【作者】 马莉燕；

【导师】 林丽；

【作者基本信息】 成都理工大学 ， 古生物学与地层学， 2010， 硕士

【摘要】 以构造成矿学、矿床学及矿床地球化学为理论指导,在研究构造背景的基础上开展了地层、矿床产状、矿石组构、矿物成分等地质调查,并结合地球化学数据来分析矿床成因。结果显示:(1)中元古代,扬子地台的结晶基底是由海底火山喷发及岩浆向上侵位作用形成的基性火山岩。在850Ma-800Ma间,沉积了板溪群的含凝灰质复理石的碎屑岩,震旦纪首先沉积的是含砾砂泥岩,而后是南沱期的冰碛砾岩,晚震旦世沉积的是的含磷白云岩、碳质页岩,而后是灯影组的白云岩。到早寒武世沉积了一套富含有机质的黑色岩系。(2)矿床呈层状及似层状分布;矿石构造主要为浸染状、碎屑条带状;镍钼矿石结构以碎屑结构、半自形构造、他形结构为主,另外可见似交代结构。矿石矿物主要为黄铁矿、镍的硫化物、“碳硫钼矿”集合体、闪锌矿、黄铜矿,透明矿石主要为磷酸盐矿物集合、重晶石、石英及方解石。镍与钼在矿石中具有不同的赋存形式,其中镍以硫化物的形式存在,如针镍矿、辉砷镍矿及二硫镍矿;而钼主要以矿物集合体的形式存在,前人多称为“碳硫钼矿”矿物。镍钼之间的接触关系为:钼矿物集合体包裹镍硫化物及黄铁矿。(3)与镍硫化物空间上共生的6个黄铁矿n(S)/n(Fe)比值均小于2。(4)测试张家界三岔村含矿剖面中的Ni、Mo、V及P2O5的含量发现,其中Ni含量为0.0082%~0.36%,在矿层处的含量为0.36%,该值达到矿床开采的最低品位0.3%。Mo的含量为0.033%到0.67%,在矿层处含量为0.67%,远大于工业开采的平均品位0.06%。V的含量在0.019%~0.19%之间,它的含量在矿层处为0.19%,也最为富集,大于工业矿床伴生组分的可采品位0.02%。P2O5的含量则为0.03%到23%,矿层处含量达到23%,该值为磷块岩矿石品级的三级。镍钼矿石中Ni、Mo、V、P2O5富集程度均明显高于围岩,也高于下部灯影组白云岩的元素丰度。(5)富集元素组合在矿石与上覆地层的黑色页岩中存在明显地差异,矿石中富集元素为Ni、Mo、V、U、Cu、Pb、Zn、Cd、Tl、Ba等亲硫元素与过渡元素,相比之下,矿层之上的黑色页岩中亲硫元素与过渡元素明显降低,而可以代表陆源碎屑来源的Nb、Ta、Zr、Hf、Rb等高场强与大离子亲石元素含量则明显增高;(6)镍钼矿石稀土元素特征:球粒陨石标准化的矿石的Eu/Eu*=1.24~1.69;Ce/Ce*=0.53-2.75,多数分布在0.5~0.7之间;Y/Ho比值为48.5~58.77;∑REE含量变化也很大,从3.63~251.81×10-6,多为10×10-6左右。寒武系底部同类型镍钼矿区中磷块岩的LREE/HREE=4.48~6.95,为轻稀土富集;球粒陨石标准化的Eu/Eu*=0.73 ~1.59;Ce/Ce*=0.32~0.60,表现为负Ce异常;Y/Ho比值为46.40~54.41;∑REE含量变化不大,属于同一数量级,为156.69~273.85×10-6。矿石围岩中的页岩也具有明显的轻稀土富集特征,LREE/HREE=2.60~9.25;球粒陨石标准化的Eu/Eu*=0.03~0.34,比值均<1,为负Eu异常;Ce/Ce*=1.51~2.75,表现为正Ce异常;Y/Ho比值为22.16~35.60;页岩中∑REE含量变化范围从75.86到212.95×10-6。综合前人相关研究及上述结果得到以下结论:(1)认为从中元古代至早古生代,湖南地区经历了从岛弧或边缘盆地到大陆裂谷再到被动大陆边缘的演化。综合考虑以下的条件:可能存在同生断裂的被动大陆边缘、扬子地台东南缘的贵州等地发现有岩浆活动的痕迹以及存在能提供成矿元素来源的古老的结晶基底这些条件,认为在这样的地质背景下能为早寒武世的大规模的热液成矿活动提供可能性。(2)根据矿物之间的接触关系将矿物的生成顺序划分为三个阶段:沉积阶段、热液阶段及改造阶段。其中第一阶段主要产物是:黄铁矿、磷酸盐矿物及含钼的磷酸盐矿物;针镍矿、辉砷镍矿、方硫镍矿、“碳硫钼矿”、闪锌矿及黄铜矿为第二阶段的产物;石英及方解石为第三阶段的产物。(3)探针观察发现磷酸盐与钼矿物之间存在共生关系,表明两者具有一致或相似的富集方式。此为研究中的新发现,这一发现可以为研究它们的成因提供对照。(4)大部分与镍矿物密切共生的黄铁矿n(S)/n(Fe)均小于2,间接地反映出镍钼矿石具有热液成因。(5)矿石均表现出Eu/Eu*>1的特征,REE总值也等稀土元素特征与现代热液喷口的相似。(6)提出以下海底热液成矿模式:在被动大陆边缘的一侧,来自于陆源的磷慢慢汇入到海洋中。随着大陆不断拉张,至早寒武世,由于侧缘岭脊依然留存,导致汇水盆地与外界隔离。封闭的汇水盆地内部生物开始繁盛。与此同时,淋滤了中元古代结晶基底的铁、镍和钼的热卤水,沿着张性断裂(同生断裂)进入到汇水盆地中,热卤水中的铁和镍与细菌作用产生的还原硫结合形成黄铁矿及镍硫化物。它们作为“质点”被生物围绕表面生长。质点表面在生物或者化学作用下吸附早先存在海水中的钼,最终形成包裹硫化物的钼矿物集合体。在区域上,由于在具有相似的背景及地质条件,因而出现了矿化点(床)大规模分布的格局。更多还原

【Abstract】 The genesis of nickel-molybdenum sulfide ore deposit was analysised based on its geological characteristics and its geochemical characteristics in the light of the theory of the Tectonometallogeny, Metallogeny and Geochemistry. Six results are obtained as follows: (1) Many basic rocks and ultrabasic rocks were found in mesoproterozoic, which was formed by continental and submarine volcanic activities. Then, tuffaceous flysch clastic rock was deposited during 850Ma-800Ma. After then, gravel sand mudstone of Liantuo was firstly deposited, and