The Huanggang Sn-Fe deposit is a large-size skarn deposit hosted by Lower Permian marble of Huanggangliang Formation.Its skarn mineral assemblage mainly consists of diopside, andradite-grossular and vesuvianite, and its retrograde minerals include actinolite-tremolite, epidote, chlorite, sericite, grossular etc.Electron microprobe analyses show that the end member of garnet in the early stage is dominated by andradite, while that in the major ore-forming stage is dominated by grossular, and that the end member of pyroxene has changed greatly, composed mainly of diopside and hedenbergite.Components of garnet and pyroxene are Adr28.69～96.44 Grs2.00～67.38(Prp + Sps)0.67～5.69 and Di11.8～94.12Hd4.08～81.28Jo1.79～20.02, respectively, their wide compositional variation range suggests that skarns were not formed under the totally enclosed equilibrium condition.The amphiboles mostly belong to magnesium-ferric-calcium amphibole, with only some individuals being ferric-hornblende.The relatively remarkable change of composition is probably attributed to the change of redox conditions resulting in different degrees of AlⅥ Si←→(Na, K) displacement, which belongs to the transforming tendency under solidus.Tetrahedral Si, Al, octahedral Al, Ti and cations in A site of amphibole change greatly, which may be caused by the composition difference of the magma in the contact metasomatic process or the change of physicochemical condition during crystallization.Electron microprobe analysis shows that the early skarns in Huanggang belong to the typical oxidation type, while the late skarns transfer to the reduction type.From the viewpoint of mineral assemblages, the skam assemblage in this area is similar to the calcareous skarn formation.Composition characteristics of skarns in the Huanggang Sn-Fe deposit are similar to those of Cu-Fe deposits of calcareous-magnesian skarn formation, while the altered mineral assemblage is close to W-Sn deposits of the calcareous skarn formation, indicating a new skarn formation.Massive intrusion of granitic magma brought a lot of metallogenic materials and heat energy needed for mineralization.In addition, the well developed faults in the Huanggang ore district also provide a channel for fluid migration.A lot of laminar skarn ores are developed in this area, and as this uniform banded structure cannot be observed in peripheral marbles, these laminar rocks seemed to be a self-organization phenomenon in the process of metasomatism and were not formed by sedimentary-exhalation.Mn/Fe ratios of pyroxenes in the Huanggang ore district range from 0.15 to 0.44, suggesting that the possibility of finding polymetallic mineralization in this area.The johannsenite in pyroxene changes remarkably in composition, and its content ranges from 1.79％ to 20.02％.There is no Mn in the marble of Huanggangliang Formation of the ore-bearing strata in the Huanggang Sn-Fe ore district, and the possibility of the derivation of Mn from the strata is very small.In contrast, the pyroxenes are Mn-enriched in the stratiform ore body away from the contact zones or ore bodies containing no Mn.MnO content (0.02％ ～0.05％) in Huanggang granites is significantly lower than the average content of MnO (0.07％) in A-type granite, and there exist no Mn-enriched accessory minerals such as ilmenite, indicating that there might have been the participation of some Mn composition of granitic magma in the skarn due to contact metasomatism.Therefore, the Mn-enriched pyroxenes probably resulted from the evolution of Mesozoic magmatic fluid, and Mn-enriched pyroxene skarns were formed by infiltration metasomatism of magmatic fluid along fracture zones between layers.These phenomena are similar to things of the skarn Pb-Zn deposits in central Fujian Province.Mn-rich pyroxene might serve as the indications for Sn, Cu, Zn and many other metallic ores in this area, and the outer contact zone of skarn and its periphral marble seem to be favorable positions for polymetallic mineralization.%为进一步查明黄岗锡铁矿矿床成因、夕卡岩矿物成分与金属矿化类型之间的联系,利用电子探针对研究区主要夕卡岩矿物的化学成分进行了详细的分析.测试结果表明,成矿早期石榴石的端员组分以钙铁榴石为主,主成矿期石榴石的端员组分以钙铝榴石为主;辉石端员组分变化较大,主要为透辉石和钙铁辉石.石榴石和辉石的矿物组分分别为 Adr28.69～96.44Grs2.00～67.38(Prp+Sps)0.67～5.69和 Di11.8～94.12Hd4.08～81.28Jo1.79～20.02,其较大的成分变化特征反映出夕卡岩不是在一个完全封闭的平衡条件下形成的.角闪石大多为镁铁钙角闪石,个别属于铁角闪石,成分变化较大的原因可能是由于氧化还原条件改变导致不同程度的 AlⅥSi←→(Na,K)的置换作用,属于一种固相线下的转变.角闪石中四次配位的 Si、Al及六次配位的Al、Ti 和 A 位置的阳离子数变化范围很大,可能是由于接触交代作用过程中岩浆的成分差异或结晶时的物理化学条件改变所引起的.富锰的辉石夕卡岩是岩浆流体顺层间破碎带渗滤交代形成的,富锰辉石可作为本区寻找Sn、Cu、Zn 等多金属的找矿标志,外接触带夕卡岩和其附近的大理岩中是多金属成矿的有利部位.
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