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.

Silicalites of Hydrothermal Origin in the Lower Cambrian Black Rock Series of South China

A silicalite bed was found in the hanging wall and foot wall of the sulfide-rich bed ofthe Lower Cambrian black rock series in South China. Its origin was not described before. Onthe oxide （SiO2-Al2O3, SiO-2-MgO, SiO2-K2O+ Na2O） diagrams for discriminating silicalitesof chemical, biological and volcanic origins （Liu Xiufeng, 1991）, most of the data points of silicalites fall within the areas representing silicaIites of chemical and volcanic origins. On the AlFe-Mn diagram for discriminating silicalites of hydrothermal and biological origins （Yamamoto,1987）, the data points fall within the areas representing silicalites of hydrothermal and hydrothermal-biological origins. On the SiO2-Al2O3 diagram for discriminating silicalites of hydrothermal and hydrogenous origins （Bonatti, 1975 ）, the data points mostly fall within thehydrothermal area. The ratios of SiO2Al2O3, SiO2/（K2O+Na2O）, SiO2/MgO, and K2O/Na2O in the silicalites stand between those of volcanic sediments and of sea floor hydrothermalsediments. The total amount of rareuearth elements in the silicalites is low; the North American Shale-normalized REE patterns decline leftward with obvious negative Ce anomaly. Thetrace elements Mo, Zn, As, Sb, Se, U, and Ba are higher than those in non-hydrothermalsediments and U/Th≥1. The present authors think that the silicalites are derived fromseafloor hot brines which had attracted elements from igneous rocks.

Biota and Organic Matter in the Late Sinian and EarlyCambrian Black Rock Series of West Hunan andIts Significance for Metallization

Abstract: A great amount of black rock series has been found in the Upper Sinian Members 2 and 4 of the Jinjiadong Formation, middle-upper Liuchapo Formation and the Lower Cambrian Xiaoyanxi Formation in West Hunan, which is associated with periodic sea-level changes. By the studies of relationships between the distribution and development of the biota and the abundance of Au, Ag, U, V, Ni, Mo and Cu in the Upper Sinian and Early Cambrian black rock series in Cili, Dayong, Yuanling, Xupu and Qianyang of West Hunan, central China, it has been revealed that the enrichment of Ag, V, and Mo is related with the development of multi-cell plants and vendotaenides, and that of Cu and Ni is related to flourishing of bacteria and shelly fossils. The black rock series in the study area contains abundant organic matter, among which the siliceous shale contains the highest TOC, amounting to 4.51–13.4%. All the values of the equivalent vitrinite reflectance (medium values) determinated with the IR-spectroscopic method in the area are over 2.65%, indicating that the organic evolution was at an overmature stage. Due to the effect of enhancement of organic maturation by hydrothermal fluids, the Upper Sinian and Lower Cambrian had a reverse organic maturity profile in most areas of West Hunan. The enrichment of Ag, V, Ni, Mo and U is a result of organic absorption, and that of Au might be attributed to the migration by hydrothermal fluids.

Diagenetic and Catagenetic Transference of Noble Metal Elements in Lower Cambrian Black Rock Series, Southwest China

Some extraditional types—black rock series types of platinum group element (PGE), gold and silver mineralization occurrences were found in the Lower Cambrian in Guizhou and Hunan provinces of southwest China where PGE concentration reaches more than 800×10 -6. Sea floor hydrothermal fluid eruption was suggested to have been the main origin of the ore-forming materials. The whole process from the sedimentation to the redistribution of the ore-forming elements occurred on the conditions of intermediate to weak alkaline, weak reduction to weak oxidation. The temperature for the sedimentation and redistribution of the ore-forming elements was lower than 210 ℃. At such a low temperature, inert elements such as PGE, Au and Ag could quite easily be remobilized.

Microthermometric measurement of fluid inclusions and its constraints on genesis of PGE-polymetallic deposits in Lower Cambrian black rock series, southern China

