| Zhilingtou gold deposit is located in the southwest of Shaoxing-Longquan Au-Ag, Cu, Pb-Zn, Mo metallogenic belt, which is the biggest gold deposit in Zhejiang province. Wall rock alterations are wide spread in this deposit. There is a close relationship between wall rock alteration and hydrothermal mineralization, thus, through wall rock alteration study we can interpret the mechanism of migration, enrichment and sediment of ore-forming material and clarify origin of deposit. Moreover, it plays an important role in mineral exploration. In this study, we collect some typical altered rocks and overlaying volcanic rocks in the Ⅴ and Ⅵ ore body in the western ore block, carry out geological and geochemical research on wall rock alteration, aiming at interpreting mineralization process, discussing origin of deposit, and providing reference to further prospecting in the depth and the periphery of the western ore block.The types of wall rock alterations include quartz, sericite, chlorite, pyrite, calcite and rhodochrosite alterations. According to cutting across relationship, the mineralization is divide into three stage:(1) Quartz-Pyrite-Au Stage,(2) Quartz-Rhodochrosite-Pyrite-Au Stage,(3)Quartz-Carbonatization Stage. The first two stages are main mineralization stage. From ore body to wall rock, the alteration zone can be divided into quartz-rich zone, beresitization with quartz zone, sericite zone and chlorite zone. In general, alteration degree fluctuates in the direction of ore body trending, which reflects that the ore body is in the shape of lenses. Gold mineralization is associated with quartz alteration, pyrite alteration and rhodochrosite alteration. Quartz alteration, pyrite alteration and rhodochrosite alteration degrees have a similar variation trend, which is opposite to that of sercite alteration and chlorite alteration. In addition, the distribution of calcite alteration is complex. Relation between alteration features and mineralization indicate that quartz alteration, pyrite alteration and rhodochrosite alteration are important sign for guiding ore prospecting in the depth and periphery area of ore district. In addition, rhodochrosite alteration is an indicator for rich ore. The volcanic rocks mainly developed calcite and pyrite alterations, which is similar to the alteration features of Pb-Zn mineralization of overlying Mesozoic volcanic rocks. Both gold mineralization and wall rock alteration emplace in the Paleoproterozoic metamorphic rocks of Badu group and do not enter overlying Mesozoic volcanic rocks, which indicate that formation of the deposit has no relationship with the Mesozoic volcanic activities.This paper summarized the characteristics of major and trace elements from altered rock and original rock. Results of elemental quantitative analysis show that Al2O3, Ti O2 and P2O5 are inactive components, Si O2, Ca O, Mn O, Au, Ag, Cu, Pb, Zn, etc. are gained and Fe2O3, Fe O, Mg O, K2 O, Na2 O, Ba, Sr, etc. are lost from the wall rocks in alteration process.Synthesizing the time-space distribution of alteration mineral and wall rock geochemistry characteristics, the author discuss the formation mechanism of alteration zone and deposit genesis, in addition, establish a pattern for wall rock alteration zonation. According to the alteration features and stable isotope analysis, we conclude that primitive hydrothermal ore-forming fluids of the deposit are mainly of magmatic water with enrichment in Si, Ca, Mn, Au, Ag, Cu, Pb, Zn, etc. and some meteoric water are added to the fluids in ore formation process. There may be concealed Yanshanian granite in the east of the mining area.On the basis of the above study, the thesis analyzes the potential for ore prospecting in Ⅵ ore body of the western ore block. Based on alteration types, spatial variation of alteration and the spacial distribution character of elements, we draw an conclusion that there is a certain prospecting potential below 140 level of the Ⅵ ore body. |
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