Harz SEDEX Project - Base metals, Silver and Gold
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.