Systematic microthermometric measurements of fluid inclusions in the PGE-polymetallic deposits hosted in the Lower Cambrian black rock series in southern China were performed, and the results suggest: (1) there exist two types of fluid inclusions. TypeⅠis of NaCl-H-2O system with low-medium salinity, and its homogenization temperatures (T-h) and salinities are {106.9}-{286.4℃} and ({0.8}-{21.8}) wt%NaCl eq. respectively; TypeⅡ is of CaCl-2-NaCl-H-2O system with medium-high salinities, and its homogenization temperatures and salinities range from {120.1℃} to {269.6℃} and ({11.4}-{31.4}) wt%NaCl eq., respectively. The typeⅡ fluid inclusions have been discovered for the first time in this kind of deposits; (2) two generations of ore-forming fluids were recognized. Characteristics of fluid inclusions in the PGE-polymetallic ores and carbonate-quartz stockworks in the underlying phosphorites are almost of no difference, they may represent ore-forming fluids at the main metallogenic stage. The peak value of homogenization temperature of those fluid inclusions is about 170℃, while their salinities possess a remarkable bimodal distribution pattern with two peak values of (27-31) wt%NaCl eq. and (4-6) wt%NaCl eq. On the contrary, fluid inclusions in the carbonate-quartz veins in the hanging wall may represent ore-forming fluids at the post-metallogenetic stage. The homogenization temperatures and the peak values of salinities are mostly 130-170℃ and (12-14) wt%NaCl eq., respectively; (3) nobel gas isotopic composition analyses in combination with the microthermometric measurements of fluid inclusions suggest that the ore-forming fluids at the main metallogenetic stage were probably derived from mixing of basinal hot brines with the CaCl-2-NaCl-H-2O system and seawater with the NaCl-H-2O system; (4) in the Early Cambrian, the basinal hot brines were trapped in the Caledonian basins, which were distributed along the southern margin of the Yangtze Craton, and where giant thick sediments were accumulated, and expelled and migrated laterally along the strata because of the pressure caused by overlying sediments. The basinal hot brines absorbed Ni, Mo, V, PGE from the surrounding rocks and were transformed into ore-bearing hydrothermal fluids with the CaCl-2-NaCl-H-2O system and medium-high salinities, then ascended along faults and mixed with seawater of the NaCl-H-2O system, and finally PGE-polymetallic deposits or occurrences were formed in the black rock series.

The Metallogenetic Processes and Environment of a Large Ag-V Deposit in Black Rock Series

Located in Western Hubei Province,this deposit is a large-scale Ag-V ore deposit,listed among the fifth type of silver deposit in China.1 Geological Characteristics It lies in the NE sector of the Yangtze flat of the Yangtze paraplatform.There are sporadically magmatic rocks and fold basement made up of upper Archaeozoicmiddle and lower Proterozoic strata.The sedimentary cover consists of Sinian-lower Paleozoic marine sediments,Mesozoic-Cenozoic intercalated marine and nonmarine sediments or nonmarine sediments.

湘西北黑色岩系中钛铀矿的结晶方式及对铀多金属成矿的指示意义

钛铀矿由于其特殊的矿物学性质,在自然界中基本均以变生态产出,因此其原始结构数据很难被准确测定。文章通过α粒子径迹蚀刻、扫描电镜背散射图像、能谱分析、元素面扫描等综合手段发现,湘西北地区黑色岩系中的钛铀矿大部分从成矿溶液中直接晶出,自形程度较高,主要呈针状、板条状;少部分以交代金红石、钛铁矿等早先矿物的方式形成,此种方式形成的钛铀矿晶型差,自形程度低,多数情况下还可见被交代矿物的残留晶形;少数钛铀矿以含矿溶液对含铀、钛的氢氧化物或氧化物进行热液改造和重结晶作用的方式形成,此种方式形成的钛铀矿矿物颗粒较为细小,大多呈针状,有时以放射状集合体的形式出现。以上发现不仅能为研究自然条件下的钛铀矿提供较为详实的实物样本,也能为开发利用黑色岩系中铀多金属的采冶工艺提供矿物学方面的依据。统计研究发现鲕粒状磷灰石,平均有机碳含量为21.18%;部分溶蚀磷灰石,平均有机碳含量为11.49%;重结晶磷灰石,大部分不含有机碳。结合黑色岩系矿物学方面的研究认为,海底喷流热水中所携带的矿化元素会通过出溶作用和还原作用在黑色岩系的微孔洞、微裂隙和矿物间隙中沉淀富集,生成钛铀矿、沥青铀矿、辉砷镍矿、方铅矿等不同类型的铀多金属矿物。

