Table of Content

20 June 2010, Volume 16 Issue 2

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Mineralization and Genesis of the Fanjiabu Gold Deposit in the Sulu
Ultrahigh Pressure Metamorphic Terrane, with a Comparison to the
Gold Mineralization in the Jiaobei Terrane

LI Jian-Wei, BI Shi-Jian, VASCONCELOS Paulo

2010, 16(2):  125-143. 

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The quartz vein-type Fanjiabu gold deposit is economically the most important gold deposit in the Sulu ultrahigh pressure metamorphic terrane, Jiaodong Peninsula. Cathodoluminescence images and trace element and U-Pb isotope compositions by laser ICP-MS indicate that zircons extracted from auriferous quartz veins are exclusively inherited magmatic zircons from wall rocks of gold veins, namely the Neoproterozoic biotite monzogranite. A total of 22 analyses on 22 zircon grains were made, and a concordant homogeneous group was formed by 15 analyses, and a weighted mean 206Pb/238U age of (726 ± 14 ) Ma (MSWD = 4.6) was yielded. The remaining 7 analyses are plotted in a discordia, with an upper intercept U-Pb age of (758 ± 25) Ma and lower intercept age of (123 ± 11) Ma (MSWD = 0.45). The lower intercept age is consistent with 40Ar/39Ar hornblende ages of (118.8±1.6) Ma to (117.5±1.5) Ma of lamprophyre dikes closely associated with gold veins, and is therefore interpreted as the timing of mineralization at the Fanjiabu gold deposit. Results of this investigation and previous studies suggest that gold mineralization in the Sulu and Jiaobei terranes were contemporaneous, taking place at ca. 120 Ma and coincident temporarily with lithospheric thinning of the North China craton. This indicates that the Fanjiabu gold deposit and, by inference, other coeval deposits in the Sulu terrane were formed as a result of thinning of lithosphere mantle beneath the North China craton. Fluid inclusion and stable isotope data show that ore-forming fluids in the Fanjiabu gold deposit were characterized by middle to high temperature, high salinity (15.5％ to 23.2％) (NaCleq) and low δ18OH2O (-3.84‰ to -4.05‰) and δDH2O (-82.5‰ to -80.8‰) values. Gold-bearing pyrite has negative δ34S values ranging from -5.5‰ to -9.1‰. These are similar to hydrothermal fluids from hydrocarbon-bearing basins and imply that ore-forming fluids of the Fanjiabu gold deposit may have been mainly derived from the Mesozoic Jiaolai basin. The basinal fluids were channeled along the Wulian-Mishan fault and its secondary structures, when gold was leached from the basement rocks and precipitated in favorable structural sites under reduced conditions. In contrast, a large number of gold deposits in the Jiaobei terrane have low salinity, high δ18OH2O and δDH2O values, and positive δ34S values. Metallogenic differences of Early Cretaceous gold deposits between the Jiaobei and Sulu terranes were caused by distinct basement rocks, fluid sources, and ore-forming environments.

⁴⁰Ar/³⁹Ar Dating of the Guanshan High Sulphidation Type Cu-Pb-Au Depositin Jiangsu Province and Its Geological Significance

LIANG Ye-Heng, SUN Xiao-Ming, ZHAI Wei, MA Chun, WU Zhi-Qiang, DING Cun-Gen, WANG Tang-Xi　

2010, 16(2):  143-148. 

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Guanshan Cu-Pb-Au deposit in Lishui basin of Jiangsu Province is a high sulphidation type epithermal deposit hosted in Late Mesozoic subvolcanic rocks. 40Ar/39Ar dating was performed on two sericite samples collected from sericitized subvolcanic wallrocks of Guanshan deposit. The results yield plateau ages of（120.8±1.0）Ma and（116.0±1.3）Ma，respectively, suggesting that the major mineralization of Guanshan belongs to the large-scale Mesozoic metallogenic event occurred in eastern China. During 125 Ma to 115 Ma, most part of eastern China was affected by extensional tectonic stress, resulting in large-scale magmatism and formed a series of fault-depressed basins, including the Lishui volcanic basin. In this basin, upwelling of deep-seated magma provided magmatic heat, triggered circulation of meteoric water, which mixed with magmatic fluid, and finally deposited the ore minerals in brittle fractures in the trachyte-porphyry wallrocks.

