Jialan Lu

Long-chain alkenones in Hotong Qagan Nur Lake sediments and its paleoclimatic implications

The long-chain alkenones present in the shallow sediment of Hotong Qagan Nur Lake in China are reported. According to the similarity of compositions and distributions of the alkenones determined commonly in the sediment section to those of marine sediment, it is reasonably referred that the alkenones might also originate from Prymnesiophyceae. In addition, the parameter U37k′; of alkenone is in positive correlation to δ18O values of authigenic calcium and magnesium minerals. This indicates that the parameter U37k∼ of long-chain alkenone is also available to indicate paleoclimate of high-salinity alkaline lake.

Germanium occurrence in Lincang superlarge deposit in Yunnan, China

A heavy-media separation has brcu carried out to study the partition of germanium in various macetals ol mineralized lignites in Lincang superlarge gerrtlilnium deposit in Yunniln, China. The result shows that Ge stays predominantly in huminites, especially in corpohuminitrs (86.04–89.16%), next in light macerals and minerals (3.20%–8.33% and 1.71%–10.27%, respectively). In addition, the EPMA and PIXE analyses suggest that no germanium minerals have been detected and Ge is well distributed in the whole mineralized lignite, bonding to O, C and H of coaly organic matter of mineralized lignites.

Natural gas releasing simulation experiment of coal in process of temperature decreasing and decompression and preliminary application in Ordos Basin

Natural gas releasing simulation experiments were carried out in laboratory for researching the gas storage capacity in state of high temperature and high pressure and its gas releasing potential in process of temperature decreasing and decompression. The exiting phase state was studied through measuring gas adsorption of coal and PVT phase calculating of natural gas. Gas volume, gas molecular and isotope compositions in process of temperature decreasing and decompression were measured, natural-gas yields released from the Upper Paleozoic coal strata after later Cretaceous (K3) were calculated and the formation of the reservoir was studied combining with the geological background. The results indicate that natural gas stored in coal has still bigger releasing potential after the uplift of Upper Paleozoic strata. There exists a weak gas supply-effluent equilibrium in the reservoir of Ordos Basin, which is another possible evidence that the Upper Paleozoic gas reservoir may be a deep basin gas reservoir.

CRUDE OIL AS CARRIER OF GOLD: PETROLOGICAL AND GEOCHEMICAL EVIDENCE FROM LANNIGOU GOLD DEPOSIT IN SOUTHWESTERN GUIZHOU, CHINA

Organic matter is related closely to mineralization of Lannigou gold deposit in southwestern Guizhou, China. Regionally, the distribution of organic carbon agrees well with that of faults within which gold deposits are hosted. Studies on organic petrology show that pyrobitumen, which is related most closely to mineralization, adheres to quartz vein or fills quartz veinlet. Proton-induced X-ray emission (PIXE) analysis shows an evident abundance of Au in pyrobitumen. Pyrobitumen paragenetically associates with pyrite and arsenopyrite which are the main carrier minerals of Au. The thermal simulation experiment indicates that about 99% of Au will be concentrated in oil phase in the coexisting system of oil and brine and rock. The role of crude oil in ore-forming process is: as carrier of Au, crude oil moves upwards, and undergoes thermal decomposition and thermochemical reduction when it encounters the oxidizing fluid within the Trassic turbidity; Au is thus released from crude oil, reduced and precipitated.

Evidence for transforming mineralization of Baiguoyuan silver-vanadium deposit hosted in black shale in Hubei, China

Baiguoyuan silver-vanadium deposit is generally thought to be of sedimentary-diagenetic origin. Based on the characteristics of barites, it is suggested that hydrothermal transformation has been involved in mineralization. The barites in black shale can be grouped into irregular ones which were formed during early diagenesis and tabular ones which were formed during late diagenesis. The tabular barites are replaced by pyrite and have formed a regular girdle around them. PlXE analysis states that Ag is greatly concentrated in pyrite replacement girdle. The girdle is the product of hydrothermal transformation. The transformation is one of the main mineralization stages of Baiguoyuan deposit.

Experimental study of gold distribution in the algae-organic matter-fluid system

ConclusionGold distribution and transformation in algae-organic matter-fluid system is very complicated. Gold is first concentrated in kerogen after algae died. With the increase of dissolved organic matter owing to the increase of temperature and pressure, part of gold simultaneously emigrates from kerogen to DOM. When DOM forms organic fluid and emigrates from the strata, gold is simultaneously carried away by organic fluid in acidic condition, but by water in alkali condition. When the auriferous fluid flows through carbonaceous strata, gold in fluid is unloaded by kerogen. Gold migration in the system, accompanied by the evolution of algae-organic matter-fluid, provides the basic information of biometallogenetic evolution of gold.

Two kinds of Carlin-type gold deposite in southwestern Guizhou, China

Based on the organic geochemical studies on two typical Carlin-type deposits in southwestern Guizhou, as well as the comparison between the two deposits in terms of geological background, igneous rock, paleo-oilfield, lithofacies and paleogeographical and geochemical features, two kinds of Carlin-type deposit were proposed: Lannigou Type and Getang Type. The former includes Lannigou, Banqi and Yata gold deposits. These deposits are hosted by turbidite, geographically situated in the southwest of the mineralized district, and related genetically to paleo-oilfields. The latter includes Getang, Zimudang and Dachang gold (mercury and thallium) deposits, situated geographically in the northwest of the mineralized district where Emeishan basalt commonly occurs. These deposits are associated with reduction of coaly organic matter.

Simulation experiments on secondary thermal stress of biodegraded bituminous sandstones

Secondary variation of reservoir is a hot problem in petroleum geochemistry field. Several kinds of secondary variations have taken place after the formation of bituminous sandstones in the Tarim Basin including biodegradation, washing, dissipation and secondary thermal stress. Biodegraded bituminous sandstones were used in the experiment. Pyrolysis experiment has been performed in a closed system, simulating secondary thermal stress with continual burial of Silurian bituminous sandstones which may cause the changes in molecular compositions, carbon isotope and physical properties of bituminous sandstones. The results are as follows: (i) Gases are mainly product during the experiment and carbon isotope of gas is lighter. (ii) Yield of C6+ hydrocarbon is relative smaller, and yielded oil is mainly light oil. (iii) Chromatogram character of biodegraded oil-sand is similar to that of saturated hydrocarbon in extracts from present-day bituminous sandstones. (iv) Porosity of bituminous sandstones gradually increases with increasing temperature. Fluorescence color of bituminous sandstones gradually become darker. Reflected light color of bitumen in bituminous sandstones becomes darker with increasing temperature and reflectivity of bitumen increases with increase in temperature. It is speculated that secondary thermal stress has great effect on molecular composition and structure of bituminous sandstones.