Report. Title Soapstone deposits of the southern Helgeland region, Nordland County, Norway. By: Tor Grenne Tom Heldal

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1 Report Title Soapstone deposits of the southern Helgeland region, Nordland County, Norway By: Tor Grenne Tom Heldal Release date:

Introduction and background The Helgeland region, located in the southern part of Nordland County (Figure 1), is known for the abundance of soapstone deposits that have been exploited from medieval

2 Introduction and background The Helgeland region, located in the southern part of Nordland County (Figure 1), is known for the abundance of soapstone deposits that have been exploited from medieval times until recently. A prominent cluster of historically interesting deposits is found in the coastal areas between the municipalities of Sømna in the south and Alstahaug in the north. None of these have hitherto been investigated with respect to present economic potential. The majority are small occurrences that have provided stone for pots and other items for local use and have not been considered here. Scattered deposits exist also further east, among which the Bjørnå deposit appears to be the most significant and the only one that has been subject of significant exploitation in modern times. All soapstone deposits of the region are located in the Helgeland Nappe Complex of the Uppermost Allochthon in the Norwegian Caledonides. They are associated with a variety of altered mafic and ultramafic rocks, including serpentinite, metagabbro, metadiorite, amphibolite and hornblende gneiss, and are generally considered as remnants of Early Ordovician ophiolites. Figure 1. Map of the southern Helgeland district, with soapstone deposits referred to in the text.

The soapstone deposits The soapstone deposits that are significant with respect to surface area and/or historical importance are Stor-Esjeøya, Brønnøy Municipality Esøya, Vevelstad Municipality

3 The soapstone deposits The soapstone deposits that are significant with respect to surface area and/or historical importance are Stor-Esjeøya, Brønnøy Municipality Esøya, Vevelstad Municipality Trolandet, Alstahaug Municipality Haltøya, Alstahaug Municipality Bjørnå, Vefsn Municipality The Stor-Esjeøya occurrence is located on the eastern side of a small islet ca. 5 km WNW of the town of Brønnøysund (Figure 1). It is spatially associated with metagabbro belonging to the Bolvær ophiolite complex. The soapstone comprises two varieties. Apparently most abundant is a foliated, relatively coarse-grained greenish grey type with some tremolitic hornblende and characteristic scattered cm-sized porphyroblasts of magnesite carbonate (Figure 2). The second variety is a more massive and fine-grained greyish type with irregular veins of white carbonate. Figure 2. Slab of soapstone from Stor-Esjeøya, showing both a foliated variety with characteristic porphyroblasts of magnesite and a massive fine-grained type. The soapstone is exposed as an up to three meter thick and 50 meter long zone close to the shoreline, where it has been worked along a steep, up to 10 meter high cliff (Figure 3). Traces of hew marks etc. from the old quarrying are more or less wiped out by weathering, but rectangular chiselled patterns are seen in places suggesting the production of building stone. Total production is difficult to estimate because waste heaps are partly under water; however, based on present terrain forms a production on the order of 100 m 3 seems possible. The base of the old quarry is about 2 meters above sea level (Figure 3) and suggests that it was abandoned prior to significant land uplift, i.e., probably in medieval times. It is possible that the stone was used for construction of the medieval Tilrem church near Brønnøysund, where the characteristic magnesite porphyroblastic soapstone can be seen in remaining ruins.

4 Figure 3. The Stor-Esjeøya soapstone quarry, viewed from ENE. The flat surface 2 m above sea level is the base of the old quarry prior to land uplift. The Esøya occurrence is located on the north side of a small islet some 20 km north of Brønnøysund (Figure 1) and is associated mainly with hornblende gneisses; green listwaenite occurs locally in eastern parts of the occurrence. The deposit is exposed over ca. 200 metres in a north-south direction, pinching out in a crevice to the south and disappearing under water to the north. The eastern part is poorly exposed but local outcrops indicate a thickness of up to about 40 metres. Exposed soapstone is generally characterized by a greenish-white talc matrix with evenly scattered 5-mm specks of dark magnesite giving the rock a vague foliation (Figure 4). Veining is virtually absent, and the soapstone has a fairly homogenous and massive appearance with an attractive light greenish colour. Traces of possibly medieval production of pots were previously known to exist in the wall of the crevice at the south end of the occurrence. Our investigations showed that historical quarrying was in fact much more extensive than previously known, apparently covering the entire soapstone lens above water level. Total production is estimated to have been at least on the order of 1000 m 3 and could have been significantly higher. Traces of the old workings are particularly well exposed along the western and northwestern parts (Figure 5), where the base of the quarry forms a flat area ca. 2 metres above present sea level, reflecting the limit of possible exploitation imposed by the higher sea level in medieval times. Hew marks show that predominantly rectangular blocks were produced. According to tradition stone from Esøya was used for the construction of the medieval church of Tjøtta.

Light brownish-grey, weathered soapstone has been worked to form a flat base of

5 Figure 4. Slab of soapstone from the Esøya occurrence. Figure 5. The Esøya soapstone occurrence viewed from NNW. Light brownish-grey, weathered soapstone has been worked to form a flat base of the quarry about two metres above present sea level, below a partly collapsed hanging-wall of hornblende gneiss (right, foreground).

Numerous soapstone occurrences are known at Trolandet, which is the southern extension of the large ultramafic body of Rødøya, as well as on the adjacent island Flatøya.

