Analysis Of Geochemical Characteristics Research Articles

Petrography and Geochemistry of Hydrothermal Alteration in the Low-Sulfidation Epithermal Kestanelik Au Deposit, Biga Peninsula, NW Turkey

In this study, the facies and degrees of hydrothermal alteration related to the low-sulfidation epithermal Kestanelik Au deposit in the Biga Peninsula metallogenic province are identified through petrographic studies and analysis of geochemical characteristics, such as mass changes, molar element ratios, and alteration indices. The gold mineralization is located in silicified zones containing veins and stockwork veinlets of silica. In the Kestanelik Au deposit, common hydrothermal alteration is mainly found in the Permian-Upper Cretaceous Çamlıca basement metamorphics and the Eocene granodiorite, and less often in the Eocene Şahinli volcanic rocks of the Karabiga Massif on the Peninsula. Based on mineralogical and geochemical studies conducted on altered samples, four different alteration facies are defined as silicic, sericitic, argillic, and propylitic, which show remarkable differences in the behavior of REEs, Si, K, Al, Na, and Ca elements. The hydrothermal fluids that caused alteration in the Kestanelik Au mineralization and host rocks had low REE contents because of REE mobilization. In addition, the kaolinization of feldspars and micas, and the chloritization of biotite and feldspars, may have caused negative Eu anomalies. The characterization of rocks subjected to hydrothermal alteration that are most influenced by diverse K-metasomatism with the largest K gains and losses in Na–Ca is illustrated by molar element ratio plots. Depending on the intensity of K-metasomatism, gold mineralization increases with increasing K trends toward gold ore veins. In the Kestanelik Au field, the argillic, sericitic, and propylitic alteration types from the zones enclosing the Au ore veins are revealed using the Ishikawa alteration index and chlorite–carbonate–pyrite index. Mass changes in the altered rocks indicate that there are gains in Si, K, and Al, and losses in Na and Ca with the increasing intensity of alteration toward the ore veins. The results confirm the presence of silicic and K–metasomatic (sericite and argillic) and propylitic (Fe-rich chloride) alteration zoning extending from the inner regions to the outer regions, which characterize the epithermal ore systems.

A Petrological, Geochemical, and Geochronological Study of Shuikou Ultrabasic Rock Mass in Wuding County, Yunnan Province, China

Geotectonically, the Shuikou ultrabasic-basic rock mass is located on the western margin of the Yangtze Platform. As revealed by field geological surveys, the Shuikou rock mass intrudes into the quartz sandstones of the Sinian Chengjiang Formation (Zac). It is dominated by pyroxenites and can be roughly divided into four lithofacies zones, namely gabbros at the outermost periphery and fine-, medium-, and coarse-grained pyroxenites from margin to center. With the transition from pyroxenites to gabbros, the Shuikou rock mass features gradual enrichment in silica and alkali overall, an increase in &#931REE and (La/Yb)N ratio, and a decrease in δEu values and Eu/Sm ratio, indicating that the Shuikou rock mass was formed from the continuous differentiation and crystallization of consanguineous magma and that low-degree partial melting occurred meanwhile. According to the U-Pb baddeleyite geochronology, the crystallization age of the Shuikou rock mass is 210.7 ± 3 Ma (MSWD = 1.01). Based on this, as well as the analysis of geochemical characteristics, the Shuikou rock mass occurred in a continental intraplate tensional environment, this is closely related to the activities of the Emeishan mantle plume during the same period.

Application of Laser Induced Breakdown Spectroscopy in Soil Element Analysis of Watershed

With the rapid development of spectroscopy technology, laser induced breakdown spectroscopy (LIBS) has become the focus of elemental analysis technology in recent years. With its advantages of non-destructive testing, rapid and multi-element detection, LIBS has been successfully applied to the analysis of geochemical characteristics of soil elements in river basins. The application of LIBS technology in soil elemental analysis of watershed is reviewed in detail. The accuracy of LIBS technology in soil element analysis is studied with the Masha River Basin as the research area. On this basis, the key problems in the process of soil element analysis, such as spectral enhancement methods and quantitative analysis methods, were analyzed. The analysis results show that the accuracy of elemental analysis between LIBS and traditional chemical methods is not much different, but the analysis time of LIBS method is shorter. Methods such as MLR, PLSR, and internal standard methods can improve the fit of the calibration curve and reduce the quantitative analysis error. By changing parameters such as laser energy and delay time, the spectral intensity can be enhanced to reduce the effects of matrix effects. In the process of elemental analysis, the effects of soil physical and chemical parameters should be considered comprehensively, and appropriate quantitative analysis methods should be adopted to improve the accuracy of the analysis results.

Discovery of Carboniferous Oil Seepage in Qaidam Basin and Its Geological Significance

In this work, the oil seepage was found in calcite veins in Keluke formation of upper Carboniferous reservoirs. Based on the analysis of geochemical characteristics, the isomerization parameter of C29 sterane 20S/(20S + 20R) was obtained as 0.39 and Ts/Tm value as 1.12, indicating that the oil seepage was mature. The Pr/Ph value was 0.64 and the tricyclic terpane was characterized by high abundance of gamacerane, C27 > C29 sterane, and a normal distribution with C23 as the dominant peak. Moreover, the oil/oil and oil/source rock correlation of oil seepage and carboniferous source rock underground and surface indicated that the oil seepage was similar to crude in Mabei-2 well (1463 m) and Sin-3 well (1076 m) but was different from the other crude in north Qaidam basin. It is inferred that the oil seepage was authigenic crude in Carboniferous, and Carboniferous source rocks have contributed to the oils in Mabei-2 well (1463 m) and Sin-3 well (1076 m). This study offers new scientific evidence for the exploring of carboniferous in Qiandam basin.

