Table of Content

20 December 2000, Volume 6 Issue 4

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Article

Characteristics and Petrogenesis of Late Mesozoic Granitic Volcanic-Intrusive Complexes in Southeastern China

WANG De-zi, ZHOU Jin-cheng, QIU Jian-sheng, FAN Hong-hai

2000, 6(4):  487-498. 

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During the late Mesozoic, magmatic activities in southe astern China were very intensive. In the products of magmatism, the gra nites-rhyolites are predominant, and the andesitic-basaltic rocks are less imp ortant. The statistica l data on the isochron ages for over 200 granite and volcanics samples show that the earl y Cretaceous ages make up about 60% of age population; and the late Jurassic, 20 %; the late Cretaceous, 10%; the middle Jurassic, 10%. The ages of Mesozoic volcanic s and related granites in southeastern China have a tendency of getting younger from the inland toward the coast. In some cases, granites and associated acid ic and interm ediate volcanic rocks are comagmatic. Under the condition of uniformity in time, space and source materials, the granities can be considered as the “roots” of t he central type volcanic apparatuses composed of rhyolites and dacites, forming so -called granitic volcanic-intrusive complexes. The granitic volcanic-intrus i ve complexes in southeastern China may be divided into three types, i.e., syntex is type, continental crust remelting type and A-type. Their petrogenesis is cont rolled by different tectonic settings, rock-forming mechanisms and source materials. The syntexis t ype is dominantly distributed in the coastal area, w hereas the continental crust remelting type is mainly located in the inner land. Th is spatial pettern is constrained by two factors: the composition of b asement rocks and the intensity of crust-mantle interactions. Underplating of basaltic magma took place more intensively in the coastal area of Zhejiang and Fujian provinces during the late Mesozoic. Therefore, the crust-mantle interaction was also more intensive in the coastal area than i n the inner l and. In the west of Wuyishan Mts., the continental crust usually possesses highe r maturity. The meta-igneous materials, such as amphibolites, are rare or absent in the baseme nt rocks of the area. The combining constraints of these two factors led t o a regular spatial distribution of above-mentioned two types of granitic volcani c-intrusive c omplexes in southeastern China. The distribution of A-type granitic volcanic-i ntru sive complexes is mainly controlled by Changle-Nanao fault zone in the coastal a rea of Zhejiang and Fujian provinces. The thickness of both lithosphere and cont inental cr ust is obviously thinned and the asthenosphere is upwelled in this r egion. It is evident that A-type granitic volcanic-intrusive complexes were fo rmed in a extensional tectonic setting and display the post-orogenic features. Since then, the Yanshanian magmatic activities were toward the end. In this pap e r, the authors show the uniformity in emplacement time, space and source mate rials for granitic volcanic-intrusive complexes, taking both Tonglu and Xiangsh an complexes as examples. Some regularities summarized may be very important for un de rstanding the genesis of granitic volcanic-intrusive complexes in southeastern China.

Studies on Fluids of the Metamorphic Peak Time for the Archaean Granulite Series in the Taipingzhai-Lozishan District, Eastern Hebei Province

LU Liang-zhao, DONG Yong-sheng

2000, 6(4):  499-508. 

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The fluid inclusions of the metamorphic peak time fo r the Archaean granulite series in the Taipingzhai-Lozishan district, eastern H ebei Province were first found in sillimanite. According to their shapes and occurrences, these inclusions ca n be subdivided into three types. The earliest type is the isolated inclus i ons and inclusions in clusters with negative hexogonal, prismatic crystal forms . They are very rare and characterized by parallelism of their elongated direct ion with c-axis of sillimanite; The second type is the inclusions with irregula r shapes. They have no spatial relation to cleavage and (00 1) parting of host mineral; The third type is most common. The inclusions are usually square or rectangular. They occur along healed (001) parting perpendicular to c-axis of sillimanite, and were entraped in the later stage of the metamorphic peak time. As a whole , the compositions of fluids in above-mentioned three types are very similer. All they are chara cterized by:①rich in carbonic materials, with XCO2+CH4≈0.64～0.93; ② low in wate r , with XH2O≈0～0.22, which coincides well with activity of H2O ( 0.04～0.31) and mole percent of water (XH2O≈0.03～0.22) based on thermodyna mic calcula tion from equilibrium assemblage of peak metamorphism; ③with XH2S,SO 2 <0.10～0.21 in some cases; ④very low content of anions in halogenic solution (mostly 0.12～0.61mol/L). These inclusions have also been found in garnet an d quartz, but in the latter case, the inclusious are characterized by abundant two-phase H2O-C O2 chemistry, with XH2O >0.25～0.33. They were probably formed in the further late regressive stag e under the low PT condition. 　　The homogenization temperature of CO2 in fluid inclusions of peak stage ranges from -28℃ to -22℃ in most samples. The corresponding density is 0.96～1.06g /c m3, and total fluid pressure (Pf) is 0.60～0. 70GPa. This value is about 0.1～0.3GPa lower than the confining pressure of r ocks ( Pl) estimated by various geobarometers. The temperature of this stage is es timated at 780℃～790℃. Based on the XH2O, XCO2 and XCH4 relationship of fluid inclusions, together with diagnoti c assemblage of peak stage, the oxygen fugacity is calculated as log fO2=-17～-15. 　　All features of peak-stage fluids are rather homogeneous in space within a give n a rea, and values of aH2O are similar in associated rocks of differe n t lithology. These evidences together with regional geology and characteristics of protolith rocks suggest that predominant amout of CO2 in fluids might be o f de ep source and related to underplating of mafic magmas from the mantle and their cry stallization. The proposed mechanism is analogous to concept of carbonic metamo rphism.

