Dannemora ore deposit is hosted by Palaeoproterozoic, Svecofennian, marble and consists of 25 bodies of skarn iron ore in limestone with an alternating high and low content of manganese. The deposit also contains a few sulphide mineralizations, which were investigated by microscopy and electron microprobe analyses to see if it is possible to use sphalerite as geobarometer and arsenopyrite as geothermometer. Arsenopyrite gave a temperature of 375±105o C, however zoned arsenopyrite crystals showed variable negative temperatures (low in As). The pressure for sphalerite was estimated in two ways, by a plot figure and by an equation by Hutchison & Scott (1981). The first calculation gave a pressure estimate of 3.7±0.4 kb, and the second a pressure of 2.2 to 4.4 kb. The sphalerite is apparently sensitive to high manganese contents (>1.0 wt %) in one sample, resulting in an unrealistic pressure of 11.3 kb. Besides minor discrepancies, the obtained data of temperature and pressure correspond well with the metamorphic grade of the area of greenschist to lower amphibolite facies.
Arkivexemplar i Uppsala universitets arkiv