湘中及周缘中奥陶统黑色细粒岩系沉积特征及环境

【目的】中奥陶统烟溪组是近年来在湘中地区新查明的一套海相富有机质黑色细粒岩系,具有较好的页岩气勘探潜力,对这套黑色细粒岩系的沉积特征研究亟待加强。【方法】通过野外踏勘、薄片鉴定等开展烟溪组岩性、岩相组合类型识别,结合元素测试判定沉积环境,采用盆地分析技术结合区域构造运动史查明原型盆地性质、形态,确定黑色细粒岩系有利沉积相带、时空展布及沉积模式。【结果】烟溪组岩性以硅质岩和碳质页岩为主,粉砂质页岩、粉砂岩等次之;硅质岩以浅海环境下生物成因为主,碳质页岩形成于安静缺氧的深水滞留环境。在烟溪组内部可识别出四类岩相组合:厚层纯碳质页岩、碳质页岩与硅质岩组合、粉砂质页岩和硅质岩组合和粉—细砂岩夹薄层泥页岩组合;根据岩相组合类型烟溪组在垂向上可分为上、中、下三段,三段在区域上的分布厚度相对稳定,具有较好的对比性,中段厚层碳质页岩是最重要的烃源层系。烟溪组在区内呈东南厚、西北薄之特征,沉积相类型包括深水盆地、深水陆棚、浅水陆棚和浊积扇,各沉积相带在奥陶纪不同时期分布位置有所不同,分区明显,连续变化。【结论】湘中及周缘地区在中奥陶世处于缺氧的滞留水体环境,是一个稳定地块内的坳陷海盆,深水陆棚相和深水盆地相是烟溪组富有机质页岩发育的有利相带。

激电测深法在南秦岭苏岭沟金矿区的勘查应用

南秦岭夏家店金矿床由夏家店、苏岭沟和刘家峡3个矿区组成,是一处典型的具有重要经济价值的黑色岩系容矿的金矿床。在苏岭沟金矿区利用激电测深(IP)方法,探测了泥盆系地层覆盖地段Ⅰ号构造带和黑色含矿岩系在深部向西延伸及其倾向埋深展布情况。根据激电测深数据获得“低阻-高极化”特征的断面激电异常曲线图并结合地质资料,解译推测了深部含矿目标层及含矿构造空间赋存状况。经钻探验证,金矿化体位置与激电测深推断的极化率异常中心埋深基本吻合。同时,建立了矿区岩(矿)石电性参数的数据库。本次研究为本矿区及矿区外围开展激电测深法探寻同类型、同特征的矿床积累了数据支撑。

黑色岩系成壤过程中镉和硒的形态转变与迁移特征

[目的]黑色岩系含有高量的镉和硒,为明确其在风化成土过程中,岩石镉和硒的形态转变和释放对周围生态环境产生影响。[方法]在浙西北寒武统荷塘组地层的黑色岩系分布区,通过沿地形不同部位(丘陵上坡、丘陵中坡、丘陵下坡、丘间谷底和河谷阶地)采集土壤剖面分层土样,探讨黑色岩系风化成土及其风化物迁移过程中镉和硒的数量与形态转变规律。[结果]从母岩经母质到土壤,土壤总镉和总硒均呈下降趋势。黑色岩系风化物镉和硒损失随沿丘陵坡地向下迁移搬运距离增加而增加,其中,由坡积物演变为洪积物的过程中,镉和硒的损失大于由残积物演变为坡积物的损失。从风化物中流失的镉和硒以流水扩散方式对下游河流冲积物发育表土镉和硒含量产生影响,但影响程度随距离增加而减小。随着风化物搬运距离增加和土壤的演变,发生碳酸盐结合态镉和残留态镉向水溶性镉、交换性镉、有机质结合态镉、氧化物结合态镉转变,残留态硒逐渐活化转变为交换性硒、有机质结合态硒、氧化物结合态硒。土壤水溶性镉、交换性镉(硒)、有机质结合态镉(硒)呈现向地表增加的趋势;硒的有机富集及表土富集现象比镉更为明显。[结论]黑色岩系风化不仅可通过残留方式直接影响其分布区土壤镉与硒的含量,也可通过流水扩散方式影响周边地区土壤镉和硒的含量。

