The Geological, Geochemical Discrimination Indicator For The Potential Of W、Sn Mineralization In Granitic Intrusions

Southeast Hunan is an important part of Nanling polymetallic belt, and granitesin it have close genetic relationship with a variety of minerals. The research on granitewhich as an important participant in mineralization process can be help to summaryeffective prospecting direction and indicator, then determine the practicableprospecting method and way. In this paper, a contrastive study on geologicalcharacteristics, geochemical characteristics and existing phase of elements wereperformed on Qianlishan metallogenic intrusion, Yaogangxian metallogenic intrusionand Wangxianling barren intrusion, the geological and geochemical discriminationindicator for the potential of W、Sn mineralization in granitic intrusions weresummarized.metallogenic intrusions formed in stage of Yanshan mostly; have smaller size,the exposed area is less than20km2, mostly appeared in irregular shape in apophysis,stock, dyke, boss and sill, have clear boundaries with wall rock; metallogenicintrusion have strong hydrothermal alteration, skarnization belt is developed incontact zone with carbonate rock; The devonian, in which W, Sn, Bi, Mo, Pb andother ore-forming elements are most enriched and have proportional relationship withF, B and other mineralizing elements, is the most advantaged wall rock.There are obvious differences between metallogenic intrusion and barrenintrusion in type of rock and geochemical characteristics, the formation ofmetallogenic intrusion have closely relationship with the magma evolution.Metallogenic intrusion has obvious features that strong magma differentiation, rich inSi, alkali, Fe, large ion lithophile elements (LILE) and high field strength elements(HFSE), loss in Mg, Ba, Sr, Ti and P, strong negative Eu anomaly, REE pattern showed "Seagull" which is a typical characteristic for “A” type of granite. The strongmagma differentiation has a close relationship with volatile components and heatproduction elements.The study on the existing phase of W, Sn, Mo showed that the content ofwolframite which account for less than70%is relatively low and the content ofscheelite is relatively high with the proportion higher than10%generally; the contentof acid insoluble tin is higher than acid soluble tin, and the proportion of acidinsoluble tin is higher than50%; molybdenum sulfide accounts for more than half ofthe total molybdenum in metallogenic intrusion, but less than40%in bareen intrusiongenerally. The atomic ratio of F/W, F/W+Sn and the heat production rate ofradioelement in unit granite (QA) are effective indicator to discriminate the ability ofmineralization and divide metallogenic types.By group of the geochemical indexs combined with their geological significance,the triangular diagrams of A/CNK-QA-F/W, A/CNK-QA-F/W+Sn, A/CNK-ALK-F/W, A/CNK-ALK-F/W+Sn were proved to be good to divide of the metallogenicintrusion and bareen intrusion. Tectonic system is one of the key factors to cause thedifference in mineralization ability of intrusions in Southeast Hunan, tectonic settingin post orogenic, which is relative stability and dominated by the stress field ofextension, is conducive to the formation of metallogenic intrusion. The potential ofmineralization in granitic intrusions for different genetic types are different,“A” typeof granite in the study area is the favorable type of metallogenic granite, and can be aindicator for the potential of W、Sn mineralization in granitic intrusions.