Electronic Microprobe Study on the Melt Inclusions in Pegmatite Minerals from Ailaoshan and Keketuohai Pegmatite Deposits

LI Zhao-Lin1;2, ZHANG Wen-1an2, LI Wen1;2, ZHAI Wei1, SHI Gui-yong1

2000, 6(4):  509-522. 

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The compositions of daughter minerals in melt an d fluid-melt inclusions in minerals from Ailaoshan pegmatite, Yunnan Provinc e and Keketuohai pegmatite, Xinjiang Autonomous Region were analyzed by electron ic microprobe. 120 analytical points from 73 inclusions we re analyzed. 10 daughter minerals (including zinc-spinel, corundum, apatite, ma gnetite, muscovite, biotite, microcline, albite, quartz and alumo silicate glass) and 27 minera l assemblages were identified. Zinc-spinel and corundum were identified for the first time in these regions. The analytical results indicate that the daughter mineral compositions and mineral assemblages in melt and fluid-melt incl usions vary with different types of pegmatites. The evolution patterns in compositions of daughter minerals and host minerals could be used as a basis to search for the evolution patterns of chemical elements during pegmatite cr ystallization. The existence of local magmatic differentiation, immiscibility an d heterogeneity was proved for the pegmatite magmas. The results of this study are significant in understanding the compositions, forming mechanism s and origins of pegmatites. It would a lso inspire further studies on magmatites, pyrolites and meteorites.

Strontium and Carbon Isotopic Calibration of the Terminal Proterozoic

YANG Jie-dong1;2, ZHANG Jun-min3, TAO Xian-cong1, WANG Zong-zhe3

2000, 6(4):  523-531. 

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Transmission electron microscopy study indicates that mic rocrystalline Fe-sulfide crystals around large pyrite crystals from Carlin mine of Nevada are marcasite. The marcasite contains Au and As. There are band-li ke features in the marcasite. These band-like areas are relatively rich in As with respect to the neighboring areas. It is proposed that the band-like area s are also relatively rich in lattice-bound Au. According to the obtained equat ion for distribution coefficients of trivalent cations in calcite, it is propose d that cationic Au3＋ were incorporated into the fine grain marcasite at the marcasite－solution interface during non-equilibrium (fast) crystallizatio n of the marcasite. The partitioning of Au3＋ in the marcasite is control led by non-equilibrium distribution coefficient (K'd). However, pyrite formed through equilibrium (slow) crysequilibrium distribution coefficient (K d) for Au3＋. Recrystallization of early-formed fine grain crystals will remove REE and Au from the crystals. Incorpor ation of larger cations of Au3+ and Au+ may result in local structural distortion with respect to normal marcasite structure, and shows the form of the band-like fea ture.

Investigation of Invisible Au in Au-bearing FeS2 Microcrystals from Carlin Gold Ore Deposit，Nevada, USA: TEM Study and Geochemical Modeling

XU Hui-fang

2000, 6(4):  532-545. 

