A Study Of Elements Geochemical Distribution In Typical Copper Deposits And Methods And Techniques Of Metallogenic Prediction, Beishan Region, China

Beishan region locates in the intersection part of Kazakhstan plate, Tarim plate and North China plate. Complex organic movement and multiple-period magmatic movements in long geological evolution history, created favorable metallogenic geological conditions in Beishan region. Two medium-scale copper deposits, one small-scale copper deposit, fiftyeight ore or mineralized occurrences have been found out in this region heretofore, which shows good prospects for copper deposits exploration. However, geological prospecting for super larger-scale or large-scale copper deposits has not been made breakthroughs, which give the facts that the geological prospecting methods and technology of copper ore, including geochemistry exploration methods and techniques, needs to be mended and improved.Two typical deposits, including Baishantang porphyry copper mine and Huitongshan copper mine, were chosen as study targets in this paper. Based the metallogenic geochemical environment theory, and taking account of enriched and depleted elements in copper mineralization process, elements geochemical distribution was systematically studied for summarizing geochemistry indexes which can effectively reflect copper ore-formation; supergene activity regular of elements was researched in order to illustrate the inheritances of elements'activity from primitive to supergene environment. Based on these results, the methods and techniques of forecasting metallogenic prospective areas about copper-polymetallic deposits and prospecting targets optimization were studied for demonstrating the direction of geological exploration.The largest reserves ore body of Baishantang mining district, whose metallogeny was controlled by Middle Hercynian rhyolite-porphyry, hosted in the contact belt between rhyolite-porphyry body and stratum of Jixian series Pitoushan group. Two groups in total of 33 exploration geochemistry indicators, consisting of 20 enriched indicators and 13 depleted indicators, were summed up by the study results of elements distribution in ore-body and hosted rocks. The study results of elements supergene activity demonstrate:1. the characteristic of elements enrichment and depletion among different parent rocks show obvious differences, and the contents of elements in soils was controlled by parent rock; 2. comparing with fine fraction, the material and chemical composition of coarse fraction of soil show more similar to parent rocks; 3. in-4～+40 fraction of soils, enriched elements show most intensive supergene enrichment, but more weaker supergene depletion of depleted elements; 4. as the distance of samples to ore-body increasing, the contents of Cu, Mo significantly decreased in-4～+40 fraction of soils, inversely, the content of Na2O increased; 5. positive and negative anomalies were delineated based on taking-4～+40 fraction in effective sampling medium, which directed the prospecting targets optimization.Huitongshan skarn copper ore-body, whose metallogeny was obviously influenced by Early Yanshan feldspar granite body, hosted in the contact belt between stratums of Ordovician Huaniushan group and feldspar granite body. Two groups in total of 24 exploration geochemistry indicators, consisting of 17 enriched indicators and 7 depleted indicators, were summed up by the study results of elements geochemical distribution in ore-body and hosted rocks. The study results of elements supergene activity reveal:1. the characteristic of elements enrichment and depletion among different parent rocks show obvious differences, and the contents of elements in soils was controlled by parent rock; 2. comparing with fine fraction, the material and chemical composition of coarse fraction of soil show more similar to parent rocks; 3. different soils show different supergene enrichments, in-40 fraction of soils, the supergene enrichment of almost elements achieve most intensively; positive correlation between elements enrichment and the contents of clay mineral and negative relationship between elements enrichments and the contents of rock-forming mineral were discovered; 4. as the distance of samples to ore-body increasing, the contents of Cu, Mo significantly decreased in-4～+40 fraction of soils, inversely, the content of Ba,Sr slightly increased; 5. based on taking-4～+40 fraction in effective sampling medium the experiment of prospecting target optimization was carried out, the results show that integrate the positive anomalies formed by enriched elements and negative anomalies formed by depleted elements in mineralization process to optimize prospecting target, can show more substantive and exact indication to discover ore-body.In the study of methods and techniques of metallogenic prospecting areas prediction,2 kinds and 4 groups in total of 13 forecasting indicators were found out on the basis of elements geochemical characteristic and the logarithmic contents linear regression analysis results between Cu and other elements; the upper limit and lower limit of anomalies were made sure by percentile method; comprehensive predictive indicator was put forward. Furthermore, basic prediction unit, anomaly maps production and classification of predictive indicators anomalies were definitely specified and detailed illuminated. Base on the aforesaid researching results,3 kinds in total of 85 comprehensive predictive indicator anomalies, including 36 A anomalies,25 B anomalies and 24 C anomalies, were delineated; 15 copper-polymetallic deposits prospecting areas were made out, and metallogenic prospect of each area was forecasted on the basis of the analysis of metallogenic geological condition of each area.Prospecting target optimization was carried out in 2 kinds in total of 5 comprehensive predictive indicator anomalies based the study of anomaly structure, the achievements were showed as following:1.in Baishantang copper deposit test region, a favorable section for Cu metallogeny, which located in the northern of the overlapping position of No.3 and No.4 ore belt, was pointed out; 2. in No.2010-1 test region, As and Sb were made sure as main metallogenic elements, a favorable metallogenic section was clearly showed; 3. results showed that No.2009-2 test region do not has distinct metallogenic prospects; 4. in No.2010-2 test region, a favorable section for Cu metallogeny was pointed out, hydrothermal type deposits unlikely formed in this section based on geological setting analysis.