1. Project Objectives

The objective of the project WISTAMERZ is the development and test of new approaches for prospectivity evaluation of large territories. The project focuses on rare and technology metals as Ga, Ge, In, Li, Sb, Se, Sn, Ta, Te, W and the area of the famous Erzgebirge. Based on a combination of new data, their integration with existing data, the development of new metallogenic models and the implementation of new data processing technologies (i.e. artificial neural networks and other data and knowledge driven approaches) the project is aiming a new level of data integration and prediction accuracy. Existing metallogenic models are reviewed regarding their general viability, metallic components and extension in space and time. Finally, the new knowledge is summarized in a new metallogenic map incl. the delineation of exploration targets. 

The project was funded by the Federal Ministry of Education and Science in the frame of the program „r4 – Innovative Technologien für Ressourceneffizienz – Forschung zur Bereitstellung wirtschaftsstrategischer Rohstoffe“ (FKZ: 033R133A).

There is a big amount of exploration data about the traditional metals Sn, W, Pb, Zn from the period 1945 – 1990. This data consists of reports, maps, drilling logs and a big amount of various primary data. It is mostly not published. The biggest archive is located at the Saxon Geological Survey in Freiberg (LfULG). Another big host of archive data is the Wismut GmbH (the former east German Uranium producer).

• In order to avoid loss of data field work data was consequently uploaded to server.Further, the analytical results have been linked with the field data, and the GIS was created. 

A simplified version of the data is published on this web site. The data of the interactive map is continuously completed with data from other projects.

• • Presentation of important facts: geology, geochemistry, tectonics, minerals
  • Presentation of the temporal succession of the various mineralisations
  • Presentation of important metallotects
  • Presentation of prospective areas
  • Creation of the cartographic concept:
  • Clarity of the map,
  • Easy to read and understand,
  • Illustration by impressive schemes,
  • Presentation of both data and their interpretation.

The zone with stratiform metal enrichments stretches over a distance of more than 140 km from WSW till ENE throughout the Erzgebirge. It is interrupted by several strongly specialised granite intrusions with a high metallogenic potential (plutons of the Western Erzgebirge, Central Erzgebirge and Northern Erzgebirge).

During the late Proterozoic and the Cambrian, turbiditic sediments with intercalations of carbonates, contemporarily intruded by granodioritic batholiths, form an active continental margin of Northern Gondwana. Carbon bearing layers in metasediments act as geochemical traps in later stages. Possibly accumulation of Fe, As, Sb, Ag, ±Au in sedimentary strata.

8.3 Der passive Kontinentalrand: 470 – 360 Mio Jahre

From the Ordovician to the Devonian, extensive plate-reorganization due to back-arc rifting form passive continental margins with sequences of turbiditic sediments with intercalations of carbonates, quartz sandstones and conglomerates. Bimodal volcanism and hydrothermal activity with metal bearing mounds and mud were interbedded with the sediments. Main metals are Fe, Zn, Cu, Sn, W, Co, Bi, Sb, Ag, and Au.

8.4 Variscan Orogeny: 340 – 330 M years

The Gondwana-Laurussia collision results in the Variscan orogeny. Peak metamorphic conditions (UHP) occurred around 340 Ma. At about 330 Ma, the orogenic collapse and exhumation of the subduction-accretionary complex led to the recently observed configuration of the nappe pile. Metal bearing mounds and muds form various stratiform mineralisations including sulfide seams, metamorphic skarns and similar metal-enriched formations. The redistribution of Hg, Sb, Au, As and Ag in different parts of the nappe pile depends on the specific metamorphic P-T conditions.

8.5 Late Orogenic Stage: 325 – 290 (?) M years

The main intrusion phase of the Variscan Granites lasts from 325 to 315 Ma, Minor extensive magmatic events occurred until 290 Ma. Rising fluid rich granitic melts assimilate metal bearing metasediments and redistribute the metal content. Sn, Li and W are enriched in suitable structures of apical parts of intrusions, volcanic pipes, breccias and fault zones, partly with a rich polymetallic component (Cu, Sb, Bi, Co, Au, In). Hydrothermal-metasomatic processes overprint preexisting stratiform deposits producing further enrichments in suitable lithologies. Hydrothermal-metasomatic processes overprint preexisting stratiform deposits producing further enrichments in suitable lithologies.

8.6 Transition and Platform Stage: 290 – 70 Mio Jahre

During the Permian to Cretaceous, fault zones with dominant NW-SE strike dissect the Erzgebirge/Vogtland into several tectonic blocks. Concurrent with the tectonic activities, heat domes produce several generations of metalliferous hydrothermal systems (e.g. fluorite, U, As, Sn, Cu, Pb, Zn, Au, Ag, relocating metals and minerals from former deposits into vein structures and seams using suitable lithologies as geochemical traps. Decreasing tectonic and thermal activities lead towards a slow cessation of endogenic activities in the upper Permian (257 Ma). In the Cenomanian to Turonian the area is partially covered by fluvial and shallow marine deposits hosting modest tin and gold placers.

