Yankuang ceshi (Sep 2022)
In-situ Micro-scale Pb Isotope Identification Characteristics of Metallogenic and Non-metallogenic Pyrites in Sandstone-type Uranium Deposits
Abstract
BACKGROUND Sandstone-type uranium deposits contain a large number of pyrites of different shapes and stages. It is difficult to accurately discriminate the pyrite formed before, during or after the metallogenic period solely by observation of pyrite morphology by mineralogy and electron probe microanalysis. Pyrites during the metallogenic period are important information carriers for the genesis and formation process of uranium deposits, and their accurate identification is of great significance. Previous studies both domestically and internationally have used the LA-MC-ICP-MS method to analyze Pb isotopes, but this method has low analytical precision for low-content Pb samples and it is difficult to obtain 204Pb data. OBJECTIVES To identify metallogenic and non-metallogenic pyrites by in situ micro-scale Pb isotopes. METHODS Femtosecond laser ablation multi-collector inductively coupled plasma-mass spectrometry (fs-LA-MC-ICP-MS) was used to determine the lead isotope of pyrite in uranium ores. RESULTS Under the mineralogy microscope, it is clear that the pyrite is related to mineralization and its 206Pb/204Pb ratio is more than ten times or even dozens of times larger than the normal Clark value. 207Pb/204Pb ratio is slightly different, and 208Pb/204Pb ratio is constant. The occurrence of strawberry-shaped pyrites, and non-metallogenic pyrites with uranium minerals growing around them but not interspersed, have normal a 206Pb/204Pb ratio. Pyrites without any contact relationship have no obvious regularity in its Pb isotopes. CONCLUSIONS In-situ micro-scale Pb isotopic difference of pyrites was combined with appropriate observation of mineralogy morphology and occurrence, resulting in pyrites in the metallogenic period being more accurately identified than previously.
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