黑龙江争光金矿床英云闪长斑岩年代学、地球化学及地质意义

摘要

黑龙江省黑河市争光金矿床位于大兴安岭东北缘多宝山矿集区东南端,于Ⅰ号矿带钻孔中发现较大规模的隐伏英云闪长斑岩体,其LA-ICP-MS锆石U-Pb谐和年龄和加权平均年龄分别为462.0±0.9 Ma(MSWD=0.0025)和462.1±1.8 Ma (MSWD=0.34),属中奥陶世晚期,代表岩体结晶年龄。岩石具高镁埃达克质岩特征： SiO2(62.54%~64.62%)≥56%,高Al,富集LILE(Rb、Ba、Sr、U)和LREE,亏损HFSE(Nb、Ta、Ti)、Y及HREE,无Eu异常；高MgO和Cr,高Mg#(56~61),低FeOT/MgO比值。Sr、Sr/Y、La/Yb及 Na2O/K2O较典型埃达克岩偏低。与多宝山花岗闪长岩可对比且具演化关系,二者均为俯冲洋壳熔融成因,随俯冲深度增加,体系温度和压力增大, H2O含量降低,主要矿物相稳定性逐渐发生改变,在16.9 Ma时间差的地质历史时期,先后形成早、中奥陶世多宝山和争光两期埃达克质岩,后者岩浆在上升过程中与地幔楔发生了一定程度的交代作用；二者均形成于陆缘弧大地构造背景。争光矿床奥陶纪成矿作用更可能与该岩体有关,熔体高氧逸度、较低聚合度及低演化和分异程度是Cu、Au成矿的有利因素。%TheZhengguang gold deposit is located in the southeast of the Duobaoshan metallogenic belt in the northeastern Great Hinggan Range, Heihe city, Heilongjiang province. Relatively large-scale tonalite porphyry, which may relate to the mineralization, has been discovered in the No.Ⅰ ore belt. The LA-ICP-MS U-Pb concordant age and 206Pb/238U weighted average age of zircons from the tonalite porphyry are 462.0±0.9 Ma (MSWD=0.0025) and 462.1±1.8 Ma (MSWD=0.34) respectively, which represent its crystallization age and belong to the late of Middle Ordovician. The tonalite porphyry exhibits geochemical features like high Mg adakitic rock, including the SiO2 (62.54%~64.62%)≥56%, high Al content, enriched in large ion lithophile elements (LILE) (Rb, Ba, Sr, U) and light rare earth elements (LREE), depleted in the high field strength elements (HFSE) (Nb, Ta, Ti), Y and heavy rare earth elements (HREE), without Eu anomaly, high Mg# (56~61), MgO and Cr contents and low FeOT/MgO ratios. The Sr contents, Sr/Y, La/Yb and Na2O/K2O ratios are lower than those of the typical adakites. There are lots of geochemical similarities between the tonalite porphyry in the Zhengguang gold deposit and the Duobaoshan granodiorite. They may have evolution relationship to some extent. They are originated from partial melting of subducted oceanic slab. And with the increase of subduction depth, the temperature and pressure increased, the H2O content decreased and the stability of the main minerals, such as plagioclase, amphibole, garnet and rutile, gradually changed. The early Ordovician Duobaoshan granodiorite and the Middle Ordovician Zhengguang tonalite porphyry belong to the two periods of adakitic magmatic activity during a period of 16.9 Ma. They both came from continental margin arc, but the Zhengguang tonalite porphyry interacted with the mantle wedge during accending. The Ordovician mineralization of the Zhengguang deposit may relate to the tonalite porphyry pluton that is characterized by high oxygen fugacity, low polymerization degree, low evolution degree and fractionation degree, which is critical for Cu and Au mineralization.