| 铜陵地区几个铜矿床中磁黄铁矿的成因和演化 |
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| THE GENESIS AND EVOLUTION OF PYRRHOTITE IN SOME COPPER DEPOSITS IN TONGLING REGION |
| The pyrrhotite samples were collected from the copper and sulfurdeposits in Mounts DG, DT and XQ etc. of the Tongling Region in Anhui Province. Mounts DG (middle and uppar Carboniferous) and DT (lower Triassic) belong to the deeper and shallower portions respectivelyof the same stratoid copper mine of the skarns type, while Mount XQcontains deposits of cupreous pyrite (middle and upper Carboniferous),which is 10 km away from the former but situated at a much shallowerdepth. Based on an overall determination of the optical and other physicalproperties as well as chemical etching of the samples collected, morethan 20 of them have been chosen for X-ray powdercrystal diffraction,Mossbauer spectrum and electronic microprobe investigations and alsothermometric study of the mineral inclusions. The results thus obtainedindicate that there are two distinct structure patterns, the hexagonal phase and the monoclinic, of pyrrhotite in the region. The Fe content (Atomic percent Fe) of the hexagonal phase is 47.24 to 47.49 and the curve of X-ray powder-crystal diffraction is a single, sharp and symmetrical reflection. The Fe content of the monoclinic phase is 46.51 and thecurve of X-ray powder-crystal diffraction is a split reflection consistingof two peaks of about equal intensity. The reflectivity, hardness, susceptibility and resistance to etching of saturated solution of chromic acidof the hexagonal pyrrhotite are all weaker than that of the monoclinicpyrrhotite, but its specific gravity is greater than the latter. They havedifferent forms of Mossbauer spectrum and different parameters. The monoclinic pyrrhotite displays various phenomena of twinning, includingthe rare polysynthetic twin (Plate Ⅰ-5) Determinations on their variousfeatures using the polished sections and powders of etched pyrrhotitewell coincide with the above-stated results, thereby proving the effectiveness of the etching determination in discriminating pyrrhotites of the twodifferent structural patterns. Samples collected from this region are mostly two phase mixtures,with the Fe content being 47.26 to 46.51. According to research on theintensity of X-ray powder-crystal curve of the 22 mixtures, quantitativedeterminations were performed on the hexagonal and monoclinic phasesin the mixtures, using the intensity ratios and composition relationshipasserted by R.G. Arnold (1966). Samples with Fe content in the range of47.30 to 47.00 are mainly hexagonal, which accounts for 23% of the total;samples whose Fe content is in the range of 47.00 to 46.80 are two phasemixtures, amounting to 50% of the total; and samples with Fe content inthe range of 46.80 to 46.51 are mainly monoclinic which is 27% of the total. It can be seen that pyrrhotite of two phase mixtures predominates inthis region. Also, there is an apparent correlation between the relativeabundance and the composition of the two phases:the Fe content of thehexagonal phase is the highest, that of the monoclinic phase is the lowest, and that of the two phase mixtures is in between, in which the hexagonal phase increases with the increase in its Fe content. The structural relationship of the two phases can be divided intotwo categories: One is of poikilitic paragenesis of nonhomogeneous grainsof hexagonal and monoclinic phases, or monoclinic phase occurringin the forms of exsolved lamellae and rhombohedral grids among thegrains of hexagonal phase (Plate Ⅰ-2,3), or vice versa, but rarely found. Inthe other category, the partial monoclinic phase is formed by alteration of the hexagonal phase. In portions of severer alteration, we can see theparagenesis of marcasite with pyrite, and paragenesis of pyrite with magnetite and minor content of hematite. |
| HUANG Ming-zhi,TANG Shao-hua,HUANG Xu-chen,ZHANG Shen-zhao.1983.THE GENESIS AND EVOLUTION OF PYRRHOTITE IN SOME COPPER DEPOSITS IN TONGLING REGION[J].Acta Geoscientica Sinica,5(1):49-70. |
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