黑色岩系型战略性关键矿产资源研究进展及主要科学问题

本文对近年来黑色岩系型战略性关键矿产的分布规律和超常富集机制等方面的研究进展进行了归纳总结,并对战略性关键矿产资源研究进行了展望。黑色岩系分为黑色页岩、煤系地层和富碳质磷块岩等沉积地层,其中黑色页岩中发生超常富集的关键金属有Se、Te、Re、Cd、Tl等稀散金属,以及PGE、Co等稀贵金属;煤系中可见Ga和Ge的超常富集(形成独立的Ga、Ge矿床),同时也可见稀土金属、稀贵金属的富集;磷块岩中常显著富集稀土,尤其是中重稀土。黑色岩系中的关键金属主要源自大陆风化、海水、热液以及生物摄取。在风化沉积作用中,硫化-还原水体环境形成的泵吸效应,有机质的还原作用,富有机质沉积体系中有机质、铁锰氧化物、磷灰石、黏土矿物等的络合和吸附是关键金属发生富集的主要机制。黑色岩系可为热液叠加过程提供成矿金属,调节热液体系的氧逸度和硫逸度,促进超大型战略性关键矿产的形成。此外,黑色岩系富集的金属在地球层圈物质循环中的聚散行为还可对其他相关成矿系统产生影响。黑色岩系中战略性关键金属的超常富集与大陆边缘、裂谷等环境下缺氧-硫化的沉积事件相关。大气氧含量的变化、超大陆的聚合和裂解、洋流环流模式的改变、冰期以及大规模火山活动导致的海洋缺氧事件等区域地质事件均可是控制黑色岩系型战略性关键金属形成及时空分布的主要因素。黑色岩系是表生风化沉积中的一种重要类型,今后应更加重视黑色岩系等表生风化沉积作用在战略性矿产资源形成中的重要性,建立和发展相关的成矿理论。

贵州三穗龙湾大型铀矿床铀的赋存状态和地球化学研究

贵州三穗县龙湾铀矿床是近年勘查发现的大型铀矿床,矿体呈层状、似层状产于震旦-寒武系老堡组黑色岩系中。前人对该矿床开展了矿床地质和地球化学研究,但铀的赋存状态、成矿物质来源和成矿环境尚不明确。本文选取龙湾矿床南部的老棚剖面为研究对象,开展矿物学和全岩元素地球化学研究。研究结果表明铀主要以沥青铀矿和钛铀矿等的独立铀矿物形式存在于磷灰石矿物边缘、裂隙及孔洞处,部分以类质同象形式赋存于磷灰石的晶格中。全岩地球化学分析结果显示样品Y/Ho值为16.3~63.2(均值为40.3),Zr/Hf值为33.6~79.3(均值为42.3),靠近上地壳的值;样品具有相对平坦的稀土元素配分模式,显示无-弱Eu正异常(δEu为0.27~1.19,均值为0.82);硅质岩Ge/Si值为1.23×10^(-6)~0.15×10^(-6)(均值为0.47×10^(-6)),均接近现代海水平均值,表明龙湾铀矿床成岩成矿物质来源主要为陆源风化碎屑物质,受到海底热水作用的影响小。样品V/(V+Ni)值为0.43~0.98(均值为0.80),Ni/Co值为1.80~58.0(均值为12.7),具有明显Ce负异常(δCe值为0.31~0.81,均值为0.60),表明龙湾铀矿床形成于还原沉积环境中。综合研究表明,在新元古代晚期-晚古生代早期,黔东地区大陆风化作用为海洋提供了铀,在还原条件下形成龙湾黑色岩系型铀矿床。

Nitrogen isotope stratigraphy of the Early Cambrian successions in the Tarim Basin:Spatial variability of nitrogen cycling and its implication for paleo-oceanic redox conditions

The Early Cambrian represents a critical time period characterized by extraordinary biological innovations and dynamic redox conditions in seawaters.Nitrogen isotopic signatures of ancient sediments have the potential to elucidate the evolutionary path of marine redox states and the biogeochemical nitrogen cycle within the water column of the Early Cambrian ocean.While existing research on this topic has predominantly focused on South China,the exploration of other continental margins has been limited,leaving contradictory hypotheses untested.In this study,pairedδ^(15)N andδ^(13)C org analyses were performed on the Lower Cambrian successions from the Shiairike section(inner ramp)and Well Tadong 2(deep shelf/basin)in the northwestern and eastern Tarim Basin,respectively.Our data from the Shiairike section reveal a discernible shift in the operation of different nitrogen cycles for the black chert-shale unit,also referred to as the black rock series in Chinese literature,of the Yurtus Formation(Fortunian stage to lower Stage 3).Oscillatingδ^(15)N values for its lower part are suggestive of alternating anaerobic assimilation of NH 4+and denitrification/anammox.This is likely attributed to a shallow,unstable chemocline consistent with the upwelling and incursion of deep,anoxic waters during a major transgression.In contrast,aerobic nitrogen cycling,indicated by positiveδ^(15)N values of>2‰,dominated the upper part alongside a reduction in upwelling intensity.On the other hand,theδ^(15)N signatures of Xishanbulake and Xidashan Formations of Well Tadong 2,which encompass a time interval from the Cambrian Fortunian Age to Age 4,are indicative of N_(2)fixation by diazotrophs as the major nitrogen source.The two studied intervals,although not time-equivalent,exhibit separated states of nitrogen cycling at least during the deposition of the Yurtus black rock series.The spatially different nitrogen cycling of the studied sections is compatible with a redox-stratified ocean during the deposition of the Yurtus black rock series.The build-up of a NO_(3)−reservoir and aerobic nitrogen cycling in seawater was largely restricted to near-shore settings whereas anaerobic nitrogen cycling dominated by N_(2)fixation served as the main nitrogen uptake pathway in off-shore settings.

