The regional distribution of zeolites in the basalts of the Faroe Islands and the significance of zeolites as palaeotemperature indicators 123 The regional distribution of zeolites in the basalts of the Faroe Islands and the significance of zeolites as palaeo- temperature indicators Ole Jørgensen The first maps of the regional distribution of zeolites in the Palaeogene basalt plateau of the Faroe Islands are presented. The zeolite zones (thomsonite-chabazite, analcite, mesolite, stilbite-heulandite, laumontite) continue below sea level and reach a depth of 2200 m in the Lopra-1/1A well. Below this level, a high temperature zone occurs characterised by prehnite and pumpellyite. The stilbite-heulan- dite zone is the dominant mineral zone on the northern island, Vágar, the analcite and mesolite zones are the dominant ones on the southern islands of Sandoy and Suðuroy and the thomsonite-chabazite zone is dominant on the two northeastern islands of Viðoy and Borðoy. It is estimated that zeolitisa- tion of the basalts took place at temperatures between about 40°C and 230°C. Palaeogeothermal gradients are estimated to have been 66 ± 9°C/km in the lower basalt formation of the Lopra area of Suðuroy, the southernmost island, 63 ± 8°C/km in the middle basalt formation on the northernmost island of Vágar and 56 ± 7°C/km in the upper basalt formation on the central island of Sandoy. A linear extrapolation of the gradient from the Lopra area places the palaeosurface of the basalt plateau near to the top of the lower basalt formation. On Vágar, the palaeosurface was somewhere between 1700 m and 2020 m above the lower formation while the palaeosurface on Sandoy was between 1550 m and 1924 m above the base of the upper formation. The overall distribution of zeolites reflects primarily variations in the maximum depth of burial of the basalt rather than differences in heat flow. The inferred thinning of the middle and upper basalt formation from the central to the southern part of the Faroes is in general agreement with a northerly source area for these basalts, centred around the rift between the Faroes and Greenland. The regional zeolite distribution pattern is affected by local perturbations of the mineral zone boundaries that reflect local differences in the temperature, perhaps related to the circulation of water in the under- ground. The zonal distribution pattern suggests that these temperature anomalies are in part related to NW–SE-trending eruption fissures or zones of weakness separating the present islands and are subparallel to transfer zones in the Faroe–Shetland Basin. Both the regional and the local distribution of zeolite assemblages are probably a reflection of the basic volcanic-tectonic pattern of the Faroe Islands. Keywords: Faroe Islands, Palaeogene basalt plateau, zeolite zone, palaeotemperature indicators _____________________________________________________________________________________________________________________________________________________________________________________ O.J., Scandinavian Asbestos & Mineral Analysis, Kildeskovsvej 62, DK-2820 Gentofte, Denmark. E-mail: Oj@oj-sama.dk © GEUS, 2006. Geological Survey of Denmark and Greenland Bulletin 9, 123–156. Available at: www.geus.dk/publications/bull GEUS Bulletin no 9 - 7 juli.pmd 07-07-2006, 14:19123 124 The zeolites of the Faroe Islands have been known for more than 300 years (Debes 1673) although the islands remained nearly unknown to mineralogists until the end of the eigh- teenth century. Because of increasing interest in mineralo- gy in the nineteenth century, the Faroe Islands were visit- ed by many naturalists. One of these was Brewster (1825), who proposed the name levyne for a new zeolite species he discovered at Dalsnípa on Sandoy. The first modern description of the distribution of Faroese minerals was published by Currie (1905), who visited the Faroe Islands and described the minerals at 120 localities. Five years later a new description of the Faroese zeolites was presen- ted by Görgey (1910). Interest in the minerals of the Faroe Islands declined during the following 70 years until Betz (1981) visited the islands and reviewed the classic locali- ties. The present author started a literature study to dis- cover, if a system of zeolite zones exists on the Faroe Is- lands similar to that described by Walker (1960) in East Iceland, but concluded that published descriptions were based on minerals from the same set of localities that were known to be rich in mineral species and where large cry- stals could be collected. This sampling bias meant that it was not possible to decide if zeolite zones existed on the Faroe Islands, so in 1979 a systematic mapping of the zeo- lites in the Faroe Islands was initiated by the present au- thor. During the following 20 years, more than 800 local- ities were visited and about 3000 rock samples were inves- tigated in the field and in the laboratory. The work was extended by studying samples from the Vestmanna-1 and Lopra-1 boreholes drilled in 1980 and 1981, respectively (Jørgensen 1984; Waagstein et al. 1984). In 1996, the Lopra-1 borehole was deepened to a total of 3565 m (Lo- pra-1/1A) and the secondary minerals in the deepened part of the Lopra well were also described by the present au- thor (Jørgensen 1997). The aim of the present paper is to describe the second- ary mineral distribution in the exposed parts of the Faroe Islands and in the Lopra-1/1A and Vestmanna-1 wells. The results of the mapping are used to estimate the palaeo- geothermal gradients and the altitudes of the palaeosur- faces at various places in the Faroes basalt succession. The following topics will be discussed: (1) the general condi- tions for the use of zeolites as palaeotemperature indica- tors and the statistical distribution of zeolites in a vertical profile, (2) the original thickness of the three basalt for- mations and the volcanic evolution of the Faroese basalt complex, and (3) the regional distribution of the zeolite zones as a function of the thicknesses of the middle and the upper basalt formations. Outline of the geology of the Faroe Islands The Faroe Islands (62°N, 7°W) have a total area of 1400 km2, an average height of 300 m above sea level and form part of the North Atlantic Brito-Arctic Cenozoic Igneous Province that extends from the British Isles to Greenland. The Faroe Islands consist almost exclusively of flood ba- salts that were erupted about 59–55 Ma (Waagstein 1988; Larsen et al. 1999). The basalts on the exposed part of the Faroe Islands are divided into a lower, a middle and an upper basalt forma- tion, separated by two horizons termed A and C in Fig. 1 (see also Fig. 4). According to Rasmussen & Noe-Nygaard (1969, 1970) the volcanic evolution of the Faroe Islands may be summarised as follows: Volcanic activity started west of the present islands with the eruption of the lower basalt formation. With time the production rate of lava slowed to a temporary standstill. During this quiet peri- od, about 10 m of clay and coal bearing sediments were deposited (the A-horizon.). Volcanic activity restarted with an explosive phase, resulting in the deposition of coarse volcanic ash and agglomerates. An effusive phase followed during which the middle basalt formation was erupted from Sandoy Nólsoy Skúvoy Stóra Dímun Lítla Dímun Streymoy Kallsoy Viðoy Fugloy Borðoy Svinoy Eysturoy 62°00'N 7°00'W 20 km0 Koltur Hestur Vágar Mykines Upper basalt formation Middle basalt formation Lower basalt formation Irregular instrusive bodies and sills Coal-bearing sequence Dykes Suðuroy Fig. 1. Geological map of the Faroe Islands. From Rasmussen & Noe-Nygaard (1969). GEUS Bulletin no 9 - 7 juli.pmd 07-07-2006, 14:19124 125 several vents and small fissures within the present group of islands. Finally, volcanic activity moved farther east, away from the present islands, causing the lava flows of the upper basalt formation to transgress the middle basalt formation from the east. The discordant surface between the middle and upper basalt formations is named the C- horizon. After the upper basalt formation was formed, the basalt plateau was intruded by dykes and sills. Large sills were intruded near the boundary between middle and upper basalt formations in Streymoy and Eysturoy. Tec- tonic activity continued long after the volcanism ended until the Faroese basalt pile acquired its present gentle easterly dip. Methodology Sampling and mineral identification Renewal of a large part of the road system of the Faroes just before initiation of the fieldwork made it possible to collect samples in fresh road cuts and new quarries along the roads. After most of the road sites had been examined, the mountains were traversed and samples collected along the old paths between the villages. In addition to the sam- ples collected by the author, the present investigation is based on 500 specimens of Faroese zeolites collected pri- vately by K. Jørgensen and on the collection of Faroese zeo- lites in the Geological Museum, Copenhagen. The minerals were identified by their crystal morpho- logy, optical properties, and X-Ray Diffraction (XRD) pat- terns or by chemical analysis carried out on a scanning electron microscope equipped with an energy dispersive analytical system. The XRD reference patterns were taken from Gottardi & Galli (1985). Mapping of the mineral zones Walker (1960, 1970) defined his zeolite zones by seven distinctive amygdale mineral assemblages. Each zone was Fig. 2. Mineral temperature scale. The five zeolite zones are defined by the index minerals chabasite + thomsonite, analcite, mesolite, stilbite + heulandite and laumontite. The temperatures are shown at zone boundaries. Abbreviations used for the various minerals are shown in Table 1. An: analcite Ap: apophyllite Ca: calcite Ce: celadonite Ch: chabasite Cl: chlorite Cld: chalcedony Ed: epidote Ep: epistilbite Ga: garronite Gi: gismondine Gy: gyrolite Ha: harmotom He: heulandite La: laumontite Table 1. Abbreviations used for mineral names Le: levyne Me: mesolite: solid Me*: mesolite: hair-like Mo: mordenite Na: natrolite Ok: okemite Op: opal Ph: phillipsite Pr: prehnite Pu: pumpellyite Qz: quartz Sc: scolecite Sm: smectites St*: stellerite † Source: Kristmannsdóttir & Tómasson (1978), Kristmannsdóttir (1982) and Jakobsson & Moore (1986) Mineral zones Approx. temperatures in °C † Ch Th* Th An Me* Ph Le Me Gy Mo St He Ep Ap La Pr Pu Ed Cl Ce Sm Qz Cld Op Ca Zeolite free zone 40–60 High temperature zone > 300 Laumontite 190–230 Stilbite-heullandite 110–130 Mesolite 90–100 Analcite Chabazite-thomsonite 50–70 0 1 2 3 4 5 6 GEUS Bulletin no 9 - 7 juli.pmd 07-07-2006, 14:19125 126 defined by the presence or dominance of certain mineral species, termed index minerals, whose names are used to designate the zones. In addition to the index minerals, other minerals may be present as indicated in Fig. 2. Walk- er’s (1960) original zones are the carbonate, chabazite- thomsonite, analcite, mesolite, laumontite, prehnite and epidote zones. The original mesolite zone was later subdi- vided into a mesolite and a stilbite-heulandite zone. This extended zone definition was adopted in the present inves- tigation (Fig. 2). The classification of the zeolite zones was normally based on the mineral assemblages of amyg- dales, and fracture fillings were used only in places with- out amygdales. Classification of the mineral assemblages from samples from the Lopra-1/1A and Vestmanna-1 boreholes was originally based on the abundance of the individual index minerals expressed as the weight% of the total mass of index minerals (Jørgensen 1984). In the present investi- gation, which is based on about 3000 samples, quantita- tive analysis was carried out only on two selected mineral assemblages, one from the middle and one from the up- per