Geological Features And Metallogenic Fluid Study Of Fluorite Deposit In Songyang, Zhejiang

Nearly80%fluorite deposits in Zhejiang are located in the fault belts, southeastZhejiang. Metallogenic conditions and regularities about the fluorite deposits in this areaarise great interests among scholars at home, and some stage achivements have beenobtained. But different opinions on the source of metallogenic materials, source ofhydrothermal heat and selection of ore-bearing host rocks in fluorite deposit still exist. Inrecent years, a new fluorite mineralized point has been discovered in Yuyan area,Songyang county, Zhejiang. Its metallogenic environment is quite typical, and during theinitial work, the author found that many advantageous metallogenic factors are focused in arather small area. Thus, the study of which will definitely exert great influence on thefluorite deposit researches and prospecting work in this area or even on the southeast ofZhejiang.On the basis of former researches, this paper takes the example of fluorite deposit inYuyan area, Songyang county. By doing large-scale geological mapping, field geologicalsurvey, prospecting and measurement, and with the application of observation undermicroscope and EMPA, this paper analyzes the geological features of the deposit; and byapplying temperature measurement of inclusions, this paper conducts the research ofmetallogenic fluids, studies some physical and chemical features of the metallogenic fluids,which will provide references for further reseaches in this area. Several thoughts have beenobtained from this study as followings:(1) The fluid inclusion study of fluorite shows that the homotemperatures of theinclusions vary in the range of126-314℃, and mostly in175-225℃, which is the majormetallogenic temperature of the fluorite deposits in this area; and by calculating thehomogenization pressure of inclusions, the metallogenic depth of this fluorite deposit is0.1～1.4km, which indicates that the deposit is an epithermal one;(2)By applying the freezing point temperature measurement, the salinity of inclusionsare mainly between0.17～9.3wt%, which indicates that salinity of the metallogenic fluidsis quite low, reflecting the hydrothermal fluids are nonsaline and ore-bearing; (3) By analyzing the homotemperatures and density values of the inclusions, theauthor believes fluorite ore-forming in Yuyan area is more than two stages, the fabric ofores at Zhimu and Yangkeng mineralized zones also reflects the characteristics ofmulti-stages;(4) F、Ca minerals in fluorite are not from the wallrocks, but rather from hydrothermalleaching of the metamorphic rocks basement. From the perspective of diversity ofwallrocks in this deposit, ore-forming has no selectivity with the wallrocks. The faultsformed by the collapse of volcanic depression in Yanshannian serve as the transportationchannel and ore host space for the ore-bearing hydrothermal, and fluorite can become oreafter precipitation in these fault interstice. Thus, in prospecting this kind of deposit cannotonly depend on the features of host rocks;(5) The fluorite deposits in this area is fluorite-quartz type. After observing oresamples in three ore districts by microscope, the author discovers its crystallizationregularities has a feature of fluorite crystalling in the first, quartz and chalcedony in thenext. The late precipitation of quartz develops strong silification around the orebody andbecomes a silicified cap. All the above can be acted as prospecting criteria.