Deru Xu

东昆仑祁漫塔格成矿带以发育大规模矽卡岩型多金属矿床为特征, 伴生战略性金属钴(Co)的超常富集。肯德可克铁多金属矿床作为其中的典型代表, 其精细的流体演化轨迹与金属沉淀机制对区域成矿规律研究具有重要指示意义。本文在系统岩相学观察基础上, 对该矿床四个成矿阶段(矽卡岩阶段、氧化物阶段、硫化物阶段及方解石阶段)中的关键热液矿物——磁铁矿与石英, 开展了高空间分辨率的LA-ⅠCP-MS原位微量元素分析。结果表明: 磁铁矿主要产于氧化物阶段(Mag-Ⅰ)与硫化物阶段早期(Mag-Ⅱ), 其微量元素特征(如Ni/Cr>1, 高Sn低Ga)证实该矿床属于热液成因的富镁矽卡岩型系统。地质温度计与(Si+Al)/(Mg+Mn)比值等地球化学参数揭示, 成矿流体并非经历单调的冷却过程, 而是在硫化物沉淀早期经历了一次显著的深部高温、强还原性岩浆热液脉冲, 并伴随水-岩相互作用的减弱。与此同时, 贯穿成矿全过程的石英(Qtz-Ⅰ至Qtz-Ⅲ)记录了体系由早期岩浆主导向晚期大气降水混入的衰减演化, 其Al/Ti、Ge/Ti比值的阶梯式攀升及微量元素的波动, 精细约束了流体由偏酸性向近中性、极低温演化的完整序列。基于此, 本文提出该矿床Co的富集受控于严苛的"氧化物-硫化物"相转变机制: 在早期高氧逸度环境下, Co主要以类质同象形式潜存于磁铁矿中; 主成矿期受流体脉冲引发的温度及氧化还原电位突变触发, Co发生活化转移, 大量进入黄铁矿晶格或析出独立钴矿物。这一微观地球化学证据不仅揭示了多期脉冲流体耦合驱动金属大规模卸载的动力学过程, 也为东昆仑区域深部寻找战略性钴资源提供了明确的矿物学勘查标尺。

The Deerni copper deposit is one of the largest in Qinghai province, China, with proven copper reserves of 0.556 Mt. To explore new copper orebodies, we conducted a geological study at western Deerni focusing on hydrothermal alterations and ore-controlling structures. Field investigation shows that the deposit is hosted mainly within the central segment of the Deerni ophiolite. Additional hosts include Lower-Permian slate, limestone, gabbro and volcanic rock, as well as the contact zone between granite and slate. Such observations indicate that the Deerni copper deposit is not only associated with the ophiolite, but its formation is also controlled by faults. Alterations including serpentinization, carbonatization, silicification and malachite, and magnetite mineralization occurred along fractures within the wall rocks and surrounding strata. This means the alteration post-dated structural activity that affected the Lower Permian strata in the region. The Deerni copper deposit is controlled by the NW-striking faults. This is evidenced by (1) slate fragments and breccias within the orebodies, (2) saw-toothed boundaries between the orebodies and host rocks, (3) copper ore veinlets and (4) striations and step patterns on the orebody surface and hanging-wall-hosted quartz veins. Mineralization controlled by NW-trending faults suggests a major orebody (‘No. 2’) likely extends to either northwest or southeast. Field investigations along with geophysical and geochemical data, thus predicted the presence of concealed copper orebodies in western Deerni. Subsequent drilling projects have verified this prediction and revealed three concealed orebodies with widths of 7.15–13.87 m and Cu grade of 1.00–11.34 wt.%, adding 10,000 tonnes to the copper reserves.

《地球科学》(ISSN 1000-2383;CN42-1874/P) (原刊名《地球科学——中国地质大学学报》ISSN 1000-2383;CN42-1233/P)，创刊于1957年，是由教育部主管、中国地质大学主办的综合性地学学术理论期刊，月刊，2015年改名为《地球科学》,她以反映中国地质大学教学与科研最新的、高水平的基础地质、应用地质、资源与环境地质及地学工程技术研究成果为主要任务。

《地球科学》(ISSN 1000-2383;CN42-1874/P) (原刊名《地球科学——中国地质大学学报》ISSN 1000-2383;CN42-1233/P)，创刊于1957年，是由教育部主管、中国地质大学主办的综合性地学学术理论期刊，月刊，2015年改名为《地球科学》,她以反映中国地质大学教学与科研最新的、高水平的基础地质、应用地质、资源与环境地质及地学工程技术研究成果为主要任务。

Diabase intrusions have been widely found in sandstone-type U deposits of the southwestern Songliao Basin, indicating diabase-related hydrothermal fluids might play an important role in this type of U mineralization. The first discovery of U-bearing carbonate minerals in the BLS U deposit provides an opportunity for understanding hydrothermal U mineralization and its relationship to diabase intrusions. U-bearing carbonate minerals occurred as thin shells generally ringing ankerite and then surrounded by colloidal pyrite through examination of scanning electron microscopy and energy dispersive spectroscopy. They can be interpreted as uranyl carbonate minerals, with the empirical formula of Ca_2.7Fe_0.9Mg_0.4 (UO₂) (CO₃)₅•9.6H₂O, based on infrared absorption spectroscopy and electron microprobe. The formation of uranyl carbonate minerals is most likely related to the CO₂-rich hydrothermal fluids from diabase intrusions according to its occurrence state, but the key factors are that the Ca-UO₂-CO₃ ternary complexes should have been produced in ore-forming hydrothermal fluids and adsorption of ankerite on ternary complexes. Thereby, a potential diabase-related hydrothermal U mineralization model for sandstone-type U deposits can be proposed. The ore-forming fluids that originated from diabase-related hydrothermal are formed through continuously extracting the adsorbed U⁶⁺ and dissolving the early U minerals. Then, U in the ore-forming hydrothermal fluids was migrated and transported probably either as uranyl carbonate ions or as Ca-UO₂-CO₃ ternary complexes. The former is easy to precipitate in the form of pitchblende dispersed in the fossil wood cells, ringing pyrite, and occurring along the edge of adsorbents at the site of reducing capacity change, while the latter will extremely inhibit the reduction of U⁶⁺, eventually leading to the precipitation of uranyl carbonate minerals ringing ankerite by adsorption. The above research results can provide mineralogical evidence for hydrothermal U mineralization in sandstone-type U deposits of the Songliao Basin.