basalt formation. The assemblages from most locali- ties consist of a large number of minerals which makes it difficult to estimate the relative abundance of the differ- ent minerals. Another complication was the fact that more than one index mineral often occurred at the same local- ity. The present investigation is therefore based on the first formed index minerals in the amygdales, i.e. the minerals that were deposited nearest to the host rock. Where more than one first formed index mineral was present at a lo- cality, the index mineral assumed to have the highest tem- perature of formation was chosen to map the zones. The mineral zones mapped in this way thus reflect the maxi- mum temperature of mineralisation. This method is differ- ent from a mapping based on abundance of the minerals, which shows the distribution of the zeolite zones as the result of the main mineralisation. Appendices A and B give the observed paragenesis in the 29 sections and two Table 2. Relative frequency (in %) of amygdales and mineralised fractures in the exposed part of the Faroe Islands Mineral Zeolites: Analcite Chabazite Cowlesite Epistilbite Garronite Gismondine Heulandite Laumontite Levyne Mesolite Mordenite Natrolite Scolecite Stellerite Stilbite Phillipsite Thomsonite Other minerals: Apophyllite Calcite Celadonite Chlorite CSH Gyrolite Smectites Silica minerals Visited localities 32 67 1 <1 4 4 30 11 17 61 8 4 1 45 37 8 64 15 36 19 8 2 12 18 19 61 61 7 0 8 0 51 5 5 56 12 10 2 24 37 17 59 12 37 15 10 5 7 7 29 160 16 65 0 0 0 10 69 6 16 65 0 0 0 55 10 6 45 13 39 13 3 0 3 3 6 85 49 71 0 3 6 0 77 29 23 86 14 9 0 26 74 3 60 29 34 11 3 3 14 36 14 148 33 78 0 0 8 5 60 29 20 63 8 0 0 20 38 3 60 20 43 38 23 0 28 23 20 302 35 76 2 0 8 8 63 3 26 60 19 5 3 13 39 11 75 27 32 27 13 8 29 26 19 235 18 62 0 0 0 3 38 5 8 48 0 3 0 6 33 10 73 3 32 14 5 0 0 16 25 52 15 66 0 0 0 0 38 0 20 50 0 0 0 9 26 15 79 0 32 15 15 21 41 41 Abundant minerals in bold face, common minerals in italics and rare minerals in normal type face. CSH is calcium silicate hydrates. Silica minerals are opal, chalcedony etc. Average Vágar Suðuroy Sandoy Streymoy Eysturoy Borðoy Viðoy GEUS Bulletin no 9 - 7 juli.pmd 07-07-2006, 14:19126 127 wells mapped. The most probable temperature range of deposition of the zeolite zones is indicated in Fig. 2. The rules of zone classification stated above could not be followed strictly everywhere. In the southern part of Suðuroy, mineralised vesicles are rare and, in this area, the mapping had to be based mainly on mineralised fractures. In the Lopra-1/1A borehole, the study was based on cut- tings. They included fragments of amygdales and miner- alised fractures, and the first formed index mineral could be determined only when part of the host rock adhered to the sample. In order to establish a correlation between the zeolite zones and the temperature of formation of the minerals, the vertical distribution of index minerals and tempera- tures was examined in a number of boreholes in the geo- thermal areas of Iceland (Kristmannsdóttir & Tómasson 1978; Kristmannsdóttir 1982). The result was the mine- ral–temperature scale shown in Fig. 2. Examination showed that the temperatures at the boundaries of individual zeo- lite zones varied from place to place. This is probably caused by the fact that zeolites can be formed within a broad range of temperatures and that variations in the chemical composition of the rock and the hydrothermal solutions can affect the formation temperature of the zeo- lites (Barth-Wirsching & Höller 1989; Breck 1974). An- other problem that makes it difficult to determine accu- rately the palaeotemperatures at the zone boundaries is the fact that zone boundaries are not well defined lines, a problem that will be discussed below. The temperatures at the boundaries of the zeolite zones are therefore indi- cated in Fig. 2 at the lowest and highest temperatures that occur at the Icelandic zone boundaries. As mentioned above, the original classification of the mineral assemblages of the Lopra-1/1A and Vestmanna-1 drillholes was based on the most abundant index zeolite. It was therefore necessary to re-classify the mineral assem- blages of the two drillholes according to the method used in the present investigation. This had a rather small effect on the zonation of the Lopra-1/1A drillhole. However, the first formed minerals from the Vestmanna-1 borehole are overgrown by abundant chabazite and thomsonite. Neglecting these later deposits, changes the zonation from a simple chabazite-thomsonite zone to an alternation be- tween the mesolite and stilbite-heulandite zones. The distribution of minerals, zones and temperatures Frequency of occurrence of minerals Table 2 shows the 17 zeolites and 8 associated minerals that were recorded in amygdales and mineralised fractures of the basalt in the islands of Suðuroy, Sandoy, Vágar, Streymoy, Eysturoy, Borðoy and Viðoy. In addition to the minerals listed, prehnite, pumpellyite, native copper and pyrite were found in the Lopra-1/1A borehole. All the zeolites listed in Table 2 have been reported previously from the Faroe Islands with the exception of garronite, CH TE LE PH AP Gy CL CA ME ST HE LA AN SU SA VA ST EY BO VI SU SA VA ST EY BO VI SU SA VA ST EY BO VI R el at iv e fr eq u en cy a s % o f lo ca lit ie s R el at iv e fr eq u en cy a s % o f lo ca lit ie s R el at iv e fr eq u en cy a s % o f lo ca lit ie s 100 80 60 40 20 0 80 60 40 20 0 50 20 30 40 10 0 S N S N S N Fig. 3. Variation diagrams of the relative frequency of minerals on Suðuroy (SU), Sandoy (SA), Vágar (VÁ), Streymoy (ST), Eysturoy (EY), Borðoy (BO) and Viðoy (VI). Contractions for zeolite names are listed in Table 1. GEUS Bulletin no 9 - 7 juli.pmd 07-07-2006, 14:19127 128 C 3500 3000 2500 2000 1500 1000 500 0 up pe r ba sa lt f o rm at io n m id dl e ba sa lt f o rm at io n lo w er ba sa lt f o rm at io n SU 1 SU 2 SU 3 SU 9 V A 1 V A 4 V A 7 W es tm an na -1 w el l ST 6 W ST 6 E SA 5 ST 1 0 SA 1 SA 3 EY 1 EY 2 EY 3 EY 4 EY 8 EY 1 0 B O 1 B O 2 B O 3 V I 1 V I 2 ST 2 W ST 2 E TH–CH zone AN zone ME zone ST–HE zone Altitude of profile A C V I 3 Fig. 4. Stratigraphic location of the zeolite zones in the 28 sections through the exposed part of the Faroe Islands. The data shown here are tabulated in Table 3. which was found for the first time at several localities dur- ing the mapping reported here. The minerals in Table 2 were divided into three classes: (1) very frequent minerals that occur at 60% or more of the localities; (2) common minerals that occur at between 15% and 60% of the localities; (3) rare minerals that oc- cur at less than 15% of the localities. The frequency of occurrence is given as percentages of localities examined on each island. From the column named average in Table 2, it is seen that chabazite, mesolite and thomsonite are the most fre- quent secondary minerals within the exposed part of the Faroe Islands, followed by stilbite, stellerite, heulandite, analcite and calcite. Epistilbite and scolecite are rare min- erals in the exposed part of the Faroe Islands, but they are common in the Lopra-1/1A well. Regional distribution of minerals and zones Fig. 3 shows how the relative frequency of a number of index minerals and associated minerals varies from island to island. For most of the minerals, the relative frequency decreases from south to north and from west to east, but for the minerals of the analcite and the chabazite-thom- sonite zone, the relative frequency increases in the direc- tion of Viðoy (Fig. 1). The variation in relative frequency of minerals reflects the regional shift in the distribution of mineral zones. The analcite and mesolite zones are the dominant mineral zones on Suðuroy. From Sandoy to Vá- gar, the analcite zone is gradually replaced by a stilbite- heulandite zone that becomes widespread on Vágar. On Streymoy and Eysturoy the stilbite-heulandite zone has a less widespread distribution, so that the stilbite-heulan- dite and the mesolite zones are of equal importance. The areal extent of the mesolite and stilbite-heulandite zones is further reduced on Borðoy and Viðoy, so the chabazite- thomsonite zone becomes the major one on these two is- lands. Description of mineral assemblages and zones Figures 5–11 show the geographic distribution of the mineral zones on the islands Suðuroy, Sandoy, Vágar, Strey- moy, Borðoy and Viðoy. In order to show the vertical dis- tribution of the mineral zones, 28 local sections were con- structed that are also shown on Figs 5–11. The sections have been arranged such that it is possible to follow the changes in the mineral zones both geographically and stratigraphically (Fig. 4). The data on which the sections are based are shown in Appendices A and B, and Table 3 gives the thickness of each zone. In contrast to the profiles drilled by the Lopra-1/1A and Vestmanna-1 boreholes, the profiles from the exposed part of the Faroes have been constructed from observa- tions along each section line, so the sections do not repre- sent a single vertical profile through the lava pile. GEUS Bulletin no 9 - 7 juli.pmd 07-07-2006, 14:19128 129 Suðuroy (Fig. 5) The distribution of the secondary minerals on Suðuroy is remarkably heterogeneous, a feature noted by Currie (1905). To the north of section SU2 that extends across the island from Fámjin to Holmssund, nearly all vesicles and fractures of the basalts are mineralised, but to the south of the section, amygdales and mineralised fractures are rare. The boundary (section SU2) between the two parts of Suðuroy forms a transition zone in which the scattered vesicles are partly mineralised by an analcite assemblage composed of hair-like mesolite, thomsonite, analcite, chabazite, calcite, quartz and chalcedony. This mineral assemblage is found all along section SU2, which means that no relationship exists between the secondary miner- als and their stratigraphic position within the lava pile. To the north of section SU2, the number of mineral species and the degree of mineralisation increases gradu- ally northwards and the area just north of Trongisvágs- fjørður is in the mesolite zone. Despite apparent regular- ity, the northern part of Suðuroy is a mosaic of small areas in which the mineral assemblages vary from place to place. The largest area of this kind occurs around the summit of Gluggarnir (443 m). At this locality, nearly all minerals listed in Table 2 are present. The southern part of the island is partly devoid of zeo- lites. The most abundant minerals are quartz, calcite and chalcedony, while mesolite, thomsonite, chabazite, anal- cite, heulandite and stilbite are less frequent. The mode of mineralisation is also different on the two parts of the island. On the northern part of Suðuroy, mineralised frac- tures and vesicles occur in equal numbers, whereas min- eralised fractures are more common than amygdales on the southern part of the island, in spite of the fact that empty vesicles occur at many localities. Because of this, section SU1 is based mainly on mineralised fractures. Despite the weak amount of mineralisation on south- SU1+LO SU2 SU5 SU9 VÁ1 VÁ4 VÁ7 ST2W ST2E Vestmanna-1 ST6W ST6E ST10 SA1 SA3 SA5 EY1 EY2 EY3 EY4 EY8 EY10 BO1 BO2 BO3 VI1 VI2 VI3 0 330 798 970 842 1241 1424 1461 1461 795 1799 1799 2344 2252 2545 2594 1831 1650 1745 2039 2080 2098 2084 2263 2091 2237 2140 2188 _ _ _ _ 350 250 219 _ 100 400 125 _ _ 50 _ _ 166 50 _ _ _ _ _ _ _ _ _ _ 530† – 480 373 300 180 463 325 272 200 385 500 340 – 200 280 270 350 300 230 300 180 503 310 150 100 _ 180 430 _ _ _ _ _ 82 50 _ 20 83 _ _ 200 116 _ 125 195 170 190 200 _ 182 190 190 208 200 _ _ _ _ _ _ _ 293 200 _ _ _ _ _ 46 _ _ _ 75 193 149 187 _ 70 415 251 375 400 Table 3. Stratigraphic position and thickness of mineral zones (see Fig. 4) ME zone† Thickness in metres CH–TH zone Thickness in metres ST-HE zone Thickness in metres * Stratigraphic height within the exposed lava pile of the Faroe Islands. The mesolite zone is composed of the upper 330 m of the Lopra-1 mesolite zone plus the 200 m thick mesolite zone of section SU1. Base level Stratigraphic height in m* Section AN zone Thickness in metres † GEUS Bulletin no 9 - 7 juli.pmd 07-07-2006, 14:19129 130 Fig. 5. Distribution of zeolite zones on Suðuroy and on sections SU1, SU2, SU5, SU9 and in the Lopra-1/1A borehole. 