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2019yearNo.38volumeNo.1phase

  • Mineral chemistry characteristics of clinopyroxene and ilmenite in basite of Lan'gan area, Anhui Province
    CAI Yitao, XU Mincheng, SHI Jianbin, YANG Xianzhong, ZHANG Jie, KANG Congxuan, CAO Zhengqi, DONG Zhongdou and MA Yuguang
    Mafic rocks are exposed in northern Anhui Province. It consists of diabase, gabbro-diabase and diabase-porphyrite, and the minerals mainly include clinopyroxene, plagioclase, hornblende and Ti-Fe oxides. In this paper, clinopyroxene and ilmenite were studied in detail using microprobe. An analysis of clinopyroxenes shows that the end members are composed of wollastonite, enstatite and ferrosilite, belonging to augite. Calculation results and chemical analysis of ratios probably indicate that the fractional crystallizing products were formed by the relatively primary magma in shallower magma chambers. The crystallizing temperature of the clinopyroxenes are 1109~1206℃ and the highest pressure is 0.6 GPa, suggesting the depth of 19.8km. The ilmenite in Lan'gan area has low MgO and MnO, high FeO, and very low Cr2O3. The mineral characteristics of clinopyroxen and ilmenite are different from features of the index minerals in typical kimberlite.
    2019  .  38(1):    1-13    [摘要](181)    [PDF](152)
  • Zircon U-Pb ages of quartz vein rocks in Tuanliangzi Formation complex of southwestern Yunnan Province: Regional metamorphism deformation age restriction of Late Triassic Lancang River tectonic belt
    LIU Guichun, SUN Zaibo, FENG Qinglai, CHEN Guangyan, LIU Junping, YU Saiying and TIAN Sumei
    Abundant tectonic hydrothermal quartz veins were found, which are parallel to the regional foliation (S2) in Mesoproterozoic Tuanliangzi Formation in southwest Yunnan, and those ancient mixtites of Tuanliangzi Formation are important tectonic rocks in southern Lancang River tectonic belt and along the west Yangtze block. Three zircon samples of quartz dykes and one zircon sample of green dyke were selected and analyzed using laser ablation inductively coupled plasma mass spectrometry (LAICP-MS). The 206Pb/238U ages can be divided into three groups, i.e., 395~461Ma, 240~260Ma and 222~228Ma, with most of them concentrated on 222~228Ma. The quartz dykes ages indicate two stages of regional metamorphism deformation (M1D1, M2D2):the first stage of metamorphism deformation(M1D1) was the result of pro-Tethys eastward subduction in Early Paleozoic(395~461Ma); the second stage of metamorphism deformation(M2D2) occurred in late Paleozoic-Mesozoic which could be divided into two periods of metamorphism deformation(M2aD2a, M2bD2b):the early period was Late Paleozoic to Early Mesozoic (240~260Ma) when the Paleo-Tethys experienced eastward subduction, whereas the late period of metamorphism deformation was caused by the closure of Paleo-Tethys Ocean basin in early Late Triassic (222~228Ma). The quartz dykes in Tuanliangzi Formation were impacted by tectonic hydrothermal event in the early Late Triassic, and were formed later than Lincang granite and the volcanic rocks of Manghuan Formation(229~235Ma), but earlier than stretch volcanic rocks of Xiaodingxi Formation and Manghuihe Formation (210~222Ma), which indicates that these syn-emplacement quartz dykes were the results of rapid exhumation that happened later than the Paleotethys ocean eastward collision with Yangtze block; in addition, the ancient Tethys Ocean had been closed earlier than early Late Triassic, suggesting minimum age limitation of quartz dykes in Tuanliangzi Formation.