6 Numerous soapstone occurrences are known at Trolandet, which is the southern extension of the large ultramafic body of Rødøya, as well as on the adjacent island Flatøya. Most significant are those occurring near the farms Haugen and Tro on Trolandet. All occurrences are found in heavily covered terrain and are poorly exposed, hindering evaluation of areal distribution. Exposed soapstone displays large variations in texture and colour, ranging from fine grained, dull brownish-grey types that show a strong planar foliation, to coarser grained types that are darker grey or occasionally are stained by green fuchsite and show irregularly folded foliation and scattered patches of carbonate. Traces of historical potstone quarrying are seen in all exposed soapstone localities at Trolandet. It is likely that exploitation dates back to medieval times, in which case the occurrences are automatically protected as ancient cultural monuments. On the island of Haltøya, 3 km NNE along strike from the ultramafic rocks of Rødøya, soapstone is found in cliffs and escarpments on both sides of a 400 meter long and meter wide depression that stretches NNE from Trangvika and across the island. Hornblende gneiss is found to the west and mica schist to the east of the depression (Figure 6). The main depression is completely covered with overburden, but it seems reasonable to assume that soapstone occurs at depth over the entire width. Figure 6. The southern end of the Haltøya soapstone zone at Trangvika. A recent exploration quarry is seen in the background. The soapstone is in contact with mica schist to the east (right side of photo); hornblende gneiss (foreground, left) is seen on the west side of the soapstone zone.

Like at Trolandet the soapstone displays considerable variation and in places shows irregularly folded foliation and a characteristic green coloration from fuchsite, but the Haltøya soapstone

Several outcrops have soapstone with a high proportion of light grey or white carbonate veins that are either broadly parallel to foliation, or highly irregular and variably disrupted, with the local

7 Like at Trolandet the soapstone displays considerable variation and in places shows irregularly folded foliation and a characteristic green coloration from fuchsite, but the Haltøya soapstone generally has a more massive appearance than those of Trolandet and probably are more suited for production of large blocks. Several outcrops have soapstone with a high proportion of light grey or white carbonate veins that are either broadly parallel to foliation, or highly irregular and variably disrupted, with the local development of large jagged patches of light carbonate in a greenish-grey to dark grey talc-rich matrix (Figure 7). Figure 7. Slabs of soapstone from Haltøya: foliation-parallel carbonate veins (above); fragments of massive soapstone in a foliated matrix with irregular folding and greenish coloration from fuchsite (left). Traces of ancient quarrying are very abundant along the soapstone zone. Planar quarry walls with hew marks from pickaxe, chisel or other handheld tools are very prominent (Figure 8) suggesting that production of building stone was important. Potstone production seems to have been of minor and local significance. Similarities in stone type at Haltøya and at the soapstone churches of Herøy and Alstahaug (12 th century) suggest that medieval quarrying was very significant here, making new exploitation difficult due to cultural heritage regulations. Marks from recent exploration are found in a few places, especially at the northern end of the zone.

Figure 8. Planar quarry walls at Haltøya, showing hew marks from pickaxe, chisel or other handheld tools. The Bjørnå soapstone deposit is located ca. 9 km SSE of the town of Mosjøen (Figure 1).

8 Figure 8. Planar quarry walls at Haltøya, showing hew marks from pickaxe, chisel or other handheld tools. The Bjørnå soapstone deposit is located ca. 9 km SSE of the town of Mosjøen (Figure 1). The soapstone forms a steeply dipping, N-S trending body at the contact between ultramafic to gabbroic rocks on the east and marbles on the west. To the north, the deposit continues, probably for several kilometres. The soapstone is moderately foliated, medium to coarse grained and has a dark greenish colour with specks of white talc and brownish carbonate (Figure 9). Pyrite grains up to 3 mm are a characteristic feature of the rock. Thin crosscutting carbonate veins are found in places. The Bjørnå soapstone was quarried from 1897 to 1960 for the restoration of the Nidaros Cathedral. The quarry is found in a heavily forested steep hillside (Figure 10). It can be reached along a forestry road that was used for transport of blocks during the production period. The soapstone was considered as being easy to work for production of ornaments; however, in recent years the restoration authorities have been increasingly aware of its susceptibility to surface weathering when used in outside constructions. A rock fall put an end to the restoration quarrying, and no later attempt of re-opening has been carried out.

9 Figure 9. Slab of soapstone from the Bjørnå deposit. Figure 10. The Bjørnå quarry viewed from the south.

10 Conclusions Most of the soapstone deposits in the Southern Helgeland region were exploited in ancient times, predominantly in the Viking Period and during the 12 th Century AD for church construction. Consequently, parts of these quarries are automatically preserved as cultural heritage, and any new exploitation has to avoid any conflict with this preservation. Furthermore, it seems clear that the remaining (available) parts of these deposits are very limited; hence it is unlikely that there is a significant economic potential left in them. The only exception is the Bjørnå soapstone; even though the exisiting quarry is difficult to re-open, there are probably sufficient reserves in the deposit for modern quarrying. However, it also seems clear that the stone is not of sufficient quality for restoration purposes and/or outdoor use of soapstone.

APPENDIX 2 Table 2. Sample descriptions

APPENDIX 2 Table 2. Sample descriptions Table 2. descriptions 225 Felsic gneiss, fine-grained and very light-gray. From the upper part of the lower of the two layers, which connect. 226 Amphibolite, even-grained, fine-grained, medium-gray, little