Abstract:Located at the juncture of Zhejiang and Fujian, the Yaokeng granite mass which intruded into the lower part of Early Cretaceous Shimaoshan Group lies in the northern side of Mazhan town of Cangnan County. This paper has conducted a detalied mineralogical, petrological and geochemical studies on this rock mass and discussed its petrogenetic type. Investigation results show that granites at Yaokeng develop typical micrographic texture and miarolitic structure,and are composed mainly of quartz (>30%), perthite (65%±), and minor arfvedsonite (2% ~3%) and biotite (1%±). Accessory minerals in these rocks include fluorite, zircon, allanite and Ti-Fe oxides. Chemically, the Yaokeng granites are rich in silica (SiO2=77.13%~77.82%) and alkali (K2O+Na2O=7.99%~8.48%), with (K2O+Na2O)/Al2O3(moecular ratio) values ranging from 0.96 to 1.02. They also have high differentiation indices (DI= 95.5~98.2) and oxidation ratios [Fe2O3/(Fe2O3+FeO)=0.56~0.96]. They are also rich in Rb, Th, Ga, LREE, Nb, Zr, Hf, with (Ga/Al)×104values equal to 3.53~3.95, poor in Sr, Ba, Cr, Co, Ni, V, and show intensive europium depletion (δEu=0.22~0.25). These features are quite similar to thoes of the typical alkali granites. Based on an integrated analysis of the geological and geochemical characteristics of Yaokeng granites, and a systematic comparison of them with Kuiqi and Taohuadao granites, this paper concludes that the Yaokeng rock mass is also a typical postorogenic alkali granite occurring in late Mesozoic magmatic belt along the coastal area of Zhejiang and Fujian Provinces.

Abstract:Two types of gabbro are exposed in Dachanaban ophiolite in North Qilian Mountains. One is in the lower part of the ophiolite, called gabbroⅠ, whereas the other intruded as dikes into pillow lava with boninite character in the upper part of the ophiolite, called gabbroⅡ. These two types of gabbro show different geochemical characteristics. GabbroⅡis characterized by rich Si, Mg and poor Ti, P, and diabaseⅡand poillow lava associated with gabbroⅡhave features of boninite, suggesting a fore_arc environment. By contrast, gabbroⅠand diabaseⅠis of N-MORB, assuming a back-arc basin setting. Geochemical characteristics of two types of gabbro suggest that their formation environment is an oceanic ridge of low spreading rate.

Abstract:Ordos basin has favorable condition for the research work. On the basis of various sorts of data, 8 parasequences were identified in Upper Ma 5 Member of the basin. Within each parasequence, content of substances indissoluble in acid, content of remnant gypsum,δ13C values and NG logging curve display regular changes, indicating the controlling role of sea_level fluctuation. These parameters can provide new methods for the division of paresequence boundaries. Among differnet diageneses, dissolution in the upper part of each parasequence is stronger than that in the lower part. In most parasequences, dolomite in the lower part seems coarser than that in the upper part, and within most beddings pressure solution also occurs more likey at the bottom than in the upper part. It is discovered that the average porosity of exposed parasequence boundaries is similar to that at sequence boundaries, suggesting the larger contribution of parasequences boundary to the preservation of porosity than sequence boundary. Hence the exposed parasequence boundaries deserve more attention. If overlapped, a set of exposed parasequences boundaries would definitely become wonderful reservoirs for oil and gas.

Abstract:The Cenozoic volcanic rocks at the center of Qiangtang are located in the area where the curst of Qianghai-Tibetan Plateau thins from south to north with an unusually concomitant increase of Paisson′s ratio. The ages of the volcanic rocks range from 44.1±1.0Ma to 32.6± 0.8Ma, older than other rocks in northern Tibet. Petrological and geochemical studies suggest that the uniform elevation of northern Tibetan Plateau is closely related to the decoupling of the lithospheric mantle, crustal extension and thinning and volcanism. Therefore, the authors infer that the beginning of the main uplift of the northern plateau occurred at about 40 Ma ago.