Zircon Geochronology, Geochemistry and Petrogenesis of Granite from the
Baimianshi Uranium Ore District in the Southern Jiangxi Province

DONG Chen-Yang, ZHAO Kui-Dong, JIANG Shao-Yong, CHEN Wei-Feng, CHEN Pei-Rong, LING Hong-Fei, YANG Shui-Yuan

2010, 16(2):  149-160. 

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The Baimianshi uranium ore district is an important volcanic-hosted uranium district in South China. The uranium ore bodies occur in basalts and sandstones in the Baimianshi volcanic-sedimentary basin. The basement of the basin is composed of the Baimianshi granite and the Xunwu metamorphic rocks. Previous studies indicated that the Baimianshi granite provided uranium for the mineralization. In this study, LA-ICP-MS U-Pb dating of zircons from the Baimianshi granite was made showing an emplacement age of (241±7) Ma. The Baimianshi granite is a medium-fine grained two-mica granite, characterized by high SiO2 contents (71.99%-73.82%), with high A/CNK ratios (1.15-1.28). It is enriched in Rb, Th, Ta and depleted in Sr, Ba, Ti and Eu, and characterized by variable REE contents with LREE enrichment and obvious Eu depletion. The Baimianshi granite has relatively high initial 87Sr/86Sr ratios (0.71162—0.71613) and low εNd(t) values (-13.9 — -12.2). Two-stage Nd isotopic model ages vary from 2.01 Ga to 2.15 Ga. Its magmatic zircons have low εHf(t) values (-15.1—-11.9), with Hf model ages of from 2.01 Ga to 2.21 Ga, which are similar to the Nd model ages. Petrography and geochemistry indicate that the Baimianshi granite belongs to strongly peraluminous S-type. Combined with geochronology and isotope compositions, it is thus considered that the Baimianshi granite might be derived from partial melting of the metamorphic rocks similar to the Taoxi Group. The geochemical characteristics of the Baimianshi granite are similar to those of other uranium-bearing granites in South China. Multi-stage metamorphism and re-melting resulted in uranium enrichment in granites. Later hydrothermal fluid activity associated with crustal extension might have leached U from the granite to form the Baimianshi U deposit.

Study on Geochronological, Geochemical Features and Genesis of the Fufang
Granitic Pluton in the Jiangxi Province, South China

ZHANG Fang-Rong, SHU Liang-Shu, WANG De-Zi, SHEN Wei-Zhou, YU Jin-Hai, XIE Lei

2010, 16(2):  161-176. 

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The Fufang granitoid pluton, outcroped in the middle part of Wuyi Mountain area, is a typical Early Paleozoic pluton in the eastern segment of South China. Based on large amount of geological data during regional geological survey, the authors carried out a systematic study on petrography, geochemistry and LA-ICM-MS zircon U-Pb dating for the Fufang pluton. This pluton is mainly composed of monzogranite, granodiorite and in less amount tonalite containing Al-rich mineral, such as garnet and sillimanite. The A/CNK values are 0.99~1.14, categorized as weakly peraluminous and strong peraluminous. In trace elements, the Fufang pluton is enriched in LILE Rb, Th, Cs and rare earth elements La, Ce, Nd, and depleted in Ba, Sr, Ta, P, Ti. Thus, the Fufang pluton is a low Ba-Sr granite on the whole. The Rb / Sr and Rb / Nb ratios are 0.56~1.19 (everaging 0.92) and
6.85 ~25.18 (everaging 15.43), respectively, higher than the average values of the upper crust in eastern China and the world. The Fufang pluton has a higher ∑REE with LREE enrichment. Their distribution patterns are clearly right-wing type with relatively clear Eu depletion (δEu = 0.44~0.61, averaging 0.53). The emplacement ages of the pluton obtained for zircons from 1 sample of granodiorite and 2 samples of monzogranite are ( 443.9 ± 3.5) Ma (MSWD = 1.09) , (443.1 ± 4.6) Ma (MSWD = 0.25) and (433.6±3.9) Ma （MSWD = 0.61）, respectively. The first two sets of data are consistent ages within error range which shows that they were resulted from the differentiation and evolution of a co-magmatic chamber. The later one is obviously later and belongs to the later stage of the Early Paleozoic. The research results show that the Fufang pluton is of S-type granite, derived from the continental crust by lower degree of partial melting and its source rocks were mainly composed of pelitic sandstone rocks. The formation was probably linked with the collision between the fragments of Cathaysia Old Land and Yangtze block or collision among the fragments of Cathaysia Old Land. The earlier granitoids of Fufang pluton were syn-orogenic, formed in a compression environment, while the later granitoids were origined in a post-orogenic extension environment.

