The Type And Metallogenesis Of Ophiolites From Hegenshan Area In Inner Mongolia

Hegenshan ophiolite belt located in the north of Xilinguole League, Inner Mongolia. It is comprised of mutually uncorrelated continous blocks trending North to East such as Hegenshan, chaokeshan, xiaobaliang, songgenwula (chonggenshan) , zhu'erhengou (wuzinihei) and so on. According to tectonic location, it located between Siberia Plate and North China Plate, that is ancient Asian ocean fold belt.The tectonic setting in this area is very complex. Because of the effetion from the multi-periods subduction, collision and joint activity between North China Plate and Siberia Plate, both micro-blocks from pre-cambian and volcanic sedimentary rocks from Paleozoic are widely existing in this area. Deep and huge fault zone are crisscrossing, all kinds of intrusive rocks develop well and numerous metallic ore deposits which belong to the important part of the Mid-Asian giant orogenic belt and metallic metallogenic belt can be found here.Hegenshan ophiotite suite has complete sequence. It is comprised of peridotites, cummulate complex, dikes and basaltic lava as the top-down sequence. Compared to the typical ophiotite suite section, it is lack of the pillow basalts. Moreover, peridotites in this suite are comprised of augite peridotites, iherzolites, hornblende pyroxenites, and they all strongly serpentinative altered.The major elements shows that the peridotites from Helanshan ophiotite are rich in Mg as well as low in Al, mainly contain metamorphic peridotite and harzburgite.REE contents are low for the meta-peridotites from Zhu'erhengou. They are significantly depleted in MREEs with a U-shaped chondrite-normalised REE pattern, suggesting high-degree mantle melting or complex geological processes or metasomatism overprints by mantle fluids during their petrogenesis. On the other hand, ultramafic cumulates from Songgen also have low REE concentrations, but depletd in LREEs, which might suggest they are mantle melting residue.The ultramafic rocks from both localities both show relative low Cu-Ni concentrations, with average Cu-Ni contents lower than primitive mantle values and, for Ni, even lower than typical ultramaifc magmas values. Their Cr contents are comparable with abundances in the pritimive mantle.The Hegenshan ophiolites are classsified as SSZ-type ophiolites, according to the recent classification of ophiolites together with their petrography and geochemistry.The common types of mineralization in the peridotites from Songgenwula and Zhuerhengou include magnetitive and chromtitive. Chromitites usually exsit in dunite , moreover, Cr₂O₃与Al₂O₃ in Cr-spinel are obviously negatively related. This can be one of the signs which can prove that the ophiolites from Helanshan are SSZ ophiolite. Magnetites are related with alteration. As the alteration more strongly, the higher content of the magnetites. This generally controlled by structure fault, maybe this is one of the reasons that causing the unmormal of the geophysical magnetic methods.Xiaobaliang Cu-Au deposit hosted on the top of the Helanshan ophiotites. From the deposit geological characteristics, Cu-Au mineralization mainly occurred inner the basaltic alterative tuffs, diabases, and volcanic breccias. The orebody usually have West-East trend. There are clay accumulations that show like the shape of limonites and powder on the ground surface. Rock geochemisty shows that, its REE distribution curve indicates that the whole content of the REE are high,and LREE are richer. This is complementary to the peridotites from Wugenlaer and Zhu'erhengou, indicating that its source region is primitive mantle, which risedualbidy are metamorphic peridotites and dunites in the bottom of the ophiotite.The article summarizes the characteristic of the Xiaobaliang Cu-Au deposit. According to the tectonic setting, deposit geological characteristics, the source region of the metal and hydrothermal, the author analyzes that the cause of the Xiaoliangba is massive sulfide deposit related the sub marine volcanic jet stream, which can be compared to the Cyprus VMS deposit.