Study On Metallogeny Geochemistry Of Epithermal Gold Deposits In Northern Heilongjiang, China

Sandaowanzi gold deposit, Dongan gold deposit and Wulaga gold deposit aretypical epithermal gold deposits occurring in northern Heilongjiang province ofChina, which locate at Aihui County, Xunke County and Jiayin County respectively.All three gold deposits locate at the circum-Pacific tectonic region and mineralizationin the Cretaceous. The features of minerals, mineral assemblages and generate orderand wall rock alteration of these gold deposits are summed up systematically. Thispaper focuses on the microscopy characteristics of the ore minerals, fluid inclusiongeochemistry, REE and trace elements characteristics and to study the source ofminerals, ore-forming fluid characteristics and evolution, mineralization depthcombining with regional tectonic setting and mineralization ages. The microscopicidentification features of adularia and its significance; the relationship of time andspace between epithermal gold deposits and porphyry Cu-Au deposits are alsodiscussed. Studies indicated that:(1) the gas-liquid two phase fluid inclusions are the main type fluid inclusions inquartz, no crystal and typical CO2three phases fluid inclusions were found. Thehomogenization temperatures of fluid inclusions in quartz at the main mineralizationstage are mainly concentrated in the range of260~290℃,250~270℃and225℃~275℃respectively, and the salinity concentrated in the range of1.5%-3%,1.4%~2.5%and1.6%~3.6%（NaCleq）respectively.(2)Primitive mantle-normalized spider diagram of trace elements in quartz at themain mineralization stage of all these three gold deposits have the followingcharacteristics: the spider diagram tilt rightward overall and showing obvious U andPb anomalies and negative Ce anomalies.(3)REE in quartz also show similarities: LREE enrichment, obvious positive ornegative Eu anomalies, no significant Ce anomaly but Yb negative anomaliesobviously. The distribution curve of REE in quartz is consitent with which in mineralbut quite different with that in related wall-rock.(4)The three deposits also have similar metallogenic fluid characteristics: lowtemperature, low salinity, reduced, the main composition of fluid is H2O, low CO2content, Cl content is higher than F in fluid, the fluid is mainly a mixture of magmaticwater and meteoric water with the later the main composition. The calculated initialmineralization depth of three deposits is quite similar, are about1km by usinghydrostatic pressure gradient. (5)Adularia were found in all three deposits which incated that the Sandaowanzigold deposit is also a low sulphidation epithermal gold deposit when combined withore-forming fluid temperature and the depth of mineralization.(6)There is a certain genetic relationship between low-sulphidation epithermalgold deposits and porphyry Cu-Au deposits but in space they usually have a longdistance. Porphyry Cu-Au deposit is closely related to high-sulfidation epithermalgold deposits but not low-sulfidation gold deposits which explains why rarelyporphyry deposits were found in the study area.