Zircon SHRIMP U-Pb Dating of the Buried Granodiorite and
Muscovite 40Ar/39Ar Dating of Mineralization and Geological Implications
of Meiziwo Tungsten Deposit, Northern Guangdong Province, China

ZHI Wei, SUN Xiao-ming, WU Yun-shan, SUN Yan, HUA Ren-min, YANG Yong-qiang, LI Wen-qian, LI She-hong

2010, 16(2):  177-185. 

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The Meiziwo tungsten deposit is located in eastern part of Yaoling-Meiziwo tungsten mineralization zone, northern Guangdong province. The ⁴⁰Ar/³⁹Ar age of muscovite formed in syn-mineralization period is (155.9±0.6) Ma, consistent with large scale tungsten and tin mineralization in the Mesozoic Yanshanian period in South China. This date represents the mineralization age of the Meiziwo tungsten deposit. The zircon SHRIMP U-Pb age of biotite granodiorite body, occurring at about 600 m level in the lower part of the mine, is (430.4±3.6) Ma. This age suggests that the granodiorite body formed in the Caledonian period has no genetic relation to the tungsten mineralization. Our new data disagree with the previously proposed model for the tungsten mineralization, i.e., two times of “five-story”mineralization overprinted each other in this deposit. The ages of the mineralization and granodiorite indicate that the formation of Meiziwo tungsten deposit may be related to an Yanshanian granite buried in a deeper level, and therefore, we expect that the ore bodies might have a larger extension in depth.

Geochronology of Youshan and Pingtian Granites in Nanling Rangeand Its Geological Implication

SUN Li-qiang, LING Hong-fei, SHEN Wei-zhou, HUANG Guo-long, TAN Zheng-zhong

2010, 16(2):  186-197. 

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In previous studies, the Youshan granite and Pingtian granite located to the east of the Zhuguangshan composite granite body in Nanling Range were considered being formed in the Yanshanian period. In this study, we present LA-ICP-MS U-Pb zircon dating results which shows that the ages of the Youshan granite and the northwestern part of the Pingtian granite are (213.4±3.0) Ma and (238.8±2.2) Ma, respectively. These results indicate that the Youshan granite was formed by the Indosinian magmatism and the Pingtian granite is probably a composite granite batholith formed in the Indosinian and Yanshanian periods. In addition, it is revealed that both granites contain zircons having inherited cores with ages of Archean and 541 Ma~1 642 Ma, implying existence of Archean crust as well as Proterozoic crust containing rocks formed by several periods of magmatism in the source. Some of the zircons from the Youshan granite display dark rims (in CL images) with Yanshanian ages, which suggests that the granite was probably affected by hydrothermal fluids during the Yanshanian period. Narrow dark rims of zircons are also observed in the Pingtian granite, suggesting effect of hydrothermal fluids.

SHRIMP U-Pb Dating of Zircons from the Late Mesozoic Basalts in Eastern
Zhejiang Province and Its Geological Significance

CUI Yu-rong, XIE Zhi, CHEN Jiang-feng, YU Yun-wen, HU Li-hai

2010, 16(2):  198-212. 

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The zircon U-Pb ages were dated by SHRIMP method for eight basaltic rocks occurred in the eastern area of Zhejiang Province，which were erupted during the Late Mesozoic and named as Lower and Upper rock series (LRS & URS). The weighted average 206Pb/238U age of the basalts from LRS is (120±1) Ma with Th/U ratios ranging from 0.65 to 2.44. The weighted average 206Pb/238U age of the basalts from URS is (103±2) Ma, with Th/U ratios ranging from 0.57 to 3.03. These data suggest that the zircons from both rock series are of magmatic origin and represent the formation times of the basalts of LRS and URS. Thus, it can be concluded that the formation time of the URS and LRS is significantly different, and the age data are consistent with the previous researches. It can also be found that most of the zircons from the LRS basalts have a relatively homogeneous ages with only a few ancient zircon relicts, which indicates that they have little crustal contamination during petrogenesis. Some zircon grains show core-rim structure with a core age of about 132 Ma and a rim age of about 120 Ma, which may indicate that the inherited grains were captured from the magma source, and imply that there exist magmatic rocks formed at about 130 Ma in the mantle or mantle-crustal boundary during the LRS magma activity. The magmatic zircons from URS basalts are very few, many detrital grains were dated with the ages covering almost all of the magmatic events in the South China block. It is suggested that the URS basaltic rocks were contaminated by clastic rocks which contained the detrital grains with different ages.