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Sr isotopes of limestones for the Precambrian-Cambrian boundary from the Xiaotan section, Yongshan, Yunnan province, and Sr and C is otope s of carbonates for the Sinian System from the Sanxia section, Hubei province have been investigated. The results were compared with the Sr and C isotopic data der ived from Mongolia, Canada, Siberia and Namibia. A variation curve of　8 7Sr/86Sr and δ13C for the seawater of the terminal Proterozo ic was pr oposed. 　　Just before the terminal Proterozoic, the δ13C value of seawater was high , about +11‰, and the　87Sr/86Sr was about 0.7072. At the period o f glaciation corresponding to the Nantuo/Ice Brook, the δ13C value of sea water was negative, about -5‰, and the　87Sr/86Sr was about 0.7 077. Later on, the δ13C value rapidly rose with at least three fluctuations. At the time corresponding to the Dengying formation, the δ13C value showed a flat terrace about +2～+3‰, and the　87Sr/86Sr about 0.7084. At t he Precambrian-Cambrian boundary, the δ13C value rapidly rose from a neg ative value to about +6‰, and the　87Sr/86Sr kept at about 0.7084 . 　　From the variation curve of　87Sr/86Sr and δ13C for seawater proposed in the present study, the strata of the terminal Proterozoic in the world can be correlated with each other.

Isochron Age of the Laowan Gold Deposit and Laowan Granite, Tongbai Region, Henan Province and Its Implications

XIE Qiao-qin, XU Xiao-chun, YUE Shu-cang

2000, 6(4):  546-553. 

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The Laowan gold deposit is a large-sized deposit recen tly discovered in northem slope of the Tongbai Mountains. It occurs in middle Pr oterozoic metamorphic basic volcanic-sedimentary rocks o f the Guishan Formation. The Laowan granite intrue d in the Laowan fault belt. The orebodies are controlled by granite. The ore grade becomes richer where the granite swells. 　　The genesis of Laowan gold deposit is complex. Some scholars considered that it belongs to the shear zone type. In this paper, in order to make sure t he relationship between the deposit and the granite, a prelimina ry study on　40Ar/39Ar dating has been carried out on three representative samples. These samples are: one q u artz sample from the second ore-forming stage of the deposit, one quartz sample from granite, and one potash-feldspar sample from granite.The　40Ar/39Ar analyses were carried out in Beiji ng Institute of Geology, Academia Sinica, by using the RGA-10 mass spectrometer. 　　The　40Ar/39Ar plateau age and isochrone age for corresponding sam ples are: for the quartz from one deposit, 91.5 and 88.9 Ma, respectively; for t he quartz from granite, 104.0 and 102.8 Ma, respectively; for the feldspar f rom granite, 108.9 and 108.7Ma, respectively. These isochrone ages indicate that the granite and the deposit were formed in late Yanshannian and have very close relationship. 　　The analysis on stress condition for mineralization of the Laowan gold deposit a n d petrogenesis of the Laowan granite suggests that they were formed in a transit ion condition f rom compressive stress to tensile stress or in a mainly tensile stress condition . In this stage, large amount of hydrothermal fluids of different origins appears, which is very favorable for ore deposition.

Application of Evidence Weight Model for Prediction of Gold Mineralization in the Northwestern Sichuan Province

ZHANG Xiao-jun1, ZHANG Jun1, QIN Ju-li2, ZHANG Jian-long2

2000, 6(4):  554-560. 

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Geographic information system (GIS) is a new technique successfully applied to g eological research. It is advantageous in processing data with spatial distrib uti on. The evidence weight model is a mathematical model combined with GIS techniqu e. Based on the spatial relation of elemental data, it synth esizes various favorable ore-forming factors (evidence layers) and can be used in mineralization prognosis and evaluation efficiently. The northwest of Sichua n Province is an important micro-fine disseminated gold resource base in China. In t his sense, it is significant to have a metallogenic analysis of the region and t o search for the areas favorable for gold mineralization. This paper is an empi rical example for application of evidence weight model in the northwestern Sichu an Province. 　　Based on the comprehensive analysis of features of gold mineralization in this r egion, five databases have been created: geology database, geophysics database, geochemistry database, remote-sensing database, and ore d eposits (occurrences) database. According to the analysis of the ore-contro lling factors in this region, we selected 10 ore-producing e vidence layers, which include the stratigraphic lithological assemblage, lin ear faults, minor plutons, joints of structure from remote sensing, geochemical anomalies of Au, As, Sb, Ag, and the gravity and magnetic anomalies d educed to different elevations. Extracting the data from the above mentioned fiv e databases, the authors calculated the evidence weight values and the correlation degrees be tween the particular evidence layers and ore-deposits (occurrences), created a n e vidence weight model of gold mineralization in the northwestern Sichuan Province . Us ing the evidence weight model in this paper, the authors analyzed the features o f gold mineralization in this region, indicated existence of four main gold min eralization zones in four different directions: the NW-directed gold mineralization zone controlled by Maqu-Lueyang structure belt, the NE-directed gold mineralizatio n zone controlled by Q ingchuan-Pingwu structure belt, the SN-directed gold mineralization zone cont rolled by Minjiang structure belt, and the EW-directed gold mineralization zone cont rolled by Xueshan structure belt. Based on the analysis of distribution charac teristics of gold mineralization zones and spatial coupling relationship s among them, the favourable areas have been predicted in three levels accordi ng to the ore formation probability values. Finally, some suggestions related to application of GIS in metallogenic prognosis are also proposed.

