河台金矿同位素地质研究

STUDY ON ISOTOPE GEOLOGY OF HETAI GOLD DEPOSIT

氢、氧同位素研究表明河台金矿床成矿溶液由变质-岩浆水和大气降水混合而成,且随着成矿作用进行,加入到热液中的大气降水就愈多.硫、铅同位素特征表明它们均来自于震旦系地层.稳定同位素结合矿床地质和地球化学研究表明成矿物质金等是通过变质作用、混合岩化作用和岩浆作用从震旦系含金矿源层中活化转移而来.

The Hetai gold deposit occurs in mylonite zones produced by ductile deformation of the Sinian strata, and is associated in space with metamorphic rocks, migmatites, and granites. δ^(18)O values of quartz from gold ores range from 7.0 to 14.5‰, with an average being 10.6‰; δD_(H_2O) values of fluid inclusions in quartz vary from -54.0 to -84.0‰, with an average being -67.9‰; Calculated δ^(18)O_(H_2O) values of fluids in equilibrium with quartz and calcite vary significantly from -5.21 to 8.04‰. δ^(18)O_(H_2O) values tend to decrease gradually with decreasing temperature. The values of δD_(H_2O) and δ^(18)O_(H_2O) show marked scattering, and fall on the δD_(H_2O) - δ^(18)O_(H_2O) diagram between meteoric -water line and the area of metamorphic and magmatic waters. The oxygen and hydrogen isotope characteristics indicate that ore-forming fluids were mixturs of meteoric, metamorphic and magmatie waters. The early hydrothermal fluids were more likely to be composed mainly of metamorphic and magamatic waters. Meteoric water might have played a more important role at lower temperature. δ^(34)S values of pyrites range from -3.1 to -1.7‰ (the average being -2.28‰), which are comparable to those from mylonites (the average of δ^(34)S - 1.9‰). The averages of ^(206)Pb/^(204)Pb in pyrite, galena, metamorphics and feldspar seperated from pegmatites and granites are 18.899, 18.828, 19.53, 18.613 and 18.532 respectively; The ^(207)Pb/^(204)Pb 15.734, 15.732, 15.88, 15.680, and 15.613 respectively; The ^(208)Pb/^(204)Pb 39.244, 39.178, 38.41, 38.726, and 38.656. All these lead isotopes are radiogenic and have high μ values, which indicate their derivation from the upper crust enriched in uranium. The calibrated lead isotopes of metamorphics (^(206)Pb/^(204)Pb being 19.10, ^(207)Pb/^(204)Pb, 15.877) are analogous to those of ore lead. Sulfur and lead isotope characteristics imply that ore-forming component may have been derived from the source strata of gold. The gold contents in the Sinian strata are very high (the average 13.6 pbb). Gold from the strata were mobilized, transported, and enriched in favourable places during regional metamorphism, migmatization, fault-metamorphism, and magmatism.