摘要:Traditionally, the lower boundary of the Aikuanian(Yanguanian) Stage has always been considered as the lower boundary of the Carboniferous in China. marked by the occurrence of the coral Cystophrentis.In recent years, some biostratigraphical research results have shown that the Cystophrentis zone is only distributed in the lower part of the Menggong'ao Formation(or the Gelaohe Formation) and that there is an interval zone namely the Cystophrentis-Pseudouralinia interval zone, wedged in just between the Cystophrertis zone and the Pseudouralinia zone in the upper part of the Menggong'ao Formation(or the GelaoheFormation). According to the current study of the conodont biostratigraphy, the coral Cystophrentis zone appears to be of latest Devonian age. So the lower boundary of the Aikuanian Stage is much lower than the lower Devonian-Carboniferous boundary and should no longer be regarded as the lower boundary of the Carboniferous in China. In this paper, two proposals for the Devonian-Carboniferous boundary in the shallow-water facies areas of China are put forward: 1) that the boundary is marked by the first appearance of the conodont Siphonodella(Eosiphonodella) simplex, and 2) that the boundary is recognized by the extinction of the coral Cystophrentis or the brachiopod Tenticospirifer.In addition, 4 species are newly estabished here: Icriodus obovatus sp. nov., Polygnathus lepidus sp. nov., Polygnathus paucidentatus sp. nov. and Polylophodonta jianghuaensis sp. nov.

摘要:After the Variscan Cycle, the global tectonic framework underwent three major adjustments. The first occurred in the Late Triassic-initial Jurassic, the second in the Late Jurassic-early Early Cretaceous and the third in the Late Cretaceous-Eogene. On that basis, the post-Variscan tectonic history is divided into three tectonic cycles——the Indosinian, Yanshanian and Himalayan Cycles. The post-Neocom(k_1~1) andpre-Aptian(k_1~2) tectonic movement marks the end of the Yanshanian orogeny in eastern China and the initiation of the subduction of the Tethyan ocean in western China and represents the boundary between the Yanshanian and Himalayan Tectonic Cycles.

摘要:Combining geomechanics with geochetnistry, this paper makes a rather systematic study on the stratigraphic division, tectonic evolution and ore genesis of the Bainaimiao ore field and, on such a basis, puts forward some new ideas. It has been emphatically pointed out that, in addition to the prominent E-W structural zone that controls the Cu-Mo deposits, there also exist N-S and NE structures which dominate Pb-Zn and Au mineralizations respectively. The formation of the copper deposit was attributed to the superimposition of three successive stages of mineralization related to volcano-sedimentation and metamorphic and magmatic hydrothermal activities respectively.

摘要:Based on lead isotope data, it has been shown that lead in the Beishan stratabound sphalerite-pyrite deposit came mainly from the oldland and its underlying basement rocks and, subordinately, the Devonian itself or the seawater at that time. As to its primary source, upper crust lead was predominant. while lower crust lead or upper mantle lead was subordinate. Sulfur was formed mainly through bacterial reduction of marine carbonates. The carbon and oxygen isotopic analyses for carbonate rocks and minerals have demonstrated that carbonate rocks in the Beishan area are normal marine sediments. The isotopic characteristics of the carbonate rocks are intermediate between those of the northern Guangdong and central Hunan, but closer to those of the central Hunan basin. The formation of the Beishan deposit underwent: a depositional-diagenetic mineralization stage and a successive post-diagenetic enrichmentremoulding one.

摘要:This paper deals with a preliminary study of 13 localities of Precambrian iron-formations in the Jiamusi median massif and determination of the gold eontent of 391 samples. It has been ascertained that the gold deposits are strictly controlled by the iron-formations and exhibit obvious stratabound features. On that basis, the paper principally discusses gold migration and enrichment. Abundant Mn and Co are contained in primary sediments of the Dongfengshan-type gold deposits, which strongly supports and supplements the idea that the gold deposits of the same kind in the world are of metamorphosed volcanoexhalative-sedimentary origin.

摘要:Phosphorite, or guano, or insular phosphorite, commonly containing 10-35% P_2O_5, is one of the sources of phosphatic fertilizer. Taking the modern insular phosphorite on the Xisha Islands as an example. this paper discusses the ore-forming mechanism of phosphate and the important contribution made by animals to this process.The phosphorite occurs in the middle part of carbonate sand cays of coral reef surrounded by longshore sandbanks, which assumes a dish-shape. The surface of the cays is covered by unconsolidated guano. The phosphorite, yellowish brown to dark brown, is made up of thick-bedded sand and gravel cemented by collophanite, and partly replaced by carbonate apatite.The mechanism of mineralization is as follows:The average content of phosphorus in the sea water is only 0.07 ppm, but through the sea food chain concentration, phosphorus content may become higher. The phytoplanktons, as producers, suck up phosphorus out of sea water. The primary consumers, zooplanktons, obtain phosphorus by eating phytoplanktons, then they are followed by the second and third consumers. Sea birds living on fish, as the third consumers, concentrate and transport the phosphorus to the carbonate sand cays. Finally layers of guano are deposited under the arbores.Under the tropical climatic conditions with high temperature and plentiful rainfall soluble matters are leached out of the guano and infiltrated into deeper horizon. In alkaline groundwater with pH greater than 7.0. the phosphoritization takes place, bioclastics are cemented and replaced by collophanite or carbonate apatite. Finally, the phosphorus is fixed and phosphate formed.

