The Dobsina Project is located in central Slovakia, directly to the north of the small mining town of Dobsina. Excellent infrastructure exists within the vicinity of Dobsina including power, water and proximity to a railhead.
- Northern (Zemberg-Terezian) Vein System:
- 1,500m strike, 300m depth and 0.7-1.5m wide sulphide mineralisation
- Lower extents veins exploited at grades of averaging 4% Co and 16% Ni and results of up to 8% Co & 17% Ni
- Upper levels reported grade of 1-7% Cu, 200-900 g/t Ag, 0.6-5.9% Sb, 0.1-0.3% Co and 0.1-0.6% Ni
- Southern (Georgi- Martini) Vein System
- ~1,500m strike length, grades of up to 2% Co and 28% Ni
- Historical production of 430,000t of high grade Cobalt-Nickel in early to late 19th Century; ore was hand sorted and shipped to England for smelting
Geology & Minerilisation
The tectonic evolution and metallogeny of Slovakia is dominated by Hercynian and Alpine orogenic events. The present geologic architecture of Slovakia was formed during the Alpine orogeny that started in middle to late Cretaceous and lead to thin-skin thrust faulting and development of mountain core complexes of the Alpine-Carpathian system.
The Dobsina area lies at a major thrust contact between two regional tectonostratigraphic units called Veporicum (crystallinicum), and Gemericum (green-schist facies metamorphic rocks).
The following styles of mineralisation are observed at Dobsina:
- Siderite hydrothermal veining (siderite-ankerite, quartz and sulphides). Based on the sulphides composition and abundance, these veins are subdivided into the four following categories:
- Siderite-sulphide- Cu Veins
- Antimony-Bismuth Veins
- Carbonate-quartz-sulphide-Ni-Co Veins
- Barite-Siderite veins with Cu-Hg
- Metasomatic Fe-carbonate replacement
- Stratiform sediment hosted Ag-Au
- Stratiform sediment hosted magnetite-hematite
Iron ore was initially mined within the Project in the 13th century and continued through to the early 20th century, several smelters operated in the vicinity of the Project. Mining of copper ore commenced in the 14th century, with intermittent production to the 19th century.
In 1780 a Saxony miner discovered the presence of Co and Ni at Dobsina, which triggered the mines expansion that lasted to the end of the 19th century. Whilst most of the cobalt-nickel mineralisation was found in hydrothermal vein systems cutting the gneiss-amphibolite, cobalt-nickel mineralisation was also found in other settings such as veinlet disseminated in siderite-ankerite lenses as well as in veins hosted in the unfolded overlying carboniferous sedimentary rocks.
Northern (Terezian) Vein System:
1,500m strike, 300m depth and 0.7-1.5m wide mineralisation. Distinct metal zonation is evident with more copper abundant mineralisation in the upper parts whereas nickel-cobalt dominant mineralisation occurs in the lower part of the vein system. Lower extents veins exploited at grades of up to 8% Co and 17% Ni. Upper levels reported grade of 1-7% Cu, 200-900 g/t Ag, 0.6-5.9% Sb, 0.1-0.3% Co and 0.1-0.6% Ni
Zemberg Vein System:
The Zemberg Vein system consists of three discrete vein sets, Severna, Hlavna and Juzna. The mineral assemblage of the veins consist of siderite, ankerite, quartz, sulphides and abundant nickel-cobalt sulphide minerals. Minor siderite-barite and copper minerals are also present. Veins commonly display crack seal texture. Rozlozsnika, 1935 commented “Zemberg ore contained an average of 4% Cobalt and 16% Ni”
Southern (Georgi- Martini) Vein System:
The Georgi-Martini vein system extends over a ~1,500m strike length, grades of up to 2% Co and 28% Ni. The Georgi Adit contains east-west trending siderite bodies with sulphide and sulphoarsenide veinlets.
Martini vein mineralisation is located along the contact of gneiss and Carboniferous clastic sediments. The vein strikes east-west and dips 80 to 90o. Vein matrix comprises of major coarse siderite and minor milky quartz cut by gersdorffite veinlets with minor chalcopyrite and rare arsenopyrite