then was Nantuo’s moraine rock. Phosphoric dolomite and carbonaceous shale of the Later Sinian was lying above Nantuo’s moraine rock, and a set of dolomite with great thickness of Dengying Formation was lying above. Black series was deposited in Lower Cambrian. (2) The occurrence of ore layer was mainly layered and resembling layered with disseminated structure and clastic-banding structure. The sulfide ore texture included clastic, semi-euhedral, unformal, including, colloidal and so on, and resembling metasomatic texture was also found here. The mineral assemblages are composed of nickel-sulfide, molybdenum mineral aggregate and some transparency minerals. The nickel-sulfide such as millerite and gersdorffite were imbedded in MoSC phase (with the approximate composition ((Mo, Fe, Ni)(S, As)2C7), which seem to be metasomatic pyrite. (3) Pyrites from different samples that was intergrowth with Ni-sulfide was analysis by electrical microprobe with energy spectrum, and the ratio of its n(S)/n(Fe) was less than 2 (2 is a theory ratio of sedimentary genesis of pyrite). (4) The Ni element content of section of black series in Sancha (Zhangjiajie) ranges from 0.0082% to 0.36%, and Ni content in the ore layer is 0.36%; Mo is from 0.033% to 0.67%, and the content of ore layer is far higher than mining content; V is from 0.019% to 0.19%, and still the content of ore layer is far higher than mining content; the content of P2O5 ranges from 0.03% to 23%. Compare to the black series as well as the underlying dolomite of Dengying Formation around, element content abounded in the ore is obviously higher. (5) The assemble style of element between ore and black series was quite different. For example, the trace element geochemical characteristics of the ore layer was highly enrichments in Ni , Mo , V , U , Cu , Pb , Zn , Cd , Tl and Ba, while high field strength elements (HFSE) and lithophile elements such as Nb , Ta , Zr , Hf , Li , Be , Rb , Cs , Th were scare remarkably in ore layer, but higher in the upper unit and lower parts in the lower Niutitang Formation. (6) Rare earth element characteristic of ores standardized by chondrite shows that Eu/Eu*=1.24 ~1.69>1,Ce/Ce*=0.53-2.75,0.5-0.7 mainly, Y/Ho ratio varies from 48.5-58.77 and∑REE 3.63-251.81, and the rare earth element characteristic of phosphorite of the same strata show that LREE/HREE=4.48~6.95, Eu/Eu*=0.73 ~1.59, Ce/Ce*=0.32~0.60 and Y/Ho is from 46.40 to 54.41, the content of∑REE is 156.69-273.85×10-6, by contrast, the shale’s Eu/Eu*=0.03~0.34, Ce/Ce*=1.51~2.75, Y/Ho is from 22.16 to 35.60 and the∑REE is from 75.86×10-6 to 212.95×10-6.Based on the results above and previous researchers, the following conclusions can be obtained: (1) According to previous study on Lithology