    2019  .  38(1):    14-21    [摘要](145)    [PDF](123)
  • A discussion on metallogenic conditions and prospecting potential of diamond in Ordos old land
    YANG Xianzhong, LI Lin, KANG Congxuan and ZHAO Wenping
    There are stable crystalline basement and deposition covers as well as faults that cut the mantle in depth, which is beneficial to kimberlite formation in the Ordos old land. Kimberlites were discovered in Liulin area of Shanxi Province. Kimberlites, potassiummagnesium lamprophyres and kimberlite-like rock related to diamond formation were found in Yingxian and Datong area of Shanxi Province, and a small amount of diamonds and a large amount of chrome spinel-indicating minerals were also found. Two chrome spinel-indicating mineral anomalies in the Xinmiao area of Inner Mongolia and the Dianta area of Shaanxi Province were delineated. Annular structures related to kimberlite magmatic activity was also found in the Dianta area of Shaanxi Province. There are metallogenic conditions and prospecting potential of original diamond in the Ordos old land.
    2019  .  38(1):    22-26    [摘要](126)    [PDF](117)
  • Distribution-controlling factors and emplacement mode of lamproite in southeastern Guizhou Province
    YANG Guangzhong, LI Yonggang, ZHANG Yulun, LUO Bangliang and HUANG Yingjun
    A large number of lamproite plutons were discovered in eastern Guizhou Provence, which are distributed either as regional elliptical pattern and/or local banding pattern. Dating information reveals that they were mainly formed in late Ordovician. Geohisto-ry analyses suggest that geological structural conditions of the substrate of the lamproite pluton regions should resemble those of the rhombic structural framework that characterized the "Jiangnan old land", after experiencing multiphase tectonic movements including Wuling Orogeny, Xuefeng Orogeny, and Yunan Orogeny as well as Duyun Movement in the Caledonian. The resulting geological structural condition thus accounted for the formation of the lamproite plutons, i.e., elliptical pattern in regional and banding pattern locally. In combination of dating data and lithofacies paleogeography studies, the authors hold that lamproite plutons were emplaced at the position with the mode of "loach throw bean-curd", which was controlled by substrate structural conditions. The prospecting and exploration policy should primarily focus on "exploring to the deep and unknown places" of existing deposits.
    2019  .  38(1):    27-35    [摘要](92)    [PDF](101)
  • Research on verification of natural heavy sand anomaly of pyrope and chrome spinel in Xiawengshao area, Shibing County, Guizhou Province
    YANG Guangzhong, LI Yonggang, LUO Bangliang, SHI Qingpeng, HUANG Yingjun and XIA Rui
    A comprehensive utilization of the previous data shows that the placer anomaly with high content of chromium-bearing pyrope and chrome spinel exists in Xiawengshao area, Shibing County, Guizhou Province. The source and diamond exploration problems remain unexplained. Because the previous data were obtained during the "Cultural Revolution" period, the reliability of data is doubtful. Targeted field investigation and sampling analysis prove that the placer anomaly is objective and reliable. The high content placer anomalies are very rarely seen. The anomaly is located in the upper part of the slope which is 200 m higher than the elevation of the modern river bed. Residual deposits were deposited in the alluvial deposits of sand and gravel in the ancient channel. Mineralogical analysis shows no obvious traces of transport and abrasion. Electron microprobe analysis indicates G9 pyrope and S5 chrome spinel, which should be mainly derived from garnet-spinel-lherzolite, being the weathering product of the parent rock-lamproite.
    2019  .  38(1):    36-43    [摘要](106)    [PDF](87)
  • The formation age of the kimberlite zone in Poli area of Mengyin, Shandong Province: Zircon U-Pb dating data of diabase
    CHU Zhiyuan, WANG Weide, LÜ Qing, LIU Weidong, KANG Congxuan and WANG Shuxing
    Kimberlite is a kind of melange with changeable chemical composition, mineral composition and structure and tends to be altered. Therefore, it is difficult to determine the emplacement age of kimberlite by dating kimberlite whole rock and all kinds of minerals, and the data obtained are very different. In this paper, the intrusive relationship between kimberlite zone and diabase in Poli of Mengyin was analyzed. Through dating the zircon U-Pb in diabase and studying the contact relationship between diabase and overlying limestone as well as the relationship between diamond sand reservoir and known diamond protoores, the emplacement age of diabase vein was determined to be the Late Yanshanian period of Mesozoic. Therefore, it is proved that the Poli kimberlite belt was formed in Late Yanshanian rather than in Caledonian period.
