Abstract:The Yidun Island Arc is a Triassic tensional island arc developed at the bese of a thin continental crust, which was tensional in the Permian and tbe eaarlier Triassic.it is characterized by .development of infra-arc rifting zone and inner-and outer- arcs. Arc volcanic rocks are mainly calc-alkaline volcanic rocks, consisting of basalt,basaltic andesite,andesite, dacite and pyioclastic rocks. Studies on their petrography, major and trace element geochemistry and phase equilibrium have shown that the calc-alkaline volcanic rocks were fomed by fractional crystallization of a calc-alkaline basaltic magma and that the andesite was formed by multi-stage crystalli- zation of calc-alkaline basaltic magma under different pressures. Model calculations show that after Ol+Cpx+Plag士Mt士Ap crystallization from calcalkaline basaltic magma under higher pressure, fractional crystallization of Hb+Cpx+Plag+Mt tooh place in derived magma, thus producing andesite magma. So, separation of a large quantity of Hb mineral is an important factor controlling the formation of andesite. nd the

Abstract:The silicalites dealt with in this paper are a kind of silica-rich rock which occur in the middle Devonian lead-zinc deposits in the Qinling Mountains. They take the form of layer which are conformable with the underlying and overlying rocks. As they are controlled by a syndepositional fault system, the silicalites are distributed in the form of lines. The geochemical properties of Fe, Ti, Al, Mn and other elements are coincident with or similar to those of Iecent and fossil hot water sediments.Moreover, the silicalites are also characterized by lower REE contents,LREE>HREE, apparently negative Ce anomaly and weakly positive Eu anomaly. The hydrogen and oxygen isotope data of the inclusions suggest that the metallogenic fluids forming the silicalites mostly came from the hydrothermal solutions in deep-seated rocks. According to the Doe method, the lead single-stage model ages calculated are mainly between 390--552Ma,older than those of the middle Devonian strata thus also implying that lead was derived possibly from the basement rocks. As main ore-bearing rocks, the silicalites are neither the product of volcanic exhalation, nor the product of marine deposition, but their features are similar to those of the sea-floor exhalogene deposit.

Abstract:There are a lot of microgranular enclaves in the late Yanshanian Qingtian biotite granite in southeast Zhejiang Province. The enclaves are generally round or sub-round with diameters from 10 to 20 cm. They are usually scattered but some of them occur in groups in the granite. The enclaves are often gray or dark-gray in colour. Generally, there are clear boundaries between the enclaves and host granite, but some show diffusion contact. A few of enclaves show fine-grained margins, i. e. chilled margins. The enclaves are mainly composed of plagioclase(An=37), hornblende, biotite, quartz, and K-feldspar. The plagioclase is zoned. Quartz and K-fel-dspar fill in the interval betWeen plagioclase, or enclose the microcrystal plagioclase and hornblendes to form intergranular texture which is similar to that of dolerite, or poikilitic texture. The accessory minerals include magnetite, ilmenite, apatite, sphene, etc. The apatite is very long with the ratio of length to width up to 30:1, and has clear basal cleavage. According to Wylie this kind of apatite is formed by sudden cooling of the magmaoc-existing with the apatite. Chemically, the enclaves belong to the calc-alkline rock serieswith SiO2=60-68%, Na2O>K2O, and A/NKC<1.In comparison to the host granite,the quartz-dioritic enclaves have higher contents of Ti, V, Cr, Co, Ni, Zr,Sr, Ca, Mg and REE. On the variation diagrams of major oxides versus SiO2 of the enclaves and the host granite, the plots show linear trends, and so do some pairs of trace-elements divided hy other trace-elements. There are different hypotheses about the origin of microgranular enclave in granitic rocks. The enclave may be regarded as xenolith, or the relict phase of partial melting of basement rocks, or a product of magma mixing,and so on. Based on field observations and petrological, geochemical, and mineralogical features of enclaves, the authors believe that magma mixing theory is most suitable for explaining the characteristics of the quartz-dio-ritic enclaves in the Qingtian biotite granite, namely, they were the products of mechanical mingling between basaltic or intermediate-basic magma and granitic magma.

Abstract:According to concept of unite and super-unite, the Darongshan-Shiwanda-shan granitic batholith in Guangxi is divided into Shinan, Kuishan, Liuwanshan and Wangchong super-unites, where the first three super-unites could be incorporated in the Darongshan-Shiwandashan rockgroup. Eech super-unite consists of several unites. The ages for these unites have been systematically determined by means of 40Ar/39Ar step-heating dating and K-Ar dating.Based on these data, a isotopic geological age table of the area is established. The age table shows that emplacement age of the Darongshan-Shiwanda-shan rockgroup ranges from 258. Ma of upper Permian to 231 Ma of middle Trias and its duration is about 27 Ma. There is the feature of parallel evolution between super-unites in the Darongshan-Shiwandashan rockgroup.Wangchong super-unite formed in 259 Ma of lower Permian.

