Summary:
The deposits are stratabound and associated with Permian sediments.
Locally, a second mineralized horizon is encountered in the White Footwall Sandstone, generally separated from the Cupriferous Shale by a 2 m to 3 m thick interval carrying only traces of sulphide mineralization. Because of its small lateral extent and patchy occurrence, this horizon has no economic importance, except where copper mineralization extends upwards through the whole interval to the Cupriferous Shale. The base of copper mineralization in the White Footwall Sandstone is sometimes marked by the so-called “bornite smear”, in which the copper content can attain 3% to 4% over a thickness of as much as 10 cm to 20 cm.
There are two contrasting structural domains within the combined Lubin and Malomice mining area. The southern part of the area, from the pre-Tertiary Zechstein outcrop to the Szklary Górne Fault Zone, about 2 km to the north, is traversed by a series of west-northwest striking faults with throws ranging from 10 m to 100 m. Movements on these faults have led to a local steepening of the strata to 10 to 15 degrees , and sometimes up to 40 degrees , and to local reversals of dip. In contrast, the northern part of the mining area is little disturbed by faults and maintains a more or less constant dip to the northeast, typically 2 to 6 degrees.
Sandstone ore constitutes 64.5% of the current Balance Reserves and provides about 76% of the mine output. The sandstone ore typically contains 0.7% to 5.5% Cu. Shale-carbonate ore is absent over large areas in the central and southeastern parts of the Lubin-Malomice concessions but it occurs on its own, without the underlying sandstone ore, in the southwest part of the Lubin mine. The copper content in shale-carbonate ore ranges from 0.7% to 16%.
The highest copper grades occur in the Cupriferous Shale, with a gradual decrease in grade both above and below this unit. On the whole, horizontal grade variations are insignificant. The ore thickness generally varies from 1 m to 7 m but, in places, exceeds 17 m. The average ore thickness for both Lubin and Malomice is 3 m. In broad terms, there is a northwesttrending zone of relatively thick ore (greater than 4.5 m) running between the central and western shafts. Another thick zone occurs to the northeast of the eastern shafts, straddling the boundary between the Lubin and Malomice mining areas. In this area, ore reaches a thickness of up to 9 m but is unusual because mineralization occurs in a basin-like depression within the White Footwall Sandstone, 3 m to 9 m from the top of the sandstone unit. There is no shale over the dome and the sandstone is overlain by reef, algal and sandy dolomites. Because of its relative position to the surrounding area and problems with access, reserves in this part of the deposit are classified as Non-Industrial.
Mineralization
The main copper minerals in all types of ore are chalcocite and digenite, which generally occur together in concentrations up to 6% by weight (wt.%). Also abundant are bornite (up to 3.5 wt.%), chalcopyrite (up to 1 wt.%), covellite (also up to 1 wt.%) and, locally, minerals from the tetrahedrite group. Accessory minerals include tenorite, azurite, cuprite, native copper, enargite, galena, sphalerite, smithsonite, loellingite, arsenopyrite, cobaltite, nickeline, native silver and stromeyerite.
Copper mineralization in the Lubin-Malomice concession covers an area of 70 km2 at depths of 638 m to 1,006 m below surface. When fully developed, a typical ore profile consists of (in descending order):
- Calcareous dolomite.
- Streaky dolomite, generally banded.
- Clayey dolomite.
- Cupriferous Shale, bituminous in the lower part and dolomitic in the upper part; upper interface sharp or transitional; thickness variable, generally 30 cm to 50 cm.
- Boundary Dolomite; grey micritic dolomite, about 5 cm thick.
- White Footwall Sandstone, fine-grained with calcareous cement passing downwards into clay cement; thickness 8 m to 10 m of which the uppermost 2 m to 3 m may be mineralized.
Sandstone Ore
The predominant mineral associations in sandstone ore at the Lubin mine are bornitechalcopyrite and bornite-chalcocite. The most common non-copper mineral is pyrite. Accessory minerals include tetrahedrite.
Shale Ore
The mineralogy of shale ore is far more complex. The content of copper-bearing minerals often exceeds 4 wt.%. Chalcocite-bornite and bornite-chalcopyrite associations predominate. Copper minerals are accompanied by pyrite, galena, sphalerite and marcasite. Shale ore also contains abundant organic carbon. There is a lateral zonation with bornite-chalcopyrite prevailing near Lubin east, bornite with chalcopyrite and minerals of the chalcocite group predominating in the vicinity of the main shafts at the Lubin mine, and chalcocite assuming the major role further northwestwards.
Shale ore is enriched in silver minerals, particularly in the eastern and central parts of the Lubin mine. Silver concentrations vary from 10 g/t to over 5,500 g/t, and occasionally to 10 kg/t. Silver occurs mainly in isomorphic admixtures in bornite, chalcocite, djurleite, digenite and galena.
Carbonate Ore
The most important copper mineral in carbonate ore is chalcocite, which is commonly associated with digenite, bornite and covellite but rarely with chalcopyrite. Bornite is less abundant, but locally predominates over chalcocite. Chalcopyrite generally accompanies bornite but occasionally predominates, in which case bornite and other sulphide minerals occur as inclusions or intergrowths. Covellite tends to be associated with digenite and bornite. Accessory minerals include tetrahedrite, which occurs on its own or with bornite, and galena. Pyrite is abundant and predominates in some parts near the hanging wall of the carbonate ore horizon. Silver is contained in stromeyerite.