| 冀东兴隆一带层状黄铁矿—铅锌矿床的地质特征及其成因 |
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| 引用本文：.1985.Geologic characteristics and genesis of the stratiform sulfide ore deposits in Xinglong region, eastern Hebei[J].Mineral Deposits,4(3):1~9 |
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| Geologic characteristics and genesis of the stratiform sulfide ore deposits in Xinglong region, eastern Hebei |
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| Abstract:There exist a number of stratiform sulfide ore deposits in the Middle Proterozoie dolomitic limestone strata. The common features of these ore deposits are as follows: Firstly, they are located linearly within the distance of 60-70 kilometers trending approximately east-west. Secondly, they occur within the same horizon. The majority of them occur within the lower part of the Upper Dolomitic Limestone Member, and some also appear within the Upper part of the Upper Shale Member. Thirdly, the sulfide ore deposits were formed in comparatively calm sea Basins. The host rocks are fine-grained sedimentary rocks, without ribble marks, cross bedding or any other signs of erosion. Fourthly, they occur as layers concordant with the stratification of the enclosing sediments. Thin stratification, lamination and framboid structure are well developed within the orebodies. Fifthly, these deposits are mineralogically quite simple, with pyrite, sphalerite, galena, and siderite as the major metallic minerals and dolomite and quartz as the main nonmetallic minerals. Colloform and cryptocrystalline structures are well developed. Framboid pyrite is commonly seer,) it may be a non-balance structure which implies that the pyrite was deposited from highly oversaturated solution. Pyrite and sphalerite are very fine with the diameters below 0.02 mm. Sixthly, the sulfur is heavy. The range of δ34S varies from 4‰ to +24‰, with mean values around 17‰. Seventhly, the lead isotope compositions are evenly distributed. In all the samples, the compositions of 206Pb,207Pb and 208Pb are rather uniform, varying within 0.4一0.9‰. Throughout the orebody as a whole, the values of 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb are extremely uniform, varying within 16.16—17.30, 15.15一15.96 and 36.12—37.73 respectively. There is also a high inter-deposit uniformity, for exemple, in the Gaobanhe ore deposit, the above three ratios are 16.71, 15.67 and 36.66 respectively; in Zimulin ore deposit, 16.25, 15.15 and 36.08; and in Gantangzi ore deposit, 16.52, 15.32 and 37.08. The average model age of lead is around 1380 Ma, which is consistent with the age of the Gaoyuzhuang Formation. The 207Pb/204Pb versus 206Pb/204Pb and 208Pb/204Pb versus 206Pb/204Pb relations in these deposits approximate to a single “growth curve”, indicating that they have common origin in a deep source with uniform U-Th-Pb ratios. Eighthly, sulfides have high selenium content. In pyrite, for example, S/Se ratios are around 27,000, which are much higher than those of sulfides formed through sea-water sulfate reduction. Ninthly, the formation temperatures of sulfides are high. The decrepitation temperatures are at l 96—330℃for pyrite, 297—340℃for sphalerite with high content of F in mineral inclusions, and the salinity is over 20％. The stratiform sulfide ore deposits in eastern Hebei are similar to the recent sulfide-rich sediments of the red sea brine pools in many respects, such as: In size: many stratiform sulfide ore bodies in Eastern Hebei extend over one thousand meters both along strike and along dip; while the sizes of the brine pools in the Red Sea are 12×5 km2 for Altantis 11.4×2.5 km2 for Discovery and 3×0.66 km2 for Chain. In temperature of the ore-forming solutions: the decrepitation temperatures of pyrite and sphalerite are concentrated in the interval 290一330℃, suggesting the probable deposition of these minerals from hot fluid with a temperature of 300℃; at the top of the brine pools, however, the temperatures are 100一150℃. In mineral constituents and fabrics: in these stratifcrm sulfides, the collolorm and cryptocrystalline structures are well developed, mineralogy is characteristically simple, dominated by pyrite, sphalerite, galena and marcasite; in the brine pools, sediments are in the state of gel, which contain many sorts of sulfides with pyrite, sphalerite and marcasite as predominant ones. In salinity: the salinity of the liquid phase in mineral inclusions is over 20%, and that of the hot brine water in these pools is around 25%. In isotopic compositions: δ34S in pyrite of these stratiform ore deposits is of positive value, the sulfides are heavy and the lead isotope compositions are uniform; the δ34S in sulfides of the brine pools is also positive and heavy, and the lead isotope is uniform too. According to the above information, the authors have come to the conclusion that sulfides were precipitated from ore-forming hydrothermal fluids which had scended along a major fracture, and these sulfides accumulated simultaneously with rock materials to from the stratiform sulfide ore deposits. The genetic model for these stratiform sulfide deposits is also given in this paper. |
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