ISSN:
1432-1866
Source:
Springer Online Journal Archives 1860-2000
Topics:
Geosciences
Notes:
Abstract The Tallberg deposit is situated in the Skellefte District in northern Sweden. It is a Palaeoproterozoic equivalent of Phanerozoic poryphyry-type deposits. The mineralization is situated within the Jörn granitoid complex and is associated with intrusive quartz-feldspar porphyries. The granitoids are coeval with mainly felsic volcanic rocks hosting several massive sulphide deposits. The alteration is generally of a mixed phyllic-propylitic type, but areas or zones associated with high gold grades exhibit phyllic alteration. Ore minerals are pyrite, chalcopyrite, sphalerite, magnetite, and trace amounts of molybdenite. In this stable isotope study, quartz, sericite, and chlorite from the alteration zones were sampled. The magmatic quartz has a ∂18O composition of + 6.2 to +6.7‰ whereas the quartz in the hydrothermal alteration zones have values ranging from +7.5 to +10.6‰. The calculated temperatures for this fractionation range from 430° to 520°C. The sericites have ∂18O ranging from +4.6 to +8.2‰ (average +6.6‰) and ∂D -31 to -54‰ (average -41‰). Chlorites range from ∂18O +4.2 to +7.7‰ and ∂D from −34 to −44‰. The range of ∂34S of 11 pyrite samples is +3.8 to +5.5‰ with an average of +4.6 ± 0.5‰, suggesting a relatively homogeneous sulphur source, probably of magmatic origin. Modelling waters in equilibrium with the minerals indicates early magmatic fluids with ∂18O of ≈ 6.5‰. This fluid mixed with a low ∂18O and high ∂D fluid, which is tentatively identified as seawater. The ∂18O signature of sericite and chlorite also indicates significant water-rock exchange, explaining the positive ∂18O values for the waters in equilibrium with the hydrated minerals.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00191510
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