Posiva publishes Working Reports and Posiva Reports. From the year 2006 nearly all the reports have been published on our webpage and they can be found in the databank. In the databank you can also find our Annual Reviews and some other publications as well. You can also find print-quality pictures and useful links in the databank.

Recent publications

Workreport 2020-16



Investigations of Low Temperature Mineral Precipitates at Kyläniemi KYL-KR1, KYL-KR2 and Olkiluoto OL-KR46, OL-KR58


Seitsamo-Ryynänen, M., Karhu, J.



Page count:



Ten fracture mineral samples from Kyläniemi and 17 samples from Olkiluoto were collected for geochemical, isotope geochemical and mineralogic investigations. The samples were collected from fractures with water conductivity or their immediate vicinity. The sites taken for the study were selected to have a different environmental history during the last 11 700 years from that characterizing the Olkiluoto island area. During this time, the Kyläniemi region was first below stagnant glacier edge several hundreds of years and has never been overlain the Baltic Sea, excluding the possible effects of marine water intrusions during the last glacial period. At Olkiluoto, the drillcore sampled has been drilled under the Baltic Sea, to an area expected to be outside the effects of meteoric water circulation after the glacial period. In addition to fracture mineral samples, a recent mineral precipitate linked to bacterial sulfate reduction on a drillhole instrumentation from the Olkiluoto Island was studied mineralogically and geochemically.

At Kyläniemi, the mineralogic studies of the fracture fillings indicate the presence of more than one calcite generation on fracture surfaces. Calcite in fracture fillings is compositionally nearly pure CaCO3, with minor amounts of Mn. The δ13C and δ18O values of fracture calcite at Kyläniemi range from -24.5 to 34.2 ‰ and -19.3 to -4.4 ‰, respectively. The isotopic composition of the most calcite fillings may be in a low temperature equilibrium with waters similar to the present-day precipitation in the area. One calcite filling at depth of 100 m contained a calcite generation highly enriched in both 13C and 18O. These values give indications of microbial methanogenesis in a low temperature environment, possibly associated with a marine water intrusion during one of the earlier interglacial periods.

 Due to shearing and tectonic movements at the Olkiluoto study site, calcite crystal morphology could not be determined from the fracture fillings, and, therefore, their relation to the previously defined morphological fracture calcite groups could not be identified. Calcite in the fracture fillings is compositionally nearly pure CaCO3, with a minor Mn content. The δ13C and δ18O values of fracture calcite at Olkiluoto range from -25.8 to 7.9 ‰ and -18.4 to -4.7 ‰, respectively.  An unusually large enrichment in 18O in the upper ~50 m of the bedrock provides strong evidence for calcite precipitation from a water type nearly equal to the composition inferred for the Littorina Sea derived water. The δ34S values of fracture pyrite in the uppermost ~60 m of the bedrock range from -37.0 to +27.9 ‰, suggesting bacterial sulfate reduction in a closed system environment.

The precipitate formed on the drillhole instrumentation consists mainly of calcite. In addition, trace amounts of nanocrystalline or microcrystalline pyrite was observed in the precipitate. The δ13C and δ18O values of calcite range from -13.2 to -9.7 ‰ and -9.1 to -7.4 ‰, respectively. Precipitation appears to have occurred in equilibrium with the water residing in the instrumentation drillhole. The δ34S values of pyrite range from -5.7 to 8.3 ‰. The relatively small variability of the δ34S values suggests sulfate reduction in an environment approaching an open system.


Paleohydrogeology fracture fillings, mineral precipitate, stable isotopes, carbon isotopes, oxygen isotopes, sulfur isotopes.


WR 2020-16_web (pdf) (10.3 MB)


Share article:
This website stores cookies on your computer. These cookies are used to improve our website and provide more personalised services to you.


To make this site work properly, we sometimes place small data files called cookies on your device. Most big websites do this too.

1. What are cookies?

A cookie is a small text file that a website saves on your computer or mobile device when you visit the site. It enables the website to remember your actions and preferences (such as login, language, font size and other display preferences) over a period of time, so you don’t have to keep re-entering them whenever you come back to the site or browse from one page to another.

2. How do we use cookies?

A number of our pages use cookies to remember your actions and preferences (such as login, language, font size and other display preferences.)

Also, some videos embedded in our pages use a cookie to anonymously gather statistics on how you got there and what videos you visited.

Enabling these cookies is not strictly necessary for the website to work but it will provide you with a better browsing experience. You can delete or block these cookies, but if you do that some features of this site may not work as intended.

The cookie-related information is not used to identify you personally and the pattern data is fully under our control. These cookies are not used for any purpose other than those described here.

3. How to control cookies

You can control and/or delete cookies as you wish – for details, see You can delete all cookies that are already on your computer and you can set most browsers to prevent them from being placed. If you do this, however, you may have to manually adjust some preferences every time you visit a site and some services and functionalities may not work.