Exploration potential of the Harz Mountains
The Harz Mountains have been a prospective region for more than two millennia. The area is known for its long history of mining, and contains several large and numerous small mineralisations. These include the world-class Rammelsberg massive sulphide deposit (SEDEX), wide-spread vein type mineralization (e.g. Clausthal-Zellerfeld and Bad Grund lead-zinc-silver mines), and many Lahn-Dill type volcanic-hosted exhalative mineralisations, including the Elbingerode massive pyrite deposit and countless small iron mines. In spite of the long mining history and its promising potential, the Harz has never been explored for blind deposits with the newest techniques.
Harz Minerals GmbH (HM), a fully owned subsidiary of Scandinavian Highlands Holding A/S, has obtained an exploration licence for a large part of the Harz Mountains covering c. 1250 km2. Exploration started in the western part of the Harz with an airborne TEM survey, and as a result of early success here, the focus of the exploration has been here.
The Gosetal Anomaly - SEDEX massive sulpjide exploration
The TEM survey of the middle Devonian Goslar Basin in the west Harz, resulted in the discovery of a set of strong anomalies, occurring less than two kilometres west of the historic Rammelsberg mine. The Rammelsberg mineralisation is a world class massive sulphide deposit with over 25% Pb+Zn+Cu, occurring in Middle Devonian shales at the margin of the Goslar Trough.
The main part of the newly found anomaly, named the Gosetal anomaly, is separated from a smaller southern one by an extensive oblique-normal fault system. The anomaly footprint area has a strike length of over 1 km, with two satellite anomalies to the northeast and south. Previous exploration drilling and mine galleries have not penetrated any of these anomalies. The Gosetal anomaly, which follows the sedimentary bedding, occurs in the same sequence of Eifelian Wissenbacher Shales as the Rammelsberg deposit. A Soil Gas Hydrocarbon geochemistry survey indicated with a strong likelihood the presence of a SEDEX mineralization in the Gosetal anomaly, giving an independent confirmation of the TEM data. The footprint of the anomaly and the strength of the TEM signal suggest a conductor of the same order of magnitude as the Rammelsberg deposit.
The TEM data consist of two components, short wavelength signals overprinted on a strong, long wavelength (> 1 km) anomaly. Two alternative solutions can explain this result, a shallow folded conductor, or a deep conductor with interference of shallow features. Interactive geophysical and geological modelling showed that a shallow conductor would lie in a stratigraphic level that was slightly higher than that of the Rammelsberg deposit, the lower alternative would fit more precisely with the stratigraphic level of the Rammelsberg ore. Both solutions put the Gosetal conductor in a small sub-basin of the Goslar Trough that also hosts the Rammelsberg deposit, bounded by two main faults.
Exploration drilling
The TEM data and geological data were used to model an upper conductor, folded in an antiform-synform pair between 100 and 400 m depth. Three drill holes were sunk late 2009 to test this model, in combination with ground- and down-hole EM surveys. The results of this first drilling phase show that the modelled conductor does not exist, but the general fold geometry was confirmed. However, the EM surveys suggest that a deeper conductor may exist, causing the strong TEM anomaly. While the model of the upper conductor has been rejected, the model of the deeper conductor has increased the potential of the project.
In the spring of 2010, further geophysical surveys will be used to better define the deep conductor. After an evaluation of the results in the summer of 2010, a second phase of exploration drilling will test the deeper target.
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