Acta Geochimica (v.29, #3)

The Kunlunguan biotite granite pluton, located in the southwestern part of the Nanling Mesozoic granite belt, is controlled by the NW-trending Nandan-Kunlunguan deep fault. LA-ICP-MS zircon U-Pb dating yielded a weighted mean 206Pb/238U age of 93.0±1 Ma (MSDW=1.7) for the main part of the pluton, implying its Late Cretaceous intrusion. The Kunlunguan body is a high-K calc-alkaline rock characterized by high silicon, alkali and aluminum, and low phosphorus and titanium. SiO2 contents of the Kunlunguan body range from 68.13% to 72.61% and K2O/Na2O ratios from 1.28 to 1.87. A/CNK values vary from 0.76 to 1.42, indicating a metaluminous to intensively peraluminous character. The rocks are enriched in Ga, Rb, Th, U and Pb but depleted in Ba, Nb, Sr, P and Ti. The REEs are characterized by remarkable negative Eu anomalies (Eu/Eu*=0.53–0.73) and exhibit right-inclined “V”-shaped patterns with LREE enrichment. Petrology, major and trace elements data all indicate that the pluton is aluminous A-type granite which intruded in a post-collisional extensional tectonic setting. It is related to back-arc extension, reflecting high-angle subduction of the paleo-Pacific plate, caused by northward movement of the Indian plate. The Nandan-Kunlunguan A-type granites belt, together with similar plutons in the coastal areas of Zhejiang and Fujian provinces, represent the two A-type granite belts under a matching tectonic system.
Keywords: A-type granite; LA-ICP-MS zircon U-Pb dating; back-arc extension; Kunlunguan biotite granite; Guangxi

An analytical procedure involving Rock-Eval pyrolysis of whole-rocks was adopted on fresh outcrop samples covering the three lithostratigraphic units in the Afikpo Basin of the Lower Benue Trough. Three petroleum systems are present in the Cretaceous delta frame: the Asu-River Group, the Eze-Aku Group and proto-Niger Delta sequences. The Afikpo Basin has been correlated to three petroleum systems in the Lower Congo Basin, Niger Delta and the Anambra Basin.The organic geochemistry of the shales, carbonaceous mudstones and coal beds show relatively moderate to high total organic carbon contents. The best potential hydrocarbon source rocks are the Eze-Aku Group and proto-Niger Delta shales, carbonaceous mudstones and coal beds where maturation was attained. The high total organic contents, thermal maturity and terrigenous characters of the Asu-River Group, Eze-Aku Group and proto-Niger Delta sediments, suggest the presence of a large amount of natural gas with a small quantity of oil accumulation. Variations in source rock facies were observed from one lithostratigraphic unit to another, and initial HI values as a function of TOC were proposed for each lithostratigraphic unit. The results also show that TOC, HI, OI, S2 and T max vary from older to younger rocks. The T max values discriminate the rocks into immature and mature source rocks. Source rocks with high T max suggest high geothermal gradient/or recycled organic matter. Also high T max and S2 yield indicate late and post maturity. Recycled organic matter is characterized by low T max. The principal source rocks for gas in the Afikpo Basin are the Eze-Aku Group and proto-Niger Delta beds deltaic systems, consisting mainly of III to IV kerogens with a subordinate amount of type II organic matter. Based on the obtained results, it is concluded that the Cretaceous shales, carbonaceous mudstones and coals in the Afikpo Basin of the Lower Benue Trough are capable of generating and expelling hydrocarbons in the case of sufficient maturity.
Keywords: organic geochemical evaluation; oil/gas-generative potential; organic matter; Cretaceous strata; Lower Benue Trough; Nigeria

Frontal affinity chromatography was applied to characterizing the mechanism of binding of silver with sediment particulates collected from Lake Ontario, Canada. The results showed that there was one major binding site for Ag+ in the particulates. The binding capacity ranges from 6.06 to 1.01 μ·mol·g−1, and the binding constant (lgK) from 6.23 to 7.43 M−1 in 0.005 M ion strength at pH=3−7. The binding capacity and affinity constant were found to be pH-dependent. It is suggested that the particulate surface site where silver was bound was the anionic base. This study would be helpful for better understanding of the fundamental environmental chemistry of silver in sediments.
Keywords: frontal affinity chromatography; silver; binding capacity; sediment

Geochemistry and mineral chemistry of Pan-African amphibolites of South Sinai, Egypt by Mohamed El-Tokhi; Bahaa Eldin Amin; Sulaiman Alabeed; Abdulla Musallam (246-254).
In the Wadi Feiran area, amphibolites occur as inclusions, bands, linear bodies of variable thickness and irregular lenses in para-geneisses. Chemical evidence indicates that these amphibolites display an igneous origin and were derived from magma essentially of tholelitic rather than alkaline composition; transitional in character between continental and island-arc. The chemistry of amphiboles, related to pressure and temperature conditions of metamorphism, showed that they were formed under low pressure and high temperature conditions.
Keywords: Pan-African amphibolite; geochemistry; mineral chemistry; Sinai, Egypt

