贵州寒武系底部黑色岩系成矿序列划分与对比

一系列的黑色岩系多金属矿床广泛分布于中国南方地区寒武系底部,前人对多金属矿特征、成因等方面进行许多研究,但对Mo-Ni、V、P和Ba矿的成矿顺序研究较少。本文对云南德泽、贵州纳雍-坝黄-天柱及湘西柑子坪等地区的寒武系底部黑色岩系多金属矿的成岩成矿环境、矿石矿物微观特征、成矿地球化学等方面研究,结合元素富集层出现先后可将寒武系底部成矿作用自下而上分为四个成矿序列:即磷矿成矿序列、重晶石矿成矿序列、钒矿成矿序列、镍钼矿序列。同时,根据岩石组合、矿物组合、含矿性等特征,将贵州境内Mo-Ni、V、P和Ba矿床划分为三个成矿区,即纳雍-遵义-福泉黔中镍钼成矿区、铜仁-镇远-岑巩黔东南钒(镍钼)成矿区、天柱-新晃重晶石成矿区。

贵州泥堡大型金矿床金的三维富集规律及成矿模式探讨

泥堡金矿床是黔西南近些年发现的大型金矿床之一,前人对金的富集规律及成矿过程开展了大量的研究,但从金的三维富集规律方面探讨金的成矿模式尚未研究。本文利用3Dmine软件对泥堡金矿床的地层、断层和矿体进行三维可视化地质建模。结果显示,矿体呈顺层状和沿断层产状产出,Au主要富集层位为上二叠统龙潭组二段和一段(P3l2、P3l1),赋存位置为构造蚀变体(Sbt)、F1断层内、F1断层两侧、背斜轴面附近、背斜轴面与断层F1之间,背斜轴面倾向一侧的背斜翼部,且Au含量具有斑块状分布和带状连续分布特点,表现出Au在局部斑块处含量高,并向四周持续递减。据此,本文结合Au的物质来源、流体来源、以及矿床中的地层岩性、断层和背斜组合等特征,获取了矿床形成的流体流向路径,提出了"S型"和"断层+背斜轴面"的成矿模式,这对于泥堡金矿床及类似的矿床开展下一步找矿和成矿预测具有一定的参考意义。

黔西北峨眉山玄武岩风化壳三稀矿产资源富集成矿规律

黔西北上二叠统峨眉山玄武岩顶部与宣威组底部之间发育一套厚度较为稳定的风化壳,其富集三稀元素。为了揭示三稀元素富集规律,选择威宁县石门坎的毛家坪剖面开展元素地球化学研究。结果表明:三稀元素主要富集于风化壳黏土岩中,且表现为上部三稀元素含量高,下部三稀元素含量低,铝土质黏土岩明显比玄武岩富集铌和稀土元素,尤其是高岭石细脉中异常富集铌(w(Nb_(2)O_(5))=0.059%)和钇(w(Y)=512.0×10^(-6)),风化壳黏土岩的化学蚀变指数(CIA)多数高达95~100,反映岩石遭受了强烈的化学风化作用。稀土元素球粒陨石标准化配分模式图和微量元素原始地幔标准化蛛网图显示,富铌和稀土元素的风化壳黏土岩物质来源为峨眉山玄武岩。地球元素特征指示成矿环境主要为还原—氧化过渡环境,峨眉山玄武岩遭受长期风化、淋漓作用是形成富稀土元素、铌铝土质黏土岩的关键。

New Evidence for Hydrothermal Sedimentary Genesis of the Ni-Mo Deposits in Black Rock Series of the Basal Cambrian, Guizhou Province: Discovery of Coarse-Grained Limestones and its Geochemical Characteristics

