桂北某铀矿区物化探特征与找矿方向研究

桂北某铀矿区位于苗儿山复式花岗岩体中段东南缘,构造发育,铀矿化点多,成矿条件有利。文章通过对桂北某铀矿区的伽马场晕、氡浓度异常、岩矿石化学、铀镭平衡系数等物化探特征进行研究,探索物化探特征与铀矿化的关系,指明该区的找矿方向。

Zinc isotope fractionation under vaporization processes and in aqueous solutions

Equilibrium Zn isotope fractionation was inves- tigated using first-principles quantum chemistry methods at the B3LYP/6-311G level. The volume variable cluster model method was used to calculate isotope fractionation factors of sphalerite, smithsonite, calcite, anorthite, for- sterite, and enstatite. The water-droplet method was used to calculate Zn isotope fractionation factors of Zn^2＋-bearing aqueous species; their reduced partition function ratio factors decreased in the order [Zn（H2O）6]^2＋ 〉 [ZnCl（H2O）5]^ ＋ 〉 [ZnCl2（H2O）4] 〉 [ZnCl3（H20）2]^-〉 ZnCl4]^2-. Gas- eous ZnCl2 was also calculated for vaporization processes. Kinetic isotope fractionation of diffusional processes in a vacuum was directly calculated using formulas provided by Richter and co-workers. Our calculations show that in addition to the kinetic isotope effect of diffusional processes, equilibrium isotope fractionation also contributed nontriv- ially to observed Zn isotope fractionation of vaporization processes. The calculated net Zn isotope fractionation of vaporization processes was 7-7.5‰, with ZnCl2 as the gas- eous species. This matches experimental observations of the range of Zn isotope distribution of lunar samples. Therefore, vaporization processes may be the cause of the large distri- bution of Zn isotope signals found on the Moon. However, we cannot further distinguish the origin of such vaporization processes; it might be due either to igneous rock melting inmeteorite bombardments or to a giant impact event. Fur- thermore, isotope fractionation between Zn-bearing aqueous species and minerals that we have provided helps explain Zn isotope data in the fields of ore deposits and petrology.

Ilvaite as a thermodynamic recorder of multistage retrograde alteration in large Galinge skarn Fe deposit, western China

The ilvaite-bearing skarn associations in the Galinge skarn deposit were studied to determine their physicochemical formation conditions.A thermodynamic model setting pressure of 50 MPa(Pf=Ps=50 MPa)was set up to trace the skarn evolution.Petrographic evidence for replacement of garnet and magnetite by ilvaite in the early retrograde stage(Stage I)combined with thermodynamic modeling suggests that the alteration may have occurred at 400470°C under moderately high fO withΔlgfO(HM)ranges from 4 to 4.2.The model is based on a maximum 22 pressure of 50 MPa calculated from magmatic amphibole geobarometer.The continuous breakdown of ilvaite with quartz to form ferro-actinolite and magnetite occur in the late retrograde stage(Stage II).The reactions occurred at 400440°C under moderate fO(ΔlgfO(HM):4 to 4.4).In Stage III,the breakdown of ilvaite to form calcite,pyrite 22 and ferroactinolite depends on XCO which can be estimated to be in a range of 0.005 to 0.05,and the reaction would 2 occur at higher temperatures with increasing XCO.Under these conditions,the breakdown occurs at 270350°C and 2 low fO(ΔlgfO(HM):up to 5.2).The thermodynamic model for continuous evolution from Stage I to Stage III 22 completely records the conditions of the retrograde alteration,which is inconsistent with the thermobarometry imprints of fluid inclusions.Therefore,the petrography and phase relations of ilvaite are useful indicators of reaction conditions in various skarn deposit types.

Petroleum systems in the Damintun Depression, Liaohe Oilfield

There are two different types of oils—high-wax oil and normal oil—found in the Damintun Depression of Liaohe Oilfield after several years of exploration and development, but their distributions and origins had confused the explorers in the oilfield. The introduction of petroleum-system concept shifts the view of geoscientists from geology and geophysics to oil, gas and their related source rocks. After detailed study, two petroleum systems have been identified in the Damintun Depression: (1) the ES42-Ar buried hill petroleum system (called the high-wax oil petroleum system) and (2) the ES41+ES34-ES4 and ES3 petroleum system (called the normal oil petroleum system). Based on the detailed analysis of the basic components, and all the geological processes required to create these elements of the two petroleum systems, it is put forward that targets for future exploration should include the area near Dongshenpu-Xinglongpu and the area near the Anfutun Sag. This provides scientific basis and has theoretical and practical meaning for the exploration and development.

Geotechnogenesis problems

Geotechgjgensis is mineralogical geochemical transformation of minerals, rocks, and ores as consequence of impact on them in the process of performing geological-exploration and irrigation works, extracting and processing mineral resources, constructing transport, civil and military objects. These effects lead to discontinuity and moving different scale fragments of upper part of lithospere and conjugate hydro-and biosphere zones. Discontinuity predttermines the disturbance of matural systems dynamic equilibriu and acceleration ofmftter transformation and migration processes. The final aim of studying geotechnogenesis minseralogy and geochemistry is the establishment of scientific foundations for developing ecological safety measures including also utilization fo geotechnogene deposits.