    2019  .  38(1):    44-50    [摘要](119)    [PDF](108)
  • The application of 3D modeling technology to the kimberlite rock tube exploration: A case study of Wafangdian in Liaoning Province
    FU Haitao
    This paper introduces the application and achievements of 3D modeling technology in the exploration of kimberlite type primary diamond deposits in Liaoning Province. Diamond ore is one of the most important minerals in Liaoning Province. The prov-en diamond ore resources/reserves in Wafangdian area of Liaoning account for more than half of the reserves of diamond resources in China. Through carrying out 3D modeling work, some new understanding about the shape of the kimberlite pipe in the area and the direction of deep prospecting was obtained. It is held that the 3D model can better display the spatial distribution of kimberlitetype diamond orebodies and provide guidance for the exploration work.
    2019  .  38(1):    51-55    [摘要](91)    [PDF](77)
  • An analysis of geological characteristics and genesis of ancient diamond placer ore in Cherokee mining area of Zimbabwe
    XIAO Bingjian, ZHAO Xiufang, WANG Qingjun, YANG Daorong, FENG Aiping, ZHAO Hongjuan, PANG Chengtao, KANG Congxuan and TANG Zhishuai
    The authors studied geological characteristics, seam features and regularity of Cherokee ancient diamond placer ore of Cherokee mining area in Zimbabwe and then established the exploration model of the ore deposits in this area. It is shown that the re-gion is structurally located at the eastern edge of the Archean craton in Zimbabwe, neighboring the Limpopo orogenic belt and the Mozambican orogenic belt in the west, and the Limpopo belt is an important diamond producing area. The area is in a favorable posi-tion for the mineralization of ancient diamond sand ore. The ore deposits occur in sand conglomerate of Proterozoic Ukendo Group, which belongs to sedimentary rocks. The diamond ore in this area is of sedimentary origin and belongs to the coastal environment structure.In the Middle Proterozoic period, the diamond in original mineral was stripped away by the weathering and carried by wind or water, then it deposited in the coastal area. The discovery and study of Cherokee ancient diamond placer ore in Zimbabwe have important guiding significance for finding more ancient diamond placer ores in China.
    2019  .  38(1):    56-61    [摘要](83)    [PDF](67)
  • Geological characteristics and structural ore-control role in Wafangdian kimberlite orefield of Liaoning Province
    WAN Fanglai, JIANG Jinjing, WANG Xuan, YANG Xianzhong and WANG Huaichu
    Wafangdian area in Liaoning Province is famous for rich diamond resources, and the diamond deposit belongs to kimberlite type. Based on the study of the regional tectonic setting and the latest project research results, the authors divided the tectonic evolution process of kimberlite orefield in Wafangdian area into seven tectonic cycles. By discussing the characteristics of different tectonic cycles in Wafangdian area of Liaoning Province and analyzing their influence on the kimberlite, the authors have reached the conclusion that the nearly EW-trending structure controlled the formation and mineralization of the kimberlite in the south of Liaoning Province during Caledonian. Yanshanian tectonic activity altered the distribution of the kimberlite. It is considered that the mineralization stage of the kimberlite rock in this area can be extended from Paleozoic to Mesozoic.
    2019  .  38(1):    62-67    [摘要](100)    [PDF](82)
  • Distribution regularity and abnormal characteristics of indicative minerals of diamond in Taojiang area, Hu'nan Province: Exemplified by diamond, chromium spinel and ilmenite
    KANG Congxuan, YANG Xianzhong, CAI Yitao, XIAO Shuyue, XIANG Hua, LI Shuai and LI Ziyun
    In order to further explore the source of diamond in sand ore and search for primary diamond in Hu'nan Province, the authors used the natural heavy sand measurement method to collect 250 samples of natural heavy sand in Majitang area, Taojiang, Hu'nan Province. Diamond indicates quite a lot of minerals and much quantity. Twelve diamonds were found, which have a single type and are about 0.3mm in diameter, yellow green in color and exhibit hexoctahedron surface; there are 8864 grains of indicating mineral chromium spinels, black-grayish black in color, intensely worn, round granular in shape; there are 2403 grains of ilmenites, black-grayish black in color, relatively weakly worn. According to the distribution characteristics of diamonds and indicator minerals in this area, fourteen anomalous zones were delineated in the study area, including five grade I anomaly area, five grade Ⅱ anomaly area and four grade Ⅲ anomaly area. It is concluded that the distribution of diamond and indicating minerals in this area is extensive, but shows no orientation enrichment, the quantity of diamond in the northern region is large, whereas that in the southern region is small; the amount of the outcropped area in the old strata is large whereas that in the new strata is small. Through the comparative study of diamond and indicative minerals, it is found that the crystal shape, color and grain size are similar to the features of diamond in the Taojiang River stone bridge diabase and the diamond found in the Ningxiang potassium magnesium alloy. It is inferred that the minerals came from the diabase/potassium magnesia porphyry and other types of rock bodies that have not yet been discovered in this area.