Abstract:The Tianshan Mountain is believed to be a typical intracontinental mountain belt; the Tianshan Mountain was formed during tectonic amalgamation of the Tarim and Tianshan block and the Siberian carton in Late Carboniferous-Permian period. A series of basaltic extrusive and intrusive units were emplaced primarily in Late Cretaceous-Plaeogene sedimentary rocks in Tuyon basin and its adjacent area, South Tianshan Mountain. Geochemical data of basalts show low Sr and Pb isotopic values and relative high Nd values (87Sr/86Sr=0.703554~0.703884;143Nd/144Nd = 0. 512838 ~ 0. 512904;206Pb/204Pb = 18. 0063 ~ 18.4720;207Pb/204Pb=15.4411~15.5060;208Pb/204Pb=37.8072~37.9290). The data of major elements, trace elements and rare earth elements indicate that these basaltic rocks are similar to alkaline basalts of Hawaiian type oceanic silands. According to Nd/Sr isotopic ratios, the Tuyon basalts might have originated from low_grade melting of a source (mantle plume) similar to that beneath the Hawaiian Islands. In Tuyon basin and adjacent areas, several fields of Cenozoic alkaline basaltic magmatism may be related to the Cenozoic activity of mantle plumes.

Abstract:Petrofacies studies show that eclogites widely distributed in Ludong orogenic belt can be divided into four types, i.e., (1) eclogites containing coesite and its fake, (2) eclogites containing kyanite zoisite, phengite etc., (3) eclogites of garnet-omphacite-quartz association, and (4) rocks of amphibole, garnet and yroxene association. Mineral intergrowths and P-T conditions of peak metamorphism suggest that these four types of eclogites are products of metamorphism under dominated high temperature and high-superhigh pressure, and PTt paths of metamorphism show clockwise evolution, reflecting the dynamic mechanism of division and ollision of tectonic plate.

Abstract:In the nine types of gold deposits so far discovered in western part of Sichuan Province,there are relatively abundant tetrahedrite_group minerals in three types of hydrothermal golddeposits:Ⅰ—carbonate rock series_hosted type;Ⅱ—ophiolitic melange rock series_hosted type;andⅢ—slightly metamorphosed fine-grained clastic rock series-hosted type. Being products of main ore-forming stages, the tetrahedrite-group minerals occur in irregular grained, veined or stockwork forms, which are combined with pyrite, chalcopyrite, galena, sphalerite, and goldsilver series minerals to constitute the gold ore. The electron microprobe analyses indicate that the tetrahedrite-group minerals include antimony-tetrahedrite and tennatite. The data show that Sb-As is of complete isomorphous replacement in the tetrahedrite-group mineral series.Tetrahedrite minerals in different types of gold deposits have different characteristic parameters. Tetrahedrite_group minerals in TypeⅠgold deposits are characterized by lower arsenic, higher silver and antimony, and intermediate iron and zinc, those in TypeⅡdeposits have antimony and iron content and lower silver, arsenic and zinc, and those in TypeⅢdeposits are enriched in zinc and arsenic, and depleted in silver, iron and antimony. Relatively enriched silver, iron, antimony are typical feature of tetrahedrite-group minerals in TypeⅣdeposits. The characteristics of gold mineralization may be reflected by the major and particular mponents of tetrahedrite-group minerals. There exists vertical change in chemical composition of minerals downward from zinc and antimony-rich tetrahedrite to iron and arsenic-rich tetrahedrite, accompanied with the decreasing trend of silver content in the TypeⅠdeposits.Their occurrence and zonal features are very important for the exploration of gold deposits in western Sichuan and similar regions.

