黑龙江佳木斯地区羊鼻山BIF型铁矿床的形成时代及地质意义

羊鼻山铁矿位于佳木斯地块中部,铁建造主要产于兴东群大盘道组第一岩段,含铁建造为一套由石榴石云母石英片岩、矽线石黑云母石英片岩和片麻岩等组成的孔兹岩系,其原岩形成于浅海陆棚沉积环境。矿石中金属矿物主要为磁铁矿,并被少量后期黄铁矿交代,非金属矿物主要为石英与矽线石,二者均呈定向排列,矿石构造以条带状构造为主,少量呈块状构造。据成矿地质条件和矿床特征,结合区域矿床对比研究,认为羊鼻山铁矿成因属BIF型,初步划归Superior型。含铁建造中矽线石黑云母石英片岩中碎屑锆石U-Pb年龄可分为4组,分别为1 006~1 212 Ma、1 238~1 480 Ma、1 521~1 742 Ma以及1 800 Ma,据最小年龄可推断羊鼻山铁矿含铁建造的沉积上限年龄为1 006Ma;1 238~1 480 Ma年龄组丰度最大,反映铁建造与围岩的剥蚀区岩石以中元古界岩浆岩为主;而最大年龄组中的2 672 Ma与2 711 Ma样品为佳木斯地块最古老的锆石之一,说明佳木斯地块存在太古代结晶基底。结合同样被认为是佳木斯地块结晶基底的麻山群近期年代学研究结果,认为兴东群应为麻山群的下伏地层。

Formation age and geological significance of Yangbishan BIF type iron deposit in Jiamusi area,Heilongjiang

Yangbishan iron deposit in Heilongjiang is located in the middle of Jiamusi Massif. The iron formation belongs mainly to the first segment of Dapandao Formation of Xingdong Group. The iron formation is composed of garnet-mica-quartz schist, sillimanite-biotite-quartz schist and gneiss, indicating that it can be classified as the khondalite series. The protolith of khondalite series reflect its neritic shelf sedimentary setting. The magnetite is the main metal mineral in ore, of which a minor amount was replaced by late pyrite. Quartz and sillimanite are the main nonmetallic minerals and both are in orientational arrangement. The iron ores in the Yangbishan deposit is predominantly banded, with minor massive. According to ore-forming geological condition and deposit characteristics, the Yangbishan ore deposit can be defined as Superior-type BIF. LA-ICP-MS U-Pb dating has been carried for detrital zircon grains from the ore-hosting sillimanite-biotite-quartz schist. The dating results can be listed as four groups, 1 006~1 212 Ma, 1 238~1 480 Ma, 1 521~1 742 Ma and > 1 800 Ma, respectively. The age of 1 006~1 212 Ma, the minimum age group, determines the sedimentary age of iron formation in Yangbishan iron deposit. The major age group (1 238~1 480 Ma) reflects the main rocks in erosion area are Mesoproterozoic magmatic rocks. While the two oldest zircons (2 672 Ma, 2 711 Ma) hold the conclusion that there developed the Archean crystalline basement in Jiamusi Massif. Combined with the previous research results of Mashan Group, it is concluded that the Xiongdong Group is the underlying strata of the Mashan Group in Jiamusi area.