Peng Sheng-lin

Subtle traps prediction using sequence stratigraphy and 3D seismic technology: A case study from Qikou depression in Huanghua basin °

Forecasting subtle traps by sequence stratigraphy and 3D seismic data is a sensitive topic in hydrocarbon exploration. Research on subtle traps by geophysical data is the most popular and difficult. Based on the sufficiently drilling data, log data, core data and 3D seismic data, sediment sequence of Qikou depression, Huanghua basin was partitioned by using sequence stratigraphy theory. Each sediment sequence system mode was built. Sediment faces of subtle traps were pointed out. Dominating factors forming subtle traps were analyzed. Sandstone seismic rock physics and its response were studied in Tertiary System. Sandstone geophysical response and elastic modulus vary laws with pressure, temperature, porosity, depth were built. Experimental result and practice shows that it is possible using seismic information forecasting subtle traps. Integrated using geology, log, drilling data, special seismic processing technique, interpretation technique, high precision horizon calibration technique, 3D seismic visualizing interpretation, seismic coherence analysis, attribute analysis, logging-constrained inversion, time frequency analysis, subtle traps object is identified and interpreted. Finally, advantage object of subtle trap in this area was determined. Bottomland sand stratigraphic and lithologic reservoirs in Qinan slope zone have been founded by means of high resolution 3D seismic data field technique, high resolution 3D seismic data processing technique and seismic wave impedence inversion technique.

Coupling mechanism of mineralization and hydrocarbon-forming in hydrothermal convection system: An example from Longtoushan Sn-polymetal deposit, Dachang

Longtoushan Sn-polymetal deposit is a large-scale deposit of high-tenor. The ore-bodies occur in reef limestone of middle Devonian. There is much anthraxolite in reef limestone and ore-bodies. The anthraxolite is the postmature result of oil-gas’ thermal metamorphism. The close relationship of anthraxolite and Sn-polymetal deposit reveals the space-time relation between oil-gas evolution and Sn-polymetal mineralization. Sulfur isotope of Longtoushan deposit is close to oil’s sulfur in Devonian, which indicates obvious relationship between the sulfur’s source of deposit and oil-gas’ activity. The forming of Longtoushan deposit relates to exhalative-sedimentary mineralization in Devonian. Because of the favorable hydrocarbon-forming condition of Longtoushan reef and surrounding basin facies’ black shale and peat, coupling of ore-formation and hydrocarbon-forming occurs in seabed’s hydrothermal convection. The distributing of ore-forming elements indicates the presence of hydrothermal convection system. The thermal fluid containing organic matters conduces to Sn-polymetal elements’ activation and transfer, and provides catalyzing condition to the transforming from SO42− to S2−. The erosion action of brine containing organic acid to reef limestone induces the growing of crannies and karst’s caverns, which provides advantageous space to Sn-polymetal mineralization. The heat source of mineralization provides thermocatalysis condition to hydrocarbon-forming. When the circulatory fluid containing oil-gas enters the high-temperature region(>150°C), the oil-gas is decomposed and anthraxolite comes into being.

Rock-forming mechanism of Fenghuangshan rockbody in Tongling area

Based on the detailed geological investigation and record of galleries and drill holes, a new idea has been advanced that granodiorite is earlier than quartz monzodiorite porphyry. Both of them are products of two different magmatic intrusive activities. The analysis results of trace elements show that the Sr content is beyond any other crustal rock and the Th content is beyond that of Ta. The whole-rock analysis indicates that rockbody is rich in CaO and poor in K2O. In the composition of Pb istope of rockbody, the ratio of 207Pb to 204Pb is less than 15.60. All these show that the magma mainly comes from the upper mantle. Ti,Zr,Cr,Nb trace elements and the relation between the Gardini index(τ) and the Rittmann index(σ) indicate that the rockbodies are formed in the orogenic belt and island arc tectonic setting. The summation (ΣREE) and the characteristic value (m(La)/m(Yb)) of the rare earth elements show that the original rock is alkalic basalt. The analysis of the characteristic values of REE and the quantitative modeling calculation indicate that the rock-forming process is dominated by mixed crystallization. According to the analysis on the rock-forming order, magmatic source, tectonic setting and rock-forming process, combined with the achievements of regional rock-controlling structures and division of sublayer of crust, it is believed that Fenghuangshan rock body derives from the deep-seated alkalic basalt magma. The rock-forming process has undertaken sialic and calcareous assimilation and contamination of two different degrees. The rock-forming model belongs to the typical assimilation and fractional cryatalization mechanism.

