科研之友
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摘要
Isotopic compositions of Mo in molybdenites were used for deciphering a possible genetic link between isotopic variations and mineralizing processes, based on a worldwide molybdenite databank. We compared the delta Mo-98/95 (hereafter referred as delta Mo-98(NIST)) of 391 molybdenite samples (193 from the literature, 198 for this study) from different localities, different types of occurrences and different ages. The 198 molybdenite samples we analysed represent various types of mineralization in 6 granites, 11 pegmatites, 6 perigranitic veins, 2 greisen, 28 porphyry deposits, 5 skarns, 1 IOCG, and 9 Alpine-type fissure veins, with ages varying from 5 Ma to 2.7 Ga. The Mo isotopic composition was determined with an MC-ICP-MS Neptune after aqua regia dissolution and adjustment to [Mo] = 1 mu g.ml(-1). Mass bias was corrected by using Zr as dopant and standard-sample-standard bracketing. The delta Mo-98(NIST) ratios were normalized to NIST3134. External reproducibility is 0.07%. (2 sigma). The overall range of the delta Mo-98(NIST) ratio in the 391 molybdenite samples varied from -1.62 to 2.27%., being higher for molybdenite formed in Alpine-type veins, greisen, perigranitic veins and IOCG, than for that in granite, pegmatite, porphyry deposits and skarns. The crystallization temperature can explain some of these differences, as polymetallic Alpine-type fissure veins broadly crystallize at lower temperatures than granite, pegmatite and porphyry deposits. For some occurrences the delta Mo-98(NIST) was determined on several molybdenite samples, showing variability at occurrence scale. For example, in the Azegour skarn (Morocco) the delta Mo-98(NIST) varies from -0.60 to 0.42 parts per thousand (n = 29), and in "Ravin de la Ruine" Alpine-type fissure veins (France) the variation is from -0.08 to 0.77 parts per thousand. (n = 3). No correlation is seen between delta Mo-98(NIST) and the age of the deposits.
- 出版日期2016-2
