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Rammelsberg |
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Germany |
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Zn Pb Cu Ag
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Super Porphyry Cu and Au
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The Rammelsberg sediment hosted zinc-lead-copper deposit is located on the northern edge of the Harz Mountains, 3 km south of the city of Goslar and 100 km south-east of Hannover in central Germany.
Mining of silver from the deposit is known to have commenced by 960 AD, although the ore may have been known as early as the first century AD.
The deposits are conformably hosted by the up to 1500 m thick Middle Devonian (Eifelian) Wissenbach shale, dated at 390 Ma. This unit is underlain by up to 1000 m of Lower Devonian littoral to neritic quartzites and sandy pelites displaying channel and graded bedding, cross-laminations, clay fragment breccias and load casts. During the early Middle Devonian, the basin architecture changed to form the Goslar Trough bounded by swells in the basement onto which the sequence thinned. The Rammelsberg orebody is on the the northern side of the Goslar Trough, where the host sequence thins onto the Westharz basement rise.
The Middle Devonian sedimentary sequence commenced with the Calceola Shales, composed of a limestone-shale facies, overlain by marly shale with a few sandstone layers and then a marly-bituminous shale sequence. This unit is overlain by the fine grained silty pelitic rocks, with a significant carbonate component, of the Sandbanded Shale. These are overlian in turn by the Lower Wissenbach Shales composed of poorly banded, very uniform black shales with interbedded tuff layers. As many as 20 tuff horizons, each up to three metres thick occur beneath the ore horizon. The upper part of this unit comprises the Ore Horizon which is mainly pelitic with a slight silt component, and contains pyrite, and banded and massive sulphides. The ore is overlain by sediments deposited within a deeper shelf environment and more pelagic conditions of the Upper Wissenbach Shales. Within the core of the Goslar Trough the Middle Devonian is over 1000 m thick, while over the top of the swell it may be condensed to as little as 10 m.
The Oker and Brocken granitic plutons, intruded into the Palaeozoic sequence in the Lower Permian (about 290 Ma), are much younger than both the mineralisation and the deformation.
The deposit lies within a Middle Carboniferous Variscan overturned syncline formed at about 340 Ma. The contacts between the sulphide deposits and wallrocks are commonly sheared and faulted and the ore has locally been deformed. A funnel-shaped zone of stockwork mineralisation and silicification known as 'kneist', is located structurally above, but stratigraphically below, the orebodies. It is a wedge shaped zone with a strike length and down dip extent of around 500 m and thickness of 100 m. This 'kneist' zone has the same mineral assemblage as the deposits plus arsenopyrite and bismuth minerals.
The main ore deposit consists of two similar, adjacent, thinly laminated bodies developed in hosts at the same stratigraphic position, namely:
i). the Old Orebody, which outcrops for a length of 600 m and extends to a depth of 310 m ; and
ii). the New Orebody, discovered by underground exploration in 1859, the top of which is from 30 to 90 m below surface, with ore extending to a depth of about 500 m.
Both deposits have lateral dimensions of around 400 to 500 x 500 to 600 m. Thicknesses vary from a few metres, to up to nearly 100 m horizontal thickness in the fold nose of the New Orebody.
The mineralisation was very fine-grained, with individual grains being barely discernible with the naked eye. The main ore is zoned, commencing with mainly pyritic ores with increasing amounts of chalcopyrite, followed by ore rich in sphalerite and some chalcopyrite, then baritic lead-zinc ore and finally baritic lead grading to barite. Silver is predominantly associated with copper and lead. On the margins, the massive sulphide has intercalations of slate. Sulphides comprise 85 to 95% of the orebodies by volume.
The original size of the orebody, including the barite zone, has been estimated as 27 to 30 Mt, of which approximately 22 Mt were mined.
The overall grade has variously been quoted as 14% Zn, 6% Pb, 2% Cu, 20% barite, 150 g/t Ag, and 1 g/t Au; and 19% Zn, 9% Pb, 1% Cu.
The deposit is now exhausted and the mine was closed in 1988. In December 1992, the former Rammelsberg Mine and the old town of Goslar were included in UNESCO's World Heritage List.
The most recent source geological information used to prepare this decription was dated: 1994.
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd. Unauthorised copying, reproduction, storage or dissemination prohibited.
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Selected References:
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Large D, Walcher E 1999 - The Rammelsberg massive sulphide Cu-Zn-Pb-Ba-Deposit, Germany: an example of sediment-hosted, massive sulphide mineralisation: in Mineralium Deposita v34 pp 522 - 538
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Leach D L, Bradley D C, Huston D, Pisarevsky S A, Taylor R D and Gardoll S J, 2010 - Sediment-Hosted Lead-Zinc Deposits in Earth History : in Econ. Geol. v.105 pp. 593-625
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Muchez P and Stassen P 2006 - Multiple origin of the Kniest feeder zone of the stratiform Zn-Pb-Cu ore deposit of Rammelsberg, Germany: in Mineralium Deposita v41 pp 46-51
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Porter GeoConsultancy Pty Ltd (PorterGeo) provides access to this database at no charge. It is largely based on scientific papers and reports in the public domain, and was current when the sources consulted were published. While PorterGeo endeavour to ensure the information was accurate at the time of compilation and subsequent updating, PorterGeo, its employees and servants: i). do not warrant, or make any representation regarding the use, or results of the use of the information contained herein as to its correctness, accuracy, currency, or otherwise; and ii). expressly disclaim all liability or responsibility to any person using the information or conclusions contained herein.
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