    2019  .  38(1):    68-75    [摘要](87)    [PDF](95)
  • An analysis of the emplacement mode and ore-search prospect of lamproite in the Maping area, Zhenyuan County, Guizhou Province
    RAO Hongjuan, CAI Yitao, YANG Xianzhong, KANG Congxuan, SHI Rui and LIN Zeyuan
    The Maping area of Zhenyuan County in Guizhou Province is the first primary diamond deposit discovered in China and is also the only outcrop of diamond-bearing parent rock area in Guizhou Province. The study of rock type, mineral composition and geochemical characteristics of lamproites and emplacement time of plutons in this area has been carried out for a long time, and most researchers hold that the plutons in the area have been denuded to the root facies, the quality of the selected diamond is poor and the prospects for prospecting are not good. The exploration of the primary diamond deposits beneath the Yangtze Craton has long been a controversial question. Zhenyuan area of Guizhou Province is the most abundant outcropping area of diamond-bearing rocks in the Yangtze Craton, and hence the study of emplacement model and ore-search prospect of lamproite in this area will be helpful to providing new ideas and methods for the research on Yangtze craton diamond prospecting and exploration so as to investigate major deep earth science problems. Through the analysis of regional information available, it is considered that a series of porphyritic lamproites exposed in the eastern part of Guizhou are controlled by the Yuping-Shidong-Sandu faults in the northeast, that at least two phases of intrusive activity of lamproite occurred in Maping area, and that, on the eastern side of the Shenchong fault, plutons might have not been denuded, and hence this area still has some ore-search prospects.
    2019  .  38(1):    76-92    [摘要](87)    [PDF](83)
  • A discussion on geological characteristics and diamond ore-bearing potentiality of the Dajingtou lamporphite, Pingyi County, Shandong Province
    WANG Yufeng, ZHOU Jun, WANG Jianping, ZHU Chenghe and YANG Xianzhong
    Since the discovery of the Dajingtou volcanic rock in Pingyi County, the problem of its lithology and the ore-bearing potentiality of diamond has not been solved. Recently, two boreholes unveiled fresh spotted rocks at the depth of 580m or so, and three diamonds were selected from them. According to the rock features, lithogeochemistry and heavy mineral characteristics, it is considered that the Dajingtou volcanic rock is lamproite-bearing diamond, which might have caused the anomalies of diamonds and heavy minerals in the lower reaches of the tube. Combined with a number of suspected lamprophyre exposed in surrounding areas, it is considered that there is a great potential for primary diamond ore.
    2019  .  38(1):    93-102    [摘要](83)    [PDF](84)
  • Re-understanding of diamond-bearing parent rocks in Zhenyuan area, Guizhou Province
    LI Yonggang, XIANG Lu, HUANG Yuancheng, RAO Hongjuan and YANG Guangzhong
    The "Eastern One" pluton in the Maping area of Zhenyuan Prefecture, Guizhou Province, is the earliest discovered prima-ry diamond deposit. It was named kimberlite at the time of discovery, based on the traditional idea then that diamond deposits only exist in kimberlite. Later, it was named lamproite, following the discovery of Argyle lamproite type primary diamond deposit in West-ern Australia. Recent researches revealed that the diamond-bearing parent rocks in Maping area are closer to the Australian typical kimberlites in terms of petrological, mineralogical and geochemical characteristics, while the pluton in Baifen area is more similar to Australian typical lamproite. It is proposed that the "Eastern One" pluton in Maping area should be named breccia tuffaceous kimber-lite, while the pluton in Baifen area should be kallite-diopside-flogopite lamproite. The pluton in the Zhenyuan Prefecture has the combined features of kimberlite and lamproite, quite similar to the pluton discovered in Western Australia. The primary diamond de-posits in Zhenyuan area, and even in the eastern Guizhou Province, are of great potential for prospecting and research.