Study on the geochemical characteristics of arc-volcanic rocks in the Chiang Rai-Lampang belt of northern Thailand by Shangyue Shen; Qinglai Feng; Wenqian Yang; Zhibin Zhang; Chonglakmani Chongpan (255-260).
On the basis of the petrographic characteristics, rock assemblages, petrochemistry, REEs, trace elements and geotectonic settings, the authors described the characteristics of continental marginal arc-volcanic rocks in the Late Permian-Early Triassic (P2-T1) volcanic rocks distributed on the eastern side of the ocean-ridge/oceanic island basalts in the Chiang Mai belt. The volcanic rock assemblage is basaltic andesite-andesite-rhyolite. The volcanic series is dominated by the calc-alkaline series, with the tholeitic series coming next. The chemical composition of the volcanic rocks is characterized by high Al2O3; the REE distribution patterns are of the LREE-enrichment rightward incline type; the large cation elements are highly enriched, and the volcanic rocks are generally enriched in U and Th and depleted in Ti, Cr and P. The petrochemical plot falls within the field of island-arc volcanic rocks, in consistency with the projected points of continental marginal arc-volcanic rocks in the Lancangjiang belt. These continental marginal arc-volcanic rocks, together with ocean-ridge/oceanic island-type volcanic rocks in the Chiang Mai belt, constitute the ocean-ridge volcanic rock-arc magmatic rock belts distributed in pairs, indicative of eastward subduction of the oceanic crust in the Chiang Mai belt. This result is of great importance in exploring the evolution of the paleo-Tethys in the Chiang Mai belt.
Keywords: Chiang Rai-Lampang belt in northern Thailand; China’ Lancangjiang belt; Late Permian-Early Triassic (P2-T1)

Distribution and mode of occurrence of radionuclides in phosphogypsum derived from Aqaba and Eshidiya Fertilizer Industry, South Jordan by M. S. Al-Hwaiti; R. A. Zielinski; J. R. Bundham; J. F. Ranville; P. E. Ross (261-269).
Phosphogypsum (PG) is a by-product of the chemical reaction called the “wet process” whereby sulphuric acid reacts with phosphate rock (PR) to produce phosphoric acid, needed for fertilizer production. Through the wet process, some impurities naturally present in the PR become incorporated in PG, including U decay-series radionuclides, are the main important concern which could have an effect on the surrounding environment and prevent its safe utilization. In order to determine the distribution and bioavailability of radionuclides to the surrounding environment, we used a sequential leaching of PG samples from Aqaba and Eshidiya fertilizer industry. The results showed that the percentages of 226Ra and 210Pb in PG are over those in the corresponding phosphate rocks (PG/PR), where 85% of the 226Ra and 85% of the 210Pb fractionate to PG. The sequential extraction results exhibited that most of 226Ra and 210Pb are bound in the residual phase (non-CaSO4) fraction ranging from 45–65% and 55%–75%, respectively, whereas only 10%–15% and 10%–20% respectively of these radionuclides are distributed in the most labile fraction. The results obtained from this study showed that radionuclides are not incorporated with gypsum itself and may not form a threat to the surrounding environment.
Keywords: radionuclide; phosphogypsum; distribution; sequential extraction; Jordan

Temporal-spatial distribution and ore-forming material source of gold, copper and silver polymetallic ore deposits in the Fuping mantle structure zone by Baode Wang; Shuyin Niu; Aiqun Sun; Yaming Liu; Yan Xie; Xiaoping Jiang; Yongli Zhao; Yincang Gao; Fuwang Zhao (270-277).
This study was conducted following research on metallogenesis in the Zhangjiajie-Xuanhua and East Hebei mantle branch structure zones. The Fuping mantle branch structure zone is one where Au, Cu and Ag polymetallic ore resources are concentrated in North Hebei. However, there has existed a long-standing controversy on the temporal-spatial distribution of ore resources and their ore-forming material sources. In terms of age dating and the comprehensive analysis of S, Pb, O, C and Si isotopes, it is considered that the temporal-spatial distribution of ore resources in this mantle branch structure zone is obviously controlled by the Fuping mantle branch structure. In space there is developed such a metallogenic pattern as to be Ag, Pb and Zn polymetallic ore deposits with gold appearing inside and copper appearing outside. Metallogenesis is dated mainly at Yanshanian, the ore-forming materials were derived predominantly from the deep interior of the Earth, and ore-forming fluids were derived largely from Yanshanian magmatism.
Keywords: Au; Ag polymetallic ore deposit; temporal-spatial distribution; ore-forming material source; Fuping mantle branch structure zone

