The Mechanism Of Electrogeochemical Halo-Formation And The Application Of Electrogeochemical Method To Exploration Of Metallic Ore Deposits

With the development of mineral exploration, most of the surface outcropping and near-surface ore deposits have been discovered, hence it becomes important for global geologists to search for deep concealed ore deposits. Therefore, geochemists have been working on various geochemical exploration methods to detect deep ore deposits all the time. The electrogeochemical method has been paid close attention by global geological geologists since it was first proposed by a USSR geologist in the 1970s. During the practice, the method is able to detect deeper ore deposits than conventional geochemical exploration methods, and can produce obvious effects. Thus it is still being studied as a main topic by geologists in 21st century. Because of different views in the halo-forming mechanism of the electrogeochemical method and disadvantages of the technique and its limitations in applications, some studies are carried out to improve the methodology system. In this way a mature set of methods and techniques is to be anticipated to be widely applied in our country. The studied contents of the thesis are as follows:1, Basic theory study of the electrochemical field on the metallic ore deposits.Through the analysis of the forming mechanism of electrochemical field of the ore bodies composed of single mineral and polymetallic ore bodies and disseminated ore bodies, the forming mechanism of the electrochemical field of the metallic ore deposits is expounded from the electrode potential of the metallic sulphide. That is: when the substance of different parts of ore body is different or the properties of the water solution media around the ore body are different, it induces different electrode potential, and natural electric field can be generated. Natural electric field is easy to be produced when ore body is crosscut by the water table; however , self-potential anomaly can also be produced when the ore body is over or below the groundwater table. The key factor is the difference of electrode potential among the different parts of the ore body. In general, the different electrode potential among minerals is critical to generate electrochemical field, and such an electrochemical field is the main form of natural electrical field for the metallic ore deposits to produce.2. The study on the mechanism of electrogeochemical halo-formationAfter doing the experiment in electrochemical dissolution in the lab and simulated experiment in the model of element dispersion around an artificial sulphide ore body, the study of the mechanism of electrochemical dissolving on metallic ore body and the migration of redox gradients of ions was carried outExperiments have been done on the electrogeochemical extraction electrified by high voltage (220V) and low voltage (9V) at the Panlong lead-zinc deposit in Dayao mountains, Guangxi, added by different electrolyte solution (water and solution of 13.6% HNO3), and onthe electrogeochemical extraction under artificial electric field as well as adsorption of foamy plastics electrode without artificial electric field at the 210 gold deposit in Xinjiang and at Yingezhuang gold deposit in Zhaoyuan, Shandong. We dialectically negates the existing halo-forming mechanism of electrogeochemical method. It is confirmed that the artificial electric field plays an important role in electrogeochemical extraction, and that the ions from the ore body are not directly extracted to element-colIectors(ECs) under artificial electric field. Meanwhile, it is confirmed that the ionic haloes in the electrogeochemical extraction come from near the surface, which are dynamic, and that the ionic haloes in the electrogeochemical extraction don't only come from the soil around the electrodes, and that indoor electric adsorption can not replace the on-the-spot electrogeochemical extraction.A new theory is advanced to propose that the ionic movement around ECs induces the migration of ions at distance and depth under the influence of the artificial electric field. Namely, the metallic minerals are dissolved under the electrochemical effects to create ionic haloes around the ore bodies, which migrate up to the near surface affected by various natural agents such as electrochemical field, earthgas, groundwater movement and so on. The source of the electrogeochemical haloes are just the near surface ions that come from the deep ore body and are the characteristics of dynamics. The artificial electric field activates and changes the bound forms of occurrence of elements in the soil, on one hand, to bring about decomposition of a great number of complex anion and other stable or sub-stable form of elements, and on the other hand, makes anions and cations move to the extraction electrode, and it accelerates the ionic movement The redox reaction around the electrodes gradually moves the ions and transfers charges which reside farther, more interior and deeper from the center of electrode, which breaks the balance of the primary redox potential field between the deep country rock and the overlying overburden. To maintain the new balance, the ions moving away from an unit volume need to be supplemented by the ions from the adjacent unit volumes. Thus, the ions of dynamic balance migrate up one by one like a relay race. If there are ore bodies under the ground, the metallic ions produced by the electrochemical dissolution of the ore bodies will migrate continuously up to form an ionic haloes of dynamic balance. Although the movement velocity of single ion is low, and the migration distance of single ion is sbort numerous ions transmit one by one to achieve migration from long distance.3-. Study on the method and technique of electrogeochemical prospecting 1) Kind study of geoelectro-extractionThe kinds of geoelectro-extraction include:shallow electro-extraction deep electro-extraction charge electro-extraction logging electro-extraction water electro-extraction etc,on the basis of the difference of the geoelectro-extraction excitement way it may be divided into two kinds:high-power excitement and low-power excitement,and they are widely used in China.So the paper emphasizes the contrast