Abstract
Granitoid-hosted mineral deposits are major global sources of a number of economically important metals. The fundamental controls on magma metal fertility are tectonic setting, the nature of source rocks, and magma differentiation. A clearer understanding of these petrogenetic processes has been forged through the accessory mineral zircon, which has considerable potential in metallogenic studies. We present an integrated zircon isotope (U-Pb, Lu-Hf, O) and trace element dataset from the paired Cu-Au (copper) and Sn-W (tin) magmatic belts in Myanmar. Copper arc zircons have juvenile εHf (+7.6 to +11.5) and mantle-like δ18O (5.2–5.5‰), whereas tin belt zircons have low εHf (−7 to −13) and heavier δ18O (6.2–7.7‰). Variations in zircon Hf and U/Yb reaffirm that tin belt magmas contain greater crustal contributions than copper arc rocks. Links between whole-rock Rb/Sr and zircon Eu/Eu* highlight that the latter can monitor magma fractionation in these systems. Zircon Ce/Ce* and Eu/Eu* are sensitive to redox and fractionation respectively, and here are used to evaluate zircon sensitivity to the metallogenic affinity of their host rock. Critical contents of Sn in granitic magmas, which may be required for the development of economic tin deposits, are marked by zircon Eu/Eu* values of ca. ≤0.08.
Highlights
The zircon Eu anomaly records magma fractionation, and using the example of Sn mineralization, an incompatible metal whose concentration is highly sensitive to the degree of fractionation, we show how zircon chemistry can be used to establish thresholds that may distinguish barren from fertile granites
Zircon 207Pb-corrected 238U/206Pb magmatic ages for copper arc granites range from 102-98 Ma, and from 76–58 Ma for the tin belt, consistent with previous studies[16, 17]
Zircons from the copper arc have positive εHf indicating a more juvenile source than those from the tin belt, which have lower εHf implying a more evolved source
Summary
Granitoid-hosted mineral deposits are typically subdivided into “Cu-Au- (±Mo)” and “Sn-W” categories, which are associated with oxidized intermediate magmas, and reduced more fractionated felsic magmas, respectively[10]. The inherited properties of the lithospheric domain from which the melt was extracted, determines the initial metal contents of the magmas. Redox exerts a genetic control on the metallogenetic potential for both Cu-Au and Sn-W mineralization[1, 9, 12], controlling sulphur speciation, with significant implications for the availability of both chalcophile and siderophile metals (Cu, Mo, Ni, Au) within the residual melt. Redox controls metal solubilities, for example Sn speciation (Sn2+ or Sn4+) determines whether Sn substitutes into crystallizing phases in oxidized melts, or remains residually enriched in more reduced magmas
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