Objective
The problem of the formation of super-large unique tungsten (W), tin (Sn) and tantalum (Ta) deposits may be correctly treated on the basis of the construction of genetic models of ore-forming systems in particular geodynamic environments. Available data point to a setting of such deposits in late collisional and anorogenic stages. Mantle-crust interactions are supposedly responsible for the origin of the ore-forming systems. Combined Sm-Nd, Rb-Sr, Pb-Pb and U-Pb data favour lower to perhaps middle crustal sources for granitoid protoliths associated with ore-forming processes. Some epsilon--Nd and epsilon--Sr data provide evidence for geologically long residence ages of these source rocks in the crust after an extraction of Sr in much older magmatic events. Supposedly, the separation of Sr and Rb with a long-lasting retention of Rb caused unusually high 87Sr / 86Sr ratios, which seem to be common in these ore deposits. The determination of the chemical and mineralogical compositions of these crustal sources will be examined. An enhancement will be assumed in W, Sn and Ta, as well as in Cs, Rb, Li, Be and F in the crustal residue after the extraction of the much older magmas. The latter were supposedly enriched in Ca and Sr. The formation of super-large ore deposits requires a huge volume of fluids. The origin of these fluids and their role in the mobilisation, transfer and concentration of ore substances will be investigated by the geochemistry of individual elements and by melt and fluid inclusion studies. The significance of C1, F, S, N and C, including reduced carbon compounds, has to be scrutinised. The final target is to determine favourable geodynamic settings, physico-chemical conditions and other factors of importance for the evolution of ore-forming systems that promote the formation of super-large W, Sn and Ta deposits.
Results are expected in the determination, i.e. the evaluation of exact data, of geotectonic, geochemical, isotope and geochronological indicators for the formation of super-large W, Sn and Ta deposits. A geotectonic position of such ore deposits is expected from active continental margin settings to continent / continent collisions and intraplate positions. Some 40 elements will be measured and many are expected to lie in a different order of precedence. Isotope data from rocks and minerals will be used to focus on stable isotopes (O, S, C) and on radiogenic isotopes (Rb-Sr, Sm-Nd, U-Pb, Pb-Pb). From the stable isotopes, useful characteristics of magmatic sources are expected. The radiogenic isotopes will provide data on crustal or mantle origin, possibly on multiple sources and magma mixing. The geochronological methods (Rb-Sr, Sm-Nd, U-Pb, Pb-Pb, K-Ar) will give age data on individual ore deposits / provinces. Exact age data from even a single ore deposit may improve the identification of an ore province and the search for new similar ore deposits. Other ore provinces may reveal an absolute different ore-forming age. Statistical methods will be used to elaborate an order of precedence of the indicators for ore-forming systems of the W, Sn and Ta deposits.
Topic(s)
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80333 München
Germany