7°00'W N 62°00'N 7°00'W20 km 5 km Thomsonite–chabasite zone Analcite zone Mesolite–scolecite zone Stilbite–heulandite zone Laumontite zone Empty vesicles 1000 0 –1000 –2000 –3000 –4000 Analcite zone Mesolite zone Stilbite–heulandite zone Laumontite zone HT zone Suðuroy SANDVIK HVALBIARFJØRDUR Skálafjall SU2 SU5 Tempilklettur Frodbiarkambur Gluggarnir Fámjin TRONGISVÁGSFJØRDUR Hólmssund HOVSFJØRDUR VÁGSFJØRDUR Lopra-1/1A Spinarnir SU1 Lambaklettur M et re s ab o ve s ea l ev el SU9 SU1 + Lopra-1/1A SU2 SU9 SU5 GEUS Bulletin no 9 - 7 juli.pmd 07-07-2006, 15:15130 131 Thomsonite–chabasite zone Analcite zone Mesolite–scolecite zone Stilbite–heulandite zone Laumontite zone Empty vesicles SKOPUN SANDUR SKÀLAVIK HUSÀVIK Dalsnipa Stórafjall Hálsur Skarvanes Tyrilsválur SØLTUVIK Sandsvatn Pætursfjall DALUR SA1 SA3 SA5 1.3° 500 400 300 200 100 0 M et re s ab o ve s ea l ev el TH–CH zone AN zone ME zone ST–HE zone Sandoy 7°00'W N 62°00'N 7°00'W 20 km SA5 SA1 SA3 5 km ern Suðuroy, a clear zonation can nevertheless be discerned along section SU1, where a 200 m mesolite zone is over- lain by a 180 m analcite zone. The mesolite zone contin- ues to a depth of 600 m below sea level in the Lopra-1/1A borehole (Fig. 5). The most abundant minerals there are mesolite, scolecite, stilbite, heulandite and mordenite. Chlorite, mesolite and scolecite were deposited first. Me- solite and scolecite are replaced by laumontite as the first formed mineral at a depth of –626 m, indicating the top of the stilbite-heulandite zone. At about –1200 m, epis- tilbite replaces stilbite as the first formed mineral so that the order of deposition becomes celadonite/chlorite-epis- tilbite-thomsonite-laumontite or celadonite/chlorite-epis- tilbite-laumontite-stilbite. Since an epistilbite zone has not yet been defined elsewhere, it was decided to include the total interval between –1200 m and –2200 m depth in the laumontite zone. A high temperature assemblage of laumonite, mordenite-prehnite, pumpellyite, chlorite, calcite and quartz is found from about –2200 m to the bottom of the Lopra-1A borehole at –3534 m. Fig. 6. Distribution of zeolite zones on Sandoy and on sections SA1, SA3 and SA5. The arrow indicates the apparent dip of the zeolite zones on section SA3. GEUS Bulletin no 9 - 7 juli.pmd 07-07-2006, 14:19131 132 800 600 400 200 0 ME zone ST–HE zone Thomsonite–chabasite zone Analcite zone Mesolite–scolecite zone Stilbite–heulandite zone Laumontite zone Empty vesicles M et re s ab o ve s ea l ev el Eysturtindur Akranesskarð VESTM ANNASUND Hestfalsgjøgv Oyragjøgv VÁ4 VÁ1 VÁ7 Kvig and alsá Br eið á Malinstindur Sandavágur Midvágur SØRVÁGUR Høgafjall SØRVÁGASFJØRDUR Reyða- stiggjatagi Rógvukollur Skjatlá 4° Vágar 7°00'W N 62°00'N 7°00'W 20 km 5 km VÀ1 VÀ4 VÀ7 The uppermost mineral zone preserved in the SU1 sec- tion is part of an analcite zone. In East Iceland, a chabazite- thomsonite zone (Walker 1960) and in East Greenland a zeolite free zone (Neuhoff et al. 1997) has been recorded in the uppermost parts of the basalt complexes whose to- tal thicknesses are 700 m and 1400 m, respectively. If equi- valent zones have ever existed on the southern part of Su- ðuroy, they must have been considerably thinner than those on Iceland and Greenland, because the palaeosurface of the lower basalt formation was about 300 m above the A- horizon (see below). Sandoy (Fig. 6) The southern part of Sandoy is strongly mineralised while the mineralisation in the northern part is weak. The area north of a line from Søltuvík to Skálavík is weakly miner- alised by quartz, calcite, chalcedony, chabazite, hair-like mesolite, thomsonite and late formed stilbite or stellerite. Nearly all fractures and vesicles are totally mineralised to the south of the line. The most abundant zeolites are anal- cite, chabazite, heulandite, mesolite, stilbite and thom- sonite. No distinct boundary has been observed between the northern and the southern part of the island. Sections SA1, SA3 and SA5 (Fig. 6) show that four Fig. 7. Distribution of zeolite zones on Vágar and on sections VÁ1, VÁ4 and VÁ7. The dip and strike of the zeolite zones is indicated on the map. GEUS Bulletin no 9 - 7 juli.pmd 07-07-2006, 15:16132 133 zeolite zones exist on Sandoy. In the area between Sandur and Søltuvik, the uppermost 50 m of a stilbite-heulandite zone are exposed. The stilbite-heulandite assemblage con- sists of chlorite, heulandite, stilbite, mordenite and occa- sionally of laumontite and apophyllite. The latter two minerals occur mostly in fractures in the basalt. However, the degree of mineralisation is low in the stilbite-heulandite zone and, by volume, only half of the vesicles are mineralised. The southern and the eastern parts of Sandoy are domi- nated by a mesolite zone. The most abundant minerals are chabazite, heulandite, mesolite (solid or hair-like), stel- lerite, thomsonite and calcite together with minor gyro- lite, gismondine and levyne. Heulandite and mesolite are the first deposited minerals. Dalsnípa at the south-east coast of Sandoy is the type locality of levyne (Brewster 1825). A detailed quantitative analysis of the mineral as- semblage and the zeolite zones in section SA3 is given below. Vágar (Fig. 7) In contrast to Suðuroy and Sandoy, Vágar is totally mine- ralised and the island may be divided into two areas. North- east of a line from Sørvágur to Sandavágur, a stilbite-heu- landite assemblage occurs at 40% of the localities that has not been observed farther south. South-east of the boun- dary line, the localities are dominated by a mesolite and analcite assemblage. Around Miðvágur hair-like mesolite with up to 100 mm long crystal needles can be found in larger fractures and cavities in the basalt. The distribution pattern of the mineral assemblages on Vágar is controlled by the rise of the stilbite-heulandite zone towards the north-east. A calculation shows that the stilbite-heulandite zone dips from between 1–3°SSW to 0.6°ESE, while the basalt flows dip 3–4°ESE, i.e. the mine- ral zones are discordant to the lava stratification. A quantitative analysis of the mineral assemblage and the zeolite zones on section VÁ1 is given below. Streymoy (Fig. 8) Streymoy can be divided into a northern, a central and a southern area. A stilbite-heulandite assemblage occurs along the coast from Tjørnuvík to Langasandur in the north. The observed minerals are stilbite, heulandite, thomsonite, compact mesolite, laumontite, gyrolite, oken- ite, tobermorite, apophyllite, celadonite and smectite. The mineral assemblage in the amygdales changes gradually towards the west. The hydrated calcium silicates, stilbite and laumontite, disappear from the amygdales although they still occur in fractures in the basalt. At Saksun near the north-west coast, the stilbite-heulandite assemblage is replaced by a mesolite assemblage, characterised by solid mesolite, thomsonite, heulandite, chabazite, calcite and montmorillionite. Gyrolite and stilbite are present, but only in fractures. The distribution pattern is reversed in the central part of Streymoy (between Langasandur, Vest- manna, Dalsnipa and Kollafjørður). There the stilbite- heulandite assemblage occurs along the west coast from Vestmanna to Dalsnipa, while a mesolite assemblage is found along the east coast between Langasandur and Kol- lafjørður. Only the mesolite assemblage is found in the southern part of Streymoy. Because of the differences in mineral distribution, sections ST2 and ST6 have been divided in- to two columns, showing the eastern and the western parts of the sections, respectively (Fig. 8). The dip of the zeolite zones in the northern part of Streymoy is 2°SW and 2°NNE the central area. The distribution of secondary minerals is rather com- plex at many localities in northern and central Streymoy and shows repetitive zoning, i.e. a regular repetition of two mineral zones. For example, on the path from Saksun to the summit of Borgin (643 m), a mesolite zone is first encountered, then a stilbite-heulandite zone, then, near the summit, a second mesolite zone. Repetitive zoning has also been observed at Loysingafjall (638 m), where the mesolite zone is overlain by a stilbite-heulandite zone, and along the main road between the villages of Vestman- na and Kvívík. Between Vestmanna and Kvívík, zones oc- cur within which the vesicles and fractures of the basalt flows are mineralised, either by heulandite, stilbite, mor- denite plus minor laumontite, or by compact mesolite, heulandite, stilbite, thomsonite and chabazite. The widths of the zones are from a few hundred metres to about 1 km. Repetitive zoning also exists in the Vestmanna-1 bore- hole. The first classification of the Vestmanna-1 mineral assemblages was based on the mass concentration of ma- jor index minerals. Since chabazite and thomsonite are the most abundant minerals, the entire mineral assem- blage was classified as a thomsonite-chabazite assemblage. During the reclassification based on the first formed min- erals for the present work, it became apparent that the drilled lava succession contains a repetitive zoning of me- solite and stilbite-heulandite assemblages (Fig. 8). It is unlikely that repetitive zoning is caused by vertical fluctuations of the geothermal gradient within such rela- tively short distances, but the repetitive zoning may re- flect flows of water of different temperature that changed GEUS Bulletin no 9 - 7 juli.pmd 07-07-2006, 14:19133 134 Streymoy 7°00'W N 62°00'N 7°00'W 20 km Thomsonite–chabasite zone Analcite zone Mesolite–scolecite zone Stilbite–heulandite zone Laumontite zone Empty vesicles TJØRNUVIK HALDARSVIK SUN DIN I SAKSUN HVALVIK HÓSVIK KOLLAFJØRDUR KALDBAKSFJØRDUR ST2E ST2W Langasandur Tórshavn KVIVIK Givrufelli Langafjall Borgin Saksunardalur Loysingfjall Vestmanna-1 ST6W Bøllufjall Hundsarabotnur Sund Hvitanes SundshalsurDalsnipa Øksnagjogv Kirkjubøur ST10 2° 3.4° TH–CH zone AN zone ME zone ST–HE zone 700 600 500 400 300 200 100 0 M et re s ab o ve s ea l ev el ST–HE zone 2 ME zone 2 ST–HE zone 1 ME zone 1 0 –100 –200 –300 –400 –500 –600 M et re s ab o ve s ea l ev el Vestmanna-1 ST 2W ST 2E ST 6W ST 6E ST 10 4° 3.4° ST 2E ST 6W ST 6E ST 10 ST 2W Saksunardalur Loysingfjall Bøllufjall Hundsarabolnur Sundshálsur Hvitanes Øksnaglógv Kirkjubøur Vestmanna-1 VESTMANNASUND Sund 1.5° 2° 5 km Givrufelli Langafjall Borgin 2° 2° Fig. 8. Distribution of zeolite zones on Streymoy and on sections ST2E, ST2W, ST6E, ST6W, ST10 and in the Vestmanna-1 borehole. The dip and strike of the zeolite zones is indicated on the map. The arrows indicate the calculated strike of the zeolite zones between the sections. GEUS Bulletin no 9 - 7 juli.pmd 07-07-2006, 15:16134 135 GØTUVIK LAMBAVIK SU N D IN I Selatrað Breiða Morskarnes Raktangi Nes Æðuvik Rituvik Runavik Lambareiði Stórafjall Syðrugøta Ritufjall Heltnará Sandfelli Urðará Glyvur Inran Svinár Nordskáli Litlafelli Skerðingur Elduvik Funningur SlættaratindurEiði Gjógv EY10 EY4 EY8 EY3 EY2 EY1 SKÁLAFJØRDUR TH–CH zone AN zone ME zone ST–HE zone 700 600 500 400 300 200 100 0 M et re s ab o ve s ea le ve l OYNDARFJØRDUR FUGLAFLØRDUR FUNNINGSFJØRDUR Oyri Kolbanargjógv Kambur 5 km 0.8° Thomsonite–chabasite zone Analcite zone Mesolite–scolecite zone Stilbite–heulandite zone Laumontite zone Empty vesicles Eysturoy 7°00'W N 62°00'N 7°00'W 20 km EY1 EY2 EY3 EY4 EY10 EY8 1.7° 2° 0.4° 