Biogenic and nonbiogenic ore-forming processes in the south Texas uranium district; evidence from the Panna Maria deposit
Biogenic and nonbiogenic ore-forming processes in the south Texas uranium district; evidence from the Panna Maria deposit
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DOI：
10.2113/gsecongeo.77.3.541
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发表时间：
1982-05
期刊：
影响因子：
5.8
通讯作者：
R. Reynolds;M. Goldhaber;D. Carpenter
中科院分区：
文献类型：
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作者：
R. Reynolds;M. Goldhaber;D. Carpenter
对位于德克萨斯州卡恩斯县始新世杰克逊群中的盘纳玛丽亚铀矿床的岩心样品进行了地球化学和岩石学研究，获得了有关矿床成因的重要信息。还原岩石中有机碳含量平均约为0.42%，与硫含量呈正相关。黄铁矿是大部分矿带和整个还原贫瘠地带的主要二硫化铁(FeS2)矿物，通常与有机碎屑共生。黄铁矿稀少，除蚀变舌附近的矿石位于一个核内，局部矿化褐煤外。FeS2矿物的硫同位素组成在-1~-34个/mil之间，最轻的34个S值(<-20个/mil)是在矿化褐煤样品和矿卷鼻部测得的。潘娜玛丽亚矿床的岩石学和地球化学特征与其他三个南得克萨斯州滚筒型铀矿床(贝纳维德斯、费尔德和兰普雷希特矿床)的岩石学和地球化学特征形成了极大的反差，这些矿床不含有机碳，硫化物含量高于潘娜玛丽亚矿床。这三个矿床的特征是富含轻同位素轻矿阶段的铁铁矿和重同位素的前矿(在贝纳维德斯)或后矿(在费尔德和兰普雷希特)黄铁矿。我们以前已经得出结论，来自下伏油气藏的含硫断层渗漏溶液在贝纳维德斯、费尔德和兰普雷希特矿床的形成中起着重要作用。尽管潘娜玛利亚矿床显示出明显的沿断裂带的排列，尽管卡恩斯县地区的下伏地层含有酸性天然气(三角洲34 S+14/mil)并产生石油，但该矿床缺乏表明其形成或保存涉及外源还原物质的特征，如断层泄漏的水溶液硫化物。相反，潘娜玛丽亚的矿化似乎受到与有机质存在直接或间接相关的内在还原物质的控制。
Geochemical and petrographic studies of core samples from the Panna Maria uranium deposit, a roll-type orebody in the Eocene Jackson Group in Karnes County, Texas, yield important information on the origin of the deposit. Organic carbon content averages about 0.42 weight percent in reduced rock and correlates postively with sulfur content. Pyrite is the dominant iron disulfide (FeS 2 ) mineral in most of the ore zone and throughout a surrounding zone of reduced barren ground, and it is commonly associated with organic debris. Marcasite is sparse except in ore adjacent to the altered tongue in one core and locally in mineralized lignite. Sulfur isotopic compositions (delta 34 S) of FeS 2 minerals range broadly from -1 to -34 per mil; the lightest delta 34 S values (less than -20 per mil) were measured in samples from mineralized lignite and from the nose of the ore roll. Petrographic and geochemical characteristics of the Panna Maria deposit contrast greatly with those of three other south Texas roll-type uranium deposits (the Benavides, Felder, and Lamprecht deposits), which are devoid of organic carbon and which contain more sulfide than does the Panna Maria. These three deposits are characterized by abundant isotopically light ore-stage marcasite and by isotopically heavy preore (in the Benavides) or postore (in the Felder and Lamprecht) pyrite. We have concluded previously that sulfide-bearing fault-leaked solutions from underlying hydrocarbon accumulations were important in the formation of the Benavides, Felder, and Lamprecht deposits. Although the Panna Maria deposit shows an apparent alignment along a fault zone, and although underlying formations in the Karnes County area contain sour gas (delta 34 S [asymp] + 14 per mil) and produce oil, the deposit lacks characteristics indicating that its formation or preservation involved extrinsically derived reductants such as fault-leaked aqueous sulfide. Mineralization of the Panna Maria, rather, appears to have been controlled by intrinsically derived reductants related either directly or indirectly to the presence of organic matter.