查看更多>>摘要：Arsenopyrite (FeAsS) and lo??llingite (FeAs2) are among the most common primary As minerals in the wastes produced by mining and associated ore processing activities. This study explores the oxidation of these minerals at high relative humidity that frequently occur in underground mines and unsaturated waste piles and tailings. Our objectives were to examine the effect of relative humidity on the mineralogy of secondary phases that formed after 40 months of exposure of arsenopyrite-rich (Apy) and lo??llingite-rich (Lo??) concentrates to six constant relative humidity (RH) levels between 75% and 100%. X-ray diffraction, electron microprobe, Raman microspectrometry, and sequential extraction results showed that the dominant oxidation product in Apy concentrates at any controlled RH level was poorly crystalline ferric arsenate (PCFA). This phase revealed increasing dehydration, and release of sulfate with increasing RH ??? 94%; indicating that high humidity accelerates the transformation process of PCFA to scorodite. Newly formed elemental sulfur, parascorodite, hydroniumjarosite, and ferric (hydr)oxides were minor (to trace) phases in Apy concentrates; and the latter two phases only formed on the surface of pyrite as a result of the limited transport of solutes between individual grains of sulfides at RH ??? 81%. In comparison, well crystallized scorodite and arsenolite were the dominant oxidation products in Lo?? concentrates at every RH. Increasing RH significantly increased the oxidation rate of sulfide and arsenide minerals in the concentrates. The highest sulfide and arsenide oxidation rates in the Lo?? concentrate occurred at RH 100%, and was approximately 40 times faster than at RH 81%. In comparison, the highest oxidation rate of sulfides in the Apy concentrate occurred at RH 94%, and was 6 to 7 times faster that than at RH 81%. Differences in the mineralogical compositions of oxidation products in the Apy and Lo?? concentrate reflect the high levels of sulfate in the Apy concentrate. This triggered formation of PCFA and retarded its transformation to scorodite. The substantial role of sulfate in the oxidation process is reinforced by the finding that stagnation of the sulfide oxidation rate in the Apy concentrate at high RH (> 94%) was probably due to the formation of ferric ion complexes in the presence of high levels of sulfate ions.
查看更多>>摘要：Forsterite (Fo)-rich olivine compositions from San Carlos (Arizona, SW USA) are commonly used as starting material in experimental petrology. In comparison to the San Carlos reference material USNM 111312/444, it has been shown that the major element variability of non-USNM San Carlos olivine is significant. We complement the characterization of the compositional variability of the non-USNM San Carlos olivine with new data, including minor and trace element analyses. High precision analyses reveal that selected minor elements (e.g., -6% NiO, -10% MnO, -16% CaO, relative) and trace elements (e.g., -75% Cr, -120% Cu, -160% P and Ti, relative) present significant concentration variations between grains. At the scale of the individual grain, however, San Carlos Fo-rich olivines appear homogeneous with no systematic core-rim variations. We also discuss the origin of olivine pyroxenites associated with the peridotite xenoliths and argue that they are derived by melt-rock reaction resulting in olivine dissolution and pyroxene precipitation from the peridotite host. Further segregation and in situ crystallization of the hybrid residual melt can produce Fe-rich olivine-poor pyroxenites. Finally, we discuss the origin of the P variability in San Carlos mantle olivine and suggest that P enrichment by metasomatism implies a highly reactive process with fast dissolution-reprecipitation of solid phases.
Xu, BoHou, Zeng-QianGriffin, William L.Yu, Jia-Xing...
16页
查看更多>>摘要：In-situ analysis of minerals, such as zircon hafnium (Hf) and oxygen (O) isotopes, has been pivotal in investigating magmatic evolution and related ore systems. In order to better constrain the petrogenesis of Cu-porphyries and related ore-forming processes in southern Tibet, we used a combined application of both zircon by Hf-O isotopes and apatite by developing geochemical indicators involving Sr-O isotopes and volatile (chlorine and sulfur) concentrations. Apatite has several advantages over zircon: it carries ore-related volatiles, is present in less-evolved magmas and is sensitive to magmatic processes. Data on major-and trace elements and Sr-O isotopes in gem-like apatite can supplement information from zircon Hf-O isotopes. We have applied these techniques to granitoids from the Jurassic arc in southern Tibet to illustrate their use in tracing volatile evolution and related genesis of porphyry systems. We demonstrate that (1) robust apatite Sr-O isotopes combined with zircon Hf-O isotopes can record recycled oceanic components in the sources of Gangdese Jurassic porphyries; (2) volatile enriched magmas metasomatised hydrous mantle wedge to form the Jurassic mineralised rocks; (3) the ore forming magma with higher contents of water, Cl and S, favoured the transfer of metals and volatiles to the upper crust and to form the Jurassic porphyry Cu-Au deposits.
NSTL
Elsevier