0.8° 2.8° 1.1° 2° 2° 2° 2° 4 ° 4° Fig. 9. Distribution of zeolite zones on Eysturoy and on sections EY1, EY2, EY3, EY8 and EY10. The dip and strike of the zeolite zones is indicated on the map. The arrows indicate the calculated dip of the zeolite zones between the sections. locally the vertical distribution of temperature. Alterna- tive explanations for repetitive zoning are: (1) local varia- tions in the chemical composition of the basalt, or: (2) mineralisation in an open and closed system, caused by variations in the percolation speed of the geothermal wa- ter (Barth-Wirsching & Höller 1989; Gottardi 1989). Eysturoy (Fig. 9) Eysturoy may be divided into two for descriptive purpos- es. North of a line from Norðskáli to Fuglafjørður, the stilbite-heulandite assemblage occurs at 64% of localities. South of that line mineral assemblage occurs at only 12% of the localities (Fig. 9). The actual strike and dip of the GEUS Bulletin no 9 - 7 juli.pmd 07-07-2006, 15:17135 136 zeolite zones can be determined by combining the dip of the zeolite zones along the sections with the dips between them. On Fig. 9 it can be seen that the strikes and dips change to follow the changes in mineralogy. North of a line from Svinár/Norðskáli to Fuglafjørður, the zeolite zones dip about 2° towards the east. To the south of the line, the dips of the zones shift gradually from 4° to the SW to 2° to the S. This means that the mineral zones are discordant to the lava bedding on the northern part of Eysturoy, but nearly concordant to it on the southern part of the island. Borðoy (Fig. 10) The mesolite, analcite and chabazite-thomsonite zones are the only ones exposed on Borðoy. At Klakkur (section BO1) the vesicles and fractures in the basalt are mineral- ised by heulandite, stilbite, mesolite (massive and hair- like), thomsonite (massive and hair-like), chabazite, levyne, phillipsite, montmorillionite and celadonite, but no clear relationship exists between the distribution of mineral and height in the lava pile. Since analcite and mesolite are the first deposited minerals in most vesicles, the mineral as- semblage of section BO1 was classified as a mesolite zone assemblage. The poor zoning west of Borðoyavik suggests 800 600 400 200 0 TH–CH zone AN zone ME zone M et re s ab o ve s ea le ve l H VAN N ASU N D H ARALD SSU N D BO RD OYAVIK Høgahadd Hálgafelli Klakkur Ánir Strond Húsadalur Norðtoftir Depil Bo rð oy + V ið oy 2° 1.1° ARNAFJORDUR BO3 BO2 BO1 Thomsonite–chabasite zone Analcite zone Mesolite–scolecite zone Stilbite–heulandite zone Laumontite zone Empty vesicles Borðoy 7°00'W N 62°00'N 7°00'W 20 km BO 3 BO 1 BO 2 5 km Fig. 10. Distribution of zeolite zones on Borðoy and on sections BO1, BO2 and BO3. The arrow shows the strike of the zeolite zones between BO2 and BO3. The common dip and strike of the zeolite zones on Borðoy and Viðoy is shown in the upper right corner. GEUS Bulletin no 9 - 7 juli.pmd 07-07-2006, 15:18136 137 Altitude metres Table 4. Quantitative analysis of section SA3, Sandoy. The table shows the number of observed and calculated amygdales containing the index mineral per 25 amygdales 0 25 50 75 100 120 150 180 200 210 220 243 270 320 340 360 375 380 400 420 446 18 18 10 16 0 4 6 2 0 2 1 0 1 1 1 0 0 0 0 0 0 NcalNobs Me 0 0 0 0 0 0 2 3 7 14 15 22 22 10 5 0 1 1 0 0 0 0.0 0.0 0.02 0.1 0.3 0.8 1.4 5.9 5.6 2.0 0.7 0.5 0.1 0.0 0.0 NcalNobs Me* 14 12 8 5 4 3 3 1 1 0 0 0 0 0 0 0 0 0 0 0 0 9.2 7.2 5.5 4.3 2.8 1.7 1.1 0.9 0.7 0.5 0.2 0.1 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.875 NcalNobs Th 0 0 0 0 0 0 0 2 3 2 0 3 5 9 10 0 14 14 23 23 23 0.1 0.1 0.1 0.2 0.3 0.5 0.7 1.0 1.5 1.8 2.2 2.8 4.4 8.5 11.2 14.0 16.3 17.1 20.1 22.8 24.6 NcalNobs Th* 14 0 11 8 0 8 5 5 4 5 0 3 3 2 1 0 0 0 1 0 0 12.8 11.5 10.2 9.2 8.2 7.4 6.3 5.2 4.5 4.2 3.8 3.3 2.5 1.5 1.1 0.9 0.7 0.7 0.4 0.3 0.3 NcalNobs An 0 0 1 1 0 2 3 0 0 0 6 6 6 8 13 0 0 0 16 0 20 1.1 1.3 1.5 1.8 2.1 2.4 2.7 3.6 4.2 4.4 4.8 5.4 6.7 9.3 11.3 12.0 13.2 13.8 15.4 17.2 19.1 NcalNobs Ch † RN,U: Correlation coefficient of the regression line InH versus U(Nobs). See equation (2). ‡ SH: Standard deviation on Hcal. in m. See equation (3). 9.1 6.6 4.1 2.4 1.3 1.1 0.6 0.4 0.1 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 RN,U† SH ‡ _ _ 0.988 _ _ 0.996 _ _ _ _ 0.991 _ _ 0.982 _ _ 0.952 10.3 13.0 15.9 21.4 24.9 11.9 21.3 18.6 15.5 12.2 44 17 14 32 56 59 13.4 11.3 NcalNobsNobsNobsNobsNobs NcalNcalNcalNcal Ch Th Me He St Table 5. Quantiative analysis of section VÁ1, Vágar. The table shows the number of observed and calculated amygdales containing the index mineral per 25 amygdales metres Altitude 0 0 0 0 0 0 2 2 3 3 6 3 5 6 _ _ 0.2 0.3 0.6 0.7 1.2 1.2 1.4 1.7 2.2 2.4 2.7 3.5 4.8 5.3 0 0 0 3 13 9 15 0 19 18 19 21 0 23 _ _ 0.8 1.7 3.9 3.9 10.1 10.7 12.6 14.8 18.4 19.4 21.1 23.8 25.0 24.8 0 0 0 0 0 1 3 6 7 9 10 0 24 0 _ _ 0.0 0.1 0.3 0.4 1.9 2.2 3.1 4.5 7.6 8.8 11.0 16.1 22.0 23.5 4 9 24 23 15 18 10 7 3 2 1 0 0 0 _ _ 3.7 11.3 22.7 24.8 17.7 16.3 11.9 7.9 3.1 2.2 1.2 0.2 0.0 0.0 3 15 21 0 7 5 0 0 0 0 0 0 0 0 _ _ 3.7 14.3 25.0 23.2 6.7 5.4 2.6 1.1 0.2 0.1 0.0 0.0 0.0 0.0 † RN: Correlation coefficient of the regression line InH versus U(Nobs). See equation (2). ‡ SH: Standard deviation on Hcal. in m. See equation (3). 10 100 200 235 340 350 380 410 460 475 500 550 610 630 RN,U† SH‡ 0.987 0.972 0.851 0.837 0.871 58 27 25 26 97 GEUS Bulletin no 9 - 7 juli.pmd 07-07-2006, 14:19137 138 that the area has been affected by several generations of mineralisation. The zoning becomes distinct farther eastwards on sec- tions BO2 and BO3. The exposed part of the mesolite zone is 500 m on BO1, but 300 m on BO2 and 150 m on BO3 (Fig.10). The analcite and thomsonite-chabazite zones also appear at higher levels on sections BO2 and BO3. The mineral zones have apparent dips of about 1º towards the north and east. The analcite zone is about the same thickness on both BO2 and BO3, which suggests that the vertical displacement of the two zones reflects differences in altitude of the palaeosurface of the basalt plateau. The lava flows of Borðoy dip 1.6º to the SE, which means that the zeolite zones are discordant to the lava bedding. Viðoy (Fig.11) The distribution pattern of the secondary minerals on Viðoy is a continuation of that on Borðoy. The mineral zones are displaced downwards compared to those of Borðoy with the result that only between 100 m and 200 m of the mesolite zone is exposed on sections VI1 and VI2. On section VI3 a lower analcite zone about 200 m thick is exposed, which is separated from the thomsonite- chabazite zone by about 130 m of repetitive zoning. The chabazite-thomsonite zone is about 430 m thick, which is the maximum thickness recorded for that zone within the basalts exposed on the Faroe Islands. Quantitative analysis of mineral distributions Once the position and temperatures are known of the boundaries of the zeolite zones, the geothermal gradient H VAN N ASU N D TH–CH zone 3 AN zone 3 TH–CH zone 2 AN zone 2 TH–CH zone 1 AN zone 1 ME zone M et re s ab o ve s ea le ve l 800 600 400 200 0 Malinsfjall Tunnafjall Enni Vl1 Vl2 Vl3 2.1° 2.1° 2° Vi ðo y + Bo rð oy Thomsonite–chabasite zone Analcite zone Mesolite–scolecite zone Stilbite–heulandite zone Laumontite zone Empty vesicles 2° VI3 VI2 VI1 VI D VI K 7°00'W N 62°00'N 7°00'W 20 km 5 km Viðoy Fig. 11. Distribution of zeolite zones on Viðoy and on sections VI1, VI2 and VI3. The dip and strike of the zeolite zones is indicated on the map. The arrows indicate the strike of the zeolite zones in the profiles. The common dip and strike of the zeolite zones on Borðoy and Viðoy is shown in the upper left corner. GEUS Bulletin no 9 - 7 juli.pmd 07-07-2006, 14:19138 139 and the altitude of the palaeosurface of the basalt plateau can be estimated using least squares regression, assuming a linear palaeotemperature gradient. However, in order to make a reliable estimate, the regression must be based on three or more zone boundaries. This requirement is ful- filled only where the Lopra-1/1A and SU1 sections can be combined. Elsewhere, the number of exposed zone bound- aries is too small to calculate a geothermal gradient. In order to overcome this limitation, an attempt has been made to estimate the position of unexposed mineral boundaries from a detailed analysis of the distribution of the exposed mineral zones. Quantitative analyses carried out on the mineral as- semblages of the Lopra-1/1A and Vestmanna-1 boreholes showed that the relative vertical frequency of the minerals followed a skewed distribution with one or more maxima (Jørgensen 1984). This observation has been used to extra- polate non exposed zone boundaries on section VÁ1 on Vágar and SA3 on Sandoy. The two sections were chosen because they are through the middle and the upper basalt formations respectively, the distribution of minerals in them is simple and nearly all rocks sampled contain a large number of well developed amygdales. In order to exam- ine the relationship between the thickness of the zeolite zones and the distribution of index minerals, the number of amygdales containing a particular index mineral was recorded for 25 amygdales (see below). To ensure that the amygdales were selected randomly, all amygdales in the samples from each locality were numbered and the 25 amygdales for examination were selected by using a com- puterised random number generator. After the amygdales had been chosen, the first formed index mineral was deter- mined and the total number of amygdales containing the same index mineral was recorded. These results are pre- sented as columns Nobs in Tables 4 and 5. Trials were carried out using different exponential dis- tribution functions to find the best correlation between altitude and number of amygdales containing the same index minerals. The experiments showed that the best fit between the observed distribution and the calculated dis- tribution was obtained by the log normal distribution function: Ni,cal = N0 exp(–½[(lnH – lnH0) / a]2) (1) where: Ni,cal is the calculated number of amygdales containing index mineral i. N0 is the total number of amygdales investigated; in this case N0 = 25. H is the altitude of the sample above sea level. H0 is the altitude where the distribution function at- tains its maximum value. a is a constant. By transforming equation (1) to a linear form and replac- ing Ni,cal by Ni,obs, we obtain: lnH = aU + lnH0, where U = ± [2 (lnN0 – lnNi,obs)]½ (2) The constants a and H0 can be determined by linear re- gression on U and lnH. The calculated number of amy- gdales (Ni,cal) containing index mineral i is shown in Ta- bles 4 and 5. A t-test shows that U and lnH fit a straight line at the 1% confidence level. The distribution curves in Figs 12 and 13 give only a best estimate for the height above sea level of the zone boundaries. To assess the degree of uncertainty of these estimates (see below) we calculate the standard deviation of the altitude (H) defined as: SH = [1/(n – 2) S (H – Hc)2]½ (3) where: n is number of pairs (H, Ni) along the distribution curve. H is the altitude of the sample above sea level. Hc is the calculated altitude of a point on the distribu- tion curves corresponding to Ni amygdales that contain index mineral i. In equation (3), n is reduced by 2 because of the loss of two degrees of freedom by the least squares estimation of a and H0 in equation (1) (Miller & Freund 1977). When Ni, H0 and a are known, Hc can be calculated from equation (1). SH for the distribution curves is shown in Tables 4 and 5 and a graphic representation of the cal- culated distributions of chabazite, thomsonite, mesolite, analcite, heulandite and stilbite on sections SA3 and VÁ1 is shown in Figs 12 and 13. The shape of the curves sug- gests that a temperature range existed around the altitude H0 in which conditions were favourable for the formation of a