| Nanmentou exploration demonstration area, which located in the north of Ningwu basin and covered by Quaternary clay layer and volcanics, is a work area of the project "The Deep ore Exploration Demon-stration in Yangtze Region", actualized by Nanjing Geological Survey Center. A large number of geological and geophysical survey was carried out in this area during the period of2007-2015, including the Gravity and Magnetic measurement with large scale, CR (Complex resistivity method), CSAMT (Controlled source audio frequency magnetic sounding) and drill hole etc. Experience and advice from those work was provided to guide deep ore prospecting.Due to the influence of various factors, there are multiple solutions of geophysical data interpretation in the process of research. In the project implementation process, some drill hole which were designed ac-cording to the comprehensive anomaly (especially the geophysical anomaly) have received prominent ef-fects, however, some are not. According to those ideas, this paper comprehensively analyzed the geophysi-cal and drill hole characteristics in this area, including researching the gravity, magnetic data and electrical profile measurement systematically on the basis of analysis of geological, geophysical and logging infor-mation of drill hole, inferring the deep geological structural in the Control of drill hole, summarizing Ore exploration method containing combination of methods, processes, effectiveness, anomalies and interfer-ence factors of iron and copper-gold deposit in northern area of Ningwu basin, which inferring to several typical deposits.Nanmentou exploration demonstration, which located in the northern area of Ningwu basin, is mainly in formation of Early Cretaceous volcano rock. Adjacent to the east of this area is Zhumen-Huanggu mountain volcanic eruption zone, which in the belt of Ji mountain-Zhumen fracture zone, and to the southwest is Gu mountain-Niangniang mountain volcanic eruption zone. Wu Zhuang explosion breccia pipe, which is in the region of Andemen-Niangniang mountain fracture eruption zone in the direction of northeast, is located in the northernwest of this area. The faults in this area are mainly in the directions of NE and NW.In this paper, petrophysical data of different lithology in this area which is collected or obtained in the experience (density, magnetic susceptibility, remanent, magnetization, resistivity, surface polarization coef-ficient) is analyzed. The factors of gravity and magnetic anomalies as well as electrical anomalies are sum-marized. The comperehensive lithology characteristics of main stratums in northern area of Ningwu basin are summarized through the statistics of the main lithology data. The local gravity and magnetic anomalies of Nanmentou area is introduced with emphasis on the basis of regional gravity and magnetic anomalies. The Bouguer gravity anomaly of Nanmentou area shows the low value, and the value increases from southwest to northeast. The main factors causing the gravity anomaly were summarized through the contin-uation chart in several height. The high gravity value in the northeast is caused by the King Mountain group rocks, while, the low gravity value in the southwest is caused by the Gu mountain group rocks. Though the analysis of residual gravity anomaly, a new view of the distinction of rock mass, volcano rock, exploration breccia pipe and volcano channel in this area was set up, and the distribution of several center of volcano eruption was verified. In this paper, horizontal derivative gravity and magnetic anomaly maps of45°and135°among the different direction show a significant trend of NE and NW, which indicates the main struc-tural features in this area were in the direction of NW and NW, moreover, apart from the known faults and eruption fault belt, some new faults F9-F12were inferred referring to the derivative anomaly of gravity and magnetic data and electrical data.In this paper, the electrical profile feature of8CR and4CSAMT was described with emphasis. Ac-cording to the characteristics of electrical profiles, as well as gravity and magnetic anomalies,9geological profiles based on the drill hole information were inferred, and moreover, comparison between drill hole curves (physical and logging) and corresponding position of the electrical profiles was actualized. Based on those comparison, a second time interpretation and summary of geophysical anomalies was achieved, which enriched the geophysical anomaly interpretation experience.From shallow to deep, the conductivity parameters (electromagnetics resistivity, apparent resistivity) of CR mainly shows the trend of "low-medium-high-medium value". A CR anomaly feature of "high ap-parent chargeability, low electrical resistivity, low apparent time constant and medium apparent Frequency correlation coefficient", which can reflect the mineral products with a certain scale was summarized, in ad-dition, it should be a feature of high gravity and magnetic anomaly or in a favorite position of mineraliza-tion. There were several identical electrical resistivity interfaces of the4CSAMT inversion profiles at the elevation of-400～-600m, which may reflect the different lithologic interface of middle stratum of Dawang Mountain group. The interface of10line was rised up nearby the drill hole4181, and it turned out to be the interface of upper andesitic breccia lava and lower (pyroxene) bornblende andesite, and therefore, an an-cient volcano channel was inferred according to the shape of the interface in this position. Moreover,2faults (F10、F11) were inferred though those electrical profiles.7drill hole was implemented to verify the anomaly, and the features of those drill hole including ge-ology, alteration, mineralization, petrophysical parameters and logging curves were analyzed and summa-rized. The lithology of the upper part of the drill cores was the clay and loam of Quaternary, while, the lower part from which was the extrusive rocks, volcano clastic rocks and sedimentary rocks in the intermit-tent period of the Gu Mountain group, Dawang moutain group and Longwang Mountain stratum. There was a set of intermediate acid intrusive rocks consist of syenite granite and adamellite in the deep of northeneast area, and there are andesitic porphyrite vein and diorite porphyrite vein of Dawang moutain group stratum in the east of this area. The kinds of alterations comprise of petrochemical propylitization, carbonation, potassic alteration and silicification. The kinds of mineralization comprise of copper, magnet-ite and specularite mineralization, most of which were veined and disseminated.Through the analysis of logging curves or petrophysical curves, it concluded that the factor causing the high value of gravity and magnetic anomaly may be the black andesite of Dawang Mountain group. The value of the electrical resistivity isoline is low in the shallow, while, high resistance, which may be caused by fresh andesite or acidic intrusive rocks, is mainly distributed in the degree of-600～-1000m. The main factors causing the high value of polarization parameters were pyrite and chalcopyrite.Through the comprehensive analysis of electrical profiles, gravity-magnetic profiles, geological features of drilling hole and logging curves etc., influence factors on the gravity and magnetic anomaly besides electrical abnormalities were summarized, and a complete insight of geological and structural features in the deep of this area was created.There are porphyrite iron ore related to acidic continental volcano rock and copper-gold deposit in Ningwu basin. Several aspects of those deposits such as geological features, the relationship with magma, metallogenic fluid source, mineralization, tectonic mineralization, etc., were discussed. According to the understanding of deep metallogenic theory made by many scholars, deep prospecting potential of this area was discussed. Several typical deposits in northern area of Ningwu basin were described from several as-pects such as geological characteristics, geophysical and geochemical anomaly and prospecting methods, meanwhile, the exploration process, methods and ore-hunting indicator were obtained. Above all, a new geological-ore prospecting model was put forward, which is of importance to the deep mineral exploration work, and moreover, new geological-geophysical prospecting model consist of the selection principle of the prospecting target area, the type of exploration target, the prospecting process, the ore-hunting indicator, interference factors, the validity of those method. In the end, a viewpoint was presented that faults of NW and NNW may be the ore breaking faults for the copper vein on the basis of comprehensive analysis for the geological-geophysical features. At last, this paper presnts that that there may be copper-gold mine in the southwest area of Nanmentou. |
PDF Full Text Request