A Developmental Differential Rotation Model of the Earth Layersphere

WANG Xin-yuan1, SUN Yan2, ZHANG Xi-hui3, Richard Ghogomu tanwi4, YANG Zhao-zhu2

2000, 6(4):  561-565. 

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Using seismological methods, Song and Paul［1］ demonstrated that the rotation of the inner core is faster than the daily rotat ion of the mantle and cr ust. This discovery revealed a noticeable phenomenon that the earth's rotatin g rate is getting slow and the inner core' s rotation is faster than that of the crust and the mantle. They are correlative phenomena of the same dynamic backgr ound. We suggest that the phenomenon is the result of the different tidal fricti on primarily from the moon and the sun. 　　Tidal function might play a very important role in crust evolution, but the succ essful research in the filed is very little till now［8］. Applying the l aw of conser vation of energy can do quantitative analysis. The losing kinetic energy of the crust and the mantle in its long-range slowing rotating may be balanced by the share of dissipated tidal energy in the earth. When calculating the loss of the kinetic energy in the earth, we introduce the prevalent PREM model and quote the parameters h（depth）and ρ (density). From rotary energy (E) formul a E=(1)/(2)Iω2t, where ωt is rotary angular velocity at t moment, I is rotary inertia，　we get ΔE exp ression: ΔE≈Iω0Ωt Where ΔE is loose d rotary energy in t time, ω0 is the beginnin g (t=0) angular velocity, Ω is rotary angular acceleration. Let the total mass of the mantle and crust be 4.10×1024kg, calculating that I≈1. 13×1037kg*m2 (see Table 1), we can see that ΔE≈4.53×1011J ,　when t=1 second. 　　Lambeck (1980) thought that dissipated tidal energy in the total earth equals 4.0×1012J*s-1 is suitable. If the slowing of the earth's rotatio n is mainly gi ven by tidal friction of earth tidal and ocean tidal, let t=1second,　then ΔE is 11 percent of the total dissipated tidal energy in the Earth. The dis sipated tida l energy in the solid inner core is very small. The tidal friction effect is dif ferential from the earth's surface to the core. Because the liquid outer core ca n partly absorb or prevent the tidal function reaching the inner core, the inner core is less influenced by tidal friction.　So, the inner core spinning velocit y is the fastest. In the same way, because the elastic asthenosphere below the l ithosphere can also do the same function as the outer core does, the main mantle sphere (main body of the mantle except the asthenosphere) spins faster than the lithosphere does. So, we can draw a differential rotation model of the three s pheres in the earth: rotation rate of the lithosphere ＜that of main mantle sphe re ＜that of the inner core. The model system is the largest one of layer-slip, plate's drift and magnetic field formation may be of the same background of geo dynamics.

Study on Sinian Geologic Events in Xuzhou-Suzhou Area and Discussion on Their Origin

PAN Guo-qiang, LIU Jia-run, KONG Qing-you, WU Qun-qi, ZHANG Qing-long, ZENG Jia-hu, LIU Dao-zhong

2000, 6(4):  566-575. 

