Abstract:A complete ophiolite section can be divided from bottom to top into four units, namely metaperidotite unit, plutonic complex unit, sheeted dike complex unit and extrusive rock unit, each unit having varied rock assemblages. The metaperidotite unit is mainly composed of harzburgite and lherzolite together with minor dunite and plagio_lherzolite. The plutonic complex unit consists of gabbro, mafic cumulate and ultramafic cumulate. There exist complicated magmatic intrusive events in the plutonic complex and sheeted dike complex units. The extrusive rock unit includes basalt, andesite, boninite and albitite as well as breccia and tuff. Researches of ophiolites and Deep Sea Drilling Project and Ocean Drilling Project, however, indicate that many sorts of ophiolites have no layered structure. Ophiolite sections can thus be classified into two types: one is the section with layered structure, and the other is the section without layered structre. These different ophiolite sections actually reflect different dynamic processes beneath oceanic ridges, which are mainly controlled by the plate spreading velocity and the amount of magmatic supply.

Abstract:There exist four layers of volcanic rocks in Sinian and Cambrian strata of Kuruktag area, Xinjiang. They occur in Early Sinian Beiyixi Formation, Late Sinian Zhamoketi Formation and Shuiquan Formation as well as Early Cambrian Xishanbulake Formation respectively. Volcanic rocks of Xishanbulake Formation and Shuiquan Formation are of alkali basalt series, those of Zhamoketi Formation are of alkali basalt series and tholeiite series, and those of Beiyixi Formation are obviously characterized by bimodal assemblage and mostly belong to alkali volcanic rocks. Their multi_element distribution patterns show continental tumescence characteristics of intraplate basalt. Fractional crystallization of plagioclase led to the existence of negative Eu_anomalies in some volcanic rocks, while the cumulation of olivine resulted in the high MgO and low SiO 2 content of some volcanic rocks. The SiO 2 saturability of volcanic rocks of Xishanbulake Formation and Shuiquan Formation is lower than that of tholeiite of Zhamoketi Formation. Correspondingly, the abundances of incompatible elements in the first two formations is higher than those in the last formation, and the differences can be attributed to the different degrees of partial melting. The intense fractionation of REE and the obvious depletion of HREE suggest that these volcanic rocks were derived from garnet lherzolite of the mantle in the continental lithosphere. The Ba/Nb, La/Nb, Ba/La, Ba/Th and Rb/Nb ratios demonstrate that these volcanic rocks were exclusively derived from the enriched mantle, mainly the EMI type mantle.

Abstract:Kuangdonggou-Liangtun syenite mass in the southern margin of Yingkou-Kuandian an- teclise within Sino-Korean paraplatform was emplaced in Gaixian Formation of Paleoproterozoic upper Liaohe Group. The isotope age of this intrusion is 2175.4 Ma, suggesting that it is one of the oldest syenite mass formed during the development of rifts after the formation of Paleoproterozoic cratonized crust. Fractional crystallization once took place in the evolution, as shown by the variation of chemical and mineral compositions of syenite magma; in addition, contamination of the upper crust material must have happened in the formation of quartz syenite. The syenite magma was probably generated from the depleted mantle mixed with materials of the lower crust, and was contaminated by materials of the upper crust. The evidence is as follows:εNdtvalue is -0.54,εSrtvalues are +26.78~+42.19; projections of Pb isotopic composition of feldspar lies between the lead isotopic growth curve of the mantle and that of the upper crust ; there exists a large proportion of EMII in the magmatic source ; a few sample points are located near the EMI branch; the syenite is enriched in U, Th and, especially, Pb but is deficient in Nb, Sr, P and Ti. The source region might have experienced weak metaso- matism before the generation of magma, and this might accounts for the formation of weakly alkaline syenite magma.

Abstract:The snowball texture in quartz and K_feldspar phenocrysts is commonly observed in some Li-F enriched and raremetal_bearing granites. The characteristics of its occurrence, the electron microprobe analyses of albite in snowball texture and other evidence indicate its genesis of magma crystallization differentiation. Based on the study of mineral crystallization sequence, solidus temperature and growth rates of quartz and albite, it suggests that Li-F-Na enriched granitic residual magma is qualified for the formation of snowball texture, and that high-ratio of Na2O/K2O and contents of F and H2O in the granitic melt are important to the formation of snowball texture. The increase of fluorine content might result in the drop of solidus temperature, thereby magma might be sufficiently differentiated, and K-feldspar and albite of near end-member compositions are formed. The high-ratio of Na2O/K2O leads albite to be crystallized firstly. The higher F and H2O contents might decrease viscosity of magma and increase the growth rate of quartz. Consequently, the albite might be wrapped by quartz phenocrysts and finally the snowball texture formed.

