四川广安市响水飞仙关组剖面特征及地质意义

四川省广安市桂兴镇响水村下三叠统飞仙关组地质剖面,位于华蓥山背斜的西翼,其古地理位置位于早三叠世川东碳酸盐台地西侧。对该剖面的详细研究,有利于恢复飞仙关期川东碳酸盐台地西侧的沉积演化过程。响水剖面飞仙关组一段属于半局限浅海陆棚和开阔台地含泥灰岩沉积。飞仙关组二段下部为碳酸盐台地西缘斜坡相及开阔台地相;其上部为较稳定的开阔台地沉积。飞仙关组三段是碳酸盐台缘鲕滩和开阔台地沉积。飞仙关组四段属于典型的混积台地潮坪沉积。川东碳酸盐台地西侧飞仙关组由两个向上变浅的沉积旋回组成,第2个沉积旋回是碳酸盐台地向西增生和鲕滩发育的主要时期。     

Influence of the olivine additive fineness on the oxidation of magnetite pellets

Olivine is used as an additive in Luossavaara–Kiirunavaara AB (LKAB) blast furnace pellets. The LKAB iron ore is magnetite which oxidizes to hematite during the sintering process. Olivine retards the oxidation of magnetite pellets if the threshold temperature of magnesioferrite formation is exceeded.In this study, we have developed a thermogravimetric measuring method to study the relationship between the olivine reactivity in green pellets and the olivine fineness. A less reactive olivine makes the pelletizing process more tolerant of excessively high temperatures in the green pellets during oxidation.The reactivity of olivine decreases when the amount of fine tail in olivine is decreased. The top size is limited by balling. Grinding tests in pilot scale show that if the olivine additive is ground in closed circuit with a ball mill keeping good control over the top size, the olivine fineness can be appreciably decreased without disturbing balling. The olivine reactivity can be decreased by 40% compared to the reference olivine in the production plant. Also, savings can be made on both the grinding energy and grinding media consumption. The results in both pilot scale and full production scale show that better oxidation in the grate due to a coarser olivine additive improves the low temperature reduction strength (LTD, ISO 13930) in pellets.The measuring method developed for the olivine reactivity enabled evaluation of different particle-sizing methods for olivine characterisation. The screening size fraction %−45 μm showed a good correlation to olivine reactivity in green pellets within a very large measuring range. The correlation of laser diffraction analysis to the olivine reactivity showed, however, that the laser diffraction measuring method is affected too much by variations in the large particles.     

Rocky relationships: the petroglyphs of the Murujuga (Burrup Peninsula and Dampier Archipelago) in Western Australia

The petroglyphs of the Murujuga (Burrup Peninsula and Dampier Archipelago) in Western Australia are of exceptional cultural value for the nation. It is Australia’s largest and most significant collection of aboriginal rock art essentially as petroglyphs, with the number estimated at more than one million engravings. The Murujuga is a textbook example of ancient and modern times colliding as it also hosts potentially polluting, major industrial complexes such as iron ore and salt ports; liquefied natural gas, liquid ammonia and ammonium nitrate plants; railway lines, pipelines and rock quarries. The work presented in this paper is underpinned by an annual monitoring study of 10 selected sites including two control sites located on Dolphin and Gidley islands and eight test sites located closer to the industrial areas. The main rock types of the Murujuga, gabbro and granophyre, have been affected by weathering consisting of a cm-thick leached zone capped by a skin of orange and red iron and manganese oxides. The petroglyphs were engraved by removing the few top millimetres of the iron oxide-rich layer and the contrast with the paler leached zone clearly showing the carved motifs. Phosphorus is abnormally enriched in the leached zone and the surface coating, with manganese exclusively on the surface coating, demonstrating the impact of bird droppings and ‘desert varnish’ on the rocks. The colour difference and the hematite–goethite ratio, measured with a field portable reflectance spectrometer, between the background and engraving provides a tool to estimate the relative age of the petroglyphs and the selection of the backgrounds. As the fine-grained granophyres were preferentially chosen from the coarser-grained gabbros to host the petroglyphs, the goethitic (or yellower) backgrounds were prepared as canvas before being engraved. Many petroglyphs register the food items of the area, which changed as the last ice age ended and sea levels rose. We hypothesise that based on their locations and colour difference the constraint for the oldest age of the petroglyphs exceeds 17 000?years BP.     