Abstract:Using infrared spectroscopy and X_ray powder diffraction method, the authors have deterined the structural ordering state and equilibrium temperature of K-feldspar collected from the Jialu gold deposit in Xiaoqinling which belongs to the faulted altered rock type. The K-feldspar is microcline to maximum microcline, whose Al occupancy t1(o)=0.73~1.00, t1(m)=0.26~0, t2(o)=t2(m)=0.03~0, with lattice parametersa0=0.8388~0.8611 nm,b0=1.2837~1.2968 nm,c0=0.7156~0.7248 nm,α=89.906~91.093°,β=115.650~116.230°,γ= 87.500~89.994°. The triclinicityΔ=0.686~1.115, and the equilibrium temperaturet=503.51~578.35℃. Based on the above results, this paper has also dealt with the relationship between the equilibrium temperature of K-feldspar and gold mineralization. The authors hold that Jialu K-feldspar is product of hydrothermal metasomatism, and its heat released in the course of adjusting structural state must have made an impact on the auriferous hydrothermal solution at the early high-temperature stage, thus activating gold complex. This action was unfavorable for gold precipitation, as is more clearly seen with the lowering of the equilibrium temperature and the rising of the triclinicity.

Abstract:Outcrops of Mesozoic volcanic rocks are quite widespread in Western Hills of Beijing.Among them, basic-intermediate volcanic rocks have phenocrysts and microcrysts of clinopyroxens. Based on a study of mineral chemistry of clinopyroxene, the author has found that clinopyroxenes are mostly augites and subordinately diopsides. The unit cell volumes, densities 183 and refractive indices of clinopyroxenes are calculated. The results show that augites have smaller unit cell volumes than diopsides. Equilibrium temperatures and pressures between clinopyroxene and melt, oxygen fugacity of magma and depth of magma chambers are computed. The depth of magma chambers of different volcanic rocks are as follows: basaltic magma of the first member of Nandaling Formation is 32km, magma of basaltic andesite and that of shoshonite-latite of the third member of Tiaojishan Formation are 24 km and 12~17 km respectively. The equilibrium temperatures between clinopyroxene and melt are as follows: basltic magma is 1229℃, magma of basaltic andesite is 1186℃, magma of shoshonite_latite is 1165~1181℃, and magma of latite is 1048~1128℃. From Early Jurassic to Early Creta- ceous, magmatic activity shows the following common characteristics: chemical composition of magma varies from basic to acid, the depth of magma chambers tends to become shallow, the equilibrium temperatures between clinopyroxene and melt change from high to low. The viewpoints are advances on the basis of analyzing mineral chemistry, rock chemistry and trace elements. The volcanic rocks studied in this paper belong to the high_potash calc-alkaline series and shoshonite series, the magmatism is controlled chiefly by partial melting, the tectonic envi- ronment of magmatic activity is mainly the inside of continental plate and subordinately island arc.

Abstract:Systematically described in this paper are characteristics of pyrites from the Xiangshan iron and pyrite deposits, such as their modes of occurrence, chemical composition, physical properties, unit cell parameters, infrared spectra and sulfur isotopic composition. The pyrites might be classified into two types. TypeⅠis statistically characterized by very fine_grained texture (0.01~0.1mm across), while TypeⅡis somewhat coarser (0.05~0.5 mm across) than TypeⅠ. Four pyrite samples show N_type electric conduction pattern with large variable pyroelectric coefficients (-97.5~246.5μV/℃), and one sample shows P-type. Unit cell parame- tersa0= 5. 41487 ~ 5. 41883°A, and the crystallochemical formula is Fe0.9946Co0.0017 Ni0.0037)1.0000S2.0279. Different types of pyrites show apparently different strong key absorption peaks with high absorption value features. In this area, every type of pyrite has relatively rich sulfur but poor Fe. Trace elements and REE geochemistry indicate that pyrites are enriched in Co, Ni, V, Ti, Cu, As, and Co/Ni ratios of all pyrites fall in a narrow range of 1~10; As/Se ratios of all pyrites range from 1.33 to 5.50.∑REE values of all pyrites are from 2.2×10-6 to 17.33×10-6, showing distinctly low Ce (δCe 0.62~0.78) and Eu (δEu 0.62~0.81). Sulfur isotopic compositions of all pyrites range from -2.11‰to 17.11‰. These data further demonstrate that these pyrites were formed by volcanic hot water deposition and that the formation of Xianshan pyrite deposits is attributed mainly to volcanic deposition.