Abstract:The Jiaodong gold ore district is one of the most important gold districts in China, and there are many lamprophyre veins in each gold deposit, which mainly spread parallel to gold ore veins. According to the intersections between the gold veins and the lamprophyre veins, the lamprophyres can be divided into three groups, belonging respectively to pre-mineralization period, mineralization period and post-mineralization period, This paper has made a detailed study on petrology, petochmistry, trace element geochemistry and oxygen, neodymium and stron- tium isotopic composition of lamprophyres from four typical gold deposits, namely Qixia,Rushan, Linglong and Jiaojia. The lamprophyres are characterized by high alkali, potassium and aluminium contents and high Mg#values, which are defined as Mg#=100 Mg/(Mg+Fe). The lamprophyres are sim-ilar to basaltic and basaltic_andesitic rocks in petrogenic character. The lamprophyres have high 87Sr/86Sr ratios, lowεNd(t) values, and theirδ18O values are between 6‰and 8‰, higher than those of generally-recognized mantle-derived rocks. There are good positive relationships 43 between Cr and Ni, K and Rb, and Sr and Ba respectively, and the ratios of these elements are close to those of rocks in the upper crust of the North China massif. All of these characteristics show that the source rocks of lamprophyres are related to the crust materials. The two-stage partial melting model of the Jiaodong Group can be used to explain the genetic mechanism of the lamprophyres.

Abstract:The paper gives detailed comment on the paper of Variation of REE content in shear zone and its mechanism———Exemplified by the ductile shear zone on the northern margin of Jiaonan orogenic belt", published in this magazine in 1998. Combined with the results of mobility of REE in various geological environments and the element migrations effected by fluid flowing in the ductile shear zones, the author expounds that fluid infiltration and rock volume loss are controlled factors of REE variation in the process of ductile shearing.

Abstract:The leucocratic constituents in serpentinite of Jinshajiang ophilite belt are called leucocratic rocks, which , assuming the massive from, are wrapped in serpentinite. Composed mainly of anorthosite and plagiogranite, the leucocratic rocks show distinct Eu positive anomaly.The REE parametric diagram and variations of Nb/Ta and Zr/Hf values suggest crystallization segregation, characterized by enrichment of incompatible elements such as Sr, Ba, Nb, Ta, Zr and Hf and depletion of Compatible elemelnts like Sr, V, Co and Ni. All of these characteristics are in contrast with their host rock_serpentinite and show that the leucocratic rocks were produced by crystallization differentiation of ultramafic magma.

Abstract:The present paper has revised and tested previous research results of theoretical analysis.Intensities of 18 characteristic peaks were picked up from 63 powder patterns of Ca-amphiboles which include 50 data from references and 13 measured data. By means of stepwise regression a series of experimental formulae were fitted between 18 characteristic reflection intensities and 11 cation site_occupanices to estimate the cation site_occupancy of Ca-amphibole with the precision of 78%~96%. As for Mg, Fe2+inΣsite (M1+M3+M2), K and vacancy Em in A site and Si in T1site, the cation site-occupancy precisions approach 90%. The precision is up to 80% for named crystal chemical class in amphibole nomenclature. It is evident that the calcula- tion of the cation site-occupancy of amphibloe group by X-ray powder diffraction is not only practical but also reliable. The authors have succeeded in extending this method to the alkali-amphibole subgroup. As Ca_Na ampohibloe subgroup is among 52 alkali_amphibloes, the method of estimating cation site-occupacies by X-ray powder diffraction is suitable for the whole amphibole subgroup.