particular zeolite. Where H < H0, palaeotemperatures decreased away from H0 to where they became too low for the zeolite to form. Where H > H0, palaeotempera- tures increased away from H0. The zeolite that was most stable at H0 would have been formed in some interval below H0 but, at higher temperatures, formation of the first zeolite would gradually be inhibited and another one would have become stable. So a zeolite will most likely be found between the maximum slopes of its distribution curve versus height, which corresponds to a palaeotem- perature interval. GEUS Bulletin no 9 - 7 juli.pmd 07-07-2006, 14:19139 140 LA zone ST–HE zone ME zone TH–CH zone Zeolite freezoneAN z o ne LA zone ST–HE zone ME zone TH–C H zone Zeolite freezoneAN z o ne LA zone ST–HE zone ME zone TH–CH zone Zeolite freezoneAN z o ne Ho Analcite–chabazite Ho Ho 1000800600400200–20 0–400–600–800–1000–1200 0 3 6 9 12 15 18 21 24 Solid mesolite–hair-like mesolite Solid thomsonite–hair-like thomsonite Ch (obs) Ch (cal) An (obs) An (cal) N um be r o f am yg da le s co nt ai ni ng A n/ C h pe r 25 a m yg da le s Altitude (m above sea level) 1000800600400200–200–400–600–800–1000–1200 0 3 6 9 12 15 18 21 24 Altitude (m above sea level) N um be r o f am yg da le s co nt ai ni ng M e/ M e pe r 25 a m yg da le s 1000800600400200–200–400–600–800–1000–1200 0 3 6 9 12 15 18 21 24 Altitude (m above sea level) N um be r o f am yg da le s co nt ai ni ng A n/ C h pe r 25 a m yg da le s Ho Ho Me (obs) Me (cal) Me*(obs) Me*(cal) Th (obs) Th (cal) Th*(obs) Th*(cal) LA zone ST–HE zone ME zone CH zone Zeolite freezone LA zone ST–HE zone ME zone CH zone Zeolite freezone Chabasite–mesolite Thomsonite–stilbite–heulandite 16001200 140010006004002000–200–400 800 3 6 9 12 15 18 21 24 Altitude (m above sea level) N um be r o f am yg da le s co nt ai ni ng C h/ M e pe r 25 a m yg da le s 1000800600400200–200–400–600–800–1000–1200 0 3 6 9 12 15 18 21 24 Altitude (m above sea level) N um be r o f am yg da le s co nt ai ni ng A n/ C h pe r 25 a m yg da le s Ch (obs) Ch (cal) Me (obs) Me (cal) Th (obs) Th (cal) He (obs) He (cal) St (obs) St (cal) + + + numbers are small. A zone boundary is defined for map- ping purposes to be reproducible with a probability of 95%. The probability (P) of discovering Ni,obs objects (amygdales containing the new zeolite i) among N0 ob- jects (amygdales) can be calculated by means of the bino- mial distribution function (see e.g. Kreyszig 1975 or Miller & Freund 1977). It can be shown that when N0 = 25 and P = 95%, then Ni,obs = 3. Fig. 12 shows that this reasoning can be applied to define the upper boundaries of the thom- sonite-chabazite, analcite and mesolite zones at the heights where the upper end of the appropriate distribution curve intersects the line Ni = 3. However, this method cannot be used on the upper boundaries of the stilbite-heulan- dite and laumontite zones, because stilbite, heulandite and laumontite do not exist as first formed index minerals in section SA3. Fig. 12 shows that solid mesolite occurs most commonly in the mesolite zone and thomsonite occurs most commonly in the stilbite-heulandite plus the meso- lite zone. If we assume that 95% of the two index miner- als occurs within the zones in question, we can define the Fig. 12. The calculated distribution of chabazite, analcite, thom- sonite (compact and hair-like) and mesolite (compact and hair- like) on section SA3, Sandoy. Fig. 13. The calculated distribution of chabazite, mesolite, thom- sonite, stilbite and heulandite on section VÁ1, Váger. The calculated distribution curves shown in Figs 12 and 13 show that the number of amygdales containing a particular zeolite decreases rapidly as |H – H0| increases. This has the practical consequence that it becomes harder to define a zone boundary by field mapping when sample GEUS Bulletin no 9 - 7 juli.pmd 07-07-2006, 14:19140 141 heights of the lower boundaries of the mesolite and the stilbite-heulandite zones where the lower end of the dis- tribution curves interest the line Ni = 3. That 95% of an index mineral occurs within the interval in question can be verified by plotting the accumulated distribution of the index mineral in a probability diagram. Analcite occurs only sporadically below 340 m on sec- tion VÁ1 (Fig. 13), so the analcite zone cannot be defined on this profile. The other zone boundaries were calculat- ed as described above. Estimation of palaeothermal gradients and altitudes of palaeosurfaces If we assume that the palaeothermal gradient was con- stant with depth, it may be estimated by linear regression on the data from the combined Lopra-1/1A plus SU1 sec- tions, the mineral zone boundaries obtained by calcula- tion and shown in Figs 12 and 13 and the temperatures shown in Fig. 2. The resulting estimates are shown in Ta- ble 6. The new estimate from southern Suðuroy is consid- ered more accurate than that in Jørgensen (1984), which was based on the mineral distribution in the Lopra-1 bore- hole only. From these palaeogeothermal gradients and as- suming a surface temperature of 7°C, the altitudes of the palaeosurface of the basalts has been estimated (Table 6). The altitude differences between the estimated palaeo- surface and stratigraphic marker horizons A and C is dif- ferent at the three localities (Table 7). On southern Su- ðuroy, the palaeosurface was about 0.7 km (± 0.3 km) above present day sea level, i.e. close to the extrapolated top of the lower basalt formation. On Vágar, the palaeo- surface was 1.9 ± 0.2 km above the extrapolated top of the lower basalt formation (or 0.5 ± 0.2 km above the top of the middle formation), while on Sandoy, the palaeo- surface was 1.7 ± 0.2 km above the top of the middle basalt formation. This suggests that the focus of volcan- ism shifted laterally with time as will be discussed below. Zeolite zone Temperatures at the zone boundaries Zeolite free 40– 60°C St–He 110– 130°C Palaeothermal gradient °C/km Altitude of palaeosurface m above sea level Correlation coefficient R Altitude of zone boundaries (m above sea level): Lopra-1/1A + SU1 VÁ1 SA3 0.9547 0.9181 0.8689 Table 6. Estimated palaeothermal gradients and the altitude of the palaeosurfaces at Lopra-1/1A and sections SU1, VÁ1 and SA3 Ch–Th 50– 70°C Me 90– 100°C La 190– 220°C –590 380 425 –1200 – 825 –2200 – – 443–983 1760–2080 1150–1524 – 1325 653 – 900 150 66 ± 9 63 ± 8 56 ± 7– – Table 7. Estimated thicknesses of the basalt formations along various sections across the Faroe Islands Altitude of palaeo surface in m above sea level (Table 6) Present stratigraphic thickness in m Local altitude (m) of A- and C-horizons Altitude of palaeosurface in m above A- or C-horizon 443–983 1760–2080 1150–1525 > 31001 14102 700–9001,3 A-horizon: A-horizon: C-horizon: 1550–1924 Sources: 1) Larsen et al. 1999, 2) Waagstein & Hald 1984, 3) Waagstein 1988. S. Suðuroy W. Vágar E. Sandoy Area Section Formation Lopra-1/1A + SU1 VÁ1 SA3 L. Formation M. Formation U. Formation A-horizon: 700 A-horizon: C-horizon: –400 –257–283 1700–202060 GEUS Bulletin no 9 - 7 juli.pmd 07-07-2006, 14:19141 142 Discussion Palaeothermometry and zone boundaries The use of zeolites as palaeotemperature indicators is based on the assumptions: (1) that the zeolite zones reflect uni- variant equilibrium with a high coefficient dP/dT of the Clausius-Clapeyron equation and: (2) that the formation temperature of the minerals is independent of the chemi- cal composition of the hydrothermal solution. Assumption (1) is fulfilled because the properties of condensed systems are nearly independent of pressure, if the pressure is not extremely high and the temperature is below the supercritical temperature (374ºC) of water. We can also estimate the error of the temperature determina- tion when we ignore the external pressure of the system. The coefficient dP/dT is known only for a small number of systems that involve zeolites, but experimental studies of the systems stilbite-laumontite-H2O and laumontite- wairakite-H2O show that dP/dT is of the order of 25–33 bars/degree in the range Pfluid = 0–2000 bars (Liou 1971; Jové & Hacker 1997). Consequently, if the external pres- sure is equal to the fluid pressure and the original thick- ness of the lava pile is 2 km, the likely maximum error of the temperature determination is 8°C, disregarding the depth between the boundary of the zeolite zone and the unknown altitude of the palaeosurface. In contrast to the effect of pressure, the chemical com- position of the rock and the hydrothermal fluids has a much larger effect on the formation temperature of the minerals. Barth-Wirsching & Höller (1989) studied the formation of zeolites in glasses of different chemical com- positions. They found that replacing rhyolitic glass by basaltic glass caused the formation temperature of differ- ent zeolites to increase by between 50°C and 100°C. This demonstrates the importance of choosing a reference area for the thermometry that consists of rocks with a chemi- cal composition similar to that of the rocks in the area studied. Other factors may also affect the formation of zeolites such as the texture of the rock, the content of glass and the porosity of the rock (Gottardi 1989). The geothermal areas on Iceland were used as a refer- ence for the thermometry in the present study. The ba- salts from the Faroe Islands are all tholeiites, but show large compositional variations that range from picritic to ferrobasaltic (Waagstein 1988). Most of the Icelandic ba- salts are also tholeiites, but minor amounts of acid rocks (rhyolites, andesites, granophyres, acid tuff ) are found, mainly associated with volcanic centres (Sigurdsson 1967). This compositional variation of the Icelandic rocks may partly explain the large variation in temperature at the boundaries of the zeolite zones mentioned above (Fig. 2). From the description of the sections shown in Figs 12 and 13 (and listed in Appendix A), it can be seen that the distribution of index minerals varies gradually between successive zeolite zones. An index mineral that defines a zone may thus overlap the boundaries of neighbouring zones which makes it difficult to define the exact bound- aries between mineral zones. The problem was solved by statistical analysis on sections SA3 and VÁ1 from which the boundaries of the zeolite zones could be defined as the locations where 3 out of 25 amygdales contain the appro- priate index mineral. The overlap problem occurs in all the sections described in Appendix A and, because of the lack of quantitative mineral data, the distributions in SA3 and VÁ1 were the only ones that could be described by a simple distribution model. On all other sections, the zone division was based on a crude estimate of the abundance of the index miner- als around the zone boundaries. Figs 12 and 13 show that the overlap between the zeolite zones varies from 100 m to 300 m. which means that, in the worst case, the zone boundaries could be determined with an accuracy of only ± 150 m when the zone boundary localities are based on a subjective estimate of the abundance of index minerals. Volcanic and tectonic evolution The average of the three calculated palaeogeothermal gra- dients is about 60°C/km and there may be a small de- crease in the gradient from the lower to the upper basalt formation. If real, this decrease could reflect either a re- duction in heat flow with time or a variation in heat flow with locality. Rasmussen & Noe-Nygaard’s (1969, 1970) summary of the volcanic evolution of the Faroe Islands that volcan- ic activity started in the west and moved eastwards with the times, must be modified, because evidence from the Lopra-1 drillhole indicates that the lavas of the lower for- mation were erupted from local centres (Waagstein 1988) and not from centres situated west of the present islands. This change might explain