Detailed Procedure for Determining the Helium Diffusion
Parameter in Apatite

ZHANG Yan, CHEN Wen, LIU Xin-yu

2010, 16(2):  213-217. 

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In this paper we present the detailed procedure to calculate the helium diffusion parameter and its closure temperature in apatite. We use the step-heating data of Wolf (1996）to show this procedure and its correction. This method is based on the Arrhenius relationship which describes the diffusivity variation with temperature. This procedure is as follows: (1) Do step-heating experiment to get the cumulative gas release fraction. (2) Calculate the lnD/a² of every step using spherical diffusion equation. (3) Make Arrhenius plot, taking the lnD/a² as y-axis and the 1/T (T is the temperature of every step) as x-axis. In this plot, if the points defined by lnD/a2 values and the 1/T values within some temperature range show linearity, it indicates that within this temperature range the apatite diffusion obeys the Arrhenius relationship and thus we can get the diffusion parameter E from the slope and the LnD0/a ² from the intercept in the Arrhenius plot. (4) Insert the value of E and LnD0/a ² into the closure temperature equation to calculate the closure temperature using iterative method. In addition, when we use the above method to calculate the helium diffusion parameter, we should pay attention to the following aspects: (1) Because 1/T is decimal fraction, for apatite diffusion data, 1/T should be multiplied by 104, making it the same order with ln D/ a². (2) When calculating the closure temperature, the unit of the cooling rate ℃/Ma should be converted to K/s. For the cooling rate, 1 ℃/Ma equals to 1 K/Ma.

SHRIMP Zircon U-Pb Age, Sr-Nd-Hf Isotopic Geochemistry and Petrogenesisof the Ehu Pluton in Northeastern Jiangxi Province

ZHAO Peng, JIANG Yao-hui, LIAO Shi-yong, ZHOU Qing, JIN Guo-dong

2010, 16(2):  218-225. 

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In this study, we present detailed SHRIMP zircon U-Pb chronology, major and trace elements, and Sr-Nd-Hf isotope data for the Ehu pluton in northeastern Jiangxi province, in an attempt to better constrain its petrogenesis. SHRIMP zircon U-Pb dating shows that the Ehu pluton was emplaced in the Early Cretaceous (121.7 Ma±2.9 Ma). Petrographic, elemental and Sr-Nd-Hf isotopic characteristics suggest that the Ehu granites are of S-type, generated by partial melting of Paleoproterozoic metasedimentary basement in the deep (>40 km) crust, with no fractional crystallization and mantle-derived magma mixing in their evolution. The upwelling of asthenosphere during the Early Cretaceous extensional tectonic regime in the region induced partial melting of the lower crust.

Vent Distribution of Wudalianchi Volcanoes Heilongjiang Province, China，and Its Relation to Faults
MAO Xiang, LI Jiang-hai, GAO Wei-yan, ZHANG Tian-ran

MAO Xiang, LI Jiang-hai, GAO Wei-yan, ZHANG Tian-ran

2010, 16(2):  226-235. 

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The Wudalianchi National Park is located in Heilongjiang province, northeastern China, where the volcanoes are the best examples of the intra-continental monogenetic volcanoes in the world. There are also numerous faults developed in the volcanic strata. If the relationship between the fault system and the distribution of volcanoes in the area could be well analyzed and interpreted, it would be of great importance for understanding the evolution of volcanic activities of this kind. Research work shown in this article is done to study the correlativity between distribution of the intra-continental monogenetic volcanoes in Wudalianchiare and the local fractures. From ground surface observation and remote sensing image interpretation, together with the study on regional structure, falults and fault zone outcroping, volcanoes erupting sequence (such as the fact that some volcanoes erupted regularly in turns, progressively from SW to NE), regional profiles and paying attention to the fact that volcanoes in different spreading directions are of different scales, we come to the conclusion that the 7 faults discovered in the area actually belong to three faults groups. The strikes of these three groups are NE, NW and nearly E-W, respectively. Regional electromagnetic data and previous research on deep structure in northeastern China also give support to the view. Fractures of these three strikes appeared in granites temporally formed before the volcanic activies in time. Seismic data, stress state in geological history, as well as study on river terraces, all demonstrate that there were no active fractures taking place during volcanic eruption period in the area. Cusequently, the fractures should exist prior to the volcanic activities in Wudalianchi area. At the times of volcanic eruptions, the faults provided pathways for the underground magmas to migrate upward towards surface, and finally led to forming this kind of volcano distribution seen nowadays on ground surface in Wudalianchi area. It means fhat three groups of volcanoes are distributed along the NE trending faults, two groups along the NW trending faults, and the other two groups nearly E-W trending.

