Samarium neodymium direct dating of fluorite mineralization
Samarium–neodymium dating of calcites shows potential for determining ages of hydrothermal mineralization.
Sr of ~0.71245 suggest an upper crustal source of the hydrothermal system, in agreement with earlier work on fluid inclusions which indicated a basinal brine origin.
0.745) for scheelite from Woxi and correspond to the Sr (T=200 Ma) ratio range of 0.743 – 0.749 for Precambrian host slates.
Crushing experiments to release inclusion fluids from gangue quartz and sulfides deposited during later stages of ore deposition in both deposits failed to provide accurate and geologically meaningful two-point (fluid-residue) tie lines in Rb-Sr isochron diagrams.
Overall, ore Pb isotopes reveal upper crustal signatures and are compatible with Pb isotope signatures of the predominant Precambrian slates in the Woxi area.
Steep trajectories through late stage quartz-sulfide mineralization in Pb isotope diagrams may hint at mixing scenarios involving Pb from the host rocks and a component with lower Pb ratios, which cannot be linked to any known reservoir in the XUB mining district.
The hydrothermal mineral fluorite (Ca F_2) displays large variations in rare earth element (REE) abundance and samarium/neodymium ratios within a single vein.
These calcite veins contain relatively high concentrations of rare earth elements with MREE-enriched patterns, and yield Sm-Nd isochron ages of 134 ± 3 Ma to 136 ± 3 Ma, with significant different initial ε values of − 12.9 and − 2.0, respectively.Sr isotopes of four out of seven residual sulfide samples from Woxi plot along a paleomixing line at an age of 199 ± 8 Ma, supporting a mixing scenario for the fluids indicated by the Pb isotopes and pointing to a possible genetic relationship with the emplacement of Indosinian—Yanshanian granitoids.The budgets of REEs, Rb-Sr and Pb in the original fluids were severely affected by contamination of these elements apparently during intense wall rock alteration but, after “sealing” of the major pathways, the mineralizing fluids tend to have better preserved their original signatures.The mid-Cretaceous age of ~111 Ma suggests the Albian/Aptian transition as the most likely period for large-scale fluid circulation during a regional extensional tectonic event, related to the opening of the North Atlantic ocean.
Up to now, there were no systematic studies of geochemistry and isotopic age for the Yixian (义县) fluorite deposit, western Liaoning (辽宁) Province, China.
Hydrothermal calcites from the Xikuangshan Mine display relatively large variations in REE abundance and Sm/Nd ratios and are characterized by MREE- and HREE-enriched and LREE-depleted patterns.