Abstract:A mathematic formula for relationship between trace element abundances in multistage magma fractional crystallization is proposed based on the study of geochemistry of the Emeishan Basalt and relevant basic-ultrabasic layered intrusions. This paper discusses the mechanism of normal and inverse evolution of trace elements and the abundance relation constant (R) in the relationship formula. For some elements the constant (R)varies considerably at different stages of magma fractional crystallization, which gives eyidences for the subdivision of these stages. The abundance relation formula could also be applied to igneous rocks formed by fractional crystallization ofmagmas with different compositions. There are sufficient data of basalts,basaltic-andesites, andesites, dacites and rhyolites in the Andes, Chile cited as instance.

Abstract:Two types of heterogeneous extinction phenomena are observed in the olivine and pyroxene crystals of a mantle-derived lherzolite xenolith from Hannuoba, Hebei Province. The laser Raman microprobic analysis indicates that, in olivine exhibiting a heterogeneous extinction character with obvious boundary, the Raman bands belonging to different symmetric species appear regularly in the spectra in different extinction zones. It is proved that there exists a sudden torsion of crystal axes along the boundary between the extinction zones. In pyroxene displaying an undulatory extinction character, the relative intensities of the Raman bands measured from neighboring points show a gradual change. It is demonstrated that the torsion of crystal axes in pyroxene lattice takes place progressively. Three deductions could be drawn from the experiments; 1. High-temperature (>1000Cº)creep strain in the upper mantle could not result in phase transition in these olivine and pyroxene crystals. 2. The two heterogeneous extinction phenomena are all torsions of crys- tal axes in essence, but the torsion units are different in size. In olivine, the size is in micrometer with thousands of unit cells included. In pyroxene, it is in sub-unit cell level. 3. Under the same pressure-temperature conditions, the type of the torsion of crystal axes occurring in a crystal lattice mainly depends on the structural character of the crystal itself.

Abstract:34 pyrope samples from the Liaoning No. 50 diamondiferous kimberlitepipe and the Kuandian alkali basalt in Liaoning Province were carefully analyzed by using infrared spectroscopy and electron microprobe. It has been found that some coarse pyrope crystals from kimberlite have constitutional water, Whose content is uniform in a grain but varies remarkably from grain to grain: the estimated content is about 0.07 % in a comparatively water-rich sample, whereas no constitutional water has been found in six pyrope samples from alkali basalt. Two kinds of spectra were recorded, i. e.three-peak band and one-peak band, in which the frequency of The band near 3570 cm-1 is obviously controlled by Mg2+ and Fe2+ in octahedral coordina-tion but has little to do with six-coordinated Cr3+ and Al3+. The model(H4O4)4- =(SiO4)4- in pyrope lattice is still problematic in interpreting all the experimental xesults: in addition to(H4O4)4-, other substitute forms axealso likely to exist.

Abstract:A careful study of cordylite-(Ce), a barium rare earth fluor-carbonate mineral, has yielded the following results: (1) The compatibility values (1-Kp/Kc) of cordylite-(Ce) are very low (-0.1896 and -0.2139 respectively for data given by Chen (1975) and ideal chemical composition). (2) The structure of cordylites (Ce) assumed by Oftedal (1931) is in contradiction with its optical properties and space group. (3) The mean occupied volume of a single large cation (unit cell volume/number of large cations per cell) of cordylite-(Ce) is unusual (86.2A3), i. e. it is much larger than the volume in similar minerals such as cebaite- (Ce)and huangheite-(Ce)(about 72 A3).(4) Cordylite-(Ce) has no coordination polyhedra similar to those in huangheite-(Ce) etc. (5) The struc-ture of cordylite-(Ce) can not be compared with that of similar minerals.The previously-given chemical composition and structure of cordylite-(Ce)is therefore incorrect, and the formula of cordylite-(Ce) should be expressedas (Na1-x, Ca0.5x) BaCe2, (CO3)4F.

Abstract:East Qinling is a major molybdenum metallogenic belt on the southern margin of the North China platform and contains Jinduicheng and Shijiawan porphyry type molybdenum deposits and Huanglongpu carbonate type molybdellilm (lead) deposit in Shanxi Province as well as Nannihu-Sandaozhuang and Shangfanggou porphyry-skarn type molybdenum (tungsten) and molybdenum(iron) deposits in Henan Province. Studies show that rhenium in molybdenite from the Huanglongpu molybdendm (lead) deposit has values of comprehensive utilization: the average Re content is 152.5 ppm, 14 times and 7 times higher than Re content of molybdenite from the porphyty type molybdenum deposit and from the porphyry-skarn type molybdenum (tungsten) deposit respectively (See Table 1). Nevertheless, as 187Re is unstable and frequently converts into 187Os, molybdenite as the major carrier of Re commonly contains different quantities of Os(See Table 1). Re and Os mainly occur in the form of isomorphism in molybdenite. As for polytypes, it is determined that molybdenite from different types of molybdenum in this region is exclusively of 2H type and 2H+3R type (See Fig. 4 and Table 2), with no relationship existent betWeen the polytype variety and the Re content or ore-forming temperature (See Table 2). It is therefore concluded that the difference in rhenium content of molybdenite from these molybdenum deposits depends mainly on geneses of these molybdenum deposits and initial rhenium concentrations of ore-forming hydrothermal fluids, whereas polytypes of molybdenite have no typomorphic significance for these types of molybdennm deposits.