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The Sinian strata in Xuzhou-Suzhou area are deposits of the epicontinental sea. They are mainly referred to the carbonate platform facies. In the supratidal to subtidal low-energy sedimental environments, sudden, violent high -energy sedimentation occasionally occur, which are often associated with some abn ormal sedimentary structures. These structures along with step-like small faul ts may indicate the ancient seismic traces. In the studied area, the Sini an seismic traces mainly include densely-spaced veins of micritic calcites, strongly scouring and erosion structures of "bag gutter" like, plastic rudites, eart hquake breccias, inter-formation folds and step-like small faults. Five disti ng uished stratomeres with closely-spaced seismic traces represen- ting five ear thqua kes phases have been recognized, which might include dozens, even hundreds of st rong earthquakes. At least two phases of hypabyssal to subsurface basic magmatic intrusions can be distinguished, occurring respectively in the early and late Sinian period. The seismic events, magmatic intrusions and sea-level changes a r e related in origin. Frequent, strong earthquake activities caused the sea-lev e l rise. The magmatic intrusions occurred in the interval between tow seismic ph ases and in the sea-level fall times. 　　The research results showed that the Sinian geologic events in the studied area might be controlled by extensional structures. The ages of these events ar e 738.6-604Ma, corresponding to the breakup times (780-600Ma) of global superc ontinent Rodinia. Therefore it is deduced that the origin of the Sinian geologi c events in Xuzhou-Suzhou area might relate to the breakup processes of Rodinia . The area from "Plaeo-Tanlu zone" to the north of boundary fault zone in the northern side of North Qinling Mountains might be the breakup zone within the North China Plate margin.

Origin of the Oil and Gas Accumulation Related to Fluorite Veins in Lower Ordovician Limestones, Tarim Basin，Northwest China：Evidences from High-Resolution Borehole Electric Image Logs

ZHONG Guang-fa1, MA Zai-tian1, Liu Rui-lin2, Qi Xin-zhong3

2000, 6(4):  576-582. 

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In this paper, we will describe a rare type of oil and gas reservoir, d iscovered by drilling in well TZx, Tarim basin, northwest China. It was formed i n fluorite veins in Lower Ordovician limestones. The characteristics and ori g in of the reservoir are studied on the basis of interpretation of high-resolut i on borehore electric images in combination with data from cores and thin section observations. 　　Although the fluorite veins and their host limestones are shown as simila r h igh-resistive white or bright yellow colors, the images revealed that the veins with structureless features are generally oblique to or even perpendicular to th e host limestones developed with horizontal stratification. Irregular dark patch es or spots, centimeters to decimeters in size, on images are interpreted as cav erns and vugs, which was confirmed by core observations. These vugs mainly o ccur in fluorit e veins and at the contacts between veins and their host limestones. They are th e major reservoir space for oil and gas. 　　It is believed that the origin of those fluorite veins is related to the lat e Early Permian volcanism in the middle and western parts of Tarim basin. They were formed by low-temperature postmagamatic hydrothermal fluids that intru d ed upward into the near-surface limestones along pre-existing fractures a nd faults. 　　The oil and gas reservoir was generated after the formation of fluorite veins du ring the Permian volcanism. Caverns and vugs developed in fluorite veins and the ir vici nity provided space for the gathering of oil and gas. The Lower Ordovician carbo nates, the good source rocks regionally, are proven to have reached their pe ak matu r ation after the Paleozoic matched well in time with the formation of caverns and vugs. W ith a total thickness of about 600 meters, the overlain Middle-Upper Ordovician mudstones and marlites efficiently hindered the oil and gas gathered in caverns and vugs from escaping upward. 　　A model on the formation of the oil and gas accumulation in fluorite veins is pr oposed. It consists of four stages as follows: (1) fractures and faults formed i n the Lower Ordovician limestones due to the Caledonean regional compression; (2 ) fluorite deposited as veins in pre-existing fractures and faults of the Lower Or dovician limestones as a result of the volcanism during the late Early Permian; (3) caverns and vugs formed in fluorite veins and their vicinity after the Permi an by dissolution; (4) oil and gas accumulated in vugs in the Mesozoic-Cenozoic .

Fractal Evaluation on Plane Distribution of Fracture Zone

HU Zong-quan

2000, 6(4):  583-587. 

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Fracture is a kind of oil and natural gas storage body with high heterogeneity. Its distribution in the 3- dimension space h as nonlinear characteristics to a certain degree. In this paper, similar dimension statistical method has been used to study the distribution of fracture zone, and the parameter is used to compare the fractures' development of several sand layers quantitatively. It has been proven theoretically that the fractal parameter of similar dimension ca n be used to evaluate quantitatively the filling capacity of fracture zone to 2 - dimension space, and the practical statistic result shows that the level of similar dimension of fracture zone coincides well with the comparing relation of pro duction situation of each sand layer.

Study on Acoustic Spectral Characteristics of Weathered Granite

LIU Tong, XU Ming-jie, HU De-zhao, GENG Jian-hua

2000, 6(4):  588-594. 

