Abstract:The Late Devonian volcanic rocks of Akenawa Hills in northern Xinjiang, as a suite of intermediate and basic rocks, are characterized by high total alkali content which ranges from 3.55 to 7.55%. On the basis of their petrology, mineralogy, petrochemistry and REE as well as trace element geochemistry, it is believed that these volcanic rocks are of alkaline basaltic series dominated by rocks of alkaline basalt group with a small part belonging to shoshonite group, exhibiting a Kenedy trend of differentiation in alkaline basalts. The volcanic rocks might be products of partial melting of the mantle;nevertheless, fractionation and crystallization of olivine might have occurred in magma during the upward migration of magma through the crust. The tectonic environment of the volcanic rocks was probably an island arc or a volcanic arc along the active continental margin underlain by continental crust basement instead of a midoceanic ridge. The formation of an island arc or a volcanicarc in the active continental margin seems to have been related to Late Devonian northeastward subduction of the secondary coeanic crust formed during Early and Middle Devonian when the studied area was in extention and nowrepresented by Aermantai-Zhaheba Ophiolitic melange zone.

Abstract:Exposed in the Ailaoshan ophiolito belt and typically representing Paleotethyan ophiolites, the Shuanggou ophiolites are composed of metaperidotite,gabbro, diabase and basalt. Chemically, metaperidotite is of LREE-enriched type, resulting Probably from the metasomatism of components enriched in large-ion lithophile elements (LILE). The melt formed by partial melting of the mantleis depleted in LREE, whereas in diabase and basalt, there exist both LREE-depleted type and LREE-enriched type, with the former corresponding to N-MORB and the latter to E-MORB. It is considered that the LREE-depleted type was derived from the depleted mantle source, while the LREE-enriched type experienced an event of LREE and LILE enrichment. The REE characteristics of Shuanggou ophiolites imply that they might have been formed in a back-arc basin environment.

Abstract:Located in East Junggar area, Xinjiang, the Beiledukuk ore belt is an independent tin metallogenic belt discovered for the first time in northern China in recent years. It has four independent tin deposits, several tinoccurrences and one tungsten occurrence. The primary tin deposits consistof quartz vein tin deposits related to S-type granites and tin depositsassociated with Artype (alkaline) granites. The belt strikes northwest alongthe northern side of the Kalamaili suture zone between Junggar and Yemaquan.The paper mainly discusses geological characteristics of the Hercynian stanni-ferous and tin-absent granites in the tin metallogenic belt. It is believed thatI-, S-and A-type granites of this area were formed during the Hercynian move-ment. The highly differentiated and evolved S-and A-type granites -elated totin mineralization are poducts of the late orogenic-postorogenic stage, formed on the basis of further evolution of early-stage (orogenic) I-and S-type gra-nites. The integrated criteria for discriminating between ore-bearing and barrengranites have been summarized, which are conductive to the search and study of tin deposits of the same types in this area and its neighboring areas.

Abstract:Based on 175 petrochemical data, this paper has defined chemical series and rock assemblages of Carboniferous volcanic rocks in the northern half of west Tianshan Mountains and dealt with their geochemical characteristics. On such a basis, the trench--arc basin system of this area is investigated.The upper unit of Middle Carboniferous in North Tianshan Mountains represents the active continental margin of Junggar plate, whereas the lower unit belongs to sediments of a forearc basin environment. Rocks of the ophiolite suite in north Tianshan Mountains are remnants of a slowly spreading ancient ooeanic crust.Lower Carboniferous volcanic rooks and Middle Hercynian granitoids along the northern margin of Central Tianshan Mountains represent the main part of the extremely thick continental island arc, while Middle and Lower Carboniferous rocks along the Awulale belt are of volcanic assemblages in an internal island arc environment. The Yishijilike belt is a back-arc basin with limited extension.

Abstract:Studies on chemical composition and trace elements and REE geochemistry of mantle peridotite in opholites of Shexian County show that its chondritenormalized patterns are of LREE--enriched type, quite different from mantle peridotite from other orogenic belts of China. The crustal sequence of Shexian ophiolites belongs to the transitional series behaeen calc-alkaline basalt and tholeiite and all through has similar trace elements and REE ratios and chondrite-normalized REE patterns, with high enrichment of large-ion lithophile elements and LREE. In Zr-Ti-Y and Hf-Ta-Th diagrams, compositional ponits of basic lava of Shexian ophiolites all fall into the area of calc-alkaline basalt. This, combined with petrological and regional geological data, has led the authors to believe that Shexian ophiolites were formed in a back-arc (interarc) basin environment.

Abstract:In this paper, the author introduces the basic principle of mineral spatial distribution in migmatites, i. e. minerals in leucosomes which have reached the magmatic stage are spatially characterized by random distribution, whereas those in leucosomes from solid materials exhibit aggregate distribution; besides, he presents two statistical methods, namely contact-frequency method and line-transection method. A study of mineral spatial distribution in migmatites suggests that there exist defects and limitations in the statistical method Put forth by previous workers. The author has deduced the equation for calculating probabilities of mineral contact types and also defined the extreme dispersion degree as the Probabilities of mineral contact types in the extremely dispersed state of minerals within a rock. Minerals show aggregate distribution in a few leucosomes, but are characterized by dispersed distribution in the overwhelming majority of leucosomes. The evidence obtained from mass balance calculation,geochemical studies and mineral thermobarometer reveals that the genetic mechanism of the migmatitic complex with thermal centers is anatexis and matasomatism, with the genetic model being "the early stage metasomatism induced by thermal anomalies, the main stage anatexis induced by the early stage metasomatism, and the last stage post-anatexis metasomatism".

