Structure Refinement of Cs-rich Na-Li Beryl and Analysis of Its Typomorphic Characteristics of Configurations

The tabular beryl found in Huya Country, Sichuan Province is a rare and special member among beryls. Chemical analysis reveals that the beryl is a new type of Cs-rich Na-Li beryl, and the content of alkalis （Li20, Na2O, K2O, Rb2O, Cs2O） is up to 2.41%. The CCD system on the SMART APEX four circle single crystal diffractometer was used in this experiment to determine the structure of the sample accurately. The beryl belongs to the hexagonal system; its space group is P6/mcc. The dimensions of the unit cell are as follows： a = 0.91961（3） nm, c = 0.91969（7） nm, c/a = 1.0000, V= 0.67357 nm3, 7 = 120°, α= 90°, β = 90°. The accurate atomic coordinates of alkali metal ions and other crystallographic parameters are also obtained： Z = 2, the calculated density D = 2.754 g/cm^3 and final R （ I 〉 2 σ （/3）= 0.046 for 5597 reflections. The crystal structure was described by coordination polyhedron. Based on the data gained, a three-dimensional graph of the crystal structure of tabular beryl was made with the ATOMS 6.0 software. The refinement of crystal structure indicates that there are two main reasons for the cause of the tabular configuration： （1） The substitution of Be by Li into the tetrahedral framework weakened the stacked six-sided rings [Si6O18]^12- of the tetrahedral Si; （2） Alkalis （mainly Na and Cs） are too large to substitute in four-fold or six-fold coordination within the structure and are accommodated in the vacant channel. The accommodation of these alkalis strengthened the structure of six-sided rings of the tetrahedral Si. And other alkali metal ions and free volatile molecules such as H2O and CO2 occupy variable positions in the channel. The equation of the electrovalence is Li＋＋Na＋→Be^2＋. According to structural and compositional differences, the monoclinic crystal of tabular beryl is considered to be a new member of the beryl group. Chemical constraints of the environment, namely, the bulk-rock chemistry and the fluid-phase composition and physical-chemical conditions during the growth of the mineral may account for these occurrences of rare elements. In addition, that Li and Be have appro^mate physical parameters is also the key factor for the substitution. The direction of the mineralized hydrothermal liquid and the special occurrence conditions of the beryl such as the pH, temperature and pressure are also considered to be the main causes of the configuration of the tabular beryl.

Typomorpic Characteristics of the Major Minerals in the Puziwan Gold Deposit,Datong,Shanxi,China

Utilizing theories of minerageny and prospecting mineralogy, the authors studied the attitude, morphotype and chemical composition of metallic minerals of pyrite, gold, chalcopyrite, galena and sphalerite, non-metallic minerals of quartz, carbonate, dolomite and rutile in the Puziwan gold deposit. The study shows the following results. （1） The mineral assemblage is complex and the species of sulfide are abundant with occurrences of sulfosalt minerals. （2） The composition in the minerals is complex and there rich micro elements, including As, Sb, Bi, Se, Te, Au, Ag, Cu, Pb, Zn, and Cr, Ni, V. The typomorphic characteristics of the association of the elements and their specific value suggest that gold mineralization is associated with shallow magmatic hydrothermal activity, the oreforming fluid is the mixture of abundant rising alkali magmatic water originating from the mantle or the lower crust and the descending acid atmospheric water. （3） Ankerite, Fe-rich sphalerite, granular Ti-rich rutile are widely distributed, which indicate great denudation depths, high mineralization temperature. The deposit is found in the middle and shallow positions of the porphyry series. The deep layers are not favorable for gold mineralization. （4） Copper minerals are rich in the ores and sulfides have high content of copper, suggesting possible porphyry-type Cu （Au） mineralization in deep positions and the surrounding areas.

A Prospecting Mineralogy Study: Arsenopyrite In Endogenetic Gold Deposits

Arsenopyrite is one of very important and common auriferous minerals in endogenetic gold deposits. In seven gold deposits, the prospecting typomorphic characteristics of arsenopyrite, such as morphological typomorphism, composition typomorphism, pyroelectricity typomorphism and so on, were established. The crystal form of arsenopyrite is simple, and the form symbols mainly are {101}, {120}, {210}, {140}, {230}, {012}, etc. The smaller grain and poor crystal form arsenopyrite indicates the better auriferous characteristics. The major elements (Fe, As and S) of gold-bearing arsenopyrite usually show Fe/As+S>0.5,As/S<1 which deviates from its theoretical value. The most important trace element is Au and next is Ag in arsenopyrite, and they often show the positive correlation. The pyroelectricity of arsenopyrite can reflect the mineralization epoch, and it also is related to the crystal form and granudarity.

Morphology,Chemistry and U-Pb Geochronology of Zircon Grains in Quartz Monzodiorite from the Sunzhuang Area,Fanshi County,Shanxi Province

The morphology, REE geochemistry and U-Pb geochronology of zircons from quartz monzodiorite in the Sunzhuang area, Fanshi County, Shanxi Province are presented in this study. The zircon crystals can be classified into four main types as： AB, L, S and P, and 24 subtypes such as AB4, ABs, Ls, and S3. The maximum crystallization temperature of zircon was estimated as 850℃, with the minimum of 550℃. The peak temperatures of the zircon crystallization range from 650℃ to 700℃. The abundances of Th and U in the zircon grains show large variation with the Th/U values 〉 0.4. The Th and U values also show a positive correlation in most zircons. The REE abundance of zircon in the quartz monzodiorite ranges from 280.4 ppm to 2143 ppm with an average of 856.4 ppm. The chondrite normalized zircon REE patterns show two types, one is characterized by HREE enrichment and LREE depletion with positive Ce-anomaly and negative Eu-anomaly whereas the other is HREE enriched and LREE depleted with negative Eu-anomaly but without positive Ce-anomaly, and relatively flat patterns. The LA-ICP-MS U-Pb geochronology on the zircons yields a mean age of 133-0.87 Ma. Our data on zircon morphology, composition and U-Pb geochronology reveal that the parent magma of the quartz monzodiorite which was emplaced during late Yanshanian had a mixed crust-mantle source, with crustal components dominating. The magma is inferred to have been water rich and alkaline with initial high oxygen fugacity. Post-magmatic hydrothermal activity occurred under relatively reducing conditions which was conductive for gold precipitation in the Yixingzhai gold deposit.