Platy limestone – geologic definition and its use as a mineral commodity

According to all the mentioned spatial and natural characteristics (e.g. occurrence, quality and reserves) and the traditional use of limestone plates, a set of geological recommendations and guidelines is proposed. The project area is vast and geologically, morphologically and climatically diverse, thus making some recommendations inapplicable across the entire project area. Instead, certain recommendations are only applicable within selected regions. The four most prominent geological sets of recommendations for the sustainable exploitation of platy limestone are listed below.

1. Use of platy limestone from active commercial quarries

Possible future use of limestone slabs for reconstruction or in new buildings could be based on the excavation of material from currently active quarries. This solution is possible for the wider area of Zadar where Benkovac platy limestone (“Benkovac Stone”) has been widely used. The stone is still commercially exploited in the quarries near Benkovac. Debelo brdo and Benkovac platy limestone types are of excellent quality. Since there are no other legal quarries of platy limestone in the project region of Croatia there is a general trend of using Benkovac platy limestone in the wider area of Dalmatia as well as in the interior of the country. Geologists propose a restriction on the use of Benkovac platy limestone (“The Benkovac Stone”) just to the hinterland of Zadar and not all over Dalmatia, as is the case at the moment. The Benovac stone is of yellowish colour which differs from other (mostly Cretaceous) greyish lithotypes of platy limestone that characterize other parts of the project area in Croatia. Therefore, in other parts of Dalmatia it would be more appropriate to use an autochthonous material if available.

In the project area of Bosnia and Herzegovina, the commercial exploitation of high-quality platy limestone is possible in active quarries at the localities of Podveležje, Raška gora, Vrdi and Zvirovići.

In other parts of the project area there are no legal commercial quarries of platy limestone.

2. Limited use of stone from abandoned quarries or potential exploitation areas for renovation of local houses

Given the complex procedure for legal exploitation of the natural stone and the fact that many regions are under special restriction for any mining activity, geologists recommend some exceptions in permitting procedures.

Over the entire RoofOfRock project area, platy limestone was traditionally exploited for local use. Many abandoned quarries were evidenced as well as many examples of best practice of the local use of limestone. Due to the large spatial extent, quality, and reserves of this building stone, the possibility for further exploitation of platy limestone in many regions in the project area (e.g. Kras in Slovenia, western Istria, central Dalmatia and in Herzegovina) is estimated as potential. Therefore, traditional local use is recommended following restricted and controlled exploitation. In each region where the need for renovation of traditional houses arises, we propose re-opening one abandoned quarry or opening a small quarry of platy limestone. The exploitation should be restricted to the renovation of local traditional architecture and under the supervision of (at least local) authorities and under strict monitoring of fossil findings.

Geological conditions allow the opening of such a quarry in almost all the studied project areas with the exception of the project area in Italy. For this area, limestone plates could be provided in the adjacent Kras area in Slovenia.

3. Stone-gathering on the surface with hand tools

In the project area, quality platy limestone is dispersed throughout many localities. In the past, people excavated stone plates without significant impact on the natural environment, mostly using traditional stone gathering techniques (in Croatian: branje kamena) (Fig. 2.39). Although the so-called traditional simple “stone-gathering” from the surface is not allowed today, we generally recommend gathering the limestone plates with simple hand tools (without machines) to be used for the renovation of existing traditional houses and other objects. We suggest the legalization of this traditional activity under the supervision of at least the local government.

Traditional gathering of limestone plates from the surface is easy in the regions where the soil layer is absent or thin. Thus, Middle Dalmatian coastal areas and islands, parts of Istria and Herzegovina are suitable for this type of building material collection. On the other hand, in the Kras/Carso or partly in Istria, the stone cannot be gathered without impacting the sensitive natural environment as the rocks are covered by a layer of soil.

It should be noted that for the second and third option, certain exemptions to the pending legislation are needed.

4. Use of fractured limestone from an active commercial quarry in the Kras/Carso area

A review of the use of limestone plates as an architectural building material revealed that, especially in the southern part of the Kras in Slovenia, a special type of limestone plate – Fractured limestone were used for roofing. They were excavated in the limestone sequences from the Repen and Lipica Formation. Rudist bioclastic limestone plates from the Repen Fm. were used for roofing in the wider area of the southern Kras.

As a possible option for the acquisition of relatively high-quality limestone plates, we propose the excavation of fractured Repen limestone from the Repen Formation. This type of limestone is exposed in a wide belt between Divača and Sežana. The most perspective location is the active Griža (Tavčar) quarry near Povir.

It should be noted that this stone occurs in a relatively limited area of the southern Kras. Quarrying for limestone plates along fractures, even with modern equipment in an active quarry, could be a complex, time-consuming and expensive process, therefore, with this technology, only a limited amount of plates for the renovation of roofs can be acquired.