The Maochang bauxite in Guizhou Province is one of the important aluminum ore deposits in southwestern China. Ferruginous spherules, measuring about a few microns across, were found in the transitional layer of the de...The Maochang bauxite in Guizhou Province is one of the important aluminum ore deposits in southwestern China. Ferruginous spherules, measuring about a few microns across, were found in the transitional layer of the deposit. The EDS and XRD results show that the microspherules are composed mostly of iron （hydr）oxide minerals （goethite） with only weak presence of aluminum and silicon. Occasionally, some pyrite micrograins with dissolved surface are found associated with goethite within the spherules. It is thus suggested that microspherules are linked to pyrite oxidization. It is also thought that microbial activities contribute not only to pyrite oxidization, but also to ball-like assemblage of the iron （hydr）oxides. The mechanism of the formation of ferruginous microspherules is also believed to be important in studying geomicrobiology of bauxite.展开更多
Colloform pyrite(CPy)is widely distributed in the Tongling mineralization cluster of the Middle-Lower Yangtze River Mineralization Belt(MLYRMB),China.There have many debates as to whether such CPy is associated with L...Colloform pyrite(CPy)is widely distributed in the Tongling mineralization cluster of the Middle-Lower Yangtze River Mineralization Belt(MLYRMB),China.There have many debates as to whether such CPy is associated with Late Mesozoic igneous or Carboniferous sedimentation.CPy from the Xinqiao deposit,a representative of the stratabound sulfide deposits in the MLYRMB,was studied by powder X-ray diffraction(XRD),field-emission scanning electron microscopy(SEM),and high-resolution transmission electron microscopy(TEM).The results show that CPy mainly comprises pyrite,pyrrhotite,quartz,and illite.Pyrite in CPy shows cubic,globule,and xenomorphic morphologies.No octahedral or pyritohedron was observed.Most of the quartz crystals display xenomorphic morphology,where pyrite mold are popular on the surface.Organic matter(OM),which is usually bound to illite,is an important component in CPy.Morphological investigations which exhibit detrital features of quartz and clay minerals indicate that they were derived from continental weathering.Specially,some hexagonal pyrrhotite nanoparticles which show mackinawite morphology are coexisted with OM.The results indicate that the transformation process of sulfides possibly is mackinawite(the precursor)—hexagonal pyrrhotite-pyrite.Thus,compositional and micro-textural characteristics of CPy in Xinqiao deposit suggest it to be a sedimentary origin rather than a hydrothermal origin which is associated with Yanshanian magmatism.Moreover,the coexistence of CPy and stratabound sulfide orebodies in the MLYRMB suggests a causal link between the two.It is considered that CPy might have served as a Cu mineralization geochemical barrier for the Cu-bearing ore-forming fluids,which originated from the Mesozoic magma in the MLYRMB.展开更多
文摘The Maochang bauxite in Guizhou Province is one of the important aluminum ore deposits in southwestern China. Ferruginous spherules, measuring about a few microns across, were found in the transitional layer of the deposit. The EDS and XRD results show that the microspherules are composed mostly of iron （hydr）oxide minerals （goethite） with only weak presence of aluminum and silicon. Occasionally, some pyrite micrograins with dissolved surface are found associated with goethite within the spherules. It is thus suggested that microspherules are linked to pyrite oxidization. It is also thought that microbial activities contribute not only to pyrite oxidization, but also to ball-like assemblage of the iron （hydr）oxides. The mechanism of the formation of ferruginous microspherules is also believed to be important in studying geomicrobiology of bauxite.
基金supported by the National Natural Science Foundation of China(Grant nos 41672038,41572029,41872043)the National Key Research and Development Program of China(Grant no.2016YFC0600209)。
文摘Colloform pyrite(CPy)is widely distributed in the Tongling mineralization cluster of the Middle-Lower Yangtze River Mineralization Belt(MLYRMB),China.There have many debates as to whether such CPy is associated with Late Mesozoic igneous or Carboniferous sedimentation.CPy from the Xinqiao deposit,a representative of the stratabound sulfide deposits in the MLYRMB,was studied by powder X-ray diffraction(XRD),field-emission scanning electron microscopy(SEM),and high-resolution transmission electron microscopy(TEM).The results show that CPy mainly comprises pyrite,pyrrhotite,quartz,and illite.Pyrite in CPy shows cubic,globule,and xenomorphic morphologies.No octahedral or pyritohedron was observed.Most of the quartz crystals display xenomorphic morphology,where pyrite mold are popular on the surface.Organic matter(OM),which is usually bound to illite,is an important component in CPy.Morphological investigations which exhibit detrital features of quartz and clay minerals indicate that they were derived from continental weathering.Specially,some hexagonal pyrrhotite nanoparticles which show mackinawite morphology are coexisted with OM.The results indicate that the transformation process of sulfides possibly is mackinawite(the precursor)—hexagonal pyrrhotite-pyrite.Thus,compositional and micro-textural characteristics of CPy in Xinqiao deposit suggest it to be a sedimentary origin rather than a hydrothermal origin which is associated with Yanshanian magmatism.Moreover,the coexistence of CPy and stratabound sulfide orebodies in the MLYRMB suggests a causal link between the two.It is considered that CPy might have served as a Cu mineralization geochemical barrier for the Cu-bearing ore-forming fluids,which originated from the Mesozoic magma in the MLYRMB.