四川盆地北缘下志留统龙马溪组重晶石发育特征及其地质意义

扬子板块北缘志留系黑色岩系中重晶石-毒重石成矿带的形成构造背景和成矿过程一直受到众多学者的关注。本文选择四川盆地北缘城口月亮坪剖面下志留统龙马溪组泥页岩中的重晶石矿物为研究对象,从岩石学、矿物学入手探讨重晶石发育特征,并结合锶同位素分析重晶石的成因及其反映的地质意义。结果显示:重晶石主要发育成岩作用为主的针状晶体、冷泉作用为主的较大粒径溶蚀状晶体、热液作用为主的树枝状晶体,以及生物作用为主的小粒径椭球体形晶体;重晶石结核以扁椭球体形顺层分布,存在同心分层结构、致密均一结构、龟裂纹充填结构,其成因以成岩作用为主,局部出现后期热液流体充填收缩缝形成的龟裂纹;层状重晶石的^(87)Sr/^(86)Sr值为0.7084,反映其形成过程受到深部幔源(低^(87)Sr/^(86)Sr值)和围岩(高^(87)Sr/^(86)Sr值)的混染作用,推测其成因为深部幔源热液与冷泉(或成岩作用)共同作用的结果。研究认为:四川盆地北缘龙马溪组沉积时期为一个具有拉张构造背景的被动大陆边缘,在北大巴山发育同沉积断裂;在龙马溪组早期四川盆地北部斜坡区受到弱的拉张作用,断裂发育规模不大,形成间歇性小规模的冷泉渗流;在龙马溪组晚期拉张作用增强,断裂加深,产生重晶石黑烟囱,大量含Ba^(2+)和H2S的热液进入海水中并在北大巴山地区形成重晶石矿床。

河南卢氏地区黑色岩系沉积型褐铁矿及其伴生钼锌组分的工业价值探讨

沉积型铁矿床以赤铁矿和磁铁矿为主,罕见沉积型褐铁矿床。黑色岩系中富集Mo、Ni、V、PGE实例较多,但黑色岩系中发现有沉积型褐铁矿床的报道少见,更未见沉积型褐铁矿床中有Mo、Zn矿化的报道。河南卢氏地区震旦系东坡组黑色岩系中发育有褐铁矿化,并伴生有钼、锌元素大规模高强度异常,前人认为是“铁帽”,深部有找寻大型硫化物原生矿床的潜力。通过对铁矿床含矿建造的重新厘定和成矿环境的恢复,以及对成矿物质来源的示踪,达到了对成矿过程的精细研究,认为区内铁矿化原始成矿方式为沉积成矿,主要以褐铁矿形式沉积,赤铁矿次之,后期强烈的构造变形使矿体遭受强烈的风化淋滤改造,致使矿床成因信息受到掩盖,是“假铁帽”。钼、锌元素以离子形式被铁质胶体和有机质吸附、携载迁移,在特定部位共同卸载沉淀,无独立的钼、锌矿物产出,没有工业价值。

Rhenium-osmium isotope constraints on the age and source of the platinum mineralization in the Lower Cambrian black rock series of Hunan-Guizhou provinces, China

