Study Of Indicator Elements For Tungsten-Tin Deposit In Nan-Ling Area And Application Of Geochemical Exploration Methods For Buried Deposit

Nan-ling metallogenic province is located in the southeast of Eurasian plate.It has experienced four stages including Jin-ning period, Caledonian period, Hercynian-Indosinian period and Yanshan-Himalaya period. Cambrian, Devonion and Carboniferous are the important tungsten-tin ore bearing stratums in this area. Tectonic, magmatic and metallogenic activities occurred frequently and intensively in this region during Sibao to Yanshan periods, and the most intensive of them is the Yanshanian granitic magmatism, which is closely related to the metallogenesis of tungsten and tin deposits.This area is an important tungsten-tin orefiled of China where many large and super-large ore deposits such as Da-chang, Qi-tianling, Xi-huashan, Shi-zhuyuan and Da-jishan tungsten-tin deposits have been targeted. Basing on the previous detailed geological, geophysical and geochemical study, Nan-ling is an ideal area for geochemincal exploration study.With the development of national economy, the demand of tungsten-tin mineral resources is growing continuously. But the reserves of surface mine and shallow mine are decreasing for long term mining activities. To solve the resource prolems, the exploring work of buried deposit is an useful method. Though there are many achievements about the basic geology and metallogenic regularity in this area, the geochemincal exploration of tungsten-tin deposits needs further study:(1) the geochemincal exploration data at1:200,000scale needs to be updated and the geochemincal exploration data at1:50,000scale is lacking. Can the geochemincal exploration data indicate the concealed mine is not clarity.(2) the data processing method of the regional geochemincal data need to be developed.(3) the application of new geochemincal exploration methods have been rarely used in the area. These issues limit our understanding of the distribution of tungsten-tin deposits and how to prospect the consealed mine.Aming at the above problems, the thesis establishes a series of exploration methods. First, in the Nan-ling area, a group of elements related to W and Sn element are selected through cluster analysis. The geochemical maps of these elements and geochemical anomaly maps of contrast values were generated to help us understading the elements distributon and indicating effect tungsten-tin deposit. Second, Tong shanling-Jiu yishan metallogenic belt in Nan-ling area is selected. Subinterval area median contrast filtering method, background correction method and factor analysis were carried out to generate the geochemical anomaly maps at1.200,000scale. And then the geochemical anomaly maps of single and integrated elements at1:50,000scale were generated to find the useful indicator elements for tungsten-tin deposits. At last the new exploration methods like hydrocarbons and mobile forms of metals methods were used in Tong Shanling-Xiang Linpu mining area. In this work,about a hundred geochemincal anomaly maps of elements were generated at1:200,000scale and at1:50,000scale. Additionally, about800soil samples and46core samples were collected and analysed. The detaile work and results are stated in the following:(1)Through processing the exploration data of nanling at1:200,000scale by cluster analysis, it’s found that the elements in the research area can be divided into four groups:the common element-group for Rock-forming mineral, the element-group related to diagenetic process and magma splitting degree, the tungsten-tin ore-formation element-group, the copper-lead-zinc ore-formation element-group mainly. Using the cotent values of thirteen elements (Au, Ag, Cu, Pb, Zn, As, Sb, F, Ba, Mo, Bi, Be, B) in the tungsten-tin ore-formation element-group and copper-lead-zinc ore-formation element-group, geochemical maps are generated based on wavelet analysis-filtering. It’s found that the high value area is mainly distributed around the rock mass, and the high values in the study area appear more in the south-eastern. Most of the high values of every element are mostly located in Chenzhou-Guiyang area, which is in center of the study area. To avoid the influence of different geologic factors in large-area regional geochemical exploration and take in more comprehensive information, anomaly maps for contrast values of single element are generated firstly. Then the anomaly maps of equal weighting contrast values of every element were generated. The anomalies can be divided into two zones:Changning-Dayu zone and Xinning-Shixing zone, and their distribution agree well with the location of the concealed intrusive bodies. By this method, the anomaly extension determined is smaller than anomaly maps of single element contrast value, and it’s easier to identify the targeted area. Additionally it brings in more comprehensive information.