Vertical Zonation of Ore-deposit and Implications for Deep Ore Prospecting：A case study of 510-1 CSAR Uranium Deposit in Zoigê,China

The No.510-1 uranium deposit in the Zoigê uranium ore field is situated on the southern margin of the western Qinling Orogenic Belt in the Tethyan tectonic domain. As a strategic resource, this deposit is significantly marked by huge abundances of uranium metals with their high grades and comprehensive utilization of some associated metals, such as Ni, Mo, Zn, V and Co (Fig.1, Chen et al., 2012; Zhao et al., 2012; Ye et al., 2015).

The 510-1 uranium deposit is hosted by the so-called "carbonaceous-siliceous-argillitic rock (CSAR)”, which consists of silicalite, limestone and slate (shale) of the lower Silurian shallow marine sedimentary series from the Yangchangou Formation. The vein-shape ore bodies mainly have a spatial relationship with the crushed siliceous limestone, and they are also controlled by the magmatism, fractures, hydrothermal fluids and geochemical environment. The wall-rock alterations primarily include silicification, carbonatization and pyritization. Furthermore, the useful U minerals are dominantly pitchblende with minor uranium black, uranite, uvanite, carnotite, because the former normally incorporates hexavalent uranium into its crystal lattice. The other paragenetic metal minerals are composed of pyrites that occur as colloidal, particulate, veined and quasi-massive shapes, as well as a little sulfides (nickel, zinc, molybdenum, vanadium and copper, etc.). Meanwhile, the gangue minerals contain a great deal of calcites, some quartzes, few barites and dolomites. The mineral assemblage of pitchblende+pyrite+calcite+quartz reflects that calcite, quartz and pyrite are the principal hydrothermal minerals closely associated with U mineralization, which can improve an excellent understanding of hydrothermal processes.

Also, the 510-1 CSAR-U deposit shows a distinct vertical zonation as follows: the ore bodies occur as a stockwork shape from the surface to level No.2 (3562m), while as thickened short linear shape with a higher grade under the larger depth (below level No.2). The quartz veins are located on the top of this deposit (level No.1 and above) (Fig.2). Not only that, both of the quartz and calcite veins are coexisting in the mid-zonation (level No.2 to No.4) as an acid (Q＞Cal, level No.2&3) and alkaline sub-zonation (Q＜Cal, level No.4). Only calcite veins together with very few quartz vein are found on the bottom (level No.5 to No.7 and below). The δEu values in these ore rocks and calcite minerals are gradually decreased from the top to bottom. On the contrary, the δCe values are increased. At the level No.5, δEu and δCe exhibit a mutation phenomenon, and trace elements, especially U, Pb, Zr, Hf, Sb, W, Sc, are highly enriched, revealing that an ore-forming fluidic geochemical interface is nearby the level No.5 (320m or so below the current surface uranium metallogenic outcrop). Overall, the vertical zonation of the deposit will benefit to deep concealed ore prospection and exploration in the Zoigê region ore field. More importantly, it also has a more predictive capacity to identify new potential areas and enhance an excellent understanding of U mineralization worldwide.

Fig.1 Geology sketch of the Zoigê uranium ore field

1-Cretaceous;2-Devonian;3-Upper Silurian;4-Middle Silurian;5-Lower Silurian;6-Former Silurian;7-Quartz monzonite;8-Diabase;9-Silicalite;10-Siliceous limestone;11-Fracture;12-Unconformity;13-Uranium deposit

Fig.2 Vertical zoning of gangue minerals in No.510-1 uranium deposit

References

Chen Y L, Wei J, Ye Y Q, Song H, Sun Z X. 2012. Significance and geochemical characteristics of REE and carbon-oxygen isotopes of calcites in the zoige uranium orefield in sichuan province, China[J]. Advances in Earth Science, 27(10): 1061-1067 (in Chinese with English abstract).

Zhao C, Chen Y L, Zhu X Y, Zhang C J, Wang Q. 2012. δ¹³C and δ¹⁸O values for carbonate from the Zoigê uranium Ore field and their genetic Significance[J]. Acta Geologica Sichuan, 32(3): 272-275 (in Chinese with English abstract).

Ye Y Q, Chen Y L, Zhao C. 2015. Vertical zoning features of the mineral assemblages in the Zoige 510-1 uranium deposit and its prospecting significance[J]. Acta Mineralogica Sinica,35(2): 239-244 (in Chinese with English abstract).

First Author：Cong Zhao  

Author Affiliation:  Sichuan Institute of Nuclear Geology, Chengdu 610061, PR China

缘 起：

       闲暇无所事，阅读、整理过往材料，并简要汇总，记下的关于若尔盖510-1碳硅泥岩型U矿床特征的科研随笔。这算是对做过的事的一个简要总结与认识。英文会议摘要原稿收录于2018年第十四届全国矿床会议论文摘要集。近期赵静博士重修字句后，行文更通俗流畅，信息表达更准确。于此，再次对她的辛勤付出表示感谢!

                                                                                                                                    更新于2022年07月04日