Geochemical characterization of felsic metavolcanic rocks hosting the Archean Taivaljärvi Ag-Zn-Pb-Au deposit in the Tipasjärvi greenstone belt, eastern Finland
1University of Oulu, Oulu Mining School, Geology
|Online Access:||PDF Full Text (PDF, 9.7 MB)|
|Persistent link:|| http://urn.fi/URN:NBN:fi:oulu-201905111739
Oulu : A. Cima,
|Publish Date:|| 2019-05-17
|Thesis type:||Master's thesis
The Taivaljärvi Ag-Zn-Pb-Au deposit is located in the Archean Tipasjärvi greenstone belt (TGB) in eastern Finland, which is part of the Tipasjärvi-Kuhmo-Suomussalmi greenstone complex. The deposit is hosted by strongly altered felsic meta-volcanic rocks and has silver as its main commodity.
Geochemical characterization of the host unit of the Taivaljärvi deposit, the Koivumäki Formation, was carried out along the entire TGB. Samples of metavolcanics rocks from different profiles across the TGB were analyzed for whole-rock major and trace element chemistry, including hanging-wall, ore zone and footwall samples from the silver mine. Detailed lithogeochemical exploration techniques were applied in order to identify potential areas for new discoveries in the belt. Once fertile areas were delineated, they were contrasted with other areas of so far unproven fertility using lithogeochemical data coupled with normative mineral plots, mass-balance calculations, alteration indexes and petrographic observations. Areas of lesser and greater potential for mineralization styles similar as those of the Taivaljärvi deposit were subsequently identified.
There are two main groups of felsic metavolcanic rocks. Those from the mine and the Kivisuo-Talassuo, Lapasuo and South Jäkäläsuo profiles are mainly rhyolites whereas those from the Palovaara, Katajasuo profiles and most of Koraminvaara profiles range from rhyodacites to dacites. All the rocks show a calcalkaline to transitional trend and a trace element signature of a continental arc geological setting.
The main alteration processes are sericitization, chloritization and silicification. Felsic metavolcanic rocks from the mine area are of FII affinities, and show gently sloping REE patterns with La/YbN ratios of 5.5–8, moderately high Zr/Y ratios, intermediate HFSE concentrations, and negative Eu anomalies (Eu/Eu* 0.35–0.55). They indicate mass gains in K₂O, SiO₂, MgO and several metals (Ag, Pb, Zn, Au), moderate mass gains in FeO as well as depletion in Na₂O and CaO. The areas that show similar trace element signatures and mass-transfer patterns together with petrographic and geochemical evidence for alteration are Lapasuo and Kivisuo-Talassuo, followed less clearly by Koraminvaara. On the other hand, the Koivumäki, South Jäkäläsuo and Palovaara areas have different characteristics, being less favorable as exploration targets.
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