    2019  .  38(1):    103-109    [摘要](88)    [PDF](74)
  • Mineral chemistry characteristics of garnets in diamondiferous basite of Lan'gan area, Anhui Province
    CAI Yitao, ZHANG Jie, KANG Congxuan, YANG Xianzhong, CAO Zhengqi, DONG Zhongdou, MA Yuguang and SHI Jianbin
    The mafic rock is exposed in northern Anhui Province, and some of them are diamondiferous rocks. In order to determine the type of garnets, the authors systematically sampled the garnets in diamondiferous basite in Lan'gan area. The MgO, SiO 2, FeO, TiO2, Al2O3, Cr2O3, CaO, MnO values of 62 single crystal garnets in this area were measured by electron microprobe spectrometer. The results show that the chemical formula of garnet group minerals is A32+B23+(SiO4)3. Group A cations are composed of Mg2+, Fe2+ and Ca2+. Group B cations are composed of Al3+, Fe3+, Mn3+ and Cr3+. The trivalent cation is mainly Al3+ while divalent cation is mainly Ca2+. It is inferred that grossularite-andradite-almandine group is the primary class in the Lan'gan area. The high calcium silicate iron garnet (majorite) was found in 62 samples. According to the composition of these majorities in Lan'gan area, the garnet of the diamondiferous basite has formation pressure of 12.1~12.8GPa, and the depth is up to 300km.
    2019  .  38(1):    110-120    [摘要](95)    [PDF](95)
  • A study of diamond indicative minerals in the depth and periphery of Xiyu, Mengyin County, Shandong Province: Metallogenic properties of kimberlite predicted by diamond indicating minerals
    ZHAO Xiufang
    The garnet, chromite and chromic diopside in kimberlite are important indicative minerals in search for diamond deposits. According to the content of the indicative minerals, the existence and ore-bearing potential of the primary diamond deposits in kimberlite can be roughly deduced. Group G10 in garnet shows the existence of diamond in kimberlite. The higher the content is, the higher the diamond grade in the rock mass is. From G10Xiyu% < G10Changma%, we can infer CXiyuChangma, and the fact proves that it is true; chromite of Group S1, S2 and S6 are associated with diamond, and chromite of Group S6 with 62 and Group S7 with 1 in Xiyu mining area is related to deep source xenoliths peridotite, which is almost from kimberlite, and has important indication significance; The more the content of chromic diopside with Cr2O3 ≥ 1.2% is, the higher the diamond grade is. By statistical analysis, the content of Cr2O3 ≥ 1.2% in surface chrome-diophanite is slightly greater than that of deep rock pipe, and the average grade of the deep orebody in Xiyu mining area is slightly lower than that in the surface orebody, which shows that the ore-bearing potential of kimberlite can be qualitatively deduced by chromic diopside. In combination with the geological work of CSAMT and drilling, the primary diamond deposits were found below-205m in the deep of the Xiyu rock pipe group, the Red Flag 15-1 rock veins were found in the periphery through the channel exploration projects, and 18 diamonds were obtained in the selection of ore samples. This proves the effectiveness and feasibility of qualitatively predicting the metallogenic properties of kimberlite with the method of indicative minerals of diamond.