8.7 Riftogenic Stage: 70 – 0 M years

The formation of the Eger rift above a mantle plume began with the intrusion of ultramafic alkaline dikes, followed by extensive volcanism (30 Ma). Small volumes of mafic and alkaline volcanics are emplaced throughout the Erzgebirge/ Vogtland area in dykes, pipes and maars. Faults were reactivated; heat domes led to continued mineralisation processes in mostly pre-existing tectonic structures (e.g. barite and fluorite veins, U, Co, Ni, Ag, As, Bi veins).

9. Delineation of mineral target areas

During the project WISTAMERZ the high mineral potential of the Lower Paleozoic sediments was recognized (Sn, W, Cu, Co, Bi, Sb, Au). Related prospective areas can be delineated for different genetic types and metals even under cover North of the Erzgebirge if the related metallogenic indications are known and present. The results of the stream sediment survey provide a strong contribution.

Rare and high-tech metals are often related to occurrences of other metals. They do not occur in separate occurrences. The respective prospecting strategy can be described as follows:

• identification of sites with anomalies of Fe, Zn, Sn, W, Cu, Pb, Ag,
• in combination with Bi, Sb, Se, Li, In.

As we can assume that all outcrops of usable mineralisation types have been identified in the past, the following situations are of interest:  

• small outcropping mineralisations of the historically known types with unknown depth of mineralisation. (e.g. Greisen in the Eibenstock Granite, Sn-Sulfid-veins in the Osterzgebirge),
• mineralisation types, which have not been considered in the past (tin- and sulfide layers in metasediments and mineralised shear zones),
• mineralisation types, which have been considered as non-promissing in the past because of obsolet metallogenic models (e.g. Greisen bodies in large granite intrusives),
• Mineralisation types, which are quickly weathering and therefore do not form prominent morphological forms (e.g. Sn and sulfide layers in metasediments and shear zones),
• areas on top of deeply concealed intrusives within the limits of the currently known metalllotects (e.g. Northern Rim of the Erzgebirge).

The delineation of the prospective area was executed by using artificial neural networks implemented in advangeo® Prediction Software. The respective workflow is presented in the following image:

Mineral predictive mapping focuses on the identification of areas prone to the occurrence/ presence of certain mineralisation types already known in the area or in a similar geological environment. In this sense, the known mineralisation points represent the depending variable, which presence is controlled by various metallogenic factors, as well as geochemical and geophysical indications. These factors and indications (the controlling parameters) can be used to identify still unknown mineral prospective areas. An artificial neural network (ANN) is used to analyse and recognise the relationships between the depending variable and the many controlling parameters. Once trained, the ANN can apply its knowledge to a larger survey area producing predictive maps, forecasting the presence of the mineralisation type under question.

Lithologically controlled Sn mineralisations contain mainly the following accompanying elements:  Fe, Zn, In, Ag, W. They are widely known in the Erzgebirge and stretch over the hidden intrusive of the Northern Erzgebirge rim from the Western Erzgebirge till the area North of Freiberg. Possibly, the so called Felsit – Formation is somehow bound to theses formations.

Lithologically controlled Sn mineralisations contain mainly the following genetic types:  Greisen (e.g. in Aplite- and Porphyre dykes, colcanic and breccia pipes, veins). They are bound mainly to the roofs of large and small intrusives. Their mineral potential can be very significant (e.g. Gottesberg) and they may contain a wide variety of metals, incl. Cu, Bi, Pb, Zn, Ag, Sb, In).

The location of fluorite deposits is controlled exclusively by tectonic structures. The respective mineralisations are bound almost exclusively to NW-SE striking fault zones.

Chemical elements with a ratio arithmetic mean/ median > 1.5 like W, Bi, Sn, Au, Ag, In, U, As, Rb, Cs, Cd, Sb, Mo, Ba, Hg obviously possess the highest mineral occurrence forming potential, while elements having a ratio of close to 1 do not possess a mineral deposit forming potential at all, as G, Ge, REE.

The consideration of the identified high absolute values of Bi, In, Li, Sb and their strong relations to elements as Fe, Zn, Sn, W underline their high mineral deposit forming potential. The respective mineral deposits can be found in very different genetic types: from greisens, quartz veins, till polymetallic veins, in stratiform metamorphogene, metamorphosed contact-metasomatic and shear zone related formations.

The geochemical properties of Ta show its metallogenic relevance in selected Sn-Li deposits of the Eastern Erzgebirge.

There is no potential for the occurrence of economic mineralisations of the metals Ga, Ge and REE.

Large deposits of the metals Sn, W, In, Cu, Co, Bi, Sb, Au are expected in stratiform bodies and large stockworks. 

The resource potential of the comparable small and easy to process hydrothermal vein deposits is obviously low. These mineralisations have been mined intensively in the past. They are mined out in their upper parts.