华北地台北缘地质构造演化及多金属成矿带的构造控制问题

华北地台北缘断续分布着一条2000多公里的元古宙多金属矿带。西起狼山群、渣尔泰群、南口群,东至辽北汛河群、辽吉辽河上亚群以至朝鲜境内的摩天岭系均有代表性矿床、矿田和成矿带。矿床皆具层控性,矿化均富集于早一中元古宙地层下部的长英质碎屑岩、沉积一浊积页岩、区域性富磷碳层向白云岩或灰岩的过渡部位。含矿建造厚度大、旋回层次多,含矿性增强。相对深度大、低能的盆地是含矿卤水流集聚的部位。在构造上矿床多处于古裂陷带,特别是古隆起的两侧。多级构造盆地之二、三级盆地较之于陆坡坳陷盆地更利于较大型矿床保存。从而,笔者归结出基本的成矿模型和找矿模型。

Geologic-Tectonic Evolution And Tectonic Control Of Polymetallogenic Belt In The Northern Margin Of North China Platform

The Proterozoic strata in the northem margin of North China Platform may be divided into three tectonic types, of which the Langshan Group and Chartai Group are typical ones produced in fault-trough belt along the continental margin, and the Changchen-Nankou Group occurs inside the continental margin, with all of them being characterized by slight metamorphism and deformation. Nevertheless, strata represented by upper subgroup of Liaohe Group belong to the continental slope accumulations noted for strong metamorphism and deformation, which experienced compression after diagenesis at 1650 Ma. In Proterozoic strata along the northern margin of North China platform extending from Langshan mountain in the west to the Hueishan mountain of North Korea in the east, some 2000 km in length, there occur such large- or medium-size deposits as those in Huogeqi, Tanyiaokou, Dongshenmiao, Duimen shan, Jiashertpan of Inner Mongolia, Gaobanhe in Hebei, Bajiazi in western Liaoning, Guanmenshan in northern Liaoning, Qinchenzi and Tuego m eastern Liaonmg, and Jiande, as well as some others in North Korea. These deposits were all formed during the period of 1800-1500 Ma, with the stromatolites of Conophyton and Kussiella association being observed above and beneath the ore bed. They belong to stratiform deposits characterized mainly by layered orebodies, produced at a certain stage of geologic evolution. Observations show that all of these deposits possess similar ore-bearing rock system. There are clastic rocks, turbidite shale and shale in lower part which gradually grade into phosphorous-bearing, carbon-bearing formation in the middle part, with polymetallic deposits existing within the transitional part from lutite to chemical sedimentary rocks (dojomites). The great thickness of ore-bearing formation with polycycles seems to have favored the accumulation of ore resources. lt is worth noticing that this kind of deposits almost always occurs m fault-depression belt where faults simultaneous with mineralization led to the formation of ore-controlling basins, of which the second class basins and, especially, the third class ores are the main positions controlling ore deposits. They are distributed along the margin of the ancient uplift. The parallel-grown faults resulted in the condition of reduction and low energy, and caused the heavy brine to flow into them. After the formation of ore deposits, this kind of confined basins was most ready to preserve ore-bodies during the long period of geologic-tectonic activities. The study of this sort of fault-depression belt and fault basin on one side of the ancient uplift, therefore, is of key importance in prospecting for polymetallic deposits along the northern margin of North China Platform.