| Lying in the northern margin of the middle section of Nanling metallogenic belt,Huangshaping lead-zinc deposit is a skarn type in Hunan province. Many scholarshave paid attention to it for its rich types; however, the researches about its diageneticand metallogenic depths have much differences in results. Based on former studies,this paper is focused on the depth study of the deposit which has been given a littleattention to and is in most controversial condition. By comparing geobarometers ofvarious types, a reasonable data for diagenetic and metallogenic depths ofHuangshaping deposit will be reached to provide theoretical foundation to deepprospecting and deep prediction.Through systematically analyzing geological characteristics of Huangshapingdeposit in Hunan province, its diagenetic and metallogenic depths are studied by usinggranite geobarometer, sphalerite geobarometer and fluid inclusion geobarometerrespectively. After comparison and analysis, the results as followed:(1) Rock related to the mineralization of this deposit has gone throughself-alteration in the forming, which leads to the changes of rock composition. As thesilicification is common for rock in its change, the calculated results of metallogenicdepth measured by granite geobarometer are low. Besides, there are some defects ofgranite geobarometer, such as the percentage of volatile matter in granite should notbe high and the mineral content, obtained according to CIPW theoretical formula, isnot accurate enough. Thus, this result is only counted as a semi-quantitative one. Inthe paper, the experiment results for relative diagenetic and metallogenic depths ofthree kinds of rocks in the Huangshaping deposit are extremely consistent with theactual geological phenomenon there. From this perspective, the methods used in thepaper have some reference value.(2) For sphalerite geobarometer, there are more requirements for experimentalconditions. At first, whether sphalerite, pyrite and pyrrhotite inter-grew and thenwhether the pyrrhotite is hexa-pyrrhotite should be clear known. As the percentage of each element has been changing from the inner part to marginal part throughout theprocess of the mine’s formation, even results of the same mineral particle measuredby EMPA would be different in different conditions. Because of characteristics of thismine’s formation, the results calculated from the same sample differ greatly.Therefore, the formulas, proposed by L T Bryndzia&SD Scott（1990） andHutchimon&Scott (1981) which have their own advantages, will be applied inaccordance with the actual situation. Based on the real geological phenomenon, areasonable result will be reached.(3) Pressure calculation of fluid inclusion has the advantage of being moreaccurate besides having well-developed theories. Since the fluid inclusion is sensitiveto pressure, changes of fluid inclusion during the structural deformation in post-oreperiod influence its temperature-measuring and calculation. However, throughpetrographical and statistics analysis, a proper pressure would be determined in theconsideration of actual geological condition.(4) On the basis of geological phenomenon and with the help of granitegeobarometer, diagenetic pressure of rock body in the Huangshaping deposit is0.7—1.5Kb, metallogenic pressure of the sphalerite is0.45—0.69kb and the formingpressure of high-salinity fluid inclusion in silica is0.8—1.5Kb. By the considerationof lithostatic pressure and pressure gradient of270bar/km, the diagenetic depth ofHuangshaping deposit is2.6—5.5Km and metallogenic depth of sphalerite is1.7—2.5Km. However, the metallogenic depth of the whole deposit in Huangshapingtown should be1.7—3Km, because molybdenite and scheelite in skarn, under thesphalerite, might have been mineralized. |
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