Approaches to location prognosis of concealed ore deposits (bodies) of productive mines

This paper demonstrates the channels and methods for location prognosis of concealed ore deposits (bodies) in the deep-seated and surrounding districts of productive mines in accordance with their special features. The system frame map is built, from quick exploration in the field to the rapid building of a model indoors. The main research points of location prognosis are also discussed in the paper, which include: 1) integrating the location with the surrounding geological areas, microscopic with macroscopic; 2) analyzing and synthesizing all geological information of different levels, depths and aspects; 3) laying stress on mineralization series; 4) paying attention to the study of the distribution law of ore bodies; 5) introducing the theory of nonlinear dynamics of ore forming processes to ordinary static prognosis; 6) the necessity of the geophysical method in recovering information of concealed ore bodies; 7) the combination of all kinds of geology, geophysics, geochemistry and remote -sensing methods.

REE characteristics and genesis of alkaline-rich porphyry, Yunnan Province

The Yunnan Himalayan alkaline-rich porphyry occurs as a compound rockbelt and consists of calca-alkalic, alkaline and peralkaline intrusions. Its origin is in debate. The paper deals with its origin by studying rock’s REE and Sr isotope. Although the rocks are different in their REE contents varying from 77.53 µg/g to 1 798.3 µg/g, they have very similar features in REE parameters. On the triangalar diagram of REEs, the sample dots are concentrated on the end area of light REEs, representing a product of low-degree melting of upper mantle or lower crust materials. The initial 87Sr/86Sr values of rocks vary between 0.706 4 and 0.709 8, showing a feature of mantle-crust mixed source. Moreover, REEs show a logarithmic linear positive correlation between them. This type of correlation strongly supports the fractional-partial melting model. The result of geochemistry inversion shows that the source rock of alkaline-rich porphyry is plagioclase-bearing harzburgite and of mantle-crust mixed type. At the early state of melting, some crust components of the source rock were partially melted into intermediate-acidic magma; with the crust components consumed, the magma evolved to basic.

Genesis of the alkali-rich porphyries in Yunnan

The alkali-rich porphyries formed in the structural relaxation epoch of the Himalayan Movement. The tectonic setting and crustal structure in which the rocks formed and the compositional regionization feature of the rocks indicate that the magma formed inside the crust, which is further proved by REE. Sr and Pb isotope data. Combined the aforesaid data with the result of REE inversion, it is suggested as a new opinion that the alkali-rich porphyries were the remelting product of the mixture of mantle rocks intrusing into the crust with crustal material.

New evidences for the formation of granitic rocks by remelting of the sial crust in Southern Hunan

Comparatively analyzing 47 REE distribution data of the Southern Hunan geosynclinal arkose-silicarenite and various period granitic rocks and the results of their partially melting experiment series in company with the occurence and petrogeochemical features of various period granitic rocks, the authors suggest that all of the above-mentioned salic rocks can be partially melt to produce granitic magma.Comparatively analyzing 47 REE distribution data of the Southern Hunan geosynclinal arkose-silicarenite and various period granitic rocks and the results of their partially melting experiment series in company with the occurence and petrogeochemical features of various period granitic rocks, the authors suggest that all of the above-mentioned salic rocks can be partially melt to produce granitic magma.