甘肃北山红尖兵山钨矿床地质特征及成矿物质来源

Geological Features and Ore-forming Material Sources of Hongjianbingshan Tungsten Deposit in Beishan Mountain, Gansu Province

对甘肃北山红尖兵山钨矿床地质特征进行了总结 ,同时 ,对代表性钨矿石样品中的黑钨矿进行了Sm_Nd同位素测定。研究表明 ,红尖兵山钨矿床的矿化类型大体可划分为云英岩型和黄玉_石英脉型。钨矿化的发生时间为海西期 (3 2 2～ 2 60Ma) ,其中云英岩型钨矿石的形成时代略早于黄玉_石英脉型矿石。云英岩型钨矿石中 2件黑钨矿样品的εNd(3 2 2Ma)值分别为 5.93和 4.2 4,与同时期亏损地幔钕同位素演化线值接近。相比之下 ,黄玉_石英脉型钨矿石中 5件黑钨矿样品的εNd(3 2 2Ma)值变化范围为 -4.16～ -8.0 5,与同时期古大陆壳钕同位素演化线值相似。云英岩型钨矿石的形成作用与亏损地幔源岩浆活动有关 ,而黄玉_石英脉型钨矿石则很可能是壳源岩浆活动的产物。

Located in the western part of the Hongshishan_Heiyingshan terrane within the Ka zakhstan_Beishan plate, the Hongjianbingshan deposit is one of the most importan t tungsten deposits in northwest China. Tungsten mineralization occurs mainly as topaz_quartz veins within rhyolite tuff and rhyodacite of Early Carboniferous B aishan Formation, and partly as massive and layered greisens in Hercynian monzog ranite stocks, controlled by a number of NE_trending fracture or fault zones. In dividual tungsten bodies can be traced along strike for 120 to 420 m, and downdi p for 800 to 1200 m, with thicknesses ranging from 0.19 to 1.32 m. Alterations r elated to tungsten mineralization consist mainly of greisenization, silicificati on, albitization, sericitization, K_feldspathization, epidotization and skarniza tion, with greisenization and albitization being most important. Ore minerals ar e relatively simple, and mainly include wolframite, cassiterite, molybdenite, bi smuthinite, galena, sphalerite, sheelite, chalcopyrite, pyrite and magnetite. Ga ngue minerals consist of quartz, topaz, helvine, K feldspar, albite, muscovite, sericite, fluorite and calcite. The WO 3 content of the W_bearing topaz_quartz veins and that of greisen blocks range from 1.23% to 1.86% (1.55% on average) an d 0.26% to 0.54% (0.40% on average) respectively. Researches on regional ore_for ming process show that the major tungsten ore_forming event of the deposit occur red during the early Hercynian orogeny (322 Ma). Seven wolframite separates from both topaz_quartz vein type and greisen block type tungsten ores were selected for Sm_Nd analysis. The ε Nd (322Ma) values of two wolframite separate s from the greisen massive ore range from 4.24 to 5.93, much higher than values of the anc ient continental crust and Precambrian metamorphic rocks. In contrast, the ε Nd (322 Ma) values of five wolframite separates from the topaz_quartz vein ores ra nge from -4.16 to -8.05, much lower than values of the greisen massive ore. Geoc hemical data, isotopic data and petrological observations all indicate that the greisen ores might have been formed by the mantle_related ore fluids, while the topaz_quartz vein ores were probably derived from crustal_derived magma fluids. The Hongjianbingshan tungsten deposit is believed to be a product of early Hercy nian igneous process along the northern margin of the Kazakhstan_Beishan plate. Meanwhile, the genetic model and mineral exploration criteria of the Hongjianbin gshan deposit can also be used as useful tools for comprehensive evaluation of c oncealed tungsten deposits in the Beishan Mountain, Gansu Province.