西藏冈底斯成矿带浅成低温热液型金锑矿床的发现及其意义——以西藏弄如日金锑矿床为例

Discovery of epithermal Au-Sb deposits in Gangdese metallogenic belt of Tibet and its significance: Case study of Longruri Au-Sb deposit

通过化探、槽探和平硐等手段,对位于冈底斯成矿带东段的弄如日金矿床进行了评价和研究,在矿区发现金矿化带4条,圈出金矿体5个,控制2.3g/t品位以上的金资源量(333+3341)为2.97t,确定该矿床属典型的浅成中低温热液型金矿床。矿区的金矿体赋存于破碎蚀变角岩和蚀变二长花岗斑岩中,受南北向正断裂系统的控制,矿化以金为主,伴有辉锑矿、雄黄、黄铁矿等矿物,可分为浅成低温热液和表生氧化2个成矿期,金可能以独立的自然金状态存在于脉石矿物的粒间或裂隙中。弄如日金矿床形成于伸展构造背景,在空间上居斑岩铜矿床外围,成矿时代为中新世—上新世,与冈底斯斑岩型铜钼矿床及其外围的矽卡岩型铅锌矿床的成矿时代基本一致,说明三者受统一的成矿作用制约,属斑岩岩浆_热液成矿系统中的浅成低温热液型金锑矿床。

Situated in Mozhugumgga County of Tibet, the Longruri Au-Sb deposit is the first epithermal Au-Sb deposit discovered in eastern Gangdese metallogenic belt. The confirmed （333 ＋ 3341 ） Au reserves are 2.97t with the grade varying form 2.3 g/t to 18.7 g/t. Five gold ore bodies were found in shattered and altered hornfels and monzonitic granite-porphyry, controlled by the NS-striking normal fault system. The mineral assemblage of the ore includes gold, stibnite, realgar, pyrite, quartz, feldspar, sericite, kaolinite, etc. The ore-forming process of the Longruri gold deposit can be divided into two stages, namely the early epithermal stage and the late oxidation-leaching stage. According to an analysis of the regional ore-control structures and the K-Ar dating data from the altered monzonitic granite-porphyry, the authors hold that the early epithermal stage in the Longruri Au-Sb deposit occurred from Miocene to Pliocene, consistent with the ore-forming epochs of porphyry copper ore deposits in adjacent regions. The Longruri Au-Sb deposit is situated on the outskirts of porphyry copper ore deposits and skarn polymetallic copper deposits. This suggests that the Longruri epithermal Au-Sb deposit, the skarn polymetallic copper deposits, and the porphyry copper ore deposits were formed in the same magma-fluid mineralization system controlled by an extensional dynamic setting in the Gangdese belt. The exploration achievements indicate that the Longruri Au-Sb deposit has further gold potential, and the Gangdese metallogenic belt is a potential ore belt which is likely not only to have abundant porphyry type copper-molybdenum, highgrade iron, and silver-bearing polymetallic deposits but also to possess rich epithermal gold and antimony deposits