New perspective of Miocene marine hydrocarbon source rocks in deep-water area in Qiongdongnan Basin of northern South China Sea

Drilling wells reveal that the organic matter abundance of Miocene marine source rocks in shallow water area of the Qiongdongnan Basin is relatively low with poor hydrocarbon generation potential. However, in some drilling wells of deep water area close to the central depression belt, Miocene marine source rocks with better organic matter abundance and hydrocarbon generation have been found, which have achieved better source rock standard based on the analysis of geochemical characteristics. Although there are no exploratory wells in deep water area of the research region, through the comparative analysis of geochemical data of several typical exploratory wells respectively from shallow water area in the basin, central depression belt margin in deep-water area of the basin and Site 1148 of deep sea drilling in the South China Sea Basin, it reveals that the tendency of the quality of source rocks becomes positive gradually from delta to bathyal environment, which then becomes negative as in deep oceanic environment. Owing to the lack of terrestrial organic matter input, the important controlling factors of Miocene marine source rocks in the Qiongdongnan Basin are ocean productivity and preservation conditions of organic matter. The element geochemistry data indicate that the tendency of the paleoproductivity and the preservation conditions of organic matter become positive as water depth increase from shallow area to bathyal area close to central depression belt. So it is speculated that there must exist high quality source rocks in the central depression area where the preservation conditions of organic matter are much better. Besides, in theory, in oxygen-poor zone of oceanic environment at the water depth 400–1 000 m, the preservation conditions of organic matter are well thus forming high-quality marine source rocks. The resulting speculation, it is reasonable to consider that there are high hydrocarbon generation potential source rocks in bathyal environment of the Qiongdongnan Basin, especially at the water depth 400–1 000 m.

Formation fluid characteristics and hydrocarbon accumulation in the Dongying sag, Shengli Oilfield

Abstract Based on the analysis of geochemical characteristics and distribution of different formation waters, a new origin identification standard was established for the formation water in the Paleogene Shahejie Formation in the Dongying Sag. The migration paths of the connate water expelled from source rocks are similar to those of the hydrocarbons coming from the same rocks, so the geochemical characteristics of the connate water coming from the source rocks can be used as auxiliary indexes to study hydrocarbon migration. Considering fluid pressure and formation water distribution, the Paleogene fluids are divided into three fluid systems: normal-pressure open fluid system, overpressure confined fluid system, and transition fluid system. The differences in hydrocarbon-bearing fluid characteristics, hydrocarbon migration dynamic, hydrocarbon-bearing fluid flow type between these fluid systems were studied. According to characteristics of the hydrocarbon-bearing fluid charging into traps, and formation water drainage pattern, three typical oil accumulation models were classified. In the overpressure confined fluid system, the main oil accumulation mode is high oil saturation fluid entering traps and displacing formation water, and “continuous” reservoirs are prone to form, and fluid oil saturation, fluid charging pressure and fluid seeping conditions affect reservoirs’ oil accumulation extent. In the normal-pressure open fluid system, the main oil accumulation modes include low oil saturation fluids enter a trap while formation water is overflowing out of the trap, and low oil saturation fluids enter a trap while formation water is seeping out of the trap. The amount of hydrocarbon-bearing fluid, fluid oil saturation, trap height, and caprock sealing ability affect reservoir's oil accumulation extent.

Geochemical Characteristics of Sedimentary Manganese Deposit of Guichi, Anhui Province, China

The sedimentary manganese deposits occurring in Gufeng formation of the Permian in Guichi area, south Anhui Province, include manganese carbonate deposit formed by sedimentation, and manganese oxide deposit made by later oxidation. The total REE contents of these samples are relatively low (< 250 × 10 −6), belonging to LREE-enriched type, showing LREE enrichment during the process of formation of Mn deposit, especially during Mn-oxidizing process. Three normalized REE patterns and SCNA-normalized trace elements spider diagrams of the Mn-bearing sequence rocks and ores in this area reflect their same origin of ore sources, which is similar to rock-forming and ore-forming conditions. The Mnforming materials primarily came from the continent with higher mature degree and single material source. The δ Eu and δ Ce negative anomaly and Ce anomaly (< -0.1) manifest that Mn-bearing sequence of the Permian was mostly formed in marine basin and oxidative environment. The Sr and Ba anomaly, Sr/Ba and Co/Ni values reflect the Mn deposit environment was of deep water and high-salinity of marine facies. Although the Ce/La (mean 1.05), Y/Ho (25 ∼ 41.5) and trace metals show a variety of correlations with Mn in the ten rock samples, which show multiple sources for the manganese, the analysis of geochemical characteristics indicate that the material sources of Mn deposit have been primarily terrestrially-derived. Another source of the manganese probably comes from the seafloor volcanism in this area. Analysis of sedimentary features and geohistoric evolvement reveals that the maximum transgression of the Qixia Period, ore district is then in deep shelf-basin sedimentary setting and the Mn-bearing sequence is deposited.