摘要:This paper presents REE abundance pattern and REE geochemistry of granodiorite porphyry, skarns, as well as late hydrothermal alterations in the Tongshan copper deposit, Guichi County and, in the light of their similarities and variations, deals with the genesis of the skarns and the transformation process of the post-skarn hydrothermal alterations. On such a basis, the inference is drawn that the skarn-forming solution was produced by further fractionation of residual magma, thus belonging to a transitional fluid between residual magma and hydrothermal solution which, with the continuous variation of its components during the metasomatism, tended to become a hydrothermal solution.

摘要:A new scheme of Late Triassic palaeophytogeographic regionalization of China is put forward on the basis of three principles given as follows:1. The palaeophytogeographic regionalization should be based on the characters of the various floras themselves. These characters include the types of the dominant floras, compositional patterns of various communities and existence of dominant genera or those genera and species characteristic of a region.2. The palaeogeographic positions of the floras in geologic time should be considered.3. The distribution of the floras was influenced in three directions——latitudinal, longitudinal and vertical——in geological time.Formerly, a number of Chinese palaeobotanists based the palaeophytogeographic regionalization only on the factor of latitude, and neglected the characters of the floras themselves and the effect of their three-directional zonation. However the discovery of the Tianqiaoling flora(located at latitude 43.5°N in NE China) rich in fossils of Dipteridaceae and Cycadophyta, indicating tropic or subtropic conditions, and a comprehensive consideration of assigning the floras of southern Tibet on the basis of palaeomagnetism, plate tectonics, etc., suggest that the palaeophytogeographic regionalization is a rather complicated subject. As the climatic conditions controlling the growth of vegetation changed in three directions one should consider not only the effect of latitudinal change(which usually causes temperature variations from south to north), but also the effect of longitudinal change(which usually brings about variations in humidity from sea to inland) and moreover the effect of vertical or elevation change(which also leads to variations in temperature and humidity). At the same time, it is also necessary to take into consideration the actual palaeogeographic positions of the floras in geologic time.Therefore, it is suggested that the Late Triassic floras in China should be grouped into three floristic regions, namely.(1) the Northern Floristic Region with the Danaeopsis-Symopteris flora,(2) the Southern Floristic Region with the Dictyophyllum-Clathropteris flora, and(3) the Yaflung Zangbo River Floristic Region. It is inferred here that the floral characters of the 3rd region are similar to those of the Dicroidium-Lepidopleris flora growing on Gondwana land at that time.

摘要:The phosphatic stromatolite discussed in this paper is a columnar type, comprised chiefly of collophane and subordinately of microcrystalline apatite. The column is composed of alternations of dark, cryptocrystalline laminae formed by the biological processes of algae and bacteria, and light, microcrystalline laminae formed by chemical precipitation. The intercolumnar filler, showing a concave anti-stromatolitic structure, is composed of alternations of loose laminae formed by mechanical deposition, and dense, crypto-, microerystalline laminae formed by chemical precipitation and algal bacterial organic process.Under the SEM, the column differs clearly from the intercolumnar filler in ultramicro-fabric. The three basic types of ultramicro-laminae that can be distinguished in the column are: prismatic apatite laminae of chemical origin, elastic apatite laminae of mechanical origin and branched-tubular apatite laminae of algal-bacterial origin, of which the first and second categories constitute light laminae and the third, dark laminae. The dark and light laminae were formed during the alternation of flourishing and dormant periods of algae and bacteria.Under the SEM. the clastic texture is obvious in the loose laminae of the intercolumnar filler. Andfour types of ultramicro-apatite assemblages can be distinguished in the dense laminae, i. e., the framboidal and the tubular apatite of algal-bacterial origin, the framboidal-prismatic and the framboidaltubular-prismatic apatite of chemical organic origin. The alternation of the loose and the dense laminae depends upon the changes of the energy in the water.In the stromatolites, no replacement phenomena have been found and there exists abundant prismatic apatite kept in the initial form of upward-crystallization, and especially, in the forms of algae and bacteria(framboidal, tubular and branched). All these undoubtedly indicate that the stromatolites were originally formed by algae and bacteria.The ultramicro-fabric features indicate that the collophane is not a simple mineral, but a disorderly arranged aggregateof ultramicro-granular apatite.