广西金秀龙华低温热液镍矿床形成研究

Longhua hydrothermal Ni deposit occurred as quartz-nickel minerals veins in the fracture zone in the Cambrian carbonaceous mudstone and siltstone at Jinxiu county, Guangxi Zhuang autonomous region, China. The main nickel mineral of the Ni ore is niccolite and niccolite-chalcedony assemblage is popular, which suggests that the Longhua hydrothermal Ni deposit was formed in low temperature environment. Geological characteristics and mineral assemblage of the Longhua low temperature hydrothermal quartz vein Ni deposit differs greatly from hydrothermal Ni deposits documented in the literature all over the world and it is suggested that the Longhua hydrothermal Ni deposit be a new type of low temperature hydrothermal Ni deposit. Based on field observation and microscopic identification of the Longhua hydrothermal Ni deposit, this project will focus on mineral assemblage and element association of the deposit, H-O-He isotope composition of the ore-forming fluids and Sr-C isotope composition of calcite from mineralized quartz vein, Pb-S isotope ratios of the ore minerals, isotope age similarities and differences of Ni mineralization and ore hosted strata and of magmatic events in the nearby ore field area, the change of element contents in ore-forming fluid during the processes of mineralizaton and its relationship to temperature , pressure and salinities of the ore forming fluid. Based on the above work, the geological and geochemical features of the Longhua low temperature hydrothermal quartz vein Ni deposit will be systematic summarized; the sources of ore forming fluids and ore forming material will be discussed; the forming processed and key factors corresponding to the formation of the Longhua low temperature hydrothermal quartz vein Ni deposit will be analyzed and forming models for the Longhua low temperature hydrothermal quartz vein Ni deposit will be proposed. This project plays a key role in understanding completely the geochemical features of Ni in low temperature hydrothermal, in proposing metallogenic theory about the formation of the new type of low temperature hydrothermal Ni deposit and in supervising prospecting of simlar type of low temperature hydrothermal Ni deposits all over the world.

广西金秀龙华镍矿主要以石英-镍矿物脉产于寒武系碳质泥岩及炭质粉砂岩破碎带中，主要镍矿物为红砷镍矿，见红砷镍矿和玉髓共生，为典型的低温热液型镍矿床。据我们查阅的不完全文献，龙华镍矿床地质特征和世界报道的主要热液镍矿床不同，应属新类型低温热液镍矿床。本项目通龙华镍矿床野外考察及光薄片鉴定，矿物及元素组合、成矿流体H-O、He同位素组成及成矿期方解石Sr-C同位素组成，硫化物Pb-S同位素组成,成矿时代、赋矿地层时代及矿区附近岩浆岩时代对比分析，成矿过程中成矿流体成矿元素含量变化及其与成矿温度、压力、盐度等的关系等，系统总结龙华低温热液镍矿床地质地球化学特征；分析低温镍矿成矿流体特征及成矿物质来源；阐明镍在低温热液中的地球化学行为；探讨低温热液镍矿床成矿过程及形成的关键控制因素，建立成矿模型。该工作对深入了解镍在低温热液中地球化学特性、建立低温热液镍矿床成矿理论及指导寻找同类矿床等有着重要意义。

广西金秀龙华石英脉型镍钴矿床产于寒武系碳质泥岩及粉砂岩中，富矿体Ni>17%, 含钴（Co>1%）,伴生Bi及Au，局部含铜。龙华镍矿矿床和世界热液镍矿床不同。项目分析了龙华镍矿床地质特征、成矿流体温度盐度及氢氧同位素、红砷镍矿及赋矿碳质泥岩Re-Os同位年龄、矿区内滴水岩体及桂东北-粤西主要岩体U-Pb年龄及地球化学特征。阐明龙华镍钴矿床成因及是否为新类型矿床。龙华镍钴矿床主要由早期浸染状矿化和晚期石英脉型富镍钴矿化组成。早期矿化主要为红砷镍呈浸染状产产于条带状豆状碳质泥质岩中，定向排列，见红砷镍矿包裹于泥岩的石英碎屑中。这表明早期矿化为更早期石英-红砷镍矿经剥蚀再沉积形成的；晚期石英脉型镍钴矿主要由红砷镍矿，少量镍黄铁矿、辉砷镍矿、辉钴矿、方钴矿、派克矿、黄铜矿、石英和碳酸盐等组成，蚀变弱，主要为硅化、碳酸盐化及绿泥石化。镍钴矿化石英包裹体均一温度110-180C，盐度（%）：4~10，成矿流体18OH2O‰=-7.7 ~ -3.0、Dv-SMOW‰= -54~ -66，靠近大气降水线；红砷镍矿和碳质泥岩Re-Os等时线年龄分别为449±35 Ma和约600Ma；滴水岩体锆石U-Pb年龄在438—441Ma之间，桂东北-粤西多个岩体锆石年龄在420-446Ma之间，显示加里东期发生强烈岩浆作用；滴水岩体SiO2%: 73-77,K2O+Na2O>8%,在Zr-1000Ga/Al图和Yb/Ta、Ce/Nb和Y/Nb图中分别位于中位于碱性A型和A1型花岗岩区域，表明其为碱性A1型花岗岩岩体锆石Hf(t)=-3.10 ~ -0.12。.龙华镍钴矿床高品位特征和五元素矿床相似，但形成温度（110C-180C）远低于五元素矿床早期矿化温度（>450C）及缺少自然银；龙华石英脉型镍钴矿床为世界未见报道的新类型浅成低温热液镍矿床，矿床成矿过程包括（1）更早期石英脉型红砷镍矿在新元古代再沉积形成浸染状矿化及矿源层，（2）加里东期低温大气降水热液溶解矿源层中的镍，形成石英脉型镍钴矿床；据矿床贫S富As，加上前人发现含砷流体中Ni含量可达80ppm，初步认为镍可能以砷络合物溶解及迁移。.位于“十杭带”上滴水A1型碱性花岗岩形成于加里东期，表明“十杭带”在里东期发生了强烈的壳幔作用。桂东-粤西在加里东期发生强烈岩活动。