Minerals from Trepča

Peter Perkins (UK)

While an undergraduate, I had the opportunity to be involved in a student exchange with IAESTE (International Association for the Exchange of Students for Technical Experience) during the summer of 1959. Although not specialising in mineralogy, I was assigned to the mine at Stari Trg with three other students from Norway, Poland and Germany. When returning to the surface after a visit into the mine, we were allowed to gather specimens from ledges where miners had left clusters of special crystals.

This article shows some of those specimens, which I collected over 50 years ago. (I have included a short glossary at the end of this article to help explain certain technical terms, which are shown in bold italics in the text.)

The Trepča mine, named after the valley in which it sits, is near the village of Stari Trg (see box, A word about Stari Trg) in Kosovo (formerly Serbia), and is 9km up in the hills to the northeast of the town of Kosovska Mitrovica. This town sits on the river Ibar, which flows NNW, its waters eventually contributing to the Danube (Fig.1).

Fig. 1. K: Kosovska Mitrovica, T: Trepča mine.

A word about Stari Trg
In Serbian, when the word ‘trg’ is used in urban areas, it means square as in Trafalgar Square, hence the Studentski Trg in Belgrade, near the University. In the countryside, it refers to a place appropriately located for villagers and traders to gather. Stari means ‘old’, so the village name means ‘Old Market’ (Fig.3). However, there are variants of this spelling. On some old maps, we see ‘Stan Trg’, as if copied from text in which the adjacent ‘r’ and ‘i’ were mistakenly read as an ‘n’. This obvious misprint was not corrected in documents related to the launch of the mining activities in 1930. Perhaps, it was left uncorrected to avoid a possible legal problem with official certificates. The village is also referred to as ‘Stan Terg’.

A word about Stari Trg

In Serbian, when the word ‘trg’ is used in urban areas, it means square as in Trafalgar Square, hence the Studentski Trg in Belgrade, near the University. In the countryside, it refers to a place appropriately located for villagers and traders to gather. Stari means ‘old’, so the village name means ‘Old Market’ (Fig.3). However, there are variants of this spelling.

On some old maps, we see ‘Stan Trg’, as if copied from text in which the adjacent ‘r’ and ‘i’ were mistakenly read as an ‘n’. This obvious misprint was not corrected in documents related to the launch of the mining activities in 1930. Perhaps, it was left uncorrected to avoid a possible legal problem with official certificates. The village is also referred to as ‘Stan Terg’.

Fig. 2 shows part of one of two maps that accompany Schumacher’s book of 1950. These maps are attributed to C B Forgan. The scattered small black rectangular symbols show the dwellings making up the settlement of Stari Trg, mainly on the south-eastern side of the valley. The map symbol for a mine shows the position of the main shaft (as it was in the 1950s).

Fig. 2. Part of one of two maps that accompany Schumacher’s book of 1950.

The river has eroded down through the overlying tuff (T) and lava (L), to expose the underlying phyllite (F). Outcrops of volcanic breccia (B) trend WNW-ESE with the eastern-most showing a pitching anticline with trachyte lava in its core.Limestone (Kr) and quartzite (Kv) outcrops are also shown. The approximately NW-SE trending broken lines are fold axes in the phyllite, representing a syncline to the south and anticline to the north. The area of vertical shading shows evidence of old workings.

Geological background

The Stari Trg Pb-Zn-Ag deposit lies within the ABCD belt (Alpine-Balkan-Carpathian-Dinaride, which is arranged in this sequence to make it alphabetical and easy to use), consisting of Palaeozoic basement rocks, sediments of Jurassic and Cretaceous age, and rocks of ophiolite affinities. These rocks were foliated in early Tertiary times. During the late Tertiary, this area was heavily affected by plutonic processes, giving rise to granodiorite magmas at depth and also lava flows and dykes of andesites, dacites and quartz latites, as well as pyroclastics.

The overall geological structure at Stari Trg is complex – an anticline plunging at 40° NW, with a volcanic breccia pipe along the hinge. Massive sulphide ore of economic importance forms continuous columnar shaped ore bodies, where the mineralisation has replaced limestone. (Fig.3 shows orereplacing limestone, adjacent to the breccia.) The ores are dominated by pyrite, pyrrhotite,sphalerite and galena, with typical carbonate gangue minerals – especially calcite and rhodochrosite – and small quantities of quartz. The ore mineralogy is varied and includes primary Pb-Zn ores, as well as secondary sulphides in cavities, including rare minerals such as boulangerite.

Fig. 3. Ore replacing limestone, adjacent to the breccia.

Mining activities

Relics of tools and signs of surface diggings show that mining of lead-silver ore in this area dates back to pre-Roman times. The Roman Empire and, later, the Ottoman Empire fought to control the silver mines here. There was intense activity beginning in 1303, financing the fortresses against the Ottoman threat along the Ibar valley. After a serious battle in June 1389, the Ottoman Empire took over the area and the mining was, for a while, well managed. A decline began in 1685.

There were troubled times during WW1 and then, in 1925, an exploration programme was carried out by a British company, Selection Trust, in the vicinity of the medieval workings. As a result, in 1927 in London, Trepča Mines Limited was set up, which commenced development in 1927 and production in 1930. Production was maintained during the German-Italian occupation (1941 to 1945) and then continued under state ownership. Average annual production from 1945 to 1990 was 580,000 tonnes and it is estimated that total production has been about 32 million tonnes (Hyseni et al.).

The minerals

The Trepča mine has yielded exceptional specimens of minerals for museums and collectors throughout the world. These only became available when the mining reached deep underground.