Abstract:This paper is devoted to the study of muscovites, the most extensively distributed rock-forming minerals in the Lancang metamorphic belt of western Yunnan. Their composition, polytypes and bo values are analysed and examined in detail, and theca regularity of their growth is tentatively discussed. It is shown that the overwhelming majority of muscovites are phengites of 3T+2M1 type whereas those associated with glaucophane are mainly 3T phengites. Studies also indicate that the Lancang metamorphic belt underwent high-pressure metamorphism of blue schist subfacies and was closely related to the evolution of paleotethys. Therefore, it can be correlated9 with other well-known high- pressure belts i n the world.

Abstract:Amounts (A%，B%) and alternating stacking regularity (Re%)of two types of crystal layer (A-mica layer, B-smectite layer) in the structure of ten recto- rite samples from China were determined by direct Fourier transform method. It is known from the determination that A% varies in the range of 50.5%一 55.8%,B% 44.2%-49.5%,and Re% 72%一98.6%.The results show that tlxe two types of crystal layer (A and B) in the structure of natural rectorate do not strictly alternate in accord with the 1:1 regularity (A≠B, 1.0196%) and exhibit fairly perfect inteTStratified structure. With A% being 55.8%(> 55%)and Re% 72%(<90%)，the No.6 sample does not have perfect interstra- tified structure and thus seems to be a randomly interstratified rectorate/ mica mineral. In this paper, the formula Re% =A3B3 × 100/AB(%)is defined as regularity of rectorate. The pyercentage method has the advantages of easy cal- culation and high data reliability.

Abstract:Located in Nanjiang County and Wangcang County of northern Sichuan, alkaline rooks in 1Vlicangshan area might be divided into ijolite-essexite series (I)and syenite series(11).Nephelines are present in large quantities, whe- reas there are no or very few alkaline dark minerals. Clinopyroxenes, amphi.- boles and nephelines in alkaline rocks are richer in aluminium than those minerals from the same sort of rocks in other areas, with: alumoferro-diopside (fassaite) exhibiting this feature most obviously. Pyroxenes from Series I are different from those from Series II in composition and evolution trend. Rooks of Series I were crystallized in the temperature range of 775-1023℃，whereas those of Series II ，700-950℃，indicating that the depth for their crystalliza- tion was larger than 10 km. The richness of aluminium in pyroxenes should be attributed to the abundant aluminium in rocks and the crystallization of minerals at fairly great depth .In other areas, alkaline rocks often have alka- line dark minerals, which contain very high Fe3+.In this area, however, the low oxygen fugacity hindered Fe2+ from converting into sufficient Fe3+, and hence it was quite impossible for alkaline dark minerals to crystallize from magma. The low-fO2 alkaline rocks without alkaline dark minerals in this area were crystallized from alkaline magma in a closed environment, whereas high- fO2 alkaline rocks that contain alkaline dark minerals in other areas were formed by crystallization of a1kulIne magma in an open system.

Abstract:Kleemanite, a rare phosphate mineral, was found in the Baokeng manganese oxide deposit, Guangdong, in 1983. It has the same mineralogical characteristics as kleemanite from the Iron Knob deposit in Australia. Its chemical composition is ZnO 20.79%，P2O5 34.76%，Fe0 0.67%，A1203 24.38 % (by EPMA) and H20 19.79% (by DTA and TGA)，giving a chemical formula of Zn1.02 (Al1.90 Feo.04) (P04)1.95 (OH)2.01.3.14 H20. Its crystals are pale yellow in color and transparent D=2.84 H=3. Average refractive index 1.606. Stronger lines in X-ray diffraction pattern are 4.76(10)，9.095 (8)，3.638(6)， 3.333(6)，3.313(6)，3.095(6)，4.91(5)，4.733(5)，3.977(5)，3.134(5)，2.857(5)。 Calculated unit cell parameters: ao=7.274A，bo=7.185A，c0=9.788A，β=110.244° and Z=2, being of monoclinic system. Space group:P2, P21, P2/m or P21/m. Infrared spectra show absozption bands at 3600, 3510, 3430, 3160, 1163, 1130, 1040, 592, 530 and 490(cm-1)，and differential thermal analysis demons- trated endothermal peaks at 235, 311 and 651(℃).

Abstract:Some minerals which were not reported in kimberlites have recently been found in kimberlites of the North China platform. Tbey are native iron, native copper, native tin, fersilicite, ferdisilicite, unnamed mineral consisting of Si, Fe and Ti, and chromian kennedyite. A preliminary study shows that they are related to deep fluids of the mantle in a strong reduction environment. The disoovery of these minerals provides evidence for fluid metasomatism in asthe-nosphere.