Geochemical Features of the Noril'sk intrusions (Siberia, Russia)
Abstract
The Siberian Trap Province consists of some volcanic formations and many intrusive bodies considered as one plume system. Pt-Cu-Ni Noril’sk deposits are the result of long interaction Tuklonsky picritic magma and surrounding rocks. But the true relations of effusive and intrusive rocks are unknown so as the high-Mg rock’s genesis and their role in ore-forming processes. In order to discover specific features and understand origin of the ore-forming magmas we compered ore-bearing (Talnakh, Noril’sk 1) and ore-free (Low Talnakh, Zelenaya Griva) inrtusions. 1.In the La/Sm - Gd/Yb and Sm/Nd - Ce/Yb diagrams the studied plutons are plotted in separated fields which coincide with fields of different effusive formations: Noril’sk 1- Mukulaevsky basalts; Low Talnakh - Nadezhdensky formation; and Talnakh - Morongovsky formation. The effusive rocks relate to a common trend explained by their difference in the grade of contamination by crust material, but the same trend for intrusive rocks cannot be to explain by this manner because their petrochemical characteristics are opposite to the ones of effusives. 2.The Talnakh massive is considerably different from the Low Talnakh and Zelenaya Griva plutons in K2O concentration. The field of the Noril’sk-1 rocks occupies an intermediate position in the TiO2/K2O - CaO/Al2O3 diagram: some part of samples are plotted in the field of ore-free intrusions. 3. Data of melt inclusions in olivines from the picritic horizons of different intrusioms show their formation under T=1220-1250oC from high-SiO2 (54 mas.% )melt. High REE concentrations determined in this mineral provide additional evidence for its intratelluric origin. So there is no total correlation between basalts and intrusions. Ore-bearing and poorly mineralized plutons cannot be reliably distinguished on the petrochemical characteristics only. We believe the high-magnesian rocks have not crystallized from the picrite magma: they have cumulative nature and they are not the primary melt products.
- Publication:
-
EGS - AGU - EUG Joint Assembly
- Pub Date:
- April 2003
- Bibcode:
- 2003EAEJA.....4252S