    2019  .  38(1):    121-131    [摘要](74)    [PDF](77)
  • Geochemical feature of olivine basaltic porphyrite in Tashan area of Xuzhou, Jiangsu Province, and its relation to diamond origin
    HUANG Youbo, ZHOU Qizhong, ZHANG Qi, FENG Xuezhi, WANG Guoqiang, ZHANG Fengming and CAI Yitao
    The petrogenesis and tectonic environment of olivine basaltic porphyrites were judged according to their geochemical characteristics in Tashan area of Xuzhou. Then the exploration prospect of diamond was discussed. The result shows that they are plotted in the intraplate tholeiitic series and are slightly enriched in LREE. They were formed by partial melting of the enriched mantle of the garnet facies through varying degrees of partial melting in the intraplate extensional tectonic background. Besides, there was a certain degree of plagioclase intergranular effect in the process of magma crystallization. The particle diamond it contains is similar to that of the Lanling area in Anhui, which shows the characteristics of the early growth of diamond. The origin should be the capture of the mantle source. In terms of geochemical characteristics, they are obvious different from the kimberlite. They had characteristics of basaltic magma in the extensional period of Paleogene and did not have the conditions to carry a large number of deep source inclusions. Therefore, it was unfavorable to form a primary diamond deposit.
    2019  .  38(1):    132-142    [摘要](84)    [PDF](87)
  • Geochemical analyses of the placer anomaly with high content of pyrope and chrome-spinel in Xiawengshao area, Shibing County, Guizhou Province
    LI Yonggang, YANG Guangzhong, SHI Rui, LIN Zeyuan, ZHANG Yulun, ZHOU Zongzan and KANG Congxuan
    Existing data reveal that there exists the placer anomaly with high content of pyrope and chrome-spinel in Xiawengshao area, Shibing County, Guizhou Province. It is distributed in the gravel-clay rock from the Neogene Wengshao Formation in Duimenpo area on the northern side of the Xiawengshao basin, and the "unexplained" deposits of sand-gravel in the slope zone, 2km south side of the Xiawengshao basin. Such a phenomenon constitutes the high content of placer anomalies, which is prominent among lots of information related to diamond prospecting in Guizhou Provence. The source of these minerals and its significance to the exploration of diamonds have remained unsolved for a long time. Based on the analysis of the "unexplained" deposits of sandgravel in the slope zone, 2km south side of the Xiawengshao basin, it is found that the 2.7grains/L and Chrome-spinel>5.0 grains/L of original magnesia-alumina pyrope prove the existence of the anomaly. Results from electron microprobe analysis revealed that the pyrope is classified as G9-pyrope, and the picotite as S5-chromite that is poor in titanium but abundant in aluminum and magnesium. Their source has little relation with kimberlite.
    2019  .  38(1):    143-151    [摘要](83)    [PDF](83)
  • Geological characteristics and prospecting significance of kimberlite pipe in Xicun area of Xuzhou, Jiangsu Province
    ZHOU Qizhong, SHI Jianbin, HUANG Youbo, FENG Xuezhi, ZHANG Qi, ZHANG Fengming, CAI Yitao, YANG Xianzhong and KANG Congxuan
    The Xicun kimberlite pipe was discovered for the first time which has ended the kimberlite-nonexistent history in northern Jiangsu Province. The geological characteristics of Xicun pipe were analyzed by petrology, geochemistry and associated minerals, and the prospecting significance was discussed. According to the regional background and the conditions of the diamond formation, it is considered that there existed basic geological conditions for kimberlite emplacement and diamond ore formation in Xicun area. The Xicun kimberlite pipe provided mother rock conditions for diamond ore. The Xicun kimberlites have similar geochemical characteristics to Shandong and Liaoning kimberlites. They were all formed by low degree partial liquation of the mantle-derived magma. Besides, they suffered hybridism of the earth crust in the process of magma rising and widespread carbonatization in the late period. The values of compatible elements are similar to those of Shandong kimberite breccia, which constitute the typical patterns of kimberlite. The heavy and light rare earth elements are characterized by strong fractionation. Associated indicator minerals include eclogite-type pyrope, chrome-rich diopside, and magnesium-rich chrome spinels, which show the characteristics of ore-bearing kimberlite.
