Studies On Geological-geochemical Characteristics Of The Budunhua Copper Deposit In Xinganmeng, Inner Mongolia

The Budunhua Copper deposit of Inner Mongolia's Xinganmeng is located on the southeast margin of the middle of Daxinganling; this region is one of the important copper metallogenic belt. The mine has been built to +70 m elevation extraction from 1970 so far, although this mine has been exploited for many years, little research has been conducted in the metallogenic regularity and minerallizition characteristics of this mine. In this paper, the author through the detailed research work by outdoor&indoor with the geological characteristics and the minerallizition conditions of this deposit, trying to conduct more in-depth explored in the field of the geological background, ore-bearing rock characteristics, deposit geology, geochemistry and genesis of this deposit, which is in order to lay a foundation for the deposit's deep and surrounding prediction and evaluation of hidden ore bodies. According to comprehensive analysis, the ahthor obtained the following understanding to Budunhua copper deposit:(1) Regional tectonic setting and its evolution history are introduced briefly, the author point out that the structural intersection part of the EW direction and NE direction control the output of this deposit, whose sub-structural units are ore-bearing structures, and the copper ore bodies are located on the sub-structural units of the NE trending structures.(2) The ore deposit alteration zoning characteristics are described, co-existing ore minerals and ore texture and structure also are studied in detail. The study found that the mining area in addition to the typical altered rocks of porphyry-type alteration, there is its particularity, that is between the K zone and sericite alteration zone; a silici-tourmaline zone is found.(3) The geochemistry of intrusive rocks such as plagioclase granite porphyry and diorite porphyry which is related to the mineral formation is discussed in detail,and this samples are also selected for SHRIMP U-Pb age dating.In conclusion, the rock is alkalineⅠ-type granite, which is rich in Mo, Sn, Cu, Pb, Zn, Ag and other trace elements, probably forming the heat source and mineral resources; the zircon grains separated from the sample give a weighted mean 206Pb/238U age of 152.6Ma, as the first accurate determination of this region's rock age, it should be able to exist as a useful complement for the large scale in eastern China--the Jurassic porphyry and porphyry-skarn copper-molybdenum mine in the second stage of Late Jurassic-Early Cretaceous porphyry-skarn Cu-Mo deposits.(4) It is found that the main copper ore bodies develop in the fine-grained sandstone, siltstone of lower Permian which have good degree of porosity. Through the analysis of its trace element, we can see that Cu, Zn, Pb, Ag, Sn have different levels of enrichment in the metamorphic siltstone. In virtue of sandstone itself has good degree of porosity and fracture, in the role of hydrothermal circulation, the stratum itself can provide ore-forming elements; in the latter part of the hydrothermal circulation system,the sandstone is also conducive to bring out into the elements, thus providing some or major ore mineral for mineralization, under favorable conditions in the structure, it also provides the necessary solution for the mineral ore space.(5) A series petrographic and microthermometric studies on fluid inclusions (FI) in various kinds of ore rocks from the Budunhua copper deposit have been carried out in this thesis. The results show that the homogenization temperatures of FI are mainly in ranges of 100～470℃, and salinity ranges from 3.39%～66.75%; there are abundant FI in the quartz, and they have group distribution characteristics.Three types of fluid inclusions have been commonly observed. They are rich liquid, gas and salt crystal (daughter mineral-bearing).The range of gas-liquid ratio is large--from 3% to 95%. The phenomenon that Low gas-liquid ratio, high gas-liquid ratio, low salinity and high salinity of fluid inclusions coexist is very prevalent. In addition, from the histograms of temperature and salinity,we take notice of that the values of the temperature and salinity ranges are not only wide, but also have a number of peaks, indicating that there shoule be a multi-stage mineralization.(6) Based on the discussions stated above, we consider that the Lower Permian strata is the material basis for mineralization,and the magmatic intrusion of Yanshanian movements is the key to ore-forming. Budunhua copper deposit is suggested to be categorized in the porphyry copper type.