The Hongniu deposit is a newly discovered skarn type copper deposit in Geza volcanic-magmatic arc which is located in the southern part of Yidun island arc. Its copper reserves have reached the large size. Distinctly different from the typical skarn deposits its skarn and hornfels usually arranged alternately, consisting with the attitude of stratum. Skarn is not in direct contact with the intrusive rocks but direct contact with the marble. There are coarse garnet and wollastonite visible in the marble. While, there also have marble xenoliths in the skarn. Therefore, the Hongniu copper deposit is the product of concealed intrusive rocks, belonging to the distal skarn type. According to the combination of skarn minerals, the skarn type can be divided into garnet skarn, garnet-diopside (or diopside-garnet) skarn, diopside skarn, idocrase-garnet skarn, wollastonite-garnet skarn, epidote-garnet skarn, actinolite-epidote skarn, wollastonite skarn and epidote skarn. Among these types, the garnet skarn, diopside skarn and wollastonite skarn are the most common. Garnet is the most important skarn mineral in the Hongniu deposit, and it is therefore significant to study characteristics of garnet due to its wide distribution, various colors and strong mineralization. Through systematic field work and the made-up of drill holes (0ZK10, 3ZK11 and 7ZK16), the paper summarizes the garnet distribution in space and mineralized characteristics in Hongniu deposit, collecting some fresh garnet skarn and a small amount of skarnized marble to make thin sections, and carrying out detailed microscopic identification, to induce the characteristics of garnet including color, shape, structure, petrography, and analyzed its chemical composition by electron probe. Garnet has two obvious stages. Early garnets are widely distributed, brown-red to brown, hypidiomorphic-idiomorphic medium grained texture, with anomalous optical characteristics on the cross-polarized light, and their particle size is generally between 0. 2 similar to 4mm, developing zonation patterns. Changes in the content scope of the SiO2 is 35. 18% similar to 37. 69%, CaO is 33. 34% similar to 36. 35%, Al2O3 is 3. 64% similar to 13. 69%, FeO is 11. 90% similar to 24. 18%, MgO is 0. 00% similar to 0. 08%, and there is a negative correlation between the content of FeO and Al2O3, while an overall positive correlation between the content of SiO2 and CaO. The end members of garnet are mainly andradite (36. 88% similar to 82. 36%), followed by grossular (16. 59% similar to 60. 75%), and there are a small number of pyrope,. almandine and spessartine, belonging to andradite-grossular series (And(37-82) Gro(17-61) Spe + Pyr + Alm(0.33-3.71)). The garnets of later stage are brownish to light red, usually veinlike distributed in skarnized hornfels and marble, also can be seen in some kinds of skarn, with hypidiomorphic-xenomorphic granular structure. Changes in the content scope of the SiO2 is 35. 06% similar to 36. 27%, CaO is 33. 07% similar to 33. 77%, Al2O3 is 0. 04% similar to 1. 05%, FeO is 27. 38% similar to 28. 18%, MgO is 0. 00% similar to 0. 04%, the composition of end members belongs to andradite. Changes in contents of major elements in zoned garnet shows a certain regularity, from the core to the rim, the content of FeO increased, the content of Al2O3 decreased, the content of andradite increased, the content of grossular decreased, reflecting the diagenetic environment was acidic and reduced with low oxygen fugacity when the garnet began to form. During the process of the crystal formation, the oxygen fugacity increased, and the ore-forming solution shifted from acidic to weakly alkaline, causing the precipitation of metal sulfide. Chalcopyrite, pyrrhotite, molybdenite usually fill between garnet grains, or form veinlets in the cracks of crystal, or replace along the garnet growth zoning surface, showing that the garnets form prior to the mineralization of copper and can provi