Saturation states of carbonate minerals in a freshwater-seawater mixing zone of small tropical island’s aquifer by Ahmad Zaharin Aris; Sarva Mangala Praveena; Mohd Harun Abdullah (278-286).
Groundwater is a crucial resource on the Manukan Island as it is the only source of freshwater available on the island. The aquifer has deteriorated to a high degree, during the last decade. Nine domestic wells were sampled from March 2006 to January 2007 to probe the hydrochemical components that influence the water quality. Geochemical data on dissolved major constituents in groundwater samples from the Manukan Island revealed the main processes responsible for their geochemical evolution. The results using statistical analyses, graphical method and numerical model output (PHREEQC) showed that the groundwater was chemically highly enriched in Na and Cl, indicative of seawater intrusion into the aquifer as also supported from the Na-Cl signature on the Piper diagram. From the PHREEQC simulation model, calcite, dolomite and aragonite solubility showed positive values of the saturation indices (SI), indicating supersaturation which led to mineral precipitation condition of water by these minerals.
Keywords: Manukan Island; seawater intrusion; hydrochemistry; saturation index

The isotopic composition of dissolved inorganic carbon (DIC) in marine and estuarine environments has been studied in some detail because of its role in determining the isotopic composition of inorganic/organic matter and its applications to the study of various natural processes. The δ13CDIC values of sea water are controlled by the sources and sinks of carbon and the results from isotope fractionation among solid, dissolved and gaseous phases. In this paper, based on the description of the stable isotope geochemical characteristics of dissolved inorganic carbon in northern South China Sea, the following conclusions were drawn: 1) the δ13CDIC values of natural waters are controlled by the sources and sinks of carbon and the results from isotope fractionation among solid, dissolved and gaseous phases. And the low seawater δ13CDIC values of northern South China Sea are accompanied by a low level of sea primary productivity in this region; 2) according to the parameter relationship (δ13CDIC-1.1 PO4) between δ13CDIC and PO4, it is indicated that northern South China Sea is the source of atmospheric CO2; and 3) nitrogen (N) and phosphorus (P) are the elements which are the basis for phytoplankton growth. Based on the analysis of seawater δ13CDIC values and PO4 and NO3+NO2 concentrations, our data show that N is a limiting nutrient in northern South China Sea.
Keywords: northern South China Sea; carbon cycle; stable carbon isotope; dissolved inorganic carbon

The Yitong Basin is an oil-bearing basin with unique characteristics in Northeast China. On the basis of apatite fission track ages and geological relationship, the tectonic uplift history of the Yitong Basin since the Oligocene was discussed. Based on apatite fission track analysis of five samples from the Luxiang and Chaluhe fault depressions and basin modeling study, it can be concluded that since the Oligocene (36.6 Ma) in the Yitong Basin, the Chaluhe fault depression has undergone two episodes of uplift during 24.9–19.1 Ma and 6.9–4.9 Ma. And the Luxiang fault depression also had undergone two episodes of uplift during 30–27.8 Ma and 22.6–11.1 Ma. Moreover, the average apparent exhumation rates for the Chaluhe fault depression and Luxiang fault depression, could be calculated to be 70.34 and 60.33 m/Ma since 21.8 Ma and 18.9 Ma, respectively. The results of thermochronological analysis can also be supported by the evidence from geological relationships such as geodynamics, volcanic activity, and stratigraphic division and correlation.
Keywords: tectonic uplift; fission track; apatite; the Oligocene; the Yitong Basin

The Tianqiao Pb-Zn ore deposit of Guizhou Province, China, is located in the mid-east of the Sichuan-Yunnan-Guizhou Pb-Zn-Ag multi-metallic mineralization area, which is representative of the Pb-Zn ore deposits in this area. It consists of three main orebodies, whose Pb+Zn reserves are more than 0.2 million ton. This paper analyzes the sulfur isotopic composition of these orebodies. The data show that the ore minerals (galena, sphalerite, pyrite) in these orebodies are enriched in heavy sulfur, with δ34SV-CDT values varying between 8.35‰ and 14.44‰, i.e. the δ34SV-CDT values of pyrite are between 12.81‰ and 14.44‰, the mean value is 13.40‰; the δ34SV-CDT values of sphalerite are range from 10.87‰ to 14.00‰, the mean value is 12.53‰; the δ34SV-CDT values of galena are range from 8.35‰ to 9.83‰, the mean value is 8.84‰, and they have the feature of δ34Spyrite34Ssphalerite34Sgalena, which indicates the sulfur isotope in ore-forming fluids has attained equilibrium. The δ34SV-CDT values of the deposit are close to those of sulfates from carbonate strata of different ages in the ore-field (15‰), which suggests that the sulfur in the ore-forming fluids should be derived from the thermo-chemical sulfate reduction of sulfates from the sedimentary strata.
Keywords: sulfur isotopic composition; ore-forming fluid; TSR; Tianqiao Pb-Zn ore deposit