The molybdenum-nickel deposits in Shuidong District of Nayong County （Guizhou Province, Southwest China） are found mainly in black shale series of Lower Cambrian Niutitang Formation, which is another Mo-Ni-rich region besides Zunyi District （Guizhou province）. Our systematic study on the Mo-Ni deposits in Tangjiaba of Nayong reveals that layered coarse-grained limestones, spherical beaded limestones concretions are hosted at the lower seam of the Mo-Ni deposits. Its strong negative carbon isotope anomaly （the carbon isotope value of the coarse-grained limestones varies from -2.148‰ to 8.223‰） is similar to that in the modern submarine black smoker chimney. The carbon in the coarse-grained limestones from black rock series of Nayong County might be deep source inorganic carbon. The seams, coarse-grained limestones, ore-bearing coarse-grained limestones and the roof and floor of the deposits are characterized by co-variation on the trace element spider diagram, showing good homology. The extraordinary enrichment of Ag, As and Sb resembles hydrothermal sedimentation. Pro-Earth＇s core elements Se is strongly enriched in Ni-Mo ore-bearing coarse-grained limestones. The ore-bearing rock series has an extremely low Th/U value （0.012-0.19）; in the logU-logTh Cartesian Coordinates, the samples of the roof and floor of the deposits and ore-bearing coarse-grained limestones are found in the East Pacific tise; and the samples of coarse-grained limestones are found between the paleo-hydrothermal dedimentary area and the East Pacific tise. The chondrite-normalized rare earth element patterns of the Ni-Mo deposits show LREE enrichment, Ce negative anomaly, and Eu negative anomaly （which is supposed to be influenced by the deep magmatic processes in an extensional environment） resembles the rare earth element distribution patterns of the fluid and its sediments in modern submarine hydrothermal system. It proves that coarse-grained limestones is characterized by typical hydrothermal limestones, being closely related with the genesis of Mo-Ni deposits in Nayong County, which provides new evidence for hydrothermal sedimentary genesis of Mo-Ni deposit and negative carbon anomaly in the basal Cambrian on a global scale.

Discovery of an abnormally high-δ^(34)S barite deposit and a new understanding of global sulfur isotope variation during geological history

The evolution of the global sulfur isotope curve was plotted based on the δ34S values of evaporates resultant from oceanic evaporation. In the long period of geological history the δ34S values showed obvious peaks for three times during the process of ancient oceans' sulfur isotope evolution, namely the Early Cambrian (+30‰), the Late Devonian (+25‰) and the Permian-Triassic transition interval (+17‰), but the causes of the abnormal rise of sulfur isotopic values during the geological period are still in question. In this paper, 18 samples collected from a large Devonian barite deposit from Zhenning County were analyzed to determine their δ34S values, revealing that the 18 samples have very high δ34S values (δ34S=41.88‰-+68.39‰), with an average close to 56.30‰, which are higher than the isotopic values of contemporary sulfates (+17‰- +25‰). A comparative analysis was conducted of the emerging of high δ34S barite deposits (from Cambrian and Devonian) and the δ34S variation curves of the ancient oceans. The results indicate that the time when the obvious peaks of δ34S values appeared and the time of massive sedimentation of high δ34S barite deposits are very close to each other, which, in our opinion, is not a coincidence. There may exist some correlations between the sulfur isotope evolution of ancient oceans during the diverse periods of geological history and the massive sedimentation of high δ34S barite deposits. Therefore, it is inferred that perhaps it was the massive sedimentation of high δ34S barites that caused the sharp rise of δ34S values in a short period of time.

黔中息烽磷矿床成矿环境、成矿作用及成矿模式探讨

息烽磷矿是贵州地区震旦纪陡山沱期磷矿的重要组成部分,以矿层厚、品位高、断裂构造发育、叠层石丰富而独具特色。通过对矿床地质特征及矿床地球化学特征综合研究认为,从陡山沱组底到顶气候经历温湿—干热—湿热变化,海平面对应经历了海进—海退—海进,其内的磷块岩和磷质岩是在热水沉积作用、生物作用和正常海水沉积作用等共同作用下形成于前滨—临滨环境。综合以上,反演息烽陡山沱期成矿过程,发现矿床经历了“海进—海退—海进”三阶段成矿,在陡山沱早期海进阶段形成下矿层,随后的海退阶段和海进阶段形成上矿层。空间上,2矿层之间夹白云岩,且交于靠黔中古陆一侧,当第2次海进越过第1次海进的前滨—临滨位置后,只形成上矿层,是开阳、息烽磷矿床1层矿体形成的对应部位。瓮福磷矿床有2层矿体,对应处于经历了“三阶段成矿”的前滨—临滨部位,且瓮福磷矿成矿时的位置高程明显低于息烽磷矿、息烽磷矿略低于开阳磷矿,通过岩性特征对比,与实际基本吻合。因此,在对陡山沱期的磷矿进行成矿预测和找矿勘查中,与息烽磷矿床相似的黔中及附近区域的动态前滨—临滨环境,均为磷矿床的找矿靶区,利用“三阶段成矿”形成相交的2矿层特点,可高效对已知矿床、矿化点和前滨—临滨带周围进行成矿预测。