study between high-power excitement and low-power excitement,the result indicates that there are both clear electrogeochemical anomaly no matter which kind of way,now we can't simply affirm any kind,however,deny another because any kind has its own excellence and flaw,we must choose appropriate way on the basis of different condition and different request,and use selectively on the basis of different phase of ore-search.2) Study of distilling electrodeThis is one of important problems of geoelectro-extraction technique.the selection of the distilling electrode directly affects the distilling result,The paper analyses and contrasts main kinds of electrode throughout the world,The new type solid electrode which has strong absorption ability to the ion of heavy metal and precious metal has been made.Many tests have been operated with the electrode in house and field,and contrast tests have been operated in Au-. Sn-. Cu-. Sb deposits etc between the electrode and other electrodes.The result shows the new electrode has better effect The excellences include-.high sensitivity-, detecting depth is large-, kinds the new electrode can detect are excessive, we can get different anomaly between surface mine and deep mine with the new electrode,anomaly basically is affected by structure,good applicability to all heavy and precious metals and settling basification matter.3) Criterion study of way and techniqueBecause effect factors of electrogeochemical measurement are very excessive and measurement data is affected by many condition (for example:specification of kryptoK plastic and filter paper- distilling liquid-, distilling time and unit of data etc) .So it is necessary that the technique is standardized.According to plentiful tests that I have done ,1 bring forward a set of applied standard inthe paper,we have acquired better effect with the standard in prospecting for ore deposits.4- Feasibility study of electrogeochemical methodFor study effect of electrogeochemical method in prospecting for hidden polymetallic deposits we have studied the feasibility in typical hidden polymetallic deposits-, all kinds of thick-bedded cover areas-, different cause of formation and different types.We have studied the feasibility in seven Au deposits-, two Cu deposits-, two Pb> Zndeposits-. two Wu-. Sn deposits and three other polymetallic deposits,and there are all clear electrogeochemical anomaly above the sections of above-mentioned mining areas.lt suggests that electrogeochemical method is effective in prospecting above-mentioned kinds of hidden polymetallic deposits and the method can be widely used in prospect ore deposits.5-. Application study on electrogeochemical method for different stages of mineral exploration1) Application at regional exploration for electrogeochemical methodThe improved CHIM is first proposed to be applied at the regional level to identify prospective target areas because it is portable, easy to operate, practical, low cost and efficient in the fieldwork. Tests were conducted to an area of 22.5km2 by 500mx500m investigation at Jinwozi to No. 210 gold ore belt in Xinjiang, six gold anomalies, four silver anomalies, three copper anomalies are discovered. At known gold mineralization, two CHEVI assemblage anomalies for Au, Ag, Cu were observed, which are of obvious concentration center, a certain concentration gradient, continuous anomaly points, and the composition of identified haloes correlates well with the position of the concealed mineralization. Around known gold mineralization, two CHEVI assemblage anomalies for Au, Ag, Cu were identified. These showed that CHIM method can be feasibly applied at the regional mineral exploration, which helps change the case that previous CHEVI method is only used for detailed exploration and at the assessment stage for verifying the geophysical and geochemical anomalies.2) Application to detailed exploration for electrogeochemical method? A research on an area of 0.96km2 for detailed exploration was carried out in order to search for deep ore deposits at the Xinzao lead-zinc mining area in Dayao mountains, GuangxL The distinct CHlM anomaly is given over the known lead-zinc ore body, and concentration center of anomalies for Cu, Pb, Zn correlate well with the position of the concealed ore body, and a predicted mineralization belt of an proximate 1.2 kilometer long was circled in the periphery of the mining area.? A research of a 1.02km2 area for detailed exploration was carried out in order to search for concealed gold deposit at the Luanjiahe fault in Zhaoyuan, Shandong. In the west part of the study area, four parallel linear anomaly belts were discovered, whose direction of stretch is in the similar direction of the extension of the fault in the area. Multi-elements anomalies of the anomaly belts are strong, and are characteristics of elements assemblage. In the east part of the study area, four anomalies of Au, two anomalies of Ag, four anomalies of As, two anomalies of Sb, three anomalies for soil ionic conductivity were discovered, which are characterized by linear. These provide important clues for further assessment of the ore potentiality of the fault.(D A research of a 0.2km2 area for detailed exploration was carried out in order to study the perspective of prospecting mineral deposits at the Taifu gold mining area in Heng County, Guangxi. Five electrogeochemical anomaly belts were circled, and gold ore bodies were discovered 100 m below the surface under JV-1 anomaly and IV-2 anomaly of IV anomaly belt through prospecting while mining, whose average grade is 5.4x10"*. Gold mineralization was discovered in drill hole of II -1 anomaly of II anomaly belt. Gold mineralization bodies were also discovered in prospecting trenches of V-2 anomaly, and whose average grade is 2.063X10-6.This research finds out that the electrogeochemical method is a better prospecting method to search for concealed ore deposit, which can be applied at all stages of mineral exploration through method and technique improvement, and it can also be applied in the most areas in China. Therefore, the working standards of the soil ionic conductivity method and the improved CHIM are made so as to be widely applied as a mature set of method and technique for mineral exploration.