Research On Mineralization Of The Lizhu Fe Polymetallic Ore Field, Zhejiang Province, China

Lizhu iron polymetallic ore field is located in the north eastern end of the Qinhang junction, which is between Yangtze and Huaxia plate, and on the northwestern side of the Jiangshan-Shaoxin discordogenic fault. The mine field is a typical skarn Fe-Mo-Cu-Pb-Zn polymetallic ore field. In this district, mines resource is lack, with the years of development of Lizhu (Mo) polymetallic deposits. To guide further exploration work, the mine belongs to severe crisis mine, and needs to carry out systematic research about the mineralization. Therefore, in full summarizing and analysis on the basis of predecessors’ achievements, through the field geological investigation, indoor analysis and test methods, guiding with the basic theory of geochemistry, mineralogy, mineral deposit geology, it makes comprehensive study on the mineralogical characteristics, fluid inclusions geology, ore and rock geochemistry, and geochronology in this paper, which is intended to clarify the basic issues of the metallogenesis problems in Lizhu iron deposit, and ultimately build a "trinity model" of geological prospecting prediction.After the research of ore deposits and regional magmatic rocks chronology, it is showed that the mineralizing age of Lizhu iron is 146.59±0.81Ma; the intrusive age of Guangshan granite is 162Ma-147Ma; the intrusive age of Shanxi granodiorite is 152Ma-150Ma. Lu-Hf isotopic analysis results showed that Guangshan granite and Shanxi granodiorite are not homologous, although the intrusive ages of them are relatively similar.The results of fluid inclusion, stable isotopes and REE study indicate that the ore-forming materials source of magnetite and molybdenite in Lizhu magnetite iron ore deposit is magma. Ore-forming hydrothermal is mainly magmatic hydrothermal, As the deposit was forming, more and more meteoric water mixed into the ore-forming fluid. The ore-forming hydrothermal has the characteristics of high temperature, low salinity and medium-density. Along with the metallogenic process, the fluid temperature and salinity of ore-forming hydrothermal was gradually decreased.The metallogenic mechanism research of the "Silicon-Calcium surface" of Lizhu iron deposit shows that, the internal mineralization mechanism of "Silicon-Calcium surface" is Dengying siliceous rocks intercalated impure carbonate rocks of the group provides a material suitable for formation of the ore-forming hydrothermal precipitation or transform conditions of acid and alkaline. External conditions embodied in the "calcium" mass of rock on either side of the interface and "silicon" qualitative property difference of rock. Physical differences result the formation of interlaminar fracture in different lithology interface, and constitute the precipitation of ore-forming hydrothermal migration and the ore-forming material benefit space. In addition, chert can play a role "barrier", blocking ore-bearing hydrothermal flow, thus in siliceous rocks of lateral migration, enrichment and precipitation of mineralization.Finally, This article constructed the "trinity model" of geological prospecting prediction,while identified that the metallogenic geological body of Lizhu iron deposit was the late fine-grained granite of Guangshan Granitic complex, and Shanxi granodiorite body was the metallogenic geological body of Huangyoutang copper polymetallic deposits. This article also described the controlling role of the region tectonic, folds and faults for the formation of the ore body, summarized the characteristic symbol of mineralization. It was considered that the alteration features in alkali metasomatism stage was the decolourization of fine-grained granite causing by sodium modification; a mass of high temperature skarn minerals such as andradite, diopside indicatd the pre-mineralization alteration, and phlogopite, epidote, chlorite formed in late skarn stages indicated a alkaline and oxide mineralization environment, signed for the mineralization characteristics of mineral.