the potash salt close to the surface are known within the basin.

The Central Asian Salt Basin is a Jurassic to Early Cretaceous evaporite basin that spans across Uzbekistan, Turkmenistan, Tajikistan and Afghanistan. Occurrences of potash salts are largely confined to the Late Jurassic Gaurdak Formation, though evaporites of Paleogene age are also known. The deposition of the salt deposit is connected to the development of the Neotethys. Maximum thickness of the Gaurdak Formation is about 1,200 m with the evaporites being thickest in the vicinity of the Gissar Range. Clastic and carbonatic sedimentary rocks make up the hanging wall of the formation. The basin was divided by uplift of the Gissar range in Miocene times into the Amu Darya Basin towards the west and the Afghan-Tajik Basin to the east. Salt rocks are present at or close to the surface around the Gissar range.