| Autor: |
Yuch-Ning Shieh, Nabil Z. Boctor, G. Kullerud |
| Rok vydání: |
1987 |
| Předmět: |
|
| Zdroj: |
Geochimica et Cosmochimica Acta. 51:1705-1715 |
| ISSN: |
0016-7037 |
| DOI: |
10.1016/0016-7037(87)90349-8 |
| Popis: |
The mercury ores of the New Idria Mining District are composed of metacinnabar and cinnabar with minor amounts of stibnite and iron disulfides. Metacinnabar from the main ore zone at the New Idria Mine contains Fe as a major impurity (0.96 to 2.80 wt.%), whereas that from the CO veins contains both Se (0.30 to 6.15 wt.%) and Fe (0.13 to 1.18 wt.%) in solid solution. The impurity content varies within the same specimen and within individual crystals as well and demonstrates lack of chemical equilibrium. Impurities tend to concentrate at the interfaces between metacinnabar and cinnabar in partly transformed crystals, thus increasing the barrier to nucleation of cinnabar and retarding or prohibiting any further transition of metacinnabar. Most of the pyrite and marcasite crystallized earlier than cinnabar and in rare cases contain nuclei of framboidal pyrite. Pyrite and marcasite crystallized as discrete phases and the latter does not show evidence of transition to pyrite. Dolomite shows normal marine carbonate δ 18 O (24.6 to 29.7‰) and δ 13 C (−1.7 to 2.5‰) values. Quartz displays δ 18 O ranging from 18.5 to 21.5‰, distinctly lower than the associated dolomites, suggesting that the two minerals may have formed at two different stages. The range of δ 34 S values for metacinnabar (0.0 to 3.2‰) overlaps with that of cinnabar (1.3 to 4.4‰). The δ 34 S for pyrite ranges from 3.1 to 13.0‰; pyrite with framboidal nuclei shows the highest δ 34 S values. The sulfur isotope data also suggest the lack of isotopic equilibrium. The source of C in the ore-forming fluids was marine carbonates leached from the Franciscan sediments. The source of S is uncertain because of lack of knowledge of the isotopic composition of total sulfur. It is likely that mixed sources of sulfur leached from sulfides in the host rocks and magmatic sulfur are involved. |
| Databáze: |
OpenAIRE |
| Externí odkaz: |
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