Databank

Workreport 1997-39

Back

Name:

Selvitys malmien esiintymismahdollisuudesta Hästholmenin alueella

Writer:

Aimo Kuivamäki; Pasi Nissinen; Antero Lindberg

Language:

Finnish

Page count:

76

Summary:

Working report: Aimo Kuivamäki, Pasi Nissinen and Antero Lindberg, 1997. An evaluation of the
mineralization potential of the Hästholmen area. Posiva Oy. Work report 97-39.

ABSTRACT

A number of greisen veins were found during a reconnaisance geological study of the
Hästholmen region during 1996. Such veins, which consist primarily of quartz, mica and
topaz, record crystallization from late stage magmatic fluids circulating within fracture
systems and are commonly associated with hydrothermal tin mineralization. For this reason
Posiva Oy decided to commission a more detailed appraisal of greisen veins at Hästholmen;
although priority was given to the immediate vicinity of Hästholmen, observations were also
made over a wider area in order to gain a regional perspective of mineralization potential of
the rapakivi granites.

A total of 19 greisen veins were recorded in bedrock in the vicinity of Hästholmen, while
evidence for greisen mineralization was additionally obtained from 35 glacial erratics. The
greisen veins have dominant modal NW - SE trend, parallel to that of principal fractures and
quartz veins in the area, and without exception dip steeply. The predominant lithology of the
mineralized boulders was equigranular rapakivi granite.

The veins tend to be relatively narrow (0.1 - 20 cm) in both bedrock and glacial erratics,
with bedrock examples having a mean length of 9.7 m, with an overall range between 1 -58
m.

Samples from selected veins were analyzed by XRF in Chemistry Laboratory of the
Geological Survey of Finland at Espoo. Major and trace element results were compared with
available published data from barren and tin-bearing rapakivi intrusions and it was
concluded that all the Hästholmen samples fall within the range of typical rapakivi granites.
Elevated Sn, Zn, Pb and Cu abundances were only recorded in a few samples and although
petrographical studies show that the veins are indeed of greisen type, enrichments are
nevertheless rather modest.

Therefore, the results of field mapping, together with microscopic and geochemical
investigations, suggest that the potential for economic mineralization in the Hästholmen area
is rather limited.
Aimo Kuivamäki, Pasi Nissinen and Antero Lindberg, 1997. An evaluation of the
mineralization potential of the Hästholmen area. Posiva Oy. Work report 97-39.

ABSTRACT

A number of greisen veins were found during a reconnaisance geological study of the
Hästholmen region during 1996. Such veins, which consist primarily of quartz, mica and
topaz, record crystallization from late stage magmatic fluids circulating within fracture
systems and are commonly associated with hydrothermal tin mineralization. For this reason
Posiva Oy decided to commission a more detailed appraisal of greisen veins at Hästholmen;
although priority was given to the immediate vicinity of Hästholmen, observations were also
made over a wider area in order to gain a regional perspective of mineralization potential of
the rapakivi granites.

A total of 19 greisen veins were recorded in bedrock in the vicinity of Hästholmen, while
evidence for greisen mineralization was additionally obtained from 35 glacial erratics. The
greisen veins have dominant modal NW - SE trend, parallel to that of principal fractures and
quartz veins in the area, and without exception dip steeply. The predominant lithology of the
mineralized boulders was equigranular rapakivi granite.

The veins tend to be relatively narrow (0.1 - 20 cm) in both bedrock and glacial erratics,
with bedrock examples having a mean length of 9.7 m, with an overall range between 1 -58
m.

Samples from selected veins were analyzed by XRF in Chemistry Laboratory of the
Geological Survey of Finland at Espoo. Major and trace element results were compared with
available published data from barren and tin-bearing rapakivi intrusions and it was
concluded that all the Hästholmen samples fall within the range of typical rapakivi granites.
Elevated Sn, Zn, Pb and Cu abundances were only recorded in a few samples and although
petrographical studies show that the veins are indeed of greisen type, enrichments are
nevertheless rather modest.

Therefore, the results of field mapping, together with microscopic and geochemical
investigations, suggest that the potential for economic mineralization in the Hästholmen area
is rather limited.

Keywords:

File(s):

Selvitys malmien esiintymismahdollisuudesta Hästholmenin alueella (pdf) (2.7 MB)


Back


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

Cookies

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 aboutcookies.org. 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.

Close