Isotopic Geochemistry of Metallogeny for the Largest Paleokarst Uranium Deposit in China
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摘要: 据对某大型古岩溶型铀矿床中铀－铅同位素体系及硫、碳、氧、氢同位素组成的研究结果，表明该矿床成矿物质源自矿区众多地层，成矿流体的变质水和古岩溶水（古大气降水）的混合水；成矿经历了古岩溶铀淋积富集，燕山早、晚期构造运动促使两次含铀热水溶液改造、叠加成矿（１３５～１１９。６５Ｍａ），成矿作用与古岩溶和区域地质构造演化密切相关，属古岩溶型热造铀矿床。Abstract: A uranium deposit is the largest paleokarst type U deposit in loth scale and tonnage in China. Thedeposit is formed below a fossil cave and in a faulting}olution breccia system in the Lower Carbonifer-ous limestone. The temperature of mineralizing fluids ranges from 1810℃to 1500 ℃Four U一Pb ages forpitchblende and whole rock ores, 135, 131, 119 and 65 Ma, have been determined, which are obviouslyyounger than those of the wall rocks. Sulfur isotope data show that the δ34 S values of pyrites from theores range from 1.00 ‰to一15. 3‰with a mean value of一6.87‰,closel to those of pyrites fromthe wall rocks(1. 00‰一15.60‰，mean- 7.06‰)，suggesting that the wall rocks are the source ofsulfur for mineralization. The five analyzed samples of calcites from the ores have δ13 Cvalues between 0.34‰and-3.19‰(mean一1.50‰).The similarity between the average carbon isotope composition of the ores(一1.50‰)and the wall rocks(0.53‰)is interpreted to result from an isotope exchange between the wall rock and mineralizing fluid. The lead isotope composition of pyrites from the ores andwhole}ock of Lower Carboiferous sugggests that the source of lead and urarnum in the deposit is vari-ous in strata of the ore field.The value of δ18O and δD for mineralizing fluids range from 1.5‰o 7.3‰ and from一30.4‰to一84.9‰,of metamorphic and meteoric waters.respectively, indicating that the mineralizing fluid is a mixed waterThe mineralizing process is clowly related to development historyof regional tectordic movemnets and multi-episode paleokarstification. Thus, it is named as hydrothermalreworked paleokarst type uranium deposit.
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Key words:
- nranmm are deposit /
- paleorarst /
- isotope geochemistry
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