(2) Tong Shanling-Jiu Yishan metallogenic belt is located in the center of Nanling. The EW granite complex belt, which controlling the distribution of W-Sn polymetallic deposits in the area, is consist of Du Pangling composite granite rock, Tongshanling granite diorite rock and Jiu Yishan composite granite rock. W-Sn resources are rich in this area and most of the known mines locate in Tong Shanling magmaticbody, Xiang Lingpu porphyry group and Jin Jiling magmaticbody. This study summarized the major point of ore deposits and mineralization in the district. Basing on the1:200,000scale geochemical exploration data, the geochemical anomaly maps of W, Sn and the other elements related to W-Sn are generated using the traditional method (mean±2standard deviations), subinterval area median contrast filtering method (SAMCF) and background correction with digital elevation model in Mapgis software.3×3grid for small window and9×9grid for large window are used in subinterval area median contrast filtering method. Compared with the traditional method, the size of anomaly areas are reduced and some anomalies in low background are delineated by SAMCF. But this contrast calculation method may exaggerate the unobvious change of element content. And the residual will be better to show the elements of the superposition of mineralization. Through the contrast test of window, the window with7×7is better in disinterring the weak anomalies and highlighting the mineralization anomalies in high background. By using the background correction, some nonmineralized anomalies in high background are restrained and some weak anomalies are strengthened, as well as a series of new anomalies are found. Therefore, the background correction has more superiority in processing this geochemical exploration data. Because of the low sampling density of1:200,000scale geochemical exploration data, some metallogenic rock body with less outcropped and conceal deposits are easily missing. In search of the control factors of mineralization regularity in this study area, four factors, which include Cu-Pb-Zn mineralization factor, W mineralization factor, Sn mineralization factor and mineralizer factor, are extracted by factor analysis. W mineralization factor concentrates in southwest and Sn mineralization factor concentrates in northeast. The size and intensity of anomalies of Cu-Pb-Zn mineralization are lesser than W-Sn mineralization.(3) The results of geochemical data analysis at1:50,000scale in Tong Shanling-Jiu Yishan area show that this group of data is influenced by the regional geology and comes from two different geochemical matrixs. So it should be divided into two groups and calculate the contrast value respectively. Then draw the anomaly map of contrast value of every element in the whole area. With writing VBA programs in Excel, drawing the fractal figure and box plots in Excel were realized. And the background values and anomaly threshold of elements were calculated in Excel, too making the processing of geochemical data simply. From element anomaly maps it can be seen that W, Sn, Mo, Bi and F composite anomalies mainly appear in the Xiang Linpu, Tong Shanling, Jiu Yishan and Hou Jiangqiao area. The elements group indicates tungsten-tin deposit obviously. The area Cu, Pb, Zn and Sb element composite anomaly is larger in the Xiang Linpu, Tong Shanling, Jiu Yishan and Hou Jiangqiao area. It is also in accordance with the known lead-zinc mine. There is potential for the prospecting of tungsten-tin deposit and lead-zinc deposit in this area.(4) Weijia tungsten ore is located at Xiang LinPu Town, Hunan Province. It is in the Xiang Linpu porphyry groups near the Tong Shanling porphyry. The large skam type deposit was detected using comprehensive exploration method during the recent exploration activities in China. Being buried deeply in500m and covered by limestone and thick soil in the surface, it is hard to be detected by traditional indicator elements. Jiang Yong lead-zinc deposit and Tong Shanling nonferrous metals deposit have been exploiting for many years. It is necessary to explore buried mines around or in the deep of the old mine. It is proved that hydrocarbons promoted the transport and enrichment of elements in the ore forming, so Weijia tungsten ore and Tong Shanling diggings are taken as a case to study the effect of hydrocarbons to the concealed deposits in coverage area. Acidolysis hydrocarbon of46rock samples in ZK801and heat release hydrocarbon of soil profiles were analyzed. The results show that the contents of hydrocarbons decrease from porphyry, ore body to wall rock, and the rates of methane, olefins and heavy alkane are different in porphyry, ore body and wall rock. The standard curves shapes of ore are similar to those of the porphyry and wall rock. The soil heat release hydrocarbons show bimodal distribution and low value above the ore body. This study proves that the hydrocarbons are more useful to indicate the concealed mine than the traditional indicator elements. For the mobile forms metal method, the contents of every element species in the soil can indicate the shallow ore body but not for the deep one. But the percentage of element species increase above the deep ore body obviously. So this discover may be a useful method for deep mine detecting in the future.Through the above research, this paper did a systematic research on the indicator elements and new geochemical prospecting method application for tungsten-tin deposit in Nanling area. However, there are still some deficiencies in this study. Further research should be carried out in the following aspects:The indicator elements should be further studied and be applicated for concealed deposits in Nanling area; To explain the reason why Tong Shanling area and Jiu Yishan area show different anomaly range and intensity, more work should be done in the rock properties and concealed rock mass; Further research should be carried out in the carbon isotope to tracing the source of hydrocarbon; About the mobile forms of metals in soil, we should try with more elements, especially in the analysis of speciations of tungsten and tin element; Finally more experiments about various concealed deposit prospecting methods should be carried out.