【作者】 招湛杰；

【导师】 陆建军；

【作者基本信息】 南京大学 ， 矿物学岩石学矿床学， 2011， 硕士

【摘要】 湘南白腊水矿床属绿泥石化花岗岩型锡矿,是近年来新发现的一种矿床类型。该矿床属芙蓉锡矿田,矿田的锡储量达60多万吨,其中90%以上的锡集中在白腊水矿床。矿床的绿泥石化与锡矿化关系密切,矿体产于强烈绿泥石化的花岗岩体内。研究表明,白腊水矿床与骑田岭多阶段花岗岩体的演化有关。该花岗岩体在不同阶段的演化过程中表现出一系列不同的地球化学特征,花岗岩中的Sn含量有随结晶分异程度的增加而减少的趋势,这可能与岩浆体系演化过程中氧逸度的降低有关。绿泥石的研究显示,绿泥石对花岗岩造岩矿物的交代顺序为：从角闪石、黑云母→斜长石、钾长石→石英；绿泥石形态特征的变化一方面与绿泥石化学成分的不同有关,另一方面与被绿泥石交代的花岗岩造岩矿物晶体结构有关；花岗岩的绿泥石交代作用越强烈,全岩的烧失量和Zn含量就越高,原岩的Cl丢失到蚀变流体中去的量也越多；绿泥石的Si含量在绿泥石交代过程中逐渐减少；长石遭受破坏溶解后释放出的Al在厘米尺度范围内发生迁移与再分配,引起绿泥石Al含量的升高；Fe从热液中带入,蚀变花岗岩中绿泥石矿物含量的多少与水-岩反应体系中Fe的多少有关；形成绿泥石所需的Mg主要来源于花岗岩暗色矿物内Mg的释放与再分配；Mn主要由外部流体带入；绿泥石化学成分特征的变化反映蚀变流体具有酸性、还原性的特征。流体包裹体的研究表明,成矿流体来源于高温高盐度的岩浆分异流体,成矿过程中有大量低温低盐度大气降水加入。富锡的岩浆分异流体与大气降水混合(可能还伴有压力的释放)而发生沸腾作用,从而导致锡矿的沉淀。成矿温度在280℃～420℃范围内,属中高温热液型矿床。根据上述花岗岩地球化学、绿泥石和成矿流体的特征,认为绿泥石化花岗岩型锡矿的最终形成,与具有高温、富含挥发份(H2O、CO2)、富K+、Na+、Cl-离子、呈酸性和还原性特征的热液流体引起的Sn、Fe的富集和迁移有关。这种热液流体与大气降水以及围岩发生反应,引起体系氧逸度、酸碱度和温度的变化,导致绿泥石的交代与锡矿的沉淀同时进行,最终形成绿泥石化花岗岩型锡矿。在南岭地区应注意在含锡钨花岗岩中寻找此类型锡矿。更多还原

【Abstract】 Bailashui tin deposit named chloritized granite type tin deposit is a new type deposit which was found in recent years in southern Hunan province.The deposit is located in Furong tin ore field which reserves more than 60 million tons of tin.More than 90% tin reserves of this ore field is concentrated in Bailashui tin deposit,which is closely related to the chloritization.The orebody occurs in the strong chloritization granite.This research indicates that Bailashui tin deposit is associated with the evolution of Qitianling multi-stage composite batholith.The granites in different stages of evolution show a range of different geochemical characteristics.The Sn content in the granite and the degree of fractional crystallization are negatively correlated,that may be related to the decreasing oxygen fugacity in the process of magmatic evolution.The study of chlorite shows that, the sequence of rock-forming minerals of the granite replaced by chlorite is:from amphibole and biotite to plagioclase and potassium feldspar,then to quartz.The variations of the chlorite shape were, on the one hand, related to the change of chlorite composition, on the other hand, related to the crystal texture of rock-forming minerals of the granite which were replaced by chlorite.The stronger the chloritization of granite was, the higher the LOI and Zn contents of whole-rock sample were.And also more Cl was lost from granite into hydrothermal liquid.The Si content of chlorite was decreasing with the increasing degree of chloritization.The Al content was released after the alteration of feldspar. The mobilization and redistribution of Al on the thin-section scale caused the Al content of chlorite increased.Fe was brought in by hydrothermal fluid.The amounts of chlorite formed are largely a function of how much Fe has been introduced into the hydrothermal system.The Mg needed for the formation of chlorite were primarily related to the redistribution of Mg which were released by mafic minerals.The Mn of chlorite was mainly brought in by the outer hydrothermal fluid.The changes of chlorite chemical composition characteristics reflect that the alteration fluid was acidic and reductive. Study on fluid inclusion shows that the ore-forming fluid was derived from high temperature and high salinity magmatic fluid during magmatic differentiation.In the process of mineralizing,a lot of low temperature and low salinity meteoric water had been brought in.The mixing of the tin-rich magmatic fluid and the meteoric water (possibly accompanied by the release of pressure)led to the boiling, which resulted in the precipitation of tin.The ore-forming temperature is in the range of 280℃to 420℃.This tin deposit belongs to medium-high temperature hydrothermal deposit.According to the features of granite geochemistry,chlorite and ore-forming fluid,we can got some conclusions:the forming of chloritized granite type tin deposit in Bailashui is related to the enrichment and migration of Sn and Fe introduced by hydrothermal fluids.The hydrothermal fluids have the characteristics of high tempera-ture, rich in volatiles (H2O, CO2), K+, Na+, Cl-,acidic and reductive.When the hydrothermal fluids reacted with the meteoric water and wall rock, the oxygen fugacity, pH and temperature in the system would changed,and then the chloritization and cassiterite precipitation were simultaneously occurred, which led to the forming of chloritized granite type tin deposit.An attention to searching for this type tin deposit in W-Sn-bearing granites in the Nanling Range should be especially paid.更多还原