the change in the palaeogeo- thermal gradients shown in Table 6. The eruption centres of the lower and middle formations were located in the Faroe Islands and the geothermal gradient was high. Move- ment away to the east during eruption of the upper for- mation led to a decrease in the gradient. GEUS Bulletin no 9 - 7 juli.pmd 07-07-2006, 14:19142 143 Regional distribution of the zeolite zones At the time when the Faroe lava pile was first mineralised, the thermal gradient seems to have been fairly constant, at least regionally and for some time. This is suggested by the rough equality of the calculated palaeogeothermal gradients from the southern, western and central part of the Faroes that represent different stratigraphic levels (Ta- ble 6). The overall regional distribution of zeolites is thus considered to reflect primarily variations in the maximum depth of burial of the basalt rather than differences in heat flow. The inferred palaeosurface on southern Suðuroy is close to the extrapolated top of the lower formation (Table 7), indicating that the total thickness of middle and upper formation lavas must have been small in this area. In contrast, in eastern Sandoy about 50 km farther north where the exposed thickness of the upper forma- tion is of the order of 1 km, the estimated palaeosurface is >1.5 km above the base of the upper formation or strati- graphically approximately 3 km above the lower–middle formation boundary. If we use the palaeogeothermal gra- dient calculated on Sandoy, then the palaeosurface of the upper formation on Viðoy may have been at about 1.3 km ± 0.2 km above sea level. These results suggest that the upper formation had a similar or only slightly smaller thickness in the north-eastern part of the Faroes compared with the central part of the islands. On the other hand, the upper formation seems to have been much thinner or non existent in both the western and southern parts of the Faroes (Table 7) and the middle formation must also have been thin in the south. The inferred thinning of the middle and upper forma- tions from the central to southern part of the Faroes is consistent with a northerly source area for these basalts, centred on the rift between the Faroes and Greenland (Waagstein 1988; Hald & Waagstein 1991; Larsen et al. 1999). The thinning of the upper formation towards the west is consistent with Rasmussen & Noe-Nygaard’s (1969, 1970) interpretation of an easterly source for this part of lava pile and may suggest a shift in the focus of volca- nism. The first order regional zeolite distribution pattern is affected by local perturbations of the mineral zone bound- aries (Fig. 4). These perturbations show up as shifts in the dip of the zone boundaries within and between neigh- bouring islands as well as shifts in the degree of minerali- sation. The latter effect is clearly seen towards the south. Southern Sandoy and northern Suðuroy are heavily min- eralised, although at different temperatures, whereas the vesicles of the basalt in the adjoining areas of northern Sandoy and southern Suðuroy usually contain no zeolites. On the northern and western islands, the zone distribu- tion shows a tendency to symmetry around the narrow NW–SE-trending sounds that separate the islands (Figs 7–9). The distributions on the neighbouring north-east- ern islands of Borðoy and Viðoy similarly seem to be mir- ror imaged, a distribution difficult to explain by varia- tions in depth of burial. It is more likely that the distribu- tions reflect local differences in palaeotemperature, per- haps related to the circulation of water underground with high temperatures in areas of up welling and low tempera- tures in areas of down welling. The symmetry of the zonal distribution patterns suggests that these temperature anom- alies are in part related to NW–SE-trending eruption fis- sures or zones of weakness separating the present islands (Noe-Nygaard 1968; Rasmussen & Noe-Nygaard 1969, 1970). They are subparallel to the transfer zones in the Faroe–Shetland Basin described by Rumph et al. (1993) and later authors, and may indicate the presence of simi- lar deep seated features. Both the regional and the local distribution of zeolite assemblages probably reflect the basic volcanic-tectonic systems that led to the develop- ment of the Faroe Islands. Acknowledgements I want to express my gratitude to the late Arne Noe-Ny- gaard and Jóannes Rasmussen for discussions and support during the first phase of this project. I also want to ex- press my thanks to the Geological Survey of Denmark and Greenland for financial support to the present project, to curator Ole V. Petersen, Geological Museum, Copen- hagen for permission to study the collection of zeolites from the Faroes and to Mrs. Kitty Jørgensen, Næstved, who kindly made her collection of zeolites from the Faroes available for my study. Finally, I want to thank Regin Waagstein, James Chalmers and Kjeld Alstrup for discus- sions and constructive criticism of the various versions of the manuscript. The comments of two anonymous review- ers are likewise greatly acknowledged. References Barth-Wirsching, U. & Höller, H. 1989: Experimental studies on zeolite formation conditions. The European Journal of Mineral- ogy 1, 498–506. Betz, V. 1981: Zeolites from Iceland and the Faroes. Mineralogical Record 12, 5–26. Breck, D.W. 1974: Zeolite Molecular Sieves: Structure, Chemistry and Use. New York: John Wiley. GEUS Bulletin no 9 - 7 juli.pmd 07-07-2006, 14:19143 144 Brewster D. 1825: A description of Levyne, a new mineral species. Edinburgh Journal of Science 2, 322–334. Currie, J. 1905: The minerals of the Faroes, arranged topographi- cally. Transactions of the Edinburgh Geological Society (session 1905–1906) 9, 1–68. Debes, L.J. 1673: Færoæ et Færoa Reserata. Hafniæ: Suptibus Dan- iels Paaulli Reg. Bibl. (In Latin and Danish). Görgey, R. 1910: Ein Beitrag zur topographischen Mineralogie der Färöer. Neues Jahrbuch der Mineralogie und Palaeontologie XXIX, 269–315. Gottardi, G. 1989: The genesis of zeolites. European Journal of Mineralogy 1, 479–487. Gottardi, G. & Galli, E. 1985: Natural zeolites. In: Wyllie, P.J., Goresy, A.E., von Engelhard, W. & Hahn, T. (eds): Minerals and Rocks No. 18. Berlin: Springer Verlag. Hald, N. & Waagstein, R. 1991: The dykes and sills of the early Tertiary Faroe Islands basalt plateau. Transactions of the Royal Society of Edinburgh: Earth Sciences 82, 373–388. Jørgensen, O. 1984: Zeolite zones in the basaltic lavas of the Faroe Islands. Annales Societatis Scientiarum Faroensis. Supplemen- tum 9, 71–91. Jørgensen, O. 1997: Zeolites and other secondary minerals in cav- ities and veins, Lopra-1/1A well, Faroe Islands, 1996, 8 pp. + plates. Unpublished Report. Technical studies prepared for Dansk Olie og Gasproduktion A/S 1997 (in archives of the Geological Survey of Denmark and Greenland, GEUS Report file 26129). Jove, C. & Hacker, B.R. 1997: Experimental investigation of lau- montite ® wairakite + H2O; a model diagenetic reaction. Amer- ican Mineralogist 82, 781–789. Kreyszig, E. 1975: Advanced Engineering Mathematics, 707–709, 783–787. New York: John Wiley. Kristmannsdóttir, H. 1982: Alteration in the IRDP drillhole com- pared with other drillholes in Iceland. Journal of Geophysical Research 87 (B8), 6525–6531. Kristmannsdóttir, H. & Tómasson, J. 1978: Zeolite zones in geo- thermal areas in Iceland. In: Sand, L.B. & Mumpton, F.A. (eds): Natural zeolites, occurrence, properties and use, 277–284. Ox- ford: Pergamon Press. Larsen, L.M., Waagstein, R., Pedersen, A.K. & Storey, M. 1999: Trans-Atlantic correlation of Palaeogene volcanic successions in the Faroe Islands and East Greenland. Journal of the Geological Society (London) 156, 1081–1095. Liou, J.G. 1971: Stilbite-laumontite equilibrium. Contribution to Mineralogy and Petrology 31, 171–177. Miller, I. & Freund, J.E. 1977: Probability and statistics for engi- neers, 50–63. Englewood, New Jersey: Prentice-Hall. Neuhoff, P.S., Watt, W.S., Brid, D.K. & Petersen, A.K. 1997: Tim- ing and structural relations of regional zeolite zones in basalts of the East Greenland continental margin. Geology 25, 803–806. Noe-Nygaard, A. 1968: On extrusion forms in plateau basalts; shield volcanoes of ‘scutulum’ type. Science in Iceland 1,10–13. Rasmussen, J. & Noe-Nygaard, A. 1969: Beskrivelse til geologisk kort over Færøerne i målestok 1:50 000. Danmarks Geologiske Undersøgelse I Række 24, 370 pp. + map vol. (in Danish with summaries in Faroese and English). Rasmussen, J. & Noe-Nygaard, A. 1970: Geology of the Faroe Is- lands (pre-Quaternary). Danmarks Geologiske Undersøgelse I Række 25, 142 pp. Rumph, B., Reaves, C.M., Orange, V.G. & Robinson, D.L. 1993: Structuring and transfer zones in the Faroe Basin in a regional tectonic context. In: Parker, J.R. (ed.): Petroleum Geology of Northwest Europe: Proceedings of the 4th Conference, 999– 1009. London: Geological Society. Sigurdsson, H. 1967: The Icelandic basalt plateau and the question of SIAL. In: Björnsson, S. (ed.): Iceland and mid-ocean ridges. Societas Scientiarium Islandica XXXVIII, 32–46. Waagstein, R. 1988: Structure, composition and age of the Faroe basalt plateau. In: Morton, A.C. & Parson, L.M. (eds): Early Tertiary Volcanism and the Opening of the NE Atlantic. Geolo- gical Society (London) Special Publication 29, 225–238. Waagstein, R. & Hald, N. 1984: Structure and petrography of a 660 m lava sequence from the Vestmanna-1 drillhole. In: Ber- thelsen, O., Noe-Nygaard, A. & Rasmussen, J. (eds): The Deep Drilling Project 1980–1981 in the Faroe Islands. Føroya Fród- skaparfelag, Tórshavn, 39–65. Walker, G.P.L. 1960: Zeolite zones and dike distribution in rela- tion to the structure of the basalts of Eastern Iceland. Journal of Geology 68, 515–528. Walker, G.P.L. 1970: The distribution of amygdale minerals in Mull and Morvern (Western Scotland). In: Murty, T.V.V.G.R.K. & Rao, S. (eds): Studies in Earth Sciences, West Commemoration Volume, 181–194. Faridibad, India: Today & Tomorrow’s Pub- lishers. Manuscipt received 3 July 2001; revision accepted 7 December 2001. GEUS Bulletin no 9 - 7 juli.pmd 07-07-2006, 14:19144 145 Appendix A: Locations of sites along the sections discussed in the paper and minerals found in vesicles and fractures at each locality. The mineral zones are defi ned in Fig. 2 Profi le Locality Altitude (m) Vesicles Fractures Zone SU1 Road exposure 0.5 km nor 25 No vesicles. He–Me. He–St–Ch. An–Ch. Ca. Qz. 2–3 SU1 The northern entrance of the Sumba tunnel 70 – He–Me. He–Ch. Me–An. Ca. Ch–An. 2–3 SU1 Road exposure at the W slope of Siglidalur 200 – Ch–An. Ca. 1–3 SU1 Road exposure at small stream on the W slope of Spinarnir 380 – Ch–Th*. Op. Qz. 1–2 SU1 288 – Ch–An. Op. Qz. Ca. 1–2 SU1 Road exposure at Stórá, 1km SE of Spinarnir 340 – Th*–An. Op. Qz. Ca. 1–2 SU1 Lambaklettur 235 – As above. 1–2 SU2 Road exposure 3 km E of Øravík 100 Empty vesicles. Ca. Qz. 1–2 SU2 Road exposure 2.5 km E of Øravík 25 Ce–An. Ch–Me*–Th*. An. Ca. St. 1–2 SU2 Exposure in Dalsá, 1.5 km W of Øravík 100 An, Me*. Ch. Ca. Cld. Cld. Qz. 1–2 SU2 Road exposure just north of Høgiklovningur, 2.5 km S of Øravík 250 Ca–An. Ph–Th*. Cld. Me*. 1–2 SU2 278 Empty vesicles. Ca. 1–2 SU2 NW slope of Nónfjall 360 Th*–An–Ch. Th–Th*–An–Ch. 1–2 SU2 The summit of Nónfjall 427 An–Me* Ca. Qz. An. 1–2 SU2 Road exposure 0.8 km S of the church in Fámjin 80 Ac. Ch. Ch. An. Qz. 1–2 SU2 Road exposure 0.5 km S of the church in Fámjin 20 An–Th. Th*–Ch. An. St. Me*. 