红牛矽卡岩型铜矿床是义敦岛弧南段格咱火山-岩浆弧新探明的铜矿床之一，目前探明铜金属资源量已达大型规模。与由侵入岩和大理岩直接接触形成的典型矽卡岩矿床不同，红牛铜矿床是隐伏岩体远程矽卡岩化的产物，其矽卡岩矿体与地层产状基本一致，通常相间排列，且距离岩体较远，大理岩中可见粗粒石榴子石和硅灰石，矽卡岩中常见大理岩捕掳体。根据矽卡岩矿物组合可将该矿床矽卡岩类型划分为石榴子石矽卡岩、石榴子石透辉石（或透辉石石榴子石）矽卡岩、透辉石矽卡岩、符山石-石榴子石矽卡岩、硅灰石-石榴子石矽卡岩、绿帘石-石榴子石矽卡岩、阳起石-绿帘石矽卡岩、硅灰石矽卡岩和绿帘石矽卡岩，其中以石榴子石矽卡岩、透辉石矽卡岩和硅灰石矽卡岩为主。石榴子石是最重要的矽卡岩矿物，分布广泛、颜色变化大，且石榴子石矽卡岩中黄铜矿、黄铁矿、磁黄铁矿化最好。本文通过对0ZK10、3ZK11和7ZK16钻孔岩芯的地质编录，查明石榴子石在红牛铜矿床的空间分布和矿化特征，采集该矿区新鲜的石榴子石矽卡岩、矽卡岩化大理岩和角岩磨制成光薄片，开展详细的显微镜下鉴定工作，观察石榴子石的颜色、粒度、结构、光性等岩相学特征，并通过电子探针分析其化学成分。红牛铜矿床石榴子石集中产出于矽卡岩中，少量产出于矽卡岩化大理岩和角岩中，具有明显的两期。早期石榴子石分布广泛，多呈褐色-红褐色，非均质性，异常干涉色，粒径一般在0.2~4mm之间，半自形-自形中细粒结构，韵律环带发育。SiO 2 含量变化范围为35.18%~37.69%、CaO为33.34%~36.35%、Al 2 O 3 为3.64%~13.69%、FeO为11.90%~24.18%、MgO为0.00%~0.08%，FeO和Al 2 O 3 含量变化呈负相关，SiO 2 和CaO含量变化整体呈正相关。石榴子石端员组分总体以钙铁榴石（36.88%~82.36%）为主，其次为钙铝榴石（16.59%~60.75%），还有少量的镁铝榴石、铁铝榴石和锰铝榴石，属于钙铁榴石-钙铝榴石系列（And 37-82 Gro 17-61 Spe+Pyr+Alm 0.33-3.71 ）。晚期石榴子石呈浅褐色-浅红色，多发育于矽卡岩化角岩和大理岩中，少量发育于矽卡岩中，半自形-他形粒状结构，均质性，全消光，常具有溶蚀结构。SiO 2 含量变化范围为35.06%~36.27%、CaO为33.07%~33.77%、Al 2 O 3 为0.04%~1.05%、FeO为27.38%~28.18%、MgO为0.00%~0.04%，属于钙铁榴石（94.42%~98.46%）。早期石榴子石韵律环带发育，其主量元素含量变化显示出一定的规律性，由核部向边缘，SiO 2 和CaO基本保持不变，FeO含量增加，Al 2 O 3 含量减少，钙铁榴石含量增加，钙铝榴石含量减少，反映在石榴子石形成早期，成岩环境为低氧逸度、酸性还原环境；形成过程中氧逸度增加，成矿溶液由酸性向弱碱性演化。黄铜矿、磁黄铁矿、辉钼矿等金属硫化物多呈他形充填于石榴子石颗粒之间，或在石榴子石的裂隙中形成细脉，或沿石榴子石生长环带面交代，表明石榴子石形成于矽卡岩早期、早于铜矿化，并为金属硫化物的沉淀富集提供了空间。

Garnet as one of the most typical and important skarn minerals in the Jiama super-large copper polymetallic deposit, Tibet, is a key point for study of skarn due to its wide distribution, various colours and strong mineralization. Through the numerous geological logging of rock/ore core and photo on its colour, crystal shape, mineral assemblage, mineralization, the feature of spatial distribution, mineralization, mineralogy and chemical composition of garnet have been concluded combined with the identification under microscope and electron probe analysis. Garnet in Jiama concentrates in the skarn and few in the hornfels, marble and porphyry close to the skarn. Garnet at Jiama is the andradite-grossularite series and andradite is the major garnet. There are colour and compostion zonations in garnet and it’s partially isotropic due to optical anomaly. The content of SiO2 and Al2O3 of the darker zones are higher than those of the lighter zones, whereas the TFeO content is opposite. Garnet formed at the earlier stage of skarnization, which is favorable for precipitation of sulfides of Cu, Mo, Pb, Zn, Au and Ag mineralization later. The features of mineralogy, component, REE, fluid inclusion and H-O isotope of garnet indicate its contact metasomatism genesis. Therefore, the Jiama ore deposit is a typical magma-derived hydrothermal contact metasomatism skarn type copper polymetallic deposit.

石石榴子石是西藏甲玛超大型铜多金属矿床的主要矽卡岩矿物，分布广、颜色变化大，石榴子石矽卡岩中矿化好，是开展甲玛矽卡岩成因研究的一个重要切入点。通过对甲玛矿区大量岩矿心的地质编录，归纳石榴子石的颜色、晶形、矿物组合、矿化等地质现象，总结石榴子石在甲玛矿床的空间分布、矿化特征等，结合显微镜下鉴定，分析石榴子石的矿物学特征，并通过电子探针分析其化学成分。甲玛石榴子石集中于矽卡岩中，少量分布于角岩、大理岩和斑岩中。石榴子石为钙铁-钙铝榴石系列，以钙铁榴石为主，发育颜色与成分环带，光性异常致部分非均质。深色环带的SiO2、Al2O3含量较浅色环带高，而TFeO含量相反。石榴子石形成于矽卡岩早期，为晚期Cu、Mo、Pb、Zn、Au、Ag等多金属硫化物沉淀富集提供了有利空间。甲玛石榴子石的矿物学特征、化学成分组成、REE特征、流体包裹体、H-O同位素特征等显示其属于接触交代成因，认为甲玛是典型的岩浆热液接触交代矽卡岩型铜多金属矿床。