Study on Fluid Inclusions of the Dayinjian Mo Deposit in Xinxian County,
Henan Province, China

LI Hong-chao, XU Zhao-wen, LU Xian-cai, Wang Xu-dong, CHEN Wei, ZHAI Dong-xin

2010, 16(2):  236-246. 

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The Dayinjian Mo deposit, as an important deposit in the Dabieshan Mo-polymetallic belt, has genetic links to monzogranite intrusion of Late Yanshanian, and has attracted extensive attention for great progress in recent exploration. Based on the petrography and microthermometry of fluid inclusions in the quartz veins formed in main mineralization stage, 4 types of primary fluid inclusions were identified, including: (1) aqueous-rich two-phase inclusions (L-type), (2) vapor-rich two-phase inclusions (V-type), (3) daughter mineral-bearing three-phase inclusion (S-type) and (4) CO2-bearing three-phase inclusions (C-type), The analysis results indicate that two main homogenization temperatures present at 280~320 ℃ and 200~220 ℃, respectively, while the salinities range in two intervals of 5.11%~9.98% (NaCleq) and 36.06%~42.78%(NaCleq), respectively. The densities of the trapped fluids vary from 0.91 g/cm3 to 1.10 g/cm3. Raman spectra of the inclusions indicate that water vapor is the dominant component with minor amount of CO2 (possibly a little N2 in some cases) in the gasous phase of the inclusions. The typical shift in oxygen isotope compositions suggests a mixing event between magmatic and meteoric water. In summary, the deposit is an intermediate-high temperature epithermal deposit, and the fluid mixing plays crucially significant roles in the mineralization.

Relationship between Reservoir Properties and Chlorite Rims: A Case Studyfrom Yanchang Formation of South Ordos Basin, North China

DING Xiao-qi, ZHANG Shao-nan, Ge Peng-li, WANG You-li

2010, 16(2):  247-254. 

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The chlorite rims are frequently observed in clastic successions. Their content and

occurrence may heavily influence the reservoir properties. By using thin section determination and

SEM, BSE, EDX analyses, we studied occurrence, timing, mechanism of generation and contribution to

porosity preservation for the samples from Yanchang Formation, South Ordos basin. The results show:

(1) There exists a spatial coupling of chlorite development with the brackish water delta front

facies depositional environment and the biotite-rich arkosic sandstone; (2) The formation timing of

chlorite is not earlier than the initial compaction stage, but not later than the appearance of

authigenic quartz; (3) Formation of chlorite rims could change the porosity micro-environment and

prevent growth of authigenic quartz on the detrital quartz surface; (4) The intercrystalline pores

in chlorite rims are of limited value for petroleum storage, but can somehow contribute to the

reservoirs as pathways for acidic fluids circulation;
(5) The constructive diagenetic role of chlorite rims is their weakening effect for the overburden

stress and restricting effect for the autigenic quartz growth in certain degree.

Thermal Evolution and History of the Permian Coal Measuresin Yongmei Depression

FANG Hong-feng, YAO Su-ping, JIAO Kun, HU Wen-xuan, CAO Jian, GAO Yu-qiao

2010, 16(2):  255-264. 

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The marine sedimentary sequence in southeastern China was widely altered by the

complicated multi-stage magmatic activities. In spite of high organic abundance in some strata, the

characteristics and controlling factors of thermal evolution and hydrocarbon generation are still

not clear, which restricts further understanding in basic petroleum geologic problems. Taking

Permian coal measures in Yongmei depression as an example, based on the determination of vitrinite

reflectance and volatile index and combined with the study of geological background and thermal

modelling, the thermal maturation of hydrocarbon source rocks and their distribution was analyzed,

and the evolution history of hydrocarbon generation was constructed. The results show that,

generally speaking, the coal hydrocarbon source rocks have attained the phase of post-mature-dry

gas. Horizontally, thermal maturation is increasing from west to east; and vertically, thermal

evolution is not related to depth of burial. According to the history of thermal evolution and

hydrocarbon generation, the Yanshanian stage is an important period for drastic change in thermal

history of the Yongmei depression. Thermal evolution of the Permian source rocks was affected and

metamorphosed by several thermal sources, among which the magmatic activities resulted in

anomalously high metamorphism of marine source rocks in this region.