1–2 SU5 Høvdatangi, Fr 0–25 Empty vesicles. Empty fractures. – SU5 Skarvatangi 60 Na–(Th, An). Me–Th. Ch. Me–Me*. Me–St. Me–An. St–Ch. St*–St. 2–3 SU5 Exposure at the road Fr 90 An–St. Me–St. Th–St. Th–Me. Me*–Ch. 2–3 SU5 – do – 130 Na. Ch. Me–Sc. Me–Ch. Th–Ga–Ch. Na–St*–St. An–Th. St–Ch. 2–3 SU5 – do – 140 An–Th*–Ch. An–Me. St–Me–St. Me–La, Ch. 2–3 SU5 – do – 250 Me–Me*. Th–Me. An. He–St. Op, Cld, Ca. 2–3 SU5 Summit of Kambur 483 Ce–He. Me in large acicular crystals like scolecite. Ce–Me*, Ce–An. He. 2–3 SU9 Hamranes and the southern entrance of the tunnel Hvalba–Sandvík 0–100 He–St. He–Me–Ch. An–Me. Me–Me*– Gy. Me–Gy+Ap. He–St–Ap. Me*–La. Th–Ch; He–(St, La). He–Ap. He–La. La–Ca. La–Gy. 2–3 SU9 The southern slope of Skálafjall 70 An–He. Me–Th. Cld. As in the vesicles. 2–3 SU9 – do – 120 As above. 2–3 SU9 – do – 160 Scolecite-like Me. An–He. Me–He. He–Me–Me*. Ca. 2–3 SU9 – do – 200 As above. 2–3 SU9 – do – 240 Me–St. He–St. He–Ch. Ca–(Ch, Le). 2–3 SU9 – do – 260 Me–Me*–Ch. Th–Ch. 2–3 GEUS Bulletin no 9 - 7 juli.pmd 07-07-2006, 14:19145 146 Profi le Locality Altitude (m) Vesicles Fractures Zone SU9 The southern slope of Skálafjall 290 Th*–Ch. Me–Me*–Ch. Ca. 1–3 SU9 The summit of Skálafjall 374 As above. 1–3 SA1 Exposure at the cost line and at road cuttings in Søltuvík 0–50 Many empty vesicles. He. St. La. Ca. La–St–Ca. Mo–He–St. Ca. 2–4 SA1 Road exposure at the road Sandur–Søltuvík, 1.5 km west of Sandur 60 He–St. He+Me–St. Th–St. He+Me–St. Ca. 2–4 SA1 Large quarry at lake Sandvatn, 1 km north of Sandur 10 No vesicles. St–La–Ca. He. St. 2–4 SA1 Sprutthol, Sandsvágur Bay 30 He–Me. Ch. Ca. St. Ca. 2–4 SA3 Húsavíklið N of Húsavík 0–75 He–Me. Ce–Me. Th–Me. St. 2–3 SA3 Road exposure 2 km W of Skálavík 78 Me–Ch. Gi. Cld. He–St–Ca. 2–3 SA3 Road exposure at Hálsur, 3 km W of Skálavík 119 Me–Th. Me–Me*. He–Th. St–St*. Ap. 2–3 SA3 Urðarklettar NW of Húsavík 120 Me–Th–Ch. An–Me–Th. 2–3 SA3 Húsavíklið N of Húsavík 150 Me–Th–Me. An. He. Ca. 2–3 SA3 Exposure at Gravaráin 140 Me–Th. He–St. He–Ch. An. St. La. 2–3 SA3 Urðatklettar, NW of Húsavík 150 Ce–Me–Th–Me*, Me–Me*–Gy. Me*. 2–3 SA3 – do – 180 Ca–Me–Me*. An–Me. 2–3 SA3 Húsavíklið, N of Húsavík 180–200 Me–Th*. An–Th–Me*. 2–3 SA3 Exposure at Gravaráin 210–220 Me–Ca–.Me*. An–Me*. An–Th*. Ca–He–St. Ca–Ap. 1–2 SA3 Exposure at Stórá 243 Me–Me*. Me–Th*–Ca. Gi. Ca–St. 1–2 SA3 Summit of Heiðafjall 266 He–Me*. An–Me*–An. Th*. 1–2 SA3 Exposure at Stórá 320–340 Me–An–Me*. Ch. Th*. 1–2 SA3 Skriðubakki 360–380 Th*–Ch. Me*–Ch. Me*. 1–2 SA3 – do – 400–420 Ch–Th*. Th*–Ch. An. Many empty vesicles. 0–1 SA3 The summit of Pætursfjæll 447 Ch–Th*. Many empty vesicles. 0–1 SA5 Dalsnípa 150 Me–An. Me–Ap–St. Th–Ap. Ch–Ap. Th–Ch. An–Ch. Le. He–St–Ap. Cld. 2–3 SA5 The S slope of Skúvoyafjall, 0.6 km NW of Dalsnipa 280 Me–St, Me–An, He. 2–3 SA5 The summit of Skúvoyafjall 354 Ce–Ch. Ce–Th–Th*. St. 1–3 SA5 Road exposure at the end of the road Dalur–Skuvoyafjall 308 He–Me. Th–Me*. Ch–Th*. 1–3 SA5 Road exposure 2 km SW of Dalur 260 Th–Ap. St–Me–Le. Th–Le. He–Me–La. 2–3 SA5 Dalur harbour 0–30 Ch. Ch–Le. An–Th–Th*. He–Me–St. Ch. Le. Me–Ap–St. Me–Me*. 2–3 SA5 Road exposure at Kinnartangi 100 Ch. Ch–Th–Ch. St–Me–Gy. Gy–Me. 2–3 SA5 The SE slope of Stórafjall 160 Ch. An–Me–Me*. St–Th. Ch. St. He. Gy. 2–3 SA5 – do – 220 Me–Me*–Ch. Th–Me. 2–3 SA5 – do – 260 As above. 2–3 SA5 – do – 300 Ph. Gi–Me*. Th*–Le. Me–Me*. 1–2 SA5 – do – 340 As above. Ch–Le. He–Me–St–Ap. 1–2 SA5 – do – 360 As above. He–Le. 1–2 GEUS Bulletin no 9 - 7 juli.pmd 07-07-2006, 14:19146 147 Profi le Locality Altitude (m) Vesicles Fractures Zone SA5 The summit of Stórafjall 396 Ch+Ph. Gi–Me*. Me*–Ch. Th–Ch. 1–2 SA5 The NE slope of Stórafjall 310 Ch. Me*–Ch. He. 1–2 SA5 Trigonometric station on the NE slope of Stórafjall 217 Ch. An. Me–Ch. He–St. He–Me–Gy. 2–3 SA5 Road exposure at Tjarnaheyggjur 60 As above. Me–Ca. 2–3 VÁ1 Reyðastiggajatangi 0–10 He–St, An. Cl–St–Ca–La. 3–4 VÁ1 Gásadalur, exposure along the path Gásadalur–Rógvukollur 100 He–St, St–La. Cl–St–La. 3–4 VÁ1 – do – 200 He, St. Me, La, An. 3–4 VÁ1 Gásadalur, exposure at the path Gásadalur– Rógvukollur 235 He–Th. La, Ca. 3–4 VÁ1 Gásadalur. The pass between Knúkarnir– Neytaskarð 340 He, St, Th, An, Cl. 3–4 VÁ1 Grunnadalur, exposure at the branching of small streams 380 Cl–He–Th, Cl–He–St, Cl–St–Me. St–La–St. 3–4 VÁ1 Rógvukollur , exposure at the W slope 380 He–Me, Me–Ch, Th–Ch–Th, Mo–He, Mo–Ch ± Cld. Me, Ca. 2–3 VÁ1 Neytaskarð, exposure at the SE slope 400–420 As above. 2–3 VÁ1 The summit of Rógvukollur 464 He–Me, Me–He–Me, Th–Me, Th–Ch, Me–Ch. 2–3 VÁ1 Djúpidalur (the NW slope of Eysturtindur), exposure at stream 470–480 He–Me, He–Ch, Me–Ch, Th–Ch. 2–3 VÁ1 500 He, Me, Th, Ch. 2–3 VÁ1 Grunnadalur, exposure at the end of small streams 550 Th–Me*–Ch. La, Ca. 2–3 VÁ1 Djúpidalur (the NW slope of Eysturtindur) 600–610 Ce–Th–Th, Ce–Ch. St–Me–La, Ca. 2–3 VÁ1 The plateau between Eysturtindur and Akranesskarð 620–640 An, Th, Me, Sm. 2–3 VÁ4 Oyrargjógv ferry harbour and the path to Sørvágur 0–136 St–St*. Ep–St. La. Th. Ch. St. La. 3–4 VÁ4 Large quarry 1 km W of Sørvágur 10 Cl–St–St*. St–La. Mo–He. Mo–Gy. An–Gy. Me–Me*–Ch. Me–Ap±Sm. He–St–St*. Ep. La, Me. 3–4 VÁ4 Sjatlá, 1.5 km N of Sørvágsvatn 45–60 Cl–He–St. St–La. Ap. 2–4 VÁ4 Exposure at N end of small road from Sørvágur, just W of Sjatlá 114 Cl–St–Me. Cl–An. Cl–Ch±Sm. St–La. Ap. 2–4 VÁ4 – do –, exposure at small tributary of Skjatlá 150 Cl–He–St. St–Ap. Cl–Me–Th. Cl–Me– Ch. Me–Ap. Me–Ch. Me–Ap. An–Ap. He–Ch. 3–4 VÁ4 – do – 190 As above. 3–4 VÁ4 – do – 220 Cl–St–St*. Cl–He ± La. Th. Mo–St. 3–4 VÁ4 End of Breiðá (Oyrargjógv) 250 Ce–Me. He–Me. 3–4 VÁ4 – do – 304 Ce–Me–Th. Ce–Th–Ch. Gy–Me. 2–3 VÁ4 Kvígandalur, exposure at the SE tributary of Kvígandalsá 250 An. He–Le. Me–Le. An–Th–Ch. 2–3 VÁ4 Husadalur, exposure at the W? tributary of Kirjuá 275 An. Me. He. Me–An. 2–3 GEUS Bulletin no 9 - 7 juli.pmd 07-07-2006, 14:19147 148 Profi le Locality Altitude (m) Vesicles Fractures Zone VÁ4 Kvígandalur, exposure at the SE tributary of Kvígandalsá 300–365 An. He. Le. Ch. 2–3 VÁ4 The cross between the path Oyrargjógv– Sørvágur and Sandavágur–Slættanes 436 Me. Th. St. Ch. 2–3 VÁ7 Road exposure 3 km north of Sandavágur 100–120 Ce–He–St. Ce–St–Me. Ce–He–Th. Ce–Mo–St. Ce–Me–St. Ce–Mo–He. Ce–He–St. Ce–Me*–Ch. Ce–Ap. 2–4 VÁ7 The western slope of Malinstindur 219 As above. 2–4 VÁ7 – do – 235 Ce–He–Me. Ce–Me–Gy. St–Ca. 2–3 VÁ7 – do – 280 Ce–Me–Ch.±Ca. ±Sm. 2–3 VÁ7 – do – 345 As above. 2–3 VÁ7 – do – 386 Empty vesicles. – VÁ7 – do – 410 Ce–He–Me. Th–Me. Th–An. St. Ch. 2–3 VÁ7 – do – 500 As above. 2–3 VÁ7 – do – 538 He. An. Me. Th. Th*. Cld. Ca. He–Me. Me*. Cld. 1–2 VÁ7 – do – 563 Me–Me*. Th*–Ph. Th*–Ch+Le. 1–2 VÁ7 The summit of Malinstindur 580 Ce–Me*. 1–2 VÁ7 – do – 620 He. Me. Ph. Ch. Th. Ca. Cld. 1–2 VÁ7 – do – 683 Me–He. Me*–Ch. Ph–Ch. 1–2 VÁ7 – do – 690 He. Ch. Le. Th. Cld. 1–2 ST2W The path Saksun–Haldarsvík: Kvíggjarhamar, Saksun 0–100 He. St. Th. Me. Ch. St–Ca–St. Gy. Tb. Ok. 2–3 ST2W The slope of the mountain between Skipá and Gellingará 150 He–Ch–Th. Me–St. 2–3 ST2W – do – 200 Me. Ca. 2–3 ST2W – do – 250 Th–Me. He–Me. Me–Ch. St. La. 2–3 ST2W – do – 310 As above. 2–3 ST2W – do – 325 Me. Me*. Th*–Ch. He–Me. Ok. Gy. Ca. 2–3 ST2W – do – 355 Me–Me*. Th–Me*. Th*–Ch. 2–3 ST2W – do – 360 Ce–Th*. He–Me*–Sm. 1–2 ST2W – do – 380 An–Th*. Th*–Le. Me*–Ca. 1–2 ST2W – do – 407 Ce–Ph–Ch. Ce–Th*–Ch. 1–2 ST2W – do – 430 Th*–Ch. 1–2 ST2W – do – 460 Empty vesicles. 0–1 ST2W – do – 555 Le–Ch. Th–Th*. 0–1 ST2W Víkarskarð 600 Ce. Th. Ch. Cld. 0–1 ST2W The NE slope of Gívrufelli 650 As above. 0–1 ST2W The summit of Gívrufelli 701 As above. 0–1 ST2E Víkarnes N of Haldarsvík 0–30 He–St. Ca. Ca–La. 3–4 ST2E The SE slope of Fjallið 100 As above + Th. Gy. Ok. To–Gy. La. 3–4 ST2E – do – 150 He. Me. Th. To–St. Th–Gy–Ap. 2–3 ST2E The summit of Fjallið 180 He–Me. He–Th*. Ca. 2–3 GEUS Bulletin no 9 - 7 juli.pmd 07-07-2006, 14:19148 149 Profi le Locality Altitude (m) Vesicles Fractures Zone ST2E The path Haldarsvík–Saksun: exposure 0.5 km SW of Haldarsvík 148 He–St. Me. Me–Th–Ch. Me–An. Ph–Le–Ch. 2–3 ST2E – do –, exposure 1 km SW of Haldarsvík 200 He–St. He–Me. 2–3 ST2E – do –, exposure at the Svínstiáir tributaries of Kluftá, 1 km SW of Haldarsvík 230 Me. Th. He. St. Ca. 2–3 ST2E – do –, exposure 1.2 km SW of Haldarsvík 250 He. Me. Mo. He. St. Ap. Ca. 2–3 ST2E – do –, exposure 1.5 km SW of Haldarsvík 280 Me–Th–Me–Gy–Sm. 2–3 ST2E – do –, exposure 1.8 km SW of Haldarsvík 350 Me–Th. 2–3 ST2E – do –, exposure 2 km SW of Haldarsvík 360 Me–Th. Me–Ph–Ch. 2–3 ST2E – do –, exposure 2.3 km SW of Haldarsvík 370 Me–Th. An–Me–Me*. 2–3 ST2E – do –, exposure 2.5 km SW of Haldarsvík 400 Th*–Ch. Me–Th*. Ph–Ch. Ch + Le. 1–2 ST2E – do – 410 Me–Me*. Ch–Le–Ch. 1–2 ST2E The SE slope of Víkartindur 420 Me–Me*–Le. Ch–Ph–Sm. 1–2 ST2E – do – 440 .Me*. Th–Th*–Ch. 1–2 ST2E – do – 500 Th*. Ch.Cld. 0–1 ST2E – do – 540 As above. 0–1 ST2E – do – 620 As above. 0–1 ST6W Road exposure at the main road Kvívík– Stykkið, 1.5 km E of Kvívík 50 He. St. La. Me. Th. Ap. He. St. Ap. Me*. Th. Ch. An. 2–4 ST6W Tunnel workplace at the village of Leynar 50 Me. St. La. 2–4 ST6W Exposure at Leynarvatn along the old road Tórshavn-Vestmanna 60–125 He. St. Wa. La. Ce. Cld. St. Ca. He. St. St*. La. Me*, Th, Le. 2–4 ST6W The path Leynarvatn–Hósvík, exposure 0.3 km NE of Leynarvatn 150–190 Ce–He–St. Ce–Me–Gy. Cld. Ph, Gy, Ap. 2–3 ST6W – do –, 0.4 km NE of Leynarvatn 210 Ce–He–St. Ce–Me–Th. Ce–St–La. 2–3 ST6W – do –, 0.5 km NE of Leynarvatn 260 Ce–Me–Th. Ce–He–Me. Ce–He–Th. Me–Ca. 2–3 ST6W The path Leynarvatn–Hósvík, exposure 0.5 km NE of Leynarvatn 300 As above. 2–3 ST6W – do –, 0.6 km NE of Leynarvatn 340 As above. 2–3 ST6W á Halsi, 1 km NE of Leynarvatn 380 As above. 2–3 ST6W – do –, 1.5 km NE of Leynarvatn 463 Ce–He–Me–Me*. Ce–Th–Ch. 2–3 ST6W – do –, 1.9 km NE of Leynarvatn 500 As above. 2–3 ST6W – do –, 2 km NE of Leynarvatn 510 Me–He–Me*. Me–Me*. Th*–Ch. He–Me. 2–3 ST6W Hósvíksskarð 520–530 Th. Th*. Ph. Ch. Le. + Ce. 2–3 ST6W The SW slope of Bøllufjall 550 As above. 1–2 ST6W The summit of Bøllufjall 584 As above. 1–2 ST6W The SW slope of Gívrufjall 530 As above. 1–2 ST6E Road exps. between við Áir and Hosvík 15 He–St*. He–St–Ap. He–St–Ch. He– Th–Ch. Th–St. Th–Ch. Ga–Th. An–Ch. An–Ap. An–Th. An–Th–Ch±Ce. He–Ch–St. Th–Gy+Ap. Ch–Th*–Ap. 2–3 ST6E The path Hosvík–Leynar: Smørdalsá 160–203 He–Me. He–Ch–Th, Me–Gy. He–An–Th. 2–3 GEUS Bulletin no 9 - 7 juli.pmd 07-07-2006, 14:19149 150 Profi le Locality Altitude (m) Vesicles Fractures Zone ST6E The path Hosvík–Leynar: Smørdalsá 240–260 Ce–Me–He. Ce–Th–Me. Cld. Me–Th–Ap–Gy. 2–3 ST6E – do – 360 As above. Ca–La. Cld. 2–3 ST6E The NE slope between Bøllufjall and Gívrufjall 436 Me–Th. He–Me–Ca. He–Th. 2–3 ST6E – do – 480 He–Me–Me*. Th–Ch. Th–Th*. 2–3 ST6E – do – 500 Th–Th*–Gy. Me*–Gy. 2–3 ST6E The NE slope of Bøllufjall 530 Th–Th*. Th–Ph, Th*–Ch. 1–2 ST6E The summit of Bøllufjall 584 As above. 1–2 ST10 Large quarry 0.5–1 km NW of Sund, Kalsbaksfjørður 15 Me. Me*. Th. An. Ph. Gi. Ap. 2–3 ST10 Exposure at Sundá, 1.2 km S of Sund 227 He. Me. Ca. 2–3 ST10 – do –, 1.6 km SW of Sund 265 Me. Th. St–He. 2–3 ST10 Quarry 0.5 km SW of Lambafelli at the high road Tórshavn–Kollafjørður 340 Ce–He. Ce–Ch–Le. Ce–An. Ce–Ch. Ce–He–Sm, Ce–He–Ch. Ce–He–Th–Ch. 2–3 ST10 Road exps. 1 km W of Sundshálsur along the high road Tórshavn–Kollafjørður 310 Ce–He–Me. Ce–Me–Ch. Ce–Th–Me. 2–3 ST10 Small quarry at end of road to the water reservoir of Havnardalur 170 He. Me. Th. Ch. 2–3 ST10 Road exposure at the road Tórshavn– Velbastaður, 0.5 km N of Velbastaður 160 Ce–Me. Ce–Th–Ch. 2–3 ST10 Exposure at the road Tórshavn–Velbastaður, just N of Velbasta ur 123 Me–Me*. Me–Ch. Me.Th–Ch. Th–Me– Me*. Cld, Ca. 2–3 EY1 Road exposure at the road Eiði–Norðskáli, 0.4–0.5 km SE of Eiði 60–100 Ap–Gy–Me. Me–Ph. He–Gy–Me. He– Me–Ch. St–Aå–Sm. Th–Ap. Th–St–Ap. Th–Ch–Sm. St–La–St*–Ca. He–St– Ch–Sm. 3–4 EY1 Localities on the road Eiði–Funningur: Quarry in Djúpidalur, 2 km east of Eiði 150 St–Gy. St–Th–Gy. Th–Ga–Th. Me–Th. Me–Ch. St–La. 3–4 EY1 50 m long road cutting on W slope of Slættaratindur, 3.5 km east of Eiði 200–230 Me–Th*–Gy. Me–Th*–Ch. Me–He–Me. He–Me. St–St*. La–Me*–Sm. He–Ap. St. Cld. Qz. 2–3 EY1 Road exposure 0.4–0.5 km E of Eiðisskarð just at the N slope of Vaðhorn 336–346 Ce–Me–Th*. Ce–Me–Ch. 2–3 EY1 The N slope of Vaðhorn 410 As above. He–St–St*. Mo–St. 2–3 EY1 – do – 435 As above. 