and Stratigraphic sequence and the related data of age determination, it is concluded that the background evolution from Mesoproterozoic to early Paleozoic in Hunan area is from island arc or marginal basin to continental rift and lastly evolving to passive continental margin. The Ni-Mo ore and phosphate ore hosted in black rock series which were deposited at early Cambrian are formed in passive continental margin. Moreover, the combination of following conditions, such as passive continental margin that may generate contemporaneous fault, the event of magmatic activity is found at southeast margin of Yangzi platform such as Guizhou, and ancient basic basement also can be the source of ore-forming elements, which provide the possibility of hydrothermal mineralization at early Cambrian. (2) Based on the relationship between minerals, the mineralization period can be divided into three stages: sedimentary stage, hydrothermal stage and reformation stage. Pyrite, phosphate, and Mo hosted phosphate are the main products of the first stage. Millerite, gersdorffite, vaesite,“MoCS”, sphalerite and chalcopyrite are the primary products of hydrothermal stage. Quartz and calcite is the product of the third stage. (3) The results of Electron microprobe analysis shows that the symbiotic phosphate and molybdenum bearing minerals may have the similar enrichment mechanism. The relationship between phosphate and molybdenum bearing minerals is a new discovery in the research. It helps the study of their genesis. (4) The ratio of n(S)/n(Fe) of most of pyrites that intergrowth with Ni-sulfide is less than 2, which -reflects that Ni-Mo sulfide ores has hydrothermal genesis. (5) The geochemical character of ores with the ratio of Eu/Eu*>1and the low content of REE is also similar to the modern hydrothermal vent’s. (6) In conclusion, the metal deposition model was supposed as follow: the elements such as phosphor which comes from continent were in poured into basin on the side of passive continental margin. The basin is getting closed because side-mountain-range still be existed with continental drawing at the early Cambrian, then the biology blooms in that closed basin, and phosphorite and molybdenum bearing minerals sediment at the same time. The iron, nickel and molybdenum that come from Proterozoic along contemporaneous fault combine with sulfur which deoxidize by bacteria in the closed basin, then leads to appearance of pyrite and Ni- sulfide which is supposed as particles. Those particles’round faces is enwrapping by molybdenum mineral aggregation in biologic or chemical reaction. The emergence of large scale black series throughout southeastern China may be because of the same background environment and geological condition.更多还原