铁氧化物氧同位素示踪原理及其在铁矿成因研究中的应用

铁氧化物(以磁铁矿和赤铁矿最为常见)是铁矿床中最主要的含铁矿物,其氧同位素地球化学对于铁矿的成因研究具有重要意义。本文在总结了铁氧化物氧同位素分馏理论、不同成因类型铁矿形成过程的基础上,对世界主要类型铁矿铁氧化物的氧同位素组成特征和分馏规律进行了总结,并以新疆智博、查岗诺尔、备战海相火山岩型铁矿为例,开展了磁铁矿氧同位素地球化学研究。结果发现,这些铁矿中磁铁矿氧同位素组成δ18OSMOW集中在1‰～3‰之间,表明其形成于岩浆作用主导的高温岩浆/岩浆-热液环境,后期低温热液作用对铁的成矿作用影响有限。     

Composition and properties of the iron hydroxides-cemented lenses in Estonian sandstone of Middle Devonian age

The formation of hematite and goethite concretions in different sedimentary rocks including sandstones is an important diagenetic process in the geologic history of the Earth. Its interpretation can also contribute to understanding the diagenetic history of Martian iron hydroxide concretions. A case study of iron-rich concretions from Estonian Middle Devonian sandstones exposed in ancient river valleys in southeastern Estonia was carried out based on the results of mineralogical, petrographical, geochemical, petrophysical and magnetic analyses. It was found that the high Fe₂O₃(total) content (25.0–39.5%), high magnetic susceptibility, bulk and grain density, very low porosity, corrosion and fracturing of the quartz grains of the platy iron concretions are in contrast with properties of the Devonian host sandstones. However the ferrous iron content (measured as FeO) of iron-rich concretions was as low as in the other Devonian rocks, suggesting an oxidizing environment and arid climate during the cementation by iron-hydroxides. The fracturing of quartz grains cemented by iron hydroxides could take place at near-surface conditions including vadose and phreatic zones in arid climate with high evaporation rates. Such climatic conditions have been reported for the Baltic region during Devonian, Upper Permian and Triassic times. We have found that goethite is prevalent in the cement, replacing clay and carbonate minerals. We assume that this iron-rich cement is originated from the mobilization of iron in host sandstones by groundwater, associated with tectonic activity at the end of the Middle Devonian, evidenced by fracturing in Devonian outcrops and caves. Although this mobilization could occur under reducing conditions, precipitation of goethite and hematite for the cementation could take place in oxidizing environment along bedding planes close to the surface during short sedimentation breaks. Another possible time for the formation of iron concretions could be Permian, under the condition of both arid climate and tectonic activity.     

四川盆地东部下三叠统飞仙关组白云岩化作用及其与储集层发育的关系*

四川盆地东部下三叠统飞仙关组鲕滩相储集层多为白云岩,主要分布于环开江—梁平盆地的台地边缘相带。岩石学和地球化学特征表明,飞仙关组鲕滩相储集层经历了多期白云岩化作用,其中最重要的一期发生于成岩早期近地表环境,由蒸发海水回流引起,形成的粉晶交代白云石构成了现今白云岩的主体。飞仙关组早期白云岩经历了不同程度的埋藏重结晶作用,形成了不同的岩石结构类型。飞仙关组白云岩的孔隙多为原岩中继承而来,白云岩化作用对储集层发育的意义并非创造孔隙,而是保存已有的孔隙。由于白云岩化作用发生的时间早以及白云岩的抗压溶性质,原生（鲕）粒间孔以及早期大气淡水溶蚀作用形成的鲕模孔/粒内溶孔可以在很大程度上保存下来,构成了现今鲕滩相储集层的主要储集空间。     