The following minerals appear in the photographs accompanying this article: galena PbS, sphalerite ZnS, pyrite FeS₂, arsenopyrite FeAsS, calcite CaCO₃, rhodochrosite MnCO₃, siderite FeCO₃, dolomite CaMg(CO₃)_2, and quartz SiO₂. The sphalerite here is the iron-rich variety, sometimes called ferroan sphalerite (Zn,Fe)S, which is black in colour. This variety is often called marmatite. In addition to these specimens currently in my collection, the plumose variety of boulangerite Pb₅Sb₄S₁₁ was collected and given in 1964 to the Natural History Museum in London.

Fig. 4. (a) Calcite showing curved aggregates of rhombohedral crystals, occurring as the last layer of a sequence. The slight curvature of the rope-like components suggested dolomite, but, an acid test with dilute HCl disproved this. Examination with UV light showed pale pink, evidence of manganese content, sufficient to justify calling it manganoan calcite. (b) Underside of previous specimen. The sequence of mineralisation shows as a narrow central zone of pyrite, a wide zone of sphalerite, a narrow zone of rhodochrosite and a final wide zone of calcite.

Fig. 5. Calcite (var. Nail Head Spar) ‘piled’ upon a base of pyrite, the upper surface of which has some arsenopyrite and small quartz crystals.

Fig. 6. Calcite (var. Nail Head Spar) sitting on rhodochrosite.

Fig. 7. Mainly rhodochrosite with pyrite and quartz prisms.

Fig. 8. Calcite (var. Nail Head Spar) showing double rhombohedra without prism faces between.

Fig. 9. (Left) mainly galena with slender prisms of quartz.Much of the quartz has very small crystals of siderite/ankerite adhering. (Ankerite is closely related to siderite and dolomite, having calcium and magnesium, as well as iron.) (Right) close-up inside the cavity of the specimen in (a), showing needle-like crystals of quartz also covered with siderite.

Fig. 10. Galena with calcite and quartz. Cubic cleavage is well shown (bottom right), with loose cleavage cubes lying in front. A small cluster of quartz prisms are seen in the centre and the calcite, which covers the back of the specimen, is seen on the right.

Fig. 11. (Left) arsenopyrite with dolomite. Unlike pyrite, arsenopyrite is orthorhombic and the diamond-shaped faces are distinctive. Some crystals here show striations, which are not uncommon. It used to be known as mispickel (from the German). (Right) close-up of arsenopyrite crystals.

Fig. 13. Sphalerite and calcite. Here the sphalerite, which occurs in the cubic system, shows typical tetrahedral form.

Fig. 14. Dolomite and calcite. The curved faces and flesh-pink colour of the dolomite are typical.

Fig. 19. Calcite showing hexagonal prisms modified by basal pinacoids.

Fig. 20. (Top) calcite (Nail Head var) on rhodochrosite and sphalerite. (Bottom) underside of the specimen showing the sphalerite. The pattern is formed by bright and dull bands, the result of lamellar twinning, which causes the cleavage direction to alternate between two alignments. Its tetrahedral form (of the cubic system) is clearly seen.

Fig. 21. Jamesonite is a sulphide of lead and antimony with iron. It commonly occurs as slender acicular crystals. Here it is associated with quartz. Left is a close up of the specimen to the right.

Ophiolites
Ophiolites are pieces of oceanic plate thrust onto the edge of continental plates (obducted). The term applies to an assemblage of igneous rocks that match the sequence found at mid-ocean ridges: basaltic pillow lava above, gabbro and peridotite below. Latite (or trachy-andesite): is an intermediate igneous rock, considered the extrusive equivalent of monzonite (syeno-diorite). Normally it is porphyritic – with phenocrysts usually of plagioclase feldspar, and a groundmass of augite and orthoclase feldspar.

Ophiolites

Ophiolites are pieces of oceanic plate thrust onto the edge of continental plates (obducted). The term applies to an assemblage of igneous rocks that match the sequence found at mid-ocean ridges: basaltic pillow lava above, gabbro and peridotite below. Latite (or trachy-andesite): is an intermediate igneous rock, considered the extrusive equivalent of monzonite (syeno-diorite). Normally it is porphyritic – with phenocrysts usually of plagioclase feldspar, and a groundmass of augite and orthoclase feldspar.

Acknowledgements

The author would like to thank Brian and Jeanette Stringfellow for photographing the minerals; Monica Price of the Museum of Natural History, Oxford for advice on the specimen in; Richard Belson and Martin Stolworthy of Norfolk Mineral & Lapidary Society for help; and Duncan Large (co-author of Hyseni, Set al.) for information and helpful advice.

About the author

The author is a retired teacher of geology and geography, and is now a U3A tutor in Diss, Norfolk.

References and further reading

Metallogenic Model of the Trepča Pb-Zn-Ag Skarn Deposit, Kosovo: Evidence from Fluid Inclusions, Rare Earth Elements and Stable Isotope Data by Sabrina Strmič Palinkaš et al in Economic Geology, Jan2013, vol 108(1), pp135-162.

The following were referred to in the text

Hyseni,S. et al. 2010. Trepča Ore Belt and Stan Terg mine – Geological overview and interpretation, Kosovo (SE Europe), GEOLOGIJA 53/1, 87-92,Ljubljana [accessed online].

“Geology and Mining in the Balkans”, Cambridge Mineral Resources plc [accessed online].

Kosich, G. 1999. A Look Back at Kosovo’s Trepča MinesSerb World USA vol XV, No 6 [serbworldusa.com/Trepca.html, accessed online].

Schumacher, I.F.1950.Die Lagerstätte der Trepča und ihre Umgebung, Izdavačko Preduzeće Saveta Za Energetiku I Ekstraktivnu Industriju Vlade FNRJ Beograd.