    2019  .  38(1):    152-162    [摘要](89)    [PDF](81)
  • Mineral chemistry, geochemistry and geological significance of Early Cretaceous mafic rock in Longyou area, Gan-Hang belt
    LU Kuan, DU Shiyan, ZHANG Ruoxi, ZOU Yan, CAI Yitao and YANG Shuiyuan
    There have been reports of diamonds found in the mafic rocks of Longyou, Zhejiang Province. However, the tectonic setting and host rock characteristics still lack detailed studies. In this paper, the authors carried out a detailed study of petrology, major and trace elements, Sr-Nd isotopic compositions and mineral chemistry for the Longyou mafic rocks in an attempt to unravel the petrogenesis, magma evolution and tectonic setting during Late Mesozoic period. Longyou mafic rocks can be classified as olivine gabbro. Isotope characteristics indicate that the olivine gabbro was derived from a deep mantle source. The major and trace elements show that they mainly underwent fractional crystallization of olivine and pyroxene, without any obvious crustal contamination. Olivine grains show a core-rim structure with the core being Mg-rich and Fe-depleted and Fo values being 90.1~91.8, which indicates that the original magma was an asthenospheric mantle. In contrast, the rim of the olivine grains is Fe-rich and Mg-depleted with Fo values being 77.4~85.3. The remarked difference in Fo values for the core and rim may indicate that the original olivine was replaced by mantle melt/fluid. Most pyroxene xenocrystals belong to diopside, and a small amount of aegirite augite is developed at the edge of some diopside xenocrystals. The diopside xenocrystal generally has a core-mantle-rim structure, exhibiting a decrease in SiO2 and increase in TiO2, Al2O3 and temperature of magmatic emplacement from the core to rim. The authors hold that this corerim trend may indicate that the pyroxenes were metasomatized by later higher temperature mantle melt/fluid. It is argued that the Longyou olivine gabbro was formed during the roll-back of the Paleo-Pacific plate along the deep faults of the Gan-Hang tectonic belt. The asthenospheric mantle melts moved upwards along these deep faults and the magma responsible for the Longyou olivine gabbro experienced the fractional crystallization between olivine and pyroxene with very low degree of or without crustal contamination. Furthermore, it is also suggested that the Longyou olivine gabbro experienced a metasomatism of higher temperature mantle melt/fluids.
    2019  .  38(1):    163-176    [摘要](79)    [PDF](83)
  • The Maping kimberlites and its xenocrysts as indicators of diamond minerogenetic condition in Zhenyuan area, Guizhou Province
    XIANG Lu, ZHENG Jianping, HUANG Yuancheng and LI Yonggang
    Zhenyuan area of Guizhou Province is one of the key areas for diamond primary ore prospecting in China. In the Maping D1 rock mass of Zhenyuan area, the kimberlite occurrence with containing primary diamonds was discovered for the first time in 1965. The rocks have structural and componential characteristics of typical kimberlites, the U-Pb geochronology and Hf isotope analyses of zircon xenocrysts entrained in the Maping D1 diamondiferous kimberlites indicate the existence of unexposed Archean basement remnants beneath the study area. Based on the regularity of crust-mantle coupling, with corresponding to the old lithospheric mantle, this nature of ancient craton is a favorable factor for diamond formation. On the other hand, the Maping kimberlites commonly contain associated minerals of Cr-pyrope with high CaO content, most of which belong to the G9 (lherzolite) type rather than the global diamond-rich harzburgite protolith type (G10), suggesting that the state of lithosphere had been partly modified at that time and may not be conducive to the formation of high-quality diamonds. Note that in the processes of diamond prospecting, it should be based on the detailed field work and comparative petrological study, and rely on the investigation of diverse xenoliths/xenocrysts carried by kimberlites and the other associated magma activities, in combination with inversing the characteristics of mantle source by the composition of magmas. Therefore, it is possible to comprehensively reveal the ancient subcontinental lithosphere about the formation age and evolution history, material composition and fine structure, as well as the thickness, thermal state, oxygen fugacity, fluid activity and some other aspects of the subcontinental lithospheric root, thus providing important evidence for diamond prospecting.
    2019  .  38(1):    177-188    [摘要](97)    [PDF](82)

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