Abstract:Macrocrystals of vesuvianite were collected from the contact zone of Ordovician limestonewith Mesozoic diorite, which coexist with Al-diopside, grossularite, minticellite, clintomite and blue calcite in the Mg-Al skarn. In general, the crystals have dimensions of 2~8 cm, with the biggest one up to 30 cm in length and 15 kg in weight. The color of vesuvianite is brown or green, occasionally with brown center and green shell. The crystals are dipyramidal commonly without or with very poorly_developed prismatic faces, and among total 11 forms the common ones are {101}, {001} and {112}. The physical properties are densityD=3.33~3.39 g/cm3, index of refractionN =1.715~1.731, and susceptibilityX=3.30×10-6~8.53×10-6cm3/g. There exists positive correlation between these physical parameters andΣFeO. On the basis of 76 data of vesuvianite composition mainly from the authors as well as from the literature, a new classification for vesuvianite is proposed in this paper. In the ternary system of Al2O3(A)-MgO(M)-FeO+Fe2O3(F), vesuvianite might be classified into seven types: Normal—(Ⅰ), Mg-Fe—(Ⅱ), Mg-Al—(Ⅲ), Fe-Al—(Ⅳ), Fe_rich—(Ⅴ),Al_rich—(Ⅵ), and Mg_rich vesuvianite—(Ⅶ). The DTA curves show that the constitutional water (OH) of vesuvianite was lost at the temperature of 1 040~1 050℃. The M ssbauer data prove that Fe3+ions occupy the 8 coordinated C site on 4_fold axis in the structure. The dipyramidal vesuvianite mentioned here is the product of hydrothermal replacement. In this paper, the source material of vesuvianite is also discussed through the comparison and analysis of REE character of vesuvianite, diorite and limestone.

Abstract:Comparative studies of some silver polymetallic deposits (Caijiaying, Xiasai, Lamo, Mount Isa and Langdal) with different genetic types show that they have almost the same ore mineral assemblages such as pyrite+pyrrhotite+galena+Fe-rich and Fe_poor sphalerite+chalcopyrite+arsenopyrite+silver sulphosalt minerals of the tetrahedrite group, and the formation of the main silver-bearing tetrahedrite and freibergite is often later than that of the main ore minerals. Therefore, it may be considered that the silver sulphosalts have not an indicating significance with regard to genetic types of these ore deposits, but reveal the similarity of the ore_forming solution and the ore-forming evolution of the ore deposits. Investigation of silver minerals in these ore deposits shows that the silver-bearing tetrahedrite and freibergite are among the most important or main industrial silver minerals. It must be pointed out that the silverbearing tetrahedrite and freibergite of the Caijiaying deposit have about the same iron and zinc content, but differ from the Fe_rich and Zn-poor tetrahedrite and freibergite in the Xiasai,Lamo, Mount Isa and Langdal deposits. Moreover, copper and silver in silver sulphosalts of the tetrahedrite group show negative correlation, and their high or low silver content bears no relation to (Fe+Zn) at atomic proportion and Sb/(Sb+As) ratio. However, for the silver sulphosalts of the majority of Cu-Ag-Sb series, As/(As+Sb) ratios are exclusively lower than 0.1, suggesting that these minerals are characterized by richness of Sb and impoverishment of As. Identification of the mode of occurrence of silver in these ore deposits provides an important basis for economic evaluation of the deposits and the flotation of silver minerals in ores.

Abstract:For the purpose of effective and reasonable development and utilization of bentonite from the Shangtianti deposit, the authors, starting with applied basic researches, carried out technological mineralogical studies of bentonite from the Shangtianti deposit. Mineral composition,structure and physico_chemical technological properties of bentonite were analysed; chemical composition, crystallochemical characteristics and interlayer charge of montmorillonite and their influence on the exploration and application were studied. Bentonite from shangtianti is Ca_Mg_bentonite and has characteristics of Cheto type ore. Montmorillonite has high degree of order and coarse crystal grains. As suspension capacity and colloid dispersion power of ores are rather low, bentonite can serve well as adsorption material. The main mineral composition of bentonite is Ca_montmorillonite, and the main impurity is cristobalite, characterized by fine grain size and uniform distribution and associated closely with montmorillonite, cristobalite is the main factor affecting purification. Technological process for purifying bentonite was designed on the basis of the above_mentioned factors. Finally, Na-bentonite of high purity was successfully prepared. The Na_montmorillonite content of the concentrate was 92.52%, and the yield was 36.87%. The pillaret montmorillonite experiments formed a product withd(001) value being 18.87°A (under the condition of calcination at 500℃), which, however, did not have a relatively large specific surface area. Based on bentonite, activated white clay was made,whose main quality indices attain or exceed the trade standards and other products of the same kind.