Redox and nonredox reactions of magnetite and hematite in rocks

Redox and nonredox reactions causing pseudomorphic replacement of hematite by magnetite and magnetite by hematite are compared.Pseudomorphic replacements resulting from redox reactions are known as martitization [replacement of magnetite by hematite due to oxidation; reaction (1)] and mushketovitization [replacement of hematite by magnetite due to reduction; reaction (2)]. These two replacements cause characteristic ore textures and volume changes (reaction (1): increase of 1.66%; reaction (2): decrease of 1.64%). These small volume changes are the reason that martitization and mushketovitization are widespread in many rocks under condition, however, that oxidizing or reducing fluids (solutions) are present.The same initial and end products may also be involved in nonredox reactions. Reaction (3) is the replacement of hematite by magnetite due to simple addition of Fe²⁺ atoms under basic conditions. This reaction causes an increase of the volume of 47.6%. Reaction (4), causing a volume decrease of 32.2%, is the replacement of magnetite by hematite due to leaching of Fe²⁺ atoms under acidic conditions. From these volume changes it is concluded that reaction (4) may occur in many rock types, whereas reaction (3) is restricted to unlithified sediments only. However, ore textures caused by nonredox reactions are unknown and therefore their occurrence in rocks is hypothetical.     

羌塘盆地中-晚侏罗世夏里期气候演化特征及其成盐意义

中-晚侏罗世随着劳亚大陆与冈瓦纳大陆的裂解、北大西洋的开启以及古特提斯洋的闭合,导致全球海平面的改变和气候波动。在中-晚侏罗世交界的卡洛期-牛津期,西特提斯域广大地区的气候从冷湿转变为干热,羌塘盆地位于特提斯喜马拉雅构造域东段,它是否也有类似的气候变化特征?文章对羌塘盆地雁石坪剖面中、上侏罗统夏里组沉积物中Ca CO3、赤铁矿和针铁矿环境代用指标进行了测定,并结合岩性和沉积相变化分析了该区古气候变化,研究结果表明:中-晚侏罗世交界时期,羌塘盆地雁石坪地区气候变化经历了早期(163.8~162 Ma)相对冷湿、中期(162~161.4 Ma)半干旱以及晚期(161.4~159.6 Ma)干旱3个演化阶段。显示羌塘盆地中-晚侏罗世交界时期(163.8~159.6 Ma)的气候变化与同一时期的西特提斯构造域气候变化趋势一致,为羌塘盆地侏罗纪可能的成盐潜力研究和评价提供了重要的古气候依据。     

应用电子探针研究蒙其古尔铀矿床含矿砂岩岩石学特征及铀矿物分布规律

国内外铁矿石价格对标基准多采用离岸价或到岸价,而非盈亏平衡运营成本,难以揭示我国铁矿石所面对的真实市场承压价格。为了厘清国际一线生产商的铁矿石盈亏平衡运营成本价格,本文对世界上最重要的条带状铁建造（BIF）矿产地——西澳哈默斯利盆地高品位赤铁矿矿床的矿化特征及代表性铁矿石产品展开系统研究,同时引入巴西铁四角地区的铁英岩型赤铁矿矿石作为对照,分析全球典型高品位赤铁矿矿石经济指标。结合前人研究成果,将西澳哈默斯利盆地与BIF相关的高品位赤铁矿的富集矿化类型划分为假象赤铁矿-针铁矿、微板状赤铁矿与河道沉积型赤铁矿,巴西铁四角主要为铁英岩型赤铁矿。上述各矿化类型对应的铁矿石产品的铁元素含量均高于56%;在杂质元素含量上,假象赤铁矿-针铁矿的磷含量高,微板状赤铁矿的磷、硫含量较高,河道沉积型赤铁矿的磷、硫含量较低,铁英岩型赤铁矿含锰。经定量估算,西澳力拓、必和必拓、FMG和巴西淡水河谷的铁矿石盈亏平衡运营成本价格分别为34.66、36.76、47.35、38.07美元/干吨,可为中国海外权益铁矿项目开发提供运营成本的参考。