黑龙江翠宏山铁多金属矿床辉钼矿Re-Os定年及S-Pb同位素特征研究

摘要

黑龙江翠宏山铁多金属矿床位于小兴安岭-张广才岭成矿带北部,属典型的矽卡岩型矿床.对于该矿床的成矿时代,前人主要通过矿区岩体定年来推测成矿时代,争议较大;对于成矿物源的研究,还缺乏同位素资料的佐证.为精确厘定矿床的形成时代,本文对该矿床两个矿段中的13件辉钼矿样品进行了Re-Os同位素定年研究.其中,翠北矿段7件辉钼矿Re-Os同位素模式年龄为205.6～202.0Ma之间,年龄加权平均值为204.9±1.3Ma,Re-Os等时线年龄为205.1±1.9Ma;翠中矿段6件辉钼矿Re-Os同位素模式年龄为206.7 ～ 200.9Ma,年龄加权平均值为204.1±2.4Ma,Re-Os等时线年龄为204.0±3.9Ma;显示翠北、翠中两个矿段的成矿时限一致.结合前人获得的矿区岩体年代学数据以及岩体与矿体之间的关系,认为二长花岗岩的成岩时代与铁多金属矿床的成矿时代一致,均发生于印支末期,二者具有密切时、空联系.矿床中辉钼矿的Re含量主要介于0.03605×10-6～1.9620×10-6之间,高者达17.108×10-6,指示Re主要为壳源特征;矿石硫化物的δ34S值为2.0‰～6.9‰,平均3.8‰,主要显示深源硫的特点,可能有少量地层硫的混入;矿石硫化物的206pb/204 Pb、207pb/204 Pb和208 Pb/204 Pb值变化范围分别为18.650～ 19.058、15.584 ～ 15.727和38.177～38.650,在铅同位素构造图解中主要落于造山带演化线附近,具有壳幔混源特点,且金属硫化物与二长花岗岩铅同位素组成的投点范围有较大的重叠区,显示矿石硫化物铅来源于印支末期形成的二长花岗岩.结合区域动力学背景分析认为,印支末期,小兴安岭-张广才岭成矿带上金属矿床成矿作用主要受古亚洲洋构造域伸展作用控制,形成如翠宏山、小西林、大西林等矽卡岩型的多金属矿床,随后进入燕山早期的早侏罗世,区域则转化为挤压环境,并受环太平洋构造域控制,形成了诸多斑岩型矿床,如霍吉河、翠玲、徐老九沟、五连岭、杏山、大黑山等矿床.%The Cuihongshan Fe-polymetallic deposit is located in the northern segment of the Lesser Xing' an-Zhangguangcai Range which is an important porphyry-skarn metallogenic belt in China.Recent studies were mainly focused on the deposit geology,and thegeochronology of granites in the Cuihongshan mining area.However,mineralization age and source of ore-forming minerals remain unclear.We present detailed Re-Os isotopic dating of molybdenites,S-Pb isotopic analysis,together with geochemistry,U-Pb geochronology data published,to reveal the ore-forming age,source of ore-forming materials of the Cuihongshan deposit and the tectonic setting for magmatism and mineralization in the Lesser Xing' an-Zhangguangcai Range.Seven molybdenite samples from Cuihongshan ore spot yield a Re-Os isochron age of 205.1 ± 1.9Ma,with model ages ranging from 205.6Ma to 202.0Ma and the weighted mean age of 204.9 ± 1.3Ma.Six molybdenite samples in Cuizhong ore spot obtaine a Re-Os isochron age of 204.0 ± 3.9Ma,with the weighted mean age of 204.1 ±2.4Ma and the model ages of 200.9Ma to 206.7Ma.The ages show that the Cuihongshan Fepolymetallic deposit occurred in the Late Indo-Chinese epoch.Together with the published ages of granites and the connection relationship between ore bodies and monzogranite in the Cuihongshan mining district,the authors hold that monzogranite (199 ± 3.1Ma) is most related to the Cuihongshan Fe-polymetallic deposit.The content of Re from the molybdenites in the Cuihongshan and Cuizhong ore spot ranges from 0.03605 × 10-6 to 0.5810 × 10-6 and 0.2585 × 10-6 tol.758 × 10-6,respectively,suggesting that the ore-forming materials may come from crustal source.The δ34S values of metal sulfide in the Cuihongshan deposit varies from 2.0‰ to 6.9‰o,averaging 3.8‰,showing a deep source of magmatic sulfur.The ratios of 206 pb/204 Pb,207 pb/204 Pb and 208 pb/204 Pb of metal sulfides range from 18.650 to 19.058,15.584 to 15.727 and 38.177 to 38.65 respectively,showing a mixture source of upper mantle and lower crust,and have similar affinity to that of the monzogranite.It also indicates that the mineralization of the Cuihongshan deposit is related to the monzogranite.Combining with the geochemical characteristics,geochronology of the region,the authors thought that the Lesser Xing' an-Zhangguangcai Range experienced a post-orogenic extensional tectonic setting controlled by the Paleo-Asian oceanic tectonic system in Late Indo-Chinese epoch.And the mineralization of the Cuihongshan,Xiaoxilin,Daxilin skarn deposit are related to the extensional tectonic setting.However,it was transition to a compressional setting constrained by Circum-Pacific tectonic system in the Early Jurassic.The mineralization of contemporaneous porphyry type deposits in the region,such as the Huojihe,Cuiling,Xulaojiugou,Wudaoling,Xingshan,Daheishan,Luming deposit,are related to the tectonic setting.