292 chemical composition data and 82 isotopic composition data of gas samples collected from the Taibei Depression of the Turpan-Hami Basin, West China, were used in the study of their origin. Non-hydrocarbon gas is poor in most samples whereas abundant nitrogen in some samples is positively correlated with δ13C1. Although methane is the main constituent, higher molecular gaseous hydrocarbons, from ethane to pentane, are detected in most samples, in accordance with the distribution of oil reservoirs. The stable carbon isotope ratios of methane, ethane and propane are defined as δ13C1: −45.5‰ to −33.5‰, δ13C2: −30.2‰ to −10.5‰, and δ13C3: 27.6‰ to −11 respectively. According to the distribution of carbon isotope ratios, 2 families of gas can be grouped, most showing normal distribution of carbon isotopes, and others having obvious heavier carbon isotopes and being of abnormal distribution. Based on the isotopic composition, the disagreement between the relationship of Δ(δ13C113C2) and δ13C2 and that of δ(δ13C113C2) and δ13C2, and the calculated Ro, there are oil-associated gas, coal-derived gas and mixture of them. Other samples with obviously heavier isotopic compositions from the Yanmuxi oilfield of the Taibei Depression have been degraded by organisms.
Keywords: Taibei Depression; natural gas; carbon isotope; mixed gas; biodegraded gas

The origin and distribution of natural gas in the frontal uplift area of the Kuqa depression, Tarim Basin by Jie Cui; Guangyou Zhu; Bin Zhang; Jin Su; Yuhong Lu; Chenglong Ma (313-318).
The frontal uplift of the Kuqa depression is an important oil and gas producing area. In this study, the distribution and origin of natural gas were discussed based on natural gas components and isotope data. The main components of natural gas were hydrocarbons with relatively high contents of C2+ component. Most gases were derived from terrestrial source rocks, and some came from marine rocks. The contents of non-hydrocarbon gases were high in the central part of the frontal uplift area and low in the two terminals. The distribution of oil composition was similar to that of natural gas, which was mainly controlled by the types of source rocks. Dry coefficient and maturity of natural gas in the frontal uplift were lower than those of gas in the Kelasu tectonic belt of the Kuqa depression, which was mainly affected by the difference of tectonic movements in both areas. In the frontal uplift, the traps were formed in the early stage and could capture the early formed oil and gas, and structural adjustment was slight in later stages, so the oil and gas could be effectively preserved. Multiperiodic oil and gas filling led to the complex distribution of natural gas.
Keywords: Kuqa depression; frontal uplift area; origin of natural gas; sotopic characteristics; coal-related gas

The distribution characteristics and existing state of cadmium in the Jinding Pb-Zn deposit were studied. It was discovered that Cd was mainly distributed in sphalerite as an isomorphic impurity. There was a good correlation between Cd and Zn in the primary ore. With the oxidation and resolution of pyrite, sphalerite, sulfide, and etc., many secondary minerals, such as colloform sphalerite and smithsonite, were formed. The distribution of Cd is not symmetrical, and enrichment and dilution were observed in partial area of the oxidation zone in the deposit. Cd, except in external pore space or cracks of secondary minerals as independent minerals, such as greenockite, was mainly distributed in sphalerite as an isomorphic impurity in the secondary sphalerate and smithsonite in the oxidation zone. The research showed that Cd showed a very strong active transfer ability in the oxidation process, not only indicating that supergene leaching might be the main reason for Cd enrichment in some Pb-Zn deposits, but also reflecting that Cd was easily mobilizeed and transferred to pollute ore areas in the oxidation process. Furthermore, Cd in oxidation ore was more easily mobilized and transferred to induce bad hazards for ore areas with the effect from AMD which was produced from oxidation of sulfides.
Keywords: Yunnan Province; Jinding Pb-Zn deposit; cadmium; existing state; distribution characteristics

This paper compile the rare-earth elements and Nd isotope data for lunar pristine rocks from investigations in recent years. Using these data, we compared the REE characteristics of lunar pristine rocks and Nd isotopic compositions of their source regions. Based on the Lunar Magma Ocean model, we then studied their formation and petrogenetic correlations of Mg suite, alkali suite, and KREEP, with especial emphasis on the importance of assimilation during early magmatism. And Nd isotopic compositions of mare basalt samples suggest that mantle sources of mare basalts should be heterogeneous, which has not yet been explained by several current models.
Keywords: Moon; pristine rock; REE; isotopic composition; source region