Mineral Chemistry and Texture Paragenesis of Alteration Minerals in the Pahtohavare Cu-Au Deposit, Sweden
The Proterozoic Pahtohavare Cu-Au deposit in the northernmost part of Sweden within the Fennoscandian shield consists of a syngenetic stratiform sulphide-magnetite mineralisation (East Ore) which is uneconomic and three stratabound to discordant epigenetic Cu-Au mineralisations (Central, South-East...
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| Format: | Bachelor Thesis |
| Language: | English |
| Published: |
2014
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| Subjects: | |
| Online Access: | http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-43869 |
| Summary: | The Proterozoic Pahtohavare Cu-Au deposit in the northernmost part of Sweden within the Fennoscandian shield consists of a syngenetic stratiform sulphide-magnetite mineralisation (East Ore) which is uneconomic and three stratabound to discordant epigenetic Cu-Au mineralisations (Central, South-East and South Ores) hosted by the Viscaria formation. These epigenetic deposits are hosted by fine-grained albite felsite formed by alteration of graphitic schist while the East Ore is hosted by tuffite. The black graphitic schist have acted as a chemical trap for the mineralising fluids explaining the decomposition of the graphite within the schist proximal to mineralised zones and altering it into albite felsite. The past tectonic events made the Kiruna area having a favorable permeability for epigenetic solutions like saline hydrothermal fluids. This favourable permeability is one of the main important characteristic which explains the formation of Pahtohavare ores. A scapolite-biotite alteration is enveloping the albite-altered mineralised zone and occurs in all stratigraphic units. One albite alteration of the tuffite is related to the intrusion of the footwall mafic sill and the other one is an additional ore-related mineralised albitization which is distinguishable by the lack of spatial relationship with the mafic sill and the occurrence of disseminated Ferro-dolomite. Chlorite has been formed by replacement of biotite and amphibole. A negative correlation between Mg and Cl contents of amphiboles is distinguishable which indicates that Mg-Cl avoidance mechanisms can control the incorporation of halogen in the amphibole structure. Scapolite from scapolite-biotite alteration surrounding the ore-bearing albite felsites and ore veins have a dominantly marialitic composition which indicates that the alteration must have been due to highly saline fluids. The occurrence of dipyre in Pahtohavare can be explained by the fact that the formation of the deposit happened in a Na-Cl rich environment. The main ore minerals are ... |
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