The shale at the bottom of the Lower Cambrian black series in South China is rich in nonferrous metals, noble metals, rare and dispersed elements and radioactive elements, known as polyelement-rich bed. In order to date and trace the source of the platinum group elements, 6 samples were collected from the Zhongnan region of Guizhou Province, and the Ganzi- ping-Sancha region of Hunan Province. The contents and isotopes of Re and Os were measured. Re and Os are positively correlated with each other and the correlation coefficient between 187Os/188Os and 187Re/188Os is 0.99856. On the 187Os/188Os-187Re/188Os diagram, 6 sample points are well-distributed along the (542±11) Ma fitting isochron in high coincidence and with 0.84±0.12 as the initial 187Os/188Os value. The result displays that the age value of the major mineralization of Re, Os and other platinum group elements is (542±11) Ma, which is identical with the stratigraphical age of the wall rocks; the polyelement beds in Hunan and Guizhou provinces bear high isochroneity; the differences of the forming times of different materials in the polyelement bed of the same area do not surpass the error limit permissible for Re-Os date fitting; there exists no distinct time interval between the formation of the diagenetic veinlets and that of the polyelement bed, or the Re-Os isotope composition has not been distinctly changed by the former process; basaltic crust might be the major source of Re, Os, other platinum group and trace elements in the Lower Cambrian polyelement bed of Hunan and Guizhou provinces.

Paleo-productivity evolution across the Permian-Triassic boundary and quantitative calculation of primary productivity of black rock series from the Dalong Formation, South China

The change of the primary productivity across the Permian-Triassic boundary （PTB） remains controversial. In this study, records from two deep-water sections in South China （Xiakou and Xinmin sections） show the primary productivity decreased gradually from the latest Permian to the earliest Triassic, and five evolutionary stages Increase-Decrease-Recovery-Recession- Stagnation） can be observed from Clarkina changxingensis-C, deflecta to Hindeodus parvus-lsarcicella isarcica zones. Pri- mary productivity decreased abruptly from the base of C. meishanensis zone. Besides, for adjusting to the deterioration of the oceanic environment, the primary producers in the oceanic surface had changed to acritarch and cyanobacteria, which were more tolerant of stressful environment. Then the producers were under huge stagnation in the H. parvus-L isarcica zone. The values of quantitative calculation of the primary productivity from the black rock series in the Dalong Formation were very high, corresponding to that of an upwelling area in modern ocean, which shows that the strata of the Dalong Formation in the study region are potential hydrocarbon source-rocks. This result may come from the fact that South China craton was located at the equatorial upwelling area during the Permian-Triassic transitions. But organic matter contents were different in various sections because they could be affected by redox conditions and diagenesis process after burial.

The occurrence state of vanadium in the black shale-hosted vanadium deposits in Shangling of Guangxi Province, China

The Shangling vanadium deposit, which occurs in the Lower Devonian Tangding formation black rock series strata, has V2O5 reserves of more than 1.5 million tons and prospective reserves of more than 2 million tons. Preliminary studies on the occurrence state of vanadium(V) in this deposit have been conducted by artificial heavy minerals concentrates, leaching experiments, scanning and transmission electron microscopy and X-ray powder diffraction.These experiments have revealed no independent vanadium mineral occurrences in the Shangling vanadium deposit and the percentages of water-soluble vanadium, hydrochloric acid soluble vanadium and HF soluble vanadium were1.93 %, 21.42 % and 76.47 %, respectively. Based on our data and earlier research, we estimate that the valences state of V absorbed onto the surface of organic matter or clastic particles are +5 and +4, accounting for 10.00 % and13.35 % of the total amount of V, respectively and the valences state of V that exist in the octahedral crystal lattice of authigenic illite include +3 and +4, accounting for71.64 % and 4.83 % of the total amount of V, respectively.By calculating the correlation between the total organic carbon and V, we infer that after deposition and before entering the crystal lattice of illite, V occurs in the form of humate complex or is adsorbed by organic matter. About4.24 % of the Al is in the octahedral crystal lattice of illite,which was replaced by the vanadium under the metallogenic environments of Shanglin.

Research on the Eco-Geochemical Effects of Black Shales in Pingli County, Shaanxi

This paper presents the results of eco-geochemical research on black rock series enriched in metallic elements in Pingli County, Shaanxi Province, which lies at the northern margin of the Yangtze Platform. There is a suite of bone coal-bearing black carbonaceous rocks in the Cambrian Donghe Formation throughout the region. Soils in Pingli contain high metallic elements derived from the bone coal and carbonaceous rocks. Edible plants growing in the soils contain high Se, Cu and Mo. Two case studies are documented. One is a black shale area with bone coal and Se enrichment, and the other is a black shale area with bone coal mine and copper mineralization. Eco-geochemical effects of metallic element-rich black shales on plants are reported in this paper.