2–3 EY1 Small quarry at the road fork Eiði, Funningur, Gjógv, 1 km west of Funningur (165) 165 He. St. Me. Me*. Ch. 2–4 EY1 Exposure at the coast line at Funningur 5–10 Mo. He. St. Me. +Ce. St. An. Me. Cld. 3–4 EY2 Exposure at the coast between Stórá and Marká 0–20 Mo. He. St. St. Qz. Cld. Ca. 3–4 EY2 The path Svínár–Funningur 30–40 He–Me. He–St–Gy. He–Me–Gy. 3–4 EY2 – do – 100 Me–Th–Ch. Th–Gi. Th–Me*. An–Ch. An–Th–Ch. Th–Gy–Ap. Me–Ap–St. 2–3 EY2 – do – 212 As above. 2–3 EY2 – do – 280 Me. Th. An. Ch. An–Th*–Gy. 2–3 EY2 – do – 346 An. Me. Me*. Th. Th*. Th–Ch–Sm. 2–3 EY2 – do – 400 Ce–Th–Th*–Ch. Ce–Ch. Th–Th*–Ch. 1–2 EY2 – do – 420 Ch–An. Ch.Gi–Th*. An–Ph–Ch. 1–2 GEUS Bulletin no 9 - 7 juli.pmd 07-07-2006, 14:19150 151 Profi le Locality Altitude (m) Vesicles Fractures Zone EY2 Kvígandalsskarð 460 Me*. Th*. Ch. Gy. Sm. 1–2 EY2 – do – 480 As above. 1–2 EY2 The E slope of Skerðingur 500 As above. 1–2 EY2 – do – 525 As above. 1–2 EY2 – do – 450 Ce–Th*. Ce–Me–Me*–Ch. 1–2 EY2 – do – 430 As above. 2–3 EY2 – do – 415 Ce–An. Ce–Qz. Cld. 2–3 EY2 – do – 380 Me. 2–3 EY2 Kvígandalur 363 He–Me. He–Th. EY2 Skipagjógv 180 Me–Th–Th*. Ch–Gi–Th. An–Th–Ap–Gy–Sm. Cl. Ca. 2–3 EY2 – do – 80 He. Me. Th. Ca. 2–3 EY2 – do – 50 Gy–He. Gy–Th–Me. 3–4 EY2 Skipagjósoyran 0–10 He. St. Th. La. Gy. He. Me–La–St. 3–4 EY3 Large quarry 1 km S of Oyri 20–30 Me–Th–Sm. Me–Th–Ch–Sm. Me–Gy– Me*. Cl–He–Th–Ap. 2–3 EY3 Oyrargjógv 100 Me–Th, Me–Gy. 2–3 EY3 – do – 210 No vesicles. He. St. Me. Th. Gy. 2–3 EY3 The path Oyri–Skálafjørður 251 Me. Th. Ch. 2–3 EY3 – do – 300 He–Me. Th–Me. Th–Ch. 2–3 EY3 – do – 340 An. Me*–Ch. 1–2 EY3 – do – 350 Me*–Ch. Th–Th*. 1–2 EY3 – do – 400 Th–St–Gy. Ch. St. 1–2 EY3 – do – 426 An–Th*. An–Th*–Ca. Ch. 1–2 EY3 – do – 495 Th*–Ch+Le. 1–2 EY3 The SW slope of Sandfelli 527 Ce–Th*–Ch. Ce–Cld. He. Me. Ca. Cld. 0–1 EY3 – do – 545 As above. As above. 0–1 EY3 The summit of Sandfelli 572 As above. As above. 0–1 EY3 The path on the S slope of Skálafjall 440 Me–Th. He–Me. 2–3 EY3 – do – 405 As above. 2–3 EY3 – do –, just at Öksnagjógv 200 As above. 2–3 EY4 Small quarry just N of Morskarnes, about 1 km N of Nesá 20 He–Th–Ch. Me–Th. He–St. He–Ap. Ca. 2–3 EY4 The W slope of Neshagi, just E of the locality above 140 Cl–Me–Th. He–Th. 2–3 EY4 Exposure at Skotá 194 As above. 2–3 EY4 – do – 230 Me–Me*. Ch. 1–2 EY4 – do – 320 Th*. Me–Me*. Ch. He–Me. He–St. 1–2 EY4 The SE slope of Kambur: exposure between the source of Skotá and Urðará 380 Me*. Ch, Le +Ce. 1–2 GEUS Bulletin no 9 - 7 juli.pmd 07-07-2006, 14:19151 152 Profi le Locality Altitude (m) Vesicles Fractures Zone EY4 The SE slope of Kambur: exposure between the source of Skotá and Urðará 400 As above. 1–2 EY4 – do – 430 Th*. Ch. Le. Ce. 0–1 EY4 – do – 462 Ch. Many empty vesicles. 0–1 EY4 The path Steffanstangi–Kambur 480 As above. 0–1 EY4 – do – 500 Th–Ch–Th*. Cld. Ca. 0–1 EY4 – do – 540 As above. 0–1 EY4 The summit of Kambur (trigonometric station) 593 As above. 0–1 EY4 The E slope of Heygshagi 440 Me*–Ch. Th*–Ch. 1–2 EY4 – do – 400 As above. 1–2 EY4 – do – 250 As above. 1–2 EY4 Markrá 250 Me–Me*. He–Th. He–Me*. 2–3 EY4 – do – 160 As above. 2–3 EY8 Road exposure at the old road Lervík– Fuglafjørður/Norðragøta, about 2 km NW of Lervík 80 Ce–Mo–He–Me. Ce–Ch. He–Me–St. 2–3 EY8 Localities along Kálvadalsá in Kálvadalur 200 Mo–He–Me–Me*. An–Th–Ch. Le–Ch–Le. He–Me–St–St*. An–Th. 2–3 EY8 – do – 270 As above. 2–3 EY8 – do – 300 He–Me*–Ch. An–Th*–Ch. 2–3 EY8 Mannsgjógv 400 An–Ph–Ch. An–Th–Ch, Me*–An. 1–2 EY8 The NE slope of Navirnar 300 He–Me–St*. He–Ch, He–Le. An–He. He–St. He–Me. 2–3 EY8 The E slope of Ritafjall 440 He–Me*–Ch. An–Th*–Ch. 1–2 EY8 – do – 490 He–Th–Ch. Me*–St*. 1–2 EY8 – do – 520 Th–Ch. Me*–Ch. He. St. Ca. 0–1 EY8 The summit of Ritafjall 560 Th.Ch. Le. 0–1 EY8 – do – 641 Th*. Nearly all vesicles are empty. 0–1 EY10 Large quarry just N of the road fork Skálafjørður–Runavík–Lambi 60–80 Me–St*. Th–St*. Th–Me–An. Th–Ch–St*. Co–Th. Ha. He–St*. He–Th–Ca. Ph–Ch–Ph. Ha–Ca. 2–3 EY10 The SW slope of Ritafelli, NE of the locality above 180 No vesicles. He–Me–Ch–Sm. Me*–Le–Ch–Sm. An–Me*–Sm. 2–3 EY10 – do – 200 Me–Me*. Ch. Th*. Ph. An–Me*–Sm. Me*–Ph– Le. Ap–Sm. 1–2 EY10 – do – 230–240 As above. 1–2 EY10 – do – 270 He–Th–Ch. Th*–Ph. An–Th*, Ch–St. An–St. Ap–Th–Ph. Ca. St–La. Me–Ap. 1–2 EY10 The edge of Ritafelli 350 St, Me*. Th*. Ph. Ch. Ce. 1–2 EY10 The SW slope of Stórafjall 380 Th*. Ch. Ph. 1–2 EY10 The W edge of Stórafjall 440 Th. Ph. Ch. An. Ce. An. St. Ch. Ph. Sm. 0–1 EY10 – do – 490 Empty vesicles. St, Th*. Ch. Ca. Cld. Sm. 0–1 GEUS Bulletin no 9 - 7 juli.pmd 07-07-2006, 14:19152 153 Profi le Locality Altitude (m) Vesicles Fractures Zone EY10 The W edge of Stórafjall 520 Th. Many empty vesicles. 0–1 EY10 The summit of Stórafjall 567 As above. 0–1 BO1 Large quarries at Klakkur 60 Me–Ch. He–Me. Cld. Mo–St–La. Ca–St. 2–3 BO1 The NE slope of Klakkur 100 Mo–An. Mo–He. Me–Ch. Ca. 2–3 BO1 – do – 140 Me–Th*. Ga–Me. Ch–Gi–Th. As in the vesicles. 2–3 BO1 The NE slope of Klakkur 160 Th–Me*–Ph. Ph–Ch. He–St. Ca–St. 1–2 BO1 – do – 210 Mo–He–Ch. Ch–Th. Th–Ph. Le–Ch. Ca–St. 1–2 BO1 – do – 260 Me–Th–La. An–St–La. An–Th–Ch. 2–3 BO1 The summit of Klakkur 414 Ch–Th. Th–Ph. 2–3 BO1 The S slope of Klakkur 380 As above. 2–3 BO1 – do – 300 Me–Th. Th*–Ch. Th–Ph–Ch. He–St–La. 2–3 BO1 – do – 260 He–Me–Th. He–Th. 2–3 BO1 The NE slope of Hálgafelli 280 Ce–He–Me–St. Ce–Me–An. 2–3 BO1 – do – 300 As above. 2–3 BO1 – do – 360 As above. 2–3 BO1 – do – 380 Ce–Mo–He–Th. Ce–He–Me. 2–3 BO1 – do – 400 Ce–St–Ch. He–Th–Me–St. 2–3 BO1 – do – 450 As above. 2–3 BO1 – do – 480 An–Me–Me*. Th–Ch. 2–3 BO1 The summit of Hálgafelli 503 Ce–He–Me. St–La. 2–3 BO2 Exposure at stream 0.6 km SW of Norðoyri 20–80 He. Me. Ch. An. Ap. St. Cld. Ca. 2–3 BO2 The W slope of Høgahædd 140 An. Me. Ch. Many empty vesicles. As above. 1–3 BO2 – do – 220 He–St. He–Ch–St. Th–Ph. St. Ca. 2–4 BO2 – do – 270 Empty vesicles. – BO2 – do – 310 He–Me–Me*. Me–An. Me–Ch. 2–3 BO2 – do – 320 Ch–Th*–Ch. He–Ch.Th*. An. 1–2 BO2 – do – 330 Me*. Th’. Ch. Ca. 1–2 BO2 – do – 360 As above. Ch. Th*. Ca. 1–2 BO2 – do – 440 Th*. Ca. Op. Cld. 1–2 BO2 – do – 474 Me. Me*. Th*. Ch. 1–2 BO2 – do – 510 Th–Th*. Ca. Cld. Many empty vesicles. 0–1 BO2 – do – 550 As above. 0–1 BO2 The summit of Høgahædd 563 As above. 0–1 BO3 Large quarry between Norðdepil and Depil 40–50 Ce–He–Th. Ce–He–Na–Th. Ce–Th–Ch. Cl–He–St–Ap. Cl–Th– Ap. Cl–Ph. 2–4 BO3 Depilsá 150 Me–Me*–Ch–Le. Me–Me*–Ch. He–Me. 2–3 BO3 – do – 200 Me*–Ch, An–Ch. 1–2 BO3 – do – 300 He–Me*–Ch. He–Th*–Ch. An–Ph–Ch. +Ce. He–St. He–Th–Ca. 1–2 GEUS Bulletin no 9 - 7 juli.pmd 07-07-2006, 14:19153 154 Profi le Locality Altitude (m) Vesicles Fractures Zone BO3 Depilsá 340 As above. 1–2 BO3 E slope of Lokki 375 Ch–Gi–Th’. Ch–An. 0–1 BO3 – do – 400 Ch–Th*–Ch. Ch–Le. 0–1 BO3 – do – 450 As above. 0–1 BO3 – do – 470 Th. Ch. Ca. He–St–Th–Ca. 0–1 BO3 E slope of Lokkanøv 460 Ce–An–Ch. Ce–Th–Ch–Th*. Many empty vesicles. 0–1 BO3 – do – 580 As above. 0–1 BO3 – do – 700 As above. 0–1 BO3 The summit of Lokki (trigonometric station) 754 As above. 0–1 VI1 The starting point of the profi le is the largest stream 0.5 km SE of Hvannasund 50 Ce–Me–St. Ce–An–Th–Me. Ce–Me–Ch. Ce–He–St–Me. Ce–Cl–St. Ce–Cl–Me– Ca. 2–3 VI1 SW slope of Enni 120–132 Empty vesicles. – VI1 SW slope of Enni 180 Mo–An. 2–3 VI1 – do – 210 An. Ph–Ch. An–Th. Me–Me*. He–Me– Ch. He–Me*–Ch. He–Ph– Ch. He–Th–Me. 2–3 VI1 – do – 225 As above. 1–2 VI1 – do – 240 Me*. Th*. An. 1–2 VI1 – do – 270 Ce–Th–Th*–Ch. Ce–Ch–Le. Ce–An– Ch. Ce–Ch–St. Ce–He. Ce–He–Cld. He–St. Cld. 1–2 VI1 – do – 310 Ch–Gi–Th*. St–Ch. Ph–Ch. Th–Th*. 1–2 VI1 – do – 360 Ce–Ch. Ce–Ph–Ch. Ce–Th*. Ch. 1–2 VI1 – do – 380 Ch. Th. Le. Sm. Cld. 1–2 VI1 – do – 420 Th*–Le–Ch–Sm. Op. Sm. 0–1 VI1 – do – 550 As above. Many empty vesicles. 0–1 VI1 – do – 600 Ca and Siderite. 0–1 VI1 The summit of Enni 651 As above. 0–1 VI2 Small quarry at the road Hvannasund– Viðareiði, 2.6 km N of Hvannasund 40–80 Ce–He–Me. Ce–He–Th. Ce–He– Ch–Sm. Ce–Ch–Sm. Ce–Ph–Me*. Ce–Me–Me*. He–Me–St. 2–3 VI2 W slope of Tunnafjall 80–100 He–Me–Me*. An–Th–Me. An–Th–Ch. An–Ph–Ch. He–St. St–Me. 2–3 VI2 – do – 150 As above. 1–2 VI2 – do – 200 As above. 1–2 VI2 – do – 225 Me*. Th*. Ch. Ph. An. He. St. Ca. 1–2 VI2 – do – 250 Me*. Th*. Ch. 1–2 VI2 – do – 300 Th*. Ch. 1–2 VI2 – do – 315 As above. 0–1 VI2 – do – 390 An. Th’. Ch. Ph. Me*. Ph. St. 0–1 VI2 – do – 460 Th*. Ch. Le. Sm. St. Sm. 0–1 VI2 – do – 520–550 Empty vesicles. Qz. Cld. Ca. 0–1 GEUS Bulletin no 9 - 7 juli.pmd 07-07-2006, 14:19154 155 Profi le Locality Altitude (m) Vesicles Fractures Zone VI2 The summit of Tunnafjall 593 Th. Th*. Ch. 0–1 VI2 The S Slope of Myrnafjall 620 No vesicles. Th. Th*. 0–1 VI2 The summit of Myrnafjall (trigonometric station) 688 Th. Th*. Only 20% of the vesicles are mineralised. 0–1 VI3 Small quarry at the road Viðareiði– Hvannasund, 2.5 km south of Viðareiði 80 He–Th*. Me–Me*–Ch–Se. As in the vesicles. 1–2 VI3 The W and the SW slope of Malinsfjall 150 He–Th*. Me–Me*–Ch. An–Me*–Ph. 1–2 VI3 – do – 200–220 Th*. Ch. Le. Me. Me*. Th. Th*. An. St. 0–1 VI3 – do – 255 Th*. Ph. An. He–St. 1–2 VI3 The W and the SW slope of Malinsfjall 310 Th*–Ch. 0–1 VI3 – do – 300–330 Me–Th*. Gi–Ch. 0–2 VI3 – do – 440 Th*. Ch. About 50% of the vesicles are empty. An–St. 0–1 VI3 – do – 540 As above. 0–1 VI3 – do – 605 Ch–Th–Le. Ca. Ca–Th–Ca. 0–1 VI3 – do – 660 All vesicles are empty. 0–1 VI3 – do – 680 As above 0–1 VI3 – do – 710 Scattered mineralisations of Th and Ch. 0–1 VI3 The summit of Malinsfjall 750 As above. 0–1 GEUS Bulletin no 9 - 7 juli.pmd 07-07-2006, 14:19155 156 Max depth Min depth Vesicles Zone Lopra-1/1A –3543 –3400 La, Pr, Ca, Cl. HT –3400 –3200 La, Mo, Pr, Cl. HT –3200 –3000 La, Mo, Pr, Sm, Qz. HT –3000 –2800 La, Pu, Qz, Cl. HT –2800 –2600 (no data) –2600 –2400 La, Ca, Pr ,Cl. HT –2400 –2200 La, Pr, Pu. HT –2200 –2000 Th, Ep, He, La, Pr, Wa, Mo, Ca, Ce, Sm, Cl, Si. 5–6 –2000 –1800 Sc, Th, Ep, He, La, An, Ca, Ce, Cl, Si. 3–5 –1800 –1600 Sc, Th, St, Ep, La, An, Ca, Ce, Sm, Cl, Si. 3–5 –1600 –1400 Sc, Th, St, Ep, He, La, An, Ca, Ce, Sm, Si. 4–5 –1400 –1200 Me, Th, St, Ep, He, La, Ce, Sm, Cl, Si. 4–5 –1200 –1000 Me, Sc, Th, Ep, He, La. 3–4 –1000 –800 Me, Sc, Th, St, Ep, He, La, An, Ca, Cl, Si. 3–4 –800 –600 Th, St, Ep, He, La, An, Cl. 3–4 –600 –400 Me, Sc, Th, Ep, He. An. Ca. 2–3 –400 –200 Me, Sc, Th, Ep, He, An, Ca, Cl, Si. 2–3 –200 0 Me, Sc, Th, St, He, An, Mo, Ca, Cl, Si. 2–3 Vestmanna-1 –600 –575 He. He–Ch. 3–4 –575 –550 He. An. St–St*. Ch–Sm. 3–4 –550 –525 He–Ch. Ap. Th–Ap. Ch–Sm. 3–4 –525 –500 He. He–Ac. Th–Ch. St–Ch. –500 –475 An–Th–Mt. Th–Sm. 3–4 –475 –450 An–Th–Sm. Th–Sm. 3–4 –450 –425 Gy–Th–Sm. An. An–Th–Sm. Th. Sm. 3–4 –425 –400 An. He–La–Ch. Me–Ch. Th–Sm. Ch–Sm. 3–4 –400 –375 He–La–Ch. Me–Ap–Ch. Me–Ch+Le–Sm. Ch–Sm. 3–4 –375 –350 Me. Gy–Th–Sm. Th–Sm. Th*–Ch. Ch+Le. 2–4 –350 –325 Ap. Th–Ap. Gy–La. Gy–Th–St. Ph. Th*–Sm. Th*–Ch. 1–4 –325 –300 He. He–Me. He–La–Ch. Mo–He–Ch, Th*–Sm. Th*–Ch, Ch–Sm. 2–4 –300 –275 He. He–Ch. Me–He–St. Th–Ga–Ch. Th*–Ph–Ch. Th*–Ch. Ch–Sm. 2–4 –275 –250 Me. Me–Th–Ch. Me–Th–Ph–Ch.. La–Me. Ap. Th–Ch–Sm. Ch–Sm. 2–4 –250 –225 Th–Gy–Sm. Th–Th*–Ch. He–Th–Ap. Le–Sm. 2–4 –225 –200 –200 –175 He. He–Ch–Ap–Sm. Me–Ch, Th–Th*– Ch. Th–Gy–Mt. Th–Ap. An. Ap. Le–Sm. 2–3 –175 –150 Me–He–Me*. Me–He–Ap. Me–Ap. Me– He–Th–Le. Me–Th–Ph–Ch. Th*–Ch –Le. Na–Ch. Ch–Sm. 2–3 –150 –125 Me. Me–Th–Ph–Ch. Ph–Sm. Me*–Ch An–Sm. 2–3 –125 –100 –100 –75 Me. Me–Th–Ch–Sm. Me+Na–Ap–Sm. Me*–Ch. An–Ep–Ch. Mo–Ch. Th–Ch. 2–3 –75 –50 He. He–Th. Mo–He. Me–Th. Na–Ch. Th–Ch. Me*–Ch. Ch–Sm. 3–4 –50 –25 Ch–Sm. Ep–Ch. 3–4 –25 0 Me. Me*. Me–Ap. Me–Th. Me*–Ch. Mo–Ch. 2–3 Appendix B. Minerals found in vesicles within different depth intervals in the Lopra-1/1A and Vestmanna-1 boreholes GEUS Bulletin no 9 - 7 juli.pmd 07-07-2006, 14:19156