Geological&Geochemical Characteristics And Ore-prospecting Of The Ⅰ~#Ore Vein In Ciweigou Gold Deposit, Yanbian Area

The Ciweigou gold deposit in Yanbian, one of typical low sulphidation (LS)epithermal gold deposits in the northeastern China, is located in the eastern section ofXing’an–Mongolia Orogenic Belt and at the edge of Western Pacific. The deposit lies inthe junction region of Dunhua-Duhuangling fault zone, Chunyang-Mijiang fault zone andTumen-Luozigou fault zone, and controlled by caldera and associated fracture systemwithin Mesozoic volcanic basin.There mainly develop the strata of the Permian Kedao Formation and the JurassicTuntianying Formation, which are discordant. There is only minor Kedao Formationlocated in the southwest of the gold deposit. The Kedao Formation is composed oftuffaceous slate and sand slate. The Jurassic Tuntianying Formation is dominated byandesitic volcanic rocks and marble.There are three ore veins within the mining area, showed as auriferous quartz-calciteveins distributed in andesitic breccia tuff of the Middle Jurassic Tuntianying Formation.Ore veins are generally northeast trending, nearly parallel, part attitude varied obviously,and "S" type spreading in plan and section,the veins along strike and inclinationsextension to Permian strata tend to narrow and wedge out.TheⅠ#ore vein is the only industrial ore vein in Ciweigou gold deposits.It is filled involcanic rock formation of Tuntianying Formation, and controlled by the fault zone. The vein extends in NE direction, tending in southeast direction. It has the length of340-1200m, thickness of1-3m, and depth of over500m, with obvious expansion,contraction, branching and merging.The content of metal minerals in the ore is low (<5%), including mainly pyrite,followed by a small amount of chalcopyrite, galena, sphalerite, magnetite is and naturalgold; non-metallic mineral are primarily quartz, valencianite, calcite and dolomite. Theshape of metal minerals in the ore is granular and xenomorphic granular, enchasemetasomatism residual and cataclastic structure. Among them, the pyrite showidiomorphic-half automorphic granular aggregate of edges and corners, sparselydisseminated in valencianite-quartz veins, calcite-quartz veins and the volcanic wall-rocks.Wall rock alteration types developing in the ore-hosting rocks of the Ⅰ#ore vein,mainly include adularization, carbonatation, sericitization, silicification, chloritization andsaussuritization. The micro temperature measurement and laser-raman spectrum analysisof fluid inclusions in auriferous quartz-calcite vein from different elevation shows that theore-forming fluid belong to low temperature, low salinity, low density NaCl-H2O (CO2)system. According the micro temperature measurement results, the mineralization pressurecan be estimated as7.99-37.89MPa, corresponding mineralization depth is0.27-1.26km.To determine the mineralization enrichment regularity and deep exploration potentialof this deposit, the primary halo geochemical characteristics of the Ⅰ#ore vein, whichhas the highest industrial value in the deposit are studied. The ore-controlling conditions,gold mineralization, alteration characteristics, correlations of the metallogenic indicatorelements, concentration zoning and zoning sequence of elements combination indicate thatthe Ⅰ#ore vein occurs whitin the Mesozoic continental volcanic rocks sequence, and isobviously controlled by NNE-trending faults in caldera. The chlorite alteration (oftenaccompanied by carbonation) is always considered as one of the important ore-prospectingclues of the high-grade ore block. The analysis of eleven trace elements in ores fromdifferent levels shows that only Hg and Ag have weak positive correlation with Au, whilenegative correlation are between Au and other elements. Combining with the result of factor analysis, it is indicated, with the exception of Au and Ag, there is no other usefulelement. According to the vertical variation of metallogenic elements and elementconcentrations zonation，it can be concluded that the Ⅰ#ore vein of the Ciweigou golddeposit is featured by the segmented enrichment, with the mineralization concentrated at220~260m and420~450m. This conclusion can play an important role in deep explorationin the Ciweigou ore deposit and geologic exploration of similar deposits in the region.