Abstract:

The Huogeqi deposit is a famous large-scale polymetaI Cu deposit in the Langshan area,Inner Mongolia. The sequence of ore-bering formation is spilite group occurring in Middle Proterozoic terrigenous rift,mineralized hydrothermal sedimentary rock and terrigenous clastic rock formation. A large part of the spIlite has metamophized into chlorite schist.The original rocks are submarine erupion intruslon rocks such as basic volcanic rock and gabbro and so on,with Na₂O content higher than K₂O，total content of REE is low in blasto gabbro but high in biotite schist,and its distribution

plotsb show enrichment of light REE and depIetion of heavy REE.The elements such as B，F，K，Ti，Zn，Rb，Sr，Nb，Ag，Ba，Pb，U，Th are relatively enriched in biotite schist,the enrichment parameters of Cu,Pb and Zn are higher than those in blasto-gabbro,which suggests that the chIlote schist is of the characteristics of hydrothemeral aIteration.Total content of REE in the banded quartzite and diopside-tremolite of the ore-bearing segment is clearly low and there is a distinct differentiation between heavy REE and light REE,and shows the featured positive Eu anomaIy. Besides the mineralized enrichment,the trace elements such as Be，B，F，Rb，Ag，Ba，Th，U also show distinct enrichment,suggesting its hydrothermal enrichment genesis.The features of the mineralization of the deposit which is controlled by the lithologic layers and enriched in partial structure are quite apparent,which show the features of hydrothermal stacking modification.Sulfur isotope with a wide range of variation shows positive values but suIfur isotope in vein ore is a little low with the values of 4.07‰ to 16.66‰，and the vaIues of δ³⁴S in stratiform ore are from10.6‰ to 24‰.The sequence of δ³⁴S of suIfate is graduaIly down from pyrite,pyrrhotite to chaIcopyrite,galena and sphaIerite.The deposit genesis analysis suggests that the Huogeqi polymetal deposit belongs to hydrothermal modification deposits of hydrothermal sedimentary deposits stacked with hydrothermal alteration．

Key words: Cu polymetal deposit, hydrothermal sedimentary, hydrothermal modification , Huogeqi, Inner Mongolia