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Study on weathered rocks is important in engi neering geology. At prese nt, longitudinal wave velocity is widely applied to reflect the weathering and c rushing degree of rocks. However, longitudinal wave velocity is only one of the parameters of rocks, and simple velocity testing will lose much useful informati on. 　　Now, some scholars are studying rock mechanics properties by other acoustic para meters, especially the acoustic attenuation index. Their important conclusion is that acoustic attenuation is more sensitive than wave velocity when reflecting the discontinuity and weathering crushing features of rock mass. 　　Based on the viscosity acoustic absorption theory, the amplitude fades according to the law of exponential function of frequency and viscosity in the course of wave propagation. The higher the frequency is, the faster the amplitude fades. H igh frequency composition of wave varies with the absorption in rock materials. Degree of frequency abundance in receiving wave is closely related to properties of rock mechanics. In our experiment, the wave shape recorded by the high preci sion multi-parameter analyzer (digital model DB4). Computer is used to analyze w ave shape data with FFT in order to convert time domain signal into frequency do main signal. Then receiving spectrum and frequency response function is gained, and their frequency distribution features are applied in the study on rock mechanics. The method avoids complexity of acoustic attenuation coefficient test. Mor eover, it can automatically and continuously collect test data. 　　Study has demonstrated that the high weathered and crushed samples have only low frequency composition, and the fresh and hard ones have abundant high frequency composition. 　　Given the same sample size and proper frequency, geometrical and diffusio n attenuation can be effectively controlled, then internal friction absorption can be regarded as the main cause of test result.

Visual Software for Evaluating and Managing Groundwater Resource in the Yangzhou City, Jiangsu Province

YAN Chang-hong1, SONG Dan-li2, ZHANG Cheng-yuan2, CHEN Bao-ren1, CHEN Song1, MA Ri-he2

2000, 6(4):  595-599. 

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The reasonable development of groundwater re source has long been taken into account by Yangzhou government. There are a lot of long-term survey datum on hydrology. In order to manage and forecast of Yangzhou's groundwater resource , a visual software system has been developed for evaluating and managing ground water resource in Yangzhou in Chinese Version of Windows with Visual Basic 6.0 P r ogramming Language. The Main characteristic of the software system is as follows :(1) It provides a database that is well compatible and can be connected with m any other types of database. (2) It has a good human-machine interface and fine visibility. (3) It's calculation model is consisted of evaluation, management a nd prediction of groundwater resource. The interface between calculation model a nd database is friendly. The function of its calculation is powerful. (4) It pro vides the Graphic function to plot results. (5) It has the help system and insta ll driver.

Application of Point Load Test to Evaluation of Strength and Bearing Capacity of Rock Foundation

DONG Ping, CAO Jian, JI Guang-qiang, HU De-zhao

2000, 6(4):  600-604. 

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Point load test can determine the poin t load strengt h indexes of rock. The result then can be used to calculate the rock's uniaxial compressive strength, from which the bearing capacity of rock foundation can be decided. This method can be used to evaluate the strength and bearing capacity of rock foundation in the artificial excavated holes for piles. Compar ed with macroscopic perception method, point load test method is more scientific. It is also more economic, simpler and easier to apply in the d igging process in comparison with static load test. In this article, we will poi nt out that point load test can promptly determine the strength of rock foundation by testi ng irregular rock specimens. Therefore, as far as specimen collection is concerned, point load test is simpler, and more ef fective than uniaxial compressive strength test and it is especially significant for the evaluation of soft rock (e.g. the red clay rock in Nanjing area). When applying point load test method to the evaluation of the strength and be aring capacity of rock foundation in the artificial excavated holes for piles, i t should be noted that the sample's length (L), width (b), and height (h) meet this condition: L≥b≥h, and h is b etween 2.5-10cm. Samples can't be tetrahedroid. For point load strength ind ex Is, the area-strength formula or its modified form ( Is=P/De 2) is the most suitable formula for its expression, where De is the equivalent diameter of the area. Applying the point load test meth od, we evaluated the strength and bearing capacity of rock foundation in many artifi cial excavated holes for piles in Nanjing area and guided the digging process wi th good results.

Discovery of Palaeoweathering Type Rare and Rare Earth Element Deposits in Nouthern China and Its Significance

WANG Yin-xi1;2, LI Hui-ming1;2, YANG Jie-dong1;2, QIU Li-wen2 CHAI Dong-hao3, CHEN Pin4

2000, 6(4):  605-606. 

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