西藏列廷冈铁多金属矿床矽卡岩矿物学特征及其地质意义

西藏列廷冈铁多金属矿床位于冈底斯北缘弧背断隆带内,是近年来勘查评价的规模可达中型的接触交代矽卡岩型矿床。矿区矽卡岩主要呈层状、似层状,矽卡岩型铁多金属矿体赋存于下-中三叠统查曲浦组(T_(1-2)c)矽卡岩和大理岩中,矿体呈透镜状、囊状、似层状产出,矽卡岩矿物较发育。为进一步查明矿床矽卡岩矿物种属及矽卡岩类型,剖析矽卡岩形成环境及其与矿化类型之间的关系,基于对矽卡岩矿物系统的显微镜下观测,利用电子探针对矿床主要矽卡岩矿物化学成分进行了系统分析。矽卡岩矿物主要为石榴子石、透辉石、角闪石、绿帘石、绿泥石等,矿床矽卡岩具典型钙矽卡岩特征。根据矿物共生组合及交代关系推断成矿流体经历了5个阶段,分别为早期矽卡岩阶段、退化蚀变阶段、早期热液阶段、石英硫化物阶段和碳酸盐阶段。特征矿物的电子探针分析结果表明,石榴子石主要为钙铁榴石-钙铝榴石系列(And_(18.37~99.89)Gro_(0.24~79.05)Ura+Pyr+Spe_(0.98~6.63)),且发育环带结构;辉石主要为透辉石-钙铁辉石系列(Di_(53.56~99.91)Hd_(1.61~44.55)Jo_(0.08~5.11));角闪石主要为阳起石,次为铁、镁角闪石,均属钙质角闪石系列;绿泥石主要为富铁的铁镁绿泥石;绿帘石贫Fe、Mg。在矿床成矿演化过程中,其成矿环境是发生改变的,早期矽卡岩阶段到最晚期碳酸盐阶段,成矿环境至少经历了从高温、偏碱性的氧化环境到相对低温、偏酸性的还原环境的转变。

Mineralogical characteristics of skarn in Lietinggang iron polymetallic deposit, Tibet and their geological significance

Located in the arc back fault zone on the northern margin of Gangdise, the Lietinggang iron polymetallic deposit in Tibet is a medium-sized contact metamorphic skarn deposit discovered in recent years. The skarns are mainly stratified and stratoid. The skarn iron polymetallic orebodies that occur in the skarn and marble of Lower-Middle Triassic Chaqupu Formation (T_1-2c) are lenticular, chambered and stratoid in form. In order to identify the mineral types and skarn types and analyze the relationship between the metallogenic environment and the mineralization type of the skarns, the authors, based on systematic microscopic observation of the skarn minerals, utilized the electron microprobe to analyse the composition of major skarn minerals in this deposit. Skarn minerals mainly include garnet, diopside, hornblende, epidote, chlorite, etc., and the skarns have typical characteristics of calcium skarn. According to the association combination and replacement relationship of the minerals, the authors infer that the ore-forming fluids experienced five stages, i.e., early-skarn stage, degeneration-alteration stage, early-hydrothermal stage, quartz-sulfide stage and carbonation stage. According to the results of electron microprobe analysis, the garnets are mainly andradite-grossular (And_18.37~99.89Gro_0.24~79.05Ura+Pyr+Spe_0.98~6.63), and the garnets always develop the zoning structure; the pyroxene is of diopside-hedenbergite series (Di_53.56~99.91Hd_1.61~44.55Jo_0.08~5.11); amphiboles are mainly actinolite and iron-magnesium hornblende belonging exclusively to the series of calcium amphibole; chlorite is mainly iron-rich iron-magnesium chlorite; epidote is poor in Fe and Mg. During the ore-forming process, the ore-forming environment varied from early-skarn stage to late carbonation stage, and the ore-forming environment at least underwent the conversion from high temperature, alkaline, oxidized environment to relatively low temperature, acid, reductive environment.