坦桑尼亚南部Mkuju河铀项目地表样品的地球化学特征:对铀地球化学勘探和物源研究的影响

Athanas S. Macheyeki , Dalaly P. Kafumu
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引用次数: 0

摘要

坦桑尼亚的铀矿主要与Karoo组有关,包括Namtumbo-Mkuju河和Madaba矿床。在坦桑尼亚中部的Manyoni和Bahi地区,Galapo和Minjingu(阿鲁沙地区)以及Chimala和Pandahill(坦桑尼亚西南部)的岩浆和碳酸盐岩系统中,还发现了第四纪-全新世的playa湖矿床。本研究的重点是坦桑尼亚南部的Mkuju河铀矿床,以表征元素分布,确定地球化学趋势和确定铀的来源。以1 km × 1 km栅格间隔从0 ~ 3 m深度共采集了64个螺旋钻样品。样品在SGS实验室(南非)使用ICP-AES和ICP-MS对王水消解后进行分析,在坦桑尼亚地质调查局使用XRF对重复样品进行分析。铀与其他元素的相关系数R范围为-0.07 (Ti) ~ 0.79 (Zn)。更强的相关性(R >;铀与亲石元素之间存在0.47),或具有亲石-亲铁或亲铜-亲铁混合行为,表明铀源多。元素阈值随深度而变化。铀、Sn、Sb的阈值呈上升趋势,Hf、P、Ca、Zr、Co、Al、Ti、Rb、Sr、Na、Tl、Th、Mn、Cr的阈值呈下降趋势。铀浓度超过4.65 ppm被认为是异常的。井下阈值变异性是元素特定的。例如,W的变异率为0%,Mo(亲铁/亲铜)的变异率为12%,Cu、Ga、Sn(亲铜/亲石)的变异率为10%至29%。HFSE亲石剂如Hf和Ta变化幅度为12 - 25%,而亲铜剂如Zn、Pb、In、as、Tb、Bi、Ag和Cd变化幅度为4 - 26%。亲铁/亲铜元素如Co、Fe、Sb和Ni表现出6 - 29%的变异性。亲石剂(如U、V、K、Al、Ce、Mg)变化幅度为5 - 40%。Mn是一种亲铁物质,其变异率最高,为43%。地球化学资料表明,南腾博地区铀异常主要来源于灰岩、黑砂岩、黑色页岩,部分来源于风化火成岩花岗岩。这暗示了沉积输入、热液成岩作用和热液岩浆-火山活动的多源成因。因此,该盆地的铀可能通过(1)同沉积作用、(2)成岩蚀变作用和(3)岩浆-热液系统形成。然而,缺乏Eh和pH数据限制了对元素迁移率的了解。这些发现为认识井下元素阈值变异性和铀矿物源提供了新的思路,为勘探地球科学家提供了有价值的指导。该方法可以应用于类似的地质环境,以改进采样策略和异常检测。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
Geochemical characteristics of surface samples in the Mkuju River uranium project, southern Tanzania: implications for uranium geochemical exploration and provenance studies
Uranium occurrences in Tanzania are mainly associated with Karoo Formations, including the Namtumbo-Mkuju River and Madaba deposits. Additional occurrences are found in Quaternary-Holocene playa lake deposits in the Manyoni and Bahi areas (Central Tanzania), Galapo and Minjingu (Arusha region) and within magmatic and carbonatite systems at Chimala and Pandahill (Southwestern Tanzania). This study focuses on the Mkuju River uranium deposits in southern Tanzania to characterize elemental distributions, identify geochemical trends and determine uranium provenance. A total of 64 auger samples were collected from depths of 0–3 m at 1 km × 1 km grid intervals. Samples were analyzed using ICP-AES and ICP-MS following aqua regia digestion at SGS Laboratories (South Africa), with duplicates analyzed via XRF at the Geological Survey of Tanzania. Correlation coefficients (R) between uranium and other elements range from -0.07 (Ti) to 0.79 (Zn). Stronger correlations (R > 0.47) were observed between uranium and lithophile elements, or those with mixed lithophile-siderophile or chalcophile-siderophile behavior, indicating multiple uranium sources. Element thresholds varied with depth. Uranium, Sn and Sb showed increasing thresholds, whereas Hf, P, Ca, Zr, Co, Al, Ti, Rb, Sr, Na, Tl, Th, Mn and Cr decreased. Uranium concentrations exceeding 4.65 ppm are considered anomalous. Downhole threshold variability was element-specific. For example, W showed 0 % variability, Mo (siderophile / chalcophile) 12 %, and Cu, Ga, Sn (chalcophile / lithophile) ranged from 10 to 29 %. HFSE lithophiles like Hf and Ta varied by 12–25 %, while chalcophiles such as Zn, Pb, In, As, Tb, Bi, Ag and Cd ranged from 4 to 26 %. Siderophile / chalcophile elements like Co, Fe, Sb and Ni exhibited 6–29 % variability. Lithophiles (e.g., U, V, K, Al, Ce, Mg) varied by 5–40 %. Mn, a siderophile, had the highest variability at 43 %. Geochemical data suggest uranium anomalies in the Namtumbo area originate mainly from greywackes, arkosic sandstones, black shales and partially from weathered igneous granites. This implies a multi-source origin involving sedimentary input, hydrothermal diagenesis and hydrothermal magmatic-volcanic activity. Therefore, uranium in this basin likely formed through (1) syn-sedimentary processes, (2) diagenetic alteration, and (3) magmatic-hydrothermal systems. However, the absence of Eh and pH data limits insight into element mobility. These findings provide new insights into downhole element threshold variability and uranium provenance, offering valuable guidance for exploration geoscientists. The approach may be applied to similar geological contexts for improved sampling strategies and anomaly detection.
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